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The effects of trapped and injected holes during degradation in metal-oxide-semiconductors is investigated to determine the transport behavior of holes. The transport behavior is described by the influence of holes on ionizing radiations. The degradation phenomena is explained by the application of theories of oxide physics.

The irradiation of lithium niobate with swift heavy ions results in the creation of amorphous nanosized channels along the incident ion path. These nano-channels are on the order of a hundred microns in length and could be useful for photonic applications. However, there are two major challenges in these nano-channels characterization: (i) it is difficult to investigate the structural characteristics of these nano-channels due to their very long length and (ii) the analytical electron microscopic analysis of individual ion track is complicated due to electron beam sensitive nature of lithium niobate. Here, we report the first high resolution microscopic characterization of these amorphous nano-channels, widely known as ion-tracks, by direct imaging them at different depths in the material, and subsequently correlating the key characteristics with electronic energy loss of ions. Energetic Kr ions (84Kr22 with 1.98 GeV energy) are used to irradiate single crystal lithium niobate with a fluence of 2 × 1010 ions/cm2, which results in the formation of individual ion tracks with a penetration depth of μ180 μm. Along the ion path, electron energy loss of the ions, which is responsible for creating the ion tracks, increases with depth under these conditions in LiNbO3, resulting in increases in track diameter of a factor of μ2 with depth. This diameter increase with electronic energy loss is consistent with predictions of the inelastic thermal spike model. We also show a new method to measure the band gap in individual ion track by using electron energy-loss spectroscopy. [ABSTRACT FROM AUTHOR]

Zirconia is viewed as a material of exceptional resistance to amorphization by radiation damage, and consequently proposed as a candidate to immobilize nuclear waste and serve as an inert nuclear fuel matrix. Here, we perform molecular dynamics simulations of radiation damage in zirconia in the range of 0.1-0.5MeV energies with account of electronic energy losses. We find that the lack of amorphizability co-exists with a large number of point defects and their clusters. These, importantly, are largely isolated from each other and therefore represent a dilute damage that does not result in the loss of long-range structural coherence and amorphization. We document the nature of these defects in detail, including their sizes, distribution, and morphology, and discuss practical implications of using zirconia in intense radiation environments. [ABSTRACT FROM AUTHOR]

Accurate information on electronic stopping power is fundamental for broad advances in materials science, electronic industry, space exploration, and sustainable energy technologies. In the case of slow heavy ions in light targets, current codes and models provide significantly inconsistent predictions, among which the Stopping and Range of Ions in Matter (SRIM) code is the most commonly used one. Experimental evidence, however, has demonstrated considerable errors in the predicted ion and damage profiles based on SRIM stopping powers. In this work, electronic stopping powers for Cl, Br, I, and Au ions are experimentally determined in two important functional materials, SiC and SiO2, based on a single ion technique, and new electronic stopping power values are derived over the energy regime from 0 to 15 MeV, where large deviations from the SRIM predictions are observed. As an experimental validation, Rutherford backscattering spectrometry (RBS) and secondary ion mass spectrometry (SIMS) are utilized to measure the depth profiles of implanted Au ions in SiC for energies from 700 keV to 15 MeV. The measured ion distributions by both RBS and SIMS are considerably deeper than the SRIM predictions, but agree well with predictions based on our derived stopping powers. [ABSTRACT FROM AUTHOR]

An investigation of the electrical properties of the interface between nano-crystalline, pyrolytic carbon, and silicon is presented. We have deposited conductive carbon films on silicon substrates by the pyrolysis of ethene and structured them into Schottky diodes in order to evaluate the electrical properties of the interface. The results show that the Schottky barrier to n-doped silicon is 0.46 eV, whereas for p-doped silicon, it is 0.66 eV. The carbon to n-type silicon barrier height is comparable to the values for metal silicide contacts in commercial devices. The results imply that no interfacial layer is formed and show the absence of Fermi-level pinning. [ABSTRACT FROM AUTHOR]

An investigation of amorphous, pyrolytic carbon for semiconductor applications is presented. We have deposited conductive carbon films on thin silicon oxide and aluminum oxide dielectrics and structured them into metal-insulator-silicon (MIS) capacitors in order to evaluate their electrical properties. The results show that the effective oxide thickness is comparable to metal electrodes, indicating that there is no depletion region between the dielectric and the carbon. The carbon electrodes exhibit very low leakage and Fowler-Nordheim tunneling on silicon oxide and Frenkel-Poole tunneling on aluminum oxide at high fields. The electrical parameters determined from the results are comparable to those for poly-silicon. [ABSTRACT FROM AUTHOR]

Nanoscale vertical interconnect structures (vias) made from chemical vapor deposited carbon have been investigated. The vias and wires were created by pyrolytic carbon deposition from acetylene at 950 °C followed by electron beam lithography and reactive ion etching. The carbon layer exhibits a resistivity of 4.5 mΩ cm in vias and wires which decreases to 1.5 mΩ cm after annealing at 1000 °C. The resistivity does not show any size effect in the vias, as it is independent of the diameter from 85 nm down to 24 nm. The maximum current density in long carbon wires was found to be 6×106 A cm-2, increasing to 3.5×108 A cm-2 for short vias. [ABSTRACT FROM AUTHOR]

Large-scale ab initio molecular dynamics method has been used to determine the threshold displacement energies Ed along five specific directions and to determine the defect configurations created during low energy events. The Ed shows a significant dependence on direction. The minimum Ed is determined to be 39 eV along the <1010> direction for a gallium atom and 17.0 eV along the <1010> direction for a nitrogen atom, which are in reasonable agreement with the experimental measurements. The average Ed values determined are 73.2 and 32.4 eV for gallium and nitrogen atoms, respectively. The N defects created at low energy events along different crystallographic directions have a similar configuration (a N–N dumbbell configuration), but various configurations for Ga defects are formed in GaN. [ABSTRACT FROM AUTHOR]

A single-crystal 3C-SiC film on a Si/SiO2/Si (separation by implantation of oxygen ) substrate was irradiated in different areas at 156 K with Au2+ ions to low fluences. The disorder profiles as a function of dose on both the Si and C sublattices have been determined in situ using a combination of 0.94 MeV D+ Rutherford backscattering spectrometry and nuclear reaction analysis in channeling geometry along the <100>, <110>, and <111> axes. The results indicate that for the same damage state, the level of disorder on the Si sublattice in 3C-SiC follows a decreasing order along the <111>, <100>, and <110> axes, while that on the C sublattice shows comparable values. Similar levels of Si and C disorder are observed along the <111> axis over the applied dose range. However, the level of C disorder is higher than that of Si disorder along all axes at low doses. The amount of disorder recovery during thermal annealing depends on the sublattice (Si or C) and crystallographic orientation. Room-temperature recovery occurs for both sublattices in 3C-SiC irradiated to a dose of 0.047 dpa or lower. Significant recovery is observed along all directions during thermal annealing at 600 K. The results are discussed and compared to those for 6H-SiC and 4H-SiC under similar irradiation conditions. [ABSTRACT FROM AUTHOR]

First-principles calculations have been carried out to study the electronic properties of A2Ti2O7 (A=Sm, Gd, Er) pyrochlores. It was found that f electrons have negligible effect on the structural and energetic properties, but have significant effect on the electronic properties. Density of state analysis shows that A-site 4f electrons do take part in the chemical bonding. Also, we found that 48f> bond is less covalent than 48f> and 48f> bonds, while 48f> bond in Gd2Ti2O7 is more covalent. It was proposed that for A2Ti2O7 (A=Sm, Gd, Er) pyrochlores, 48f> bonds may play more significant role in determining their radiation resistance to amorphization. [ABSTRACT FROM AUTHOR]

Ab initio total energy calculations have been performed to investigate the properties of intrinsic defects in GaN. It is found that the nitrogen defects are more stable than the Ga defects under nitrogen-rich conditions, and the results are generally consistent with those obtained by recent first-principles calculations. For the four types of nitrogen interstitials investigated, relaxation of all configurations leads to a [formula] split configuration. The most stable configuration for Ga interstitials is the Ga octahedral interstitial, but the energy difference between the octahedral and tetrahedral configurations is small (<0.35 eV) and depends on the basis set employed. While the bond distance in the N–N split interstitial is very close to that of a free N2 molecule, the Mulliken charge analysis indicates that the N atoms are partially charged, which is in contrast with previous theoretical suggestions. Based on the calculated results, the relative stabilities of various defects in GaN are determined. [ABSTRACT FROM AUTHOR]

Two types of room-temperature detectors of terahertz laser radiation have been developed which allow, in an all-electric manner, the determination of the plane of polarization of linearly polarized radiation and the Stokes parameters of elliptically polarized radiation, respectively. The operation of the detectors is based on photogalvanic effects in semiconductor quantum well structures of low symmetry. The photogalvanic effects have nanosecond time constants at room temperature, making a high time resolution of the polarization detectors possible. [ABSTRACT FROM AUTHOR]

Single crystal 6H-SiC wafers were fully amorphized at room temperature or 200 K using 1.0 or 2.0 MeV Au+ ion irradiation. The thickness of the amorphized layers has been determined using Rutherford backscattering spectrometry under ion channeling conditions. Microstructures of the irradiated SiC have been examined using cross-sectional transmission electron microscopy. The depth profiles of both the Si and C atoms have been studied using both x-ray photoelectron spectroscopy (XPS) and time-of-flight energy elastic recoil detection analysis. Neither Si nor C in the amorphized SiC exhibits a significant mass transport by diffusion during the irradiation and subsequent storage at room temperature. There is no observable phase segregation of either Si or C in the amorphized SiC. Ar+ ion sputtering leads to modifications of the composition, structure, and chemical bonding at the 6H-SiC surface. The Si–Si bonds at the sputtered surface (amorphized) do not appear, as suggested by the XPS; however, Raman backscattering data reveal the existence of the Si–Si bonds in the bulk amorphized SiC, in addition to the C–C and Si–C bonds that the XPS also identified. [ABSTRACT FROM AUTHOR]

Damage accumulation on both the Sr and Ti sublattices in strontium titanate (SrTiO3) has been investigated under 1.0 MeV Au+ irradiation at 360 and 400 K, close to the critical temperature for amorphization (∼370 K). Under irradiation at 360 K, the relative disorder on both sublattices follows a nonlinear dependence on ion dose. Amorphization starts from the damage peak region (at a depth of 60 nm) and grows toward the surface and into the bulk. At 400 K, the evolution of point defects to extended defects occurs as ion fluence increases. The disorder initially peaks at a depth of 60 nm, saturates at a disorder level of ∼0.75, and then decreases with further irradiation. At an ion fluence of 6.0×1015 cm-2, an amorphous layer of ∼10 nm thickness is formed at the sample surface. After annealing at 375 K for 1 h, the buried amorphous layer formed during irradiation at 360 K is recrystallized with planar defects and dislocation loops. However, the surface amorphous layer formed at 400 K irradiation remains amorphous, and fewer defects are observed in the irradiated region. Irradiation-enhanced recrystallization due to high flux electron energy deposition is observed. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of Gd2(Ti1-yZry)2O7 (y=0–1) pyrochlores following a 2.0-MeV Au2+ ion-beam irradiation (∼5.0×1014 Au2+/cm2) have been investigated by Ti 2p and O 1s near-edge x-ray absorption fine structure (NEXAFS). The irradiation of Gd2(Ti1-yZry)2O7 leads to the phase transformation from the ordered pyrochlore structure (Fd3m) to the defect fluorite structure (Fm3m) regardless of Zr concentration. Irradiated Gd2(Ti1-yZry)2O7 with y<=0.5 are amorphous, although significant short-range order is present. Contrasting to this behavior, compositions with y>=0.75 retain crystallinity in the defect fluorite structure following irradiation. The local structures of Zr4+ in the irradiated Gd2(Ti1-yZry)2O7 with y>=0.75 determined by NEXAFS are the same as in the cubic fluorite-structured yttria-stabilized zirconia (Y–ZrO2), thereby providing conclusive evidence for the phase transformation. The TiO6 octahedra present in Gd2(Ti1-yZry)2O7 are completely modified by ion-beam irradiation to TiOx polyhedra, and the Ti coordination is increased to eight with longer Ti–O bond distances. The similarity between cation sites and the degree of disorder in Gd2Zr2O7 facilitate the rearrangement and relaxation of Gd, Zr, and O ions/defects. This inhibits amorphization during the ion-beam-induced phase transition to the radiation-resistant defect fluorite structure, which is in contrast to the ordered Gd2Ti2O7. [ABSTRACT FROM AUTHOR]

Micro-Raman spectroscopy has been widely used to measure local stresses in silicon and other cubic materials. However, a single (scalar) line position measurement cannot determine the complete stress state unless it has a very simple form such as uniaxial. Previously published micro-Raman strategies designed to determine additional elements of the stress tensor take advantage of the polarization and intensity of the Raman-scattered light, but these strategies have not been validated experimentally. In this work, we test one such stategy [S. Narayanan, S. Kalidindi, and L. Schadler, J. Appl. Phys. 82, 2595 (1997)] for rectangular (110)- and (111)-orientated silicon wafers. The wafers are subjected to a bending stress using a custom-designed apparatus, and the state of (plane) stress is modeled with ABAQUS. The Raman shifts are calculated using previously published values for silicon phonon deformation potentials. The experimentally measured values for σxx, σyy, and τxy at the silicon surface are in good agreement with those calculated with the ABAQUS model. [ABSTRACT FROM AUTHOR]

A single crystal 6H-SiC wafer was sequentially implanted in two areas at 873 and 295 K using 2.0 MeV Au2+ ions under off-axis conditions. Identical Au depth profiles, as a function of atomic areal density, were obtained for both irradiation temperatures. X-ray photoelectron spectroscopy (XPS) and analytical electron microscopy were used to determine the one-dimensional expansion in the amorphous state produced at 295 K relative to that in the slightly damaged state produced at 873 K, based on the Au reference markers. In addition, the redshift of the plasmon-loss peak in the electron energy loss spectroscopy (EELS) was used to measure the local density changes. Comparison of the three methods indicates that the XPS and EELS methods were the most reliable, yielding a volume expansion of (11.5±2)% for the amorphous state in 6H-SiC at 295 K. The volume expansion in the slightly damaged state at 873 K was determined to be 0.9% by EELS. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Damage accumulation in 4H–SiC under 1.1 MeV Al22+ irradiation is investigated as a function of dose at temperatures from 150 to 450 K. Based on Rutherford backscattering spectroscopy and nuclear reaction analysis channeling spectra, the damage accumulation on both the Si and C sublattices have been determined, and a disorder accumulation model has been fit to the data. The model fits indicate that defect-stimulated amorphization is the primary amorphization mechanism in SiC over the temperature range investigated. The temperature dependence of the cross section for defect-stimulated amorphization and the critical dose for amorphization indicate that two different dynamic recovery processes are present, which are attributed to short-range recombination and long-range migration of point defects below and above room temperature, respectively. As the irradiation temperature approaches the critical temperature for amorphization, cluster formation has an increasing effect on disorder accumulation, and ion flux plays an important role on the nature and evolution of disorder. Dislocation loops, which are mostly formed under high ion flux, act as sinks for point defects, thereby reducing the disorder accumulation rate. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Simulations of displacement cascades in silicon carbide (SiC) indicate that most defects created are point defects, where interstitials are displaced only a small distance from the nearest vacancies. Of the interstitial defects produced in SiC, about 40% survive as freely migrating interstitials that can contribute to microstructural evolution during irradiation of SiC. The stable defect configurations in this study were created with low-energy recoils using molecular dynamics (MD) simulation. These stable Frenkel pairs have been annealed at different temperatures, using MD methods, to determine the time required for interstitials to recombine with vacancies. The MD data have been analyzed using an Arrhenius relation, and the activation energies for defect recombination processes range from 0.22 to 1.6 eV for C Frenkel pairs and from 0.28 to 0.9 eV for Si Frenkel pairs. These low activation energies for spontaneous recovery of Frenkel pairs in SiC are qualitatively consistent with the recovery processes observed experimentally on both the Si and C sublattices below room temperature. Based on the data analysis, the spontaneous recombination distance is estimated to be 0.66 and 0.70 a[sub o] for the C and Si sublattices, respectively. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Gold nanoclusters dispersed in single crystal MgO have been prepared by ion implantation at 975 K and subsequent annealing at 1275 K for 10 h. The morphological features, size, and crystallographic orientation of the Au nanoclusters with respect to the MgO matrix, as well as the interface structure between the Au nanoclusters and MgO, have been investigated using transmission electron microscopy. During annealing, the Au clusters nucleate coherently in the MgO lattice, leading to an epitaxial orientation relationship of [010][SUBMgO]//[010][SUBAu] and (200)[SUBMgO]//(200)[SUBAu] that is maintained for all the Au clusters. Above a critical size of ∼5 to 8 nm, a coherent-semicoherent interface transition is observed for the Au clusters in MgO. This critical cluster size is larger than the critical size ∼3 nm based on energetic considerations. This discrepancy is discussed with respect to the point and extended defect structures at the interface between the Au clusters and the MgO matrix. The Au clusters larger than this critical size exhibit faceting on the {001} planes and internal dislocations. It is further suggested that the density of quantum antidots should depend on the size of the Au clusters. [ABSTRACT FROM AUTHOR]

The effects of implantation temperature and ion flux on damage accumulation on both the Si and C sublattices in 4H-SiC have been investigated under 1.1-MeV Al[sup 2+, sub 2] irradiation at temperatures from 150 to 450 K. The rate of damage accumulation decreases dramatically, and the damage profile sharpens due to significant dynamic recovery at temperatures close to the critical temperature for amorphization. At 450 K, the relative disorder and the density of planar defects increase rapidly with the increasing ion flux, exhibiting saturation at high ion fluxes. Planar defects are generated through the agglomeration of excess Si and C interstitials during irradiation and post-irradiation annealing at 450 K. A volume expansion of ∼8% is estimated for the peak damage region. [ABSTRACT FROM AUTHOR]

Damage evolution and subsequent recovery in 4H-SiC epitaxial layers irradiated with 1.1 MeV A1[sup 2+, sub 2] molecular ions at 150 K to ion fluences from 1.5 × 10[sup 13] to 2.25 × 10[sup 14] A1 cm[sup -2] were studied by Rutherford backscattering spectroscopy (RBS) and [sup 12]C(d,p)[sup 13]C nuclear reaction analysis (NRA) using a 0.94 MeV deuterium (D[sup +]) beam in channeling geometry. Disorder on both the Si and C sublattices was measured simultaneously from the RBS scattering and NRA reaction yields. The relative disorder on both sublattices follows a nonlinear dependence on ion fluence that is consistent with a model based on simple defect accumulation and a direct-impact, defect-stimulated process for amorphization. At low ion fluences, the relative disorder on the C sublattice is higher than that on the Si sublattice. Isochronal annealing up to 870 K revealed the existence of three distinct recovery stages at ∼350, 520, and 650 K for low to intermediate damage levels. In highly damaged samples, where a buried amorphous layer is produced, the onset of a fourth recovery stage appears above 800 K. Similar recovery behaviors on both the Si and C sublattices suggests some coupling of recovery processes for Si and C defects. [ABSTRACT FROM AUTHOR]

Presents a study which examined disorder accumulation and annealing behavior on the gallium sublattice in gallium nitride using Rutherford backscattering spectrometry. Applications of gallium nitride; Results and discussion; Conclusions.

Investigates the magnetic anisotropy in Co films epitaxially grown on Cu(001) by measurement of magneto-optical Kerr hysteresis loops during film growth. Magnetic anisotropy oscillations in Co films grown on Cu(001).

Presents a study that investigated the use of laser reflective interferometer to monitor diamond film growth in a hot-filament chemical vapor deposition reactor. Description of the method; Reflection intensity versus time data for chemical vapor deposited diamond film growth; Discussion on thin-film interference fringes caused by multiple reflections in the film.

Presents a study of palladium oxide thin films by ellipsometry, optical transmission and Raman scattering. Experimental details; Ellipsometry and transmission on palladium oxide films on fused silica; Oxidation rate measurements; Conclusions.

Reports on the diode current detection of extended x-ray absorption fine structure (EXAFS) in gallium arsenide. Significance of EXAFS spectroscopy; Method for measuring EXAFS; Comparisons between the functions from diode current measurements and the functions from fluorescence measurements.

Presents information pertaining to the silicon-containing amorphous hydrogenated carbon films. Information on the Raman spectroscopy; Reference to the depositing of the silicon-containing amorphous hydrogenated carbon films; How electron probe microanalysis measurements were used; Indication of results.

Investigates the molecular beam epitaxy of Ge1-xCx alloys on Si(100). Use of in situ reflection high-energy electron diffraction, ex situ x-ray diffraction, transmission electron microscopy and Raman spectroscopy; Variation of carbon concentrations; Evaluation of the stability of thin films; Relationship with the microstructure's planar defect density.

Presents a study which examined the deposition of epitaxially oriented films of cubic silicon carbide on silicon by laser ablation. Film preparation and general characterization; Film and interface microstructure; Conclusion.

Presents a study which analyzed powdered samples of the type Ce[sub1-x]RE[subx]O[sub2-y], where RE=La, Pr, Nd, Eu, Gd, and Tb, are synthesized over the range 0≤x≤0.5 starting from nitrate solutions of the rare earths. Methods used to analyze the samples; Effect of the correcting for the Grüneisen shift from the lattice expansion on the frequency shift; Cause of the changes in the Raman spectrum.

Presents a study that examined the synthesis of platinum oxide thin films by reactive sputtering. Characterization of the thin films; Factors that influence the characteristics of the thin films; Examination of the Raman spectra of the thin films.

Investigates the oxide field dependence of hole trapping and interface state generation in silicon oxide layers using homogeneous nonavalanche injection of holes. Factors that influence the presence of very high fields in metal-oxide-semiconductor transistor; Details on the experiment; Discussion on the result of the study.

We have used molecular-dynamics simulations to examine the displacement threshold energy (Ed) surface for cations and anions in Gd2Ti2O7 and Gd2Zr2O7 pyrochlores. In both pyrochlores, the Ed surface is highly anisotropic and it requires less energy to displace anions than cations. Both anion and cation Ed values are higher in the titanate compared to the zirconate. Titanium displacement energies are in excess of 170 eV for all directions examined, because cation exchange is less energetically favorable in Gd2Ti2O7 compared to Gd2Zr2O7. These high-energy Ti displacements result in the formation of defect clusters that may prevent efficient defect recovery. This provides an explanation for the difference in susceptibility to amorphization between titanate and zirconate pyrochlores. [ABSTRACT FROM AUTHOR]