Laser microstructuring of Si surfaces for low-threshold field-electron emission

Dense arrays of high aspect ratio Si micro-pyramids have been formed by cumulative high intensity laser irradiation of doped Si wafers in an SF6 environment. A comparative study using nanosecond (XeCl, 308 nm) and femtosecond (Ti: Sapphire, 800 nm and KrF, 248 nm) laser pulses has been performed in this work. The influence of pulse duration and ambient gas pressure (SF6) is also presented. Scanning electron microscopy has shown that upon laser irradiation conical features appear on the Si surface in a rather homogenous distribution and with a spontaneous self alignment into arrays. Their lowest tip diameter is 800 nm; while their height reaches up to 90 mum. Secondary tip decoration appears on the surface of the formed spikes. Areas of 2 X 2 mm(2) covered with Si cones have been tested as cold cathode field emitters. After several conditioning cycles, the field emission threshold for the studied Si tips is as low as 2 V/mum, with an emission current of 10(-3) A/cm(2) at 4 V/mum. Even though these structures have smaller aspect ratios than good quality carbon nanotubes, their field emission properties are similar. The simple and direct formation of field emission Si arrays over small pre-selected areas by laser irradiation could lead to a novel approach for the development of electron sources. (C) 2003 Elsevier B.V. All rights reserved.

An electrokinetic sensor for studying immersed surfaces, using focused ultrasound

A novel method for obtaining information on the charge density of an immersed surface is presented. The technique uses focused ultrasound to excite oscillatory fluid motion in the plane of the solid-liquid interface, over a localised area. The displacement current (resulting from the motion of fluid-borne ions in the outer double-layer) is detected by electrodes in the liquid. The method is demonstrated as a means for monitoring protein adsorption, and for monitoring interactions between two different proteins. A second electrokinetic effect at the interface is identified, isolated from the first, and shown to provide additional information on the compressibility and charge density of the double-layer. © 2001 Elsevier Science B.V. All rights reserved.

ROLE OF CHLORINE AND ALKALI PROMOTERS IN ETHYLENE EPOXIDATION OVER SINGLE CRYSTAL SILVER SURFACES.

Experiments with N//2O were carried out with a view to obtaining additional information about the reactivity of oxygen surface species. On clean Ag, N//2O decomposition was found to be an activated process which led exclusively to the deposition of O(a) species. The presence of preadsorbed oxygen or subsurface oxygen served to enhance the deposition rate of O(a). Subsequent dosing with ethylene at 300 K of such an oxygen-populated surface followed by TPR examination showed it to be active for ethylene oxide formation. Control experiments established that adventitious decomposition of N//2O at the reactor walls or specimen supports followed by possible re-absorption of O//2(a) was an entirely negligible process. ) The oxidation activity of N//2O was also investigated at elevated pressures in the batch reactor.

Surface Stress Induced By Adatoms Adsorption On Solid Surfaces

Based on the statistical thermodynamics theory, a theoretical model of adsorbate induced surface stress of adatoms adsorption on solid surface is presented. For the low coverage, the interaction between the adsorbed molecules is entirely negligible and the adsorption induced surface stress is found to be the function of the coverage and the adsorption energy change with strain. For the high coverage, the adsorbate-adsorbate interaction contributes to the adsorption-induced surface stress effectively. In the case of carbon adsorption on the Ni(100) surface, the value of 0.5 is obtained as a characteristic coverage to decide whether to take the interaction between the adsorabtes into consideration and the results also show that the adsorption induces a compressive surface stress.

An Electrowetting Model For Rough Surfaces Under Low Voltage

Electrowetting is one of the most effective methods to enhance wettability. A significant change of contact angle for the liquid droplet can result from the surface microstructures and the external electric field, without altering the chemical composition of the system. During the electrowetting process on a rough surface, the droplet exhibits a sharp transition from the Cassie-Baxter to the Wenzel regime at a low critical voltage. In this paper, a theoretical model for electrowetting is put forth to describe the dynamic electrical control of the wetting behavior at the low voltage, considering the surface topography. The theoretical results are found to be in good agreement with the existing experimental results. (c) Koninklijke Brill NV, Leiden, 2008.

Adsorption of His-tagged peptide to Ni, Cu and Au (100) surfaces: Molecular dynamics simulation

Molecular dynamics (MD) simulations are performed to study the interaction of His-tagged peptide with three different metal surfaces in explicit water. The equilibrium properties are analyzed by using pair correlation functions (PCF) to give an insight into the behavior of the peptide adsorption to metal surfaces in water solvent. The intermolecular interactions between peptide residues and the metal surfaces are evaluated. By pulling the peptide away from the peptide in the presence of solvent water, peeling forces are obtained and reveal the binding strength of peptide adsorption on nickel, copper and gold. From the analysis of the dynamics properties of the peptide interaction with the metal surfaces, it is shown that the affinity of peptide to Ni surface is the strongest, while on Cu and An the affinity is a little weaker. In MD simulations including metals, the His-tagged region interacts with the substrate to an extent greater than the other regions. The work presented here reveals various interactions between His-tagged peptide and Ni/Cu/Au surfaces. The interesting affinities and dynamical properties of the peptide are also derived. The results give predictions for the structure of His-tagged peptide adsorbing on three different metal surfaces and show the different affinities between them, which assist the understanding of how peptides behave on metal surfaces and of how designers select amino sequences in molecule devices design. (c) 2007 Elsevier Ltd. All rights reserved.