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Alignment of liquid crystals using Langmuir?Blodgett films of unsymmetrical bent-core liquid crystals
摘要： The properties of the thin films of liquid crystal (LC) molecules can be governed easily by external fields. The anisotropic structure of the LC molecules has a large impact on the electrical and optical properties of the film. The Langmuir monolayer (LM) of LC molecules at the air–water interface is known to exhibit a variety of surface phases which can be transferred onto a solid substrate using the Langmuir?Blodgett (LB) technique. Here, we have studied the LM and LB films of asymmetrically substituted bent-core LC molecules. The morphology of LB film of the molecules is found to be a controlling parameter for aligning bulk LC in the nematic phase. It was found that the LB films of the bent-core molecules possessing defects favour the planar orientation of nematic LC, whereas the LB films with fewer defects show homeotropic alignment. The defect in LB films may introduce splay or bend distortions in the nematic near the alignment layer which can govern the planar alignment of the bulk LC. The uniform layer of LB film facilitates the molecules of nematic to anchor vertically due to a strong van der Waals interaction between the aliphatic chains leading to a homeotropic alignment.
关键词： field emission scanning electron microscope,atomic force microscope,Langmuir?Blodgett film,liquid crystals,Brewster angle microscopy,Langmuir monolayer
更新于2025-11-21 11:01:37
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Ar-Plasma-Modulated Optical Reset in the SiO <sub/>2</sub> /Cu Conductive-Bridge Resistive Memory Stack
摘要： Our study using conductive atomic force microscope shows that the resistive switching voltage in the SiO2/Cu stack is reduced by 33% after Ar plasma treatment of the oxide. Besides, the negative photo-conductivity (NPC) effect, normally observed on many locations following electrical soft-breakdown, is suppressed. The NPC effect arises because the electrically-formed filamentary conductive path, comprising both Cu and oxygen vacancies, may be disrupted by the recombination of the vacancies with nearby light-excited interstitial oxygen ions. Increase of the O-H peak, as seen from FT-IR spectroscopy, indicates that surface defects generated by the Ar plasma may have adsorbed water molecules, which in turn act as counter anions (OH?) accelerating Cu-ion diffusion into the oxide, forming a more complete Cu filament that is non-responsive to light. The finding offers the possibility of both electrical and optical resistance control by a simple surface treatment step.
关键词： Ar plasma treatment,negative photo-conductivity,conductive atomic force microscope,resistive switching,SiO2/Cu stack
更新于2025-09-23 15:21:01
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Spectroscopic ellipsometry and morphological characterizations of nanocrystalline Hg1-xMnxO oxide diluted magnetic semiconductor thin films
摘要： The structural, optical spectroscopic ellipsometry and morphological properties of nanocrystalline Hg1-xMnxO (0 ≤ x ≤ 0.2) oxide diluted magnetic semiconductor thin films synthesized by electron beam deposition technique have been investigated by means of X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and atomic force microscopy (AFM) techniques. All the deposited films crystallize in the form of a hexagonal crystal structure. The integration between X-ray and atomic force microscopy data shows a very good agreement for the nanosize nature of the deposited films. For the surface roughness, good matching between the results of SE and AFM measurements was observed. In the spectral range 200–1200 nm, the real part (ε1) and imaginary part (ε2) of the dielectric constant of nanocrystalline Hg1-xMnxO films have been extracted from SE measurements. At fixed energy value, the ε1, consequently the refractive index is found to decrease with increasing Mn2+ dopant. In contrary, the energy gap (Eg) of the deposited films determined from the ε2 is found to increase as the Mn2+ concentration increases. The variation of both the ε1 and Eg as a function of Mn2+ concentration is understood based on Lorentz-Lorenz relation and sp-d exchange interaction, respectively. The results reported here show that Mn-doped HgO nanocrystalline films could be employed in the fabrication of nanoscale optical and magneto-optical devices.
关键词： Atomic force microscope,Vapor deposition,Spectroscopic ellipsometry,Optical properties,Semiconductors,AFM,Optical materials,Nanostructured materials,Thin films,X-ray diffraction
更新于2025-09-19 17:15:36
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Imaging Carrier Inhomogeneities in Ambipolar Tellurene Field Effect Transistors
摘要： Developing van der Waals (vdW) homojunction devices requires materials with narrow bandgaps and simultaneously high hole and electron mobilities for bipolar transport, as well as methods to image and study spatial variations in carrier type and associated conductivity with nanometer spatial resolution. Here we demonstrate the general capability of near-field scanning microwave microscopy (SMM) to image and study the local carrier type and associated conductivity in operando by studying ambipolar field effect transistors (FETs) of the 1D vdW material tellurium in 2D form. To quantitatively understand electronic variations across the device, we produce nanometer resolved maps of the local carrier equivalence backgate voltage. We show that the global device conductivity minimum determined from transport measurements does not arise from uniform carrier neutrality, but rather from the continued coexistence of p-type regions at the device edge and n-type regions in the interior of our micron-scale devices. This work both underscores and addresses the need to image and understand spatial variations in the electronic properties of nanoscale devices.
关键词： 2D Materials,Field-Effect Transistor,Microwave,Near-Field Microscopy,Atomic Force Microscope
更新于2025-09-19 17:15:36
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[IEEE 2019 IEEE Conference on Control Technology and Applications (CCTA) - Hong Kong, China (2019.8.19-2019.8.21)] 2019 IEEE Conference on Control Technology and Applications (CCTA) - Novel Micro Scanning with Integrated Atomic Force Microscope and Confocal Laser Scanning Microscope
摘要： Integrated atomic force microscope (AFM) and confocal laser scanning microscope (CLSM) can quickly obtain the three-dimensional (3-D) surface of the sample in large scanning range and recover the region of interesting (ROI) in nanoscale resolution. However, the traditional cooperative algorithm for integrated microscopes occupies too much scanning time. In this work, we develop a novel cooperative algorithm for the integrated microscopes to reduce scanning time of AFM and achieve higher scanning speed. First, the calibration of the microscopes will be implemented. Next, CLSM starts a large range scan first and then define the region of interesting (ROI) by edge detection. And then, the scan regions of the AFM are arranged based on the ROI and adaptive scanning region method is proposed to reduce the scanning time. Furthermore, variable speed scanning based on the height information obtained from CLSM image is applied to increase the AFM scanning speed. Finally, the scanning images obtained from AFM and CLSM are merged together. A series of experimental results show that proposed cooperative algorithm can save approximately 69.2% of scanning time compared with that obtained by traditional cooperative algorithm.
关键词： Atomic force microscope (AFM),adaptive scanning range,confocal laser scanning microscope (CLSM),regions of interest (ROI),variable speed scanning
更新于2025-09-16 10:30:52
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An apparatus based on an atomic force microscope for implementing tip-controlled local breakdown
摘要： Solid-state nanopores are powerful tools for sensing of single biomolecules in solution. Fabrication of solid-state nanopores is still challenging, however; in particular, new methods are needed to facilitate the integration of pores with larger nanofluidic and electronic device architectures. We have developed the tip-controlled local breakdown (TCLB) approach, in which an atomic force microscope (AFM) tip is brought into contact with a silicon nitride membrane that is placed onto an electrolyte reservoir. The application of a voltage bias at the AFM tip induces a dielectric breakdown that leads to the formation of a nanopore at the tip position. In this work, we report on the details of the apparatus used to fabricate nanopores using the TCLB method, and we demonstrate the formation of nanopores with smaller, more controlled diameters using a current limiting circuit that zeroes the voltage upon pore formation. Additionally, we demonstrate the capability of TCLB to fabricate pores aligned to embedded topographical features on the membranes.
关键词： dielectric breakdown,atomic force microscope,nanopore fabrication,tip-controlled local breakdown,solid-state nanopores
更新于2025-09-12 10:27:22
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Micron-Sized Constrictions Fabricated Using the Femtosecond Laser Technique on YBCO Thin Films
摘要： In this paper, I report on the fabrication of micron-sized constrictions in YBCO thin films using the femtosecond laser technique. The constrictions are S-shaped superconducting weak links fabricated on YBCO thin films. The constrictions show a measurable superconducting current flowing through them. Current-voltage (I–V) characteristics were used to determine the critical current IC of the constrictions at 77 K. The width of the constrictions was determined at the narrowest point using SEM (scanning electron microscope). Three micron-sized constrictions were fabricated with a width of 2.88 μm, 1.72 μm, and 1.69 μm and a length of 5 μm. Based on the width and length of these constrictions in relation to the coherence length (ξ) of the YBCO, these constrictions should conduct supercurrent by Abrikosov vortices. The SEM images show that the femtosecond laser heats the samples beyond the geometric boundary, damaging some of the superconductive phases of the YBCO constrictions. As a result, the constrictions conduct current by one-dimensional depairing.
关键词： Atomic force microscope (AFM),Abrikosov vortices,Flux pinning,YBCO thin film,Lasers,Critical currents,Scanning electron microscopy (SEM)
更新于2025-09-11 14:15:04
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Raman Spectroscopy of Folded Tetralayer Graphenes Prepared by Atomic Force Microscope
摘要： In this work, we report that when a modulated force is applied to the edge of a bilayer graphene with an atomic force microscope (AFM), two kinds of folded tetralayer graphenes can be obtained: one has one rupture and the other has two ruptures. The twist angle between two bilayer graphenes is found to be in the range of 1.8°～27.7°. Systematic Raman studies show that the position, width, and intensity of 2D and G peaks of the folded tetralayer graphene depend sensitively on these angles. Meanwhile, the intensity enhancement of G mode of twisted tetralayer graphenes has been observed at twist angles of 11.5° and 13.2°. At these two twist angles, the 2D peak of twisted tetralayer graphenes can be fitted by three Lorentzian peaks at laser energy of 2.33 and 2.41 eV. Using an AFM probe to fabricate twisted graphene has the advantages of high yield, controllable positions, and no introduction of chemical pollutants, which has many potentials in future electronics.
关键词： twist angle,atomic force microscope,folded tetralayer graphenes,Raman spectroscopy,2D and G peaks
更新于2025-09-10 09:29:36
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Ductile behavior of optical glass in single point diamond turning
摘要： Single point diamond turning tests were carried out on a B270 type glass. Sub-micrometer cutting conditions were applied in order to generate ductile response during single point machining. The profile generated by the rapid removal of the tool tip from the machined surface, analyzed by atomic force microscopy, showed that the brittle-to-ductile transition occurs at a few tenths of micrometers. According to the machining results, the maximum feed rate capable of generating a ductile mode machining behavior is of 0.9 micrometer/revolution. Furthermore, it was shown that with the cutting depth lower than 0.100 micrometer/revolution, the material removal mechanism is totally ductile. Ribbon-like chips were not observed when ductile machining was performed, as commonly seen during ductile machining of semiconductor crystals. The chips removed had a small needle-like shape. This material’s fragile behavior during machining may be related to high densification during tool/material interaction with subsequent elastic recovery response.
关键词： soda-cal-silicates,Atomic Force Microscope,Brittle-to-ductile transition,diamond turning
更新于2025-09-09 09:28:46
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Robust nonlinear control of atomic force microscope via immersion and invariance
摘要： This paper reports an immersion and invariance (I&I)–based robust nonlinear controller for atomic force microscope (AFM) applications. The AFM dynamics is prone to chaos, which, in practice, leads to performance degradation and inaccurate measurements. Therefore, we design a nonlinear tracking controller that stabilizes the AFM dynamics around a desired periodic orbit. To this end, in the tracking error state space, we define a target invariant manifold, on which the system dynamics fulfills the control objective. First, considering a nominal case with full state measurement and no modeling uncertainty, we design an I&I controller to render the target manifold exponentially attractive. Next, we consider an uncertain AFM dynamics, in which only the displacement of the probe cantilever is measured. In the framework of the I&I method, we recast the robust output feedback control problem as the immersion of the output feedback closed-loop system into the nominal full state one. For this purpose, we define another target invariant manifold that recovers the performance of the nominal control system. Moreover, to handle large uncertainty/disturbances, we incorporate the method of active disturbance rejection into the I&I output feedback control. Through Lyapunov-based analysis of the closed-loop stability and robustness, we show the semiglobal practical stability and convergence of the tracking error dynamics. Finally, we present a set of detailed, comparative software simulations to assess the effectiveness of the control method.
关键词： output feedback control,chaos,immersion and invariance,disturbance rejection control,atomic force microscope
更新于2025-09-04 15:30:14