Variable Angle of incidence Spectroscopie Ellipsometry (VASE), Rutherford Backscattering (RBS) and Cross-sectional Transmission Electron Microscopy (XTEM), are used to measure heterojunction layer thicknesses in an AlGaAs/GaAs sample. All three techniques yield the same thickness values within error limits.

Previously, it was shown that superlattices implanted with Si at 77K, exhibited more extensive damage and uniform compositional mixing upon subsequent annealing than samples implanted at room temperature.[l,2] The current work focuses on the damage in samples implanted with Si at 77K. The study shows that for a given dose, the amount of damage depends upon the layer thickness and the composition. Specimens of bulk GaAs, Al 3Ga. 7As, 7.5 nm GaAs -10 nm Al. 3Ga. 7As superlattice (SL1), 5.5 nm GaAs −3.5 nm AlAs superlattice (SL2), and 8.0 nm GaAs −8.0 nm AlAs superlat-tice (SL3) were implanted at 77K with 100 KeV Si, with doses ranging from 3 × 1013 cm−2 to 1 × 1015 cm−2. The samples were examined by ion channelling and cross sectional transmission electron microscopy (TEM). At 77K and a dose of 1 × 1014 cm−2, the GaAs and SLi showed an amorphous layer, while no damage peak was observed in SL2. The 77K amorphization thresholds of the Al 3Ga. 7As alloy, SL2, and SL3 were 2.5 × 1014 cm−2, 4 × 1014 cm−2, and 1 × 1015 cm−2 respectively. The sharpness of the amorphization threshold varied with the material.

Transmission electron microscopy has been used to observe the effects of single ion and Ar cluster impacts. The impact of either single ions or cluster ions produces nanometer-sized craters on Au and ejects nanoparticles. The impact of single ions causes ejection of nanometer-sized particles of gold at the same rate as the rate of cratering leading to the conclusion that the two processes are coupled. The sputtering yield for cluster irradiation of Au exhibits a near cosine dependence on the ejection angle while the amount of Au in visible nanoparticles varies as the cube of the ejection angle.

Several previous studies have shown that the size distributions of smaller nanoparticles (n less than or equal to 40 where n is the number of atoms in a given cluster) generated by ion sputtering obey an inverse power law, with an exponent varying between -8 and -4, dependent upon the total sputtering yield. Such large negative exponents have not been explained by any simple physical mechanism. We reported electron microscopy studies of the size distributions of the larger nanoparticles (n > 500) that are sputtered from the surface by high-energy ion impacts. These measurements also yielded an inverse power law, but one with an exponent of -2, and one that is independent of total sputtering yield. This inverse-square dependence indicates that the clusters are produced when shock waves, generated by sub-surface displacement cascades, impact and ablate the surface. Many smaller clusters can result from fragmentation of these larger ones, which helps explain the large negative exponents that have been reported previously. In this paper, we briefly review the previous results. In addition, we present new results demonstrating that the same inverse-square size distribution is generated in both transmission and reflection sputtering geometries.An important corollary from these results is that the sputtered nanoparticles consist of simple fragments of the original surface, that is particles which have not experienced any large thermal excursions. Hence high-energy ion sputtering should provide a convenient method for synthesizing a broad distribution of nanoparticles of a wide variety of alloy phases. (C) 2003 Elsevier B.V. All rights reserved.

Starting from two-step anodizing recipes available in the literature, we fabricated selfsupporting ordered ion-implantation masks that are several mm2 in area and 1–4 νm thick. SEM micrographs reveal self-organized structures with straight open pores, 25–150 nm in diameter, extending completely through the mask. As reported previously, the pore diameter and spacing depend critically upon the anodization parameters, e.g., type of acid and its molality, the applied voltage and the solution temperature. Ion-milling procedures were developed for opening the bottoms of the anodized pores. These masks appear quite robust during exposure to ion beams of 1-MeV He, Ne, and Kr. The steps necessary to fabricate the implantation masks, including opening the pores, are briefly described. Here we present new results obtained with a mask fabricated with pore dimensions as small as 25 nm in diameter, i.e., at the limit of what is technically feasible. Measurements are reported of the angular dependence of the transmitted ion current; these results are consistent with the physical dimensions of the opened pores. TEM images of a partial array obtained by implantation through the 25-nm pores are also shown.

A grain-size-dependent reduction in the room-temperature thermal conductivity of nanocrystalline yttria-stabilized zirconia is reported for the first time. Films were grown by metal-organic chemical vapor deposition with controlled grain sizes from 10 to 100 nm. For grain sizes smaller than approximately 30 nm, a substantial reduction in thermal conductivity was observed, reaching a value of less than one-third the bulk value at the smallest grain sizes measured. The observed behavior is consistent with expectations based on an estimation of the phonon mean-free path in zirconia.

Polycarbonate (LexanTM) (PC) was implanted with 2 MeV B+ and O+ ions separately to fluences of 5 × 1017, 1 × 1018, and 5 × 1018 ions/m2, and characterized for changes in surface hardness and tribological properties. Results of tests showed that hardness values of all implanted specimens increased over those of the unirradiated material, and the O+ implantation was more effective in improving hardness for a given fluence than the B+ implantation. Reciprocating sliding wear tests using a nylon ball counterface yielded significant improvements for all implanted specimens except for the 5 × 1017 ions/m2 B+-implanted PC. Wear tests conducted with a 52100 steel ball yielded significant improvements for the highest fluence of 5 × 1018 ions/m2 for both ions, but not for the two lower fluences. The improvements in properties were related to Linear Energy Transfer (LET) mechanisms, where it was shown that the O+ implantation caused greater ionization, thereby greater cross-linking at the surface corresponding to much better improvements in properties. The results were also compared with a previous study on PC using 200 keV B+ ions. The present study indicates that high energy ion irradiation produces thicker, more cross-linked, harder, and more wear-resistant surfaces on polymers and thereby improves properties to a greater extent and more efficiently than lower energy ion implantation.

DC magnetron sputtered-MoS2 films of thicknesses between 500angstrom and 7500angstrom were deposited on NaCl, Si, sapphire, Si3N4 and ZrO2 substrates, and were subsequently ion irradiated by a 5 x 10(15) cm-2 dose of 2MeV Ag+ ions. Transmission electron microscopy (TEM), Rutherford backscattering (RBS) and Auger Electron Spectroscopy (AES) were utilized to study the microstructural and compositional changes of the film due to irradiation. The friction coefficient and sliding life were determined by ball-on-disc tests under both inert and humid conditions.Both as-deposited and ion-irradiated films were found to be amorphous, having a stoichiometry of MoS1.8. A low friction coefficient in the range of 0.03 to 0.04 was measured for both as-deposited and ion irradiated films. However, the sliding life of Ag+ ion-irradiated film was found to increase ten fold to thousand-fold compared to as-sputtered films on all the ceramic surfaces studied The improvement in wear life was correlated with a significant improvement in adhesion of the film with the substrate and a small increase in the density of the ion irradiated film.

: The objective of this research is to develop the use of high energy (MeV) and medium energy (keV) ion beams for the purpose of selectively modifying the optical properties of superlattice systems consisting of mixed III-V compound semiconductors. In particular, the research was directed at the AlGaAs/ GaAs multilayer superlattice system and its potential use in fabricating a monolithically integrated distributed feedback laser for use in optoelectronic circuits. The optical properties of such semiconductor superlattice systems have been shown to be sensitive to ion bombardment and its associated implantation and mixing process. The use of ion beams makes it possible to modify these structures through selective masking so that optical elements such as lasers, waveguides, and switches could be fabricated under the constraints imposed by monolithic integration. In particular, investigations were made into the effects of implantation controlled disordering of AlGaAs and GaAs through impurity, defect, and ion beam mixing effects. The results of this work were applied to the development and fabrication of an ion implanted distributed feedback (DFB) type laser in a multilayer superlattice system.

Zinc selenide and zinc sulfide are excellent optical materials for applications in the visible and infrared regions of the spectrum. Since these materials possess low mechanical strength and toughness, they are vulnerable to erosion and impact damage in severe environments. In order to improve their physical hardness without degrading their spectral transmission, high-energy (1 MeV) hydrogen ions were implanted into the surfaces of ZnSe, water-clear ZnS (CleartranTM), and ZnS/ZnSe composite (TuftranTM. A systematic study of the effect of ion fluence (0.1 to 3 × 1017/cm2) on surface hardness and optical transmission was performed. Substantial improvement in microhardness has been found which increases with dosage. The hardness of TuftranTM leveled off at a dose of 3 × 1016/cm2, while that of ZnSe and CleartranTM continued to improve with ion fluence. The hardness of ZnSe was increased by a factor of 78% at a dose of 3 × 1017/cm2, without degrading important optical properties.

A modified approach to silicon-on-insulator (SOI) by bond-and-etch-back technology was studied where a high-energy (MeV) boron implant was utilized as an etch stop to eliminate the need for an epitaxial layer growth in forming a device film. Also a second (retro) MeV implant, applied after the first stage of the etch-back process, was investigated as an improved method for achieving uniform thinning of a thick (3 μm) SOI film. Significantly improved thickness uniformities (σ<10 nm across a 3×3 in. area) were obtained by this method for a 490-nm-thick silicon device film.

The use of MeV boron implantation as an etch stop for epi-less bond etch silicon on insulator (EL-BESOI) has recently been reported. In that work a 490-nm device film was demonstrated with thickness uniformity on the order of 8 nm. Details on the characterization of materials properties and carrier recombination lifetimes in the device material were not presented. Since the device film will have had a high energy (2.5 MeV) boron beam pass through it as part of the etch stop processing, such a study is needed to confirm that, after annealing, the material is not left in a damaged or defective state. In the present work the authors study these properties with the objective of examining such SOI layers with nominal 250-nm thickness. A significant amount of the materials characterization can be accomplished prior to bonding since the device wafer can be deep implanted at 2.5 MeV and then examined near its surface where the final device material will reside. The final SOI material is evaluated relative to electronic defect states by way of minority carrier recombination lifetime measurements done in a side-by-side comparison of MOSFET devices in the SOI material relative to similar bulk monitor devices. Material quality is determined relative to benchmark lifetimes that are above and below 20 μs

The objective of this research is to develop the use of high energy (MeV) and medium energy (keV) ion beams for the purpose of selectively modifying the optical properties of superlattice systems consisting of mixed III-V compound semiconductors. In particular, the research was directed at the AlGaAs/GaAs multilayer superlattice system and its potential use in fabricating a monolithically integrated distributed feedback laser for use in optoelectronic circuits. The optical properties of such semiconductor superlattice systems have been shown to be sensitive to ion bombardment and its associated implantation and mixing process. The use of ion beams makes it possible to modify these structures through selective masking so that optical elements such as lasers, waveguides, and switches could be fabricated under the constraints imposed by monolithic integration. In particular, investigations were made into the effects of implantation controlled disordering of AlGaAs and GaAs through impurity, defect, and ion beam mixing effects. The results of this work were applied to the development and fabrication of an ion implanted distributed feedback (DFB) type laser in a multilayer superlattice system.

The density, composition and microstructure of Al2O3 films grown by the ion-beam-assisted deposition (IBAD) technique were studied. This technique involves direct evaporation of Al2O3 by electron (e) beam while simultaneously bombarding with 300-500 eV O2+ ions. The arrival rates of ions and atoms were adjusted by varying the ion current and deposition rate respectively. The composition and density of the films were determined by a combination of Rutherford backscattering spectroscopy, thickness profilometry and cross-section transmission electron microscopy, while the microstructure was studied by plan-view transmission electron microscopy. The hydrogen content of the films was also analyzed using the proton recoil detection technique.IBAD of Al2O3 resulted in an amorphous phase with substrate at room temperature and a crystalline eta phase at a substrate temperature of about 600-degrees-C. The IBAD films at 600-degrees-C had bulk-like densities (about 3.7-3.9 cm-3) and they were free from pores. The stoichiometry of these films was about the same as the bulk stoichiometry. The IBAD film at 600-degrees-C contained a very small quantity of hydrogen atoms (about 1.48 x 10(21) cm-3) as compared with a regular e-beam-deposited film (about 4.4 x 10(22) cm-3).

We report that two GaAs-AlAs superlattices of different layer thickness show dramatically different crystal damage when ion irradiated under identical conditions. The samples, held at 77 K, were implanted with 100 keV 28Si at doses of 3×1013 cm−2 to 1×1015 cm−2. Ion channeling results show amorphization threshold doses of 1×1015 cm−2 for the 7.0 nm GaAs-8.5 nm AlAs superlattice and 4×1014 cm−2 for the 3.5 nm GaAs-5.0 nm AlAs superlattice. At low doses, the shorter period superlattice was more robust, with no damage peak observed in ion channeling spectra for doses as high as 1×1014 cm−2. For a dose of 7×1013 cm−2, double crystal x-ray diffraction measurements show a 6 arcsec broadening of the (004) peak, relative to that of the unimplanted sample, for both superlattices. However, only the finer period superlattice exhibits a broadening (10 arcsec) of the (224) diffracted peak indicating a distortion in an additional direction. A mechanism involving the formation of slightly misaligned crystal domains is suggested to describe the behavior of the finer period superlattice.

AISI 446 steel exhibited parabolic rate kinetics from the beginning during isothermal oxidation in oxygen at 850°C. On the other hand, a pronounced transient oxidation with faster kinetics was observed in Ce- and Xe-implanted AISI 446 steels. The implantation, however, did not affect the steady-state parabolic rate constant, 3.77±0.18×10−5 mg2/cm4 min. The initial response of implanted steels to oxidation with pronounced transient oxidation was attributed to the physical defects of implantation. The oxide grains formed on AISI 446 early in the process of oxidation were rich in Fe and Cr, and after long exposure the spinel MnCr2O4 became the major constituent of the scale. Ce-implantation did not have any effect on the corrosion behavior of AISI 446 in H2/H2O/H2S/Ar at 850°C. The scale had three zones: an outer layer with FeS, (FeCr)S, and spinel oxide; an intermediate layer of (FeCr)S; and an inner layer of Cr-rich oxide and (FeCr)S below the original metal surface.

The use of keV ion implantation of boron for the bond and etch-back SOI (BESOI) technique is addressed. Ion implantation of boron at 2.5 MeV was used in order to place the boron peak and residual tail of the boron distribution deep enough, so that a region of the original silicon material with acceptably low boron concentration persists near the active-layer-SiO2 interface. The objective was to determine whether improvements in final uniformity were possible using the MeV implants compared to the more conventional epi-layer technique. Results show that a final thickness of 0.3 μm of single crystal silicon on insulator can be produced with thickness nonuniformity of 28 to 30 nm averaged over 9 points on a 2"×2" area. The final oxidation-stripping steps contributed to most of this nonuniformity. Additional difficulties arose as a result of the extensive oxidation stripping used in the terminal processing steps. Etch pit analysis of the final material revealed substantial oxidation induced stacking faults in the finished material (~300 cm-2, average length ~50 μm)

This work is part of a study to understand the process by which energetic ion bombardment can be used to mix the chemical components of AlGaAs and GaAs superlattice (S/I.) layers of nominal 35 to 50Å thickness. Data reported here involve the retention and build-up of collision cascade damage in the S/I. and its relationship to amorphization and chemical mixing in these systems.

: Diamondlike carbon (DLC) coatings have been deposited on seven infrared transmitting substrates utilizing three different techniques: ion-beam deposition, rf-plasma discharge, and hollow cathode discharge methods. Optimum deposition parameters for each technique have been established as a function of substrate material. Extensive characterization of the DLC films was also performed. Rutherford backscattering and proton recoil detection techniques were used to analyze carbon and hydrogen content and impurities. These films contain typically 70% C and 30% H. Transmission electron microscopy was used to analyze the crystallinity, void structure, surface microstructure, and thickness of the films which were found to be amorphous and dense. Optical properties such as refractive index, extinction coefficient, and optical band gap of the films were determined by variable angle spectroscopic ellipsometry (VASE) over the special range from 300 nm to 10.6 micron. Optical properties were found to be related to the preparation procedure used. The thermal stability, moisture penetration, rain erosion, and sand ballistic impact effects on these DLC films were extensively investigated. The effect of high energy ion radiation on DLC films was studied. Details of preparation methods and characterization of DLC films are presented. Keywords: Protective coatings; Antireflection coatings; Optical coatings; Thin films; Ellipsometry.