bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization Of Glass-Ceramic Dielectric Thick Films With Cu Conductors for Multilayer Packages
Authors: Cho Yong S. , Koyuncu Metin , Schulze Walter A. , Amarakoon Vasantha R. W.
Published: April 2011

Compatibility and characteristics of multilayer dielectric thick films with Cu interlayers are influenced by composition and processing parameters. In this work, cordierite based dielectric thick films on a Cu plated alumina substrate were investigated in terms of microstructure and property by changing composition of oxide additives, PbO and Cu2O for a given heating schedule. A nonstoichiometric cordierite composition, 2.4MgO 2Al2O3 5SiO2 was used with nucleating agents, B2O3 and P2O5. The dielectric ink consisting of cordierite glass frit and acrylic based binder vehicles was deposited on oxidized Cu layers via screen printing. The thick film layers were fired at 950°C for 30 min in N2 atmosphere. Dissolution of the oxidized Cu into the cordierite layer was observed. The addition of a small amount of Cu2O to the cordierite layer was effective in preventing the dissolution and enhancing thermal expansion. Crystallization was also influenced by the Cu2O addition. A lower activation energy value of 79 kcal/mol for crystallization, calculated from DTA runs, suggested that Cu20 could be used to form the cordierite glass-ceramic at a lower temperature. In the case of no additive, the activation energy for crystallization was 98 kcal/mol. The addition of Cu2O increased dielectric constant. For 3wt% PbO and 1wt% Cu2O, the dielectric constant and loss were determined at 1 MHz as 6.1 and 0.0046, respectively.
Electron-Beam Moiré Study Of Local Deformation In Conductive Adhesives
Authors: Drexler E. S. , Berger J. R.
Published: April 2011

Electron-beam (e-beam) moiré is a recently developed technique for micro-mechanics. It allows one to combine the resolution of the scanning electron microscope (SEM) with the strain measurement capabilities of moiré. With e-beam moiré we are able to study locally the effect of temperatures ranging between −50 and 150 °C on conductive adhesives (CAs) and their interfaces. With this technique we measured the local displacements due to the thermal expansion of the copper and the CA. The modified lap-shear specimens were made of copper-to-copper attached with CAs and cured according to the manufacturer's instructions. A cross section of each material was polished and a moiré grating was written on the surface using e-beam lithography techniques. Digital images of the moiré were collected from the SEM at regular temperature intervals. The images were compared and the displacements measured. Local regions of large displacements were observed in the paste specimen. Permanent deformations in the film specimen resulted from exceeding the glass transition temperature of the CA.
Foamed Elastomers For Packaging Interconnections, Testing And Burn‐In Applications
Authors: Liao Y. , Shih D.Y. , Hedrick J.L. , Lauro P.A. , Fogel K.E.
Published: April 2011

The present study is directed to a new foamed elastomer composition for supporting the interconnecting conductive wires in the Elasticon™ interposer connector for the packaging interconnections, test and burn‐in applications. The compressibility of interposer connector can be tailored by introducing controlled volume fraction of foam into elastomer or filled elastomer. The foamed elastomer has been successful applied to a new Ball Grid Array (BGA) module testing socket to meet the contact force requirement.
Tunnel Effects in Luminescence Spectra of InGaN/AlGaN/GaN Light-Emitting Diodes
Authors: Yunovich A. E. , Kovalev A. N. , Kudryashov V. E. , Manyachin F. I. , Turkin A. N. , Zolina K. G.
Published: April 2011

Tunnel effects in luminescence spectra and electrical properties of blue InGaN/AlGaN/GaN LEDs were studied. The tunnel radiation in a spectral region of 2.1–2.4 eV predominates at low currents (J<0.2 mA). The role of tunnel effects grows as the maximum of the main blue line in LEDs is shifted to short wavelengths. The position of the tunnel maximum ћωmax is approximatly proportional to the voltage eU. The spectral band is described by the theory of tunnel radiative recombination. Current-voltage characteristics have a tunnel component at low direct and reverse currents. The distribution of charged impurities was received from dynamic capacitance measurements. There are charged layers at heterointerfaces and adjacent compensated layers in the structures. There is a high electric field in the active layer. The energy diagram is analysed.
Observation of Near Band Edge Transition in Aluminum Nitride Thin Film Grown by MOCVD
Authors: Tang Xiao , Hossain Fazla R. B. , Wongchotigul Kobchat , Spencer Michael G
Published: April 2011

The Cathodoluminescence (CL) measurements of undoped and carbon doped aluminum nitride (AlN) thin films near the band-edge region were performed at 300, 77 and 4.2 K, respectively. These films were grown on three different substrates: 6H-SiC, 4H-SiC and sapphire. A dominant peak was observed in undoped samples around 5.9 eV. This peak can be further resolved into three distinct peaks at 6.05, 5.85, and 5.69 eV for AlN on sapphire. The temperature dependence of the peak positions and line widths were investigated. These peaks are believed to be due to exciton recombination. Also, the absorption spectra of carbon doped AlN on sapphire were analyzed to study the Urbach tail parameters which play an important role in near band-edge transitions.
Visible Blind uv GaN Photovoltaic Detector Arrays Grown by rf Atomic Nitrogen Plasma MBE
Authors: Van Hove J.M. , Chow P.P. , Hickman R. , Wowchak A.M. , Klaassen J.J. , Polley C.J.
Published: April 2011

RF atomic nitrogen plasma molecular beam epitaxy (MBE) was used to deposit gallium nitride (GaN) p-i-n junction photovoltaic detectors on (0001) sapphire. The detectors consisted of a bottom contact layer n-type silicon doped to 5 × 1018 cm−3. The intrinsic layer was undoped and possessed an n-type background carrier concentration of 1 × 1016 cm−3. The top /p-GaN layer was doped with magnesium to give a Hall concentration of 5 × 1017 cm−3. The p-type GaN cathodoluminescence (CL) spectra showed a strong 372 nm emission level in contrast to the 430 nm level observed in MOCVD samples. These layers were fabricated into 1 × 10 element detector arrays using a chlorine-based reactive ion etch (RIE) and refractory metal ohmic contacts. Peak responsivity of 0.11 AAV on detectors without anti-reflection coating were obtained at the GaN bandedge of 360 nm. The ultraviolet (UV) to visible rejection ratio was greater than 103 − 104 and was accredited to the reduction of the yellow defect levels in MBE material. Preliminary results on AlxGa1−xN detectors with responsivity peaks at 313 and 343 nm are presented as well.
GaN Quantum Dots in AlxGa1-xN Confined Layer Structures
Authors: Tanaka Satoru , Hirayama Hideki , Iwai Sohachi , Aoyagi Yoshinobu
Published: April 2011

Nanoscale GaN quantum dots were fabricated in AlxGa1-xN confined layer structures via metalorganic chemical vapor deposition (MOCVD), by using a ‘surfactant’ which can modify the GaN growth mode on AlGaN surfaces. A two dimensional growth mode (step-flow-like) of GaN films on AlxGa1-xN (x=0∼0.2) surfaces, that is energetically commenced under the conventional growth conditions, was intentionally changed into a three dimensional mode by adding tetraethyl-silane (TESi) used as a surfactant onto the AlGaN substrate surface prior to the GaN deposition. The surfactant is believed to inhibit the GaN film from wetting the AlGaN surface due to the change in surface free energy. The resulting morphological structures of GaN dots were found to be sensitive to; the doping rate of TESi, the Al content (x) of the AlxGa1-xN layer, and the growth temperature. A very intense photoluminescence (PL) emission was observed from the GaN dots embedded in the AlGaN layers. The quantum size effect in terms of the blue-shift in a PL peak position was verified using the GaN dot samples having different dot sizes.
Growth of AlBN Solid Solution by OMVPE
Authors: Shin M. , Polyakov A. Y. , Qian W. , Skowronski M. , Greve D. W. , Wilson R. G.
Published: April 2011

Layers of AIBN were grown on sapphire by organometallic vapor phase epitaxy (OMVPE) at 1050°C using triethylboron (TEB), trimethylaluminum (TMA) and ammonia as precursors. Boron is readily incorporated into the layers and its concentration in the solid phase can be made fairly high, up to at least 40%. However, single phase AIxB1–xN films can only be grown for compositions not exceeding x=0.01. For higher B concentrations a second B-rich phase is formed. This phase is shown to be most probably wurtzite BN based on the results of transmission electron microscopy and x-ray diffraction. The growth of this phase occurs within the framework of wurtzite AIN islands providing the sites for lateral growth of wurtzite BN. This leads to formation of columnar structure of AIN and BN crystallites oriented in the basal plane and existing side by side. This is one of the first observation of purely thermal growth of sp3 bonded BN.
Growth of Cubic GaN by MBE and Its Properties
Authors: Yoshida S. , Okumura H. , Feuillet G. , Hacke P. , Balakrishnan K.
Published: April 2011

Molecular beam epitaxy (MBE) technique is a useful method to grow III-V nitrides, especially those having a metastable crystal structure, like cubic GaN (c-GaN), because of the capability of in situ observation of growing surfaces and its non-equilibrium growth mechanism. We have grown c-GaN on GaAs and 3C-SiC substrates by gas source MBE using dimethylhydrazine or activated nitrogen beam as an N source, and measured their luminescent and optical properties. This paper summarizes the MBE growth and properties of c-GaN, comparing with those of hexagonal one, and the control of the crystal structures is discussed in terms of growth method, orientation of substrate surfaces and growth conditions.
A Study of Mixed Group-V Nitrides Grown by Gas-Source Molecular Beam Epitaxy Using a Nitrogen Radical Beam Source
Authors: BI W. G. , Tu C. W. , Mathes D. , Hull R.
Published: April 2011

We report a study of N incorporation in GaAs and InP by gas-source molecular beam epitaxy using a N radical beam source. For GaNAs grown at high temperatures, phase separation was observed, as evidenced from the formation of cubic GaN aside from GaNAs. By lowering the growth temperature, however, GaNAs alloys with N as high as 14.8% have been obtained without showing any phase separation. For InNP, no phase separation was observed in the temperature range studied (310 – 420 °C). Contrary to GaNAs, incorporating N in InP is very difficult, with only less than 1% N being achieved. Optical absorption measurement reveals strong red shift of bandgap energy with direct-bandgap absorption. However, no semimetallic region seems to exist for GaNAs and a composition-dependent bowing parameter has been observed.
Effect of Stoichiometry on Defect Distribution in Cubic GaN Grown on GaAs by Plasma-Assisted MBE
Authors: Ruvimov S. , Liliental-Weber Z. , Washburn J. , Drummond T. J. , Hafish M. , Lee S. R.
Published: April 2011

High resolution electron microscopy has been applied to characterize the structure of β-GaN epilayers grown on (001) GaAs substrates by plasma-assisted molecular-beam-epitaxy. The rf plasma source was used to promote chemically active nitrogen. The layer quality was shown to depend on growth conditions (Ga flux and N2 flow for fixed rf power). The best quality of GaN layers was achieved by “stoichiometric” growth; Ga-rich layers contain a certain amount of the wurtzite phase. GaN layers contain a high density of stacking faults which drastically decreases toward the GaN surface. Stacking faults are anisotropically distributed in the GaN layer; the majority intersect the interface along lines parallel to the “major flat” of the GaAs substrate. This correlates well with the observed anisotropy in the intensity distribution of x-ray reflexions. Formation of stacking faults are often associated with atomic steps at the GaN-GaAs interfaces.
GaN Crystals Grown in the Increased Volume High-Pressure Reactors
Authors: Porowski S. , Bockowski M. , Lucznik B. , Wroblewski M. , Krukowski S. , Grzegory I. , Leszczynski M. , Nowak G. , Pakula K. , Baranowski J.
Published: April 2011

GaN single crystals are grown from the solution of atomic nitrogen in liquid Ga at N2 pressure up to 20 kbar. The crystals reaching dimensions of 1cm, with dislocation density of 103 - 105 cm-2 are currently obtained and successfully used for homoepitaxy by MOCVD and MBE.

The increase of the maximum size of GaN crystals with stable morphology requires the increase of the volume of the crucible. Beside the obvious geometric factors, the increase of the volume of the furnace and crucible allows to achieve much better control of supersaturation profiles in the solution and therefore better control of growth process. It helps to avoid morphological instabilities and leads to the growth of transparent, inclusion free crystals.

In the paper, the results of crystallization of substrate quality GaN crystals obtained with the use of large volume high pressure reactor will be presented. The crystals were characterized by High Resolution X-ray Diffraction and Atomic Force Microscopy. It will be shown that the quality of GaN crystals does not deteriorate with the increasing size and that epi-ready surfaces of GaN substrates can be obtained. Two-dimensional growth by propagation of monoatomic steps of GaN homoepitaxial layers will be presented as a verification of the quality of GaN substrates.
Material and Device Characteristics of MBE-Grown GaN Using a New rf Plasma Source
Authors: Beresford R. , Stevens K. S. , Cui Q. , Schwartzman A. , Cheng H.
Published: April 2011

A new rf plasma nitrogen source has been characterized for growth of GaN on basal-plane sapphire by molecular beam epitaxy. For rf power of 500 W and N2 flow rate of 2 sccm, a maximum GaN growth rate of 0.80 μm/hr is obtained, implying a source efficiency greater than 5%. It is found that the GaN surface roughness is extremely sensitive to V:Il ratio near unity and independent of growth rate in the range 0.3-0.8 μm/hr. Roughness as small as 1.0 nm (rms) is measured by atomic-force microscopy. Microstructure of the high-growth-rate films is similar to other GaN films, as observed in cross-section transmission electron microscope images. The electroluminescence spectra from homojunction light-emitting diodes exhibit a band of nearultraviolet emissions corresponding to the energy separation of the intentional donor and acceptor levels on the two sides of the junction. The intensity of these emissions relative to the visible spectrum increases with drive current density, implying saturation of deep trap levels responsible for the visible light output.
Nitrogen Plasma Pretreatment of Sapphire Substrates for the GaN Buffer Growth by Remote Plasma Enhanced MOCVD
Authors: Hong Kim Min , Sone Cheolsoo , Hyung Yi Jae , Ok Heur Soun , Yoon Euijoon
Published: April 2011

Low-temperature GaN buffer layers with smooth surfaces and high crystallinity could be prepared by a remote plasma enhanced metalorganic vapor deposition after the pretreatment of substrates with rf nitrogen plasma. Smooth AIN thin layer was formed on the (0001) sapphire substrate by the nitrogen plasma pretreatment for an hour. The AIN layer provided the nucleation sites for the subsequent buffer layer growth, thus highly preferred (0001) GaN buffer layers could be grown on the pretreated substrate. Formation of the AIN layer on sapphire and the surface smoothness were affected by pretreatment parameters such as exposure time, temperature, and rf power.
Persistent Photoconductivity in n-Type GaN
Authors: Wickenden A. E. , Beadie G. , Koleske D. D. , Rabinovich W. S. , Freitas J. A.
Published: April 2011

Persistent photoconductivity has been observed in n-type Si-doped GaN grown on sapphire substrates by metalorganic vapor phase epitaxy. The effect has been seen both in films which are of electrically high quality, based on low temperature photoluminescence (PL) and Hall analysis, and in films which either appear to be compensated or which exhibit strong donor-acceptor pair recombination. The photoconductivity has been observed to persist for several days at room temperature (300K). Modeling of the resistance recovery by a stretched exponential treatment may suggest a distribution of deep level defect centers in the Si-doped GaN films.
Studies of Electrically and Recombination Active Centers in Undoped GaN Grown by OMVPE
Authors: Polyakov A. Y. , Govorkov A. V. , Smirnov N. B. , Shin M. , Skowronski M. , Greve D. W.
Published: April 2011

Deep centers were studied in GaN samples grown by organometallic vapor phase epitaxy (OMVPE). Electron traps 0.2 eV and 0.5 eV below conduction band edge and 0.25 eV and 0.50.85 eV above the valence band edge were detected by means of deep levels transient spectroscopy (DLTS), photoelectron relaxation spectroscopy (PERS) and thermally stimulated current spectroscopy (TSC). The photoconductivity at low temperature is shown to be persistent and the magnitude of photosensitivity is dependent on the way the samples are grown. Microcathodoluminescence (MCL) and electron beam induced current (EBIC) measurements indicate that the density of deep recombination centers near the dislocation walls between the misoriented GaN domains is lower than inside the domains. Spatially resolved PERS measurements show that the concentration of the 0.85 eV level is higher in the low angle grain boundary regions that produce bright contrast in EBIC and MCL.
Photoluminescence of Fe-Complexes in GaN
Authors: Thurian P. , Hoffmann A. , Eckey L. , Maxim P. , Heitz R. , Broser I. , Pressel K. , Meyer B-K. , Schneider J. , Baur J. , Kunzer M.
Published: April 2011

We report a photoluminescence (PL) and photoluminescence excitation (PLE) investigation of the deep iron acceptor in hexagonal GaN. Codoped samples give rise to a new zero-phonon line (ZPL) at 1.268 eV. The spectral shape of its phonon side band is very similar to that of the Fe3+ -spectrum. A lifetime of 2.6 ms was measured for this ZPL which indicates a spinforbidden transition. In contrast to isolated Fe3+, no Zeeman-splitting is observed. PLE spectra of the Fe3+ (4T1-6A1) zero-phonon line at 1.299 eV in semi-insulating GaN samples reveal intracenter excitation processes via excited states of the Fe3+ center. Three excited Fe3+ crystal field states at 1.299 eV (4T1), 2.01 eV (4T2), and 2.731 eV (4E) above the 6A1, ground state were identified. PLE spectroscopy for the 1.268 eV zero-phonon line reveals resonances at 2.3 eV and 2.65 eV. The 1.268 eV ZPL is tentatively attributed to a Fe-complex with a nearby donor.
Raman Analysis of Electron-Phonon Interactions in GaN Films
Authors: Bergman L. , Bremser M. D. , Christman J. A. , King S. W. , Davis R. F. , Nemanich R. J.
Published: April 2011

Raman analysis of film quality, phonon-plasmon coupling, and phonon-exciton interaction in GaN films with varying Si doping levels is presented. The films exhibit a small stress component ∽0.1 GPa, calculated from the frequency shift of the E2 mode. No correlation between the stress and the doping concentration was found. No forbidden Raman lines were detected in the spectra, implying high quality oriented films. The Raman lineshape of the E2 mode is a Lorentzian with similar linewidths at room temperature and at 10K indicating a homogeneous lifetime broadening mechanism which is not significantly affected by the change in temperature. The linewidth is also independent of Si concentration. The phonon-plasmon mixed frequency modes were calculated to be at ω−.=86 cm−1 and at ω+=741 cm−1 The modes are not present in the spectra and the only effect of the plasmons is a change of the Al(LO) lineshape. Analysis of the A1(LO) line indicated a uniform spatial doping distribution. A resonance effect was observed for the symmetry-allowed A1(LO) mode at T=10K with sub bandgap excitation light. The resonance interaction is consistent with the free exciton model.
Electronic Structure of Biaxially-Strained Wurtzite Crystals GaN and AlN
Authors: Majewski J. A. , Städele M. , Vogl P.
Published: April 2011

We present first-principles studies of the effect of biaxial (OOOl)-strain on the electronic structure of wurtzite GaN, and A1N. We provide accurate predictions of the valence band splittings as a function of strain, which may facilitate the interpretation of data from strained samples. The conduction and valence band effective mass tensors for A1N and GaN are also presented. The computed crystal-field and spin-orbit splittings in unstrained materials as well as the computed deformation potentials are in accord with available experimental data. We show that the numerically computed band energies can be excellently represented in terms of a 6-band k · p model. The present calculations are based on the first-principles pseudopotential method within the local-density formalism and include the spin-orbit interactions non-perturbatively.
Theory of Interfaces in Wide-Gap Nitrides
Authors: Nardelli M. Buongiorno , Rapcewicz K. , Briggs E. L. , Bungaro C. , Bernholc J.
Published: April 2011

The results of theoretical studies of the bulk and interface properties of nitrides are presented. As a test the bulk properties, including phonons of GaN at the Γ-point, are calculated and found to be in excellent agreement with the experimental data. At interfaces, the strain effects on the band offsets range from 20% to 40%, depending on the substrate. The AlN/GaN/InN interfaces are all of type I, while the Al0.5Ga0.5N on A1N zinc-blende (001) interface is of type II. Further, an interface similar to those used in the recent blue laser diodes is of type I and does not have any electronically active interface states. The valence band-offset in the (0001) GaN on A1N interface is -0.57 eV and the conduction band-offset is 1.87 eV.
Reactivation of Acceptors and Trapping of Hydrogen in GaN/InGaN Double Heterostructures
Authors: Pearton S. J. , Bendi S. , Jones K. S. , Krishnamoorthy V. , Wilson R. G. , Ren F. , Karlicek R. F. , Stall R. A.
Published: April 2011

The apparent thermal stability of hydrogen passivated Mg acceptors in GaN is a function of the annealing ambient employed, with H2 leading to a reactivation temperature approximately 150°C higher than N2. The dissociation of Mg-H complexes and the loss of hydrogen from GaN are sequential processes, with reactivation occurring at ≤700°C for annealing under N2, while significant concentrations of hydrogen remain in the crystal even at 900°C in implanted samples. The hydrogen is gettered to regions of highest defect density such as the InGaN layer in a GaN/InGaN double heterostructure. The addition of an accelerating potential for 2H+ ions in the plasma did not greatly affect the deuterium profiles.
Nano-Structured Silicon-Based Films with Visible Light Emission Synthesized by Laser Ablation
Authors: Makimura T. , Kunu Y. , Ono N. , Murakami K.
Published: April 2011

Applying laser ablation technique, we have synthesized two types of SiO2 films that include nanometer-sized Si particles. One is synthesized by alternative deposition of Si nanoparticles layers and SiO2 layers. The synthesized film exhibits red photoluminescence (PL) with a peak energy below 1.5 eV. The other is synthesized by annealing at 1000°C of SiOx films, which are formed by laser ablation in diluted O2 gas. We find that there is a narrow range of composition for efficient red PL. Based on the experimental results, we tentatively discuss a possible model for the origin of the red PL.
Semiconductor Nanocrystals: Exciton Quantum Mechanics, Single Nanocrsytal Luminescence, and Metastable High Pressure Phases
Authors: Nirmal M. , Brus L. E.
Published: April 2011

We review three areas where significant progress has recently occurred in our understanding of semiconductor nanocrystals. The first two involve luminescence properties of single and ensembles of Cadmium Selenide (CdSe) nanocrystallites (Quantum Dots) between 10 and 50 Å in radius. The size, magnetic field, and temporal dependence of emission from ensembles of nanocrystallites at cryogenic temperatures uncovers the fundamental mechanism of radiative recombination in these nanocrystals. Effective mass models that take into account the electron-hole exchange interaction can quantitatively account for observed luminescence Stokes shifts. Furthermore, the magnetic field dependence of luminescence lifetimes and longitudinal-optical (LO) phonon ratios demonstrate that the exciton ground state in these nanocrystals is optically passive (“dark exciton”) with spin projection ±2. Picosecond time resolved measurements probe exciton relaxation into this level. Recent results on the spectroscopy of single CdSe nanocrystals at room temperature are also presented. Remarkably, emission from a single CdSe nanocrystal under C.W illumination is observed to turn on and off discretely (fluorescence intermittency) on a ∼0.5s timescale. The excitation intensity dependence, and the influence of a passivating high band gap shell of Zinc Sulfide (ZnS) encapsulating the CdSe nanocrystal on the on/off times, suggest that this phenomenon is caused by photoionization. Finally, the third area originates in diamond anvil studies of the solid-solid phase transitions of nanocrystals under pressure. These studies show that a single nucleation event occurs per nanocrystal, and that as a consequence the nanocrystals change shape. The kinetic activation barrier increases with increasing size. Under suitable conditions nanocrystals in dense, six-coordinate high pressure phases may be metastable at STP.
Photoluminescence Mechanism of Silicon Quantum Dots and Wells
Authors: Kanemitsu Y. , Okamoto S.
Published: April 2011

We discuss the mechanism of efficient photoluminescence (PL) from Si quantum dots and wells. Luminescence properties of SiO2-capped Si nanocrystals are different from those of H-terminated Si nanocrystals, but are very similar to those of Si quantum wells sandwiched by SiO2 layers. The size-dependence of PL properties and resonantly excited PL spectra of SiCb-capped Si dots and wells indicate that excitons are localized near the interface between the crystalline Si core and surface oxide layer, and the strong coupling of electronic and vibrational excitations causes the broad PL spectrum. The exciton localization plays an essential role in the efficient luminescence process in nanoscale Si/SiO2 systems.
Electronic States of Nanocrystalline Carbon
Authors: Lopinski G. P. , Merkulov V. I. , Lannin J. S.
Published: April 2011

Electron energy loss spectroscopy (EELS) has been used to investigate the electronic states of isolated, nanocrystalline carbon particles. Small carbon nanocrys-tals were prepared via sputter deposition onto SiO2 substrates, followed by annealing to 700C. The structure and size distribution of the particles have been characterized by Raman scattering, Auger electron spectroscopy and electron microscopy. EELS observations indicate that a semimetal to semiconductor transition occurs for particles smaller than lnm. In addition, hydrogen adsorption is found to significantly affect the electronic states of these particles, indicating that both finite size and dangling bond effects modify the properties of small carbon nanocrystallites.
Structure and Vibrational Properties of Isolated Carbon Nanocrystallites
Authors: Merkulov V. I. , Lannin J. S. , Cowley J. M.
Published: April 2011

Small isolated nanocrystallites of carbon have been prepared on amorphous SiO2 and studied by interference enhanced Raman scattering (IERS) and scanning transmission electron microscopy (STEM). A new mode of dark field STEM, using a thin annular detector, has allowed imaging of 1–2 nm graphite-like particles using (002) diffraction. For such small particles, the Raman spectra provide the first evidence for changes in the phonon density of states of a nanocrystalline system.
Raman Spectroscopy of Ge Nanocrystals Grown by Self-Organization Processes
Authors: Stella A. , Bottani C. E. , Cheyssac P. , Kofman R. , Milani P. , Tognini P.
Published: April 2011

We report Raman spectroscopy measurements on Ge nanocrystals with average radii ranging from about 65 Å down to 10 Å (with a size dispersion lower than 20 %).

Ge has been deposited by UHV evaporation on an amorphous substrate, kept at such a temperature as to produce the Ge nanodroplets nucleation in the liquid phase.

A nanocrystalline size dependence of the Raman spectra has been observed and explained in the framework of a phonon confinement model. We have observed the softening of the TO Raman peak predicted by the theory when the dimensions of the particles are decreased. Moreover the observed inhomogeneous broadening of the Raman lines has been correlated with the size distribution of the particles in the samples.

Our results provide a characterization of Ge nanoparticles exhibiting a good crystalline nature, down to about 10 Å, and in conditions of substantial absence of perturbations of the environment.
Determination of Optical Properties of the Micro-Facetted InGaAs Quantum Wells and Quantum Wires Using Magnetophotoluminescence
Authors: Kim Sung-Bock , Ro Jeong-Rae , Lee El-Hang
Published: April 2011

We report optical properties of the micro-facetted InGaAs quantum wells and quantum wires on non-planar substrates employing magnetophotoluminescence (MPL). The InGaAs/GaAs structures were grown by chemical beam epitaxy on V-groove patterned GaAs substrates. In the presence of a magnetic field of 18 T, the diamagnetic shifts of exciton ground states of the (001)-and side-QWLs are ΔE=15.6 and 10.3 meV, respectively. In MPL of the facetted microstructure, we found that the different diamagnetic shifts strongly depend on the magnitude of the effective magnetic field as well as the quantum confinement. From comparing the intensities and full widths at half maximum, we easily found that side-QWLs are of higher quality than (OOl)-QWLs. We also fabricated InGaAs/GaAs quantum wires with a size of about 200 Å × (500–600) Å. By fitting the diamagnetic shifts (ΔΕ = 9.5 meV) of the exciton ground state with the calculated results of a variational method, we estimated that the reduced mass of the exciton is approximately 0.052 me.
The Investigation of Donor and Acceptor States in the Nanoparticles of PbI2 Layered Semiconductor
Authors: Lifshitz E.
Published: April 2011

The nanoparticles of PbI2 layered semiconductor, embedded in Sio2 films, were prepared by the sol-gel method. The low-temperature luminescence of PbI2 nanoparticles consists of a series of exciton lines in the region of ∼2.5eV and additional donor-acceptor recombination luminescent bands at lower energies, centered at 2.44eV (Green) and 2.07 eV (red), respectively. This paper reports the investigation of the nonexcitonic transitions, associated with of the Green and Red bands. The correlation between donor-acceptor recombination emission processes and lattice imperfections was examine, utilizing optically detected magnetic resonance (ODMR) spectroscopy. The results identified the following imperfection sites of both the Green and Red bands: an acceptor site associates with an isotropie Lead vacancy defect, [V]Pb2+ and a donor site, associate with an anisotropie Iodine vacancy, [V°]jodine. However, the results pointed on differences in relaxation processes of these bands. The relaxation processes correspond to the existence of competitive nonradiative recombination, spin-lattice relaxation and thermalization among the spin substrates. Thus, the results suggest that the Red band corresponds to stoichiometric defects at the surface, while the Green band corresponds to the same stoichiometric defects at the interior part of the nanoparticles.
Atomic Layer Etching of Porous Silicon
Authors: Libon I. H. , Voelkmann C. , Petrova-Koch V. , Koch F.
Published: April 2011

In this work we describe the controlled shifting of the PL peak of p+ (10 mΩcm) porous silicon (PoSi) by means of atomic layer etching (ALEP). We hereby study the cluster-size dependence of the PL of this material. By this technique of repeated oxidation by H2O2 and stripping of the oxidized surface layer, we reduced the size of the crystallites layer by layer. In all previous reports the PoSi PL appeared to have a natural lower energy limit of ≈ 1.4 eV. We report for the first time a continuous shift of the PoSi PL peak between 1.01 and 1.20 eV. This observation allows us to draw conclusions for the luminescence mechanism: it proves that geometrical quantum confinement in Si crystallites is responsible for the efficient room-temperature PL in PoSi near the indirect bandgap of c-Si. Together with observations of size-independent PL peaks around 1.6 eV in thermally oxidized samples this result indicates that the PoSi PL cannot be described by one origin alone. Both the existence of molecular centers and the geometrical quantum confinement are valid in their specific range of etching and post-anodic treatment parameters.
Electron Time-of-Flight Measurements in Porous Silicon
Authors: Rao Prasanna , Schiff E. A. , Tsybeskov L. , Fauchet P. M.
Published: April 2011

Transient photocurrent measurements are reported in an electroluminescent porous silicon diode. Electron drift mobilities are obtained from the data as a function of temperature. Electron transport is dispersive, with a typical dispersion parameter α≈ 0.5. The range of mobilities is 10−5 − 10−4 cm2Vs between 225 K amd 400 K. This temperature-dependence is much less than expected for multiple-trapping models for dispersion, and suggests that a fractal structure causes the dispersion and the small mobilities.
Nonlinear Electrical Functions of Porous Silicon Light-Emitting Diodes
Authors: Ueno K. , Ozaki T. , Koyama H. , Koshida N.
Published: April 2011

Some nonlinear electrical characteristics in electroluminescent porous silicon (PS) diodes with a relatively thin PS layer (0.5–5 μm thick) are described. The experimental PS diodes were composed of a semitransparent Au film, a PS layer, p- or n-type Si substrate, and an ohmic back contact. The PS layers were prepared by anodizing Si wafers in an ethanoic HF solution. In some cases, the PS layers were treated by rapid thermal oxidization (RTO) process. When the bias voltage is applied, the PS diodes show the electrical behavior like the metal-insulator-semiconductor (MIS) diodes. The negative-resistance characteristics and memory effect are also observed. These results indicate that the quantum-structured nature of the PS layer appears not only in the optical properties but also in the electrical properties.
Thin Microcrystalline Silicon by a Microwave Remote Plasma Deposition Scheme for Heterojunction Solar Cells and Thin Film Transistors
Authors: Jagannathan B. , Wallace R. L. , Anderson W. A.
Published: April 2011

A microwave remote plasma system, operating in an electron cyclotron resonance (ECR) condition, has been designed to deposit microcrystalline silicon (μ c-Si). The plasma properties have been studied by Langmuir probe measurements in the deposition region. Microcrystalline silicon films of thickness < 0.3 μm have been grown by the decomposition of 2% SiH4/Ar diluted in H2. The films were analyzed for dark and photoconductivity, crystallinity and total H2 content. Raman spectroscopy indicates >50% crystallinity for films deposited between 300–400 °C at pressures of 10 mTorr with an input power in the range of 200–600 W for a H2/SiH4 ratio of 60. An increase in deposition temperature from 300 to 400 °C resulted in an increase in conductivity along with a decrease in the activation energy. H2 evolution studies indicate that the purely μ c-Si films show a total 2.5% H2 content compared with the 16.5% seen for the totally amorphous films. Better structural and electrical properties have more recently been obtained using 2% SiH4/He mixtures.
Microstructure of Thin Film Photoconductors and its Correlation with Optical and Electronic Properthss
Authors: Klement U. , Horst D. , Ernst F.
Published: April 2011

The objective of this work is to find a material to replace amorphous hydrogenated silicon used as photosensitive part in the “retina” of an “electronic eye”. For that reason, ZnS, ZnSe, CdS and CdSe were chosen for investigations. Thin films, prepared by chemical vapour deposition, were characterized by transmission electron microscopy. The observed microstructures were correlated with the optoelectronic properties of these materials. CdSe was found to be the most promising material for our application. Hence, the influence of a dielectric interlayer and the effects of additional annealing treatments were analyzed for CdSe and will be discussed with respect to the optimization of the material.
Single-Crystal Si Films Via a Low-Substrate-Temperature Excimer-Laser Crystallization Method
Authors: Sposili Robert S. , Crowder M. A. , Im James S.
Published: April 2011

This paper describes an extension of the sequential lateral solidification (SLS) method for producing single-crystal Si regions in predetermined locations on thin Si films on SiO2. This is accomplished by manipulating the shape of the solidification front in order to exploit the tendency of grain boundaries to propagate nearly perpendicular to the melt interface. Specifically, we employ a chevron-shaped beamlet to select and grow the grain at the chevron's apex for propagation, resulting in a well-defined single-crystal region. Many such chevrons are processed concurrently—each one leading to a single-crystal region at a precisely determined location, and each one being large enough for complete inclusion of an entire thin-film transistor (TFT) device. Microstructural examination of defect-etched SLS material using optical microscopy reveals unambiguously that single-crystal regions free of high-angle grain boundaries are produced.
Sintering of Sputtered Copper Nanoparticles on (001) Copper Substrates
Authors: Yeadon M. , Yang J. C. , Ghaly M. , Olynick D. L. , Averback R. S. , Gibson J. M.
Published: April 2011

The sintering of sputtered copper nanoparticles with a thin film copper substrate has been studied in real time using a novel in-situ UHV TEM. Particles were generated by dc sputtering in argon and transferred directly into the microscope along a connecting tube. The particles were deposited onto a clean (001) copper substrate of thickness 40nm. As-deposited particles assume a random orientation on the copper substrate as evidenced by electron diffraction patterns. Upon annealing, however, the particles were observed to reorient and assume the orientation of the substrate. Reorientation of individual, isolated particles occurred at ∼200°C, primarily by grain-boundary motion and not by surface diffusion.
The Formation of Metal/Metal-Matrix Nanocomposites by the Ultrasonic Dispersion of Immiscible Liquid Metals
Authors: Keppens V. , Mandrus D. , Rankin J. , Boatner L. A.
Published: April 2011

Ultrasonic energy has been used to disperse one liquid metallic component in a second immiscible liquid metal, thereby producing a metallic emulsion. Upon lowering the temperature of this emulsion below the melting point of the lowest-melting constituent, a metal/metal-matrix composite is formed. This composite consists of sub-micron-to-micron-sized particles of the minor metallic phase that are embedded in a matrix consisting of the major metallic phase. The zinc-bismuth case was used as a model system, and ultrasonic dispersion of a minor bismuth liquid phase was used to synthesize metal/metal-matrix composites. These materials were subsequently characterized using scanning electron microscopy and energy-dispersive x-ray analysis.
Energetic-Particle Synthesis of Nanocomposite Al Alloys
Authors: Follstaedt D. M. , Knapp J. A. , Barbour J. C. , Myers S. M. , Dugger M. T.
Published: April 2011

lon implantation of O into Al and growth of Al(O) layers using electron-cyclotron resonance plasma and pulsed laser depositions produce composite alloys with a high density of nanometer-size oxide precipitates in an Al matrix. The precipitates impart high strength to the alloy and reduced adhesion during sliding contact, while electrical conductivity and ductility are retained. Implantation of N into Al produces similar microstructures and mechanical properties. The athermal energies of deposited atoms are a key factor in achieving these properties.
Nanocrystalline Solid Solutions of Cu/Co and Other Novel Nanomaterials
Authors: Edelstein A. S. , Harris V. G. , Rolison D. , Perepezko J. H. , Smith D.
Published: April 2011

A brief review will be given of the preparation, synthesis and properties of the Cu/Co system. The special case of the synthesis of nanocrystalline Cu.80Co.20 by precipitation and reduction of hydroxides is discussed in more detail. It was found that the lattice constant of nanocrystalline Cu.80Co.20. determined from x-ray diffraction measurements, approximately fits Vegard's Law and the average nearest neighbor distance from both the Cu and Co atoms, determined from EXAFS measurements, ir shifted from their bulk values. Samples given the minimum heat treatment needed to reduce the hydroxides contained Co-rich regions. Heat treatments cause the Co to segregate preferentially onto the surface of the Cu crystals. The presence of the Co delays the oxidation of the Cu surfaces.
Micro-Tensile Testing of Nanocrystalline Al/Zr Alloys
Authors: Legros M. , Hemker K. J. , LaVan D. A. , Sharpe W. N. , Rittner M. N. , Weertman J. R.
Published: April 2011

A novel micro testing machine has been used to perform tensile tests on nanocrystalline Al/Zr microsamples with grain sizes ranging from 10 to 250 nm. The problems associated with testing such small specimens (200μm × 200μm in the gage section) were overcome by using a contact-free interferometrie strain gage (ISDG) and alignment and low friction loading were assured by use of a linear air bearing. The postulated relationship between yield stress and hardness was investigated and will be discussed. The effect of the microstructure and the grain size of the compacts on their mechanical behaviour are also analysed.
Preparation of Ceramic Nanocomposite with Perovskite Dispersoid
Authors: Nagai T. , Hwang H. J. , Sando M. , Niihara K.
Published: April 2011

In order to introduce ferroelectricity into structural ceramics, we synthesized novel ceramic composites containing submicron sized perovskite-type ferroelectrics (ceramic / perovskite-type ferroelectrics nanocomposites). Although perovskite compounds easily react with other ceramics, MgO/BaTiO3 nanocomposites were successfully fabricated using conventional sintering technique. The microstructure of nanocomposites and the phase stability of the dispersed BaTiO3 particulate are discussed.
Preparation and Characterization of Ag-Cluster in Poly(Methylmethacrylate)
Authors: Yanagihara Naohisa , Ishii Yoshitaka , Kawase Takanori , Kaneko Toshimare , Horie Hisashi , Hara Toru
Published: April 2011

Solid sols of silver in poly(methylmethacrylate), Ag/PMMA, were prepared by bulk polymerization of methyl methacrylaite (MMA) with benzoyl peroxide (BPO) as an initiator in the presence of silver(I) trifluoroacetate. Ag/PMMAs were characterized by visible spectroscopy. Effects of the concentration of initiator, the concentration of silver (I) complex and the heat-treatment time on the formation of silver cluster were studied in detail.
Enhancement of Ion Mobility in Aluminosilicate-Polyphosphazene Nanocomposites
Authors: Hutchison J. C. , Bissessur R. , Shriver D. F.
Published: April 2011

Nanocomposites of poly(bis-(2(2-memoxyethoxy)ethoxy)phosphazene) (MEEP) or cryptand[2.2.2] with the aluminosilicate Na-montmorillonite (NaMont) were studied to develop new solid electrolytes with high conductivity and a unity cation transport number. An aluminosilicate was chosen because the low basicity of the Si-0-Al framework should minimize ion pairing. To further reduce ion pairing, solvating molecules or polymers such as cryptand[2.2.2] or MEEP were introduced into the aluminosilicate. When compared to pristine Na-montmorillonite, impedance spectroscopy indicates an increase in conductivity of up to 100 for MEEP-NaMont intercalates, and of 50 for cryptand[2.2.2]·NaMont intercalates. The MEEP·NaMont intercalate exhibits high ionic conductivity anisotropy with respect to the montmorillonite layers (σpara./σperp. = 100), which is consistent with increased tortuosity of the cation diffusion path perpendicular to the structure layers. The temperature dependance of the conductivity suggests that cation transport is coupled to segmental motion of the intercalated polymer, as observed previously for simple polymer-salt complexes. Nanocomposites of solvating polymers or molecules with aluminosilicates provide a promising new direction in solid-state electrolytes.
The Effect of sulfating on the Crystalline Structure of Sol-Gel Zirconia Nanophases
Authors: Bokhimi  , Morales A. , Novaro O. , Portilla M. , Lopez T. , Tzompantzi F. , Gomez R.
Published: April 2011

Nanophases of sol-gel zirconia were prepared with HCl, C2H4O2 and NH4OH as hydrolysis catalysts, and sulfated with H2SO4. They were analyzed by using X-ray powder diffraction, and their crystalline structure was refined by using the Rietveld method. All samples annealed below 300 °C were amorphous. The non-sulfated samples crystallized around 350 °C, while the sulfated samples crystallized around 600 °C, when they started loosing sulfate ions. In the initial stage of crystallization, both the tetragonal and monoclinic nanophases coexisted, with the tetragonal as the main phase. Annealing the samples at higher temperatures transformed the tetragonal nanophase, stabilized by OH ions, into the monoclinic one.
Synthesis of self-assembled functional molecules in mesoporous materials
Authors: Honma Itaru , Sasabe H. , Zhou H-S.
Published: April 2011

Self-assembled functional molecules in mesoporous materials are synthesized directly either by co-assembly of dye-bound surfactant of ferrocenyl TMA with silicate or Pc (phthalocyanine) molecules doped in the C16TMA micelles with oxides framework such as V2O5, MoO3, WO3and SiO2. The process provides well-organized molecular dopoed mesoporous structure by direct and simple procedure.
Shear Transmission in lamellar Ti-48at.%Al
Authors: Wiezorek J. M. K. , Zhang X. D. , Clark W. A. T. , Fraser H. L.
Published: April 2011

The transmission of shear across the interfaces between lamellae of γ-TiAl and α2-Ti3Al has been studied in the case of a room temperature deformed Ti-48A1 alloy containing a significant proportion of the lamellar microstructure. The mechanisms of shear transmission due to dislocation slip has been studiedusing transmission electron microscopy. Dislocations with Burgers vectors given by b=1/3 <1120>are the only products of slip transmission from the γ-TiAl phase to the α2-Ti3Al phase, and essentially no dislocations with b=1/3 <1126> i.e. c-component dislocations, have been observed. Slip transmission has been associated with impingement of certain cross-lamellar twins, formed by deformation in γ-TiAl, with the α2 lamellae. Dislocation based models for the slip transmission processes are proposed.
Slip of c + a/2 Dislocations in Ti3Al Single Crystals Strained in Tension Along the C-Axis
Authors: Minonishi Y. , Legros M. , Caillard D.
Published: April 2011

In situ TEM straining experiments have been performed on a Ti3Al single crystal, along the c-axis, in order to study the slip of 2c+a dislocations in pyramidal planes. The results show that slip takes place in π1 planes, in contrast with what has been observed after compression tests (slip in π2 planes), and that rows of loops are nucleated in the slip plane. The mechanisms which may control slip in the π1 planes are briefly discussed.