bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure of Si:H Films Fabricated by Plasma-Enhanced Cvd using Hydrogen Diluted Plasma
Authors: Edelman F. , Chack A. , Weil R. , Beserman R. , Werner P. , Rech B. , Roschek T. , Beyer W.
Published: April 2011

The structure of undoped Si:H films deposited at a high rate of 6-9 Å/s in an RF (13.56 MHz) plasma from hydrogen-silane gas mixtures at various substrate temperatures was studied using TEM (with in-situ annealing), XRD, Raman spectroscopy, optical absorption and hydrogen effusion. It is found that under our conditions the amorphous to crystalline transition occurs in a relatively narrow range of parameters, influenced mainly by hydrogen dilution and to a lesser degree by the substrate temperature. In the crystalline range the material is found to be nanocrystalline (average grain size 20 nm) and the crystals are essentially stable up to 800°C annealing. The crystal structure of a mixed amorphousnanocrystalline phase of samples deposited near the edge of crystallinity is also found to be rather stable. Nanocrystalline Si films deposited under these latter deposition conditions reveal in hydrogen effusion a relatively compact material and show high solar cell efficiencies (6-8%) when incorporated as i-layers in pin solar cells.
High Resolution Electron Microscopy (HREM) Study of Chemically Vapor Deposited Polycrystalline Si1-xGex Thin Films
Authors: Qin W. , Ast D. G. , Kamins T. I.
Published: April 2011

The microstructure of polysilicon and Si0.69Ge0.31 thin films, grown by chemical-vapordeposition (CVD) on oxidized silicon wafers covered with a very thin polysilicon seed layer, was investigated using high-resolution electron microscopy (HREM). The plan-view HREM images showed that polysilicon films contained less substructure inside grains and had fewer multiple twins and more extended twin bands than Si0.69Ge0.31. On the other hand, only SiGe contained multiple twins with five-fold symmetry. The atomic model of the second-order symmetric twin boundary proposed for Si and based on the insertion of five-member and seven-membered rings was found to describe the atomic structures of second-order symmetric twin boundaries in Si0.69Ge0.31 as well. Within the accuracy of HREM, the repeat unit of the boundary was the same in Si0.69Ge0.31 and Si.
Localized Measurement of Strains in Damascene Copper Interconnects by Convergent-Beam Electron Diffraction
Authors: Nucci Julie A. , Keller Robert R. , Krämer Stephan , Volkert Cynthia A. , Gross Mihal E.
Published: April 2011

Convergent beam electron diffraction (CBED) was used to measure localized lattice strains in damascene copper interconnects. This method provides data from areas of approximate diameter 20 nm, enabling evaluation of strain states within individual grains. Lattice parameters were determined by measuring the deficient higher order Laue zone (HOLZ) line positions in experimental zone axis patterns and subsequently comparing them to kinematical and dynamical simulations. Quantitative comparison was accomplished using a least squares analysis of distances between line intersections. Deposition-induced strains between 0.06% and 0.14% were measured in 2.0 µm wide lines. The uncertainty in strain determination was approximately 0.02%, as limited by the precision in HOLZ line detection. In addition to enabling localized analysis of strain states, another advantage of using CBED is that the microstructure can be fully evaluated. Used in conjunction with global methods such as X-ray diffraction, CBED may provide unique insight into localized failure phenomena such as electromigration void formation in damascene copper.
Studies of Copper Surfaces modified by Thermal and Plasma Treatments
Authors: Beyer G.P. , Baklanov M. , Conard T. , Maex K.
Published: April 2011

It was found that copper surfaces, which had been exposed to a clean room atmosphere, were covered by a layer, whose chemical composition can be described by Cu(OH)2·CuCO3. This layer can effectively be removed by either a short thermal treatment in vacuum at 350°C, a hydrogen plasma treatment, or a combination of both. Ex-situ photoelectron spectroscopy measurements show little difference of the chemical composition of the surface after the respective treatments. The thermal treatment, however, gives rise to re-crystallisation of the copper film due to the difference in temperature of deposition and the anneal. Ex-situ ellipsometry measurements indicate that the hydrogen plasma not only removes Cu(OH)2·CuCO3 but also passivates the copper surface.
Formation of AlxOyNz Barriers for Advanced Silver Metallization
Authors: Wang Y. , Alford T.L.
Published: April 2011

Silver has been explored as a potential candidate for future advanced interconnects due to its lowest electrical resistivity, when compared with Al and Cu. As in the case of Cu metallization, an additional layer between the Ag film and underneath dielectric is necessary in order to improve adhesion and to block the diffusion of Ag atoms. In this study, thin aluminum oxynitride (AlxOyNz) diffusion barriers have been formed in the temperature range of 400-725 °C by annealing Ag/Al bilayers on oxidized Si substrates in ammonia ambient. Rutherford backscattering spectrometry showed that the out-diffused Al reacted with both the ammonia and oxygen in the ambient and encapsulated the Ag films. Higher process temperatures and thinner original Al layers showed to improve the resistivity of the encapsulated Ag layers. The resulting Ag resistivity values are ∼1.75 ± 0.35 µΩ-cm. The thermal stability test of these diffusion barriers showed that these barriers sustained the interdiffusion between Cu and Ag up to 620 °C at least for 30 min in either vacuum or flowing He-0.5% H2. This temperature is a 200°C improvement over previously reported values for the self-encapsulated Cu and Ag films. X-ray diffraction spectra showed no formation of any high resistive intermetallic compounds, i.e., Ag3Al, Ag2Al, and AlAg3.
Morphological, Chemical and Structural Study of Sputtered Al/Al2O3 Multilayers
Authors: Paven-Thivet C. Le , Aubert P. , Fusil S. , Zozime A. , Malibert C. , Houdy Ph.
Published: April 2011

For purpose of enhancement of mechanical properties, Al/Al2O3 films, with thickness A in the nanometric scale, were deposited on silicon substrate by reactive rf sputtering, at substrate temperatures Ts ranging from −90°C to 600°C. The characterisation (FEG-SEM, AFM, SIMS, XRR) has shown that Al/Al2O3 films are granular and rough, in correlation with the behavior of single alumnium films. The minimal roughness values are obtained at low Ts (−90°C and 25°C). The Λ = 20 rim-films are real multilayers, as confirmed by SIMS and XRR. Nevertheless, the multilayering character, i.e. the existence of multilayers, decreases when Ts increases. At low Ts, the relevant parameter to explain the weakness of stratification of Al/Al2O3 films is the roughness of layers, while at high Ts, the chemical interdiffusion clearly dominates, resulting in a no periodic structure at Ts = 600°C.
Deposition Of Nanotubes and Nanotube Composites Using Matrix-Assisted Pulsed Laser Evaporation
Authors: Wu P. K. , Fitz-Gerald J. , Pique A. , Chrisey D.B. , McGill R.A.
Published: April 2011

Using the Matrix-Assisted Pulsed Laser Evaporation (MAPLE) process developed at the Naval Research Laboratory, carbon nanotubes and carbon nanotube composite thin films have been successfully fabricated. This process involves dissolving or suspending the film material in a volatile solvent, freezing the mixture to create a solid target, and using a low fluence pulsed laser to evaporate the target for deposition inside a vacuum system. The collective action of the evaporating solvent desorbs the polymer/nanotube composite from the target. The volatile solvent is then pumped away leaving the film material on the substrate. By using this technique singlewall- nanotubes (SWN) have been transferred from the target to the substrate. The SWN sustain no observable damage during the deposition process. Using SWN in combination with polymers as the target material, SWN/polystyrene and SWN/polyethylene glycol composite films were made. These films can be deposited on a variety of substrates, e.g., Si, glass, plastic, and metal, using the same target and deposition conditions. SEM micrographs show that the SWN were uniformly distributed in the film. Using a simple contact mask, SWN composite films 20 um diameter patterns can be produced.
Formation of Cellular Crystalline Submicrostructure in the Butter with Additives
Authors: T. A. Rashevskaya , I. S. Gulyi , M. M. Nishchenko , S. P. Likhtorovich
Published: April 2011

Ecological situation of the last decades has driven an interest to the production of nutrients with natural food supplements. We have developed a number of cream-butter sorts containing vegetable additives, which are recommended as the dietary and prophylactic food supplements [1]. These kinds of butter exhibit unusual plasticity and enhanced durability, which are attributed to the features of their microstructure formation.
Electroluminescent Oxide Phosphor Thin Films Prepared by a Sol-gel Process
Authors: Minami Tadatsugu , Miyata Toshihiro , Shirai Tetsuya , Nakatani Toshikuni
Published: April 2011

Ga2O3:Mn and (Ga2O3-SnO2):Eu thin films have been prepared by a sol-gel process. High luminance emissions were obtained in TFEL devices: green using a Ga2O3:Mn and red using a Ga2O3:Eu or a SnO2:Eu thin-film emitting layer. These sol-gel prepared devices were produced without using any vacuum processes and always exhibited higher luminances than equivalent devices prepared by r.f. magnetron sputtering: 40, 309 and above 1000 cd/m2 using SnO2:Eu, Ga2O3:Eu and Ga2O3:Mn phosphor thin films, respectively, in TFEL devices prepared by the sol-gel process and driven at 1kHz.
Effect of Excimer Laser Fluence Gradient on Lateral Grain Growth in Crystallization of a-Si Thin Films
Authors: Lee Minghong , Moon Seungjae , Hatano Mutsuko , Suzuki Kenkichi , Grigoropoulos Costas P.
Published: April 2011

In order to clarify the relationship between excimer laser fluence gradient and the length of lateral grain growth, the laser fluence is modulated by a beam mask. The fluence distribution is measured by using a negative UV photoresist. The lateral growth length and the grain directionality are improved with increasing fluence gradient. Lateral growth length of about 1.5 [.proportional]m is achieved by using a single laser pulse without substrate heating on a 50 nm-thick a-Si film by enforcing high fluence gradient. Electrical conductance measurement is used to probe the solidification dynamics. The lateral solidification velocity is found to be about 7 m/s.
Fabrication of High-Density Carbon-Nanotube Coatings on Microstructured Substrates
Authors: Chen Zheng , Tzeng Yonhua , Liu Chao
Published: April 2011

Fabrication and characterization of carbon nanotubes deposited on microstructured Ni substrate are presented. The highly active surface-area of the microstructured Ni substrate provides highdensity nucleation sites for carbon nanotubes. Coated fine Ni powder also serves as a catalyst for the nanotube growth. Hydrocarbon mixtures were used as the carbon source for the chemical vapor deposition process. Carbon nanotubes deposited on the microstructured Ni substrate were examined by SEM. An ultra high vacuum chamber was used to characterize the field emission properties of carbon nanotube coatings.
Raman Study of Single Wall Carbon Nanotube Doped by Alkali Metals
Authors: Bendiab N. , Anglaret E. , Righi A. , Sauvajol J.L.
Published: April 2011

Single wall carbon nanotube (SWNT) doped by alkali-metals are investigated by Raman scattering. For saturation-doped compounds, the most striking intrinsic features are two low-frequency peaks assigned to modes involving both radial motions of tubes and alkali-atoms vibrations. On the other hand, the evolution of the Raman spectra with doping was studied in-situ. Two different stable phases are identified and associated to distinct organizations of the tubes and of the alkali-atoms.
Anodized Aluminum Oxide Films as Nanostructured Template for the Grow of Carbon Nanotubes
Authors: Sui Y.C. , González-León J.A. , Bermùdez A. , Acosta D.R. , Feuchtwanger J. , Flores J.O. , Cui B.Z. , Mata-Zamora M.E. , Saniger J.M.
Published: April 2011

A summary of our recent work related to the growth of carbon nanotubes (CNTs) inside the pores of anodized alumina oxide (AAO) films is presented. The surface topography of the AAO film was studied by atomic force microscopy, while the internal pore structure of the AOO templates was concluded from the shape of the CNTs obtained. The effect of the different experimental approaches and of the anodization voltage value on the features of the pores and CNTs is also discussed, as well as the catalytic effect in the acetylene pyrolysis of the Co particles and internal alumina walls. The CNTs wall structure observed by HRTEM and its implication on some physico-chemical properties of the CNTs are also presented.
Mechanical and Tribological Properties of Carbon Nanotubes Investigated with Atomistic Simulations
Authors: Ni Boris , Sinnott Susan B.
Published: April 2011

Atomistic simulations are used to better understand the behavior of bundles of single- walled carbon nanotubes that have been placed between two sliding diamond surfaces. A many-body reactive empirical potential for hydrocarbons that has been coupled to a Lennard-Jones potential is used to determine the energies and forces for all the atoms in the simulations. The results indicate that the degree of compression of the nanotube bundle between the nanotubes has a significant effect on the responses of the nanotubes to shear forces. However, no rolling of the nanotubes is predicted in contrast to previous studies of individual nanotubes moving on graphite.
Evaluating the Purity of Single-Wall Nanotube Materials
Authors: Dillon A.C. , Gennett T. , Parilla P.A. , Alleman J.L. , Jones K.M. , Heben M.J.
Published: April 2011

Carbon single-wall nanotubes (SWNTs) have a variety of unique physical, electronic and mechanical properties. However, the SWNTs must be thoroughly purified if they are to be used in the wide array of projected applications and basic studies. Although numerous purification schemes have been employed in the literature, none of them provides an accurate estimate of the SWNT content in the final materials. Here we describe a simple 3-step purification process coupled to an accurate method for determining SWNT wt.% contents in both the crude and purified samples. We employ a laser vaporization synthesis technique and take care to avoid both forming graphite-encapsulated metal particles and incorporating sputtered target material into the collected soot. It is then possible to employ a dilute nitric acid reflux to digest the metal particles and to functionalize and redistribute the non-nanotube carbon fractions in the soots forming a uniform and reactive coating on the SWNTs. This coating is selectively removed by oxidation in air at 550 °C. Thermogravimetric analysis (TGA) and inductively coupled plasma spectroscopy (ICPS) are used to evaluate the purity of the material at each step of the process, and illustrate that the crude materials contain 6 wt.% metal and 10-35 wt.% SWNTs. The purified materials are found to be >98 wt.% pure with metal contents of < 1 wt.%. Using the 98 wt.% pure materials as a yardstick, we are able to evaluate the accuracy of several other methods commonly employed in determining nanotube purity levels including transmission and scanning electron microscopies (TEM and SEM) and Raman spectroscopy. We show that determining nanotube contents in various materials requires careful scrutiny and the application of multiple techniques.
Surface Patterning by Laser Induced Localized Chemistry
Authors: Lachish-Zalait Aurélie , Zbaida David , Klein Eugenia , Elbaum Michael
Published: April 2011

A method is described for creating microscale-patterned surfaces by direct-write lithography. A tightly focused, low-power infrared laser beam is applied to a homogeneous precursor solution containing soluble reagents. When the laser is focused directly at a glass-solution interface, it initiates the local precipitation of a solid product that attaches firmly to the substrate. Operating the laser momentarily forms isolated spots, while moving the microscope stage or the laser spot draws continuous lines. The method has been demonstrated for metallic silver and gold, for oxidized copper, and for molybdenum disulfide, suggesting a broad generality in the range of suitable materials. Silver patterns were further modified by chemical reactions. Their morphology and physical properties can be altered during deposition by the use of capping agents, which may provide a handle for further functionalization.
Enlargement of Crystal Grain Size and Significant Inclusion of Hexagonal Diamond Phase in Ultra Pure Microcrystalline Silicon
Authors: Kamei Toshihiro
Published: April 2011

We have shown significant effects of atmospheric impurities on crystal grain sizes of hydrogenated microcrystalline Si (μc-Si:H), the growth surface of which is totally covered by hydrogen. By reducing impurity concentrations, two growth modes emerge, bordered at 250°C. In particular, at higher temperature growth mode, strong (220) preferential growth takes place, resulting in increased grain size. Appearance of this growth mode seems to be related to surface monohydride. Sharp x-ray diffraction peak in lower angle than (111) is observed, which stems from (10-10) crystal plane of hexagonal diamond Si. Its formation is related to (220) oriented crystallites. Implication of these results is the possibility of Si polytype control.
Nucleation-Control and Enhancement of Solid-Phase-Crystallization of SiGe-Heterostructure
Authors: Yamaguchi S. , Park S. K. , Sugii N.
Published: April 2011

The crystallization of SiGe-heterostructure in which a thin Ge layer put between Si layers has been investigated. When the Ge layer is inside the Si layer, the crystallization phenomena are similar to those of SiGe alloy layer; Ge completely diffuses in Si layer during the crystallization. When the Ge layer is at the interface between the Si layer and the quartz substrate, significant enhancement of crystallization has been found. In this structure, decrease in surface free-energy increases the nucleation rate at the interface and causes anomalous localization of Ge at the interface. When the Ge layer is on the surface of the Si layer, the crystallization property is quite different from the other structures. The underlying Si layer has large and aligned grains when the furnace annealing is assisted by the laser-annealing.

A part of this work was carried out under the ASET program supported by NEDO, Japan.
Reconciliation of the microcrystalline and the continuous random network model for amorphous semiconductors
Authors: Bording J.K. , Tafto J.
Published: April 2011

We show by molecular dynamics simulations, that the radial distribution function of an amorphous material does not change significantly by introducing a considerable volume fraction of nanocrystals. The nanocrystals, embedded in a continuous random network, ensure a certain degree of medium range order in the amorphous material. Our simulations, which are on germanium, show that microcrystals smaller than 2 nm can comprise at least 20 % of the volume without significantly changing the radial distribution function from that of pure continuous random network. By increasing the size of the crystals, without altering the crystal to amorphous volume ratio, the radial distribution changes. The molecular dynamics simulations show that the nanocrystals are unchanged at low temperature. At higher temperature the mobility and critical size of the grains increase, transforming the sub-critical crystalline grains into the surrounding continuous random network matrix.
Comparison of 500nm InGaN/GaN QW Emission Properties Induced by Piezoelectric Field Effect and Phase Separation
Authors: Kee Bong , Koh J.M. , Yoon Euijoon
Published: April 2011

Two kinds of InGaN/GaN single quantum well with emission wavelength of 500nm were obtained by employing piezoelectric effect and phase separation with different growth methods. Their emission properties are studied by measuring temperature and photo-excitation power dependent photoluminescence and electrolluminescence. The 500nm luminescence from the sample obtained by piezoelectric effect shows very weak temperature and excitation power dependent, on the other hand, it shows profound band tail broadening at both high temperature and low excitation power for phase separated sample which mean the strong localized state exist. We observed highly bright spots with longer wavelength then that of matrix in the phase separation sample and we believe that high emission efficiency can be obtained from these indium rich clusters.
Current Injection UV-Emission from InAlGaN Multi-Quantum-Well Light-Emitting Diodes
Authors: Kinoshita A. , Hirayama H. , Ainoya M. , Kim J. S. , Hirata A. , Aoyagi Y.
Published: April 2011

InAlGaN quaternary material is very attractive for realizing ultraviolet (UV) emitting devices working at 300 – 350 nm wavelength range. We demonstrate current injection into 340 nm-band InAlGaN based UV light emitting diodes (LEDs), for the first time, fabricated by metal organic vapor phase epitaxy (MOVPE). We performed current injection into AlGaN/AlGaN multi quantum well (MQW), bulk InAlGaN quaternary and InAlGaN/InAlGaN MQW LEDs through Mg-doped AlGaN/GaN superlattice hole conductive layers. The injected current density was ranging 0 – 0.5 kA/cm2 under pulsed or CW operation. The intensity of both photoluminescence (PL) and electroluminescence for InAlGaN quaternary-based LED was much higher than that for AlGaN based LEDs at room temperature. From these results InAlGaN quaternary-based QWs are expected to realize high intensity UV LEDs and LDs.
Improved Optical Quality of BAlGaN/AlN MQW Structure Grown on 6H-SiC Substrate by Controlling Residual Strain Using Multi-Buffer Layer
Authors: Takano Takayoshi , Kawanishi Hideo , Kurimoto Makoto , Ishihara Yoshiyuki , Horie Masato , Yamamoto Jun
Published: April 2011

BAlGaN and (BAlGaN/AlN) multi-quantum-wells (MQWs) structure were grown on 6H-SiC substrate by a low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). Estimated boron compositions of the BAlGaN quantum wells by an Auger electron spectroscopy (AES) analysis were 0% to 13%. Photoluminescence (PL) spectra around 260 nm were observed at room temperature. The full-width at half maximum (FWHM) of PL spectra for BAlGaN/AlN MQW structure(with 2% of boron) was narrowed from 360 meV to 179 meV, as the residual strain in the BAlGaN well layer was decreased from 1.3% to 1.0% by increasing the Al content in the quantum wells.
Indium incorporation and surface segregation during InGaN growth by molecular beam epitaxy
Authors: Chen Huajie , Feenstra R. M. , Northrup J. E. , Neugebauer J. , Greve D. W.
Published: April 2011

InGaN alloys with (0001) or (000) polarities are grown by plasma-assisted molecular beam epitaxy. Scanning tunneling microscopy images, interpreted using first-principles theoretical cal- culations, show that there is strong indium surface segregation on InGaN for both (0001) and (000) polarities. The dependence on growth temperature and group III/V ratio of indium incorporation in InGaN is reported, and a model based on indium surface segregation is proposed to ex- plain the observations.
The Effect of Buffer Layers in Mocvd Growth of Gan Film on 3C-SiC/Si Substrate
Authors: Park C. I. , Kang J. H. , Kim K. C. , Lim K. Y. , Suh E.-K. , Nahm K. S.
Published: April 2011

The growth of GaN films on Si substrates is very attractive work because of irreplaceable merits of Si wafer such as low cost, high surface quality, large area wafer availability, high conductivity and well-established processing techniques.

In this work, we studied the effect of buffer layers to grow high quality GaN films on 3C- SiC/Si(111) substrates. GaN films were grown on 3C-SiC/Si(111) by metalorganic chemical vapor deposition (MOCVD) using various buffer layers (GaN, AlN, and superlattice). The surface morphology and structural and optical properties of GaN films were investigated with atomic force microscopy (AFM), x-ray diffraction (XRD), Raman spectroscopy, and Photoluminescence (PL), respectively. GaN films grown using superlattice buffer layer showed only c-oriented (0002) plane of GaN from the XRD analysis. Raman spectra showed that the E2 high mode agreed with the selection rule was well observed in all GaN films. The A1(TO) and E1(TO) mode were appeared for GaN grown without buffer layer, whereas the E1(TO) mode was additionally appeared in the GaN films grown with GaN buffer layer. In the PL spectra at low temperature, the peaks associated with band edge emission and donor-accepter pair (D0A0) were observed in GaN films grown without buffer layer or with GaN buffer layer and AlN buffer layer. GaN films grown with superlattice buffer layer showed band edge and very weak D0A0 emission. The root mean square (RMS) roughness of the GaN film grown on superlattice buffer layer was only 4.21 Å Our experimental results indicated that the buffer layer affects crucially the qualities of GaN films grown on the 3C-SiC/Si substrate. Superlattice buffer layer improved the surface morphology as well as structural and optical properties of GaN films.
Nucleation of GaN on (0001) sapphire during MOCVD growth: an atomic force and high resolution electron microscopy study
Authors: Degave F. , Ruterana P. , Nouet G. , Je J.H. , Kim C.C.
Published: April 2011

The morphology and microstructure of GaN nucleation layers have been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The nucleation layers were grown at 500°C by metalorganic chemical vapour deposition (MOCVD) on (0001) sapphire. Different deposition times were used in order to investigate the evolution of the nucleation layer and try to understand the growth mechanisms. Systematically, it was found that the thinnest layers are mainly defect free and have a cubic structure. The (111) GaN planes are parallel to (0001) sapphire. It is shown that the nucleation follows the Volmer- Weber mechanism and as the islands height increases, the transformation from cubic to wurtzite starts from the substrate surface.
Stability, diffusion, and complex formation of beryllium in wurtzite GaN
Authors: Limpijumnong Sukit , Walle Chris G. Van de , Neugebauer Jörg
Published: April 2011

We have studied the properties of Be dopants in GaN using first principles calculations. Substitutional Be on a Ga site acts as an acceptor, but interstitial Be poses a potential problem because of its low formation energy and donor character. We study the diffusion of interstitial Be and find it to be highly anisotropic. We also study the formation of complexes between substitutional and interstitial Be, and between substitutional Be and hydrogen. We have calculated the Be-H vibrational modes to aid in experimental identification of such complexes.
Characteristics of Fielo-GaN Grown by Hydride Vapor Phase Epitaxy
Authors: Usui Akira , Sunakawa Haruo , Kobayashi Kenji , Watanabe Heiji , Mizuta Masashi
Published: April 2011

The crystal quality of facet-initiated epitaxial lateral overgrowth (FIELO) -GaN, in particular, that in the vicinity of the GaN surface, is reported. It is shown that the surface smoothness of FIELO-GaN enables us to use it as an “epi-ready” substrate. The crystallinity of FIELO-GaN is evaluated by x-ray rocking curve (XRC) measurements. We indicate that the FWHM of XRC should be reduced with the decrease of the dislocation density. We previously reported that the dislocation behavior of FIELO-GaN causes the tilting of the c-axis in the overgrown regions. By using scanning reflection electron microscopy (SREM), however, we show that the tilting on the surface of thick FIELO-GaN was negligibly small.
Photo- and cathodoluminescence investigations of piezoelectric GaN/AlGaN quantum wells
Authors: Goldys E.M. , Godlewski M. , Phillips M.R. , Toropov A.A.
Published: April 2011

We have examined multiple quantum well AlGaN/GaN structures with several quantum wells of varying widths. The structures had strain-free quantum wells and strained barriers. Strong piezoelectric fields in these structures led to a large red shift of the PL emission energies and long decay times were also observed. While the peak energies could be modelled using the effective mass approximation, the calculated free exciton radiative lifetimes were much shorter than those observed in experiments, indicating an alternative recombination mechanism, tentatively attributed to localised excitons. Cathodoluminescence depth profiling revealed an unusually small penetration range of electrons suggesting that electron-hole pairs preferentially remain within the multiple quantum well region due to the existing electric fields. Spatial fluctuations of the cathodoluminescence intensity were also observed.
IR-VUV Dielectric Function of Al1−xInxN determined by Spectroscopic Ellipsometry
Authors: Kasic A. , Schubert M. , Rheinländer B. , Off J. , Scholz F. , Herzinger C. M.
Published: April 2011

Spectroscopic Ellipsometry from the mid-infrared (mid-ir) to the vacuum-ultraviolet (vuv) spectral range (350 cm−1 … 8.8 eV) is used to study the optical properties of hexagonal MOVPE-grown Al1−xInxN films for 0.11 ≤ × ≤ 0.21. The AlInN E1(TO) phonon shows a onemode behavior in contrast to recent theoretical predictions [H. Grille, Ch. Schnittler, and F. Bechstedt, Phys. Rev. B 61, 6091 (2000)]. Approximately 120 nm thick Al1−xInxN films grown on slightly compressively strained hexagonal GaN buffer layers reveal the influence of in-plane strain on the E1(TO) phonon mode frequencies. Al1−xInxN deposited directly on [0001] sapphire substrate possesses E1(TO) mode frequency which indicate fully relaxed film growth. For highquality Al0.890In0.110N one A1(LO) phonon mode was observed. Furthermore, we present the complex dielectric function of hexagonal Al0.872In0.128N from the mid-ir to vuv spectral range.
Growth and Characterization of Epitaxial Al1−xInxN Films Grown on Sapphire (0001) by Plasma Source Molecular Beam Epitaxy
Authors: Lukitsch M. J. , Auner G. W. , Naik R. , Naik V. M.
Published: April 2011

Epitaxial Al1−xInxN films (thickness ∼150 nm) with 0 ≤ × ≤ 1 have been grown by Plasma Source Molecular Beam Epitaxy on Sapphire (0001) at a low substrate temperature of 375°C and were characterized by reflection high energy electron diffraction (RHEED), x-ray diffraction (XRD), and atomic force microscopy (AFM). Both RHEED and XRD measurements confirm the c-plane growth of Al1-xInxN films on sapphire (0001) with the following epitaxial relations: Nitride [0001] ∥ Sapphire [0001] and Nitride < 0110 > ∥ Sapphire <2110>. The films do not show any alloy segregation. However, the degree of crystalline mosaicity and the compositional fluctuation increases with increasing In concentration. Further, AFM measurements show an increased surface roughness with increasing In concentration in the alloy films.
Review of Facet Controlled Epitaxial Lateral Overgrowth (FACELO) of GaN via Low Pressure Vapor Phase Epitaxy
Authors: Hiramatsu Kazumasa , Miyake Hideto
Published: April 2011

Facet structures of GaN grown by epitaxial lateral overgrowth (ELO) via low pressure-metalorganic vapor phase epitaxy (LP-MOVPE) are controlled by growth conditions such as reactor pressure and growth temperature, where this technique is called FACELO (Facet Controlled ELO). The mechanism of the morphological change is discussed based on stability of the surface atoms. The propagation mechanism of the threading dislocations for the different GaN facet structure is also investigated. The distribution and density of the threading dislocations are observed by the growth pit density (GPD) method. Two typical models employing the FACELO are proposed; in one model, the dislocation concentrates only on the window area and, in the other model, only in the coalescence region in the center of the mask. In the latter model, the dislocation density is dramatically dropped to the order of 105−6 cm−2 with good reproducibility.
Growth and Characterization of GaN Underlying Layer Used in Blue-Violet GaN-Based Laser Diodes on Sapphire
Authors: Funato Kenji , Hino Tomonori , Tomiya Shigetaka , Miyajima Takao , Asano Takeharu , Tojyo Tsyuyoshi , Hashimoto Shigeki , Yanashima Katsunori , Uchida Shiro , Tmamura Koshi , Kobayashi Toshimasa , Ikeda Masao
Published: April 2011

The underlying GaN layers on which laser diodes are fabricated have been improved through two steps. In the first step, GaN single layer on sapphire was investigated. The residual strain and etch pit density were measured. We found that they reflect the optical quality. We found that the threading dislocation can be reduced to 4 × 108 cm−2. The optical quality depends on the residual strain and dislocation density. In the next step, we have utilized epitaxial lateral overgrowth ELO) technique. The optimized GaN layer on sapphire with the smallest dislocation density was used as seed layer. In the wing region of ELO-GaN, the threading dislocation density was reduced to 1 × 106 cm−2. On the other hand, in the seed region, dislocation density remained 4 × 108 cm−2. Photoluminescence intensity in the wing region was three times as large as that in the seed. The laser diodes were fabricated on the ELO-GaN layer, so that the ridge stripe was fabricated over the wing region, and its properties were compared with those of laser diodes on sapphire. It was found that the lifetime can be increased by using the ELO-GaN layer as the underlying layer.
A Growth Technique to Make Extensive Atomically Flat Silicon Surfaces
Authors: Lee Doohan , Schroeder Todd , Engstrom James , Blakely Jack
Published: April 2011

We have carried out a series of experiments aimed at producing arrays of mesas on both Si(001) and Si(111) which are free from atomic steps. These are of interest in CMOS technology and for quantum well structures. They also provide interesting substrates for fundamental surface science experiments. In previous work we have created atomically flat regions surrounded by ridges through an evaporation method. The present work ‘inverts’ the previous process by using a pattern of trenches to define the mesas and then depositing Si to grow the atomic steps off the edges. The mesas are created on Si wafers, which are ~1° from the (111) and (001) plane by lithography and reactive ion etching. Step-free mesas were formed on Si(111) but not yet on Si(001). Both the evaporation and this new growth technique rely on step flow to move the steps to the edges of the flat areas. Although the evaporation method is simpler, an advantage of the growth technique is that it can be carried out at lower temperature. The maximum size of mesa that can be made free of atomic steps depends on the combination of temperature and deposition rate. On very large step-free terraces nucleation of islands and concentric arrays of mono-atomic steps are observed; these correspond to the vacancy pits observed with the evaporation method.
Ab initio study of Ge Adsorption on H-terminated Si(001) Surfaces
Authors: Ohno Takahisa , Nara Jun , Ezaki Takahide
Published: April 2011

The Ge adsorption and diffusion processes on the monohydride terminated Si(001) surface are investigated by using first-principles total-energy calculations and kinetic Monte Carlo simulations. We find that the adsorbed Ge atoms tend to exchange sites with substrate Si dimer atoms. The site exchange plays an important role, which provides the most stable geometry and the easiest diffusion pathway. The Ge adatom migrates in the subsurface region instead of on the surface. The temporal variation in the adsorption geometry during diffusion is found. The Si atoms can become the surface diffusion species instead of the Ge atoms, as a result of the site exchange.
Structural and mechanical properties of amorphous Zr–based alloy thin films
Authors: Mayr S.G. , Moske M. , Samwer K.
Published: April 2011

The evolution of surface structures of coevaporated and sputtered amorphous Zr65Al7.5Cu27.5films with varying deposition conditions is investigated primarily with scanning tunneling microscopy (STM). While vapor deposited thin films reveal pronounced structure formation, depending on parameters, such as substrate temperature, film composition (variation of the Al versus the Cu content) and the angle of incidence, comparable sputtered films hardly show any structure formation. With the help of a numerical analysis of the STM data, surface diffusion, self–shadowing and energy transfer in the case of sputtering can be identified as the main structure forming mechanisms. Presuming these atomic processes, it is possible to model the main experimentally observed features of amorphous thin film growth by the use of stochastic continuum growth equations, which are numerically solved. Additionally, the connection to intrinsic stress formation during film growth is discussed.
Ultrafast Magnetization Reversal Dynamics on A Micrometer-Scale Thin Film Element Studied by Time Domain Imaging
Authors: Choi B.C. , Ballentine G. , Belov M. , Hiebert W.K. , Freeman M.R.
Published: April 2011

Picosecond time scale magnetization reversal dynamics in a 15nm thick Ni80Fe20 microstructure (10μm×2μm) is studied using time-resolved scanning Kerr microscopy. The time domain images reveal a striking change in the magnetization reversal mode, associated with the dramatic reduction in switching time when the magnetization vector is pulsed by a longitudinal switching field while a steady transverse biasing field is applied to the sample. According to the time domain imaging results, the abrupt change of the switching time is due to the change in the magnetization reversal mode; i.e., the nucleation dominant reversal process is replaced by domain wall motion if transverse biasing field is applied. Furthermore, magnetization oscillations subsequent to reversal are observed at two distinct resonance frequencies, which sensitively depend on the biasing field strength. The high frequency resonance at f=2 GHz is caused by damped precession of the magnetization vector, whereas another mode at f≈0.8 GHz is observed to arise from domain wall oscillation.
The Ehrlich-Schwoebel Effect for Vacancies: Low-Index Faces of Silver
Authors: Haftel Michael I.
Published: April 2011

We employ surface-embedded-atom-method potentials to investigate the diffusion barriers of vacancies diffusing over and near steps on the low index faces of silver. Barriers for vacancy terrace diffusion, diffusion over step-edges, and diffusion along step edges, including around corners, are calculated. Vacancies are significantly less mobile than adatoms and have large Ehrlich-Schwoebel (ES) barriers on all three faces. For Ag(100) the diffusion barrier for vacancies along step-edges is virtually the same (474 meV) as on the terrace. As in diffusion near the step edge, vacancies encounter a significant increase (213 meV) in the activation barrier when diffusing around the corner of a vacancy island (the corner analogue of the ES barrier), but the excess barrier around a kink all but disappears because exchange diffusion is favorable there. The consequences of the vacancy diffusion barriers on 3D pitting and on island diffusion and coarsening are discussed.
Growth of Epitaxial Al2O3 Films on Silicon by Ionized Beam Deposition
Authors: Whangbo SangWoo , Choi YunKi , Chung Kwun Bum , Jang HongKyu , Whang ChungNam
Published: April 2011

Epitaxial Al2O3 films have been successfully grown on an oxidized silicon substrate by the ionized beam deposition using an Al ion beam in oxygen environments. The crystalline quality dependence of the Al2O3 films on the growth temperatures was investigated. Using in situ reflection high energy electron diffraction, the orientation relationships between epitaxial Al2O3 films and Si substrate were found to be (100) Al2O3//(100) Si with [110] Al2O3//[110] Si and (111) Al2O3//(111) Si with [112] Al2O3//[112] Si. The stoichiometry of the films was found to be similar to that of sapphire from XPS measurements.
AFM and TEM Examination of Surface Grains in LPCVD Silicon Films
Authors: Kharas Dave , Gambino R. J. , Golubovic-Liakopoulos N.
Published: April 2011

Polycrystalline silicon is an important technological material in microelectronics, and more recently in microelectromechanical systems (MEMS). For MEMS applications polysilicon films with residual tensile stress are often used, requiring film growth in the transition zone from 550-600°C. In this study polysilicon films were grown in a hot walled LPCVD reactor at 590°C to a thickness of 450 nm. The tensile as-deposited stress in the wafers was found to decrease with distance from the reactor front and served as a marker for the changing microstructure and surface roughness of the film as measured by Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). It was found that the surface contained a high density (≍30 /µm2) of grains that protruded 30 nm above the mean film surface. The size and volume of these grains increased linearly with decreasing stress until the surface saturated and became uniformly rough. The nature of these surface grains, their spatial characteristics, and their annealing behavior is discussed.
Nano-Scale Heteroepitaxy Control of Magnetic Oxide Thin Films on Ultra-Smooth Sapphire Substrates
Authors: Takakura Masahiro , Miyahara Takafumi , Tashiro Junichi , Sasaki Atsushi , Furusawa Mitsuyasu , Yoshimoto Mamoru
Published: April 2011

We have examined the novel heteroepitaxy of magnetic oxide thin films on ultra-smooth sapphire substrates by laser MBE for fabrication of low-dimensional structures. Employing the atomically controlled substrate surfaces with atomic steps and terraces, we demonstrate the deposition of magnetic oxide nanowires (~0.5 nm high and ~20 nm wide) and nanodots of (Mn, Zn) ferrite, Fe3O4 and NiO.
Thermodynamics and Kinetics of Shear Induced Melting of a thin Lubrication film Trapped between Solids
Authors: Popov V.L. , Persson B.N.J.
Published: April 2011

Shear melting of a thin layer trapped between two crystalline solids is considered in the frame ofü the Landau's theory of phase transitions. Kinetics of melting and solidifying by static and periodic loading is analyzed.
Bismuth Contribution to the Improvement of the Positive Electrode Performances in Ni/Cd and Ni/MH Batteries
Authors: Pralong V. , Delahaye-Vidal A. , Beaudoin B. , Tarascon J-M.
Published: April 2011

In this study we investigated the evolution of nickel hydroxide, which acts at the positive electrode of the Ni/Cd, Ni/MH and Ni/H2 alkaline batteries. We found that the addition of bismuth oxide in the course of the active material preparation prevents the dissolution-re-crystallization processes of the nickel hydroxide that are harmful to the electrode efficiency. From XRD and SEM studies, it is shown that treatment of the bismuth doped-nickel hydroxide by hydrogen in 5 N KOH electrolyte prevents metallic nickel formation. Moreover, it appears to stabilize the α-type nickel hydroxide structure, preventing its transformation into the β-Ni(OH)2 phase. Finally, an implementation of these findings towards the most efficient use of nickel positive electrodes is shown.
Mechanism of Quality Factor Compensation by Nb2O5 Addition for Dielectric Properties of Low-T Sintered ZST Microwave Ceramics
Authors: Park Yong H. , Shin Moo Y. , Kim Hyung H. , Ko Kyung H.
Published: April 2011

It has been known that some additives such as Nb2O5 are efficient quality factor compensators to potential additives for low-T sintering of (Zr0.8Sn0.2)TiO4such asZnO. The compensation mechanism of Nb2O5was analyzed in the light of its effects on the Zn incorporation in grains. ZST ceramics were prepared by conventional mixed oxide method and their microwave dielectric properties including quality factor, permittivity and temperature coefficient frequency (TCF) were measured at X-band. After sintering at 1350 and 1400oC, samples were post-annealed at 900∼1100oC. It was found that as Nb2O5 was added, the quality factor of 6 mol % ZnO-ZST specimens increased from 24000 to 44000 without any sacrificing of other dielectric properties such as permittivity and TCF. According to TEM and XRD, Nb addition tends to enhance Zn diffusion toward grain boundaries while Nb moved in the opposite direction. Due to the fact that no second phases were formed, it was assumed that the redistribution of Zn and Nb could play a major role in the enhancement mechanism of quality factor. Post-annealing can also be a secondary booster for the quality factor of ZST. After annealing at 900∼1100oC, the quality factor of a specimen with additives, increased again up to 48000 due to further decrease of oxygen vacancies resulting from further out-diffusion of Zn toward grain boundaries and incorporation of Nb into the grain.
Solid-State NMR Investigation Of Mixed-Alkali Distribution In Phosphate Glasses
Authors: Prabakar S. , Mueller K.T.
Published: April 2011

The correlation between 31P and 23Na (or 133Cs) nuclei in a mixed-alkali phosphate glass has been investigated by TRAnsfer of Populations by DOuble Resonance (TRAPDOR) NMR spectroscopy. The variation in spatial proximity between 31P nuclei in phosphate tetrahedra and sodium (or cesium) modifier ions has been demonstrated in a phosphate glass with molar composition 25 Cs2O: 31 Na2O: 44P2O5. Interactions between 31P and 23Na (or 133Cs) nuclei are shown to exist even at low dephasing times indicating the short-range nature of these couplings. The ratios of resonance intensities from Q1 and Q2 phosphate units show different trends depending on whether couplings to 23Na or 133Cs are investigated, demonstrating the differing structural roles of the modifier alkali cations within the glass.
Modification of Ferroelectric Properties of TGS Crystals Grown under a dc Electric field
Authors: Arunmozhi G. , Nogueira E. , Gomes E.de Matos , Lanceros-Mendez S. , Margarida M. , Costa R. , Criado A. , Mano J. F.
Published: April 2011

Ferroelectric triglycine sulphate crystals have been grown under the influence of an intense electric field of 6×104 V/m. Relative to crystals grown under ambient conditions (TGS) the crystals grown under the electric field (TGS-E) display a dielectric permittivity a factor of two lower. Significant differences are observed in the Curie-Weiss behavior of the ferroelectric phase, in the x-ray diffraction patterns and in the differential calorimetry measurements.
Transition Metal Based Zeotypes: Inorganic Materials at the Complex Oxide – Zeolite Border
Authors: Henry Paul F. , Hughes Robert W. , Weller Mark T.
Published: April 2011

The synthesis of compounds of the type CsAIIIMIVO4 and (Cs,Rb)AIIPO4 (AIII = Al, Ga, Fe; AII = Ni, Co, Cu; M = Si, Ge, Ti,), using gel decomposition techniques at high temperatures is described. Several new materials in this family have been characterised using powder X-ray diffraction and are shown to adopt the zeolite ABW framework topology. Evidence for the large monovalent cation templating the formation of the ABW framework is presented. Extension of the method to other AIII and MIV (A = Mn, Co, B, In; M = Sn, Zr) framework cations, which are known to adopt tetrahedral geometry in other structures, has proved unsuccessful.
Preparation of New Bismuth Oxides by Hydrothermal Reaction
Authors: Kumada N. , Takei T. , Kinomura N. , Sleight A. W.
Published: April 2011

Hydrothermal reactions using NaBiO3·nH2O produced a variety of newbismuth oxides that were not prepared by high temperature reaction. Some of them have pentavalent bismuth such as Bi2O4O, LiBiO3, ABi2O6 (A = Mg, Zn) and AgBiO3. When using transition metal or rare-earth metal solutions, new bismuth oxides with trivalent bismuth were obtained. In the case of Cr(NO3)3 solution a chromium bismuth oxyhydroxide, HBi3(CrO4)2O3, was prepared at 180°C, while in A2CrO4 (A = Li, Na, K) solution a new bismuth chromium oxide, Bi8(CrO4)O11, was prepared above 180°C. When A2MoO4 (A = Li, Na, K) solution was used, a new phase appeared above 220°C. By using A2WO4 (A = Li, Na, K) solution β-Bi2O3 and Bi2WO6 were obtained above 220°C.