Post Anodization Research Articles

The annealing treatment of interface states in planar and recessed-anode AlGaN/GaN Schottky barrier diodes

The recessed-anode AlGaN/GaN Schottky barrier diodes (SBDs) were fabricated by self-aligned process, and the effect of annealing of planar and recessed-anode AlGaN/GaN SBDs were investigated. The interface states of AlGaN/GaN SBD were treated by post anode annealing (PAA), which may be attributed to the reduction of metal-induced gap states (MIGS) at Schottky interface. The interface state density (NSS) of planar and recessed-anode AlGaN/GaN SBDs are suppressed by PAA processes to 1.6 × 1013 eV−1cm−2 and 3.9 × 1014 eV−1cm−2, respectively. It is found that after annealing of AlGaN/GaN SBDs, the SBDs stability is enhanced, the leakage current is reduced, the ideal factor is optimized, and the ON-resistance is reduced. The PAA process can effectively improve the performance of AlGaN/GaN SBDs, which is a key technology to optimize GaN SBDs.

Surface preparation effects on anodization and corrosion resistance of pure titanium grade 2

Abstract A layer of TiO2 nanotubes is widely used as a surface application on Titanium (Ti) implants because the nanotubes help promote cell adhesion and provide better cell response than the metal surface. Although several studies have reported the relationship between TiO2 nanotubes and cell osseointegration rate, the corrosion rate of the TiO2 nanotube layer under the circumstance of usage has yet to be fully evaluated. In this work, we have studied the effect of surface preparation conditions on the corrosion behavior of a TiO2 nanotube layer on a pure Ti substrate. The surface of the titanium substrate was prepared by different methods, followed by one-step anodization to obtain a TiO2 nanotube array. A surface roughness non-contact tester and field emission scanning electron microscope were used to characterize the surface roughness and surface morphology of the as-received, mechanically polished, and chemically polished substrate both pre and post anodization. The corrosion behavior of the prepared substrates was also investigated in Phosphate Buffered Saline solution using potentiodynamic polarization technique. The results suggest that surface roughness at the nanoscale of the prepared surfaces has no relationship with corrosion resistance. However, after anodization, the corrosion rate has a good relationship with the standard deviation of inner tube/pore diameter.

Effect of post anode annealing on W/Au and Ni/Au multi-channel AlGaN/GaN Schottky diode

In this paper, multi-channel AlGaN/GaN Schottky diodes (MC-SBDs) with W/Au and Ni/Au anode metal were fabricated on the Si substrates, and the effect of post anode annealing (PAA) was investigated. The temperature of PAA varies from 300 °C to 550 °C. Benefitting from the multi-channel structure, low on-resistance ( R ON ) of 3.11 Ω mm are obtained for Ni and W after 300 °C PAA. Meanwhile, the onset voltage ( V ON ) of W is 0.34 V, much lower than 0.71 V for Ni. With PAA temperature rising, the V ON and barrier height ( φ b ) increase for both metals at the beginning because of the repair of etching damage. However, these parameters will decrease when the temperature exceeds the optimal value due to the deterioration of the Schottky interface. Correspondingly, the reverse current ( I REV ) drops first and then rises. The optimal PAA temperature is 450 °C for Ni and 500 °C for W. Furthermore, the temperature-dependent characteristics are also measured for comprehensive evaluation. The results show that the PAA has little effect on temperature-dependent forward characteristics for both Ni and W. However, the PAA can improve the high-temperature stability of I REV for Ni, whereas this advantage has not been observed on W, which is related to different leakage current mechanisms. • Successfully fabricated multi-channel AlGaN/GaN Schottky diodes on Si substrate. • Comparison of the device characteristics of W and Ni as anode metal. • Study on different post anode annealing temperatures. • Temperature-dependent I–V characteristics after post anode annealing.

Design and beam dynamics of a Transmission Electron Microscope electron gun assembly

We present the design and beam dynamics analysis of a Transmission Electron Microscope illumination system. A LaB6 emitter is used as a cathode/source with an emissive surface area of diameter 50 μm generating fixed emission current of 5 mA which is biased by −300 V with Wehnelt electrode. The gun is comprised of five electrostatic lenses in-between the focusing and anode electrodes to accelerate and focus the beam with integrated energy of 160 keV in the post anode region with diameter around 228 μm. Finally, the beam is focused using the condensed electro-magnetic lenses of field strengths 183 mT and 331 mT, respectively to spot size 1.8 μm in the post-lens position. The obtained focal spots are largely symmetric along the two transverse directions. The illumination system geometry offers full beam collimation control. The study provides a theoretical basis for the structure and optics design of the Transmission Electron Microscope.

Macro-micron-nano-featured surface topography of Ti-6Al-4V alloy for biomedical applications

One of the critical issues in the development of novel metallic biomaterials is the design and fabrication of metallic scaffolds and implants with hierarchical structures mimicking human bones. In this work, selective laser melting (SLM) and electrochemical anodization were applied to fabricate dense Ti-6Al-4V components with macro-micron-nanoscale hierarchical surfaces. Scanning electron microscopy (SEM), 3D laser scanning microscopy (3D LSM), contact angle video system, fluorescence microscopy and spectrophotometer were used to investigate the properties of the samples. The results reveal that the SLMed post-anodization (SLM-TNT) exhibits enhanced or at least comparable wettability, protein adsorption and biological response of mesenchymal stem cells (MSCs) in comparison with the three reference configurations, i.e., the polished Ti-6Al-4V (PO-Ti64), the SLMed Ti-6Al-4V (SLM-Ti64) and the polished Ti-6Al-4V post-anodization (PO-TNT). The improved cytocompatibility of the samples after SLM and anodization should be mainly attributed to the nanoscale tubular features, while the macro-micron-scale structures only lead to slight preference for cell attachment.

Rutile nanotubes by electrochemical anodization

We present a facile method to synthesize rutile titanium dioxide nanotubes (R-TiNT), directly in powder form through rapid breakdown electrochemical anodization by modifying the post anodization processing and annealing temperature.

Simulation and test of a thermioic hairpin source DC electron beam gun

A hairpin source electron gun was simulated and tested for its emission characteristics. We calculated beam emittance 4.3π-mm-mR and average current density 5.80A/cm2 which corresponds to power density 5.80×104W/cm2 with 0.9mm of beam waist diameter at 113mm in the post anode region. The simulation and test results were found in agreement at 10kV of acceleration potential. We also calculated the variation of current density and emittance with acceleration potential up to the saturation limit of the gun (100kV). The gun is useful for electron optical devices, electron accelerators and deep weld joints of refractory metals.

Evaluation of mesoporous silicon substrates strain for the integration of radio frequency circuits

Mesoporous silicon can be used as isolating substrate for the integration of radiofrequency (RF) passive devices. The higher is the porous silicon (PS) thickness, the better are the RF performances. However, an increase of PS thickness induces a raise of strain in the substrate.In this work, the strain of 6 inches PS substrates which has been generated during electrochemical etching and post anodization annealing steps are studied. It is shown that, if the anodization process is not well-controlled, the consequences can be cracks of the PS layer or a high wafer curvature which prevents device from integration with a standard process. It is also demonstrated that different kinds of defects due to PS stress can be also observed on full wafer PS layers and localized PS substrates as well.

Note: Simulation and test of a strip source electron gun.

We present simulation and test of an indirectly heated strip source electron beam gun assembly using Stanford Linear Accelerator Center (SLAC) electron beam trajectory program. The beam is now sharply focused with 3.04 mm diameter in the post anode region at 15.9 mm. The measured emission current and emission density were 1.12 A and 1.15 A/cm(2), respectively, that corresponds to power density of 11.5 kW/cm(2), at 10 kV acceleration potential. The simulated results were compared with then and now experiments and found in agreement. The gun is without any biasing, electrostatic and magnetic fields; hence simple and inexpensive. Moreover, it is now more powerful and is useful for accelerators technology due to high emission and low emittance parameters.

Optimization of the hairpin-source electron gun using EGUN

We present a comparison of the experimental and simulated results of the thermionic hairpin-source, electron beam assembly using the SLAC electron beam trajectory program (EGUN). The gun was optimized for maximum emission current density and beam convergence in the post anode region. Therefore, by optimizing different parameters, an emission current density of 32 A/cm2 with maximum beam convergence of 0.9 mm was obtained. This corresponds to a power density of 3.29 × 105 W/cm2 at the focus point. As this was accomplished without the aid of magnetic focusing, the assembly was much simplified. The gun can now be used for electron devices and accelerator technology which require high current and power densities.

Optimization of Electrostatic Focusing for Line Source Electron Beam Emitter Assembly

Abstract We studied and analyzed the design of line source electron gun numerically and verified results experimentally. A minimum beam diameter of 0.9 mm is achieved in the post anode region at a distance of 20 mm from the centre of cathode surface. Simulated and experimental results are in good agreement showing the maximum focusibilty, emission and beam uniformity throughout the emission surface. The gun is simple without any magnetic field and extra biasing to the focusing electrode. The gun is extremely useful for all type of metallurgical applications in general and for surface coating and surface modification experiments in special.

Pulse electrochemical method for porosification of silicon and preparation of porSi powder with controllable particles size distribution

AbstractWe have proposed to use a special electrochemical regime to introduce a preferable grain size into the entirely porosified Si material. This periodic pulse electrochemical regime permits layering of the entire porosified film and defines its preferable partition in the post anodization mechanical treatment. Thus, a preferable grain size is “hidden” in the grown porSi film and is revealed only under additional mechanical treatment like milling. The pore dimension and total porosity are controlled by applied current density at the work pulse and prefabricated (hidden) grain size is introduced during an application of the cut or/and relaxation pulses. We have applied a described procedure to produce a sub‐micrometric grain porSi powder and report results on SEM analysis of the material fabricated in different pulse regimes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Post-Anodization Implantation and CVD Techniques for Passivation of Porous Silicon

ABSTRACTProper surface passivation is critical for achieving stable, efficient PL from light-emitting porous silicon (LEPSi). As-anodized LEPSi is passivated by hydrogen which desorbs at a temperature as low as 400 °C. For device purposes, it is necessary that porous Si can tolerate at least 450 °C for post anodization annealing/metallization steps. We have established that, if the hydrogen at the surface is substituted by oxygen, the resulting Si-Ox passivation is significantly more stable. One way of achieving this is to implant low energy/low dose oxygen to form a thin coating of SiO2 on the surface. Post implantation FTIR data report the absence of Si-H peaks. XPS data indicate the formation of nearly stoichiometric SiO2 at the surface. Similar results were achieved by implanting with nitrogen to form Si3N4. As an alternative to implantation, we have deposited thin capping layers of SiO2, Si3N4 and SiC by plasma-enhanced chemical vapor deposition (PECVD) which resulted in a similar degree of passivation. Wafers were pre-treated at 400 °C to remove hydrogen from the surface. Finally, we carried out a low-pressure CVD (LPCVD) oxide deposition on LEPSi. Post implantation/CVD annealing was done at temperatures up to 600 °C. In most cases, little or no change was observed in the resultant PL intensities.

Collective Ion Acceleration in the Vacuum Systm with Insuilated Anode

Experiments are described of ion acceleration in diode with insulated anode mounted on two E-beam generators that deliver 2kJ and 1 kJ of energy in 1 MeV; 50 ns and 0.35 MeV, 80 ns pulses accoraingly. The maximum yield of protons 1014±3.1013 with energy in (1.9 + 2.7) MeV range were measured with accompanying electron beam current 18 kA and electron energy 0.8 MeV on 2 kJ maching. The suppression of charging prepulse by inserting a dielectric piece in cathode terminal on it resulted in increased ion energy up to 5 MeV and total yield of protons with energy in the (2.7 + 5) MeV region up to 1013±3.12 By application of several (from 1 to 3) post anode electrodes on 1 kJ machine the. energy of ions were increased up to 4.2 MeV, which corresponds to (Ei/Ee)max = 14.Reproducibility and effectiveness of acceleration processes were investigated.