bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ion Beam Stabilization of FePt Nanoparticle Arrays for Magnetic Storage Media
Authors: Baglin J.E.E. , Sun Shouheng , Kellock A.J. , Thomson T. , Toney M.F. , Terris B.D. , Murray C.B. 
Published: June 2019

AbstractWe describe the use of ion beam induced crosslinking to harden the organic matrix material of self-assembled arrays of monodisperse (4 nm) FePt nanoparticles, providing diamondlike carbon barriers to inhibit agglomeration of the nanoparticles under heat treatment. Such stabilization is necessary for the particles to survive the >500°C annealing required for growth of the fct L10 phase of FePt, whose magnetic anisotropy is necessary for application of such arrays for high density recording. Selective area irradiation of continuous nanoparticle coatings, using ion beams patterned over a full disk by stencil mask or with ion projection optics, followed by dissolution of the unexposed coating, is proposed as a means of fabricating extended bit patterns consisting of isolated “islands” of FePt nanoparticles, with characteristic dimensions of tens of nanometers.
A New Pathway for Si Nanocrystal Formation: Oxi-Reduction Induced by Impurity Implantation
Authors: Jacobsohn L.G. , Zanatta A.R. , Lee J.K. , Cooke D.W. , Bennett B.L. , Wetteland C.J. , Tesmer J.R. , Nastasi M. 
Published: June 2019

AbstractIn this work we show the feasibility of producing silicon nanocrystals by means of a new method based on the oxi-reduction of silicon dioxide induced by the presence of an impurity and annealing. The choice of magnesium as the impurity relies on its chemical properties of oxireducing the SiO2 matrix while avoiding the formation of Si-based compounds. The samples were obtained by 3×1016 and 1×1017 at/cm2 ion implantation into fused silicon dioxide followed by annealing in vacuum at 900 °C for 2 or 10 h. Rutherford backscattering spectrometry (RBS) characterized the chemical content and the Mg depth distribution. In all cases, photoluminescence measurements that showed a broad band starting around 1.8 eV with increasing emission intensity for lower energies, indicating the presence of Si nanocrystals. The analysis of the photoluminescence data in the framework of the quantum confinement theory suggests the existence of relatively large Si nanocrystals. The presence of these nanocrystals was also confirmed by Raman spectroscopy.
Luminescence of Silicon Nanocrystals in SiO2: Effects of Excitation Spectrum
Authors: Hryciw A. , White C.W. , Chow K.H. , Meldrum A. 
Published: June 2019

AbstractSilicon nanocrystals formed by ion implantation and annealing of fused silica wafers show a strong, broad photoluminescence (PL) peak centered at a wavelength between 750 and 900 nm, depending on the processing conditions. This luminescence has been extensively investigated and trial device structures based on these materials have been built. However, relatively few studies also report the optical absorption spectra. In fact, the absorbance of these specimens is quite low (usually < 10%) at wavelengths greater than 450 nm (i.e., at the pump wavelengths typically used for PL studies). This suggests that in numerous studies of Si nanocrystals produced by ion implantation, only a small fraction of the nanocrystals is responsible for the observed PL at the typical pump wavelengths. In this study, we investigated how the PL spectrum and intensity depend on the power and wavelength of the pump laser. We find that the PL intensity approaches saturation at high pump fluences, and that the peak emission wavelength is sensitive to the excitation power. These observations can be attributed to the dynamics of the excitation/recombination processes at different energies, and indicate that considerable care must be taken when comparing the emission spectra of different specimens. Our data are uniformly consistent with a mechanism of light emission involving subgap states (i.e., radiative trap sites) and are not supportive of a “pure” quantum confinement model.
Gold clusters: the role of the ion energy in their formation
Authors: Thune Elsa , Carpene Ettore , Sauthoff Katharina , Seibt Michael , Reinke Petra 
Published: June 2019

AbstractThe rapidly growing interest in the deposition of size-selected nanoclusters on surfaces is motivated both by technology and by basic physical questions. Due to their finite size, small particles have totally different material properties compared to their bulk crystalline counterparts. Clusters have been deposited by a monoenergetic, mass-selected ion beam with low energies (10-500 eV) on amorphous carbon substrates, which are used to minimize the influence of surface crystallography and ion-induced structural changes. Gold clusters were deposited as a model system to study the ion energy dependence, the temporal evolution, and the influence of the temperature on the cluster distribution. For impact energies below 100 eV, surface processes dominate the cluster nucleation and growth. If higher energies are used, an increasing number of ions is implanted below the surface and different processes control the cluster formation. When the energy increases above 350 eV, the cluster size drastically drops below 5 nm. The clusters are analysed with different methods such as Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), and X-Ray Photoelectron Spectroscopy (XPS) to determine their size distribution, composition and structure.
Magnetite/Nickel andMagnetite/Cobalt Multilayer Nanostructures Obtained by Pulsed Laser Deposition
Authors: Sorescu Monica , Grabias Agnieszka , Diamandescu Lucian 
Published: June 2019

AbstractNanostructured magnetite/T multilayers, with T = Ni, Co, Cr, have been prepared by pulsed laser deposition. The thickness of individual magnetite and metal layers takes values in the range of 5 - 40 nm with a total multilayer thickness of 100 -120 nm. X-ray diffraction has been used to study the phase characteristics as a function of thermal treatment up to 550 °C. Small amounts of maghemite and hematite were identified together with prevailing magnetite phase after treatments at different temperatures. The mean grain size of magnetite phase increases with temperature from 12 nm at room temperature to 54 nm at 550 °C. The thermal behavior of magnetite in multilayers in comparison with powder magnetite is discussed.
Synthesis, Characterization, Sintering and Leaching of Thorium – Uranium (IV) Phosphate Diphosphate Solid Solutions from Low-Temperature Precursors
Authors: Dacheux Nicolas , Clavier Nicolas , Podor Renaud , Coustumer Philippe Le 
Published: June 2019

ABSTRACTIn the field of the immobilization of high level activity and long life radwaste for a deep underground repository, several phosphate matrices were already proposed to delay the release of actinides to the biosphere. Among them, Thorium Phosphate-Diphosphate (TPD) and associated solid solutions were considered. In order to improve the homogeneity of the samples prepared, a new way of preparation based on the precipitation in closed containers, at 150°C, of the Thorium-Phosphate HydrogenPhosphate hydrate (TPHP) or associated Thorium – Uranium (IV) Phosphate HydrogenPhosphate hydrate (TUPHP) was developed. Well crystallized and single phase TUPD solid solutions of general formula Th4−xUxP6O23 were prepared after heating above 950°C. Dense TUPD pellets were also obtained through a two-steps procedure involving a uniaxial pressing of the powder at room temperature then a heating treatment at 1250°C for 10 hours. Several properties of the pellets such as their chemical durability during leaching tests were considered carefully. All the normalized dissolution rates of powdered and sintered TUPD solid solutions remained low by comparison to that reported for several other ceramics studied in the same objective.
Strengthening Porous Skeletons by Metal Deposition from a Nanoparticle Suspension
Authors: Crane Nathan B. , Sachs Emanuel M. , Frank Andreas 
Published: June 2019

ABSTRACTSolid freeform fabrication (SFF) processes such as three-dimensional printing (3DP) and selective laser sintering (SLS) produce porous bodies that must be densified for many applications. New homogenous infiltration techniques can produce dense, homogenous parts of selected standard alloys, but the increased infiltration temperature dramatically increases creep deflection under self-weight. This paper reports on a method that improves dimensional stability by reducing creep deflection rates at high temperature. This method is applicable to all metal skeletons that must be strengthened without increasing shrinkage. In this method, the skeletons are reinforced by the addition of nanometer-sized particles dispersed in a liquid. The liquid is applied to the structure either during 3DP printing or after forming (3DP, SLS, pressing). The liquid is then evaporated, depositing the metal in the skeleton. The metal nanoparticles are sintered to density below the sintering temperature of the micron-scale skeleton particles. This concept is demonstrated using a suspension of 8–10 nm iron particles infiltrated into lightly sintered porous steel skeletons. When heated with an unsupported overhang to a typical infiltration temperature, creep deflection was reduced 50–80% with 0.5–1 wt% added metal.
SFF of Ceramic Parts: Literature Overview and Direct Experiments
Authors: Babini Gian N. , Fedele Andrea , Settineri Luca 
Published: June 2019

ABSTRACTThe great development of Solid Freeform Fabrication (SFF) techniques from their introduction into the market, more than 20 years ago, has fueled their diffusion in the mechanical sector to the point that they are today an indispensable component of the process of designing, engineering and producing a mechanical parts.At the same time, these techniques found application in different and even distant sectors, like biomedicine or architecture. This lead to the necessity of developing SFF processes suitable for materials different from those they were at the beginning thought for. Such techniques, taken from the original ones or entirely developed ex-novo, allowed for a surprising differentiation of the applications.The fabrication of ceramic parts by SFF techniques is a relatively new field which is widening the role of such materials in sectors not traditionally covered.The present paper reports a state of the art of the techniques that appear more effective for the production of ceramic goods, with representative or even functional properties.Further, some results of 3D Printing experiments of alumina parts will be presented.
Three Dimensional Hydrogen Microscopy in Diamond
Authors: Dollinger Günther , Reichart Patrick , Bergmaier Andreas , Hauptner Andreas , Wild Christoph 
Published: June 2019

AbstractWe introduce proton-proton scattering at a microprobe of 17 MeV protons to quantitatively image three dimensional hydrogen distributions in polycrystalline diamond at a lateral resolution better than 1 μm and high sensitivity. The images show that most of the hydrogen of a <110>-textured undoped polycrystalline diamond film is located at grain boundaries. The average amount of hydrogen is (8.1±1.5)·1014 atoms/cm2 along the grain boundaries which corresponds to about a third of a monolayer. The content within the grain is below the detection limit of 1.4·1016 atoms/cm2 (0.08 at-ppm).
Non Destructive Electrical Defect Characterisation and Topography of Silicon Wafers and Epitaxial Layers
Authors: Dornich K. , Hahn T. , Niklas J.R. 
Published: June 2019

AbstractRecent progress in experimental technique made it possible to improve the sensitivity of microwave detected photoconductivity by several orders of magnitude. This opens completely new possibilities for a contact less non-destructive electrical defect characterization of silicon wafers and even of epitaxial layers on substrates with extremely low resistivity. Electrical properties such as lifetime, mobility and diffusion length can be measured without contacts also at very low injection levels with a resolution only limited by the diffusion length of the charge carriers. The doping level of the material plays no major role.Owing to the high sensitivity, thermal excitation of charge carriers out of defect levels filled during the photo pulse can also be observed. This leads to defect specific photoconductivity transients which deliver pieces of information like DLTS, however, again without contacts, non critical doping, and with high spatial resolution.
Morphology, Defects and Thermal Stability of SiGe grown on SOI
Authors: Xie Qianghua , Kottke Mike , Wang Xiangdong , Canonico Mike , White Ted , Nguyen Bich-Yen , Barr Alex , Thomas Shawn , Liu Ran 
Published: June 2019

AbstractSiGe/SOI films have been investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM) and Raman spectroscopy. For low Ge composition (∼ 20%), strain relaxation in the SiGe layer is minimal (<0.25%). For higher Ge content (32%), the tensile strain in a Si capping layer grown on top of SiGe/SOI is 0.46% (a stress of 0.81 GPa). TEM has revealed that most of the resulting defects at the SiGe/SOI interface and move downward. The misfit dislocation (MD) linear density is 17/μm, being consistent with the strain relaxation of the SiGe layer as determined by Raman spectroscopy. Upon thermal annealing, residual strain in the SiGe films has been further relaxed via two major routes (a) introduction of more MDs, and (b) development of surface undulation. High strain relaxation has been achieved in a SiGe layer grown on a higher-Ge content buffer layer.
Characterization of Ultrathin Strained-Si Channel Layers of n-MOSFETs Using Transmission Electron Microscopy
Authors: Anjum Dalaver H. , Li Jian , Xia Guangrui , Hoyt Judy L. , Hull Robert 
Published: June 2019

AbstractStrained-Si based Field Effect Transistors (FETs) have enabled improvement of carrier transport in Metal Oxide Semiconductor (MOS)-based devices, both in the ON state of the device and in the sub-threshold region. This leads to devices with higher ratios of on-to-off current, improvements in the device sub-threshold slope, lower voltage operation, and carrier mobility enhancement. However, in order to understand the fundamental physics of these devices, it is important to address the stress conditions of the strained-Si channel layers after device processing, particularly after the ion-implantation process. In this work, we have studied Si+ self ion-implantation and thermally annealed strained-Si channel layers in n-MOSFETs. It has been observed that the density of defects in the strained-Si layer depends upon implant dose as well as thermal treatment. Using energy dispersive spectroscopy (EDS) spectra, it is found that Ge is present in the strained Si layer when analyzed after Si+ implantation and rapid thermal annealing. The presence of Ge in the strained Si channel layer causes relaxation of strain. This is verified by Convergent Beam Electron Diffraction (CBED) by measuring the lattice constant of the strained channel. It is concluded that electron mobility enhancements can be degraded in n- MOSFETs due to presence of both Ge up-diffusion and defects.
Transmission Electron Microscopy Study of Nonpolar a-Plane GaN Grown by Pendeo-Epitaxy on (11

2

0) 4H-SiC.
Authors: Zakharov D.N. , Liliental-Weber Z. , Wagner B. , Reitmeier Z.J. , Preble E.A. , Davis R.F. 
Published: June 2019

AbstractPendeo-epitaxy has been applied to nonpolar a-plane GaN layers in order to observe if such process will lead to defect reduction in comparison with direct growth on this plane. Uncoalesced and coalesced a-plane GaN layers with thicknesses 2μm and 12μm, respectively, have been studied by conventional and high resolution electron microscopy. The following structural defects have been observed in pendeo-epitaxial layers: (1) basal stacking faults, (2) threading dislocations, and (3) prismatic stacking faults. A drastic decrease in the density of threading dislocations and stacking faults was observed in ‘wing’ areas with respect to ‘seed’ areas. Cross-section images reveal cracks and voids at the areas where two coalesced wings meet each other. High resolution electron microscopy shows that the majority of stacking faults are low-energy planar defects of the types I1, I2 and I3. The I3 type basal stacking fault, predicted theoretically, was observed experimentally for the first time.
Compositional Changes in the Infrared Optical Properties of Cr Doped CdZnTe Crystals
Authors: Hömmerich U. , Bluiett A.G. , Nyein EiEi , Trivedi S.B. , Shah R.T. 
Published: June 2019

AbstractWe are currently investigating the infrared (IR) optical properties of Cr doped ternary cadmium chalcogenides for potential applications in solid-state lasers and passive optical Qswitches. In this paper, we present compositional changes in the IR optical properties of Cr doped Cd1-xZnxTe single crystals with x=0.05, 0.1, and 0.2. Undoped CdZnTe crystals were grown by vertical Bridgman technique. Cr doping of CdZnTe was achieved through either in-situ doping or through a thermal diffusion process. For comparison, Cr: CdTe and Cr: ZnTe crystals were also prepared. The optical properties of Cr2+ ions were strongly dependent on the host composition and spectral blue shifts were observed with increasing Zn content in Cr: CdZnTe. The IR absorption peak of Cr2+ ions shifted from ∼1910 nm for Cr: CdTe to ∼1815 nm for Cr: Cd0.8Zn0.2Te. Less pronounced blue shifts were observed for the IR emission from Cr: CdZnTe crystals. The spectral shifts can be explained by the decrease in bond-length when going from CdTe to CdZnTe leading to an increased crystal-field effect experienced by Cr2+ ions. A slight broadening of the absorption and emission was also observed in ternary Cr: CdZnTe compounds compared to Cr: CdTe, which suggests that Cr2+ ions were incorporated in multiple lattice sites in CdZnTe. Moreover, the Cr2+ emission dynamics revealed a slightly non-exponential decay behavior for Cr: CdZnTe crystals, whereas the decay time of Cr: CdTe was single-exponential.
Si3H8 Based Epitaxy of Biaxially Stressed Silicon Films Doped with Carbon and Arsenic for Cmos Applications
Authors: Bauer M. , Zollner S. , Theodore N. D. , Canonico M. , Tomasini P. , Nguyen B.-Y. , Arena C. 
Published: June 2019

AbstractArsenic doped Si:C films were grown epitaxially using Silcore® (Si3H8), methylsilane and arsine as source gases with growth rates up to 90 nm/min at 550°C. We observed a strong dependence of C and As incorporation on growth rate, caused by a growth rate dependent surface segregation behavior of C and As. High-resolution x-ray diffraction measurements of the epi layers reveal a perpendicular lattice constant as low as 5.323 Å. This corresponds to a biaxial stress of more than 2 GPa. Grazing exit (224) x-ray diffraction reciprocal space maps show the full tetragonal strain expected from the C content, suggesting that no relaxation of the films has occurred. Spectroscopic ellipsometry (SE) spectra were acquired in the 0.74 to 6.6 eV photon energy range. For intrinsic Si:C alloys, the E1 critical point shows the expected blueshift due to the alloying. For Si:C:As, a strong broadening of the E1 and E2 transitions exists, due to scattering of Bloch electrons in the crystal by As atoms. Additionally, free carrier effects lead to a decrease (increase) of the real (imaginary) part of the dielectric function in the near-infrared, consistent with a free carrier concentration in excess of 5×1020 cm-3. Transmission electron microscopy (TEM) of As doped Si:C films confirmed single-crystal epitaxial growth.
Transmission Electron Microscopy Studies of Strained Si CMOS
Authors: Xie Qianghua , Fejes Peter , Kottke Mike , Wang Xiangdong , Canonico Mike , Theodore David , White Ted , Sadaka Mariam , Vartanian Victor , Thean Aaron , Nguyen Bich-Yen , Barr Alex , Thomas Shawn , Liu Ran 
Published: June 2019

AbstractIn this paper, various types of defects (both threading dislocation and misfit dislocations) in strained Si (sSi) have been analyzed by transmission electron microscopy (TEM). Germanium upper-diffusion has been studied by scanning transmission electron microscopy (STEM) for strained Si on SiGe/SOI. SGOI-devices processed using an optimized thermal budget show minimal Ge diffusion and minimal process related defects. Correlation between the device performance (such as leakage current and reliability) and structural information found in TEM has been established.
Radiative Versus Nonradiative Decay Processes in Germanium Nanocrystals Probed by Time-resolved Photoluminescence Spectroscopy
Authors: Giri P. K. , Kesavamoorthy R. , Panigrahi B. K. , Nair K.G.M. 
Published: June 2019

AbstractGe nanocrystals (NCs) of diameter 4–13 nm are grown embedded in a thermally grown SiO2 layer by Ge ion implantation and subsequent annealing. Steady state and time-resolved photoluminescence (PL) studies are performed on these embedded Ge nanocrystals to understand the origin of the PL emission at room temperature. Steady state PL spectra show a broad peak consisting of a peak at ∼2.1 eV originating from Ge NCs and another peak at ∼2.3 eV arising from ion-beam induced defects in the Ge/SiO2 interface. Time-resolved PL studies reveal double exponential decay dynamics of the PL emission on the nanoseconds time scale. The faster component of the decay with large amplitude and having a time constant τ1∼3.1 ns is attributed to the nonradiative lifetime, since the time constant reduces with increasing defect density. The slower component with time constant τ2∼10 ns is attributed to radiative recombination at the Ge NCs. These results are in close agreement with the theoretically predicted radiative lifetime for small Ge NCs.
Elastic Stress Relaxation at Nanoscale: A Comprehensive Theoretical and Experimental Investigation of the Dislocation Loops Associated with As-Sb Nanoclusters in GaAs
Authors: Chaldyshev V.V. , Kolesnikova A.L. , Bert N.A. , Romanov A.E. 
Published: June 2019

AbstractA comprehensive experimental and theoretical investigation was performed for the system of As-Sb nanoclusters and nanoscale dislocation loops in GaAs:Sb films grown by molecular beam epitaxy at low temperature and subsequently annealed. A model was developed for the elastic stress relaxation, self-energies and interactions in such cluster-loop nanosystems. The model was based on the experimental investigation of the microstructure of the As-Sb nanoclusters by transmission electron microscopy. The atomic structures of the As-Sb nanoclusters and dislocation loops, as well as their orientation relationships were determined. A strong anisotropic mismatch between the As-Sb nanoclusters and GaAs matrix has been revealed. This mismatch was proven to be a reason for the formation of the prismatic nanoscale dislocation loops nearby the nanoclusters. Our theoretical model explores the elastic properties of an inclusion with uniaxial dilatation. For such inclusions, the elastic stresses and stored energy are determined in a closed analytical form. The theoretical analysis predicts a specific non-linear dependence of the dislocation loop diameter on the cluster diameter, which fits well the experimentally observed one. It is demonstrated that both the change in the inclusion self energy due to diminishing dilatation and the interaction between the dislocation loop and inclusion are important in the relaxation phenomena at stressed nanoscale inclusions in semiconductors.