Non-contact Mode Atomic Force Microscopy Research Articles

Active fault tolerant control for high-precision positioning of a non-contact mode uncertain atomic force microscopy

A non-contact mode atomic force microscope with chaotic dynamics may exposed to unknown faults, disturbances or uncertain parameters that are not always be compensated using classical control methods. Therefore, a fault tolerant controller must be designed for accurate tracking of the tip-position of the end-effector. In this paper, first, an unscented Kalman filter is designed for joint estimation of the states and parameters for an atomic force microscopy under process noise. The velocity of the end-effector, sample height and unknown fault are simultaneously estimated by measuring the tip position of randomly excited microscopy. Second, unscented Kalman filtering based model predictive controller is proposed for the accurate tracking of the tip-position. To prevent the disadvantage of the model-based controller design, an uncertainty or unknown fault function of the system is estimated by unscented Kalman filter such that the unmodeled dynamics of the system are compensated while the control signal is produced. Note that the controller voltage being applied to the microscopy is produced based on the estimated states and parameters of the atomic force microscopy. The numerical applications present that satisfactory tracking performance for tip position is obtained by the proposed fault tolerant controller such that extended Kalman filtering-based tracking results are also compared and discussed.

Structural, optical and photoresponse characteristics of metal-insulator-semiconductor (MIS) type Au/Ni/CeO2/GaN Schottky barrier ultraviolet photodetector

GaN based metal-insulator-semiconductor (MIS) type ultraviolet photodetector was fabricated and investigated using high-k dielectric CeO2 as an insulating oxide layer. Using XRD analysis, the phase formation of the as-deposited CeO2 films on GaN was found to be cubic fluorite. Non-contact mode atomic force microscopy technique was utilized and explored the surface morphology of CeO2 films on GaN composed of prearranged clusters of spherical shape with an average rms surface roughness of 0.428 μm. XPS analysis has revealed the existence of two oxidation states such as Ce3+ and Ce4+ in the Ce3d spectral envelop. Using absorbance versus wavelength data, the Tauc's plot was plotted and calculated a direct optical bandgap of 3.52 eV. The current-voltage (I–V) characteristics extracted from the device revealed the symmetric behavior or formation of back-to-back Schottky barrier at the metal-semiconductor (MS) interface. Photoresponsivity of the device at +10 V bias was calculated as 28.99 A/W and it is higher compared to the values extracted from metal-semiconductor-metal (MSM) type UV PDs reported in the literature. Furthermore, the transient response characteristics of the prepared device showed good stability with almost same rise time and fall time of ~2.73 s and ~5.35 s, respectively. Based on the device performance, the proposed MIS type structure could be a suitable for the development of ultraviolet photodetectors.

Effect of Temperature on Structural and Optical Properties of Methyl-Ammonium Bismuth Iodide Thin Films.

Organic-Inorganic perovskites are promising materials for an alternative to silicon technology for cost-effective performance of photovoltaic's (PVs). Lead-based hybrid perovskite has lower stability and high toxicity. The bismuth-based hybrid perovskite, Methyl Ammonium Bismuth Iodide (MABI) could be as an alternative to the lead-based system. In the present work, we present the structural and optical studies on hybrid MABI perovskite thin films synthesized at different temperature. Bandgap analyzed from UV-Vis absorption spectroscopy have shown the formation of MABI complex in thin films prepared from the single step spin coating and dip coating method. Further, the MABI formation confirmed by Raman analysis. Optical and structural properties obtained are comparable to earlier reported theoretical studies. The roughness of highly stable annealed film was analyzed by non-contact tapping mode atomic force microscopy.

Crystallinity of the epitaxial heterojunction of C60 on single crystal pentacene

The structure of pn heterojunctions is an important subject in the field of organic semiconductor devices. In this work, the crystallinity of an epitaxial pn heterojunction of C60 on single crystal pentacene is investigated by non-contact mode atomic force microscopy and high-resolution grazing incidence x-ray diffraction. Analysis shows that the C60 molecules assemble into grains consisting of single crystallites on the pentacene single crystal surface. The in-plane mean crystallite size exceeds 0.1µm, which is at least five time larger than the size of crystallites deposited onto polycrystalline pentacene thin films grown on SiO2. The results indicate that improvement in the crystal quality of the underlying molecular substrate leads to drastic promotion of the crystallinity at the organic semiconductor heterojunction.

Effect of degree of crystallinity on elastic properties of silicon carbide fabricated using polymer pyrolysis

In this study, silicon carbide (SiC) is fabricated using polymer infiltration and pyrolysis (PIP). Allylhydridopolycarbosilane (AHPCS) is used as the preceramic polymer. Final processing temperatures are varied to observe the change in microstructure as well as physical and mechanical properties. Density, porosity and thermal conductivity are determined as a function of processing temperatures. Microstructural characterization, done using atomic force microscopy (AFM) and X-ray diffraction (XRD), has revealed the presence of nanocrystalline domains with grain sizes in the range of 5–20nm. The degree of crystallinity is determined using non-contact mode atomic force microscopy. The degree of crystallinity follows an increasing trend with processing temperature. Hardness and modulus are determined using nanoindentation, and are found to be influenced by the degree of crystallinity.

Using dislocations to probe surface reconstruction in thick freely suspended liquid crystalline films.

Surface interactions can cause freely suspended thin liquid crystalline films to form phases different from the bulk material, but it is not known what happens at the surface of thick films. Edge dislocations can be used as a marker for the boundary between the bulk center and the reconstructed surface. We use noncontact mode atomic force microscopy to determine the depth of edge dislocations below the surface of freely suspended thick films of 4-n-heptyloxybenzylidene-4-n-heptylaniline (7O.7) in the crystalline B phase. Here, 3.0±0.1 nm high steps are found with a width that varies with temperature between 56 and 59°C. Using a strain model for the profile of liquid crystalline layers above an edge dislocation to estimate the depth of the dislocation, we find that the number of reconstructed surface layers increases from 4 to 50 layers as the temperature decreases from 59 to 56°C. This trend tracks the behavior of the phase boundary in the thickness dependent phase diagram of freely suspended films of 7O.7, suggesting that the surface may be reconstructed into a smectic F region.

Control of bistability in non-contact mode atomic force microscopy using modulated time delay

The control of bistability in non-contact mode atomic force microscopy subjected to a harmonic base excitation and in the presence of time-delayed feedback is investigated in this paper. We consider the case where the time-delayed feedback gain is modulated with a frequency higher than the natural frequency of the system and the frequency of the base displacement. We assume that the tip–sample interaction force is described by Lennard–Jones potential, and we consider a lumped single degree of freedom model describing weakly nonlinear dynamics of the microcantilever in the range of attracting force. Analytical investigation is performed to obtain approximation of the frequency response of the microcantilever as well as the regions of bistability in different parameter planes. The influence of the time-delayed feedback gain on the bistability behavior as well as the vibration amplitude of the tip motion is studied near primary resonance for different parameter variation.

4H-SiC기판 위에 Aerosol Deposition으로 증착된 Al2O3박막의 후열처리 효과

<TEX>$Al_2O_3$</TEX> films on silicon carbide were fabricated by Aerosol deposition with annealing temperature at <TEX>$800^{\circ}C$</TEX> and <TEX>$1,000^{\circ}C$</TEX>. The effect of thermal treatment on physical properties of <TEX>$Al_2O_3$</TEX> thin films has been investigated by XRD (X-ray diffraction), AFM (atomic force microscope), SEM (scanning electron microscope), and AES (auger electron spectroscopy). Also electrical properties have been investigated by Keithley 4,200 semiconductor parameter analyzer to explain the interface trapped charge density (<TEX>$D_{it}$</TEX>), flatband voltage (<TEX>$V_{FB}$</TEX>) and leakage current (<TEX>$I_o$</TEX>). <TEX>$Al_2O_3$</TEX> films become crystallized with increasing temperature by calculating full width at half maximum (FWHM) of diffraction peaks, also surface morphology is observed by topography measurement in non-contact mode AFM. <TEX>$D_{it}$</TEX> was <TEX>$2.26{\times}10^{-12}eV^{-1}.cm^{-2}$</TEX> at <TEX>$800^{\circ}C$</TEX> annealed sample, which is the lowest value in all samples. Also the sample annealed at <TEX>$800^{\circ}C$</TEX> has the lowest leakage current of <TEX>$4.89{\times}10^{-13}A$</TEX>.

Tip-based nanoscale selective growth of discrete silicon nanowires by near-field laser illumination

Growth of discrete silicon nanowires is reported with nanoscale location selectivity by employing near-field laser illumination. An uncoated dielectric atomic force microscope (AFM) tip provides a nanometer-scale light source that is sufficiently localized to induce nucleation and subsequent growth of a single nanowire under its optical near-field. Far-field laser-induced heating is additionally supplied to the substrate to both relieve the required near-field light budget and also assist stable epitaxial growth. Specific catalysts are selected for the nanowire growth by non-contact mode AFM imaging. Through real-time monitoring of the deflection of the AFM cantilever during the growth process, the gap between the tip and the sample and hence truly near-field illumination are maintained throughout the growth process. The study shows that tip-based near-field laser illumination could be an effective tool for the direct integration of semiconductor nanowires.

Preparation and characterization of mixed monolayers and Langmuir−Blodgett films of merocyanine 540/octadecylamine mixture

Mixed monolayer of merocyanine 540 (MC540) dye and octadecylamine (ODA) at the air/water interface has been prepared using the co-spreading method. The pressure–area (π–A) isotherm studies revealed that the mixtures of MC540/ODA at a different ratio formed a stable monolayer at the air/water interface and these floating layers were easily transferred onto hydrophilic substrates as the Y-type Langmuir–Blodgett (LB) film. The specific area per molecule in the π–A isotherm of the mixed monolayer of MC540/ODA was larger than that of the pristine ODA. The area can also get increased up to 40mN/m surface pressure by the increase of the dye concentration in the mixtures. The LB films of MC540/ODA mixture were formed at 30mN/m surface pressure by transferring the mixed monolayer at the air/water interface on hydrophilic glass substrate via vertical dip-coating as mono- and multilayer films. The photophysical properties of MC540 in chloroform and LB films have been investigated using the absorption, steady-state and time-resolved fluorescence spectroscopy techniques. H-aggregate formation of MC540 both in chloroform and LB film were concluded from the spectroscopic results. The morphology of the one-layer mixed LB film of MC540/ODA on the glass substrate has been characterized by AFM (atomic force microscopy). The non-contact mode AFM image of the one-layer mixed LB film showed that the film surface consisted of MC540/ODA nanoclusters. In conclusion, our results contribute to understanding the strong interaction between MC540 and ODA at the air/water interface, and show the effects of some parameters on the mixed LB films of MC540.

Surface morphology and optical property of thermally annealed GaN substrates

Boule of GaN crystal was grown with 50mm diameter and 3mm thickness by hydride vapor phase epitaxy and cut using a wire saw to produce freestanding wafers. These were, mechanically polished with diamond slurry and followed with chemical mechanical polishing for final surface preparation. Surface morphology was examined by non-contact mode atomic force microscopy before and after thermal annealing process performed at 700, 800, 900, and 1000°C for 1h, in air. Wafers with optimum surface quality submitted to thermal annealing treatment at 900°C were characterized by reduced scratched density and residual stress, and surface roughness of 0.096nm. Surface quality improvement was confirmed by relatively large recovery of the room temperature near band edge luminescence intensity.

Shear-Induced Self-Assembly of Native Silk Proteins into Fibrils Studied by Atomic Force Microscopy

Noncontact mode atomic force microscopy was used to investigate native silk proteins prepared in different ways. Low protein concentrations revealed that single protein molecules exhibit a simple, round shape with apparent diameters of 20-25 nm. Shearing the native protein solutions after extraction from the gland and prior to drying led to a beads-on-a-string assembly at the nanometer scale. Protein concentration had a significant effect on the morphology of the protein assemblies. At higher protein concentrations, shear-induced alignment into nanofibrils was observed, while lower concentrations lead to the formation of much thinner fibrils with a width of about 8 nm.

Silicon MIS diodes with Cr 2O 3 nanofilm: Optical, morphological/structural and electronic transport properties

In this work we report the optical, morphological and structural characterization and diode application of Cr 2O 3 nanofilms grown on p-Si substrates by spin coating and annealing process. X-ray diffraction (XRD), non-contact mode atomic force microscopy (NC-AFM), ultraviolet–visible (UV–vis) spectroscopy and photoluminescence (PL) spectroscopy were used for characterization of nanofilms. For Cr 2O 3 nanofilms, the average particle size determined from XRD and NC-AFM measurements was approximately 70 nm. Structure analyses of nanofilms demonstrate that the single phase Cr 2O 3 on silicon substrate is of high a crystalline structure with a dominant in hexagonal (1 1 0) orientation. The morphologic analysis of the films indicates that the films formed from hexagonal nanoparticles are with low roughness and uniform. UV–vis absorption measurements indicate that the band gap of the Cr 2O 3 film is 3.08 eV. The PL measurement shows that the Cr 2O 3 nanofilm has a strong and narrow ultraviolet emission, which facilitates potential applications in future photoelectric nanodevices. Au/Cr 2O 3/p-Si metal/interlayer/semiconductor (MIS) diodes were fabricated for investigation of the electronic properties such as current–voltage and capacitance–voltage. Ideality factor and barrier height for Au//Cr 2O 3/p-Si diode were calculated as 2.15 eV and 0.74 eV, respectively. Also, interfacial state properties of the MIS diode were determined. The interface-state density of the MIS diode was found to vary from 2.90 × 10 13 eV −1 cm −2 to 8.45 × 10 12 eV −1 cm −2.

Imaging Wet Individual Single Walled Carbon Nanotube at Atomic Level

Wet individual Single walled carbon nanotube was observed at an atomic level with high resolution. This ob- servation was achieved in a liquid cell containing water using a modified non-contact mode atomic force microscopy (NC-AFM) which, we believed, becomes the powerful tool for imaging nano-material in atomic scale. Consequently, the topography image showed many hexagons network of carbon atoms forming the outer surface of SWCNT. The analysis of the scanned SWCNT, by NC-AFM probe, revealed the presence of two sites of an armchair and zigzag structures.

The effect of ozonation on aggregation of humic substances on mica studied by atomic force microscopy

Humic substances influence adsorption and aggregation of colloids and ions in natural aquatic environment and thereby affect drinking water treatment by ozonation. In this paper the effect of ozonation on the ability of humic substances to form supramolecular structures was investigated by atomic force microscopy (AFM) surface topography. Ozonated and unozonated solutions of Suwannee River humic acid and fulvic acid were deposited onto molecularly smooth mica surfaces, left to dry and then imaged by AFM in non-contact mode. Two solutions with pH 4 and pH 7 were investigated. At each pH, significant differences in the aggregation behavior between these humic substances before and after ozonation were observed. In particular, ozonation increased the aggregate size of fulvic acid at the neutral pH. Size exclusion chromatography also revealed similar molecular weight distributions for the humic substances after ozonation. It was argued that difference in the molecular hydrophobicity or factors other than molecular weight could be responsible for the observed aggregation behavior. The outcome of this study is important for a better understanding of supramolecular structures of humic substances in ozonation, particularly those in drinking water treatment.

Functionalization of nickel oxide using alkylphosphonic acid self-assembled monolayers

Self-assembled monolayer formation of alkylphosphonic acids on the native nickel oxide surface has been accomplished. These monolayers are the first formed on the native nickel oxide surface that did not require electrochemical reduction of the surface to metallic nickel. Two different deposition methods, immersion and aerosol spraying, were used to form monolayers on the oxide surface. Both methods led to complete monolayer formation, with the aerosol method requiring shorter deposition time, lower temperature and decreased solution concentration compared to the immersion method. These deposition methods now allow nickel oxide substrates to be functionalized easily. Monolayer formation was investigated by diffuse reflectance Fourier transform infrared spectroscopy, non-contact mode atomic force microscopy, contact angle measurements and matrix-assisted laser desorption ionization mass spectrometry. Furthermore, cyclic voltammetry and electrochemical impedance spectroscopy studies show that the monolayer increased surface resistance to oxidation.

Quantitative characterisation of damage mechanisms in ancient ceramics by quantitative X-ray powder diffraction, polarisation microscopy, confocal laser scanning microscopy and non-contact mode atomic force microscopy

Ceramic technology is civilisation’s oldest tradition and one of our most current areas of knowledge. Pottery, ceramics, and their industrial production materials have been rooted in the historical and cultural structure of a nation and civilisation for thousands of years and retain their importance today. The origin of the surveyed material in this paper relates to areas of the Elamite Period (1500 BC) in South-West IranThe main purpose of the identification is to pay attention to the textural formation of the material, which is dependent on the mineralogical chemical performance in such systems. In this investigation, the texture of damage and phase segregation was determined. The phase analyses of crystalline composition were determined by quantitative X-ray powder diffraction (QXRD) measurements with Rietveld refinement. The results were matched with microscopic methods in order to arrive at a chemical petrological conclusion. The chemical compositions of the phases and the variation of elements between boundaries and the core were obtained by correlation of QXRD and X-ray fluorescence results and verified through EDX measurements. According to XRD polarisation microscopy studies, the research materials can be divided into two groups according to their matrix structure. The first group displays a calcareous matrix, which mainly consists of CaCO3 with a minor content of SiO2. The second group consists mainly of SiO2 and other silica compositions, such as alkali-feldspars, plagioclases and pyroxene. With respect to thermodynamic stability of pyroxene, the stability area of the solid solution in such systems varies between 750 and 870°C. Here, AFM in non-contact mode was carried out. The aim of this combined method was to confirm the damage process with regard to the structural conversion in the interface between selected minerals and the matrix (quartz, plagioclase, Kali-feldspar). Thus it was ultimately possible to obtain a quantitative characterisation of the micro- and nanostructure of these historical materials. As a result of this data, it is possible to define much more precise requirements for modern methods of restoration of materials, in order to gain higher durability and rentability cycles.It is possible to explain the techniques which have been used in ancient times in terms of material science methods, with the so called ‘ceramography’. In fact, the word ceramic is of Greek origin and means potter’s earth; however the tradition is much older. Traditional ceramics are those derived from naturally occurring raw materials and include clay based products. These were the most readily available raw materials for the ancient potters. It means that pottering might be actually the human development reference. Ceramics were the first products of people who sought materials which were required to demonstrate good plasticity behaviour in forming, high durability during firing, and an aesthetically pleasing end result.

Effect of Cu+2 Doping on the Nano-Scale Surface Roughness of Polyacrylamide Thin Replicas

High sensitive non-contact tapping mode atomic force microscopy has been used to study the effect of Cu+2 doping on the nano-scale surface roughness of polyacrylamide replicas. The study was carried out by determining the root mean square roughness of the polymer surface as a function of doping concentration on glass substrates. Results show that doping with Cu+2 leads to the formation of multi-scale features that increase in size and number with the doping concentration, which results in increasing the surface roughness.

Suppression of spurious vibration of cantilever in atomic force microscopy by enhancement of bending rigidity of cantilever chip substrate

To improve the precision of dynamic atomic force microscopy (AFM) using cantilever vibration spectra, a simple but effective method for suppressing spurious response (SR) was developed. The dominant origin of SR was identified to be the bending vibration of the cantilever substrate, by the analysis of the frequency of SR. Although a rigid cover pressing the whole surface of the substrate suppressed SR, the utility was insufficient. Then, a method of enhancing the bending rigidity of the substrate by gluing a rigid plate (clamping plate, CP) to the substrate was developed. This chip can be used with an ordinary cantilever holder, so that the reproducibility of SR suppression when attaching and detaching the cantilever chip to the holder was improved. To verify its utility, the evaluation of a microdevice electrode was performed by ultrasonic atomic force microscopy. The delamination at a submicron depth was visualized and the detailed variation of the delamination was evaluated for the first time using clear resonance spectra. The CP method will particularly contribute to improving dynamic-mode AFM, in which resonance spectra with a low quality factor are used, such as noncontact mode AFM in liquid or contact resonance mode AFM. The effect of the CP can be achieved by fabricating a substrate with a thick plate beforehand.

AFM and Mössbauer spectrometry investigation of the nanocrystallization process inFe–Mo–Cu–B rapidly quenched alloy

In this paper, the effect of heat treatment on the development of nanocrystallites in rapidly quenchedFe79Mo8Cu1B12 alloy is investigated. The surface morphology is examined using non-contact mode atomicforce microscopy (AFM). The results are compared with those obtained by transmissionMössbauer spectroscopy (TMS), conversion electron Mössbauer spectrometry (CEMS) andx-ray diffraction (XRD). It was found that the sample is not fully amorphous even in theas-quenched state. Minor amounts of bcc-Fe grains were detected on the wheel side ofthe ribbon-shaped samples while no indications of the crystalline phase wereobserved in the bulk. The crystallization onset is observed after annealing at410 °C, when bcc-Fe nanograins are quite well developed. More intense crystallization is evidencedafter annealing at higher temperatures, when the content of the crystalline phase increasesprogressively. The second crystallization, not discussed in the present paper, is characterizedby the occurrence of additional crystalline phases, and appears after annealing at650 °C. We suggest a crystallization model assuming no drastic change in the size of the primarilyformed bcc-Fe nanograins with temperature as proved by XRD. The increase in annealingtemperature induces the formation of a higher number of crystalline particles, which formlarge irregular agglomerates (80–130 nm in height), in accordance with the AFM data.