John A. Schreifels

Microwave annealing of Mg-implanted and in situ Be-doped GaN

An ultrafast microwave annealing method, different from conventional thermal annealing, is used to activate Mg-implants in GaN layer. The x-ray diffraction measurements indicated complete disappearance of the defect sublattice peak, introduced by the implantation process for single-energy Mg-implantation, when the annealing was performed at ≥1400 °C for 15 s. An increase in the intensity of Mg-acceptor related luminescence peak (at 3.26 eV) in the photoluminescence spectra confirms the Mg-acceptor activation in single-energy Mg-implanted GaN. In case of multiple-energy implantation, the implant generated defects persisted even after 1500 °C/15 s annealing, resulting in no net Mg-acceptor activation of the Mg-implant. The Mg-implant is relatively thermally stable and the sample surface roughness is 6 nm after 1500 °C/15 s annealing, using a 600 nm thick AlN cap. In situ Be-doped GaN films, after 1300 °C/5 s annealing have shown Be out-diffusion into the AlN layer and also in-diffusion toward the GaN/SiC in...

Ultrahigh-temperature microwave annealing of Al+- and P+-implanted 4H-SiC

The GMU work is supported by Army Research Of- fice Dr. Prater under Grant No. W911NF-04-1-0428 and a subcontract from LT Technologies under NSF SBIR Grant No. 0539321.

Characteristics of in situ Mg-doped GaN epilayers subjected to ultra-high-temperature microwave annealing using protective caps

Different protective caps (AlN, MgO, graphite) are investigated for their feasibility for protecting GaN surfaces during ultra-high-temperature (>1300 °C) microwave annealing. Compared to other capping materials, pulsed-laser-deposited AlN is found to protect the GaN surface more effectively, during ultra-fast microwave annealing at temperatures as high as 1500 °C. The RMS surface roughness (0.6 nm) of the GaN sample annealed at 1500 °C with an AlN cap in place is similar to the value (0.3 nm) measured on the as-grown sample. The photoluminescence and electrical measurements have indicated a decrease in the compensating deep donor concentration for the increasing microwave annealing temperature, as long as the surface integrity of the GaN epilayer is preserved. These results indicate the attractiveness of the AlN cap for microwave annealing of ion-implanted GaN.

Contour temperature programmed desorption for monitoring multiple chemical reaction products

A simple method for obtaining a comprehensive overview of major compounds desorbing from the surface during temperature programmed desorption (TPD) experiments is outlined. Standard commercially available equipment is used to perform the experiment. The method is particularly valuable when high molecular mass compounds are being studied. The acquisition of contour temperature programmed desorption (CTPD) spectra, sampling 50-dalton mass ranges at a time in the thermal desorption experiments, is described and demonstrated for the interaction of benzotriazole adsorbed on a Ni(111) surface. Conventional two-dimensional TPD spectra can be extracted from the CTPD by taking vertical slices of the contour.

Two‐level liquid‐nitrogen‐cooled sample mounting assembly for surface analysis

A design for a sample mounting assembly is discussed that permits standard ultrahigh vacuum surface analysis experiments to be performed both on well defined surfaces, such as single crystals, and on externally prepared surfaces.

Decomposition products of N,N′-disalicylidene-1,2-propanediamine adsorbed on 304 stainless steel

Abstract The compound, N,N′-disalicylidene-1,2-propanediamine, is commonly added to jet fuels to counteract the catalysis of thermally induced autoxidation by certain dissolved metals. The behavior of the metal deactivator additive (MDA) in thermally stressed jet fuel has raised questions on whether it decomposes after coming into contact with hot metal surfaces within the aircraft fuel system. Temperature programmed desorption (TPD) was performed to detect decomposition products of MDA on the 304SS surface. A method of scanning a relatively large mass range during desorption was developed to acquire 3-dimensional contour TPD (CTPD) plots of adsorbed species on the surface. Compounds with molecular masses of 107, 133, 232 and 290 were detected and their structures proposed. Conventional TPD spectra of selected molecular masses were then taken as a function of exposure. Mechanistic pathways for decomposition of MDA and formation of new compounds on the surfaces are proposed.

A comparison of X-ray photoelectron spectroscopy and Auger electron spectroscopy depth profiles for magnesium implants

Abstract The analysis of depth profiles when magnesium is present gives rise to several analytical problems with either X-ray photoelectron spectroscopy (XPS) or Auger electron spectroscopy (AES). With both techniques the relative sensitivity is low for the main transition usually employed, i.e., the 2s photoemission line in XPS and the KLL transition in electron-excited AES. With XPS, the Al X-ray-excited Mg KLL peak has a relative intensity that is greater than the 2s transition, but not with Mg radiation. The peak-to-peak height of the electron-excited AES peak can vary with the chemical state of Mg. Also, in some instances overlapping peaks can cause problems. In this study Mg was implanted into metal foils at various levels. Depth profiles were obtained with both XPS and AES, and the instrument-based quantitative analysis computer routines were used with slight modifications. It was found that each technique had its own set of advantages, and both approaches gave roughly comparable profiles. The estimated maximum amounts were below those anticipated from the implant conditions. As expected with XPS, chemical effects could easily be determined. However, a relative sensitivity factor was needed to use the X-ray-excited KLL Auger transition. With AES certain low-level contaminants were more easily detected and monitored. Overall, the XPS profiles appeared to offer better results in most respects for these systems. Other factors, e.g., time of analysis, data treatment methods, detection limits, etc., will be discussed also.

Biofunctionalization of Si nanowires using a solution based technique

Here we present a solution based functionalization technique for streptavidin (SA) protein conjugation to silicon nanowires (Si NWs). Si NWs, with a diameter of 110 nm to 130 nm and a length of 5 μm to 10 μm, were functionalized with 3-aminopropyltriethoxysilane (APTES) followed by biotin for the selective attachment of SA. High-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) showed that the Si NWs were conformally coated with 20 nm to 30 nm thick APTES, biotin, and SA layers upon functionalization. Successful attachment of each bio/organic layer was confirmed by X-ray photoelectron spectroscopy (XPS) and fluorescence microscopy. Fluorescence microscopy also demonstrated that there was an undesirable non-specific binding of the SA protein as well as a control protein, bovine serum albumin (BSA), to the APTES-coated Si NWs. However, inhibition of BSA binding and enhancement of SA binding were achieved following the biotinylation step. The biofunctionalized Si NWs show potential as label-free biosensing platforms for the specific and selective detection of biomolecules.

Immobilization of proteins on semiconductor nanowires for biosensor development

Silicon (Si), silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO) and other semiconductor nanowires (NWs) show great promise as sensing elements for the electrical detection of biomolecules [1–3]. In order to enable chemiresistor-type NW devices that utilize direct electronic sensing of biomolecules, one must first develop an analyte-specific functionalization of the nanowire surface and deduce mechanisms by which the functional and analyte molecules bind to the surface. Here we present a solution based bioconjugation technique for the attachment of protein molecules to the NW surfaces. Example of selective immobilization of streptavidin on biotinylated Si, SiC, and GaN NWs was studied and verified by a suite of surface characterization techniques.

Low‐cost microcomputer control of multiplexing during Auger analysis of thin films

A simple inexpensive peak detector circuit is described that permits the calculation of peak‐to‐peak heights during Auger analyzed depth profiles of solid surfaces. This circuit is interfaced with and controlled by a microcomputer where data can be stored and subsequently analyzed.