Papers by Keyword: Atomic Force Microscope (AFM)

Abstract: AFM is used to study tooth surfaces (enamel and cementum) in order to compare the pattern of particle distribution and demineralization process in the two dissimilar tooth hard tissues. Our approach is focusing mainly on the qualitative observations of tooth surface morphology and quantitatively measuring the early stages of mineral loss. The native enamel presented globular particles tightly packed. After polishing the aprismatic layer, the particles observed were relatively larger and more organized than ones in the outmost enamel surface. The cementum had small grains arranged in some degree of ordered packing with varying crystallite orientations. After different time treatment with citric acid solution, all the sample surfaces became more irregular and had the deeper grooves. The maximum mineral loss was greatest for the cementum sample and lowest for the native enamel. The demineralization difference between the enamel and cementum shows the structure and component play important roles in the morphological changes of demineralization. These demonstrate that the microstructure and demineralized difference between enamel and cementum obtained with AFM are complementary to the usual SEM images and TEM data. AFM is suitable for measuring early stages of tooth surface demineralization.

Abstract: The single crystal of Si is still one of the most important candidates among other materials including Single crystals of SiC, GaN, C(diamond) or compound semiconductors. The innovative process as called CMG(Chemo-Mechanical-Grinding) for Si wafer has been recently developed which is different from conventional CMP(Chemo-Mechanical-Polishing ) process. The CMG process can be done under dry conditions using CeO2 based solid bulk abrasives. The microstructures for surface and subsurface of Si single crystal after CMG process were analyzed using TEM/EDX, AFM, MFP-3D Microscope. The mechanism of CMG process was also investigated by X-ray diffraction and ICP chemical analysis using products by chemical reaction between Si and CeO2 abrasives. The results showed that Si single crystal after CMG had, 1) no defects even Si lattice revel or mechanical imperfections,2) better surface roughness as compared to CMP process. The CMG mechanism concluded that CeO2 reacted with Si producing Ce-Si-O amorphous phase.

Abstract: Transparent conducting indium tin oxide (ITO) thin films were deposited on glass substrates by magnetron sputter type negative metal ion source (MSNIS) using ITO target and then the effect of post deposition annealing temperature on the optoelectrical property of ITO film has been investigated. The resistivity and optical transmittance of ITO films that prepared at 70°C (without intentional substrate heating) with optimized deposition condition reached at 6.2×10-4  cm and 80%, respectively. As increasing post deposition annealing temperature, a rapid decrease is observed in the resistivity. The lowest resistivity of 1.7×10-4  cm and the highest optical transmittance of 83% were obtained at the post annealing temperature of 300°C. From the XRD and SEM measurements, the increment of the optical transmittance and conductivity by post deposition annealing treatment is attributed to the enhanced crystallinity of the ITO film.

Abstract: Effects of the scratching feed on machined surface and scratching forces are studied by using AFM-based nanomachining process scratching along the long axis of the cantilever. Results show: A deeper structure and rougher surface can be obtained at a smaller feed. An increase in the feed results in increases in scratching forces and the resultant force and a decrease in the normal force. Finally, all forces reach to a saturation value. The ratio of the cutting force to the thrust force in the plane perpendicular to the cutting edge can reveal effects of ploughing and cutting between the tip and the sample in the nanomachining process. Correspondingly, different states (cutting or ploughing) play a key role in formation of the machined surface at different feeds.

Abstract: An atomic force microscope (AFM) with suitable tips has been used for nano fabrication/nanometric machining purposes. In this paper, acoustic emission (AE) was introduced to monitor the nanometric machining of a brittle material (silicon) using AFM. In the experiments, AE responses were sampled, as the tip load was linearly increased (ramped load), to investigate machining characteristics during continuous movement. By analyzing the experimental results, it can be concluded that measured AE energy is sensitive to changes in the mechanism of material removal including the ductile-brittle transition during nanometric machining. The critical depth of cut value for the transition is evaluated and discussed.

Abstract: Atomic force microscopy (AFM) is widely used in many fields, because of its outstanding force measurement ability in nano scale. Some coating layers are used to enhance the signal intensity, but these coating layers affect the spring constant of AFM cantilever and the accuracy of force measurement. In this paper, the spring constants of rectangular cantilever with different coating thickness were quantitatively measured and discussed. The finite element method was used to analyze the nonlinear force-displacement behavior from which the cantilever’s normal and torsional spring constants could be determined. The experimental data and the numerical results were also compared with the results from other methods. By considering the influence of coating layers and real cantilever geometries, the more accurate force measurements by AFM cantilever can be obtained.

Abstract: We have designed and fabricated diamond-shaped AFM cantilevers capable of performing multi-functioning tasks by using single crystal silicon (SCS) micromachining techniques. Structural improvement of the cantilever has clearly solved the crucial problems resulted from using conventional simple beam-AFM cantilever for mechanical testing. After forcecalibration of the cantilever, indentation tests are performed to determine the mechanical behaviors in micro/nano-scale as well as topographic imaging. A diamond Berkovich tip of which radius at the apex is approximately 20 nm is attached on the cantilever for the indentation test and 3D topography measurement. The indentation load-depth curves of nano-scale polymeric pattern (PAK01-UV curable blended resin) are measured and surface topography right after indenting is also obtained. Development of this novel cantilever will extend the AFM functionality into the highly sensitive mechanical testing devices in nano/pico scale.

Abstract: Two different types of experimental methods have beeen developed for measuring lateral interaction forces between two solid surfaces for nano- and micro-meter scale contacts. One is the type of direct measurement methods which typically utilize AFM instrumentations. In the direct lateral force measurements some size-scale effects are commonly observed due to the effects of adhesion and surface roughness. A recent development of a fine AFM lateral force calibration method, a diamagnetic lateral force calibrator, has made it possible to study such size-scale effects systematically. The other type is the field projection method which requires a high resolution measurement of a deformation field near the edge of a contact. For such measurements a comprehensive map of deformation measurement techniques is introduced in a domain of spatial and strain resolutions. This technique provides a way of assessing the non-uniform distribution of the surface interaction forces for nano and micro-meter scale contacts.

Abstract: The impact of high temperature annealing using graphite encapsulation (formed by baking photoresist) on the electrical properties of Ni Schottky diodes formed on the annealed surfaces is studied. The surface morphology is also characterized by atomic force microscopy (AFM). Annealing for 10 minutes at temperatures up to 1800 °C with graphite encapsulation actually reduces the high-current ideality factor of the diodes while raising the current-voltage barrier height (linearly extrapolated to unity ideality factor) from 1.453 V to 1.67-1.73 V. Excess leakage current occurs only in a subset of diodes, which are believed to be affected by extended defects. The AFM images show no significant surface roughening, and the graphite can be removed after processing. This encapsulation method is found to be highly effective in preserving the electronic properties of the surface during high temperature annealing.

Abstract: AlNi and Ni2Si based ohmic contacts to p-type 4H-SiC have been produced using low energy ion implantation, a Ti contact layer, and sequential anneals. Low resistivities were promoted by degenerately (>1020 cm-3) doping the surface region of 4H-SiC epilayers via Al+ implantation. High acceptor activation and improved surface morphology was achieved by capping the samples with pyrolized photoresist and using a two-step anneal sequence in argon. Ti/AlNi/W and Ti/Ni2Si/W stacks of varying Ti and/or binary layer thickness were compared at varying anneal temperatures. AlNi based samples reliably and repeatedly achieved specific contact resistivities as low as 5.5 x10-5 ohm-cm2 after annealing at temperatures of 700-1000°C. For the Ni2Si samples, resistivities as low 4.5x10-4 ohm-cm2 were reached after annealing between 750 and 1100°C. Similarly, a set of Ti/AlNi/Au samples, with or without Ge as an additional contact layer, were prepared via the same procedures. In this case, specific contact resistivities as low as 5.0 x10-4 ohm-cm2 were achieved after annealing the Ti/AlNi/Au samples between 600 and 700°C for 30 minutes in a dynamic argon atmosphere or under high vacuum. The lowest resistivities were realized using thicker (~ 40 nm) Ti layers. I-V analysis revealed superior linear characteristics for the AlNi system, which also exhibited a more stable microstructure after anneal. SIMS and RBS were used to analyze the stability of the stacks subsequent to thermal treatment. AFM analysis demonstrated the superiority of photoresist capping over alternatives in minimizing surface roughness. Linear ohmic behavior after significantly reduced anneal temperature is the main observation of the present study.