Recent Developments in Graphene-Based Two-Dimensional Heterostructures for Sensing Applications

C H A P T E R

11 Recent Developments in Graphene-Based TwoDimensional Heterostructures for Sensing Applications Pratik V. Shinde, Manav Saxena and Manoj Kumar Singh Centre for Nano and Material Sciences, Jain University, Jain Global Campus, Bengaluru, India

11.1 INTRODUCTION In a world of technologies, progress is determined to a great extent by the growth of material chemistry. These advanced materials play a crucial role in our daily lives. When a new material with unusual dimensionality and properties is created new avenues will open. Historically, people have explored material synthesis, composition, and structures to improve their properties. Since the 1980s low-dimensional materials have led material science because of their unique properties compared to bulk materials [1]. Low-dimensional materials fall into the following classes: two dimensional (2D), one dimensional (1D), and zero dimensional (0D). Due to their unique properties 2D materials have attracted attention in condensed matter physics and in chemistry. The current 2D material library is shown in Table 11.1. This library increases every day as research progresses. 2D materials that include metals, semiconductors, and insulators show a broad range of electronic properties. 2D materials have properties such as high surface area, surface state free nature,

Fundamentals and Sensing Applications of 2D Materials DOI: https://doi.org/10.1016/B978-0-08-102577-2.00011-7

407

Copyright © 2019 Elsevier Ltd. All rights reserved.

408

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

TABLE 11.1 Graphene Family

Current 2D Library. Graphene

Hexagonal Boron Nitride (h-BN)

Boron-CarbonNitrogen (BCN)

Fluorographene

Graphene Oxide (GO)

Metallic Dichalcogenides: 2D MoS2 , WS2 , MoSe2, WSe2 Chalcogenides

Semiconducting Dichalcogenides:

NbS 2, NbSe 2, TaS 2, TiS 2, NiSe 2 and so on

ZrS2 , ZrSe 2 , MoTe 2, WTe 2 and so on

Layered Semiconductors: GaSe, GaTe, InSe, Bi2Se3 and so on Hydroxides:

Micas, BSCCO

MoO3 , WO3 Perovskite Type:

2D Oxides

Layered Cu Oxides

TiO2, MnO2, V 2O5 , TaO3, RuO2 and so on

Ni(OH)2, Eu(OH)2 and so on

LaNb2O7, Bi4Ti3O12, (Ca,Sr)2Nb3O10

and so on

Others

Yellow shaded area shows monolayer materials that are stable under ambient temperatures. Orange shaded area is stable in air. Pink shaded area shows materials unstable in air but stable in inert atmosphere. Green shading indicates 3D compounds that have been successfully exfoliated. “Others” indicates 2D crystals—including borides, carbides, nitrides, and so on.

distinctive optical bandgap, quantum spin Hall effect, and strong light matter interactions [1,2]. Physical properties such as magnetism, superconductivity, charge density wave (CDW), and crystal structure (2 H, 1 T) of 2D materials and 2D transition metal dichalcogenides (TMDCs) is shown in Fig. 11.1. There are two approaches to the synthesis of 2D materials. First is the top-down-bottom exfoliation approach while the other is a bottom-up-based approach. In general the first approach includes mechanical exfoliation and liquid exfoliation, while the latter approach includes chemical vapor deposition (CVD), physical vapor deposition, or vapor phase transport. Geim and coworkers isolated graphene by mechanical exfoliation using Scotch tape in 2004 [3,4]. This method gives highly pure 2D material, but the number of layers, their size, orientation, and phase are not controlled [5]. For large-scale production this method is not useful. Liquid exfoliation is useful for the low-cost production of 2D materials, but for some applications the size and quality of 2D materials are major issues. In this regard, CVD is more efficient because high-quality and large-area 2D materials can be prepared at a reasonable cost [6 8]. Graphene is just one example of the large 2D materials family. A new class has emerged of atomically thin 2D materials known as TMDCs. These have the formula MX or MX2 where M is a transition metal like Mo, W, Pd, etc. and X is a chalcogenide like S, Se, and Te, for example, MoS2, WS2, MoSe2. Many stable combinations are possible with transitions metals such as hafnium, zirconium, titanium, nickel,

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

11.1 INTRODUCTION

409

FIGURE 11.1

Physical properties of 2D materials and 2D transition metal dichalcogenides (TMDCs) such as magnetism [ferromagnetic (F)/antiferromagnetic (AF)], superconductivity, charge density wave (CDW), and crystal structure (2 H, 1 T).

and with nontransition metals like gallium, indium, bismuth, and tin. 2D TMDCs attract attention for capacitive energy storage [9,10] and sensing applications [11,12] due to their large specific area and van der Waals (vdWs) gap between each neighboring layer. The isolation of new 2D materials motivates researchers to fabricate vdWs heterostructures using atomically thin 2D materials as the building blocks. Each block has its own optical, electrical, and thermal properties. By stacking these blocks it should be possible to achieve new structures with different properties [13 15]. These 2D materials create heterostructures by adding layer-on-layer in a perpendicular direction to the atomic layer. 2D material-based heterostructures have novel electron-electron coupling and electron-phonon coupling, generated due to layer-layer interactions [16,17]. 2D material heterostructures may have improved device performance compared to single crystal, for example, by providing stronger mechanical flexibility [18,19]. Tuning of the energy band alignment and charge carrier mobility is possible by changing components of the heterostructures. Unlimited combinations

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

410

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

of heterostructures are possible because a number of 2D materials are available with different properties. But it remains a challenge to fabricate the entire 2D material family and to utilize these for fabrication of heterostructures on a large scale. These vdWs heterostructures have numerous novel physical phenomena and novel applications such as ultrahigh-speed photodetectors [15], correlated light emitters [20], newgeneration field-effect transistors [21], high-sensitivity sensors [22], and memory devices [23].

11.2 GRAPHENE AND TWO DIMENSIONAL TRANSITION METAL DICHALCOGENIDES Graphene has generated great interest over the past decade. In the late 1930s researchers studied the thermal stability of a single-atomthick sheet. They predicted that, due to the minimization of surface energy it is impossible to isolate free-standing graphene at room temperature [24,25]. But in 2004 Geim and colleagues successfully isolated monolayer graphene by mechanical exfoliation. Graphene has a honeycomb lattice structure with a D6h point group [26,27]. The nonequivalent carbon is inverted onto each other by inverse symmetry operation from D6h point group. Graphene has exciting properties like a large theoretical specific surface area (2630 m2 g21) [28], high thermal conductivity (B5000 Wm21 K21) [29], high Young’s modulus (B1.0 TPa) [30], high intrinsic mobility (200000 cm2 v21 s21) [31,32], and good optical transmittance (B97.7%) [33]. These extraordinary features of graphene come from a combination of its dimensionality and a very peculiar band structure. Graphene, while being an interesting material for many applications, is chemically inert, and so another molecule with the desired properties is required to functionalize it, which in turn results in the loss of some of its exotic properties. Another increasing material is black phosphorous (BP), which is also known as phosphorene [34 37]. BP has a vertically staggered hexagonal lattice geometry with highly anisotropic properties. Monolayer BP has a bandgap 1.5 eV [35] and good carrier mobility up to 1000 cm2 V21 s21 [37]. BP may be referred to as a bridge between graphene and TMDCs. Although graphene has many enchanting properties, its lack of electronic bandgap stimulated research in other 2D inorganic materials like MoS2, WS2, MoSe2, TiS2, with a semiconducting nature. These emerging metal dichalcogenides have a sandwich structure of transition metal (Mo, W, Ti, Nb) between two chalcogen layers (S, Se, Te). In this structure, between the layers, weak noncovalent bonding takes place, while covalent bonds give them in-plane stability [38]. TMDCs have a variety of composition and properties but despite this there is one interesting common feature present in all monolayer TMDCs that is they all grow FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

11.3 FABRICATION OF HETEROSTRUCTURES FROM TWO DIMENSIONAL CRYSTALS

411

in triangular shapes varying with edge composition [39,40]. Depending on the arrangement of atoms, 2D TMDCs can form two crystal structures: a trigonal prismatic (2 H) phase and an octahedral (1 T) phase. At room temperature, a 2 H phase of MX2 material is the most stable phase, while the 1 T phase can be acquired by Li-intercalation or electron beam irradiation [41]. TMDCs provide access to a range of properties related with their atomic-scale thickness, direct bandgap strong spin-orbit coupling and glowing electronic and mechanical properties [42]. These properties are in many ways unusual from their bulk counterparts. The properties of TMDCs can be tailored because of different crystalline structure and stacking sequences of their layers properties. TMDCs are used in many devices like photodetectors, photovoltaic devices, transistors, memory devices, and sensing devices [5]. Depending on composition TMDCs may be classified as semiconductor (MoS2, WS2), semimetals (WTe2, TiSe2), true metals (NbS2, VSe2) and superconductors (TaS2, NbSe2) [43]. The most frequently studied member of the family is monolayer MoS2; its production was firstly achieved in 1986 [44]. MoS2 not only has good chemical stability and mechanical flexibility but also superior optical and electrical properties [43,45]. The semiconducting nature of MoS2 is because of its ultrathin direct bandgap, between 1.3 and 1.9 eV (B1.8 eV) due to quantum confinement effect [46,47]. It has a much higher optical absorption coefficient (107 m21 in visible range) which can be used to fabricate ultrasensitive photodetectors [48,49]. Also it has high current on/ off ratio (B107 2 108) and larger work function (5.1 eV) [48]. The larger bandgap, work function and larger absorption efficiency have given MoS2 an edge over graphene which is why MoS2 is referred to as a “beyond graphene” material. The library of TMDCs opens up the possibility of fabricating novel heterostructures with new physics and material science.

11.3 FABRICATION OF HETEROSTRUCTURES FROM TWO DIMENSIONAL CRYSTALS Since the first fabrication of a graphene/h-BN heterostructures by exfoliation [50], research on 2D materials heterostructures has exploded. The fabrication of heterostructures with tuned properties depends on the interaction strength of the layers of materials. Owing to the layer structure of 2D crystals, the fabrication of heterostructures can be lateral or vertical. Lateral 2D heterostructures can be integrated by arranging 2D materials into monolayer or in-plane designs, while vertical 2D heterostructures are integrated by vertical stacking of the 2D materials. Covalent bonds present between the layers and vdWs bonding play a key role in 2D crystal heterostructures. Weak vdWs forces bind layers together and a strong covalent bond gives in-plane stability to the FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

412

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

heterostructures [51]. Such anisotropic bonding enables control of heterostructures material properties in distinctive ways. Since weak vdWs forces play a prime role in interlayer coupling, without dangling bond on the surface, the lattice-matching requirement is relaxed in heterostructures [52]. When stacking of different crystals takes place, synergetic effects becomes indispensable [53]. The reality is that the size of the 2D crystal heterostructures is key for a wide range of applications. There is a need to increase the size of 2D crystal-based heterostructures to make them compatible with 2D crystals. Recently researchers found out that franckeite minerals naturally show almost pristine alignment in crystal lattices with the absence of tapped residues between layers, which is more advantageous than humanmade vdWs heterostructures [54]. The fabrication of vertical stacking and lateral stitching of 2D material-based heterostructures with controllable growth is still a challenge. According to the design of heterostructures, fabrication methods also vary. In this chapter we present various fabrication methods of heterostructures such as mechanical exfoliation, molecular beam epitaxy (MBE) method, hydrothermal synthesis, and CVD.

11.3.1 Mechanical Exfoliation After monolayer graphene was isolated by mechanical exfoliation, researchers devoted great attention to 2D materials [55 58]. These materials are stacked or stitched together to form 2D material heterostructures. In this method, Scotch tape was used to manually produce 2D material flakes [55]. Vertical heterostructures are possible by stacking arbitrary stable 2D materials layers with vdWs forces. However, for lateral heterostructures fabrication is much more difficult because atoms from different 2D materials need to bond together to form effective lateral heterojunctions [59]. Depending on the interaction strength of the two layers of crystals, physical properties of heterostructures also vary. For example, scattering from charge impurities, substrate surface roughness, and optical phonons of SiO2 limits the carrier mobility of graphene on SiO2 while atomically flat and free charge trapping h-BN layers are superb substrates for graphene [2]. Although this method is a quick and convenient way to fabricate vertical heterostructures, layer-by-layer stacking remains unmanageable and layers become randomly placed. With the use of adhesive tape, it is possible to create high-quality monolayer material for fundamental study, but this method is impractical for large sheet production [2]. The exfoliation and restacking approach offers a remarkable deal of flexibility for fabrication of various 2D material heterostructures. Fig. 11.2A and B shows optical microscope images of monolayer MoS2 and monolayer MoSe2 respectively, exfoliated by mechanical exfoliation from bulk crystals [60]. On Si-SiO2 substrate monolayer MoS2

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

11.3 FABRICATION OF HETEROSTRUCTURES FROM TWO DIMENSIONAL CRYSTALS

413

FIGURE 11.2 (A) Optical microscope images of monolayer MoS2. (B) Optical microscope images of monolayer MoSe2. (C) Fabricated MoS2/MoSe2 heterostructure. Source: Images reprinted (adapted) with permission from F. Ceballos, M.Z. Bellus, H.Y. Chiu, H. Zhao, Ultrafast charge separation and indirect exciton formation in a MoS2 MoSe2 van der Waals heterostructure. ACS Nano 8 (12) (2014) 12717 12724. Copyright (2014) American Chemical Society.

FIGURE 11.3 (A) Scanning electron microscopy (SEM) images of the flowerlike MoS2/ CdS heterostructures. (B) Transmission electron microscopy (TEM) images of MoS2/CdS heterostructures.

was transferred on monolayer MoSe2 for the fabrication of MoS2/MoSe2 heterostructures. This fabricated MoS2/MoSe2 heterostructures as shown in Fig. 11.2C [60].

11.3.2 Hydrothermal Synthesis Hydrothermal synthesis is considered to be the most promising method for heterostructures synthesis. It is relatively inexpensive, shows high efficiency, and gives good crystallized products [61,62]. Typically, a homogeneous solution is added into a Teflon-lined stainless-steel autoclave and then heated at different temperatures. Zhang successfully synthesized the flowerlike MoS2/CdS heterostructures by a one-step hydrothermal route [62]. Hydrothermally synthesized MoS2/ CdS heterostructures scanning electron microscopy (SEM) images are shown in Fig. 11.3A. Approximately 800 nm size flowerlike MoS2/CdS

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

414

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

heterostructures are seen in the image. Transmission electron microscopy (TEM) images of heterostructures are shown in Fig. 11.3B. TEM confirms the flowerlike morphology of the heterostructures [62].

11.3.3 Molecular Beam Epitaxy The MBE method is widely used for fabrication of high quality and homogeneous wafer-scale epitaxial layers. In this method, high-purity material is heated by electron beam evaporators until they begin to sublimate slowly in an ultrahigh vacuum. The gaseous elements react with each other and condense on a substrate. This epitaxial growth of films depends on the deposition rate [63]. This method has advantages like instant introduction and control over multiple sources, easy doping of materials, and controllability of atomic layers [64]. This fabrication approach provides better crystalline and ultrathin heterostructures. The method is highly reproducible [65] with control over atomic layers and thickness. Graphene/h-BN heterostructures have been fabricated on copper substrates by an MBE method [64]. Raman spectra of graphene/ h-BN stacked heterostructures is shown in Fig. 11.4A. G and 2D peaks show the existence of graphene while 1364 cm21 peak confirms evidence of h-BN. SEM images of the growth of high-quality graphene/ h-BN stacked heterostructures are shown in Fig. 11.4B. The inset shows a large triangular h-BN flake of about 20 μm.

11.3.4 Chemical Vapor Deposition In recent years the CVD technique has been used for the fabrication of 2D material heterostructures. CVD is a useful technique for the

FIGURE 11.4 (A) Raman spectra of graphene/h-BN heterostructures. (B) Scanning electron microscopy (SEM) images of graphene/h-BN heterostructures.

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

11.3 FABRICATION OF HETEROSTRUCTURES FROM TWO DIMENSIONAL CRYSTALS

415

FIGURE 11.5

Schematic diagram of thermodynamics and kinetic functionality of chemical vapor deposition (CVD).

controllable synthesis of 2D materials [66 68]. CVD not only provides large-area 2D materials for mechanical assembly but also direct growth of various stacking structures. Generally CVD requires a very high temperature to activate the gaseous precursors and successive gas solid phase reactions on the substrate. Even if the input of precursors is the same, the structure, composition, and properties of formed products vary depending on various factors. Temperature triggering, substrate engineering, precursor design, gas flow or pressure growth time, and cooling rate are factors that play a crucial role in the CVD mechanism [1]. Fig. 11.5 is a schematic representation of how parameters like precursor, substrate, temperature, and pressure affect mass and heat transfer, growth of materials, and their interface reactions. In CVD, high-purity precursors are needed to avoid undesirable contamination and unwanted side reactions. In the vapor deposition process materials are deposited on the substrate such as Si/SiO2 [69], mica [70], copper [71], polyimide [72], and nickel [73]. Temperature mainly decides the composition and uniformity of products because it affects mass transport of species and their reaction at the vapor-solid interface. When nucleation at the vapor-solid interface takes place, high temperatures lead to a thermodynamic process while low temperatures lead to a kinetic process. At lower pressure, reactions are more controllable because volume flow and velocity of gas are greatly increased, but the concentration of precursor decreases. By tuning these factors, the controlled growth of heterostructures is possible. Fig. 11.6 shows the formation of vertical and lateral heterostructures. In the first step one layer of 2D material is deposited on the substrate. In the second step another material is deposited or transferred onto the first layer. This is the most important step because it

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

416

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

FIGURE 11.6 Schematic diagram of the formation of vertical and lateral heterostructure.

FIGURE 11.7 One-step vapor phase growth mechanism of heterostructure.

decides the type of heterostructures. If two layers stack one on top of the other, vertical heterostructures are formed, and if they connect to one plane, this is known as lateral heterostructures. Recent developments in CVD provide high controllability over size, number of layers, as well as stacking or stitching modes in fabrication of heterostructures. 2D crystal heterostructures growth by CVD may be one or two steps. A one-step vapor phase growth of heterostructures is shown schematically in Fig. 11.7. Ajayan’s group showed a one-step CVD growth of WS2-MoS2 lateral and vertical heterostructures [7]. Chen’s group first showed the two-step CVD growth of MoS2-MoSe2 lateral heterostructures [74]. To date many 2D material heterostructures are synthesized by a CVD method such as graphene/h-BN [75], MoS2/h-BN [76], WS2/h-BN [77], WS2/MoS2 [78], MoS2/WSe2 [79], and SnS2/MoS2 [80]. MoS2/graphene heterostructures are also fabricated by CVD method. Raman spectra and optical image of the MoS2/graphene heterostructures fabricated by a two-step mechanism is shown in Fig. 11.8A and B [81]. The optical image clearly shows the MoS2/graphene film on the top of the side. Raman spectra of MoS2/graphene heterostructures are shown (top, red star) and graphene Raman spectra (bottom, black star) [81].

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

11.4 TWO DIMENSIONAL CRYSTAL-BASED HETEROSTRUCTURES SENSORS

417

FIGURE 11.8 (A) Raman spectra of MoS2/graphene heterostructures. (B) Optical image of the MoS2/graphene heterostructures. Source: Images reprinted (adapted) with permission from Q. Liu, B. Cook, M. Gong, Y. Gong, D. Ewing, M. Casper, et al., Printable transferfree and wafer-size MoS2/graphene van der Waals heterostructures for high-performance photodetection. ACS Appl. Mater. Interfaces 9 (14) (2017) 12728 12733. Copyright (2017) American Chemical Society.

11.4 TWO DIMENSIONAL CRYSTAL-BASED HETEROSTRUCTURES SENSORS The massive demand for highly sensitive, selective, reliable, and portable, low-power-consuming sensors has triggered research into new sensing materials based on 2D crystals. These materials have attracted attention due to such properties as large surface-to-volume ratio, planar crystalline structure, many active sites, and low electronic noise. Combining these properties to fabricate lateral and vertical heterostructures for a wide range of applications is the most important task. A chemical sensor is a device that provides information about the chemical composition of its environment. Here we briefly discuss different types of sensors such as humidity sensors, gas sensors, and surface plasmon resonance (SPR) sensor fabricated from heterostructures materials.

11.4.1 Humidity Sensor The humidity sensor is a device that senses, measures, and reports the relative humidity (RH) of air or determines the amount of water vapor present in gas mixture (air) or pure gas. Humidity sensing is related to a water adsorption and desorption process [82]. Humidity sensors are used for monitoring industrial as well agricultural products [83]. Humidity sensors are used in equipment such as incubators, sterilizers, and pharmaceutical processing equipment [83].

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

418

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

Various types of humidity sensors are available, and these operate on different principles such as capacitive [84], resistive [85], semiconductor [85], optical [86], and surface acoustic waves [87]. Some advantages to capacitive sensors include low power consumption, good linearity, and wide range RH detection, but a complicated fabrication process is the major drawback [88 90]. Resistive sensors overcome these problems with their ease of fabrication, high sensitivity, low cost, and low power consumption [91 96]. Metal oxide [97], polymers [98], and carbonbased [99] materials are the most frequently used materials for the fabrication of humidity sensors. These materials have low cost and high sensitivity as well as good compatibility. But metal oxide sensors degrade in humidity [100] and polymers have poor stability in highly humid environments [101]. Slow response/recovery time and high operating temperatures remain design challenges for these sensors. Recently researchers have constructed heterostructures-based humidity sensors. These show a high performance with fast response time and selectivity. Molybdenum disulfide (MoS2) is one of the most studied materials for sensing and it has a high on/off ratio [102] and a low power consumption [103]. Sensors based on MoS2/Si nanowire heterojunctions show high sensitivity, a fast response time, and excellent stability at different RH values [101]. These sensors show better performance with both forward as well as reverse voltage. Fig. 11.9A shows current-voltage (I V) curves of sensors at different RH values ranging from 11% to 95% under forward voltages where the current increases with an increase in RH values. The graph of increase in sensitivity with respect to an increase in RH values is shown in Fig. 11.9B. The highest sensitivity obtained is 392% at 95% RH. Fig. 11.9C shows the current response of MoS2/Si nanowires heterojunction in switching between dry air and different RH values at a bias voltage 15 V. When the device comes into contact with dry air or humid gas it behaves as a reversible switch between high and low conductance with high stability and repeatability. Fig. 11.9D shows a single-cycle response time of the sensor at different RH. At the highest RH value the response and recovery time is 26.4 and 15.1 s respectively. At reverse voltage these MoS2/ Si nanowires heterojunction sensor shows promising results like a forward voltage [101].

11.4.2 Gas Sensor There is a need to detect hazardous gases with highly sensitive and efficient sensors [104]. Sensors play an important role in environmental monitoring and industrial product monitoring and tracking. Semiconductor-based metal oxide has attracted attention for gas sensors

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

11.4 TWO DIMENSIONAL CRYSTAL-BASED HETEROSTRUCTURES SENSORS

419

FIGURE 11.9 (A) I V curves of MoS2/SiNWA heterojunction at voltage under varied relative humidity (RH) values. (B) The dependence relation between sensitivity and relative humidity. (C) Current response of MoS2/Si nanowires heterojunction to dynamic switches between dry air and varied RH values at Vbias 5 5 V. (D) Single-cycle response with different RH values.

because of its properties such as simplicity of fabrication, simplicity of operation, high sensitivity, extensive detection range, compact size, and low cost [105 107]. However, semiconductor metal oxide sensors operate at high temperature (100 C 400 C) [108]. Issues include high power consumption and ignition of flammable and explosive gases, and due to growth of oxide grains they have low reliability [108,109]. To lower the temperature and improve sensitivity, these obstacles can be removed using such techniques as doping of novel metals [110 112], designing unique nanostructures as sensing material [113,114], ultraviolet illumination [115 119], and formation of heterostructures [120 122]. In gas sensing, sensitivity of the material depends on the adsorption and desorption processes, while the speed of these processes is responsible for the response and recovery time. 11.4.2.1 Nitrogen Dioxide Sensor Nitrogen dioxide (NO2) is one of the most common, and pungent reddish-brown oxidizing air pollutant forms in fuel engines, chemical factories, and power plants by combustion-emission processes [123].

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

420

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

Even a few ppm exposures of NO2 can cause inflammation of lung tissue, irritation to the throat, bronchiolitis fibrosa obliterans, and silofiller’s disease in humans. The increased amount of gas in the environment causes acid rain and photochemical smog [124,125], contributing to the atmospheric reactions that form ground-level ozone. There is therefore an urgent need to expedite the development of highly sensitive, selective, and highly responsive NO2 gas sensor devices. Jung et al. [126] fabricated a highly transparent, flexible, and sensitive NO2 gas sensor based on an MoS2/rGO composite. The sensor detects concentrations as low as 0.15 ppm of NO2. Also, they have successfully improved the sensitivity to NO2 gas by at least 300% compared to pure rGO thin film gas sensors. Wang et al. [127] reported WO3 nanorods and sulfonated reduced graphene oxide-(S-rGO-) based NO2 gas sensors working at room temperature. The optimized sensor exhibits excellent reproducibility, selectivity, and extremely fast recovery kinetics and it possesses a high response toward 20 ppm. NO2 is 149% in 6 s, which is 100 times faster than that of the corresponding WO3/rGO sensors. 11.4.2.2 Hydrogen Sensor Hydrogen is a lighter gas than air and is a colorless, odorless gas at atmospheric conditions. It is a very clean energy source with use in fuel cells as well as in internal combustion engines. However, the reaction of hydrogen with an oxidizing agent (nitrous oxide), halogens (fluorine and chlorine), and unsaturated hydrocarbons (acetylene) is extremely exothermic [128]. So there is a strong need to develop “alarm” sensors that will detect hydrogen at a concentration well below the lower explosion limit in air. As shown in Fig. 11.10A, a CeO2/SnO2 heterostructure shows good response to hydrogen gas without going into saturation with increasing gas concentration [129]. Compared to pure CeO2 and SnO2 sensors, CeO2/SnO2 heterostructures are more stable. The CeO2/SnO2 heterostructures sensor shows a good response to even low H2 concentration. Fig. 11.10B shows the response and recovery time to hydrogen gas at different concentrations (5 10 ppm), which indicates that the sensor has a high reproducibility. Fig. 11.10C and D shows the response and recovery time plots of the sensor at 300 C, which are 17 and 24 s respectively. The CeO2/SnO2 sensor shows a sensitivity of 19.2 ppm21 due to the higher surface area and large amount of oxygen adsorption [129]. 11.4.2.3 Hydrogen Sulfide Sensor Hydrogen sulfide (H2S) is a toxic gas with an unpleasant smell that is like rotten eggs. It is colorless and flammable. It naturally occurs in natural gas, crude petroleum, volcanic gases, and hot springs. It is also produced from the decomposition of organic matter or waste produced by

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

FIGURE 11.10 (A) Response curves of the CeO2, SnO2, and CeO2-SnO2 nanostructures exposed to different concentrations of H2 gas at 300 C. (B) Response curves of CeO2-SnO2 sensor at different concentrations and temperatures versus time. (C) Response times of CeO2-SnO2 toward H2 gas at 300 C. (D) Recovery curves of CeO2-SnO2 sensor at different concentrations and temperatures versus time.

422

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

FIGURE 11.11 (A) The adsorption and reaction model on the surface of MoO3/rGO hybrid. (B) The responses of MoO3/rGO hybrids with different amount of graphene at 40ppm H2S gas in 70 C 220 C temperature range.

humans and animals. If the concentration of H2S increases to greater than 250 ppm, then it is a risk for human health. Sometimes a high concentration may cause death [130]. Therefore H2S sensors for instantaneous monitoring and control of H2S gas are needed. Recently MoO3 has been used for H2S gas sensors due to structural advantages like anisotropic structure, high electron mobility, and large surface-to-volume ratio [131]. But lower sensitivity and higher operating temperatures restrict its use as a sensor. MoO3 sensing properties may improve with graphene by fabrication of MoO3/rGO hybrids. Compared to MoO3, the MoO3/rGO hybrids show higher response and lower operating temperatures [132]. The adsorption and reaction model on the surface of the MoO3/rGO hybrid is shown in Fig. 11.11A while Fig. 11.11B shows the responses of MoO3/rGO hybrids with a different amount of graphene at 40 ppm H2S gas in the 70 C 220 C temperature range. A MoO3/5 wt% rGO hybrid has the highest response of 59.7 to 40 ppm H2S gas, which is three to four times higher than pure α-MoO3. Fig. 11.12 shows the transient response of pure α-MoO3 and MoO3/5 wt % rGO hybrid at the same operating temperature as H2S gas of different concentrations. The response time and recovery time of the sensor is about 9 and 17 s respectively. As Fig. 11.13 shows, the sensor based on the MoO3/5 wt% rGO hybrid not only has good stability but also has better reproducibility [132].

11.4.3 Surface Plasmon Resonance Sensor SPR is widely used for biological and environmental sensing. SPR sensors also play a role in medical imaging and remote sensing applications. Kretschmann [133] and Otto [134] are the two types of

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

423

11.4 TWO DIMENSIONAL CRYSTAL-BASED HETEROSTRUCTURES SENSORS

(A) 140 110ºC MoO3/5 wt% rGO

Sensor response (Ra/Rg)

120

MoO3

100

20

80 ppm H2S

40

40 ppm H2S

5 ppm H2S

10 ppm H2S

60

20 ppm H2S

80

0 0

Sensor response (Ra/Rg)

(B)

100 360 540 720 900 1080 1260 1440 1620 1800 1980 Time (s)

140 110ºC MoO3/5 wt% rGO

120

MoO3

100 80 60 40 20 0 0

10

20

30 40 50 60 Concentration (ppm)

70

80

90

FIGURE 11.12 (A) Transient response. (B) Responses of pure α-MoO3 and MoO3/5 wt % rGO hybrid at the same operating temperature as H2S gas with different concentrations. (B) 70

70 60 50 40

110ºC 40 ppm H2S

MoO3/5 wt% rGO

30 20 10

Sensor response (Ra/Rg)

Sensor response (Ra/Rg)

(A)

60 110ºC 40 ppm H2S

50

MoO3/5 wt% rGO 40 30

0 –10 –5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 Time (day)

20 0

2

4

6 8 Frequency

10

12

14

FIGURE 11.13 (A) Stability of MoO3/5 wt% rGO hybrid sensor. (B) Cycling response of MoO3/5 wt% rGO hybrid sensor.

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

424

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

configuration on which SPR biosensors are based. The conventional SPR sensor is based on the Kretschmann structure, in which a thin film of gold (Au) is coated on the prism to stimulate surface plasmons. The Kretschmann configuration is widely used because it does not require a thin air gap between the prism base and metal film. The SPR phenomenon measures the change in optical reflectivity of thin metal film like gold or silver, which arises due to changes in refractive index at the metal surface [135]. That means resonance occurs at the surface only when incident rays of p-polarized light that fall on the interface match with the wave vector of the surface plasmon. Silver has good sensitivity [136,137], but its poor stability [138] makes it unsuitable for an SPR sensor. However thermal and chemical stability as well as good optical performance of gold make it an ideal metal for an SPR sensor [138,139]. SPR sensors are known for superior accuracy, quick response, and label-free detection [140,141]. SPR technology is also easy to multiplex, is compact, and reliable for DNA hybridization [142 144]. Recent studies have shown that graphene can be used as a substrate in enhanced SPR sensors. Due to its high adsorption surface area [145 150], graphene is an important material in sensing fields. The high surface area offers a better contact with analyte as well as extensive field enhancement at the substrate interface [49]. For more than 10 layers of graphene deposited on a metallic SPR sensing substrate (50 nm) the graphene-based SPR sensor shows higher sensitivity [49]. Compared to graphene sensors, heterostructures based on graphene show higher sensitivity [49,151 153]. The advantage of heterostructures is that adsorption increases at the surface due to vdWs force of attraction and enhancement of field at the interface. Recently the 2D material molybdenum disulfide (MoS2) has attracted attention because of its analogous structure to graphene. MoS2 is a semiconductor material with ultrathin direct bandgap. It has a higher optical absorption coefficiency and larger work function. Therefore MoS2 is considered a promising resource for SPR biosensors with higher sensitivity. A MoS2-graphene hybrid nanostructure sensor shows sensitivity enhancement in the SPR biosensors. A five-layer Au-MoS2-graphene hybrid-based SPR biosensor is shown in Fig. 11.14 [154]. The prism is first coated with Au, then MoS2 followed by graphene coated onto the MoS2. This SPR sensor has a high sensitivity of 87.8 degree/RIU, and it can detect DNA hybridization. At 633 nm operating wavelength with 50 nm gold layer thickness it has a detection accuracy of 1.28 and a quality factor of 17.56 [154]. These sensors are used for medical diagnostics [155,156], enzyme detection [157,158], food safety testing [159,160], and environmental monitoring [161,162]. Another 2D material called blue phosphorene (blueP) can be used in SPR sensors. A blueP/MoS2 heterostructure fabricated on an Ag layer sensor shows high sensitivity [163]. Sensing performance at λ 5 662 nm

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

11.4 TWO DIMENSIONAL CRYSTAL-BASED HETEROSTRUCTURES SENSORS

425

FIGURE 11.14 The five-layer Au-MoS2-graphene hybrid-based surface plasmon resonance (SPR) biosensor.

is listed in Table 11.2, showing that Ag 1 blueP/MoS2 heterostructures have the highest sensitivity and detection accuracy, higher than the graphene SPR sensor [163].

11.4.4 Nitrite Sensor Nitrite exists in natural waters, soil, and physiological systems [164]. It is an essential part of beverages and food products preservatives [165]. For humans and animals, the high concentration of nitrite can be poisonous. Nitrite is a carcinogenic material and decreases the ability of hemoglobin to carry oxygen in the human body [166,167]. Thus there is a requirement for sensitive and rapid nitrite sensors for public health and environmental security. Electrochemical sensors based on rGO/MoS2 can be used for nitrite detection. rGO/MoS2/GCE sensors show high sensitivity, high stability, wide linear concentration ranges, and low detection limits [168]. Fig. 11.15A shows CV of electrodes in 0.1 M phosphate buffer solution (PBS) toward 500 μM nitrite showing an rGO/MoS2/GCE sensor oxidation current value of 45 μA with a potential of B0.85 V. The rGO/ MoS2/GCE sensor shows better catalytic activity than pure rGO and

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

426

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

TABLE 11.2

Comparison of Sensing Performance at λ 5 662 nm.

Configuration (CaF2 1 Prism)

Change in resonance angle ΔθSPR (degree)

Sensitivity (degree/ RIU)

Full width at half maximum, (FWHM) (degree)

Detection accuracy (DA) (1/degree)

Ag

0.859

186.83

0.945

1.058

Ag 1 Graphene

0.877

190.570

1.52

0.658

Ag 1 BlueP/MoS2

0.905

196.798

1.45

0.690

FIGURE 11.15

(A) CV curves of the as-prepared electrodes in 0.1 M phosphate buffer solution (PBS) (pH 5 7.0) with 500 μM nitrite. (B) CV curves of the rGO-MoS2/GCE electrode in 0.1 M PBS (pH 5 7.0) under different concentrations of nitrite: 100, 300, 500, 700, and 1000 μM (scan rate: 50 mV s21).

MoS2 sensors. Fig. 11.15B shows that as the concentration of NO2 2 increases from 100 to 1000 μM the oxidation peak also increases. That means rGO/MoS2 heterostructures show excellent electro catalytic properties [168]. At 0.80 V and 0.2 4800 μM nitrite concentration, the step amperometric current (I t) graph of rGO/MoS2/GCE sensors and the inset image show amperometric current at lower NO2 2 concentration as shown in Fig. 11.16A. The rGO/MoS2/GCE sensor reaches 95% of the steady state value within 3 s after the incorporation of palpable nitrite concentration [168]. Fig. 11.16B is the current (μA) versus concentration (μM) graph of the amperometric response with stirring rate of 200 rpm. The sensor shows superior linear response in the range of 0.2 to 4800 μM. The rGO/MoS2 heterostructures sensor shows an improved response for nitrite detection [168].

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

11.5 CONCLUSION

427

FIGURE 11.16 (A) The amperometric current responses of rGO-MoS2/GCE for successive addition of nitrite range from 0.2 to 4800 μM in 0.1MPBS (pH 5 7.0). Inset image (i): amperometric current response of 0.2 to 50 μM. (B) The linear plot of oxidation current plateau value versus nitrite concentration.

11.5 CONCLUSION In recent years we have witnessed the growth of 2D material-based van der Waals heterostructures, where it is possible to control layer structure, arrange the atoms as wanted, and synthesize the new materials with innovative properties. The choice of vdWs heterostructures is limited only by the imagination, and the extensive availability of 2D materials and parameters opens infinite probabilities that will lead to the design of new generations of heterostructure materials. The 2D features and stability of building blocks makes heterostructures an ideal material for the electronic devices. This chapter provides information about heterostructure-based sensors and also briefly covers recent development in material chemistry as well as fabrication methods of 2D crystal-based heterostructures. It summarized recent progresses on 2D materials, their properties, and applications. We discussed the properties of heterostructures with fabrication methods. We showed how heterostructures have been fabricated by methods such as mechanical exfoliation, MBE, hydrothermal, and CVD. Compared to other methods, CVD shows advantages such as large area and high quality sheets of heterostructures. We further discussed application of heterostructures for sensors. Heterostructure materials have high sensitivity, fast response times, and excellent stability compared to the individual atoms. This brief review is an attempt to show the importance of vdW heterostructures and their use for sensing. Recent findings in this field show that their influence will be noticeable in the near future. The emergence of diverse structural properties in vdWs heterostructures opens new avenues for fundamental scientific studies and device

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

428

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

design. Research on heterostructures will lead material chemistry in the future beyond simple graphene and other 2D materials.

References [1] Z. Cai, B. Liu, X. Zou, H.M. Cheng, Chemical vapor deposition growth and applications of two-dimensional materials and their heterostructures, Chem. Rev. 118 (2018) 6091 6133. [2] M.Y. Li, C.H. Chen, Y. Shi, L.J. Li, Heterostructures based on two-dimensional layered materials and their potential applications, Mater. Today 19 (6) (2016) 322 335. [3] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, et al., Electric field effect in atomically thin carbon films, Science 306 (5696) (2004) 666 669. [4] K.S. Novoselov, D. Jiang, F. Schedin, T.J. Booth, V.V. Khotkevich, S.V. Morozov, et al., Two-dimensional atomic crystals, Proc. Natl. Acad. Sci. U.S.A. 102 (30) (2005) 10451 10453. [5] H. Li, J. Wu, Z. Yin, H. Zhang, Preparation and applications of mechanically exfoliated single-layer and multilayer MoS2 and WSe2 nanosheets, Acc. Chem, Res. 47 (4) (2014) 1067 1075. [6] Q. Liu, B. Cook, M. Gong, Y. Gong, D. Ewing, M. Casper, et al., Printable transferfree and wafer-size MoS2/graphene van der Waals heterostructures for highperformance photodetection, ACS Appl. Mater. Interfaces 9 (14) (2017) 12728 12733. [7] Y. Gong, J. Lin, X. Wang, G. Shi, S. Lei, Z. Lin, et al., Vertical and in-plane heterostructures from WS2/MoS2 monolayers, Nat. Mater. 13 (12) (2014) 1135. [8] S. Mathur, S. Barth, Molecule-based chemical vapor growth of aligned SnO2 nanowires and branched SnO2/V2O5 heterostructures, Small 3 (12) (2007) 2070 2075. [9] H. Tributsch, Hole reactions from d-energy bands of layer type group VI transition metal dichalcogenides: new perspectives for electrochemical solar energy conversion, J. Electrochem. Soc. 125 (7) (1978) 1086 1093. [10] B. Mendoza-Sa´nchez, Y. Gogotsi, Synthesis of two-dimensional materials for capacitive energy storage, Adv. Mater. 28 (29) (2016) 6104 6135. [11] M.S. Pawar, P.K. Bankar, M.A. More, D.J. Late, Ultra-thin V2O5 nanosheet based humidity sensor, photodetector and its enhanced field emission properties, RSC Adv. 5 (108) (2015) 88796 88804. [12] M. Pawar, S. Kadam, D.J. Late, High-performance sensing behavior using electronic ink of 2D SnSe2 nanosheets, Chem. Select 2 (14) (2017) 4068 4075. [13] L. Britnell, R.V. Gorbachev, R. Jalil, B.D. Belle, F. Schedin, A. Mishchenko, et al., Field-effect tunneling transistor based on vertical graphene heterostructures, Science 335 (6071) (2012) 947 950. [14] B.W. Baugher, H.O. Churchill, Y. Yang, P. Jarillo-Herrero, Optoelectronic devices based on electrically tunable p n diodes in a monolayer dichalcogenide, Nat. Nanotechnol. 9 (4) (2014) 262. [15] W. Zhang, C.P. Chuu, J.K. Huang, C.H. Chen, M.L. Tsai, Y.H. Chang, et al., Ultrahigh-gain photodetectors based on atomically thin graphene-MoS2 heterostructures, Sci. Rep. 4 (2014) 3826. [16] N. Mori, T. Ando, Electron optical-phonon interaction in single and double heterostructures, Phys. Rev. B 40 (9) (1989) 6175. [17] G.S. Eliel, M.V. Moutinho, A.C. Gadelha, A. Righi, L.C. Campos, H.B. Ribeiro, et al., Intralayer and interlayer electron phonon interactions in twisted graphene heterostructures, Nat. Commun. 9 (1) (2018) 1221.

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

REFERENCES

429

[18] L. Liao, J. Bai, Y. Qu, Y.C. Lin, Y. Li, Y. Huang, et al., High-κ oxide nanoribbons as gate dielectrics for high mobility top-gated graphene transistors, Proc. Natl. Acad. Sci. 107 (15) (2010) 6711 6715. [19] L. Liao, Y.C. Lin, M. Bao, R. Cheng, J. Bai, Y. Liu, et al., High-speed graphene transistors with a self-aligned nanowire gate, Nature 467 (7313) (2010) 305. [20] G. Clark, J.R. Schaibley, J. Ross, T. Taniguchi, K. Watanabe, J.R. Hendrickson, et al., Single defect light-emitting diode in a van der Waals heterostructure, Nano Lett. 16 (6) (2016) 3944 3948. [21] T. Georgiou, R. Jalil, B.D. Belle, L. Britnell, R.V. Gorbachev, S.V. Morozov, et al., Vertical field-effect transistor based on graphene WS2 heterostructures for flexible and transparent electronics, Nat. Nanotechnol. 8 (2) (2013) 100. [22] B. Cho, J. Yoon, S.K. Lim, A.R. Kim, D.H. Kim, S.G. Park, et al., Chemical sensing of 2D graphene/MoS2 heterostructure device, ACS Appl. Mater. Interfaces 7 (30) (2015) 16775 16780. [23] S. Bertolazzi, D. Krasnozhon, A. Kis, Nonvolatile memory cells based on MoS2/graphene heterostructures, ACS Nano 7 (4) (2013) 3246 3252. [24] R.E. Peierls, Quelques proprietes typiques des corpses solides, Ann. IH Poincare 5 (1935) 177 222. [25] L.D. Landau, On the theory of phase transitions, Ukr. J. Phys. 11 (1937) 19 32. [26] J.W. Jiang, J.S. Wang, B. Li, Thermal conductance of graphene and dimerite, Phys. Rev. B 79 (20) (2009) 205418. [27] S.H. Zhang, W. Yang, Perfect transmission at oblique incidence by trigonal warping in graphene PN junctions, Phys. Rev. B 97 (3) (2018) 035420. [28] J.C. Ng, C.Y. Tan, B.H. Ong, A. Matsuda, Effect of synthesis methods on methanol oxidation reaction on reduced graphene oxide supported palladium electrocatalysts, Proc. Eng. 184 (2017) 587 594. [29] A.A. Balandin, Thermal properties of graphene and nanostructured carbon materials, Nat. Mater. 10 (8) (2011) 569. [30] C. Lee, X. Wei, J.W. Kysar, J. Hone, Measurement of the elastic properties and intrinsic strength of monolayer graphene, Science 321 (5887) (2008) 385 388. [31] K.I. Bolotin, K.J. Sikes, Z. Jiang, M. Klima, G. Fudenberg, J. Hone, et al., Ultrahigh electron mobility in suspended graphene, Solid State Commun. 146 (9-10) (2008) 351 355. [32] S.V. Morozov, K.S. Novoselov, M.I. Katsnelson, F. Schedin, D.C. Elias, J.A. Jaszczak, et al., Giant intrinsic carrier mobilities in graphene and its bilayer, Phys. Rev. Lett. 100 (1) (2008) 016602. [33] Y. Zhu, S. Murali, W. Cai, X. Li, J.W. Suk, J.R. Potts, et al., Graphene and graphene oxide: synthesis, properties, and applications, Adv. Mater. 22 (35) (2010) 3906 3924. [34] M. Naguib, V.N. Mochalin, M.W. Barsoum, Y. Gogotsi, 25th anniversary article: MXenes: a new family of two-dimensional materials, Adv. Mater. 26 (7) (2014) 992 1005. [35] J. Qiao, X. Kong, Z.X. Hu, F. Yang, W. Ji, High-mobility transport anisotropy and linear dichroism in few-layer black phosphorus, Nat. Commun. 5 (2014) 4475. [36] H. Liu, A.T. Neal, Z. Zhu, Z. Luo, X. Xu, D. Toma´nek, et al., Phosphorene: an unexplored 2D semiconductor with a high hole mobility, ACS Nano 8 (4) (2014) 4033 4041. [37] L. Li, Y. Yu, G.J. Ye, Q. Ge, X. Ou, H. Wu, et al., Black phosphorus field-effect transistors, Nat. Nanotechnol. 9 (5) (2014) 372. [38] R. Lv, J.A. Robinson, R.E. Schaak, D. Sun, Y. Sun, T.E. Mallouk, et al., Transition metal dichalcogenides and beyond: synthesis, properties, and applications of singleand few-layer nanosheets, Acc. Chem. Res. 48 (1) (2014) 56 64. [39] S. Helveg, J.V. Lauritsen, E. Lægsgaard, I. Stensgaard, J.K. Nørskov, B.S. Clausen, et al., Atomic-scale structure of single-layer MoS2 nanoclusters, Phys. Rev. Lett. 84 (5) (2000) 951.

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

430

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

[40] J.V. Lauritsen, J. Kibsgaard, S. Helveg, H. Topsøe, B.S. Clausen, E. Lægsgaard, et al., Size-dependent structure of MoS2 nanocrystals, Nat. Nanotechnol. 2 (1) (2007) 53. [41] S.J. Sandoval, D. Yang, R.F. Frindt, J.C. Irwin, Raman study and lattice dynamics of single molecular layers of MoS2, Phys. Rev. B 44 (8) (1991) 3955. [42] S. Manzeli, D. Ovchinnikov, D. Pasquier, O.V. Yazyev, A. Kis, 2D transition metal dichalcogenides, Nat. Rev. Mater. 2 (8) (2017) 17033. [43] M. Chhowalla, H.S. Shin, G. Eda, L.J. Li, K.P. Loh, H. Zhang, The chemistry of twodimensional layered transition metal dichalcogenide nanosheets, Nat. Chem. 5 (4) (2013) 263. [44] P. Joensen, R.F. Frindt, S.R. Morrison, Single-layer MoS2, Mater. Res. Bull. 21 (4) (1986) 457 461. [45] X. Huang, Z. Zeng, H. Zhang, Metal dichalcogenide nanosheets: preparation, properties and applications, Chem. Soc. Rev. 42 (5) (2013) 1934 1946. [46] J. Li, Q. Ji, S. Chu, Y. Zhang, Y. Li, Q. Gong, et al., Tuning the photo-response in monolayer MoS2 by plasmonic nano-antenna, Sci. Rep. 6 (2016) 23626. [47] J.K. Ellis, M.J. Lucero, G.E. Scuseria, The indirect to direct bandgap transition in multilayered MoS2 as predicted by screened hybrid density functional theory, Appl. Phys. Lett. 99 (26) (2011) 261908. [48] O. Lopez-Sanchez, D. Lembke, M. Kayci, A. Radenovic, A. Kis, Ultrasensitive photodetectors based on monolayer MoS2, Nat. Nanotechnol. 8 (7) (2013) 497. [49] S. Zeng, S. Hu, J. Xia, T. Anderson, X.Q. Dinh, X.M. Meng, et al., Graphene MoS2 hybrid nanostructures enhanced surface plasmon resonance biosensors, Sens. Actuators B: Chem. 207 (2015) 801 810. [50] C.R. Dean, A.F. Young, I. Meric, C. Lee, L. Wang, S. Sorgenfrei, et al., Boron nitride substrates for high-quality graphene electronics, Nat. Nanotechnol. 5 (10) (2010) 722. [51] A.K. Geim, I.V. Grigorieva, Van der Waals heterostructures, Nature 499 (7459) (2013) 419. [52] Y. Liu, N.O. Weiss, X. Duan, H.C. Cheng, Y. Huang, X. Duan, Van der Waals heterostructures and devices, Nat. Rev. Mater. 1 (9) (2016) 16042. [53] K.S. Novoselov, A. Mishchenko, A. Carvalho, A.C. Neto, 2D materials and van der Waals heterostructures, Science 353 (6298) (2016) aac9439. [54] A.J. Molina-Mendoza, E. Giovanelli, W.S. Paz, M.A. Nin˜o, J.O. Island, C. Evangeli, et al., Franckeite as a naturally occurring van der Waals heterostructure, Nat. Commun. 8 (2017) 14409. [55] Q.H. Wang, K. Kalantar-Zadeh, A. Kis, J.N. Coleman, M.S. Strano, Electronics and optoelectronics of two-dimensional transition metal dichalcogenides, Nat. Nanotechnol. 7 (11) (2012) 699. [56] P. Rivera, K.L. Seyler, H. Yu, J.R. Schaibley, J. Yan, D.G. Mandrus, et al., Valleypolarized exciton dynamics in a 2D semiconductor heterostructure, Science 351 (6274) (2016) 688 691. [57] W.J. Yu, Z. Li, H. Zhou, Y. Chen, Y. Wang, Y. Huang, et al., Vertically stacked multiheterostructures of layered materials for logic transistors and complementary inverters, Nat. Mater. 12 (3) (2013) 246. [58] W.J. Yu, Y. Liu, H. Zhou, A. Yin, Z. Li, Y. Huang, et al., Highly efficient gate-tunable photocurrent generation in vertical heterostructures of layered materials, Nat. Nanotechnol. 8 (12) (2013) 952. [59] H. Wang, F. Liu, W. Fu, Z. Fang, W. Zhou, Z. Liu, Two-dimensional heterostructures: fabrication, characterization, and application, Nanoscale 6 (21) (2014) 12250 12272. [60] F. Ceballos, M.Z. Bellus, H.Y. Chiu, H. Zhao, Ultrafast charge separation and indirect exciton formation in a MoS2 MoSe2 van der Waals heterostructure, ACS Nano 8 (12) (2014) 12717 12724.

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

REFERENCES

431

[61] G. Tang, Y. Wang, W. Chen, H. Tang, C. Li, Hydrothermal synthesis and characterization of novel flowerlike MoS2 hollow microspheres, Mater. Lett. 100 (2013) 15 18. [62] C. Wang, H. Lin, Z. Xu, H. Cheng, C. Zhang, One-step hydrothermal synthesis of flowerlike MoS2/CdS heterostructures for enhanced visible-light photocatalytic activities, RSC Adv. 5 (20) (2015) 15621 15626. [63] H. Qi, L. Wang, J. Sun, Y. Long, P. Hu, F. Liu, et al., Production methods of van der Waals heterostructures based on transition metal dichalcogenides, Crystals 8 (1) (2018) 35. [64] Z. Zuo, Z. Xu, R. Zheng, A. Khanaki, J.G. Zheng, J. Liu, In-situ epitaxial growth of graphene/h-BN van der Waals heterostructures by molecular beam epitaxy, Sci. Rep. 5 (2015) 14760. [65] J. Park, W.C. Mitchel, L. Grazulis, H.E. Smith, K.G. Eyink, J.J. Boeckl, et al., Epitaxial graphene growth by carbon molecular beam epitaxy (CMBE), Adv. Mater. 22 (37) (2010) 4140 4145. [66] X. Duan, C. Wang, J.C. Shaw, R. Cheng, Y. Chen, H. Li, et al., Lateral epitaxial growth of two-dimensional layered semiconductor heterojunctions, Nat. Nanotechnol. 9 (12) (2014) 1024. [67] Y.I. Zhang, L. Zhang, C. Zhou, Review of chemical vapor deposition of graphene and related applications, Acc. Chem. Res. 46 (10) (2013) 2329 2339. [68] H. Zhang, Ultrathin two-dimensional nanomaterials, ACS Nano 9 (10) (2015) 9451 9469. [69] B. Liu, M. Fathi, L. Chen, A. Abbas, Y. Ma, C. Zhou, Chemical vapor deposition growth of monolayer WSe2 with tunable device characteristics and growth mechanism study, ACS Nano 9 (6) (2015) 6119 6127. [70] Q. Ji, Y. Zhang, T. Gao, Y. Zhang, D. Ma, M. Liu, et al., Epitaxial monolayer MoS2 on mica with novel photoluminescence, Nano Lett. 13 (8) (2013) 3870 3877. [71] X. Li, W. Cai, J. An, S. Kim, J. Nah, D. Yang, et al., Large-area synthesis of highquality and uniform graphene films on copper foils, Science 324 (5932) (2009) 1312 1314. [72] Y. Gong, B. Li, G. Ye, S. Yang, X. Zou, S. Lei, et al., Direct growth of MoS2 single crystals on polyimide substrates, 2D Materials 4 (2) (2017) 021028. [73] C. Du, N. Pan, CVD growth of carbon nanotubes directly on nickel substrate, Mater. Lett. 59 (13) (2005) 1678 1682. [74] X. Chen, Y. Qiu, H. Yang, G. Liu, W. Zheng, W. Feng, et al., In-plane mosaic potential growth of large-area 2D layered semiconductors MoS2 MoSe2 lateral heterostructures and photodetector application, ACS Appl. Mater. Interfaces 9 (2) (2017) 1684 1691. [75] S.M. Kim, A. Hsu, P.T. Araujo, Y.H. Lee, T. Palacios, M. Dresselhaus, et al., Synthesis of patched or stacked graphene and hBN flakes: a route to hybrid structure discovery, Nano Lett. 13 (3) (2013) 933 941. [76] A. Yan, J. Velasco Jr, S. Kahn, K. Watanabe, T. Taniguchi, F. Wang, et al., Direct growth of single-and few-layer MoS2 on h-BN with preferred relative rotation angles, Nano Lett. 15 (10) (2015) 6324 6331. [77] S. Behura, P. Nguyen, S. Che, R. Debbarma, V. Berry, Large-area, transfer-free, oxideassisted synthesis of hexagonal boron nitride films and their heterostructures with MoS2 and WS2, J. Am. Chem. Soc. 137 (40) (2015) 13060 13065. [78] Y. Yu, S. Hu, L. Su, L. Huang, Y. Liu, Z. Jin, et al., Equally efficient interlayer exciton relaxation and improved absorption in epitaxial and nonepitaxial MoS2/WS2 heterostructures, Nano Lett. 15 (1) (2014) 486 491. [79] C. Zhang, C.P. Chuu, X. Ren, M.Y. Li, L.J. Li, C. Jin, et al., Interlayer couplings, Moire´ patterns, and 2D electronic superlattices in MoS2/WSe2 hetero-bilayers, Sci. Adv. 3 (1) (2017) e1601459.

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

432

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

[80] B. Li, L. Huang, M. Zhong, Y. Li, Y. Wang, J. Li, et al., Direct vapor phase growth and optoelectronic application of large band offset SnS2/MoS2 vertical bilayer heterostructures with high lattice mismatch, Adv. Electron. Mater. 2 (2016) 11. [81] Q. Liu, B. Cook, M. Gong, Y. Gong, D. Ewing, M. Casper, et al., Printable transferfree and wafer-size MoS2/graphene van der Waals heterostructures for highperformance photodetection, ACS Appl. Mater. Interfaces 9 (14) (2017) 12728 12733. [82] B.M. Kulwicki, Humidity sensors, J. Am. Ceramic Soc. 74 (4) (1991) 697 708. [83] Z. Chen, C. Lu, Humidity sensors: a review of materials and mechanisms, Sens. Lett. 3 (4) (2005) 274 295. [84] K.I. Han, S. Kim, I.G. Lee, J.P. Kim, J.H. Kim, S.W. Hong, et al., Compliment graphene oxide coating on silk fiber surface via electrostatic force for capacitive humidity sensor applications, Sensors 17 (2) (2017) 407. [85] T.A. Blank, L.P. Eksperiandova, K.N. Belikov, Recent trends of ceramic humidity sensors development: a review, Sens. Actuators B: Chem. 228 (2016) 416 442. [86] S. Sikarwar, B.C. Yadav, Opto-electronic humidity sensor: a review, Sens. Actuators A: Phys. 233 (2015) 54 70. [87] H.S. Hong, D.T. Phan, G.S. Chung, High-sensitivity humidity sensors with ZnO nanorods based two-port surface acoustic wave delay line, Sens. Actuators B: Chem. 171 (2012) 1283 1287. [88] P.M. Harrey, B.J. Ramsey, P.S. Evans, D.J. Harrison, Capacitive-type humidity sensors fabricated using the offset lithographic printing process, Sens. Actuators B: Chem. 87 (2) (2002) 226 232. [89] J. Lee, S. Mulmi, V. Thangadurai, S.S. Park, Magnetically aligned iron oxide/gold nanoparticle-decorated carbon nanotube hybrid structure as a humidity sensor, ACS Appl. Mater. Interfaces 7 (28) (2015) 15506 15513. [90] R.S. Jachowicz, S.D. Senturia, A thin-film capacitance humidity sensor, Sens. Actuators 2 (1981) 171 186. [91] P.G. Su, C.S. Wang, Novel flexible resistive-type humidity sensor, Sens. Actuators B: Chem. 123 (2) (2007) 1071 1076. [92] F.L. Meng, Z. Guo, X.J. Huang, Graphene-based hybrids for chemiresistive gas sensors, TrAC Trends Anal. Chem. 68 (2015) 37 47. [93] D. Burman, R. Ghosh, S. Santra, P.K. Guha, Highly proton conducting MoS2/graphene oxide nanocomposite based chemoresistive humidity sensor, RSC Adv. 6 (62) (2016) 57424 57433. [94] D.I. Lim, J.R. Cha, M.S. Gong, Preparation of flexible resistive micro-humidity sensors and their humidity-sensing properties, Sens. Actuators B: Chem. 183 (2013) 574 582. [95] A.D. Smith, K. Elgammal, F. Niklaus, A. Delin, A.C. Fischer, S. Vaziri, et al., Resistive graphene humidity sensors with rapid and direct electrical readout, Nanoscale 7 (45) (2015) 19099 19109. [96] D.H. Kim, Y.S. Shim, J.M. Jeon, H.Y. Jeong, S.S. Park, Y.W. Kim, et al., Vertically ordered hematite nanotube array as an ultrasensitive and rapid response acetone sensor, ACS Appl. Mater. Interfaces 6 (17) (2014) 14779 14784. [97] L. Khandare, S.S. Terdale, D.J. Late, Ultra-fast α-MoO3 nanorod-based Humidity sensor, Adv. Dev. Mater. 2 (2) (2016) 15 22. [98] R. Nohria, R.K. Khillan, Y. Su, R. Dikshit, Y. Lvov, K. Varahramyan, Humidity sensor based on ultrathin polyaniline film deposited using layer-by-layer nanoassembly, Sens. Actuators B: Chem. 114 (1) (2006) 218 222. [99] J.W. Han, B. Kim, J. Li, M. Meyyappan, Carbon nanotube based humidity sensor on cellulose paper, J. Phys. Chem. C 116 (41) (2012) 22094 22097.

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

REFERENCES

433

[100] S.Y. Park, J.E. Lee, Y.H. Kim, J.J. Kim, Y.S. Shim, S.Y. Kim, et al., Room temperature humidity sensors based on rGO/MoS2 hybrid composites synthesized by hydrothermal method, Sens. Actuators B: Chem. 258 (2018) 775 782. [101] Z. Lou, D. Wu, K. Bu, T. Xu, Z. Shi, J. Xu, et al., Dual-mode high-sensitivity humidity sensor based on MoS2/Si nanowires array heterojunction, J. Alloys Compd. 726 (2017) 632 637. [102] W. Wu, D. De, S.C. Chang, Y. Wang, H. Peng, J. Bao, et al., High mobility and high on/off ratio field-effect transistors based on chemical vapor deposited single-crystal MoS2 grains, Appl. Phys. Lett. 102 (14) (2013) 142106. [103] P.J. Jeon, J.S. Kim, J.Y. Lim, Y. Cho, A. Pezeshki, H.S. Lee, et al., Low power consumption complementary inverters with n-MoS2 and p-WSe2 dichalcogenide nanosheets on glass for logic and light-emitting diode circuits, ACS Appl. Mater. Interfaces 7 (40) (2015) 22333 22340. [104] A. Kaushik, R. Kumar, S.K. Arya, M. Nair, B.D. Malhotra, S. Bhansali, Organic inorganic hybrid nanocomposite-based gas sensors for environmental monitoring, Chem. Rev. 115 (11) (2015) 4571 4606. [105] X. Zhou, S. Lee, Z. Xu, J. Yoon, Recent progress on the development of chemosensors for gases, Chem. Rev. 115 (15) (2015) 7944 8000. [106] N. Barsan, D. Koziej, U. Weimar, Metal oxide-based gas sensor research: how to?, Sens. Actuators B: Chem. 121 (1) (2007) 18 35. [107] M. Poloju, N. Jayababu, E. Manikandan, M.R. Reddy, Enhancement of the isopropanol gas sensing performance of SnO2/ZnO core/shell nanocomposites, J. Mater. Chem. C 5 (10) (2017) 2662 2668. [108] S. Park, S. An, Y. Mun, C. Lee, UV-enhanced NO2 gas sensing properties of SnO2core/ZnO-shell nanowires at room temperature, ACS Appl. Mater. Interfaces 5 (10) (2013) 4285 4292. [109] B. Fabbri, A. Gaiardo, A. Giberti, V. Guidi, C. Malagu`, A. Martucci, et al., Chemoresistive properties of photo-activated thin and thick ZnO films, Sens. Actuators B: Chem. 222 (2016) 1251 1256. [110] G. Gundiah, A. Govindaraj, C.N. Rao, Nanowires, nanobelts and related nanostructures of Ga2O3, Chem. Phys. Lett. 351 (3-4) (2002) 189 194. [111] Y.H. Gao, Y. Bando, T. Sato, Y.F. Zhang, X.Q. Gao, Synthesis, Raman scattering and defects of β-Ga2O3 nanorods, Appl. Phys. Lett. 81 (12) (2002) 2267 2269. [112] H. Kim, C. Jin, S. Park, S. Kim, C. Lee, H2S gas sensing properties of bare and Pdfunctionalized CuO nanorods, Sens. Actuators B: Chem. 161 (1) (2012) 594 599. [113] D.P. Volanti, A.A. Felix, M.O. Orlandi, G. Whitfield, D.J. Yang, E. Longo, et al., The role of hierarchical morphologies in the superior gas sensing performance of CuObased chemiresistors, Adv. Funct. Mater. 23 (14) (2013) 1759 1766. [114] T. Wagner, S. Haffer, C. Weinberger, D. Klaus, M. Tiemann, Mesoporous materials as gas sensors, Chem. Soc. Rev. 42 (9) (2013) 4036 4053. [115] W.I. Laminack, J.L. Gole, Light enhanced electron transduction and amplified sensing at a nanostructure modified semiconductor interface, Adv. Funct. Mater. 23 (47) (2013) 5916 5924. [116] P. Wang, Y. Fu, B. Yu, Y. Zhao, L. Xing, X. Xue, Realizing room-temperature self-powered ethanol sensing of ZnO nanowire arrays by combining their piezoelectric, photoelectric and gas sensing characteristics, J. Mater. Chem. A 3 (7) (2015) 3529 3535. [117] J. Cui, L. Shi, T. Xie, D. Wang, Y. Lin, UV-light illumination room temperature HCHO gas-sensing mechanism of ZnO with different nanostructures, Sens. Actuators B: Chem. 227 (2016) 220 226. [118] N.D. Chinh, N.D. Quang, H. Lee, T.T. Hien, N.M. Hieu, D. Kim, et al., NO gas sensing kinetics at room temperature under UV light irradiation of In2O3 nanostructures, Sci. Rep. 6 (2016) 35066.

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

434

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

[119] R. Jaisutti, M. Lee, J. Kim, S. Choi, T.J. Ha, J. Kim, et al., Ultrasensitive roomtemperature operable gas sensors using p-Type Na: ZnO nanoflowers for diabetes detection, ACS Appl. Mater. Interfaces 9 (10) (2017) 8796 8804. [120] H.R. Kim, A. Haensch, I.D. Kim, N. Barsan, U. Weimar, J.H. Lee, The role of NiO doping in reducing the impact of humidity on the performance of SnO2-based gas sensors: synthesis strategies, and phenomenological and spectroscopic studies, Adv. Funct. Mater. 21 (23) (2011) 4456 4463. [121] M. Yuasa, T. Kida, K. Shimanoe, Preparation of a stable sol suspension of Pd-loaded SnO2 nanocrystals by a photochemical deposition method for highly sensitive semiconductor gas sensors, ACS Appl. Mater. Interfaces 4 (8) (2012) 4231 4236. [122] P. Sun, C. Wang, J. Liu, X. Zhou, X. Li, X. Hu, et al., Hierarchical assembly of α-Fe2O3 nanosheets on SnO2 hollow nanospheres with enhanced ethanol sensing properties, ACS Appl. Mater. Interfaces 7 (34) (2015) 19119 19125. [123] S.S. Shendage, V.L. Patil, S.A. Vanalakar, S.P. Patil, N.S. Harale, J.L. Bhosale, et al., Sensitive and selective NO2 gas sensor based on WO3 nanoplates, Sens. Actuators B: Chem. 240 (2017) 426 433. [124] R. Kumar, O. Al-Dossary, G. Kumar, A. Umar, Zinc oxide nanostructures for NO2 gas sensor applications: a review, Nano-Micro Lett. 7 (2) (2015) 97 120. [125] B. Zhang, M. Cheng, G. Liu, Y. Gao, L. Zhao, S. Li, et al., Room temperature NO2 gas sensor based on porous Co3O4 slices/reduced graphene oxide hybrid, Sens. Actuators B: Chem. 263 (2018) 387 399. [126] M.W. Jung, S.M. Kang, K.H. Nam, K.S. An, B.C. Ku, Highly transparent and flexible NO2 gas sensor film based on MoS2/rGO composites using soft lithographic patterning, Appl. Surface Sci. 456 (2018) 7 12. [127] T. Wang, J. Hao, S. Zheng, Q. Sun, D. Zhang, Y. Wang, Highly sensitive and rapidly responding room-temperature NO2 gas sensors based on WO3 nanorods/sulfonated graphene nanocomposites, Nano Res. 11 (2) (2018) 791 803. [128] F. Rigas, S. Sklavounos, Evaluation of hazards associated with hydrogen storage facilities, Int. J. Hydrogen Energy 30 (13-14) (2005) 1501 1510. [129] D.E. Motaung, G.H. Mhlongo, P.R. Makgwane, B.P. Dhonge, F.R. Cummings, H.C. Swart, et al., Ultra-high sensitive and selective H2 gas sensor manifested by interface of n n heterostructure of CeO2-SnO2 nanoparticles, Sens. Actuators B: Chem. 254 (2018) 984 995. [130] W.H. Tao, C.H. Tsai, H2S sensing properties of noble metal doped WO3 thin film sensor fabricated by micromachining, Sens. Actuators B: Chem. 81 (2-3) (2002) 237 247. [131] S. Bai, C. Chen, M. Cui, R. Luo, A. Chen, D. Li, Rapid synthesis of rGO MoO3 hybrids and mechanism of enhancing sensing performance to H2S, RSC Advances 5 (63) (2015) 50783 50789. [132] S. Bai, C. Chen, R. Luo, A. Chen, D. Li, Synthesis of MoO3/reduced graphene oxide hybrids and mechanism of enhancing H2S sensing performances, Sens. Actuators B: Chem. 216 (2015) 113 120. [133] E. Kretschmann, H. Raether, Radiative decay of non radiative surface plasmons excited by light, Zeitschrift fu¨r Naturforschung A 23 (12) (1968) 2135 2136. [134] A. Otto, Excitation of nonradiative surface plasma waves in silver by the method of frustrated total reflection, Zeitschrift fu¨r Physik A Hadrons and nuclei 216 (4) (1968) 398 410. [135] C.T. Campbell, G. Kim, SPR microscopy and its applications to high-throughput analyses of biomolecular binding events and their kinetics, Biomaterials 28 (15) (2007) 2380 2392. [136] C.T. Li, K.C. Lo, H.Y. Chang, H.T. Wu, J.H. Ho, T.J. Yen, Ag/Au bi-metallic film based color surface plasmon resonance biosensor with enhanced sensitivity, color contrast and great linearity, Biosens. Bioelectron. 36 (1) (2012) 192 198.

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

REFERENCES

435

[137] Z. Wang, Z. Cheng, V. Singh, Z. Zheng, Y. Wang, S. Li, et al., Stable and sensitive silver surface plasmon resonance imaging sensor using trilayered metallic structures, Anal. Chem. 86 (3) (2014) 1430 1436. [138] G. Wang, C. Wang, S. Sun, An optical waveguide sensor based on mesoporous silica films with a comparison to surface plasmon resonance sensors, Sens. Actuators B: Chem. 255 (2018) 3400 3408. [139] L. Wang, Y. Sun, J. Wang, X. Zhu, F. Jia, Y. Cao, et al., Sensitivity enhancement of SPR biosensor with silver mirror reaction on the Ag/Au film, Talanta 78 (1) (2009) 265 269. [140] J. Homola, S.S. Yee, G. Gauglitz, Surface plasmon resonance sensors, Sens. Actuators B: Chem. 54 (1-2) (1999) 3 15. [141] M.S. Rahman, K.A. Rikta, L.B. Bashar, M.S. Anower, Numerical analysis of graphene coated surface plasmon resonance biosensors for biomedical applications, Optik-Int. J. Light Electron Opt. 156 (2018) 384 390. [142] M. Hossain, M. Rana, DNA hybridization detection based on resonance frequency readout in graphene on Au SPR biosensor, J. Sens. 2016 (2016). [143] A.I. Lao, X. Su, K.M. Aung, SPR study of DNA hybridization with DNA and PNA probes under stringent conditions, Biosens. Bioelectron. 24 (6) (2009) 1717 1722. [144] H. Fu, S. Zhang, H. Chen, J. Weng, Graphene enhances the sensitivity of fiberoptic surface plasmon resonance biosensor, IEEE Sens. J. 15 (10) (2015) 5478 5482. [145] L. Wu, H.S. Chu, W.S. Koh, E.P. Li, Highly sensitive graphene biosensors based on surface plasmon resonance, Optics express 18 (14) (2010) 14395 14400. [146] P.K. Maharana, R. Jha, S. Palei, Sensitivity enhancement by air mediated graphene multilayer based surface plasmon resonance biosensor for near infrared, Sens. Actuators B: Chem. 190 (2014) 494 501. [147] K.N. Shushama, M.M. Rana, R. Inum, M.B. Hossain, Graphene coated fiber optic surface plasmon resonance biosensor for the DNA hybridization detection: simulation analysis, Optics Commun. 383 (2017) 186 190. [148] B. Ruan, J. Guo, L. Wu, J. Zhu, Q. You, X. Dai, et al., Ultrasensitive terahertz biosensors based on fano resonance of a graphene/waveguide hybrid structure, Sensors 17 (8) (2017) 1924. [149] Z. Lin, Y. Jia, Q. Ma, L. Wu, B. Ruan, J. Zhu, et al., High sensitivity intensity-interrogated Bloch surface wave biosensor with graphene, IEEE Sens. J. 18 (1) (2017) 106 110. [150] Y. Xiang, J. Zhu, L. Wu, Q. You, B. Ruan, X. Dai, Highly sensitive Terahertz gas sensor based on surface plasmon resonance with graphene, IEEE Photonics J. 10 (1) (2018) 1 7. [151] Z. Lin, L. Jiang, L. Wu, J. Guo, X. Dai, Y. Xiang, et al., Tuning and sensitivity enhancement of surface plasmon resonance biosensor with graphene covered AuMoS2-Au films, IEEE Photonics J. 8 (6) (2016) 1 8. [152] L. Wu, Y. Jia, L. Jiang, J. Guo, X. Dai, Y. Xiang, et al., Sensitivity improved SPR biosensor based on the MoS2/graphene aluminum hybrid structure, J. Lightwave Technol. 35 (1) (2017) 82 87. [153] L. Wu, J. Guo, X. Dai, Y. Xiang, D. Fan, Sensitivity enhanced by MoS2 graphene hybrid structure in guided-wave surface plasmon resonance biosensor, Plasmonics 13 (1) (2018) 281 285. [154] M.S. Rahman, M.S. Anower, M.R. Hasan, M.B. Hossain, M.I. Haque, Design and numerical analysis of highly sensitive Au-MoS2-graphene based hybrid surface plasmon resonance biosensor, Optics Commun. 396 (2017) 36 43. [155] J.W. Chung, S.D. Kim, R. Bernhardt, J.C. Pyun, Application of SPR biosensor for medical diagnostics of human hepatitis B virus (hHBV), Sens. Actuators B: Chem. 111 (2005) 416 422.

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS

436

11. RECENT DEVELOPMENTS IN GRAPHENE-BASED TWO-DIMENSIONAL

[156] J. Ladd, A.D. Taylor, M. Piliarik, J. Homola, S. Jiang, Label-free detection of cancer biomarker candidates using surface plasmon resonance imaging, Anal. Bioanal. Chem. 393 (4) (2009) 1157 1163. [157] A.N. Naimushin, S.D. Soelberg, D.K. Nguyen, L. Dunlap, D. Bartholomew, J. Elkind, et al., Detection of Staphylococcus aureus enterotoxin B at femtomolar levels with a miniature integrated two-channel surface plasmon resonance (SPR) sensor, Biosens. Bioelectron. 17 (6-7) (2002) 573 584. [158] A. Pathak, S. Parveen, B.D. Gupta, Fibre optic SPR sensor using functionalized CNTs for the detection of SMX: comparison with enzymatic approach, Plasmonics 13 (1) (2018) 189 202. [159] M. Soler, M.C. Estevez, M. de Lourdes Moreno, A. Cebolla, L.M. Lechuga, Labelfree SPR detection of gluten peptides in urine for non-invasive celiac disease followup, Biosens. Bioelectron. 79 (2016) 158 164. [160] F. Fathi, H. Mohammadzadeh-Aghdash, Y. Sohrabi, P. Dehghan, J.E. Dolatabadi, Kinetic and thermodynamic studies of bovine serum albumin interaction with ascorbyl palmitate and ascorbyl stearate food additives using surface plasmon resonance, Food Chem. 246 (2018) 228 232. [161] Y. Liu, Q. Liu, S. Chen, F. Cheng, H. Wang, W. Peng, Surface plasmon resonance biosensor based on smart phone platforms, Sci. Rep. 5 (2015) 12864. [162] J. Cao, T. Sun, K.T. Grattan, Gold nanorod-based localized surface plasmon resonance biosensors: a review, Sens. Actuators B: Chem. 195 (2014) 332 351. [163] A.K. Sharma, A.K. Pandey, Blue phosphorene/MoS2 heterostructure based SPR sensor with enhanced sensitivity, IEEE Photonics Technol. Lett. 30 (7) (2018) 595 598. [164] Y. Dubowski, A.J. Colussi, C. Boxe, M.R. Hoffmann, Monotonic increase of nitrite yields in the photolysis of nitrate in ice and water between 238 and 294 K, J. Phys. Chem. A 106 (30) (2002) 6967 6971. [165] M.K. Rayman, B. Aris, A. Hurst, Nisin: a possible alternative or adjunct to nitrite in the preservation of meats, Appl. Environ. Microbiol. 41 (2) (1981) 375 380. [166] R. Yue, Q. Lu, Y. Zhou, A novel nitrite biosensor based on single-layer graphene nanoplatelet protein composite film, Biosens. Bioelectron. 26 (11) (2011) 4436 4441. [167] D. Zhang, H. Ma, Y. Chen, H. Pang, Y. Yu, Amperometric detection of nitrite based on Dawson-type vanodotungstophosphate and carbon nanotubes, Anal. Chim. Acta 792 (2013) 35 44. [168] J. Hu, J. Zhang, Z. Zhao, J. Liu, J. Shi, G. Li, et al., Synthesis and electrochemical properties of rGO-MoS2 heterostructures for highly sensitive nitrite detection, Ionics 24 (2) (2018) 577 587.

FUNDAMENTALS AND SENSING APPLICATIONS OF 2D MATERIALS