bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular Modeling of Slip Supposed to Occur in the Shock Initiation of Crystalline PETN
Authors: Ritchie James P. 
Published: March 2011

AbstractSome molecular modeling of slip using both rigid and flexible molecules of PETN in perfect, but finite, lattices has been performed. Studies of rigid displacement show slip on (001)<010> to be relatively unhindered. The shock orientation with a maximum resolved shear stress in this direction would, therefore, be expected to be insensitive. Molecular mechanics calculations have also been performed. The results show that it is likely that molecular deformations occur and have an important effect in determining the shear strength of crystalline PETN.
Si and Ge Nanocrystallites Embedded in CaF2 by Molecular Beam Epitaxy (MBE)
Authors: Taylor A. P. , Kim B. M. , Persans P. D. , Schowalter L. J. 
Published: March 2011

AbstractThin films of CaF2 containing layers of Si and Ge nanocrystallites were grown epitaxially on Si( 111) substrates by MBE while varying the substrate temperature. The sticking coefficient of both Si and Ge to CaF2 are less than unity at the temperatures studied. Evidence that chemical reactions are minimal between Si and CaF2 leading to the formation of volatile species such as SiFx is presented and it is surmised that the dominant mechanism for re-evaporation is thermal desorption. Both Si and Ge sticking coefficients vary exponentially with 1/T and activation energies are determined. A cluster growth model describing the evolution of the amount of Si in clusters over time is given. Solving in the limit of low cluster coverage, a solution that varies linearly with time and exponentially with 1/T is obtained. Weak room temperature photoluminescence from Si nanocrystallites in CaF2 is seen, however, it is unclear whether the luminescence is coming from the Si nanocrystallites or the CaF2. Second harmonic generation is observed from samples containing single layers of Ge in CaF2.
Pholuminuksence Studies on Porous Silioon Quantum Confinement Mechanism
Authors: Zhang Shulin , He Kuoksan , Hou Yangtian , Wang Xin , Li Jingjian , Diao Peng , Qian Bidong , Cai Shengmin , Fujishijma Akira 
Published: March 2011

AbstractA novel step—like and pinning behavior of photoluminescence peak energy connected with changes in the concentration of HIF and current density were for the first time observed for p— type porous silicon. Based on a theoretical calculation of the electron structure of the silicon quantum wire it is argued that these behaviors can be explained in terms of a novel formation mechanism model of porous silicon.
Characterization of Ge and C Implanted Sil-xGex and Sil-y-zGeyCz Layers
Authors: Gupta Ashawant , Cheng Yao-Wu , Qiao Jianmin , Rahman M. Mahmudur , Yang Cary Y. , Im Seongil , Cheung Nathan W. , Yu Paul K.L. 
Published: March 2011

AbstractIn an attempt to substantiate our previous findings of boron deactivation and/or donor complex formation due to high-dose Ge and C implantation, SiGe and SiGeC layers were fabricated and characterized. Cross-sectional transmission electron microscopy indicated that the SiGe layer with peak Ge concentration of 5 at% was strained; whereas, for higher concentrations, stacking faults were observed from the surface to the projected range of Ge as a result of strain relaxation. Results of spreading resistance profiling were found to be consistent with the model of dopant deactivation due to Ge implantation and subsequent solid phase epitaxial growth of the amorphous layer. Furthermore, for unstrained SiGe layers (Ge peak concentration ≥7 at%), formation of donor complexes is indicated. Preliminary photoluminescence results correlate with the spreading resistance profiling results and indicate shallow donor complex formation.
Multi-Wavelength Ellipsometry for Effective Characterization of Thin Epitaxial Si1−xGex Layers on Silicon Substrate
Authors: Eichler Michael , Weidner Marita , Morgenstern Thomas 
Published: March 2011

AbstractThe range of composition (x) is one of the parameters we often have to measure if Si1-xGex layers are generated by chemical vapour deposition (CVD). It is important in this case, in which way the optical properties of Si1-xGex layers depend on the range of composition. We are interested in using multi-wavelength ellipsometry as a technique for rapid, nondestructive characterization of these samples, without large preparations, especially for series of measurements (2D profiles or wafer-lots). The number of unknown parameters and the multiple solutions are reduced by using several wavelengths during the measurement. The calculation is prepared by the help of parameter-correlation based on results of spectroscopical ellipsometry. To examine the results, thickness and composition were controlled for selected samples by cross-sectional transmission electron microscopy (XTEM) and X-ray double crystal diffractometry (DCD).
Selective Removal of Silicon-Germanium: Chemical and Reactive Ion Etching
Authors: Johnson F. Scott , Misra Veena , Wortman J. J. , Martin Leanne R. , Harris Gari A. , Maher Dennis M. 
Published: March 2011

AbstractThe use of both chemical and reactive ion etching for the selective removal of SixGe1-x alloys with respect to both silicon and silicon dioxide has been investigated. We have found that a solution of NH4OH:H2O2:H2O is effective in selectively etching the SixGe1-x films with respect to both of these materials. The chemical composition of the substrate surface after removal of insitu doped SixGe1-x films was evaluated using EDS and SIMS. Diffusion from insitu doped Si0.7Ge0.3, followed by selective removal, was used to demonstrate self-aligned npn dopant profiles with narrow base widths. Reactive ion etching of SixGe1-x alloys was investigated using SF6, CF4, and Cl2 based chemistries. Pressure, power, and gas flow ratios were optimized to provide the least isotropic etch possible for SixGe1-x films containing approximately 40% Ge. Selectivity and degree of anisotropic etching were determined as a function of Ge content for samples with 0% to 100% Ge. Samples were analyzed using SEM and ellipsometry. Highest selectivities were achieved using SF6 and O2.
Nanocrystalline SiC Formation From Sputter-Deposited Non-Equilibrium a-SixC1−x Alloys
Authors: Wang Hong , Ma Z. , Allen L. H. , Rigsbee J. M. 
Published: March 2011

AbstractThere exists considerable interest in the synthesis of nanocrystalline SiC particles embedded in an a-SixC1−x:H matrix. This study investigated the formation of nanocrystalline SiC by annealing a non-equilibrium a-Si0.35C0.65 alloy sputter deposited onto oxidized (100) Si. Evolution of the microstructure was characterized by thin film sheet resistance measurements, glancing angle X-ray diffraction (GAXRD) and transmission electron microscopy (TEM). It was found that films annealed at temperatures below 850°C remained amorphous. Annealing at temperatures above 850°C resulted in the formation of SiC nanocrystallites, as revealed by GAXRD and TEM. The electrical conductivity also showed an abrupt increase around 950°C. Prolonged annealing resulted in a further increase in conductivity, implying that the transformation continued. Annealing at 1100°C for 3 hours increased the film conductivity by two orders of magnitude relative to the as-deposited film.
No Correlation Between Porous Silicon Photoluminescence and Surface Hydrogen Species
Authors: Geoqrg S.M. , Robinson M.B. , Dillon A.C. 
Published: March 2011

AbstractThe photoluminescence (PL) of porous silicon has been attributed to quantum confinement, amorphous silicon, or surface species such as hydrogen, polysilanes or siloxene. Our research has tested the early claims that surface hydrogen is responsible for PL. Our initial studies examined the effect of thermal annealing on surface hydrogen and PL in situ in an ultrahigh vacuum chamber. The results showed that the PL decreased between 450–550 whereas H2 was desorbed from surface SiH2 species between 500–575 K. There was no direct correlation between the PL and the loss of SiH2 surface species. Our most recent investigations have monitored PL and surface hydrogen species as a function of HF etching time for electrochemically anodized porous silicon samples that were not initially photoluminescent. While the surface hydrogen species continually decreased versus HF etching time, the photoluminescence did not appear until after HF etching times of 20–80 minutes depending on initial sample porosity. These results again illustrated that there is no direct correlation between the PL and surface hydrogen species.
SiGe/Si Quantum Wells by MBE : A Photoluminesence Study
Authors: Houghton D.C. , Rowell N.L. , Noel J.-P. , Aers G. , Davies M. , Wang A. , Perovic D.D. 
Published: March 2011

AbstractStrained Sil-xGex quantum wells and multi-quantum wells, synthesized by solid source ebeam evaporated MBE on Si(100) substrates have been studied by low temperature photoluminescence (PL) spectroscopy. Phonon resolved transitions originating from excitons bound to shallow impurities in Sil-xGex layers were observed over the temperature range 2K to 100K and used to characterize Sil-xGex/Si heterostructures. Thin Sil-xGex quantum wells exhibited phonon-resolved PL spectra, similar to bulk material, but shifted in energy due to strain, quantum well width and Ge fraction. In single quantum wells confinement shifts up to ∼200 meV were observed (1.2 nm wells with x = 0.38) and NP linewidths down to 1.37 meV were obtained. The confinement shifts were modeled by hole confinement in Sil-xGex wells. An annealing study was performed to investigate the role of Si-Ge interdiffusion on luminescence. Both the geometrical shape and optical emission of the quantum well were found to significantly change through intermixing. In addition to near edge luminescence a broad band of intense luminescence was obtained from several Sil-xGex/Si heterostructures. Some layers exhibited both types of PL spectra. However, the broad PL band (peak energy ∼120meV below the strained bandgap) was predominant when the alloy layer thickness was greater than 2 - 10nm, depending on x, growth temperature, and substrate surface preparation. The strength of the broad PL band was correlated with the areal density of strain perturbations (∼109cm−2 per quantum well corresponding to a spacing of 300nm in the plane of the well; local lattice dilation ∼ 1.5 nm in diameter) observed in plan-view TEM. The first few wells of MQW exhibited only band edge luminescence as was revealed by etching off the upper MQW periods. In addition, post growth anneals at temperatures in the range 700°C to 1100°C were found to enhance band edge luminescence, while the broad luminescence band decayed to zero intensity. Interdiffusion at these these temperatures has been shown to dramatically change the QW shape and consequently interfacial asperities would be expected to disappear, consequently only shallow phonon resolved luminescence is observed in PL after annealing. The influence of PL measurement parameters such as excitation power density and PL sample temperature on the relative strengths of band edge versus broad band luminescence were also consistent with the presence of exciton traps at sites of reduced bandgap.
Models and Mechanisms for the Luminescence of Porous Si
Authors: Koch F. 
Published: March 2011

AbstractExplanations for the efficient, visible luminescence of porous Si fall broadly into three categories. At the extremes are the pure quantum-well point of view and the molecular agents hypothesis. We make here the case for a model in which the dominant absorption characteristics are those of a quantum well, but luminescence occurs via boundary states on the nanocrystalline particles. This so-called “smart quantum-well” mechanism accounts for the multiple emission bands of porous Si in a natural way. In particular, the infrared band is assigned as an electronic transition to a deep level. From this we determine the conduction band shift with particle size.
Photoluminescence Study of Radiative Recombination in Porous Silicon
Authors: Wang Chun , Gaspari Franco , Zukotynski Stefan 
Published: March 2011

AbstractPhotoluminescence has been studied in porous silicon. Two types of radiative recombination centers have been identified. One gives rise to luminescence at about 820 nm and is believed to be related to Si-H bonds. The second gives rise to luminescence at about 770 nm and is likely associated with S-O bonds. Above about 20K radiative recombination is assisted by excited states of the recombination centre located about 10 meV above the ground state. The Si-H recombination centre is a single electron center whereas the Si-O center appears to be a multi-electron center.
Correlation of Electrical, Structural, and Optical Properties of Erbium in Silicon
Authors: Benton J. L. , Eaglesham D. J. , Almonte M. , Citrin P. H. , Marcus M. A. , Adler D. L. , Jacobson D. C. , Poate J. M. 
Published: March 2011

AbstractAn understanding of the electrical, structural, and optical properites of Er in Si is necessary to evaluate this system as an opto-electronic material. Extended x-ray absorption fine structure, EXAFS, measurements of Er-implanted Si show that the optically active impurity complex is Er surrounded by an O cage of 6 atoms. The Er photoluminescence intensity is a square root function of excitation power, while the free exciton intensity increases linearly. The square root dependence of the 1.54μm-intensity is independent of measurement temperature and independent of co-implanted species. Ion-implantation of Er in Si introduces donor activity, but spreading resistance carrier concentration profiles indicate that these donors do not effect the optical activity of the Er.
X-Ray Diffraction and Reflectance, Raman Scattering and Photoluminescence Characterization of Thermally Annealed Epitaxial SI1-XGEX Layers
Authors: LíbeznÝ M. , De Wolf I. , Poortmans J. , Van Ammel A. , Caymax M. , HolÝ V. , Vižď F. , KubĚna J. , Werner K. , Ishida M. 
Published: March 2011

AbstractSil-xGex, undoped strained layers with a pure Si-capping layer were grown epitaxially by UHV CVD on Si (100) substrates. The samples were subjected to thermal treatments corresponding to typical deviceprocessing. Effects connected with thermally induced relaxations were studied by Raman scattering, XRD, photoluminescence (PL) and defect etching. The thickness of the layers was determined from X-ray reflectance measurement. Strain values for the as-grown and relaxed samples were extracted from Raman scattering, XRD measurements and defect etching and correlated. Sil-xGex-layer related peaks were observed in PL spectra of several samples. An explanation why those peaks are not observed in all the samples is suggested.
Intrinsic Optical and Electrical Properties of Strain-Adjusted Short-Period SimGen Superlattices
Authors: Olajos Janos , Engvall Jesper , Grimmeiss Hermann G. , Kasper Erich , Kibbel Horst , Presting Hartmut 
Published: March 2011

AbstractInterband optical transitions are observed in a series of strain-adjusted, short-period Si/Ge superlattices by means of photocurrent spectroscopy, infrared absorption, photo (PL)- and electroluminescence (EL). The onsets of the interband absorption in the energy range of 0.7 - 0.9 eV are in good agreement with the observed PL and EL. Bandgap-related EL is observed in mesa diodes at room temperature, whereas the PL disappears at about 40K. In samples, annealed at growth temperatures (550°C) and higher, a systematic shift of the bandgap is observed which is discussed in terms of a process involving interdiffusion of the Si and Ge atoms. Photocurrent measurements at low temperatures support the model from PL studies suggesting that the photogenerated electrons are immobile in the SLS at low temperatures and have to be thermally ionized from shallow levels.
Load- and Depth-Sensing Indentation Tester for Properties Measurement at Non-Ambient Temperatures
Authors: Yoder Karl B. , Stone Donald S. 
Published: March 2011

ABSTRACTThe ability to measure the temperature-dependence of the hardness of thin films is useful from both an applications and a scientific standpoint. For this reason, we have designed and constructed a load- and depth-sensing indentation tester combining sub-nanometer resolution with the ability to operate over a range of temperatures, currently 150K to 400K. This paper describes the new experimental apparatus and reports preliminary data on 440C stainless steel substrates with and without a 0.75 μm ZrN coating.
Mechanics of Contacts at Less than 100Å Scale: Indentation and AFM
Authors: Jarvis S.P. , Weihs T.P. , Oral A. , Pethica J.B. 
Published: March 2011

ABSTRACTUnderstanding of both low load Nanoindentation and Atomic Force Microscopy relies on a knowledge of the mechanical response of contacts at the few nanometre scale. To investigate this area we have developed a new type of AFM/Indenter which applies forces (<1nN up to 1mN) to a tip mounted on a cantilever. The displacement of the cantilever is detected using laser heterodyne interferometry. The combination gives a direct measurement of contact compliance at very low loads. Contacts of diameter below 100Å can be repeatably made.We show that a water film is generally present in the contact during operation in air, and show how its size can be estimated from our data. One implication is that ambient operation of AFM in both repulsive and attractive modes may necessitate the presence of a liquid lubricating film, explaining the relative lack of damage in many AFM measurements. The estimation of contact area from stiffness is complicated by this layer. We show that the contact stresses are likely to be very high.
Long-Term Stability of Nickel in Resonant Micro-Mechanical Devices
Authors: Povirk G.L. , Bernstein J. , Brown S.B. 
Published: March 2011

ABSTRACTA nickel micromechanical device was resonated and the natural frequency of the structure was monitored over time. Any structural rearrangement or damage initiation in the material was expected to cause a corresponding change in the resonant frequency of the device. The resonant frequency of the device was initially about 31.8 kHz and the frequency was found to decline over time at a rate of 0.17 Hz/s.
A Quantitative Model for Interpreting Nanometer Scale Hardness Measurements of Thin Films
Authors: Poisl W.H. , Fabes B.D. , Oliver W.C. 
Published: March 2011

ABSTRACTA model has been developed to determine the hardness of thin films from the measured change in hardness with indenter displacement using a depth-sensing indentation instrument. The model is developed by dividing the measured hardness into film and substrate contributions based on the projected areas of both the film and substrate under the indenter. The model incorporates constraints on the deformation of the film by the surrounding material in the film, the substrate, and friction at the indenter/film and film/substrate interfaces. These constraints increase the pressure that the film can withstand and account for the increase in measured hardness as the indenter approaches the substrate.The model is evaluated by fitting the predicted hardness versus depth curves to data obtained from titanium and Ta2O5 films of varying thicknesses on sapphire substrates. The model predicts a lower interfacial strength for Ta2O5 films on sapphire with a carbon layer between the film and the substrate than that obtained for a film without an interfacial carbon layer.
Observation and Modelling of Electromigration-Induced Void Growth In AI-Based Interconnects
Authors: Kraft O. , Bader S. , Sanchez J.E. , Arzt E. 
Published: March 2011

ABSTRACTAccelerated electromigation tests on unpassivated, pure aluminum interconnects were performed. The failure mechanisms were observed by interrupting the tests and examining the conductor lines using an SEM. Because the metal thin film was subjected to a so-called laser reflow process before patterning, grain boundaries were visible in the SEM as thermal grooves. Voids were observed to move along the line and to grow in a transgranular manner, and a characteristic asymmetric void shape was identified which seems to be related to the failure mechanism. It is argued that substantial progress in modelling and understanding of electromigration failure can be made by consideration of such void shape effects.
X-ray Determination and Analysis of Residual Stresses in Uniform Films and Patterned Lines of Tungsten
Authors: Maniguet L. , Ignat M. , Dupeux M. , Bacmann J.J. , Normandon Ph. 
Published: March 2011

ABSTRACTThe determination by X-ray diffraction of the elastic strain tensors and the corresponding stress tensors in uniform films and patterned lines of tungsten was used to investigate the effect of line width. The stresses were found to increase with increasing line width. These experimental results are discussed with respect to the values obtained from a model using a distributed force in the line. The results of the calculations are in agreement with the X-ray measurements. The edge effects appear to be significant for tungsten lines.
Stress in Copper Thin Films with Barrier Layers
Authors: Vinci Richard P. , Bravman John C. 
Published: March 2011

ABSTRACTWafer curvature and grazing incidence x-ray scattering (GIXS) techniques were used to investigate the biaxial stresses induced in blanket Cu films during a thermal cycle to 460°C and back to room temperature. Cu was deposited by DC sputtering at ambient temperature. Several different barrier layer materials — SiO2, W, Ta, TiN, and Si3N4 — were used to compare any effect barrier choice might have on Cu microstructure evolution and mechanical behavior. Ta and Si3N4 encouraged a strong (111) Cu texture. A W barrier led to an untextured microstructure which underwent large, uneven grain growth during thermal cycling. Several samples were capped with a Ta layer which affected the stress behavior during cooling by inhibiting dislocation motion. An inverse relationship between strength and thickness was also documented.
Stress Mapping Near Simulated Defects in Thin Film Wiring Using X-ray Microbeam Diffraction
Authors: Dehaven Patrick , Goldsmith Charles 
Published: March 2011

ABSTRACTThe stress distribution about a series of deliberately fabricated defects in a Cu/Ni/Au/Cr redundant metal stack deposited on a Cr/Cu/Cr serpentine has been studied via x-ray microbeam diffraction using the sin2ψ technique. Strong directional anisotropies in the stress were found for both the second level nickel and copper. The extent of nickel stress relaxation from the edge of a defect far exceeded that predicted by a simple metal on substrate model. The size of the defect did not appear to significantly influence the stress distribution in the second level metal; however, the data suggest that the linewidth may influence the magnitude of the stress along the length of a line when near a defect or other sharp discontinuity.
The Influence of Mechanical Stress on Hot-Carrier Degradation in Mosfet'S
Authors: De Wolf Ingrid , bellens Rudi , Groeseneken Guido , Maes Herman E. 
Published: March 2011

ABSTRACTNon-uniform hot-carrier degradation in n-channel polycide-gate MOSFET's with different thicknesses of the poly-Si film, and in p-channel polycide-gate MOSFET's with TiSi2- or CoSi2-gate-silicide, is studied. The n-MOSFET's with the thinnest poly-Si film, show an increased interface trap generation, while the influence of the gate-silicide material on the degradation behaviour of the p-MOSFET's is found to be very small. The results are evaluated in terms of the effect of mechanical stress on the degradation characteristics: favourable for compressive mechanical stress and unfavourable for tensile stress. A correlation with stress measurements by micro-Raman spectroscopy is made.