bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of a Single Crystal Silicon Substrate for AM-LCD Using Vertical Etching of (110) Silicon
Authors: Yoon Jun-Bo , Lee Ho-Jun , Han Chul-Hi , Kim Choong-Ki
Published: April 2011

In this paper, feasibility of crystalline silicon (c-Si) substrate for transmissive active matrix liquid crystal displays (AM-LCDs) has been investigated. The transparent pixel areas of AM-LCD were formed by vertical etching of (110) silicon substrate using anisotropie etching property of aqueous KOH. Combining this vertical etching process with the conventional MOSFET fabrication process, the pixel switching devices, peripheral circuits and transparent apertures were successfully integrated on the same c-Si substrate. The pixel NMOS devices exhibit an electron mobility of about 600cm2/V-s, a subthreshold slope of 65mV/decade and ON/OFF current ratio of 9 decades at 5V drain voltage. And the gate delay time is 3.3ns at 10V power voltage, measured from a ring oscillator which has enhancement-load type NMOS inverters having the (W/L) iload- (W/L) driverer of 25μm/15μm - 50μm/10μm.
Efficient Nonradiative Recombination Centers in MBE-Grown Si and SiGe/Si Heterostructures
Authors: Chen W. M. , Buyanova I. A. , Henry A. , Ni W.-X. , Hansson G. V. , Monemar B.
Published: April 2011

We carry out an investigation of grown-in nonradiative defects in Si and SiGe/Si heterostructures grown by molecular-beam-epitaxy (MBE). A number of such defects are observed by the optical detection of magnetic resonance (ODMR) technique, in samples with various structures and growth conditions. These defects are shown to provide efficient nonradiative shunt paths for carrier recombination, competing with and reducing radiative recombination processes. It is revealed that the dominant nonradiative defect is a low-symmetry vacancy-related complex, evident from a characteristic hyperfine structure due to 29Si ligands (with nuclear spin I=1/2 and natural abundance of 4.67 %) connected to the dangling bonds. The introduction of these defects is believed to be largely due to a low surface adatom mobility during the low temperature growth. By varying the substrate bias during the MBE growth, it is shown that the formation of these nonradiative defects can be effectively enhanced by exposure to accelerated positive ions, presumably dominated by the Si+ ions. Effects of hydrogenation on these defects are also studied.
Point Defect Supersaturation During Zinc Diffusion into InP
Authors: Wittorf D. , Jäger W. , Rucki A. , Urban K. , Hettwer H.-G. , Stolwijk N. A. , Mehrer H.
Published: April 2011

Formation of defects during Zn diffusion into undoped and Fe-doped InP single crystals at 700°C has been observed by transmission electron microscopy for various diffusion conditions. The observations are correlated with Zn concentration profiles obtained by electron microprobe measurements and secondary-ion mass spectrometry. The results allow the conclusion that indiffusing interstitial Zn can occupy In sublattice sites via a kick-out reaction. Under appropriate diffusion conditions supersaturations of In self-interstitial atoms result leading to defect formation. Observations in Fe-doped InP suggest that Zn also replaces Fe on In sublattice sites leading to redistribution and to precipitation of Fe.
Minority Carrier Diffusion Length Improvement in Czochralski Silicon by Aluminum Gettering
Authors: Joshi Subhash M. , GÖsele Ylrich M. , Tan Teh Y.
Published: April 2011

Gettering is widely used for fabricating integrated circuits using Si substrates, and has great potential for solar cell fabrications as well. Recently available solar cell efficiency studies have shown the benefits of the wafer backside Al, attributable to effects of gettering, a wafer backside field, and passivation of grain boundaries and dislocations. In this paper, we report experimental results which showed unambiguously that Czochralski Si wafer bulk minority carrier diffusion lengths can be significantly improved due to gettering of impurities by wafer backside Al, which also provided a protection from environmental contamination.
Characterization of the Damage on the Back Side of Silicon Wafers
Authors: Lindo S. E. , Matney K. M. , Goorsky M. S.
Published: April 2011

Gettering represents a standard procedure to remove harmful impurities from device active regions of a silicon wafer. An affordable technique for the creation of a defect free (denuded) zone is the introduction of gettering sites on the wafer back side via mechanical damage (i.e. lapping). However, optimizing the extrinsic gettering process requires a technique to quantify the extent of damage introduced through a typical back-side damaging step. Here, we present results from a study using triple axis x-ray diffraction. We characterized the level of damage present in wafers subjected to different lapping conditions. By comparing reciprocal space maps from samples that had undergone different lapping steps, we concluded that all the as-lapped samples showed similar levels of damage in terms of both strain variations and lattice tilts. However, the integrated diffuse scattering intensities decreased from medium to soft t.-double-soft lapping, which confirmed that the double soft lapping introduced the least damage. Typically, the damage step introduced a symmetrical distribution of both lattice strain and lattice tilts (mosaicity) in the surface layer. KOH etching was employed to determine the depth of the damaged layer. In all cases the as-lapped samples had integrated intensities two orders of magnitude greater than those of the etched samples. Analysis of the residual damage present in the lapped samples after chemical etching confirmed that the more aggressive lapping conditions introduced damage of greater depth.
Spectroscopy of Transition-Metal-Hydrogen Complexes in Silicon
Authors: Stavola Michael , Uftring S.J. , Evans M.J. , Williams P.M. , Watkins G.D.
Published: April 2011

Transition-metal-hydrogen complexes have been introduced into bulk Si samples that contained Pt, Au, or Rh by the indiffusion of hydrogen at 1250°C from H2 gas. The structure and electrical properties of a PtH2 complex in Si have been studied by vibrational spectroscopy and electron paramagnetic resonance (EPR). The PtH2 complex has been found to introduce two levels in the Si bandgap. There is one paramagnetic charge state for which EPR provides detailed structural information and two nonparamagnetic charge states. The hydrogen vibrations of all three charge states of PtH2 have been assigned. In addition to the PtH2 complex, the hydrogen vibrations of several additional complexes in Si samples that contain hydrogen and Pt, Au, or Rh have been identified.
Low-Temperature Diffusivity of Hydrogen in Different Silicon Substrates
Authors: Deng Xiaojun , Sopori Bhushan L.
Published: April 2011

The diffusivity of deuterium (D) at 250°C was determined in silicon samples grown by different techniques. It is found that the diffusivity increases with the growth speed, increase in carbon content and a decrease in oxygen concentration of the substrate. These growth conditions correlate well with the concentration of vacancy-type defects in the as-grown state. Hence, we conclude that a vacancy mechanism is responsible for low-temperature hydrogen diffusion in silicon. The highest diffusivity for hydrogen, calculated from these data, was found to be 3 × 10−7 cm2/s.
Control of Oxygen Content in Heavily Sb-Doped CZ Si Crystal by Adjusting Ambient Pressure
Authors: Izunome Koji , Huang Xinming , Togawa Shiniji , Terashima Kazutaka , Kimura Shigeyuki
Published: April 2011

In Czochralski-grown (CZ) silicon single crystals, antimony (Sb) doping decreases the oxygen concentration by enhancing oxygen evaporation from the melt surface. In this study, Ar ambient pressures of around 100 Torr over the silicon melt were found to suppress evaporation of oxide species. To clarify the effect of the growth chamber ambient pressure on oxygen concentration, heavily Sb-doped CZ silicon crystals were grown under Ar pressures of 30, 60, and 100 Torr. Increasing Ar pressure increases the oxygen and Sb concentrations at the melt surface. The oxygen concentration under an Ar pressure of 100 Torr was 1.2 times higher that under 30 Torr when the solidified fractions are 0.5 or larger. The oxygen evaporation rate is controllable by gas phase transport of Sb2O at high Ar pressures.
Noncontact Photoconductivity Amplitude Technique to Characterize Polishing- and Slicing-Induced Residual Damage in Si Wafers
Authors: Ogita Y. , Nakano M. , Masumura H.
Published: April 2011

The photoconductivity amplitude (PCA) technique with UV laser carrier excitation has been proposed to characterize surface property and subsurface damage. Combining this new technique with mechanochemical polishing has determined the depth profile of the slicing-induced residual damage. Combining SC1 cleaning with this technique allows to determine the depth profile of residual damage induced by mirror polishing. This result leads that the mirror polishing-induced damage can be removed by the SC1 cleaning.
X-ray Topography of Strain Fields Induced by 100 MeV Ti7+ Ion Irradiated Si(100)
Authors: Sharma B. B. , Gupta S. R. , Sharma R. K. , Kumar V. , Tiwari U. , Sen P. , Mehta G. K.
Published: April 2011

The lattice deformation caused by 100 MeV Ti7+ ion irradiation in Si (100) has been studied using X-ray topographic techniques. An important finding is the appearance of a strain field perpendicular to the ion beam direction in the irradiated region well separated from the projected range of implanted ions. This in-plane strain extends in the bulk of the sample and is not merely confined to the surface. The implanted region has been found to experience an out of plane strain which is expected to be tensile in nature.
Metastable Defect at Si-SiO2 Interfaces
Authors: Jing Z. , Lucovsky G. , Whitten J. L.
Published: April 2011

An important issue in semiconductor device operation is the rate at which current or voltage stress creates defects that degrade eventually device operation. Based on recent results on nitrided gate dielectrics, we have concluded that bonded-H at the Si-SiO2 interface plays a role in the formation of metastable defects that can be activated, and subsequently neutralized, by sequential trapping of injected holes and electrons. In this paper, differences in defect behavior for Si-SiO2 interfaces that have exposed to nitrogen (N-) atoms or N-H groups are discussed. Based on these results, a microscopic model for interfacial defects is proposed.
DX-Like Centers in IV-VI.
Authors: Khokhlov Dmitriy R.
Published: April 2011

Up to the recent times it was believed that observation of the DX-centers is restricted to the rather wide-bandgap III-V and II-VI semiconductors. However it becomes obvious now that some of the narrow-gap IV-VI semiconductors doped with the group III elements reveal the features of DX-centers. A range of features, such as negative-U behavior, large lattice relaxation, metastability of the local excited states, narrow bandgap - make the effects resulting from the DX-like behavior much more complicated than in the “classical” materials with the DX-centers. We review the most unusual recent results obtained in the field that originate from the specifics of the DX-like centers in IV-VI.
Are the Models of the Triply Charged Gallium Vacancy and Doubly Charged Gallium Interstitial Alive or Dead?
Authors: Cohen R. M. , Chen C. Y. , Li W. M. , Simons D. S. , Chi P. H.
Published: April 2011

We have found that the measured diffusivity can be quite different than predicted by recent models of multiply-charged defects. Key problems dealing with the measurement and the interpretation of diffusion mechanisms are discussed. Using a few common variations in GaAs epilayer growth, we have obtained diffusivities which range over several orders of magnitude at the same temperature. Making use of the relatively weak In-As bond, we have used In as a marker to measure group III interdiffusion, DIII. DIII is consistent with the results of others using Al as a marker in n-type GaAs, but orders of magnitude smaller than predicted by the triply charged Ga vacancy, V3−Ga, model of Tan and Gosele. Although diffusion can be attributed to a negatively charged vacancy in n-type GaAs, In is found to often move by a kick-out mechanism in p-type GaAs. It appears likely that many early experiments with n- and p-type GaAs-AlAs interdiffusion were affected by large concentrations of Ga interstitials, IGa, caused by Fermi energy pinning at the growing surface. We present the first direct experimental evidence for the existence of a positively charged Ga interstitial. Our results, combined with those of others, suggest that VGa has a single negative charge associated with it. Because epilayer growth conditions appear to cause the point defect concentrations to deviate substantially from equilibrium, we conclude that the exact charge states of VGa and IGa still remain to be determined.
Magnetic and Structural Properties of Iron Nitride thin Films Obtained by Argon-Nitrogen Reactive Radio-Frequency Sputtering
Authors: Chatbi H. , Bobo J.F. , Vergnat M. , Hennet L. , Ghanbaja J. , Lenoble O. , Bauer Ph. , Piecuch M.
Published: April 2011

Fe-N thin films have attracted considerable attention because they are potential candidates for magnetic recording with their large saturation magnetization and their good corrosion resistance1. It has even been demonstrated that saturation magnetization can be larger than the bulk iron one for low nitrogen contents2. The origin of the enhanced magnetic moment could occur from the metastable α″ Fe16N2 phase or from an expanded bcc FeN structure which is also called α FeN.
Epitaxial Growth OF (001)- and (111)-Oriented PTMNSB Films and Multilayers
Authors: Kautzky M.C. , Clemens B.M.
Published: April 2011

In this paper we report the successful growth of single-phase epitaxial PtMnSb films and multilayers by dc magnetron cosputtering, both in the (001) orientation on MgO(001) and W(001), and in the (111) orientation on Al2O3 (0001). Single-layer films in the thickness range 50Å≤t≤1000Å were grown and characterized using x-ray diffraction (XRD), magneto-optic Kerr effect (MOKE), and vibrating sample magnetometry (VSM). The in-plane orientation relationships, as determined by asymmetric XRD, were PtMnSb[100]∥MgO[110], PtMnSb[100]∥W[100], and PtMnSb[101∥Al2O3[2110]. The crystalline quality of the films was found to depend strongly upon the substrate, growth temperature, film thickness, and presence of a capping layer, but rocking curve widths of 1° or less were achieved on each substrate. Measurement of the in-plane strain showed that the films were almost entirely relaxed, with strains <1%. In-plane magnetization was observed in all cases, with moments and coercivities in the 400-500 emu/cm3 and 100-200 Oe ranges respectively. Polar Kerr spectra showed large rotations (0.75° - 1.03°), whose peak wavelengths appear to depend on both film structure and optical interference effects.
Universal mB/T Scaling of the Giant Magnetoresistance in Cu-Co Granular Ribbons Produced by Controlled Melt-Spinning
Authors: Madurga Vicente , Ortega R.J. , Vergara J. , Elvira R. , Korenivski V. , Rao K.V.
Published: April 2011

Studies of the evolution of electrical resistance in an external applied magnetic field, B, as well as with temperature, T, on Cu86Co14 and Cu92Co8 as quenched and annealed melt-spun ribbons, reveal that magnetoresistance, MR, ΔR(B,T)=R(B)-R(0) scales with B/T. Furthermore, it found that annealing up to 600 °C scales the magnetic moment of the Co-rich superparamagnetic nanoparticles such that, the data for the field dependence of the MR obtained at various temperatures collapses onto the same unique and universal curve f(mB/T) with the Langevin variable mB/T governing the overall behaviour.
Environmental Effects on Interface Behavior in Graphite / Epoxy Single Fiber Composites
Authors: Schadler Linda S. , Koczak Michael J. , Amer Maher S.
Published: April 2011

Toray M40 graphite fiber / Epon 828 epoxy resin single fiber composites with both sized and unsized fibers were exposed to distilled water at 50°C and 100°C, 10% NaOH and HCl aqueous solutions at 50°C, and air at 100°C. Micro Raman spectroscopy was used to measure the strain and interfacial shear stress profiles as a function of environmental exposure. It was found that the degradation mechanism is primarily a mechanical failure of the fiber/matrix interface.
Tailoring the Structure of Polymer Brushes Through Copolymer Architecture
Authors: Gersappe Dilip , Fasolka Michael , Israels Rafel , Balazs Anna C.
Published: April 2011

Polymers tethered by one end onto a solid surface are referred to as polymer “brushes”. We consider brushes composed of copolymers that contain both A and B monomers. The A monomers are compatible with the surrounding solvent, while the B sites are solventincompatible. The solvent incompatibility causes the B sites to associate into domains or clusters within the layer. We use Monte Carlo computer simulations and self-consistent field calculations to determine the effect of copolymer architecture on the structure of the polymer brush. In particular, we alter the copolymer sequence distribution (the arrangement of the A and B monomers along the length of the chain) and determine how both the vertical and lateral morphology of the brush are effected by these variations. The results provide guidelines for controlling the size and shape of the B domains, and consequently, the morphology of the tethered layer.
Natural Poly(Hydroxybutyrate-Hydroxyvalerate) Polymers as Degradable Biomaterials
Authors: Chaput Cyril , Yahia L'Hocine , Selmani Amine , Rivard Charles-Hilaire
Published: April 2011

Poly(ß-hydroxybutyrate-co-ß-hydroxyvalerate) have been recently proposed as degradable biomaterials for drug delivery systems, sutures, bone plates and short-term implants. Three PIBF\HV (7, 14 & 22 % HV) films were analyzed for in vitro cytotoxicity and aqueous accelerated degradation, in vivo degradation and tissue reactions. The PHB/HV materials and extracts elicit few or mild toxic responses, do not lead in vivo to tissue necrosis or abscess formation, but provoke acute inflammatory reactions slightly decreasing with the time. The degradation of PHB/HV polymers present low rates in vitro as well as in vivo. The weight loss rate generally increases with the copolymer composition (HV content) and ranges from 0.15–0.30 (in vitro) to 0.25 %day (in vivo). Compositional and physico-chemical changes in PHB/HV materials were rapidly detected during the accelerated hydrolysis, but were much slower to appear in vivo. The structural and mechanical integrity of PHB/HV materials tend to disappear early in vitro as well as in vivo. After 90 wks in dorsal muscular tissues of adult sheep, there was no significant dissolution of the PHBiIV polymer, 50–60% of the initial weight still remaining. PHB/HV polymers are biodegradable materials, either by hydrolysis or implantation, but with extremely low dissolution or degradation rates.
Adhesion and Thermal Deformation of Ceramic/ Polymer Heterostructures
Authors: Madras Cynthia , Wong Peter Y. , Miaoulis Ioannis N.
Published: April 2011

The adhesion and thermal properties of optical ceramic structures bonded by a polymer interlayer are explored. The mechanical, adhesion and optical properties of the heterostructure are dependent on the thickness of the bond and on the residual thermal stresses developed during the bonding process. The thermomechanical properties of a bonded structure over a range of temperatures are investigated, focusing on the thermal expansion and operating temperature limits of the polymer bond. The temperature and stress histories during manufacturing are determined through both numerical modeling and experimental analysis. The effect of stress relaxation and initial stresses on the behavior of the bonding material are examined for different processing conditions. The bond material relaxation time constant, activation energy, viscosity, and shear modulus are approximated from observation of the temperature-dependent behavior of the structure.
Direct Surface Analysis of Organic Contamination for Semiconductor Related Materials
Authors: Lee J. , Odom R. W. , Strossman G. S. , Lindley P. M.
Published: April 2011

Direct surface analysis of Si wafers and environmental materials such as polymers for wafer carriers and for high purity water systems is important to identify contaminants and their sources. Organic contaminants on the surfaces are difficult to analyze; however, their adverse effects have been cited in recent years. This paper demonstrates the detection and identification of surface contaminants using Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) on semiconductor related materials. The analytical information provided by TOF-SIMS can be useful for maintaining material cleanliness or for failure analysis.
Outplating of Metallic Contaminants on Silicon Wafers From Diluted Acid Solutions
Authors: Rotondaro A. L. P. , Hurd T. Q. , Schmidt H. F. , Teerlinck I. , Heyns M. M. , Claeys C.
Published: April 2011

The outplating behaviour of Fe and Cu was investigated for diluted solutions of HCl and HNO3. The deposition of the metallic contaminants was found to be strongly dependent on the type of surface that is exposed to the contaminated solution. Cu deposits heavily on bare silicon surfaces, whereas only low levels of Fe deposition are observed. On the other hand, on thermal oxide surfaces, the levels of deposited Fe are consistently higher than the Cu ones. The acid used appears to have no major impact on the deposition process. The pH of the solutions has a major effect on the Cu deposition and a minor effect on the Fe case.
Correlation of Roughness and Device Properties for Hydrogen Plasma Cleaning of Si(100) Prior to Gate Oxidation
Authors: Montgomery J. S. , Barnak J. P. , Silvestre C. , Hauser J. R. , Nemanich R. J.
Published: April 2011

Hydrogen plasma treatment was used as a cleaning and conditioning step prior to gate oxide deposition in the fabrication of cluster-based MOS field effect transistors. Surface roughness was measured by atomic force microscopy and compared to current-voltage characteristics of the MOSFET devices. The MOSFET devices were evaluated on the basis of threshold voltage, peak mobility, interface scattering, and surface roughness coefficient. Following a 10 minute Hplasma exposure at a substrate temperature of 150°C the rms roughness increased from 1.1±0.3 Å to 17±9 Å. The rms roughness for samples treated for 10 minutes at 700°C was 4±1 Å. Analysis of the MOSFET devices treated in the low temperature range (200°C) show significant degradation due to the H-plasma interaction. Threshold voltage for the devices exposed to a 2 minute H-plasma at a temperature of 200°C was 0.72±0.02 V. In contrast the threshold voltage for the 600°C, 2 minute plasma exposure was 0.86±0.03 V. The peak mobility for those devices was 370 cm2/V-s. Further device analysis was accomplished from the current-voltage measurements to extract a value of interface scattering and surface roughness scattering for each device. Interface scattering and surface roughness scattering do not increase for H-plasma process temperatures of 450 – 700°C. An H-plasma treatment for 2 minutes at 500°C also resulted in no observable increase in rms roughness, a threshold voltage of 0.92±0.03 V, a peak mobility of 410 cm2/V-s, and no increase in interface scattering and surface roughness scattering.
In Situ Auger Spectroscopy Investigation of InP Surfaces Treated in RF Hydrogen and Hydrogen/Methane/Argon Plasmas
Authors: Parmeter J. E. , Shul R. J. , Miller P. A.
Published: April 2011

We have used in situ Auger spectroscopic analysis to investigate the composition of InP surfaces cleaned in rf H2 plasmas and etched in rf H2/CH4/Ar plasmas. In general agreement with previous results, hydrogen plasma treatment is found to remove surface carbon and oxygen impurities but also leads to substantial surface phosphorus depletion if not carefully controlled. Low plasma exposure times and rf power settings minimize both phosphorus depletion and surface roughening. Surfaces etched in H2/CH4/Ar plasmas can show severe phosphorus depletion in high density plasmas leading to etch rates of ∼ 700 Å/min, but this effect is greatly reduced in lower density plasmas that produce etch rates of 30–400 Å/min.
Preferential Etching of Si(111) and Si(001) in Dilute NH4F Solutions: as Probed by In Situ STM
Authors: Itaya Kingo , Yau Shueh-Lin , Kaji Kazutoshi
Published: April 2011

In situ scanning tunneling microscopy (STM) was used to examine the etching process of n-Si(11) and Si(001) electrodes in dilute NH4F under cathodic potential control. For Si(111), time-dependent STM images have revealed the pronounced effect of the microscopic structure of surface Si atoms on their dissolution rates. The multiple hydrogen bonded Si atoms at the kink sites and dihydride steps eroded faster than the monohydride terminated Si. Presumably, the higher polarity at these defect sites is responsible for the difference. Steric consideration further favors the higher activity at the more open kink sites. The monohydride terminated Si(111) surface represents the most stable surface structure, which guides the dissolution of the Si(001) surface to the formation of {111} facets. The initial stage {111} facet formation on a Si(001) surface was revealed by in situ STM.
Characterization of Defects Produced in TEOS Thin Films due to Chemical-Mechanical Polishing (CMP)
Authors: Kaufman F. B. , Cohen S. A. , Jaso M. A.
Published: April 2011

Time zero breakdown electrical measurements, SIMS, Bias Temperature Stress (BTS), and Triangular Voltage Sweep (TVS) techniques performed on MOS capacitors have been used to characterize two types of defects produced in TEOS thin films subjected to CMP process planarization. Microcracking of the insulator, resulting in degradation in breakdown characteristics, and uptake of K+ions (from the polishing slurry) are found to occur. These defects are thought to be caused by the chemical and mechanical stress to which the oxide surface is subjected during the CMP process. The effects of polish pad type, non K+ion containing slurry and post-CMP wet etch steps were all found to influence the extent of damage observed in polished films.
Modeling and Simulation of Pulsed Laser annealing and ablation of Solid Materials
Authors: Liu C. L. , Wood R. F.
Published: April 2011

Several different aspects of laser annealing and laser ablation have indicated the need for two-dimensional (2-D) modeling of heat transfer and phase-change effects. We have in mind particularly the laser-induced formation and propagation of buried liquid layers for the case of a-Si on a crystalline silicon substrate, questions related to the early stages of the laser ablation of insulators such as MgO where it is believed that the absorption of the laser radiation occurs at localized but extended regions of high concentrations of defects, and the ejection of particulate material during laser ablation. To deal with these phenomena, a 1-D computational model originally developed for laser annealing has been extended to two-dimensions. the 2-D modeling examines the heat flow and phase changes associated with localized heat sources embedded in a planar material. Concepts such as the state diagram and state array used in the 1-D work have been extended to 2-D and refined. the 2-D program has been rewritten for massively parallel machines such as the intel Paragons in ORNL's Center for Computational Sciences, thus allowing larger and more accurate calculations for complex systems to be carried out in reasonable times.
Amorphous Diamond-Like Carbon Film Growth by KrF-and Arf-Excimer Laser Pld: Correlation with Plume Properties
Authors: Puretzky A. A. , Geohegan D. B. , Jellison G. E. , Mcgibbon M. M.
Published: April 2011

A comparative study of arF- and KrF-laser deposition of amorphous diamond-like carbon (DLC) films and relevant carbon plasmas has been performed. Spectroscopic ellipsometry and EELS analysis of the DLC films deposited on Si <100> and NaCl substrates were utilized to characterize the high quality arF- and KrF-laser deposited films (up to 84% of sp3 bonded carbon in 7 J/cm2 -ArF-laser DLC film). Gated ICCD imaging, luminescence and ion current probe diagnostics of the carbon plume have revealed quite different properties of carbon plasmas generated by arF- and KrF- lasers. KrF-laser (6.7 J/cm2) irradiation produces a less energetic carbon plasma containing larger amounts of C2 and probably larger clusters compared with arF-laser irradiation at the same energy fluence. We conclude that the more energetic and highly-atomized arF-laser carbon plasma results in the better diamond-like properties.
Ion Beam Deposition of Boron-Aluminum Nitride Thin Films
Authors: Edgar J.H. , Eddy C.R. , Sprague J.A. , Sartwell B.D.
Published: April 2011

Analysis of the phase behavior, structure, and composition of aluminum nitride thin films with up to 22% boron prepared by ion-beam assisted deposition is presented. the c-lattice constant of the film decreased with increasing boron content as expected from the formation of an aIN - wurtzite BN alloy. there was no evidence for separate boron nitride precipitation from either X-ray diffraction or FTIR. IN contrast, auger electron spectroscopy of the boron present in the films suggested that two types of boron bonding was present.
Dissociative Chemisorption at Hyperthermal Energies: Benchmark Studies in Group IV Systems
Authors: Xia L.-Q. , Jones M. E. , Maity N. , Roadman S. E. , Engstrom† J. R.
Published: April 2011

We present a review of our recent work concerning supersonic molecular beam scattering of thin film precursors from the Si(100) and Si(111) surfaces. Both SiH4 and Si2H6 exhibit translationally activated dissociation channels at sufficiently high incident kinetic energies, (E┴) 0.5 eV. the dominant variables under our reaction conditions are the incident kinetic energy and the angle of incidence, whereas mean internal energy and substrate temperature play relatively minor roles. the former two variables couple to produce a universal relationship between the reaction probability and a scaled kinetic energy given by (E┴) = Eі[(l-Δ)cos2θі + 3Δsin2θі], where θі is the angle of incidence, a is a corrugation parameter, and 0 ≤ Δ ≤ 1. IN addition to the reaction probability, the reaction mechanism for Si2H6 is also dependent upon incident kinetic energy and surface structure, where a SiH4(g) production channel is observed on the Si(111)-(7x7) surface at low to moderate incident kinetic energies. the reactions of SiH3CH3 and PH3 provide convenient comparative examples. Methylsilane, reacting on a β-SiC surface, exhibits a translationally activated dissociation channel, similar to what is observed for SiH4 and Si2H6. Phosphine, on the other hand, exhibits the characteristics of trapping, precursor-mediated dissociative chemisorption. these results act to underscore the important role played by the frontier orbital topology, even at hyperthermal incident kinetic energies.
Effects of Carbon-Ion Irradiation-Energies on the Molecular Beam Epitaxy of GaAs and Ingaas
Authors: Makita Y. , Iida T. , Shima T. , Kimura S. , Obara A. , Harada K. , Tu C.W. , Uekusa S. , Matsumori T. , Kudo K. , Tanaka K.
Published: April 2011

Carbon ion (C+) irradiation during molecular beam epitaxy (MBE) growth of GaAs/GaAs and in0.53.Ga0.47As/InP layers was carried out using CIBMBE (combined ion beam and molecular beam epitaxy) method as a function of wide acceleration energy (Ea=30 eV-30 keV) at a constant ion beam current density. Judging from the monitored current density and the net hole concentration (INA-ND|) obtained from Hall effect measurements, activation rate as high as 88% was achieved for as-grown GaAs layers by C+ ion irradiation of Ea=~170eV. It was revealed that by annealing at 800°C, a slight enhancement (~ 10%) of INA-ND| is practiced for Ea <~ 130eV but a significant increase of INA-ND| is realized for Ea>~lkeV. IN in0.53Ga0.47As/InP layers with increasing Ea, a type conversion of electric conduction from n to p was found to occur at Ea= ~70~100eV. these observations describe that Ea plays a vital role to determine the location of incorporated electrical and optical active impurities in GaAs and inGaAs. Further for comparison, C+-implanted GaAs layers were prepared by high-energy (400 keV) ion-implantation as a function of substrate temperature (T1=RT-600 °C). For C dose concentration of lxl018cm-3\ the highest activation rate of ~20 % was obtained at T1=~150 °C. This result states that CIBMBE method is a superior doping method in view of activation rate of introduced dopants and the formation of damage-free ion-irradiated layers.
Velocity Selection of Laser Ablated Metal Atoms by a Novel Non-Mechanical Technique
Authors: Fajardo Mario E. , Macler Michel
Published: April 2011

We present the results of experiments on velocity selection of fast laser ablated al, Ga, and in atoms by a novel, non-mechanical, technique. Pulses of atoms with broad velocity distributions are produced by laser ablation of a single component pure metal target in vacuum. after a delay of ~ 1 μs, there exists a strong one-to-one correlation between atomic velocity and distance traveled from the ablated surface. Thus, a second pulsed laser, delayed by ~ 1 μs and crossed at a right angle to the atomic beam, can be used to photoionize only those atoms with unwanted velocities, i.e.: atoms moving too fast or too slow to be hidden behind an opaque mask placed ~ 1 cm from the ablated surface. the photoions, and any ions surviving from the ablation event, are subsequently deflected from the beam by a static magnetic field. by a fortunate coincidence, al, Ga, and in atoms all have very large single photon photoionization cross sections at 193 nm, the output wavelength of the arF excimer laser; thus, well over 95% of the unwanted atoms can be easily photoionized and rejected. We have demonstrated velocity selected al, Ga, and in atom fluxes equivalent to Ф ~ 1011 atoms/(cm2-eV-pulse) at a working distance of 10 cm.
Characterization of Carbon Nitride Films Produced by Pulsed Laser Deposition
Authors: Friedmann T. A. , Tallant D. R. , Barbour J. C. , Sullivan J. P. , Siegal M. P. , Simpson R. L. , Mikkalson J. , McCarty K. F.
Published: April 2011

Carbon Nitride (CNX) films have been grown by ion-assisted pulsed-laser deposition (IAPLD). Graphite targets were laser ablated while bombarding the substrate with ions from a broad-beam Kaufman-type ion source. the ion voltage, current density, substrate temperature, and feed gas composition (N2 in ar) have been varied. the resultant films were characterized by Raman, Fourier transform infrared (FTIR), and Rutherford back scattering (RBS) spectroscopy.

Samples with -30% N/C ratio have been fabricated. the corresponding Raman and FTIR spectra indicate that nitrogen is incorporated into the samples by insertion into sp2-bonded structures. a low level of C=N triple bonds is also found. as the ion current and voltage are increased with a pure ar ion beam, Raman peaks associated with nanocrystalline graphite appear in the spectr A. adding low levels of nitrogen to the ion beam first reduces the Raman intensity in the vicinity of the graphite disorder peak without adding detectable amounts of nitrogen to the films (as measured by RBS). at higher nitrogen levels in the ion beam, significant amounts of nitrogen are incorporated into the samples, and the magnitude of the "disorder" peak increases. by increasing the temperature of the substrate during deposition, the broad peak due mainly to sp2-bonded C-N in the FTIR spectra is shifted to lower wavenumber. This could be interpreted as evidence of single-bonded C-N; however, it is more likely that the character of the sp2 bonding is changing.
Observations on the Growth of YBa2Cu3O7 Thin Films at Very High Laser Fluences
Authors: Biggers. Rand R. , Grant Norton M. , Maartense I. , Peterson T.L. , Moser E. K. , Dempsey D. , Brown Jeff L.
Published: April 2011

The pulsed-laser deposition (PLD) technique utilizes one of the most energetic beams available to form thin films of the superconducting oxide YBa2Cu3O7 (YBCO). IN this study we examine the growth of YBCO at very high laser fluences (25 to 40 J/cm2); a more typical fluence for PLD would be nearer to 3 J/cm2. the use of high fluences leads to unique film microstructures which, in some cases, appear to be related to the correspondingly higher moveabilities of the adatoms. Films grown on vicinal substrates, using high laser fluences, exhibited well-defined elongated granular morphologies (with excellent transition temperature, Tc, and critical current density, Jc). Films grown on vicinal substrates using off-axis magnetron sputtering, plasma-enhanced metal organic chemical vapor deposition (PE-MOCVD), or PLD at more typical laser fluences showed some similar morphologies, but less well-defined. Under certain growth conditions, using high laser fluences with (001) oriented substrates, the YBCO films can exhibit a mixture of a- and c-axis growth where both crystallographic orientations nucleate on the substrate surface at the same time, and grow in concert. the ratio of a-axis oriented to c-axis oriented grains is strongly affected by the pulse repetition rate of the laser.
Growth of Highly Doped P-Type Znte Films by Pulsed Laser ablation in Molecular Nitrogen
Authors: Lowndes Douglas H. , Rouleau C. M. , Mccamy J. W. , Budai J. D. , Poker D. B. , Geohegan D. B. , Puretzky A. , Zhu Shen
Published: April 2011

Highly p-doped ZnTe films have been grown on semi-insulating GaAs (001) substrates by pulsed-laser ablation (PLA) of a stoichiometric ZnTe target in a high-purity N2 ambient without the use of any assisting (DC or aC) plasma source. Free hole concentrations in the mid-1019 cm-3 to 1020 cm-3 range were obtained for a range of nitrogen pressures the maximum hole concentration equals the highest hole doping reported to date for any wide band gap II-VI compound. the highest hole mobilities were attained for nitrogen pressures of 50–100 mTorr (~6.5–13 Pa). Unlike recent experiments in which atomic nitrogen beams, extracted from RF and DC plasma sources, were used to produce p-type doping during molecular beam epitaxy deposition, spectroscopic measurements carried out during PLA of ZnTe in N2 do not reveal the presence of atomic nitrogen. This suggests that the high hole concentrations in laser ablated ZnTe are produced by a new and different mechanism, possibly energetic beam-induced reactions with excited molecular nitrogen adsorbed on the growing film surface, or transient formation of Zn-N complexes in the energetic ablation plume. This appears to be the first time that any wide band gap (Eg 2 eV) II-VI compound (or other) semiconductor has been impurity-doped from the gas phase by laser ablation. In combination with the recent discovery that epitaxial ZnSe1-xSx films and heterostructures with continuously variable composition can be grown by ablation from a single target of fixed composition, these results appear to open the way to explore PLA growth and doping of compound semiconductors as a possible alternative to molecular beam epitaxy.
Inhibited SN Surface Segregation in Epitaxial SNxGE1-x Alloy Films Grown by Pulsed Laser Deposition
Authors: Taylor M.E. , He G. , Saipetch C. , Atwater H.A. , Watson Thomas J.
Published: April 2011

Epitaxial and compositionally homogeneous SnxGe1-x alloy films have been grown on Si (001) by pulsed laser deposition using elemental Sn and Ge targets. these results demonstrate that pulsed laser deposition can be used to grow alloys by overcoming the strong tendency for Sn surface segregation seen in growth by other methods such as molecular beam epitaxy.
Deposition of Molten Eutectic Solder using Jet Printing Techniques
Authors: Snyder Michael D. , Lasky Ronald
Published: April 2011

This paper discusses the use of Ink Jet printing techniques to dispense small (50 to 75 micrometer diameter) particles of molten eutectic solder individually at programmable dispense rates from drop on demand to several thousand per second. Alternative jet dispensing techniques are discussed. The technology could allow the selective application of programmable amounts of solder on precision circuit boards and wafer substrates, while avoiding the high cost and flexibility limits associated with hard tooling. Large solder features can be constructed by dispensing individual droplets and relying on surface tension to draw them together to form a large single feature. Alternatively, columnar features can be created by successively dispensing solder droplets at the same site, allowing time between successive droplets to avoid forming a single large spherical feature.

Several potential application areas in industry are discussed along with some of the issues associated with the projected performance of the method in the accuracy and speed domains.
Laser Machining and Metallization of VIAS in Aluminum Nitride
Authors: Raman Sudhakar , Lumpp Janet K.
Published: April 2011

A via metallization technique involving excimer laser ablation of aluminum nitride substrate with a metal backing, attached with cyanoacrylate adhesive was investigated. The objective was to develop a procedure to ensure good electrical interconnection between the thick film conductor pads and the walls of the via. An aluminum nitride compatible Ag-Pd thick film paste was used in this experiment. Two different sequences were tested: In the first sequence both sides of the aluminum nitride substrate were printed and fired and then the vias were laser drilled. In the second sequence, one side of the substrate was printed and fired first, then the vias were laser drilled and the second side was printed and fired. In both of the above sequences, laser ablation of the printed conductor and redeposition of the ablated metal backing are necessary for making a proper contact with the thick film conductor pads.
Electronic Packaging Education in U.S.
Authors: Tummala Rao R.
Published: April 2011

The loss of U.S. electronics market share during the last three decades is attributed to both the engineering education and the research emphasis away from manufacturing and systems. The engineering education in U.S., in spite of great progress during the last decade, is incomplete and fragmented and requires a comprehensive and system-level strategy.
Deposition of Potassium Niobate Thin Films by Metalorganic Chemical Vapor Deposition and their Nonlinear Optical Properties
Authors: Nystrom M. J. , Wessels B. W. , Chen J. , Studebaker D. , Marks T. J. , Lin W. P. , Wong G. K.
Published: April 2011

Ferroelectric potassium niobate thin films have been deposited by conventional, low pressure metalorganic chemical vapor deposition on several types of oxide substrates. The films were epitaxial with a c-axis orientation normal to the substrate. Atomic force microscopy revealed a surface roughness of 1 - 4 nm. Transmission electron microscopy showed the film/substrate interface to be semi-coherent with lattice misfit accommodated by misfit dislocations. The nonlinear optical properties of the KNbO3 films were measured by a transmission technique. The room temperature, effective second order nonlinear coefficient was 13 pm/V.
Highly Active and Thermally Stable Ctlromophores and Polymers for Electro-Optic Applications
Authors: Jen Alex K-Y. , Chen Tian-An , Rao Varanasi Pushkara , Cai Yong-Ming , Liu Yue-Jin , Drost Kevin J. , Mininni Robert M. , Dalton Larry R. , Bedworth Peter , Marder Seth R.
Published: April 2011

We have developed two new classes of highly active and thermally stable nonlinear optical (NLO) chromophores based on the use of efficient thiophene conjugating units, a N,N-diphenylamino electron-donating group, and a 1,1′-dicyanovinyl substituted electron-accepting group. We have also developed a facile and generally applicable method to functionalize NLO chromophores onto high temperature polymers to demonstrate both high electro-optic (E-O) coefficients and long-term alignment stability at 100 °C.
Dynamic Mechanical Analysis and Dielectric Relaxation for Second Order Nonlinear Optical Applications
Authors: Sullivan Leah A. , Lackritz Hilary S.
Published: April 2011

Relaxation dynamics of poly(methyl methacrylate) (PMMA) and doped PMMA systems are investigated as a function of processing temperature and frequency. Polymer relaxations and changes in local mobility are responsible for chromophore reorientation and lead to a loss in second-order nonlinear optical (NLO) properties. Studying polymer relaxations enables the temporal and thermal stability of the NLO polymer systems to be more accurately and readily predicted. The polymer dynamics are studied by correlating mechanical and dielectric relaxations to polymer and chromophore relaxations that occur during chromophore reorientation in second harmonic generation experiments. Dielectric and mechanical relaxation techniques enable polymer relaxation dynamics to be observed over a broad frequency range. The plasticization effect of the NLO chromophores on the polymer relaxation dynamics is also investigated.
Integrating cell Transplantation and Controlled Drug Delivery Technologies to Engineer Liver Tissue
Authors: Mooney D. J. , Sanog K. , Kaufmann P.M. , Mcnamara K. , Vacanti J.P. , Langer R.
Published: April 2011

Engineering liver tissue using hepatocyte transplantation may provide a new approach for treating a variety of liver diseases. However, techniques to transplant hepatocytes and promote their survival must be developed. We have developed systems to transplant hepatocytes on highly porous (95%), biodegradable sponges, and to regulate the survival of cultured hepatocytes by releasing specific growth factors in the cellular environment. Sponges were fabricated from poly (L, lactic acid) (PLLA) and polyvinyl alcohol using a particulate leaching technique. Epidermal growth factor and insulin, critical factors for hepatocyte growth and survival in culture, were incorporated into microspheres fabricated from poly (lactic-co-glycolic acid) (PLGA) utilizing a double emulsion technique. The incorporated factors were released in a controlled manner over one month in vitro, and the released factors maintained their biological activity, as measured by their ability to promote hepatocyte growth and survival in culture. The growth factor-containing microspheres could be transplanted with hepatocytes using the porous sponges, and the localized, sustained release of these factors improved hepatocyte engraftment 2-fold. These studies suggest that hepatocyte containing tissues can be engineered using cell transplantation, and that regulating the microenvironment of transplanted cells can control their engraftment.