Efficient cold cathode emission in crystalline-amorphous hybrid: Study on carbon nanotube-cadmium selenide system

Accepted Manuscript Efficient cold cathode emission in crystalline-amorphous hybrid: Study on carbon nanotube-cadmium selenide system S. Sarkar, D. Banerjee, N.S. Das, U.K. Ghorai, D. Sen, K.K. Chattopadhyay PII:

S1386-9477(17)31463-7

DOI:

10.1016/j.physe.2017.11.003

Reference:

PHYSE 12951

To appear in:

Physica E: Low-dimensional Systems and Nanostructures

Received Date: 22 September 2017 Revised Date:

27 October 2017

Accepted Date: 3 November 2017

Please cite this article as: S. Sarkar, D. Banerjee, N.S. Das, U.K. Ghorai, D. Sen, K.K. Chattopadhyay, Efficient cold cathode emission in crystalline-amorphous hybrid: Study on carbon nanotube-cadmium selenide system, Physica E: Low-dimensional Systems and Nanostructures (2017), doi: 10.1016/ j.physe.2017.11.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Graphical Abstract Title: Efficient Cold Cathode Emissionin Crystalline-Amorphous Hybrid: Study on Carbon Nanotube-Cadmium Selenide System

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Author: S.Sarkar, D. Banerjee, N.S. Das, U. K. Ghorai, D. Sen and K.K.Chattopadhyay

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Efficient Cold Cathode Emissionin Crystalline-Amorphous Hybrid: Study on Carbon Nanotube-Cadmium Selenide System S.Sarkar

a, c, Ξ)

b,$)

, D.Banerjee

, N.S. Dasa, #), U.K. Ghoraid), D. Senc), and K.K.Chattopadhyaya, c, *)

a)

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School of Material Science and Nanotechnology Jadavpur University, Kolkata 700032, India b) Dr. M.N. Dastur School of Materials Science Engineering; Indian Institute of Engineering Science and Engineering, West Bengal, India. c) Thin Film and NanoScience Laboratory, Department of Physics, Jadavpur University, Kolkata 700032, India d) Department of Industrial Chemistry & Swami Vivekananda Research centre, Ramakrishna Mission Vidyamandira, Belur Math, Howrah-711202

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Abstract

Cadmium Selenide (CdSe) quantum dot (QD) decorated amorphous carbon nanotubes (a-CNTs) hybrids have been synthesized by simple chemical process. The samples were characterized by field emission scanning and transmission electron microscopy, Fourier transformed infrared spectroscopy, Raman and UV-Vis spectroscopy. Lattice image obtained from transmission electron microscopic study confirms the successful attachment of CdSe QDs.

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It is seen that hybrid samples show an enhanced cold emission properties with good stability. The results have been explained in terms of increased roughness, more numbers of emitting sites and favorable band bending induced electron transport. ANSYS software based calculation has also supported the result.

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Also a first principle based study has been done which shows that due to the formation of hybrid structure there is a profound upward shift in the Fermi level, i.e. a decrease of work function,

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which is believed to be another key reason for the observed improved field emission performance

Keywords: 1.Amorphous CNT; 2.Quantum Dots; 3.Fieldemission; 4.Electron microscopy Corresponding author:[email protected] (KKC) [email protected] (DB) # Present Address:Department of Basic Science and Humanities, Techno India, Batanagar Ξ Present Address: Department of Electronics and Communication Engineering Siliguri Institute of Technology $

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1. Introduction During the lastfew decades, the researches on zero and one dimensional nanostructures have gained a lot of interest among researchers. The discovery of carbon nanotubes (CNTs), by Iijima

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in the year of 1991 was one of the most important milestones in this direction [1]. CNTs with dimension ranging from 1 to 100 nm have shown remarkable and unique electronic, mechanical and physical properties. Researchers have extensively studied different properties of CNTs for

devices

and

evenin

transistor

[2-4].CNTs

are

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their possible applications in versatile areas like,electrodes of rechargeable batteries, gas sensing also

being

investigated

for

their

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excitingfieldemission (FE) property for their possible application in display devices [5-6]. There are many published reports on the fascinating FE property of CNTs [7-10].It is shown by different researchers that it is possible to get better FE performance from CNTs if their walls are decorated with different functional nanostructures [11-12].Different organic and inorganic

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nanostructures like TiO2, ZnO, MnOx,CoS or PMMA have successfully been used to develop hybrid CNT field emitters and for other applications [13-17]. However, most of the researches on CNTs are centered on crystalline CNTs, synthesis of which

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requires complex steps, high synthesis temperature and yet the yield is poor. Amorphous CNTs (a-CNTs) on the other hand, can be prepared easily as reported in our previous works by very

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simple low temperature solid state reaction with very high yield[18]. Recently a-CNTs have been studied for its possible application as field emittersandsupercapacitors also [19, 20]. It is noteworthy that the crystalline CNTs rarely having any surface defects thus are very inert in nature and difficult to make them functionalized with foreign materials. Our reported a-CNTs have advantages in this regard over crystalline CNTs due to amorphousness of the material and

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thus inherently possessing large numbers of defects. A-CNTs already contain a large numbers of defects and dangling bonds and thus can be easily functionalized with foreign nanostructures. As mentioned before for the sake of obtaining better properties it is common to attached different

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nanostructures (0, 1, 2 or 3 dimensional) of versatile materials onto the CNTs wall. Among these, zero dimensional particles, also known as quantum dots (QDs) have attracted the attention of the current researchers as they show versatile size dependent properties. Also anchoring

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different one or two dimensional nanostructures of various materials with these QDs can dramatically change the properties of hosts [21-23]. Among various well studied QDs like

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carbon, silicon, lead sulfide, zinc oxide and many other cadmium selenide (CdSe) is an important material, QDs of which are recently being used in making green LEDs, solar cells and other optoelectronic applications. CdSe QDs being an important group II-VI semiconductor has been studied extensively for it exciting optical properties [24, 25].

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There are some reports of synthesis of CdSe based hybrids and its’ optical properties [26-28] but so far the authors are concerned the literature remains silent regarding the exciting FE property of CdSe-a-CNT hybrids.

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Keeping all these in mind we have for the first time reported the synthesis of a-CNT-CdSe hybrids by a simple low temperature process with good yield with possible application as cold

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cathode. It has been shown that due to anchoring of the wall of a-CNTs with QDs the FE properties of the host material has been enhanced significantly. Also several theoretical approach like density functional theory (DFT) or ANSYS- Maxwell’ software based calculations have supported the experimental findings.

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2. Experimental and Characterization The synthesis of a-CNTs has already been reportedin our previous work [29].Briefly,ferrocene and ammonium chloride were taken in 1:2 weight ratio mixed thoroughly and transferred to an

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alumina boat. The alumina boat was heated at 250 oC for 30 minutes in an air furnace and then the oven was allowed to cool naturally to obtain a black powder.The black powder was washed repeatedly with dilute HCl and di-ionized water for several times and filtered. The final product

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was obtained only after drying the filtrate overnight at 80oCin an air furnace. The as synthesized a- CNTs were used for making composite with CdSe QD without further modifications.

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CdSe QDs were prepared separately by inverse micelle technique almost similar as reported by Hamizi e t al [30]. In short, 60 ml oleic acid and paraffin oil was mixed and 2 gm of CdO was added to the solution. The solution was heated at around 150oC in an enclosed and sealed container and stirred for long. In a separate container Se was mixed with paraffin oil at 225oC

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and vigorously stirred. The solution, containing CdO was next added to solution containing Se and stirred at high rpm. The solution was centrifuged at12000 rpm. Four samples of CdSe QDs were prepared by varying the synthesis time for 30 seconds, 1, 5 and 10 minutes for the

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preparation of CdSe QDs.

For attaching CdSe QDs onto a-CNTs’ walls the as synthesized certain amount ofCdSe QDs

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were added to 20 ml of pyridine solution and ultrasonicated for 90 minutes[31]. The as prepared a-CNT was added to 50 ml of methanol and stirred for 30 minutes in a separate container. Then the dispersions containing CdSe QDs and the other dispersions containing a-CNTs were mixed and continuously stirred.

The final hybrid samples were obtained after filtering and drying the residue in an air oven for several hours. Four hybrid samples named S1, S2, S3 and S4 were synthesized that are

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associated with four Quantum Dots (QDs) synthesized for four different times as mentioned before. To be specific S1, S2, S3 and S4 are hybrid samples where CdSe QDs were synthesized for 30 seconds, 1, 5 and 10 minutes respectively.

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The as prepared samples were characterized by X-ray diffraction (XRD, BRUKER D8 Advance),field emission scanning electron microscope (FESEM, Hitachi, S-4800), high resolution transmission electron microscopy (HRTEM, JEOL-JEM 2100),Fourier transformed

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infrared spectrophotometer (FTIR-8400S) andRaman spectrometer (λex = 532 nm).

The field emission property was investigated by our custom-made high vacuum field electron

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emission set up. Field emission measurements have been studied in diode configuration. The system consisted of a cathode (the sample under test) and a stainless steel tip anode (tip diameter was ~ 1 mm) mounted in a liquid nitrogen trapped rotary-diffusion high vacuum chamber with an appropriate chamber baking arrangement. The chamber was evacuated to maintain a base

3. Results and Discussion 3.1. Microscopic study

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pressure of ∼ 10−7 mbar. A view port was also created toobserveany discharge from the samples.

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Fig.1(a-d) shows the FESEM images of the as-prepared a-CNTs coated with CdSe QDs with higher magnified image shown inset. It is seen in all the pictures thata-CNTs have been formed

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over a large area with high yield. The long and 1 dimensional nature of the a-CNTs with diameter around 120 nm and length of few micrometers can be seen clearly in all the pictures [31]. Also one can see the uniform attachment of spherical particles of foreign material onto the wall of a-CNTs. The particles are having dimensions of few nm thus can be considered to be quantum dots. Much information about the size and shape of the quantum dots cannot be

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extracted from almost identical nature of FESEM images. However for having a magnified view of the attachment of the QDs onto a-CNTs’ wall TEM study has been done. Fig.2.a shows the HRTEM image of the a-CNT with higher magnified image shown inset,

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whereas Fig.2(b, c and d) shows the TEM images of the hybrid samples S1, S2 and S4 respectively. HRETM image of Fig.2 a shows the individual nature of a-CNT, whereas Fig.2b, c & d show theeffect of CdSe QD Hybridization with a-CNTs. From the TEM image the

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hollowness and tubular structure of the as synthesized a-CNTs can clearly be seen and thus the formation of CNTs can be confirmed. The diameter of the tube can be seen to be ∼ 120 nm thus

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supporting the FESEM results. The individual wall thickness of the sample is around 10-15 nm as can be seen from TEM image. From the other images of the hybrid samples (Fig.2 b, c, d) the attachment of the spherical particle onto the a-CNTs’ wall can clearly be seen. The attached particles are of spherical in nature with diameter around 8-10 nm thus can be considered to be

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quantum dot. The lattice pattern of the individual particles has been shown inset. The lattice spacing (d) value has been measured to be (0.351) thus corresponds to the (100) plane of the hexagonal CdSe. Thus from the microscopic study the formation of a-CNT-CdSe QD hybrid

3.2. FTIR Study

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samples can be confirmed.

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Fig.3 shows the FTIR spectra of all the hybrid samples taken in absorption mode between wave number ranges 800-4000 cm-1. It is seen that all the four samples generates almost identical spectra with few distinct absorption peaks around 1060, 1550, 1663 and 2350 cm-1. Also there are broad band between 2800-3000 cm-1 and above 3500 cm-1. The peak at 1060 cm-1 is the characteristic of different Si-O-Si absorption band [32] comes probably from the silicon substrate used for sample mounting. The peak around 1550 cm-1

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signifies amide vibration marking the covalent bonding between as prepared a-CNTs and CdSe QDs [31]. The peaks around1670 and 2350 cm-1 signifies the presence of C=C stretching and CO2[31, 33].the last one comes as the contamination from the atmosphere. The broad band

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between 3000-3500 cm-1signifies the presence of –OH groups. The band between 2800-3000 cmis due to the presence of different C-Hn bonds. Also in some reports the existence of additional

peaks around 2855 and 2917 cm-1 has been associated with pyridine, used in making the CdSe

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QDs [31]. 3.3. Raman study

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Fig.4shows the Raman spectra of all the a-CNT-CdSe hybrid samples. It is seen that spectra contains two well-known broad peaks centring around 1360 and 1580 cm-1 that are associated with D and G band respectively for all the samples. Also a signature of 2D band around 2750 cm -1

can be seen for all the samples.

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It is to be noted that the ratio of the area under G (AG) and D (AD) peak which are basically the characteristics of sp2 bonded carbon in all possible form and that of sp2 hybridized carbon present in rings and not chains can be used to determine the corresponding parameter present in the

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sample [34]. The area of G and D band has been calculated from the deconvoluted Raman spectra which is shown inset of Fig.4 (for S1). Also the full width at half maxima (FWHM) of G

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band represents the structural disorder that arises from bond angle and bond length distortion. Raman spectra can also be used for the determination of sp3 content in the sample using the following equation:

(1) Where, γGis the peak centre of G band in µm-1 unit.

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Table 1 summarizes all the above parameters for all the pure and hybrid samples. It is seen that there is a monotonic shift of position of both D and G band but in reverse direction and also sp3

3.4. Field emission study 3.4.1. Experimental findings

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content in the hybrid samples decreases slightly.

the well-known Fowler-Nordheim equation [35]

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Theoretically the emission current and the macroscopic electric field are related to each other by

I = AatF−2φ −1 ( βE )2 exp{−bvFφ 3/ 2 / βE} (2)

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Where A is the effective emission area, ß is the enhancement factor, tF , vF are the values of special FE elliptic function for a particular barrier height ф [36], a and b are respectively the first and second Fowler–Nordheim (F-N) constants having values a= 1.541434×10-6AeV V-2 and b=6.830890×109eV-3/2V m-1. The F-N equation when simplified takes the form as

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ln{J / E 2 } = ln{t F−2 aφ −1β 2 } − [{vF bφ 3 / 2 β −1} / E ] (3) where J= I/A is the macroscopic current density.

Hence plot of ln{J/E2} vs. 1/E should be a straight line and its slope and intercept gives the

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valuable information about the enhancement factor, local work function etc. An experimental F-

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N plot has been modeled which can be expressed as

ln{J / E 2 } = ln{raφ −1 β 2 } − [{sbφ 3 / 2 β −1} / E] (4)

Where r and s are respectively the intercept and slope correction factors. Typically, the value of s is nearly unity but r may have values, which may be as high as 100 and even greater. The experimental J-E curves of all the hybrids and corresponding F-N plots are shown in Fig.5(a) and (b) respectively. It can be seen that the sample S2 gives the best emission characteristics compared to other whereas S1 gives the worst result. The low field region characteristic has been 8

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shown separately inset Fig.5a. The turn-on field (ETO) which, has been defined as the field required to obtain a current density J = 5 µA/cm2 has been reduced from 12.3 to 6.74 V/µm as shown inset Fig.5 b. The enhancement factor (β) and effective work function (φeff) can be

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calculated from the slope (m) of the F-N plot using the relations m = -bф3/2/ß and фeff= ф/ß2/3. Here Φ is bulk work function of the material which is 5 and 5.22 eV for carbon and CdSe respectively [37]. It can be seen that except the slope (m) the other two parameters Φ and b

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remains constant and thus β and фeff with m only. The variation of relative m of different samples with respect to S1 has been shown inset Fig.5 b. It can be seen that the relative

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enhancement factor also becomes the maximum for the sample S2 thus giving the best FE characteristics as can be seen from Fig.5 b. The pristine a-CNTs are not very good field emitter as has been reported in our previous work and have turn on field over 15 V/mm under alike condition [38].

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It should be noted the stability of the field emission current against time is one of the most important parameter for real operation. Thus here the stability curve of the sample S2, has been given in Fig.6. It is seen the sample gives stable field emission over considerable

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period of time.

The enhancement in FE characteristics of hybrid samples have been justified by simulation study

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using ‘ANSYS- Maxwell’ software. Fig.7 (a and b) shows the field distribution of both the pure a-CNTs and CdSe QD decorated samples. An effort has been made to develop a realistic system composed of pure and hybrid samples. The system was modeled assuming array of three parallel pure and coated a-CNTs separated by distance which is equal to the diameter of the individual aCNT. It can be seen from the color contrast that there is an enhancement of field in case of hybrid samples which is even more at the tip of the individual QDs. Thus the experimental result

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is well justified. There are several reasons behind the betterment of field emission from hybrid sample. Firstly, the attached QDs onto the a-CNTs’ wall serve as additional emission sites that contribute to the emission current density. Also this additional tip attracts the field lines giving

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rise to higher field concentration (enhancement factor ß) as shown in Fig.8 a. The hybrid structure shows favorable band structure shown in Fig.8 b. As CdSe is n type semiconductor with work function more than that of graphite (CNT) electrons cross metal semiconductor

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junction from metal to semiconductor and ultimately come into vacuum under the influence of electric field. The best FE characteristics obtained from S2 compared to other hybrid samples

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can be due to the favorable size and density of the QDs which has an optimum values helping cold emission from this hybrid. These QDs size, density as well as diameter and separation of as prepared a-CNTs has profound effect on the field emission characteristics i.e. turn on field, current density etc. of the sample. Thus when all these parameters are optimized one may get the

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best performance from the as prepared hybrid sample. Table 2 [39-45] gives a comparative study regarding the field emission characteristics of some very established field emitter. One can see that as prepared hybrid sample gives almost comparable characteristics with

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further advantage regarding the cost effective, simple high yield synthesis of sample. 3.4.2. Theoretical Support

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We also have used the Density Functional Theory (DFT) based calculation for having a more rigorous insight regarding the reason associated with the better tunnelling performance of the hybrid sample. DFT based first principles calculations in the current work were performed using Vienna Ab initio Simulation Package (VASP) [46-49] which implements a periodic, supercell based approach. Perdew–Burke–Ernzerhof (PBE) [50] functional within the generalized gradient approximation (GGA) was used to describe the exchange and correlation terms and ion cores

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were described using Projector-augmented waves (PAW) method [51, 52]. Plane wave basis up to energy cut off 400 eV were utilized in all calculations. As the present calculations include fairly large supercells, a Γ point centred, 2×2×2 k point grid was used to carry out Brillouin zone

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integrations. A vacuum slab of 25 Å was deployed along the direction perpendicular to the atomic plane (z axis) to mitigate any spurious interaction with periodic images. During structural optimization, atomic coordinates were allowed to relax until the change in the total (free)

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energies were smaller than 1×10-3eV. To facilitate improved accuracy, dispersive forces were taken into account using Grimme’s DFT+D3 [53] method. All computations were performed in

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spin unrestricted manner.

A 4×3×1 supercell of ~4.915 Å thick (1 0 0) surface of bulk CdSe (IT#: 186, P63MC) containing 48 Cd and 48 Se atoms was used to construct the under layer. The ACNT overlayer containing 152 C atoms was constructed by introducing 8 double vacancy defects in 7 repeat units of (6, 6)

the composite structure.

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single wall CNT containing 168 C atoms. A minimal ~1.090% lattice mismatch was observed in

Fig.9 shows the pictorial representation of basic a-CNT-CdSe hybrids that has been assumed for

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this calculation with inset shown the front view of a-CNT and CdSe unit cell structures. Our calculation shows that the due to CdSe attachment no development of CdSe induced impurity

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states close to the Fermi level is raised (plots are not shown here). A plot of electrostatic potential with respect to fractional coordinate has been plotted for all the samples (shown in Fig.10) showing a decrease in work function of the hybrid sample with respect to the pure QD. The values of Φs are found to be 5.34,4.93and 4.78 eV for pure QD, hybrid and pure a-CNTs respectively. However the FE performance of pure a-CNTs are found to be worst which is believed to be due to the lesser conductivity and thermal stability of the corresponding sample.

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4. Conclusions a-CNTs-CdSe QD hybrids have been synthesized via very simple low temperature chemical routes with high yields. Microscopic analysis confirmed the successful attachment of CdSe QDs

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onto a-CNTs' wall. FTIR spectroscopic studies revealed the different chemical bonds present in the sample. All the samples were further characterized by Raman spectroscopy and the spectroscopic study reveals that with increase in synthesis time there is a decrease in sp3 content.

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It has been shown that the there is considerable enhancement of the field emission properties of either of the host materials and there are an optimum synthesis time for the QDs. Above which

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FE characteristic gets further decreased. The optimum sample gives the best FE characteristics with turn on field as low as 6.74 V/µm and very high enhancement factor. The density functional theory suggest that there is a decrease in work function of the pure QDs. This along with the other reasons like enhanced roughness, more emission sites, favorable band bending are believed

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to be the key factor for the better FE characteristics of the hybrid sample. Also ANSYS-Maxwell software based calculation has also supported our experimental result. Acknowledgement:

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The authors wish to thank Department of Science and Technology (DST; SERB; Gov’t of India), University Grant Commission [(UGC, Gov’t of India) under University with potential for

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excellence (UPE-II) scheme] for the financial support during the execution of the work. SS wishes to acknowledge the encouragement and support of Siliguri Institute of Technology, West Bengal.

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References [1] Iijima, Sumio. "Helical microtubules of graphitic carbon." nature 354, no. 6348 (1991): 56. [2] Gooding, J. Justin. "Nanostructuring electrodes with carbon nanotubes: A review on

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electrochemistry and applications for sensing." ElectrochimicaActa 50, no. 15 (2005): 30493060.

[3] Wang, S. G., Qing Zhang, D. J. Yang, P. J. Sellin, and G. F. Zhong. "Multi-walled carbon

SC

nanotube-based gas sensors for NH 3 detection." Diamond and Related Materials 13, no. 4 (2004): 1327-1332.

M AN U

[4] Kim, Sung Ho, Wooseok Song, Min Wook Jung, Min‐A. Kang, Kiwoong Kim, Sung‐Jin Chang, Sun Sook Lee et al. "Carbon nanotube and graphene hybrid thin film for transparent electrodes and field effect transistors." Advanced Materials 26, no. 25 (2014): 4247-4252. [5] Bonard, Jean-Marc, Frédéric Maier, Thomas Stöckli, André Châtelain, Walt A. de Heer,

TE D

Jean-Paul Salvetat, and LászlóForró. "Field emission properties of multiwalled carbon nanotubes." Ultramicroscopy 73, no. 1 (1998): 7-15. [6] Jang, HoonSik, Hyeong-Rag Lee, and Do-Hyung Kim. "Field emission properties of carbon

EP

nanotubes with different morphologies." Thin Solid Films 500, no. 1 (2006): 124-128. [7] Banerjee, D., D. Kumar, N. S. Das, S. Sarkar, and K. K. Chattopadhyay. "Unique of

zero–one–two

dimensional

carbon–titania

hybrid

for

cold

cathode

AC C

combination

application." Physica E: Low-dimensional Systems and Nanostructures 74 (2015): 244-250. [8] Banerjee, D., D. Nawn, and K. K. Chattopadhyay. "Effect of Trace Amount Amorphous Carbon Nanotubes on Polypyrrole: A Potential Material for Field Emission Display." Science of Advanced Materials 6, no. 4 (2014): 640-647. [9] Chen, Y., Z. Sun, Jun Chen, N. S. Xu, and B. K. Tay. "Field emission properties from

13

ACCEPTED MANUSCRIPT

aligned carbon nanotube films with tetrahedral amorphous carbon coatings." Diamond and related materials 15, no. 9 (2006): 1462-1466. [10] Kumar, Dheeraj, Diptonil Banerjee, SouravSarkar, Nirmalya S. Das, and Kalyan K.

RI PT

Chattopadhyay. "Easy synthesis of porous carbon mesospheres and its functionalization with titania nanoparticles for enhanced field emission and photocatalytic activity." Materials Chemistry and Physics 175 (2016): 22-32.

SC

[11] Lee, Duck Hyun, Jin Ah Lee, Won Jong Lee, and Sang Ouk Kim. "Flexible Field Emission of Nitrogen‐Doped Carbon Nanotubes/Reduced Graphene Hybrid Films." small 7, no. 1 (2011):

M AN U

95-100.

[12] Nguyen, Duc Dung, Nyan-Hwa Tai, Szu-Ying Chen, and Yu-LunChueh. "Controlled growth of carbon nanotube–graphene hybrid materials for flexible and transparent conductors and electron field emitters." Nanoscale 4, no. 2 (2012): 632-638.

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[13] Jiang, Jinlong, Huaqing Fang, Xia Zhang, Kaichen He, Zhiqiang Wei, Xianjuan Pang, and Jianfeng Dai."Electrochemical synthesis of aligned amorphous carbon nanotubes/TiO2 nanotubes heterostructured arrays and its field emission properties." Diamond and Related Materials 74

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(2017): 205-211.

[14] Ho, Yong Min, Wei Tao Zheng, Ying Ai Li, Jian Wei Liu, and Jun Lei Qi. "Field emission

AC C

properties of hybrid carbon nanotube− ZnO nanoparticles." The Journal of Physical Chemistry C 112, no. 45 (2008): 17702-17708. [15] Meman, NedaMohammadi, MahnazPourkhalil, AlimoradRashidi, and BahmanZareNezhad. "Synthesis, characterization and operation of a functionalized multi-walled CNT supported MnOxnanocatalyst for deep oxidative desulfurization of sour petroleum fractions." Journal of Industrial and Engineering Chemistry 20, no. 6 (2014): 4054-4058.

14

ACCEPTED MANUSCRIPT

[16] Wang, Huijun, Jingjing Ma, Sheng Liu, LongyingNie, Yaqin Chai, Xia Yang, and Ruo Yuan."CoS/CNTs hybrid structure for improved performance lithium ion battery." Journal of Alloys and Compounds 676 (2016): 551-556.

RI PT

[17] Banks-Sills, Leslie, David Guy Shiber, Victor Fourman, Rami Eliasi, and AmitShlayer. "Experimental determination of mechanical properties of PMMA reinforced with functionalized CNTs." Composites Part B: Engineering 95 (2016): 335-345.

SC

[18] Jha, A., D. Banerjee, and K. K. Chattopadhyay. "Improved field emission from amorphous carbon nanotubes by surface functionalization with stearic acid." Carbon 49, no. 4 (2011): 1272-

M AN U

1278.

[19] Jha, A., U. K. Ghorai, D. Banerjee, S. Mukherjee, and K. K. Chattopadhyay. "Surface modification of amorphous carbon nanotubes with copper phthalocyanine leading to enhanced field emission." RSC Advances 3, no. 4 (2013): 1227-1234.

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[20] Zhu, Shi Jin, Jie Zhang, Jun Jun Ma, Yu Xin Zhang, and KeXin Yao. "Rational design of coaxialmesoporousbirnessite manganese dioxide/amorphous-carbon nanotubes arrays for advanced asymmetric supercapacitors." Journal of Power Sources 278 (2015): 555-561.

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[21] Karpulevich, A. A., E. G. Maksimov, N. N. Sluchanko, A. N. Vasiliev, and V. Z. Paschenko. "Highly efficient energy transfer from quantum dot to allophycocyanin in hybrid

AC C

structures." Journal of Photochemistry and Photobiology B: Biology 160 (2016): 96-101. [22] He, Xiancong, Yuanyuan Sun, Nujiang Tang, and Youwei Du. "Photoconductivity enhancement of reduced graphene oxide with reduced oxide graphene quantum dots hybrids film." Materials Letters 188 (2017): 29-32. [23] Sarkar, S., D. Banerjee, U. K. Ghorai, N. S. Das, and K. K. Chattopadhyay. "Size dependent

15

ACCEPTED MANUSCRIPT

photoluminescence property of hydrothermally synthesized crystalline carbon quantum dots." Journal of Luminescence 178 (2016): 314-323. [24] Bae, Wan Ki, JeonghunKwak, Ji Won Park, Kookheon Char, Changhee Lee, and

RI PT

Seonghoon Lee. "Highly Efficient Green‐Light‐Emitting Diodes Based on CdSe@ ZnS Quantum Dots with a Chemical‐Composition Gradient." Advanced Materials 21, no. 17 (2009): 16901694.

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[25] Lee, HyoJoong, Mingkui Wang, Peter Chen, Daniel R. Gamelin, Shaik M. Zakeeruddin, Michael Gratzel, and Md K. Nazeeruddin. "Efficient CdSe quantum dot-sensitized solar cells

M AN U

prepared by an improved successive ionic layer adsorption and reaction process." Nano letters 9, no. 12 (2009): 4221-4227.

[26] Şişman, İlkay, OktayTekir, and HüseyinKaraca. "Role of ZnOphotoanode nanostructures and sensitizer deposition approaches on the photovoltaic properties of CdS/CdSe and CdS 1− x

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Se x quantum dot-sensitized solar cells." Journal of Power Sources 340 (2017): 192-200. [27] Liang, Yichen, Wei Wang, Jong-Sik Moon, and Jeffrey G. Winiarz. "Enhancement in the photorefractive performance of organic composites photosensitized with functionalized CdSe

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quantum dots." Optical Materials 58 (2016): 203-209. [28] Surana, Karan, Pramod K. Singh, Hee-Woo Rhee, and B. Bhattacharya. "Synthesis,

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characterization and application of CdSe quantum dots." Journal of Industrial and Engineering Chemistry 20, no. 6 (2014): 4188-4193. [29] Sarkar, Sourav, Diptonil Banerjee, NirmalyaSankar Das, and Kalyan Kumar Chattopadhyay."A simple chemical synthesis of amorphous carbon nanotubes–MnO2 flake hybrids for cold cathode application." Applied Surface Science 347 (2015): 824-831. [30] Hamizi, NorAliya, and MohdRafie Johan. "Synthesis and size dependent optical studies in

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CdSe quantum dots via inverse micelle technique." Materials Chemistry and Physics 124, no. 1 (2010): 395-398. [31] Tan, Kim Han, and MohdRafie Johan. "Surface structure and optical property of

nanoparticle research 15, no. 9 (2013): 1920.

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amorphous carbon nanotubes hybridized with cadmium selenide quantum dots." Journal of

[32] Grill, Alfred. "Porous pSiCOH ultralow-k dielectrics for chip interconnects prepared by

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PECVD." Annual Review of Materials Research 39 (2009): 49-69.

[33] Alam, Al-Mahmnur, Byung-Yong Park, Zafar Khan Ghouri, Mira Park, and Hak-Yong

M AN U

Kim. "Synthesis of carbon quantum dots from cabbage with down-and up-conversion photoluminescence properties: excellent imaging agent for biomedical applications." Green Chemistry 17, no. 7 (2015): 3791-3797.

[34] Chattopadhyay, K. K., D. Banerjee, N. S. Das, and D. Sarkar. "Easy synthesis of amorphous

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graphene and related hybrids for cold cathode application." Carbon 72 (2014): 4-14. [35] Fowler, Ralph Howard, and L. Nordheim. "Electron emission in intense electric fields." In Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering

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Sciences, vol. 119, no. 781, pp. 173-181. The Royal Society, 1928. [36] Murphy, Edward Leo, and R. H. Good Jr. "Thermionic emission, field emission, and the

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transition region." Physical review 102, no. 6 (1956): 1464. [37] Li, Guohua, TianyouZhai, Yang Jiang, Yoshio Bando, and Dmitri Golberg. "Enhanced field-emission and red lasing of ordered CdSe nanowire branched arrays." The Journal of Physical Chemistry C 115, no. 19 (2011): 9740-9745. [38] Jana, S., D. Banerjee, A. Jha, and K. K. Chattopadhyay. "Fabrication of PbS nanoparticle

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coated

amorphous

carbon

nanotubes:

structural,

thermal

and

field

emission

properties." Materials Research Bulletin 46, no. 10 (2011): 1659-1664. [39] Lee, D. H., Lee, J. A., Lee, W. J., & Kim, S. O. (2011). Flexible Field Emission of

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Nitrogen‐‐Doped Carbon Nanotubes/Reduced Graphene Hybrid Films. small, 7(1), 95-100. [40]Zhu, Y. W., Zhang, H. Z., Sun, X. C., Feng, S. Q., Xu, J., Zhao, Q., ... & Yu, D. P. (2003). Efficient field emission from ZnOnanoneedle arrays. Applied Physics Letters, 83(1),

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144-146.

[41]Lee, C. J., Lee, T. J., Lyu, S. C., Zhang, Y., Ruh, H., & Lee, H. J. (2002). Field emission

Letters, 81 (19), 3648-3650.

M AN U

from well-aligned zinc oxide nanowires grown at low temperature. Applied Physics

[42]Zhu, Y. W., Yu, T., Cheong, F. C., Xu, X. J., Lim, C. T., Tan, V. B. C., ... & Sow, C. H. (2004). Large-scale synthesis and field emission properties of vertically oriented CuO

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nanowire films. Nanotechnology, 16(1), 88.

[43]Banerjee, D., &Chattopadhyay, K. K. (2012). Synthesis of crystalline carbon nanofernlike structure by dc-PECVD and study

of its electrical and field emission

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properties. Materials Research Bulletin, 47(11), 3868-3874. [44]Kale, V. S., Prabhakar, R. R., Pramana, S. S., Rao, M., Sow, C. H., Jinesh, K. B.,

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&Mhaisalkar, S. G. (2012). Enhanced electron field emission properties of high aspect ratio silicon nanowire–zinc oxide core–shell arrays. Physical Chemistry Chemical Physics, 14(13), 4614-4619.

[45]Kim, B. H., Kim, M. S., Park, K. T., Lee, J. K., Park, D. H., Joo, J., ...& Lee, S. H. (2003). Characteristics and field emission of conducting poly (3, 4-ethylenedioxythiophene) nanowires. Applied physics letters, 83(3), 539-541.

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[46] Kresse, Georg, and Jürgen Hafner. "Ab initio molecular dynamics for liquid metals." Physical Review B 47, no. 1 (1993): 558. [47] Kresse, G., and J. Hafner. "Ab initio molecular-dynamics simulation of the liquid-metal–

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amorphous-semiconductor transition in germanium." Physical Review B 49, no. 20 (1994): 14251.

[48] Kresse, Georg, and Jürgen Furthmüller. "Efficiency of ab-initio total energy calculations for

SC

metals and semiconductors using a plane-wave basis set." Computational Materials Science 6, no. 1 (1996): 15-50.

M AN U

[49] Kresse, Georg, and Jürgen Furthmüller. "Efficient iterative schemes for ab initio totalenergy calculations using a plane-wave basis set." Physical review B 54, no. 16 (1996): 11169. [50] Perdew, John P., Kieron Burke, and Matthias Ernzerhof. "Generalized gradient approximation made simple [Phys. Rev. Lett. 77, 3865 (1996)]." Phys. Rev. Lett 78, no. 7

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(1997): 1396.

[51] Blöuml, P. E. "Projector augmented-wave method [J]." Phys Rev B 50, no. 24 (1994): 17953-17979.

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[52] Kresse, Georg, and D. Joubert. "From ultrasoftpseudopotentials to the projector augmentedwave method." Physical Review B 59, no. 3 (1999): 1758.

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[53] Grimme, Stefan, Jens Antony, Stephan Ehrlich, and Helge Krieg. "A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu." The Journal of chemical physics 132, no. 15 (2010): 154104.

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Figure Captions Fig.1: FESEM images of sample S1 (a), S2 (b), S3 (c) and S4 (d) with higher magnified images shown inset.

Fig.3: FTIR spectra of a-CNT-CdSe hybrids. Fig.4: Raman spectra of a-CNT-CdSe QD hybrids

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shown inset.

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Fig.2: HRTEM images of sample S1 (a), S2 (b), S3 (c) and S4 (d) with higher magnified images

Fig.5: (a) Field emission J-E curves of all the hybrids with (b) corresponding F-N plots. Inset (a)

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J-E curves for low field region and inset (b) values of ETO and slopes of F-N plots. Fig.6: Stability curve of the best field emitter (S2)

Fig.7: ANSYS field distribution for (a) pure, (b) CdSe QD modified a-CNTs and (c, d) are corresponding higher magnified images.

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Fig.8: (a) Schematic of field enhancement at the QD particles attached to a-CNTs and (b) band bending at a-CNTs-CdSe junction.

a-CNTs and QDs

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Fig.9:Pictorial representation of the unit cell structures of hybrid sample and inset same for pure

Fig.10:The average potential profile along the length of the vacuum slab for all the pure and

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hybrid samples.

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Fig.2: S. Sarkar et al.

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S2

S4

3000

3500

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Abs (a.u.)

S3

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2830 2350

1060

1550 1663

S1

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800 1200 1600 2000 2400 2800 3200 3600 4000

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Wavenumber (cm-1)

Fig.3: S. Sarkar et al.

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Intensity (a.u)

S1

1200

1600

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S2 S4

Intensity (a.u)

S1 S3

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2000

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Raman Shift (cm -1)

500

1000

1500

3000

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Raman

2000 2500 Shift (cm-1)

Fig.4: S. Sarkar et al.

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0.1

60 40

S1 S3

20

S2 S4

0 -20 2

4

6

8

10

12

Applied Electric Field E(V/µm)

S1 S3

14

S2 S4

-0.1 -0.2 -0.3 S1

-0.4 -0.5

12

10

S4

S3

8

S2

-0.6 6

S2

3.5 3.0 2.5

S3

2

4

6

8

10

12

14

16

18

1.5 1.0

S1

0.10

0.15

Sample

0.20

0.25

0.30

1/E (µmV-1)

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Applied Electric Field E (V/µm)

200 175 150

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Fig.5: S. Sarkar et al.

At Field Applied = 11 V/µm

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Current Densitty ( µm/cm2)

0.05

S4

2.0

Sample

-0.7

0

S2 S4 (b)

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80

Relative Slope (F-N plot)

(a)

100

S1 S3

0.0

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120

ETO (V/µ m)

140

ln (J/E2) [ln{µAcm2µm2V-2)

(µ A/cm 2)

100

75

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240 220 200 180 160 140 120 100 80 60 40 20 0

Current Density J

Current Density J (µA/cm2)

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50 25

0

-20 0

20 40 60 80 100 120 140 160 180 200 220

Time (Minute)

Fig.6: S. Sarkar et al.

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Fig.7: S. Sarkar et al.

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Fig.8: S. Sarkar et al.

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0

-20 -5

-5 -10

0

5

10

15

20

25

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0

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average electrostatic potential vacuum level CdSe QD fermi level

-10

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Average Electrostatic Potential (eV)

Fig.9: S. Sarkar et al.

-5

0

5

30

35

a-CNTs 10

15

20

25

30

35

15

20

25

30

35

0

-10

a-CNTs-CdSe QD

-20 -5

0

5

10

Fractional coordinate

Fig.10: S. Sarkar et al. 28

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Table 1:Different parameters as obtained from Raman spectra S1

S2

S3

S4

D band (cm -1)

1371

1394

1400

1403

G band (cm -1)

1591

1591

1597

1593

AG/AD

0.17

0.11

0.23

0.17

sp3 content

0.19

0.19

0.16

0.18

FWHM of G band (cm -1)

82

75

91

73

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Sample

System

Turn on field V/µm) 2.35-1

Nitrogen-Doped CNT/Reduced Graphene Hybrid

2.4

Defined at

Highest Current density[Approximate]

Reference

J = 10 µA/cm2

1.1 (mA/cm2) at 3.9 V/µm

[39]

--------

2.4 (mA/cm2) at 7 V/µm

[40]

1 (mA/cm2) at 11 V/µm

[41]

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ZnOnanoneedle

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Table 2: Comparison with the other established field emitter regarding the current density

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ZnO nanowires

J = 0.1

3.5-4.5

---------

0.45 (mA/cm2) at 7 V/µm

[42]

24-4.8

J = 3 µA/cm2

50 (µA/cm2) at 22.5 V/µm

[43]

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µA/cm2

J = 1 µA/cm2

3.2 (µA/cm2) at 11 V/µm

[44]

J = 10 µA/cm2 100 (µA/cm2) at 4.5 V/µm

[45]

CuO nanowires Carbon nanofern Silicon Nanowires

conducting poly (3,4-

9.1

3.5-4

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ethylenedioxythiophene) nanowires

a-CNT-CdSe QDs

12.3-6.74

J = 1 µA/cm2

227 (µA/cm2) at 15.33

Present

V/µm

work

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ACCEPTED MANUSCRIPT Title: “Efficient Cold Cathode Emissionin Crystalline-Amorphous Hybrid: Study on Carbon Nanotube-Cadmium Selenide System” Author: S.Sarkar, D. Banerjee, N.S. Das, U. K. Ghorai, D. Sen and K.K.Chattopadhyay 1. Amorphous Carbon nanotubes (a-CNTs) were synthesized by chemical method.

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2. CdSe quantum dots have been decorated onto a-CNTs' wall. 3. ANSYS predicts an enhancement in cold emission property due to functionalization. 4. This prediction has been confirmed from experiment as well.

5. DFT study confirms the decrease of work function for hybrid samples compared to

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the pure quantum dots.