Thermomechanically and electromagnetically actuated piezoresistive cantilevers for fast-scanning probe microscopy investigations

Sensors and Actuators A 276 (2018) 237–245

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Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna

Thermomechanically and electromagnetically actuated piezoresistive cantilevers for fast-scanning probe microscopy investigations W. Majstrzyk a,b,∗ , A. Ahmad b , Tzv. Ivanov b , A. Reum c , T. Angelow b , M. Holz c , T. Gotszalk a , I.W. Rangelow b a

Faculty of Microsystem Electronics and Photonics, Wroclaw University of Science and Technology, Janiszewskiego 11/17, Wrocław, 50-372, Poland Department of Microelectronic and Nanoelectronic Systems, Faculty of Electrical Engineering and Information Technology, Ilmenau University of Technology, Gustav-Kirchhoffstr. 1, 98693, Ilmenau, Germany c Nano Analytik GmbH, Ehrenbergstraße 11, Ilmenau, 98693, Germany b

a r t i c l e

i n f o

Article history: Received 25 August 2017 Received in revised form 20 March 2018 Accepted 17 April 2018 Available online 22 April 2018 Keywords: Lorentz force Active cantilever AFM Actuation techniques Wheatstone bridge Self-actuation Self-sensing

a b s t r a c t The self-actuating and self-sensing cantilevers make it possible to perform precise non-contact atomic force microscopy (AFM) surface investigations. The measurement and control precision in the bandwidth of up to 2 MHz is ensured by integration of the most important microscope components: the tip deflection actuator and the tip deflection detector with the spring beam. In this way the vast majority of the parasitic disturbances like resonances of a bulk piezoactuator used for the cantilever excitation are eliminated. In this paper we describe thermomechanical and electromagnetic technologies for the actuation of the cantilever vibration whose oscillation is detected using the piezoresistive deflection sensor. We present how to control the cantilever mechanics using both actuation methods. We discuss the differences in power consumption when the cantilever is actuated and what are the surface scanning features of both technologies. We show that an atomic force microscope is capable of retaining its imaging speed and resolution when its cantilever is actuated in the thermomechanical and electromagnetic way. The obtained results illustrate that the selection of the proper actuation method extends applicability of the proposed AFM technologies. © 2018 Elsevier B.V. All rights reserved.

1. Introduction Scanning probe microscopy (SPM) and especially atomic force microscopy (AFM) [1] have gained great popularity in many research laboratories, as both technologies enable high resolution and high sensitivity measurements of surface properties in contact and noncontact modes [2,3]. Moreover, the SPM methods enable investigations of not only the surface topography but many other surface properties like e.g. contact potential difference (CPD) [4], temperature [5], surface magnetization [6], chemical bond forces [7,8] biomolecule surface activity [9]. The SPM technologies made it possible not only to measure but modify or pattern the surface properties and consequently fabricate nanodevices like transistors or nanowires [10–14]. Despite the noticeable progress in the SPM technology its important limitations must be also identified. As

∗ Corresponding author at: Faculty of Microsystem Electronics and Photonics, Wroclaw University of Science and Technology, Janiszewskiego 11/17, Wrocław, 50-372, Poland. E-mail address: [email protected] (W. Majstrzyk). https://doi.org/10.1016/j.sna.2018.04.028 0924-4247/© 2018 Elsevier B.V. All rights reserved.

today’s standard SPM investigations are mostly done by a single cantilever, the investigations throughput is limited [12,15]. Many research groups proposed techniques to address this issue mainly by multiplying number of the cantilevers operating in parallel [16] or increasing the scanning speed by probe miniaturization [17]. However, the described techniques are hard to implement when optical systems are used to detect the cantilever deflection. In this case the most efficient solution is given by the piezoresistive technology, in which a piezoresistive deflection sensor is integrated with the spring beam [18–21]. The piezoresistive cantilevers enable high resolution investigations in almost all SPM techniques [18]. Moreover, piezoresistive sensor response can be precisely calibrated as the function of the force acting on the probe or the tip displacement [22]. It must be noted additionally, that the full operationality in the SPM experiments can only be obtained when the so the called active SPM cantilevers are applied. In the active cantilever technology, the spring beam integrates not only a force or displacement sensor but a deflection actuator as well. In contrast to the standard solutions utilized in the laboratory single cantilever SPM systems, in which an external piezoelectric actuator is applied, the described solution

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ensures high actuation reliability as deflection of every cantilever can be controlled and tuned separately. Many different techniques for actuation of microcantilever sensors have been presented so far, including electrostatic [23], magnetic [24], piezoelectric [20,25], electromagnetic [26–28] and thermal [16,18] schemes. Each of these techniques has been well described and for each one advantages and disadvantages can be identified. When the piezoresistive technology is concerned the most appropriate actuation solutions rely on thermomechanical or electromagnetic concepts [29]. In our previous works we described arrays of up to 128 cantilevers [30–32] integrating single piezoresistors and thermal deflection actuators [33]. When application of smaller arrays or single cantilevers is needed a cantilever set-up integrating a piezoresistive Wheatstone bridge deflection sensor and a deflection actuator, ensuring high deflection sensitivity, high thermal stability and actuation reliability is the best solution [29,34–39]. In order to realize thermomechanical and/or electromagnetic actuation scheme a conductive loop must be integrated with the piezoresistive cantilever. When the loop is biased, thermal energy is dissipated in the spring beam leading to the structure deflection [35]. Moreover, when the entire structure is immersed in the magnetic field, Lorentz force, which is induced in the loop, makes the spring-beam deflect. In general, the thermal method proved to be the efficient method to control the multiresonance vibration of up to 2 MHz enabling imaging of the self-assembled molecular layers (SAMs) [40]. The limitation of the thermomechanical technology is the liquid measurement environment, which disturbs the heat transport in the actuated beam. In comparison with the thermomechanical technology in the electromagnetic scheme the electrical current in the cantilever loop is smaller and when the spring beam is isolated it is also possible to perform experiments in the conductive liquids. On the other hand the investigations in experimental systems sensitive to the magnetic field, like scanning electron microscopes (SEMs) are difficult and in this case the thermomechanical technology is the proper solution. In this paper we describe SPM imaging technology, in which the Wheatstone bridge piezoresistive cantilevers with integrated actuators for electromagnetic and thermomechanical actuation is described. The layout of the metallic loop was designed to excite in the efficient way thermally induced beam oscillation. Moreover the same actuator can be applied in order to actuate electromagnetically multiresonance tip oscillation. We show the response of the piezoresistive deflection detector and function of the thermal and electromagnetic actuator. We also present the high speed surface imaging of the test calibration samples done in thermal and electromagnetic schemes. 2. Active cantilever The silicon micro-cantilever used in our experiments is an active beam [12] shown in Fig. 1. The deflection readout is realized by the use of a piezoresistive sensor integrated near cantilever supporting point [33,41]. These sensors are connected together to form Wheatstone bridge. Micro-cantilevers with piezoresistive sensors can achieve force resolution of 8.6 fN*Hz0.5 at 1 kHz [42]. These sensors have been reported to outperform traditional optical techniques, especially in Very High Frequency regime (VHF) [43] (Figs. 2 and 3). 2.1. Thermomechanical actuation The described active cantilever integrates a thermomechanical deflection actuator. It is made out of Al or Al/Mg-alloy [32,37] deposited to form a conductive loop. Its resistance is around 20  and it covers large part of the cantilever surface. When the heat is

Fig. 1. (Color online) image of a piezoresistive active cantilever used in the experiments. Piezoresistive sensor bridge is marked by green lines, Al conductive path is marked by yellow lines. Inserted grayscale SEM image shows the tip shape.

dissipated in the aluminum alloy loop the cantilever is deflected due to different coefficients of the thermal expansion of Al-alloy and Si [44]. In our design Al, SiO2 , Si3 N4 and Si are used with coefficient of the thermal expansion equal to 23.1e-6 K − 1, 0.5e-6 K − 1, 2.3e-6 K − 1 and 2.6e-6 K − 1 respectively. Due to the fact that Al is the material of the highest expansion coefficient and it forms the top layer, the cantilever will only bend downwards when heated. However, it must be also noted, that by cantilever loop pre-biasing with the offset current it is possible to induce initial structure prebending. In this way by subsequent proper current modulation it is possible to actuate bidirectional cantilever deflection. Assuming that the bias current contains DC and AC components, the dissipated power can be calculated basing on the formula: 2 P(ω) = R[IDC + IAC sin(ωt)]2 = R[IDC +

+2IDC IAC sin(ωt) −

2 IAC

2

cos(2ωt)]

2 IAC

2 (1)

where IDC – is the DC loop current, IAC – the amplitude of the AC loop current, R – the loop resistance. In Eq. (1) three components can be distinguished: Pstatic – the constant power causing static deflection of the cantilever, Pω – the power dissipated at the same frequency as the frequency of the bias current and P2ω – the power dissipated at the doubled actuation current frequency. Eq. (1) directly implies two ways how the active cantilever can be excited to the resonance vibration. With the lack of IDC cantilever vibrates at the doubled frequency of the driving IAC current – this is the so called 2␻ actuation scheme. In this case in order to obtain the resonance cantilever oscillations an microscope user has to apply the bias current of the frequency which is equal to the half of the cantilever resonance. The 2␻ technology is very useful as the frequencies of the actuation and deflection signals are separated which avoids any parasitic signal interferences. With the 1␻ actuation scheme it is necessary to bias the microheater with IDC and IAC signals. Then the cantilever oscillates with both 1␻ and 2␻ frequencies. However, when the resonance vibration are induced by the 1␻ current component the frequency of 2␻ vibration is much bigger than the beam resonance and can be neglected. Angelov et al. [37] analyzed the stress distribution in the cantilever beam using Duhamel-Neumann law, which correlates the can-

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Fig. 2. a) Active piezoresistive cantilever plane view with direction of bending indicated by green arrow. It’s direction is valid when temperature rises, b) cross section of the active cantilever. Since the Al layer has 10 times higher coefficient of the thermal expansion than Si, the thermomechanical actuation will cause downward cantilever bending.

Fig. 3. 3D model of the cantilever with graphical explanation of the electromagnetic actuation. The colored arrows represent directions of the vectors from Eq. (5).

tilever structure with the increase in the cantilever temperature. Duhamel-Neumann law for a cantilever is described by the formula: x (x, z) =

E(x, z)(z − z0 (x)) + 0 (x, z) − E(x, z)˛(x, z)(x) (x)

(2)

where E(x,z) is Young’s modulus, ˛(x,z) – the coefficient of thermal expansion, (x)=T(x)-T0 – is the temperature difference with respect to temperature of fixed end,  0 (x,z) - is the pre-stress in layers, (x) – is the curvature of the beam and z0 (x) – initial bending of the cantilever. The x and z coordinates are oriented along cantilever length and thickness, respectively. In this way the thermomechanical static actuation of up to 10 ␮m has already been reported [36] with agreement between the experimental data and the analytical model. This makes such a cantilever suitable to replace the Z-axis piezoelectric actuator used in the standard atomic force microscopes. 2.2. Electromagnetic actuation The electromagnetic technique idea comes from the principle of Lorentz force exerted on a moving charged particle in electric and magnetic field according to the equation:  F = q(E + v × B),

(3)

where q is the charge of the particle, E is the electric field vector, v is the velocity of the particle and B is the magnetic field vector. When a (semi)conductor is placed in the magnetic field then Lorentz force

will be exerted on every charge flowing in that (semi)conductor. The resulting net force will be equal to:  × L,  FL = iB

(4)

where L – is the length of the conductive material and i – is the current flowing in this medium. In case of the silicon cantilever integrating a U-shaped conductive electrical loop [26,27] or the cantilever made out of highly doped semiconductor [45], Lorentz force can be used as the actuation force. When the magnetic field is uniform and its vector is perpendicular to the path then Lorentz force acts only at the end of cantilever according to the formula: FL (ω) = i ∗ sin(ωt)BL,

(5)

which clearly shows that the cantilever motion can be excited as the pure harmonic motion controlled only by the bias current. In the electromagnetic technology the bias current flowing through the loop causes Joule’s heat dissipation leading to the parasitic thermomechanical cantilever actuation. As Lorentz force is the product of the bias current and the magnetic field it is advisable to increase the magnetic induction and reduce the bias current in order to reduce the heat dissipation. The stronger magnetic field can be achieved when the strong neodymium magnets or the socalled Halbach magnet arrays are used [46]. This actuation type has potential to replace piezoelectric Z-axis scanners as it can be used to control simultaneously resonant vibrations of the cantilever as well as its static bending. Furthermore, the atomic force microscope utilizing the electromagnetically actuated sensors provides

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Fig. 4. Fast and closed-loop nano analytik GmbH scanner (30 × 30 x 10 ␮m scanning range) with a) thermo-mechanically and (b) electromagnetically actuated piezoresistive cantilever. The frame with permanent neodymium magnets is replaceable.

quantitative data about the force and the tip deflection if only the magnetic field is known and the loop current is measured. 3. Experimental setup In this section, we will describe actuation properties of both methods as well as present results of the surface imaging. In our experiments we used a commercial atomic force microscope system from nano analytik GmbH [47] operating in ambient conditions - Fig. 4. The applied machine is the top, closed loop scanner system enabling high speed (up to 100 lines/s) surface imaging [48]. 4. Experimental procedure and results In this section we describe experiments done to obtain excitation characteristics of the cantilever and assess AFM performance when we excited the cantilever thermomechanically or electromagnetically. The following procedures were performed: - broadband signal sweep was applied to obtain information about cantilever modal characteristics and identify first flexural mode frequency, - thermomechanical (1␻ and 2␻) and electromagnetic techniques were applied to induce cantilever resonance vibration, - comparison of the actuation efficiency in 1␻ and 2␻ thermomechanical schemes was done, - relation between average power needed to require the same level of response of thermomechanical and electromagnetic actuation for cantilevers of different resonant frequencies (thicknesses) was determined, - comparison of static cantilever bending induced in thermomechanical and electromagnetic actuation schemes was done. Next we tested the surface scanning capabilities of the active piezoresistive cantilevers: - comparison of the surface scanning speed was done, when active cantilevers were thermomechanically and electromagnetically excited, - HOPG surface topography was recorded in the electromagnetic technology. During the experiments the only difference in our setup was a presence of permanent magnets mounted over the investigated cantilever. For the experiments involving thermomechanical 1␻ or 2␻ actuation scheme we used the setup shown in Fig. 4a. For

Fig. 5. Resonance vibration of the thermomechanically actuated (2␻ scheme) piezoresistive cantilever recorded in the frequency bandwidth of 2 MHz.

the experiments involving electromagnetic actuation we applied setup presented in Fig. 4b. In case of the electromagnetic actuation it is important to notice, that the thermomechanical effects are also present, as the heating cannot be completely avoided but their contribution is minimized in comparison with the pure thermomechanical scheme. 4.1. Determination of cantilever modal characteristic Each actuation experiment in resonance began with the thermomechanical actuation 2␻ scheme done in the broad frequency range. The current was swept up to 1 MHz, to obtain cantilever modal response up to 2 MHz and identify desired vibrational modes – Fig. 5. It enabled us to record 5 flexural and 2 torsional cantilever vibrations modes. Then the frequency range was narrowed to assess performance in the first eigenmode which is typically used in AFM to conduct noncontact surface scanning. In these investigations we biased the cantilever microheater with current of 8 mARMS which corresponded to 1.3 mW power dissipated in the microbeam. The same resonance curves were recorded when the cantilever was excited electromagnetically by the bias current of 500 ␮A corresponding with 6 ␮W power dissipated in the sensor. The performed experiments showed that the system applied by us could be used in surface investigations in both actuation technologies at flexibly selected resonance frequency.

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resonance. In this way frequency separation between the excitation and vibration signals was ensured [49–51]. We recorded the cantilever response when again power of 25 ␮W was dissipated. It should be noted that much higher amplitude was obtained when the cantilever was excited electromagnetically than in the 2␻ thermomechanical method - Fig. 6 (see blue and black graph lines). Next the cantilever was actuated in 1␻ mode, when the bias current contained DC component and the frequency of AC component was tuned to match with the cantilever resonance frequency. The vibration amplitude of 90% of the piezoresistive deflection sensor output FS was obtained when power of 5 mW was dissipated in the deflection actuator. This shows that the electromagnetic actuation enables actuation of the resonance vibration with much higher efficiency than the thermomechanical one. However, it should be also noticed that the thermomechanical actuation technology is simpler in implementation as no magnetic field sources are needed to be integrated in the microscope measurement head. Fig. 6. Active piezoresistive cantilever tuning results in different actuation scenarios. The x axis represents driving signal frequency. We see that without DC component thermomechanical actuation does not contribute to the results obtained by electromagnetic actuation. In resonance mode these two act independently. For this particular cantilever we needed almost 200 times less power to achieve the same amplitude of the cantilever vibration.

Fig. 7. Piezoresistive bridge sensor response to dissipated power for both thermomechanical 1␻ and 2␻ scheme. The response in 1␻ is 1.45 times higher than response in 2␻.

4.2. Actuation results at single frequency In the first eigenmode investigations, the amplitude of vibration was set to 90% of the full scale (FS) response of the piezoresistive deflection sensor, which corresponded with the cantilever vibration amplitude of 100 nmpk-pk . Cantilever was kept well above the sample to obtain the free vibration characteristics. In Fig. 6 we show the amplitude and phase curves recorded at the resonance for the thermomechanical 1␻, 2␻ as well as electromagnetic schemes, the cantilever resonance frequency was 33 kHz. Our investigations started with the assessment of the electromagnetic scheme performance. We bias Lorentz loop only with AC current as to excite cantilever vibration and reduce heat dissipation corresponding with the DC current component. The amplitude of the bias current was adjusted to obtain 90% of the piezoresistive deflection sensor output FS. The average power required to obtain such a response was equal to 25 ␮W (Fig. 7). Next we removed magnets and investigated actuation performance in 2␻ scheme, which meant that the heater was biased with the AC current of the frequency equal to the half of the cantilever

4.3. Comparison between thermomechanical 1␻ and 2␻ technologies In order to compare 1␻ and 2␻ technologies we recorded and analyzed the cantilever response when the same DC power was dissipated in the cantilever. According to Eq. (1), 1␻ actuation achieves best performance √ (related to DC power) when IDC = IAC / 2. This will result in P1␻ being √ 2 time higher than PDC while in 2␻ actuation scheme P2␻ is always equal to PDC. However, maximum peak power occurring in 1␻ is approximately 1.45 times higher than in 2␻ technology. Thus in terms of the maximum of the dissipated power 1␻ and 2␻ technologies exhibit the same efficiency. This experiment shows that there is the trade-off between 1␻ and 2␻ actuation schemes. 2␻ technology offers frequency separation between drive and response signals. However, higher power is needed in 2␻ scheme to maintain the same level of response (vibration amplitude) as in 1␻ scheme. In case of the scanning control algorithm, the 1␻ actuation should be also optimized to always use the parameter set that gives the most efficient actuation.

4.4. Relation between electromagnetic and thermomechanical actuation at different frequencies The characterization presented in Fig. 6 was repeated for a set of 12 cantilevers of the same planar dimensions and different thickness. Thus the resonance frequencies of the cantilevers varied in the range from 20 to 100 kHz. We calculated the ratio of the power needed to excite the same amplitude of the resonance vibration in thermomechanical 1␻ and electromagnetic actuation schemes (Fig. 8). The highest efficiency of the electromagnetic actuation in this design can be obtained for the cantilevers with smaller resonance frequency (smaller stiffness), whereas the thermomechanical scheme is more appropriate for the spring beams with higher stiffness (higher resonance frequency). The response to electromagnetic actuation linearly depends on the spring beam stiffness which strongly depends on the cantilever thickness. On the other hand, the thermomechanical actuation operates on the basis of differences among the thermal expansion of the layers forming the cantilever. The actuation sensitivity depends stronger on the ratio of the beam layers rather than the entire structure thickness [52]. It should be also noted, that in case of the electromagnetic actuation smaller power dissipated in the sensor is associated with the application of a strong magnet, which is in many cases of disadvantage. On the other hand, in the thermomechanical scheme much

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Fig. 10. AFM 2D topography image of HOPG sample done with the use of electromagnetic actuation. Power necessary to drive cantilever was equal to 80 ␮W. The recorded profiles of the sample topography indicate that the proposed architecture configuration is capable of imaging single atomic steps on HOPG surface.

Fig. 8. Comparison of thermomechanical 1␻ and electromagnetic actuation schemes for the piezoresistive cantilevers with various resonance frequency and the same planar dimensions. The difference of the resonance frequency is caused by different cantilever thickness.

ical actuation contributes to the structure deflection much stronger than Lorentz force. This results from the fact, that the in contrast to the resonance vibration bigger part of the dissipated power is transduced into the mechanical deflection of the structure as no AC power components are transported through the spring beam. 4.6. Topograhy investigations using cantilver operating in thermomechanical 1␻ and electromagnetic technologies

Fig. 9. Static deflection of the active piezoresitive cantilever resulting from thermomechanical and electromagnetic actuation.

bigger power must be applied in the spring beam but the structure of the measurement head is simplified. 4.5. Static deflection control in electromagnetic and thermomechanical actuation technologies The complete characterization of both actuation schemes includes also the metrology of static deflection drive. Fig. 9 shows the cantilever bending when the DC current passes through the metallic path acting as the microheater or Lorentz loop. The static thermomechanical actuation was measured when the permanent magnets were removed out of the atomic force microscope head Fig. 9 (see the black graph line). The cantilever deflection was also measured when the magnets were installed in the microscope head Fig. 9 (see the red graph line). However, in this case combined phenomena of thermomechanical and electromagnetic driving were recorded, as the current passing through the loop caused the thermomechanical stress between the metallic wire and the silicon microbeam. In order to analyze only the electromagnetic effects both curves were subtracted and the characteristics illustrating the electromagnetic actuation were obtained Fig. 9 (see the green graph line). It should be noticed, that in the static case the thermomechan-

We performed the test surface topography measurements when the cantilever was excited to resonance vibration in 1␻ thermomechanical and electromagnetic schemes. The sample used for these experiments was a 30 nm high Si/SiO2 calibration grating of 2.5 ␮m pitch. We applied the piezoresistive cantilever with the resonance frequency of 37 kHz. The cantilever resonance was excited thermomechanically or electromagnetically when power of 5 mW was dissipated in the microheater or when Lorentz loop was biased with the current of 1 mA (corresponding with 25 ␮W dissipated in the microbeam). It should be also stressed, that the application of novel magnetic materials (like N52 grade NdFeB) makes it possible to reduce the bias current and the parasitic thermomechanical effects even further. The surface was scanned with 30 lines/s frequency. In order to speed up the surface imaging we applied the adaptive control algorithm, which enabled us to image the topography at the frequency of up to 70 lines/s [53,54]. Table 1 contains the topography images recorded at different scan rates using different actuation technologies. The obtained results show that cantilever with electromagnetic actuation scheme is able to maintain the same scanning speed without a loss in the image quality and to utilize adaptive control algorithm as in the case of the thermomechanical investigations described in [53,54]. This stems from the fact that both technologies are fast and precise enough to drive the cantilever at the resonance with high quality factor and this is the main factor limiting the scanning speed [55]. One of the best known methods to test the resolution of the atomic force microscope is to image the atomic steps on the surface of a highly ordered pyrolytic graphite (HOPG) sample. The HOPG surface was already successfully imaged using piezoresistive thermomechanically actuated (active) cantilevers [8]. Fig. 10 shows the image of HOPG surface recorded, when the piezoresistive cantilevers were electromagnetically driven at the resonance of 37 kHz, which is a novel AFM solution. The surface scan was performed with 1 line/s frequency. The set-point amplitude, defining the cantilever vibration, was set to 25 nm. The current necessary to drive the cantilever was equal to 2 mA (corresponding with 80 ␮W power dissipated in Lorentz Loop). This indicates that the proposed AFM technology does maintain resolution and image quality when the cantilever is excited to resonance vibration electromagnetically.

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Table 1 Fast scan images using thermomechanical and electromagnetically actuated cantilevers at various scanning frequencies. The distance between the vibrating tip and the surface was maintained using standard and the so called adaptive control algorithms [45]. Lines/s

Thermomechanical 1␻

Electromagnetic

Thermomechanical + Adaptive Speed [54]

Electromagnetic + Adaptive Speed

10

30

50

70

In this section we described experiments done to assess actuation capabilities of thermomechanical and electromagnetic schemes. We measured cantilever excitation characteristics and assesed AFM scanning capabilities. The scanning experiments done with our AFM show that the electromagnetic and thermomechanical actuation techniques for the resonance beam are exchangeable. The only factors, which must be taken into account are, whether the sample or the measurement head is sensitive to the magnetic field, liquid or/and temperature.

5. Summary In this article we discussed the properties of thermomechanically or electromagnetically driven piezoresistive cantilevers for the AFM surface imaging. We characterized and directly compared the properties of both actuation schemes and identified the possible application fields of the proposed techniques. The electromagnetic actuation seems to be very efficient when resonance imaging of relatively flat surface is foreseen. The thermomechanical deflection drive makes it also possible to control static cantilever deflection, and therefore is more suitable when samples of higher roughness are scanned. Moreover, the thermomechanical scheme is the preferred one, when used in the systems sensitive to the external magnetic field like scanning electron microscopes or when the magnetic samples are investigated. The integration of the piezoresistive deflection detector enables reliable, sub-0.1 nm precise control, and metrology of the probe deflection. In this way new possibilities for the SPM investigations done in combination with scanning electron, optical microscopes and nano-manipulators will be possible without curtailments in the resolution or speed of the AFM-imaging. The surface topography images obtained with the speed of up to 70 lines/s were presented indicating that the proposed actuation technology is capable of fast speed sample imaging.

The resolution possibilities were proven by imaging of the atomic steps on the HOPG surface.

Acknowledgements This project has received funding from the European Union’s Seventh Framework Program for research, technological development and demonstration under Grant Agreement No. [318804] [Single Nanometer Manufacturing for beyond CMOS devices (SNM)]. The investigations of the electromagnetic actuation were done within the NCN OPUS 9 Grant - “Metrology of molecular interactions using electromagnetically actuated MEMS force sensors-MetMolMEMS” (Grant No. 2015/17/B/ST7/03876).

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Biographies Wojciech Majstrzyk was born in Zarow, Poland in 1989. In 2013 he received the MSc degree from Faculty of Microsystem Electronics and Photonics of Wroclaw University of Technology. Currently he is pursuing his PhD degree at Wrocław University of Technology, focusing on application of cantilevers array for force and mass measurements. Ahmad Ahmad received the licentiate degree in electrical engineering from Tischrin-University, Latakia/Syria, in 1998, and the Diplom-Ingenieur degree in electrical engineering and information technology from Ilmenau University of Technology, Germany, in 2007. He is currently a PhD student and a research associate with the Department of Micro- and Nanoelectronic Systems, Ilmenau University of Technology. His research interests include FPGA-based control techniques for high-speed atomic force microscopy and lithography. Tzvetan Ivanov received Master degree in Solid State Physics at Sofia University and Ph.D. degree at Kassel University. He is currently working as a Researcher in the Ilmenau University of Technology. His research interests include development of micromechanical systems. In 2007, Alexander Reum completed his studies of computer science at the Schmalkalden University of Applied Sciences. Since then, he’s working as a research associate at the Dept. of Micro- and Nanoelectronic Systems, Ilmenau University of Technology. Currently he’s busy writing user interface software and tools for AFM-related research.

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Tihomir Angelov received his MSc degree in electronic engineering from the Technical University of Varna in 2013. He is currently a PhD student and a research associate in the Department of Micro- and Nanoelectronic Systems, Ilmenau University of Technology. His research interests include low noise analog and digital electronics, systems for control and digital signal processing. Mathias Holz received Master degree in Electronics from Department of Micro- and Nanoelectronic Systems, Ilmenau University of Technology. Currently he is General Manager of nano analytik GmbH. Teodor Paweł Gotszalk was born in Wrocław, Poland. He received the MSc degrees from the Faculties of Electronics and of Electrical Engineering of Wrocław University of Technology in 1989 and 1991, respectively. In 1996, he received the PhD degree from the Institute of Electronic Technology of the Wrocław University of Technology. He has been honored with Siemens Research Award (2000) and the prize of Polish Science Foundation FNP (1997) for his scientific work. He is the head of the Division of Micro- and Nanostructures Metrology at the Faculty of Microsystems Electronics and Photonics of Wrocław University of Technology. He has authored over 100 scientific publications Ivo W. Rangelow received the MS and PhD degrees in electronics in 1979 and 1983, respectively. His actual works are focused on sub- 10 nm scanning probe lithography based lithography. He was a guest professor with the University of Vienna, Wroclaw University, and the University of Berkeley. He has authored or co-authored over 300 scientific papers and 48 patents. He is currently the director of the Institute of Microand Nanoelectronics with Ilmenau University of Technology.