Papers by Keyword: STM

Abstract: In this work, an investigation of the mechanically exfoliated MoS₂ under the influence of heat treatment was carried out. Optical and atomic force microscopy techniques were applied to determine the number of layers. Resonant Raman investigation was performed, which clearly showed systematic layer-dependent spectral features. The surface morphology of MoS₂ was investigated with the STM. Atomic-resolution images of MoS₂ is were obtained. Three types of atomic defects were identified as substitutions of donor and acceptor atoms in the Mo atomic layer below the topmost sulfur layer.

Abstract: Graphene, the most unique member of carbon family has fuelled a huge interest across the globe with its superior mechanical, chemical, optical and electronic properties. It has opened enormous avenues for humankind in terms of different applications. Since its discovery in 2004, people have tried various techniques to extract graphene, such as mechanical exfoliation, chemical exfoliation, epitaxial growth, CVD (chemical vapour deposition) etc. However, the above methods are not optimal for mass production, neither are they simple and cost effective. The present work highlights synthesis of graphene through electrochemical approach and its subsequent characterization. Pyrolytic graphite is subjected to intercalation of two different concentrations of HNO₃ electrolyte. XRD, FESEM and TEM were utilised to understand the structure and morphology of the obtained few-layer graphene nanosheets (FLGNs). Scanning probe spectroscopy is a useful technique for understanding the morphological structure of a sample at atomic level. Authors have utilised AFM which shows the thickness of the FLGNs to be in the range of 5-6 nm. STM studies of graphene nanosheets revealed atomic scaled periodicity and atomic flatness.

Abstract: Top-gated field-effect transistors have been created from bilayer epitaxial graphene samples that were grown on SiC substrates by a vacuum sublimation approach. A high-quality dielectric layer of Al₂O₃ was grown by atomic layer deposition to function as the gate oxide, with an e-beam evaporated seed layer utilized to promote uniform growth of Al₂O₃ over the graphene. Electrical characterization has been performed on these devices, and temperature-dependent measurements yielded a rise in the maximum transconductance and a significant shifting of the Dirac point as the operating temperature of the transistors was increased.

Abstract: C(4×4) reconstruction on arsenic-rich GaAs(001) surface after phase transition has been investigated from the experiment and simulation. We found that the c(4×4) As-rich reconstruction structure of the GaAs (001) surface can be best depicted with the model which there are three As-As dimers without Ga-As dimers in a reconstructed unit cell, and these dimers are found to be aligned perpendicular to the As dimers on β2(2×4) surface.

Abstract: Scanning tunneling microscope (STM) has several advantages, such as high resolution, and is wildly used. Piezoelectric scanner brings the horizontal resolution of STM up to 0.1 nm, and is it derived by piezoelectric ceramic. Piezoelectric scanner has piezoelectric ceramic’s character. So, piezoelectric scanner output must be calibrated at regular intervals. Graphite atom arrange in a special manner. In the same layer, the distance between adjacent atoms is the same, 0.25nm. This feature can be used to measure length and calibrate small scale scanning. For the 512 × 512 resolution image, the maximum scan range that can distinguish atoms is 30nm2. More large area of atomic image needs to use image stitching technology. By image stitching, small scale scanning, less than 1μm can be calibrated.

Abstract: Low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and scanning tunnelling microscopy (STM) were used to study the reactive diffusion of one monolayer of silicon deposited at room temperature onto a Ni (111) substrate. We have done isochronal and isothermal kinetics by AES, and we observed in both cases a kinetics blockage on a plateau corresponding to around one third of a silicon monolayer. STM images and LEED patterns both recorded at room temperature just after annealing, reveal formation of an ordered hexagonal superstructure corresponding probably to a two-dimensional surface silicide.

Abstract: The use of integration of copper interconnects in semiconductor devices has greatly advanced the development of integrated circuits and has enabled ever higher device densities. Unfortunately the oxides of copper are poorly suited to semiconductor manufacture. As Cu (I) and Cu (II) oxides are not self-limiting they can pose serious issues from a cleaning and queue time management perspective. In both post-etch and post-CMP cleaning applications it is critical that both types of Cu oxide are removed without damage to either Cu or the dielectric. With the most advanced sub 32nm nodes simply removing the oxides is not sufficient; their re-growth must also be prevented using surface passivation.

Abstract: The megasonic cleaning efficiency is evaluated as a function of the angle of incidence of acoustic waves on a Si wafer. Acoustic Schlichting streaming alone is not able to remove nanoparticles smaller than 400 nm. It is shown that oscillating or collapsing behavior of bubbles are responsible for removing nanoparticles smaller than 400 nm during a cleaning process with ultrasound. Optimal particle removal efficiency is obtained around the angle of acoustic transmission of the silicon wafer.

Abstract: The self-assembly behaviour of a novel cationic porphyrin-anthraquione (Por-AQ) hybrid ([AQATMPyP]I3) on highly oriented pyrolytic graphite (HOPG) was studied at room temperature in air by scanning tunneling microscopy(STM). According to theoretical calculation, it is testified that [AQATMPyP]I3 molecule mainly exists in the closed structure. The STM results reveal the presence of large-scale domains of ordered adlayer of this hybrid compound on HOPG. The STM images show a structure constituted by parallel rows. The width of each row is approximately 2.5nm.

Abstract: The so-called “growth” of graphene was performed using a horizontal chemical vapor deposition (CVD) hot-wall reactor. In-situ etching in the mixture (H2-C3H8) was performed prior to growth at 1600oC temperature under 100 mbar. Systematic studies of the influence of the decomposition temperature and time, substrates roughness, etching of the substrates, heating rate, SiC dezorientation and other process parameters on the graphene thickness and quality have been conducted. Morphology and atomic scale structure of graphene was examined by Scanning Tunnelling Microscopy (STM), Transmission Electron Microscopy (TEM) and Raman scattering methods.