bluuebunny/crossref_metadata_2025 huggingface dataset:
Schottky Barrier Heights of A1/p-Sil-xGex
Authors: Jiang R. L. , Li J. , Zhou X. C. , Liu J. N. , Zheng Y. D.
Published: April 2011

Electrical properties of Al/p-Sil-xGex Schottky contacts were investigated. The Sil-xGexstrained layers were grown by using Rapid Thermal Process/Very Low Pressure-Chemical Vapor Deposition. It was found that Schottky barrier height decreased with increasing Ge fraction. The decrement is in accordance with the decrement of the bandgap of the strained Sil-xGex. The Fermi level at the interface is pinned at about 0. 43eV below the conduction band. The influence of strain relaxation for SiGe alloy layers and the Si cap layers on the properties of Schottky contacts were also investigated.
X-Ray Standing Wave and High Resolution Diffraction Study of Si/Ge Superlattices
Authors: Lagomarsino S. , Castrucci P. , Calicchia P. , Cedola A. , Kazimirov A.
Published: April 2011

In modern technology more and more attention is given to epitaxial superlattices. III/V, and more recently Si/Ge superlattices are widely studied because of their applications in integrated optoelectronics. Since the physical properties are strongly dependent on structural characteristics, it is evident that accurate characterization methods are required in order to improve their quality and obtain optimal behavior. X-ray high resolution diffraction is extensively and successfully used to this purpose. In general diffracted intensity is measured close to strong substrate reflections where satellite peaks from superlattice take place. If the crystalline quality, mainly concerning thickness layer uniformity and interface abruptness is good, several orders of diffraction from the superlattice are visible, and fitting based on kinematical or dynamical diffraction can provide information about many structural parameters of the superlattice. However from diffracted intensity the information about the phase of the structure factor is lost. It is well known that the X-ray Standing Wave (XSW) technique can provide direct information about the phase [1]. In this paper we present measurements and calculations relative to the extension of the XSW method to the study of MBE-grown Si/Ge superlattices. The novelty consists in using the superlattice satellite peaks close to a strong reflection from the substrate to form the standing wave field which in turn excites the atoms whose fluorescence is measured. These satellite peaks correspond to high-order diffraction for the superlattice periodicity.
Thermal Mismatch Strain Relaxation Mechanisms and Hysteresis in Pb1−SnxSe-on-CaF2/Si Structures
Authors: Zogg H. , Müller P. , Fach A. , John J. , Paglino C. , Teodoropol S.
Published: April 2011

The strain induced by the thermal mismatch in Pbl−xSnxSe and other IV–VI compound layers on Si(111)-substrates relaxes by glide of dislocations in the main <110> {001}-glide system. The glide planes are arranged with 3-fold symmetry and inclined to the (111)-surface. Despite a high threading dislocation density (> 107 cm−2) in these heavily lattice mismatched structures, the misfit dislocations move easily even at cryogenic temperatures and after many temperature cycles between RT and 77K. The cumulative plastic deformation after these cycles is up to 500%! Despite a pronounced deformation hardening occurs, the structural quality of the layer is only slightly adversely affected as regards additional threading dislocations created. The interaction probability between these dislocations is estimated to be about 10−5.
Strained-Si Mos Field-Effect Transistors: Building Devices on Relaxed -SI1−xGEx Buffer Layers
Authors: Welser Jeffrey J.
Published: April 2011

The experimental application of strained-Si / relaxed-Si1−xGex heterostructures to n-MOSFETs is discussed, focusing on the enhanced mobility provided by the strain. This paper provides an overview of the theoretically-predicted electronic properties of these heterostructures, as well as their growth. Several practical issues which arise in MOS applications are covered, including the effect of the relaxed-Si1−xGex, buffer layers on diode performance, and the observation of self-heating effects in the output characteristics of the MOS transistors.
Capacitance-Voltage Characteristics of p-Si/SiGeC Mos Capacitors
Authors: Rim Kern , Takagi S. , Welser J. J. , Hoyt J. L. , Gibbons J. F.
Published: April 2011

The first measurements of Si/SiGeC valence band offsets have been performed using heterostructure p-type MOS capacitors. Single crystalline epitaxial layers of SiGeC and Si were grown by the rapid thermal CVD technique, limited reaction processing, using ethylene as the carbon source. Films with carbon contents of up to ∼1.2% were studied. X-ray diffraction analysis shows the strain compensating effect of carbon in SiGeC. Substitutionality of carbon in SiGe was also confirmed by Fourier transform infrared spectroscopy measurements. MOS capacitors were fabricated by thermal oxidation (750°C) of the epitaxial Si cap on top of the SiGeC layer. Quasi-static and high frequency capacitance-voltage measurements show wellbehaved characteristics for the samples with carbon contents up to approximately 1%. Onedimensional Poisson simulations of the C-V curves were used to extract the valence band offset between Si and SiGeC. For a fixed germanium fraction, the offset decreases with increasing carbon content. However, for a given lattice mismatch, the offset for Si/Si1−x−yGexCy is larger than the measured value for Si/Si1−zGez.
How Surface Roughening and Dislocation Formation Mutually Influence Each Other During Heteroepitaxial Growth
Authors: Christiansen Silke , Albrecht M. , Michler H. , Strunk H.P.
Published: April 2011

Using finite elements we quantitatively calculate the inhomogeneous strain distribution associated with the so called crosshatch pattern. This pattern is a twodimensional, pseudoregular surface undulation that generally arises as an intermediate stage of heteroepitaxial growth of low misfitting semiconductor layers. This stage is characterized by an interplay of elastic and plastic relaxation processes. The calculations yield (i) the elastic strain energy density distribution and corresponding degree of elastic relaxation and (ii) the shear stress distribution in the glide system, in which misfit dislocations form. As a main result shear stresses due to the crosshatch pattern within the substrate are identified that cause misfit dislocations to multiply in the substrate.
Implant Enhanced Diffusion of Boron in Silicon Germanium
Authors: Fang Wingra T. C. , Griffin Peter B. , Plummer James D.
Published: April 2011

In this work, the inert and implant enhanced diffusion of boron in silicon germanium (SiGe) was studied by means of a boron box-shaped profile grown inside Si0.905 Ge0.095 or Si0.785Ge0.22 layers. The SiGe layers were capped with silicon for stability and to ensure no lattice damage in the SiGe layers during the implant. Assuming boron moves by interstitial-mediated diffusion in SiGe, the results suggest that decreases in the mobile boron diffusivity, not decreases in interstitial concentration, cause much of the decrease in average boron diffusivity with increasing Ge fraction. Implant enhancements decreased as the germanium percentages increased, possibly indicating higher interstitial concentrations in SiGe than in Si.
Luminescence in Si/Strained Si1−xGex Heterostructures
Authors: Sturm J.C. , Amour A. St. , Lacroix Y. , Thewalt M.L.W.
Published: April 2011

This paper quickly reviews the structure of band-edge luminescence in Si/strained Si1−xGex heterostructures, and then focusses on two recent developments -- the origin of “deep” sub-bandgap luminescence which is sometimes observed in structures grown by Molecular Beam Epitaxy (MBE) and the understanding of the temperature dependence of the band-edge luminescence (up to room temperature). Strong evidence will be presented that the origin of the deep luminescence is radiation damage, and that generated defects are segregated or trapped in the SilxGex layers. The modelling of the temperature dependence by twocarrier numerical simulation is presented for the first time. The work and experimental data show convincingly that the strength of the luminescence at high temperature is controlled by recombination at the top silicon surface, which in turn can be controlled by surface passivation. At high pump powers and low temperatures, Auger recombination reduces the lifetime in the Si1−xGex layers, and leads to a luminescence vs. temperature which is flat up to 250 K and which is reduced only by a factor of three at room temperature.
Heavy Phosphorus Doping in Molecular Beam Epitaxial Grown Silicon and Silicon/Germanium with a Gap Decomposition Source
Authors: Lippert G. , Osten H. J. , KrÜger D.
Published: April 2011

Donor-doping in silicon molecular beam epitaxy (MBE) is still an open problem, due to the low solid solubility and the strong segregation behavior (Sb, As) or to the high vapor pressure of the doping elements (P, As). Based on its high solubility elemental P2 would be the best candidate for heavy n-type doping. A new developed phosphorus source, based on the decomposition of solid GaP with a simultaneously mass separation of the parasitic Ga atoms has been applied. Homogenous P-doping higher than 1019 cm3 in Si and strained SiGe has been achieved. No surface accumulation of phosphorus was observed. The parasitic Ga incorporation is about three orders of magnitude below the P concentration. In this paper we will demonstrate the use of such cell to incorporate electrical active phosphorus during MBE growth. The incorporation probabilities into Si and strained SiGe will be compared. The dependence of segregation-/diffusion processes of phosphorus on growth temperature during the MBE will be shown. SIMS investigations on undoped Si layers reveal no P or Ga “memory effect” of the UHV equipment.
Challenges for Sige-Heterotechnology
Authors: Presting H.
Published: April 2011

Heterostructure devices composed of silicon, silicon-germanium or germanium layers have substantially broadened the spectrum of the well established Si microelectronics. The achieved results for devices, such as the SiGe base heterobipolar transistor (SiGe HBT), the n-. and p-channel SiGe modulation doped field effect transistor (SiGe MODFET) and optoelectronic devices (SiGe LED and photodiode) point to the outstanding potential of this novel heterosystem. Today the SiGe HBT is the world fastest Si based transistor with a wide application area from conventional microelectronic applications to microwave power generation in a frequency regime where up to now only III-V semiconductor devices have prevailed. In addition novel SiGe optoelectronic devices, such as SiGe LED and Si/Ge photodetector in the near infrared spectral region (1.3µ) could pave the way for Si based optical interconnect devices monolithically integrated on a Si IC chip (chip to chip coupling). Growth aspects, strain effects, band alignment and novel bandstructure effects in this material system will be reviewed, its effect on the device performance will be discussed.
Structural Properties of InAs/AlSb Superlattices
Authors: Jenichen B. , Neuroth H. , Brar B. , Kroemer H.
Published: April 2011

Short-period (InAs)6/(AlSb)6 superlattices (SL) with AlAs-like and InSb-like interfaces (IF) grown on a relaxed AlSb buffer layer are studied by X-ray reflectivity and diffractometry measurements. Reflectivity measurements reveal average IF roughnesses between 0.6 and 1.0 nm. Measurements of the diffuse scattering show that the roughness is highly correlated from layer to layer. Triple crystal area scans illustrate that the inhomogeneous deformation of the buffer layer leads to a certain symmetric peak broadening. In the case of AlAs-like IFs an additional broadening of the SL peaks reveals lattice parameter gradients over the superlattice. This asymmetric peak broadening may be attributed to a further relaxation of the superlattice, which is inhomogeneous with depth. The diffusion of As into the AlSb layers leads to a peak shift and modifies the intensity ratios of the different satellite reflections. The best structural quality is achieved for superlattices with InSb-like IFs.
Dynamics of Surface Segregation During InGaAs Mbe
Authors: Evans Keith R. , Kaspi R. , Ehret J.E. , Skowronski M.
Published: April 2011

The dynamics of In surface segregation during molecular beam epitaxy growth of In.22Ga.78As/GaAs quantum wells (QWs) are studied by temperature-programmed desorption (TPD). The TPD spectra show two In peaks: a low temperature (low-T5) peak and a high temperature (high-T5) peak, which arise from desorption of surface segregated In and dissociation of the underlying InGaAs lattice, respectively. Integration of the low-Ts peak provides quantitative determination of the surface segregated In population ΘIn, as a function of InGaAs layer thickness, incident arsenic dimer flux [(Fi(As2)], InGaAs growth temperature, and GaAs cap thickness. The surface segregated In population ΘIn, is observed to grow with InGaAs thickness, until reaching a temperature-dependent steady state value between 1.0 and 2.0 monolayers after approximately ten monolayers of growth, and then decays during GaAs overlayer growth. The variation of ΘIn with thickness closely mimics the resulting vertical composition profile, which is characterized by an In-depleted bottom interface and segregation of In into the GaAs cap. Based on these results, a sequence of: 1) In predeposition, 2) InGaAs growth, and 3) thermal desorption of Eh is proposed to produce a more square InGaAs/GaAs QW than can be obtained by more standard MBE approaches.
Surfactant-Mediated Growth of Aigaas by Molecular Beam Epitaxy
Authors: Kaspi Ron , Evans Keith R. , Reynolds Don C. , Brown Jeff , Skowronski Marek
Published: April 2011

Antimony was used as a surfactant during solid-source molecular beam epitaxy of AIGaAs layers. A steady-state surface-segregated population of Sb was maintained at the AIGaAs growth surface by providing a continuous Sb2 flux to compensate for loss due to thermal desorption. Above ∼ 650 °C, the incorporation rate of Sb was negligible, thereby allowing the deposition of AlGaAs layers despite the presence of Sb at the surface. A significant improvement in the optical quality of Al0.24Ga0 76As layers was observed by photoluminescence. In addition, extended reflection high energy electron diffraction oscillations and a reduction in Al0.24Ga0.76As surface roughness was observed when Sb was employed as a surfactant.
On thon the Photoemission from Quantum Confined Strained III–V Systems
Authors: Ghatak Kamakhya P. , Nag B. , Mazumder G.
Published: April 2011

In this paper we have studied the photoemission from quantum wells (QW), quantum wells wires (QWWs) and quantum dots (QDs) of quantum confined strained III–V compounds on the basis of a newly formulated electron dispersion law. It is found taking such quantum confined Hg1–xCdxTe and In1–xGaxAsyP1–y lattice matched InP as examples that the photoemission increases with increasing energy of the incident photons in a ladder like manner and also exhibits oscillatory dependences with changing electron concentration and film thickness respectively for all types quantum confinement. The photoemitted current is greatest in strained QDs and least in unstrained QWs. In addition the theoretical results are in agreement with the experimental datas as given elsewhere.
Spatial Concentrations of Silicon Atoms in RF Discharges of Silane
Authors: Roth R. M. , Spears K. G. , Wong G.
Published: April 2011

A capacitively coupled rf glow discharge of silane in argon was studied to determine the spatial concentration of silicon atoms. Laserinduced fluorescence was used to determine the ground state concentration profiles. The fluorescence profiles clearly show the sharp boundaries of the sheath regions. The dc bias voltage, silane mole fractions, flow rates, and chamber pressure were all varied to establish the sensitivity of the silane profiles. The existing theory of sheath formation is used to qualitatively understand the existence of sharp spatial boundaries and the sensitivity of the anode sheath region to plasma chemistry.
Effects of the Combined Exposure of Silicon to Beams of Low-Energy Argon Ions and Halogen-Containing Molecules
Authors: Kolfschoten A. W.
Published: April 2011

This paper reviews our results of modulated ion beam studies of the ion-assisted etching of Si. It is shown that the experimental data of the Si(C12, Ar+) reactive system can be described by a model based upon an ion-bombardment induced amorphousness of the Si substrate and the formation of a mixed surface region of several atomic layers of chlorine, argon and silicon. It is also shown that the model is in general agreement with the experimental data of the Si(XeF2, Ar+) and C(H, Ar+) systems.
Cl2 Chemically Assisted Sputter-Etching of Permalloy
Authors: Vasile M. J. , Mogab C. J.
Published: April 2011

Redeposition-free patterns have been etched in 3000Å thick permalloy films using the technique of chemically assisted sputter-etching. This technique involves the simultaneous adsorption of a reactant gas from a molecular beam source and normally incident argon ion bombardment. Experimental conditions with Cl2 adsorption can be maintained to etch the permalloy at 80Å/min and to etch positive photoresist at 110Å/min. These etch rates are not significantly different from rates obtained with argon ion milling, even though the permalloy surface is known to incorporate Cl2. Re-deposited material observed with Cl2 chemically assisted sputtering has been shown to be water soluble, and can be completely removed from feature side-walls prior to stripping the resist. Linewidth measurements show that no feature broadening occurs on 2 micron line and space patterns, within the precision of the measurement (±0.2 micron).
Applications of Optical Emission Spectroscopy to Semiconductor Processing
Authors: Shabushnig John G. , Demko Paul R. , Savage Richard N.
Published: April 2011

Optical emission spectroscopy (OES) has proven to be a valuable tool in the development and production of state-of-the-art semiconductor devices. Application to the plasma etching of a variety of materials necessary for integrated circuit fabrication is discussed, with particular emphasis placed on etch endpoint analysis. The utility of OES techniques in monitoring photolithographic processes is also presented.
Silane Discharge Gas and Surface Reactions
Authors: Gallagher Alan
Published: April 2011

In order to control the quality and properties of hydrogenated amor-phous silicon (a–Si:H) semiconductors produced by discharge deposition, we would like to control the gas species produced in the discharge and to understand how these deposit and influence the film properties. One would like to separately consider the gas processes that yield the mix of species arriving at the surface, and then the surface processes. I will somewhat follow that separation here, but it appears that many of the species found in the gas may, in fact, be released from the surface. Thus, the gas species appear to result from gas and surface reactions, and a sequential separation is actually not possible. Similarly, the study of the surface deposition process requires forming various radical species as well as an a–Si:H surface, which inevitably will involve the gas processes. Thus we really have coupled problems.
Fabrication of Semiconductor Nanostructures With an Atomic Force Microscope
Authors: Snow E. S. , Campbell P. M.
Published: April 2011

An AFM-based nanolithography process is described. We employ the local electric field of a metal-coated AFM tip which is operated in air to selectively oxidize regions of a H-passivated Si surface. The resulting oxide, ∼ 3 nm thick, is used as a mask for selective etching of the unoxidized regions of Si. This AFM-based fabrication process is fast, reliable, simple to perform and is well suited for device fabrication. We apply this technique to the fabrication of Si and GaAs nanostructures, as well as to the fabrication of a nanometer-scale Si side-gated transistor. In addition, we discuss the ultimate resolution limits of the technique.
SPM-Based Lithography for Electronics Device Fabrication: New Strategies and Directions
Authors: Dagata J. A.
Published: April 2011

Direct patterning of a semiconductor surface to produce an ultrathin oxide mask has proven to be a promising approach for integrating lithographic methods based on scanned probe microscopy (SPM) into existing electronics device processing. The resulting masks are capable of withstanding the necessary etching and thermal cycling required for pattern development. Recent work has validated the concept for the fabrication of silicon devices. The current challenges which face this active research area will now require a detailed, predictive understanding of the mechanism responsible for oxidation within an SPM junction in order for the process to optimized with respect to write speed, resolution, and reliability.
Creating Three-Dimensionally Confined Nanoscale Strained Structures Via Substrate Encoded Size-Reducing Epitaxy and the Enhancement of Critical Thickness for Island Formation
Authors: Konkar A. , Madhukar A. , Chen P.
Published: April 2011

Substrate encoded size-reducing epitaxy (SESRE) is utilized to fabricate, in-situ, threedimensionally confined InAs volumes on <100> oriented square mesas patterned onto GaAs(001) substrates. As a function of InAs deposition thickness two remarkable results are found: (i) the strain relief available in mesas of linear size ≤ 100 nm allows the mesa top InAs layers up to thickness ∼ 11 ML to remain coherent and maintain 2D morphology even though on unpatterned substrates onset of 3D island formation at ∼ 2 ML InAs is well documented. (ii) With increasing deposition, once the InAs thickness on mesa tops of linear size ∼ 75 nrn reaches ∼ 11 ML, no further growth occurs even for deposition amounts in excess of twice this value. This suggests complete migration of In away from the mesa top to the sidewalls once the InAs thickness on the mesa top reaches ∼ 11 ML even though, at the early stages of deposition, In migrates from the sidewalls to the mesa top. A strain-induced “self-limiting” growth behavior on sub 100nm mesas is thus indicated for the first time.
Probing the Limits of Silicon-Based Nanoelectronics
Authors: Wind S. J. , Taur Y. , Mii Y. , Frank D. J. , Wong H.-S. , Buchanan D. A. , Rishton S. A. , Bucchignano J. J. , Lii Y. , Jenkins K. A.
Published: April 2011

The ability to reduce device features to increasingly smaller dimensions offers the potential for remarkable circuit performance and low power consumption. CMOS (Complementary Metal-Oxide-Semiconductor) devices with 100 nm channel lengths offer a 2X performance gain over 0.25 μm technology at a reduced power supply as well as the potential for a 20X reduction in active power at comparable performance levels. Continued scaling of devices beyond 100 nm dimensions faces various fundamental limitations. Overcoming these limitations will require technological innovation in both device design and fabrication.
Silicon Nanofabrication and Chemical Modification by UHV-STM
Authors: Lyding J. W. , Shen T.-C. , Abeln G. C. , Wang C. , Foley E. T. , Tucker J. R.
Published: April 2011

Patterning on the 10 Å size scale has been achieved with a UHV-STM for Si(100)-2×1:H surfaces. Hydrogen passivation serves as a monolayer resist which the STM locally desorbs, exposing clean Si(100)-2×1 for selective chemistry. Two mechanisms have been identified for hydrogen removal by STM electrons: in the field emission regime direct electron stimulated desorption of hydrogen occurs whereas, in the lower energy tunneling regime, hydrogen desorption results from vibrational excitation of the Si-H bond at high tunneling currents. Furthermore, we find that atomic hydrogen is liberated in contrast to molecular hydrogen evolved during thermal desorption. Selective oxidation and nitridation of the STM-patterned areas has been achieved.
High Rate Dry Etching of GaN, AIN and InN in ECR Cl2/CH4/H2/Ar Plasmas
Authors: Vartuli C. B. , Pearton S. J. , Abernathy C. R. , Shul R. J. , Kilcoyne S. P. , Crawford M. Hagerott , Howard A. J. , Parmeter J. E.
Published: April 2011

Etch rates for binary nitrides in ECR Cl2/CH4/H2/Ar are reported as a function of temperature, rf-bias, microwave power, pressure and relative gas proportions. GaN etch rates remain relatively constant from 30 to 125 °C and then increase to a maximum of 2340 Å-min−1 at 170 °C. The AIN etch rate decreases throughout the temperature range studied with a maximum of 960 Å-min−1 at 30 °C. When CH4 is removed from the plasma chemistry, the GaN and InN etch rates are slightly lower, with less dramatic changes with temperature. The surface composition of the III–V nitrides remains unchanged over the temperatures studied. The GaN and InN rates increase significantly with rf power, and the fastest rates for all three binaries are obtained at 2 mTorr. Surface morphology is smooth for GaN over a wide range of conditions, whereas InN surfaces are more sensitive to plasma parameters.
Lateral Diffusion Limitations of Ingaas/Gaas for Nanostructure Fabrication
Authors: Redinbo Gregory F. , Craighead Harold G.
Published: April 2011

We have investigated the technique of implantation enhanced interdiffusion (IEI) for optical nanostructure fabrication in strained InxGal-xAs/GaAs quantum wells. Implantation masks with widths from 40 nm to 40 μm were fabricated on the surface of InxGal-xAs/GaAs (x+0.1, 0.2) 3.5 nm quantum well material which was implanted with 100 kV As+ with doses ranging from 5 × 1012 to 8.5× 1013 ions/cm2. After mask removal and a high temperature anneal, cathodoluminescence (CL) spectroscopy was used to investigate the optical properties of the resulting structures. We have measured electron-heavy hole recombination energy shifts due to quantum well interdiffusion of up to 60 meV for the highest doses used here with broad area implants. However, while quantum well emission under large (40 μm) masks is preserved, smaller masks show an emission blue shift not due to ions penetrating through the mask. A simple model of the width dependence of this shift yields an enhanced lateral diffusion length of approximately 1 μm which is many times larger than the lateral straggle of the implanted As+. We conclude that lateral diffusion effects may impose a limit on nanostructure fabrication in the InxGal-xAs/GaAs system with this technique.
Metal-Parylene Interconnection Systems
Authors: Dabral S. , Zhang X. , Wang B. , Yang G.-R. , Lu T.-M , McDonald J.F.
Published: April 2011

This paper reports the results of a study to integrate a metal-parylene interconnection system. The advantages and issues are highlighted. Fabrication steps for packaging geometries as well as proposed fabrication steps for VLSI applications are discussed. The relevant material properties for interconnection system design have been compiled.
High Temperature Alternating Copolymers As Dielectric Materials: Synthesis, Structure And Properties
Authors: Ree M. , Goh W.H. , Park J.-W. , Lee M.-H. , Rhee S.B.
Published: April 2011

A new diamine monomer, N,N'-bis(4-aminophenyl)-2,5-(diisopropoxycarbony)benzene-l,4-dicarboxamide was synthesized. Using the diamine, several alternating copolyimide precursors were successfully synthesized by its condensation polymerization with dianhydrides. The structure and properties (mechanical properties and thermal expansivity) of alternating copolyimides imidized thermally were characterized, and compared with those of the corresponding randomcopolyimides prepared from the copoly(amic acid)s. The alternating copolyimides exhibited relatively higher chain order and in-plane orientation in films than the random copolyimides. The higher chain order and in-plane orientation led to the higher tensile modulus and lower thermal expansivity in the alternating copolyimides. Such effect of comonomer sequence was found to be highly pronounced in copolyimides consisting of comonomers which have a large difference in the chain rigidity. It was demonstrated in this study that the formation of alternating copolyimides is a suitable route to improve the performance of properties.
Low Dielectric Constant Thermostable Polymers
Authors: Sillion B. , Rabilloud G. , Garapon J. , Gain O. , Vallet J.
Published: April 2011

The dielectric properties of the heat-resistant heterocyclic polymers are governed by their chemical structure and the absence of unwanted dipoles. A polyphenylquinoxaline is taken as an example of the effect of the dipole symmetry. In the particular case of polyimides, it is obvious that the dehydrocyclization of the intermediate polyamic acid has to be completed to produce the lowest achievable permittivity. This is illustrated by the polycondensation in solution of the polyimides based on 4,4'-(9H-fluoren-9-ylidene)-bisbenzeneamine. In addition, the spatial conformation of the macromolecular chain can also play an important role. The chemistry of a polyimide prepared from 4,4'-(1,3-benzenedicarbonyl) bis(1,2-benzenedicarboxylic acid dianhydride) allows to discuss this topic. However, a dielectric constant of 2.7 seems to be the ultimate value achievable for dense films prepared with the most performing polymers. The introduction of homogeneously distributed micro-voids allows the preparation of dielectric films with a permittivity lower than 2.0. The modification of a polymer with tertiobutyl carbonate (t.BOC) groups is a promising approach because it offers a large processability window.
A Multilayer Approach to the Design of Fine Dispersed Metallic two Component Materials
Authors: Eisenmenger-Sittner C. , Behr R. , Bergauer A. , Hejl A. , Bauer W.
Published: April 2011

In the common applications of multilayer materials a strict separation of the single layers as well as very sharply defined interlayer interfaces are highly desired. On the otherhand there exists a large class of materials which consist of small particles dispersed in a matrix with mechanically different properties.

In this paper the theoretical concepts of producing this second class of materials via a multilayer deposition approach are presented. Although the focus is on the preparation ofsputter deposited immiscible metallic two component materials, the concepts presented arevalid for a greater variety of materials and deposition techniques.

The phase distribution as well as the roughness evolution of a material consisting of oneisland- and one layer forming component is quantitatively described by considerations about the minimization of the surface free energy of the whole system. On the atomistic level the formation of critical nuclei on an arbitrarily shaped surface is briefly discussed and a connection to the thermodynamic minimization of the surface free energy is made.
Charge Transfer from PbS Quantum Dots to Insulating TiO2 Matrix
Authors: Könenkamp R. , Hoyer P.
Published: April 2011

We report on the photoconductivity of thin films consisting of a porous nanocrystalline TiO2 matrix and quantum size PbS clusters adsorbed on the inner surfaces of theTiO2. The PbS clusters are typically a few nm in size and are not connected. Due to quantum confinement the bandgap of the clusters is widened to around 2 eV from the 0.41 eV value for PbS bulk. The clusters thus absorb in the visible spectrum. However, due to their spatial separation, photoconductance through the film requires carrier transfer through the TiO2 matrix. Our data show this to occur only for clusters <25 Å, for which the conduction band edge lies above the TiO2 conduction band edge. For larger clusters the band alignment at the TiO2/PbS interface appears to be unfavorable for carrier transfer; these clusters do not contributeto photoconduction.
Magnetic Properties and Structural Transformation in Copper-304 Stainless Steel Multilayer Materials
Authors: Parvin K. , Weathersby S.P. , Barbee T.W. , Weihs T.P. , Wall M.A.
Published: April 2011

Multilayer foils of Cu-304 stainless steel (304SS) with equal layer thicknesses in the range t=5.0-500 Å and total thicknesses 10-20 μm have been synthesized using magnetron sputtering at ambient substrate temperature. The x-ray diffraction data of as-deposited films show two structural regimes: small thickness (t=5-10 Å) which is characterized by epitaxial FCC growth of 304SS on copper, and large thickness (t=13.5-500 Å) which shows epitaxial FCC 304SS growth near the interface and BCC 304SS growth away from the interface. FCC structured films show very small magnetic moments at room temperature similar to bulk 304SS stable FCC phase. However, a strong magnetic moment is observed for thicker samples due to ferromagnetic metastable 304SS BCC phase. Two opposing transformations occur in the 304 layers as the samples are heated. The first transformation is from the metastable BCC 304SS to the stable FCC phase. This transformation produces a strong drop in magnetic moment and is clearly visible in the large period multilayers which contain high volume fractions of BCC 304SS. The second transformation is from the original FCC phase to a new stable BCC phase in the 304SS near the copper-304SS interfaces.The transformation is produced by diffusion of nickel from the 304SS into the surroundingcopper and the chemical destabilization of the FCC phase which starts near 400 ºC.This transformation produces a sharp increase in magnetic moment. The magnetic signal drops to zero near 675 ºC which is the Curie temperature of ferromagnetic BCC Fe.75 Cr25..
Absolute Calibration of Sims Depth Profiles of a-SiNx:H/a-Si:H and a-SiOx:H/a-Si:H Multilayers
Authors: Li Jianwei , Chabala Jan M. , Levi-Setti Riccardo
Published: April 2011

We calibrated secondary ion mass spectrometry (SIMS) depth profiles of a-SiNx:H/a-Si:H and a-SiOx:H/a-Si:H multilayer samples by comparing them to high-spatial-resolution SIMS maps of cross sections through the layers. Both profiles and images were acquired with a focused scanning 45 keV Ga+ ion microprobe. During depth profiling an area gating technique was used to improve depth resolution. At the beginning of the profile the resolution was 8 nm. By cutting the multilayer films at a small angle through the layers, we obtained SIMS images of cross sections through thesemultilayer samples. The resolution along the expanded direction is about 10 nm. By comparing the depth profiles and the cross section images, we determined the ionbeam-induced atomic mixing in the samples, as a function of depth and the sputtering yield for each layer.
Structure of Magnetic Multilayers and Magnetoresistance
Authors: Shinjo Teruya
Published: April 2011

Magnetoresistance (MR) studies on non-coupled type multilayers are briefly surveyed. As a possible method to enhance MR effect, measurements with current in outof–plane directions are described. Non–coupled type multilayers were prepared on microstructured substrates with V–shaped grooves to measure the MR in a new geometry, with current at–an–angle–to–the–plane, and actually an enhanced MR ratio was observed.
Characterization of Asymmetric Polydiacetylene Ultrathin Films
Authors: Cheong D. W. , Shivshankar V. , Wang H. C. , Sung C. M. , Kumar J. , Tripathy S. K.
Published: April 2011

Nonlinear optical (NLO) ultrathin films of a preforrned asymmetric polydiacetylene have been fabricated by Z-type Langmuir-Blodgett film deposition from the air-water interface. Induced in-plane orientation of the polydiacetylene backbone on the substrates has been confirmed by UV/Vis, FT-IR dichroism, and degenerate four wave mixing (DFWM) studies. All the measurements indicate that the backbone is prefe rentially oriented along the dipping direction. Second harmonic generation study suggests that the LB multilayers form an asymmetric structure (Z-type) due to the accumulation of 2-dimensional ordered monolayer and the dominant induced second order polarization is in the plane of the film. The film morphology and molecular orientation have been investigated by atomic force microscopy (AFM).
Solid State Reaction of Al and Zr in Al/Zr Multilayers: A Calorimetry Study
Authors: Blobaum K.J. , Weihs T.P. , Barbee T.W. , Wall M.A.
Published: April 2011

The exothermic, solid state reaction of Al and Zr has been studied in thick AL/Zr multilayers using Differential Scanning Calorimetry and X-ray diffraction. The multilayersamples were magnetron sputter deposited into highly textured alternate layers of Al and Zr with nominal composition A13Zr. The samples used in this study were 47μm thick with a 427Å period. When samples were isochronally scanned from 25º to 725ºC, a large exotherm at ˜350ºC was followed by one or two smaller exotherms at ˜650ºC. The first exotherm is dominated by a diffusionbased reaction of Al and Zr that produces two phases in isochronal scans: amorphous AI-Zrand cubic A13Zr, and two additional phases in isothermal anneals: A12Zr and tetragonal AI3Zr. The exothermic heat from this multi-phase reaction is measured using isochronal scans and isothermal anneals, and the heat flow is analyzed using a l-D diffusion based model. An average activation energy and a diffusion constant are determined. In the isothermal scans, the total exothermic heat increases linearly with √ime, and layer thicknesses vary linearly with heat.
In-Situ Observation of Stress in Cu/Pd Multilayers
Authors: Ueda T. , Simenson G.F. , Nix W.D. , Clemens Bruce M.
Published: April 2011

Stress evolution was studied during growth of Cu/Pd multilayers using an in-situ, laserbased wafer curvature technique which allowed measurement of stress changes associated with sub-monolayer thickness increases. The apparent stress in the Cu layers changes during growth, from compressive, for thickness less than about 0.5 nm, to tensile for thicknesses above this. The stress behavior in the Pd layers depends on the thickness of the underlying Cu layer. Pd deposited on thick (2 nm) Cu layers is under an apparent compressive stress, while Pd deposited on thin (< 1 nm) Cu layers is initially under a tensile stress but changes to a compressive stress at about 0.5 nm. The overall compressive stress maxima observed in multilayers at a bilayer period of 2 nm is explained by this in-situ behavior. The stress behavior in this system is consistent with either island growth of Cu, or thickness dependent alloying behavior, or both.
Crystallization in Metal-Metalloid Multilayers
Authors: Sinclair R. , Konno T. J. , Itoh T. , Zhu N. C.
Published: April 2011

We have studied the reactions which occur in metal-metalloid multilayers made from elements which have binary eutectic phase diagrams. The metal mediates crystallization of the amorphous as-deposited metalloid by crystal nucleation inside the metal layer followed by rapid diffusion through the metal from amorphous to crystalline phases. The metalloid crystallization temperature is significantly reduced by this reaction. Systems showing this behavior are Al-Si, Ag-Si, Ag-Ge, Co-C, Ni-C and Fe-C. We believe, therefore, that it is a general phenomenon which we have now extended to the case of Ag-SiC.
Residual Stress, Mechanical Behavior and Electrical Properties of Cu/Nb Thin-Film Multilayers
Authors: Griffin A. J. , Embury J. D. , Hundley M. F. , Jervis T. R. , Kung H. H. , Scarborough W. K. , Walter K. C. , Wood J. , Nastasi M.
Published: April 2011

The effect of compositional wavelength on the residual stress, electrical resistivities and mechanical properties of Cu/Nb thin-film multilayers sputtered onto single-crystal Si substrates was evaluated. Electrical resistivities were measured down to 4 °K using a standard four-point probe measurement system. A differential specimen-curvature technique was used to detennine residual stress, and a mechanical-properties microprobe was employed to obtain hardness and elastic modulus. Characterization techniques included profilometry, Ion-Beam Analysis (IBA) and Transmission Electron Microscopy (TEM). The hardness of the Cu-Nb multilayers increased with decreasing compositional wavelength so that the layered structures had hardness values in excess of either of the constituents and the hardness predicted by the rule of mixtures. A peak in the net residual compressive stress of the multilayers was observed at a compositional wavelength of 100 nm. No resistivity plateau was observed within the composition wavelength range studied.
Interfacial Reactions and Thermal Stability of Ultrahigh Vacuum Deposited Multilayered Mo/Si Structures
Authors: Liang J.M. , Chen L.J.
Published: April 2011

Interfacial reactions and thermal stability of ultrahigh vacuum deposited multilayered Mo/Si structures have been investigated by high resolution transmission electron microscopy in conjunction with fast Fourier transform and auto–correlation function analysis. For samples with nominal atomic ratios Mo:Si = 1:2 and 3:1, well defined multilayered Mo/Si structures were obtained after annealing at 250 °C for 30 min. On the other hand, distinct multilayered MoSi2/Si structure was formed only for Mo:Si = 1:2 samples after annealing at 650 °C for 1 h.

Multiphases were observed to form simultaneously in samples annealed at 400–500 °C. After 650 °C annealing for 1 h, tetragonal MoSi2 was the only silicide phase observed for the Mo:Si = 1:2 samples, whereas both tetragonal and hexagonal MoSi2 were present in Mo:Si = 3:1 samples. The stability of the multilayered Mo/Si structures was found to depend critically on the atomic ratios of constituent elements, bilayer period and annealing conditions. The results are interpreted in terms of the delicate balance between intermixing of constituent atoms and silicide formation.
Production of Mo/si Multilayers At Increased Substrate Temperatures: The Effect On D-Spacing, Interface Roughness and Density.
Authors: Voorma H.-J. , Louis E. , Koster N.B. , Bijkerk F. , der M.J. van
Published: April 2011

To obtain the optimal growth conditions of Mo/Si multilayer structures, produced with e-beam evaporation, the effect of using enhanced deposition temperatures is investigated in detail. We describe the variations of the structure for multilayers deposited at substrate temperatures ranging from 300 K to 550 K. A temperature of 490 K was found to be the optimum resulting in low interface roughness and moderate inter-diffusion. The decrease of the dspacing at the optimum substrate temperature, compared to coatings deposited at room temperature, is explained by a change in free volume of the Si layer.
Evolution of Co/Ge Films on Si(100) and Ge(100) Substrates
Authors: Carlow G.R. , Lowes T.D. , Grunwell M. , Zinke-Allmang M.
Published: April 2011

We present results on the evolution of Co/Ge films on Si(100) substrates. Room temperature deposition of 18 nm thick Ge films followed by 5 nm thick Co films was done by Molecular Beam Epitaxy (MBE) and then post-deposited annealing was done at 700 C. Using combinations of Scanning electron microscopy, Auger electron spectroscopy and Rutherford backscattering spectroscopy, we determine that the Co and Ge are clustering on the Si surface at these annealing temperatures. During the clustering, the Co is diffusing into the Si substrate leaving a Ge-rich clustered morphology. To test the effect of the Si substrate on the evolution of the films, Co films were deposited on Ge(100) substrates and annealed at 700 C. Clustered morphologies are seen on the Ge substrates and Co in-diffusion is also occurring. The morphologies on the Ge substrates are significantly different from those on the Si substrates.
An Electrical Model for Multilayered n+/n and Heterostructure Planar Ohmic Contacts
Authors: Reeves Geoffrey K. , Leech Patrick W. , Harrison H. Barry
Published: April 2011

The standard Transmission Line Model (TLM) is an electrical network that is commonly used to model planar two-layer (metal-semiconductor) ohmic contacts. More complex multilayered planar structures have led to the development of more complex models. A Tri-Layer Transmission Line Model (TLTLM) was recently proposed in order to more accurately represent an alloyed ohmic contact. The TLTLM also enables other layered planar contact structures such as non-alloyed n+/n, heterojunction and metal-silicide-silicon contacts to be analysed. In this paper, it is shown that when the TLTLM is combined with a modified TLM network, important device properties such as contact and parasitic resistance can be derived for device structures using several epilayers such as FET's. An example is given of the current distribution in an FET and the calculation of the parasitic resistance in the gate-drain channel and the contact resistance of the drain.
Elastic Properties of CVD Diamond Via Dynamic Resonance Measurements
Authors: D'Evelyn Mark P. , Slutz David E. , Williams Bradley E.
Published: April 2011

Control of the mechanical properties of CVD diamond is essential to achieve optimal performance in various applications. While several methods have been applied to the measurement of the Young's modulus of thick-film CVD diamond, in general these methods are not suitable for diamond characterization on a production scale. In addition, many of these methods cannot determine the shear modulus (or Poisson's ratio), which is necessary for a complete description of the elastic properties. We have developed a simple dynamic resonance method for determining both the Young's and shear modulus of free-standing CVD diamond in the shape of rectangular plates or round disks. The specimen is supported along nodal lines of flexural or torsional modes. Oscillations induced by impact from a falling ceramic bead are sensed by a microphone, and the resonant frequencies are determined by a signal analyzer. The Young's and shear modulus are calculated from the frequencies of the fundamental flexural and torsional modes, respectively, using quasi-analytic formulas. CVD diamond grown by several methods routinely achieves Young's and shear modulus values above 1000 GPa and 500 GPa, respectively, in good accord with theoretical values for pure polycrystalline diamond.
An Indentation Test for Measuring Adhesion Toughness of Thin Films Under High Residual Compression With Application to Diamond Films
Authors: Drory M. D. , Hutchinson J. W.
Published: April 2011

Adhesion measurement of brittle coatings on ductile substrates is examined with emphasis on diamond–coated metals. The experimental aspects of determining film adhesion is discussed through measurement of the interface toughness by a brale indentation method.
Thin Film Decohesion and Its Measurement
Authors: Bagchi A. , Evans A. G.
Published: April 2011

The mechanics of thin films are used to define quantitative procedures for predicting interface decohesion motivated by residual stress. The emphasis is on the role of the interface debond energy, especially methods for its accurate and reliable measurement. Experimental results are reviewed and possible mechanisms are discussed.
Shock Wave Synthesis of Diamond and other Phases
Authors: Decarli Paul S.
Published: April 2011

Shock wave synthesis of diamond was an unexpected result of experiments designed to explore the effects of shock waves on a variety of materials. The initial announcement in 1959 was controversial; shock synthesis of diamond had been shown to be unlikely, on the basis of kinetic arguments. Jamieson confirmed the identification and suggested a diffusionless mechanism, c-axis compression of rhombohedral graphite. Subsequent work has provided strong evidence that shock wave synthesis of cubic diamond is a conventional thermally activated nucleation and growth process. Thermal inhomogeneities provide the requisite high temperatures; quenching via thermal equilibration is implicit in the process. Shock synthesis of adamantine BN phases appears to be quasi-martensitic; a martensitic mechanism may partially account for the Lonsdaleite (hexagonal diamond) observed in some meteorites and in some artificial shock products. Diamond is also formed as a detonation product in oxygen-deficient explosives. The polycrystalline product of shock synthesis is similar to natural carbonado. The association of carbonado with an ancient giant impact crater is noted.