Saydulla Persheyev

BV-2 microglial cells sense micro-nanotextured silicon surface topology†

Artificial biomimetic substrates provide useful models for studying cell adhesion, signaling, and differentiation. This article describes biological interactions with a new type of tunable, micro-nanotextured silicon substrate, generated by irradiation of a hydrogenated amorphous silicon film with a large beam, excimer laser (248 nm). In this study, we demonstrate that BV-2 microglial cells can sense differences in laser processed silicon surface topology over the range of 30 nm to 2 μm, where they undergo marked morphogenic changes with increasing feature size. The cells adopt a more elongated shape in the presence of the modified surface structure and exhibit increased levels of actin-rich microdomains, suggesting enhanced adhesion. The excimer laser modification of hydrogenated amorphous silicon to generate micro-nanostructures realizes large area benefits as well as providing a biomaterial where the external and internal structure can be altered and tuned for various applications.

On Ultrafast Photoconductivity Dynamics and Crystallinity of Black Silicon

We investigate the carrier dynamics of thin films of black silicon, amorphous hydrogenated silicon which under laser annealing forms a microstructured surface with extremely high broadband optical absorption. We use Raman spectroscopy to determine the degree of crystallinity of the annealed surfaces, and investigate the dependence on crystallinity and fabrication method of the photoconductivity. Time-resolved THz spectroscopy is used to determine the evolution of the carrier scattering time and confinement of carriers on the picosecond time scale. We conclude that a fabrication method with high energy leading edge of the annealing laser results in black silicon with the largest photon-to-electron conversion efficiency, largest mobility, and longest carrier lifetime.

Atmospheric adsorption effects in hot-wire chemical-vapor-deposition microcrystalline silicon films with different electrode configurations

Hot-wire chemical-vapor-disposition (CVD) thin silicon films are studied by means of dark conductivity, FTIR, hydrogen evolution, and SEM surface characterization. Three types of metastability are observed: (1) long term irreversible degradation due to oxidization processes on the film surface, (2) reversible degradation determined by uncontrolled water and/or oxygen adsorption, and (3) a fast field-switching effect in the film bulk. We propose that this effect is associated with the morphology changes during film growth and an electrical field induced by adsorbed atmospheric components on the film surface. It is found that metastable processes close to the film surface are stronger than in the bulk.

Metastability in Undoped Microcrystalline Silicon Thin Films Deposited by HWCVD

Films deposited by the Hot Wire CVD method were studied by means of dark conductivity, FTIR, Hydrogen Evolution, SEM and AFM surface characterization. Three types of metastability were observed: a) long term irreversible degradation due to oxidization processes on the film surface, b) reversible degradation determined by uncontrolled water adsorption, c) fast field switching effect in the film bulk. Oxygen and hydrogen content and its bonding configurations have been analyzed by hydrogen evolution and infrared spectroscopy methods on the films deposited on glass substrates and silicon wafers subsequently. It has been found that metastable processes close to the film surface are stronger than in the bulk. The switching effect is the fast increase of charge carrier density observed on bottom chromium contacts under a condition of air admittance. We propose this effect is associated with morphology changes during film growth and electrical field induced by adsorbed atmospheric components on the film surface.

Excimer Laser Microstructuring of Amorphous Silicon Films for Electron Field Emission Applications

The hydrogenated amorphous silicon (a-Si:H) films on molybdenum coated glass substrates were microstructured by irradiating the films using KrF excimer laser with a slope beam profile. By varying the laser processing parameters i.e., the laser pulse energy, the number of laser pulses and the laser energy distribution along the sample scan directions, the homogeneous, high density, and conical polycrystalline silicon features can be fabricated on the thin film surfaces. The electron field emission measurement results show that this kind of laser processed a- Si:H films possess good field emission characteristics with a low turn on electric field of less than 15 V/�� m and a larger saturation emission current. The diode configured field emission display devices have been demonstrated by using the laser irradiated a- Si:H films as the electron cold cathode emitters.

Time-resolved terahertz spectroscopy of black silicon

The ultrafast photoconductivity dynamics of black silicon is measured by time-resolved terahertz spectroscopy. Black silicon is produced by laser annealing of an a-Si:H film. We show that the decay time of the photoconductivity depends on the annealing method and fluence used in the production process.

Diffusion of Chromium in Thin Hydrogenated Amorphous Silicon Films

The diffusion of a chromium bottom contact has been studied through thin 10-nm amorphous silicon film. The concentration of the diffused impurity has been analyzed by an X-ray photon spectroscopy technique and the diffusion coefficient was estimated. Diffusion annealing was carried out in vacuum (10−6 mTorr), the temperature was kept at 400°C, and the annealing time was varied from 0 to 300 min. The authors propose that diffusion of chromium in thin hydrogenated amorphous film is limited by silicide formation at the metal-silicon interface.

A new method of manufacturing high aspect ratio structures using SU8 negative photoresist

SU8 Negative photoresist is finding high demand in applications such as MEMS sensors and waveguides. The possibility of photolithographic patterning and high physical and dielectric properties are attracting ever more users among workers in the electronics industry and increasingly in biomedical applications. In our work we employ an original method of exposing of SU8 and create high aspect ratio structures on glass and other substrates. Dry plasma etching results of negative epoxy-based photoresist by Inductively Coupled Plasma system using gases O 2 and CF 4 are presented.