bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanofiber Formation in Spider Dragline-Silk as Probed by Atomic Force Microscopy and Molecular Pulling
Authors: Oroudjev Emin , Hayashi Cheryl Y. , Soares Jason , Arcidiacono Steven , Fossey Stephen A. , Hansma Helen G.
Published: April 2011

Despite the extensive interest in its remarkable materials properties, the structure of spider dragline silk is not yet known. Indirect structural information is thus of particular interest. New data are presented here from two probe microscopy techniques – atomic force microscopy (AFM) and single-molecule force spectroscopy, or ‘molecular pulling.’ Using a soluble synthetic protein from dragline silk, segmented silk nanofibers have been observed by AFM. Molecular pulling (Force Spectroscopy) has revealed sawtooth-like rupture peaks, indicative of the sacrificial bonds and hidden lengths seen in molecules of other self-healing biomaterials. A model is presented for the folding of single dragline-silk molecules and the arrangement of these molecules into nanofibers. The relationship is discussed between these molecular / nanoscale results and the materials properties of natural and artificial dragline silks.
Confocal optoelectronic holography microscope for materials and structural characterization of MEMS
Authors: Furlong Cosme , Siegel Adam M. , Pryputniewicz Ryszard J.
Published: April 2011

In this paper, we describe confocal optoelectronic holography microscopy (COEHM) technique specifically being developed for characterizing the shape of MEMS and microelectronics. This is particularly important because shape is directly related to the functionality, performance, and integrity of the microstructures of interest. A specific feature of COEHM is that it allows characterization of high aspect ratio MEMS and microelectronics. Representative applications demonstrating the capabilities of COEHM are presented. It is shown that measurement resolution is highly dependent on the numerical aperture (NA) of the optical components comprising COEHM and on the quality of image digitization. By utilizing optical components characterized by a magnification factor of 50x and a NA of 0.45, measurement resolution of 25 nm is achieved. The resolution is increased to 8 nm when utilizing optical components characterized by a magnification factor of 100x and a NA of 0.73.
Structure and Electronic Properties of Molecularly-capped Metal Nanoparticles: The effect of Nano-size, Metal Core and Capping Molecule Probed by X-ray Absorption Spectroscopy
Authors: Zhang Peng , Sham Tsun-Kong
Published: April 2011

We have conducted an investigation using TEM, XRD and synchrotron based X-ray absorption fine structure (XAFS) to probe the structural and electronic characteristics of several molecularly capped metal nanoparticles (NPs). Three series of NPs were employed in the XAFS study to address the effect of nano-size, metal-core and capping molecules on the structure and properties of the NPs. They are (1) thiol-capped Au NPs from 1.6nm to 4.0nm, (2) thiol-capped Au and Pd NPs of ∼2nm and (3) Au NPs of ∼4nm capped by thiol and tetraoctylammonium bromide (TOAB). The results on their local structure, bonding and d-charge distribution are presented.
Strain relaxation of strained-Si layers on SiGe-on-insulator (SGOI) structures after mesa isolation
Authors: Usuda Koji , Mizuno Tomohisa , Tezuka Tsutomu , Sugiyama Naoharu , Moriyama Yoshihiko , Nakaharai Shu , Takagi Shin-ichi
Published: April 2011

Strained-Si-On-Insulator (Strained-SOI) MOSFETs are one of the most promising device structures for high speed and/or low power CMOS. In realizing strained-Si MOS LSI, fabrication of strained-Si MOSFETs with small sizes are indispensable and thus, the investigation of the strain relaxation is an important issue. Therefore, the strain relaxation of strained-SOI mesa islands with small active area was investigated in this study. Thin strained-Si films were grown on thin relaxed SiGe-on-insulator (SGOI) structures (x=0.28). The isolation process was carried out by using chemical-dry-etching (CDE) to fabricate samples with small active areas. Using Raman spectroscopy with resolution of > 1 micron meter, strained-Si islands on SGOI substrates with the size of 5 micron meter square were investigated. Rapid-thermal-annealing (RTA) in N2 atmosphere was performed to study the strain relaxation during heating processes. As a result, it was confirmed that the strained-Si layers grown on relaxed SiGe (x=0.28) before and after mesa isolation, down to 5 micron meter in size, had almost no relaxation after the RTA process at 1000°C. Furthermore, it was confirmed that the nano-beam electron diffraction (NBD) measurement showed similar tendency regarding the strain relaxation.
Triple-probe Atomic Force Microscope: Measuring a carbon nanotube/DNA MIS-FET
Authors: Shimotani Kei , Watanabe Hiroyuki , Manabe Chikara , Shigematsu Taishi , Shimizu Masaaki
Published: April 2011

We have constructed an advanced electric probing system, which is a triple-probe atomic force microscope (T-AFM). The T-AFM consists of “Nanotweezers” and an AFM with a carbon nanotube probe. Using this system, we fabricated a single-walled carbon nanotubes (SWNTs)/deoxyribonucleic acid (DNA) three-terminal device and measured the current-voltage (I-V) curves of this device. In this three-terminal device, DNA strands were entangled with the SWNT bundle, and behaved as a gate-insulator-layer. This three-terminal device worked as a metal-insulator-semiconductor field effect transistor (MIS-FET) with depletion switching behavior.
The Role of Carbon Contamination in Suspended Gold Nanowires
Authors: Legoas Sergio B. , Galvão Douglas S. , Rodrigues Varlei , Ugarte Daniel
Published: April 2011

Metallic nanowires represent very interesting systems due to new phenomena such as quantum conductance and unexpected long interatomic distances attaining 0.3–0.5 nm. These large distances represent a challenge for physical interpretation. In this work we present experimental data from transmission electron microscopy and results from ab initio density functional calculations for suspended gold chains. We show that large distances as 0.5 nm can be easily explained by the presence of carbon atoms as contaminants, while distances ranging from 0.29 up to 0.36 nm might be explained as resulting of a mixture of clean stressed and contaminated linear chains.
Quantitative Morphology of Aluminum Silicate Nanoaggregates
Authors: F Crosta Giovanni , Sung Changmo , Kang Bongwoo , Ospina Carolina , J Stenhouse Peter
Published: April 2011

Aluminum silicate nanoaggregates grown on organic multilayer templates were imaged by a transmission electron microscope. Images were processed by fractal and FOURIER analysis. The estimated mass fractal dimension suggested that aggregate formation was diffusion limited. Nonlinear filtering of FOURIER spectra, which included comparison with a model spectral density, yielded «enhanced power spectra». Some morphological descriptors were extracted from the latter. The main result, materials classification, was attained by a two-scale procedure. Some descriptors were related to the material properties such as nanoparticle size distribution and sharpness of aggregate boundaries.
Effect of Thermal and Mechanical Treatments on the Cathodoluminescence of Tin and Titanium Oxides
Authors: Maestre D. , Plugaru R. , Cremades A. , Piqueras J.
Published: April 2011

The luminescence of titanium oxide and tin oxide has been investigated by cathodoluminescence in the SEM, as a function of the structural changes induced by thermal treatments. The evolution of the luminescence of TiO2 rutile, anatase and mixture phase with the annealing temperature is related to the process of thermal induced grain texture and to transition of metastables phases to the stable rutile. The emission band is peaked at 480 nm for the composite phase and at 580 nm for anatase and rutile phases respectively. A broad band in the 520–560 nm region is present in the spectra of both anatase and rutile phase. Thermal annealing leads to a red shift of the luminescence emission, with the emission band peaked at around 820 nm. In sintered tin oxide the main emission bands appear centered at about 480 nm and 630 nm. The intensity of these bands increases with annealing temperature up to 1200°, whereas for samples annealed at 1500° these emissions are quenched. Mechanical ball milling has been used to produce nanocrystalline SnO2 grains to investigate the influence of the presence of nanocrystals on the CL emission.
Nanoimpedance Microscopy and Spectroscopy
Authors: Shao Rui , Kalinin Sergei V. , Bonnell Dawn A.
Published: April 2011

One of the key limiting factors in current-based scanning probe microscopies (SPM) is the quality of tip-sample contact and stray capacitance in the probe-surface junction. We conduct impedance spectroscopy over a broad frequency range (40Hz∼110MHz) through an AFM tip to quantify local electrical properties. Equivalent circuit for the tip-surface contact is constructed based on the impedance data and is used to study the mechanisms of relaxation in the near-tip region. Relative contributions of tip-surface contact and materials properties to the signal are discussed. This technique, referred to as Nanoimpedance Microscopy/Spectroscopy, is demonstrated in the imaging of an electronic ceramic: a ZnO varistor. Analysis of impedance spectra allows separation of tip-surface interactions and grain boundary behavior.
Cathodoluminescence and microRaman study of GaN ELO structures
Authors: Martínez O. , Avella M. , Jiménez J. , Gérard B. , Galloway S.
Published: April 2011

Epitaxial Lateral Overgrowth (ELO) is an effective method to reduce dislocations in heterostructures with large lattice mismatch. This method has been widely used to improve the quality of GaN layers. We present herein a study of the properties of ELO GaN layers grown by HVPE from an MOVPE GaN buffer layer. Cathodoluminescence shows a strong enhancement of the luminescence emission in the ELO regions, where TEM has proven the absence of dislocations. Local cathodoluminescence spectra show that this enhancement is mostly due to the yellow luminescence band. Besides Donor-Acceptor Pair recombination bands are observed in the near band gap spectral range. Raman data show that the ELO layers present a good crystalline quality. The Raman spectra did not reveal the presence of free carriers in concentration high enough to allow the presence of Longitudinal Optic Phonon Plasmon Coupled modes. The results are discussed in terms of the incorporation of impurities in the ELO layers together with the formation of compensating deep acceptors, probably VGa.
Determination of the Plastic Behavior of Low Thermal Expansion Glass at the Nanometer Scale
Authors: Tejeda Richard , Engelstad Roxann , Lovell Edward , Anderson Anthony , Yang Dehua , Blaedel Kenneth
Published: April 2011

The nanometer-scale plastic behavior of two low thermal expansion glasses (ULE® and Zerodur®) was determined through a combination of nanoindentation experiments and finite element modeling. The finite element models were then extended to investigate aspects of the performance of these materials as extreme ultraviolet lithography reticles.
Observation of the Morphology of ZnO:Al Nanocoating by Pulsed Laser Deposition on ZnS:Ag Phosphor for Degradation Repression
Authors: Nagare Sanshiro , Ollinger Michael , Singh Rajiv , Senna Mamoru
Published: April 2011

Degradation due to electron beam irradiation is a significant problem for ZnS based phosphors, particularly for flat panel displays. In this study, ZnS:Ag phosphor particles were coated by nanoparticles of ZnO:Al by pulsed laser deposition (PLD), to suppress the cathodoluminescence (CL) degradation process under electron bombardment at 15 k V. The pressure of the vacuum chamber and the deposition time were changed to control the morphology of the coating, i.e. thickness, continuity, and uniformity. CL degradation of the phosphors was slowed down for all cases by the nanocoating. The relationship between the CL degradation and the morphology of the coating material was examined by an SEM combined with a simultaneous CL measurement device. Degradation mechanisms were elucidated in terms of the morphology of the coating material and the change in the surface atomic species during irradiation of the electron beam.
Organic Light Emitting Devices Fabricated from Semiconducting Nanospheres
Authors: Piok Thomas , Wenzl Franz P. , Gamerith Stefan , Gadermaier Christoph , Patil Satish , Montenegro Rivelino , Kietzke Thomas , Neher Dieter , Scherf Ullrich , Landfester Katharina , List Emil J.W.
Published: April 2011

Organic light emitting diodes (OLEDs) have been fabricated from organic semiconducting polymer nanospheres (SPNs) which have been deposited from aqueous dispersions. The active layer of the devices consists of a single, homogeneous layer of light emitting SPNs, as verified by optical, interferometric and surface probe measurements. Different batches of SPNs with different SPN diameters have been tested (69nm, 95nm, 126nm and 150 nm). All SPN-based OLEDs exhibit a light emission onset corresponding to the SPN energy gap (ca. 2.7 eV for m-LPPP, a semiconductingpara-phenylene ladder polymer). The low onset is attributed to field enhanced injection of charge carriers at the aluminum cathode due to the formation of stalactite-type nanostructures. A detailed comparison of the SPN-based and bulk semiconducting polymer films reveals no differences in the basic optoelectronic properties.
Deformation and Coble Creep of Nanocrystalline Materials
Authors: Pande C.S. , Masumura R. A.
Published: April 2011

Modeling of strengthening by nanocrystalline materials need consideration of dislocation interactions and sliding due to Coble creep, both of which may be acting simultaneously. Such a mechanism is considered in this paper. It is shown that a model based on using Coble creep (with a threshold stress) for finer grains and conventional Hall-Petch strengthening for larger grains, appears to be most successful in explaining experimental results provided care is taken to incorporate into the analysis the effect of grain size distribution occurring in most specimens. A generalized expression relating yield stress to grain size is also proposed.
Fluorinated Single Wall Nanotube/Polyethylene Composites for Multifunctional Radiation Protection
Authors: Pulikkathara Merlyn X. , Shofner Meisha L. , Wilkins Richard T. , Vera Jesus G. , Barrera Enrique V. , Rodríguez-Macías Fernando J. , Vaidyanathan Ranji K. , Green Catherine E. , Condon Clay G.
Published: April 2011

Fluorinated Single Wall Nanotubes (f-SWNTs) have been processed in polyethylene by an incipient wetting technique to achieve a well dispersed nanocomposite for radiation protection. In some cases, samples were further processed using the rapid prototyping method of extrusion freeform fabrication. Composites were exposed to 40 MeV proton radiation with a flux of about 1.7×107 protons/cm2/sec to a total fluence of 3×1010 protons/cm2.This exposure is consistent with a long-term space mission in low earth orbit. The samples were evaluated by means of Raman spectroscopy and thermogravimetric analysis (TGA). These results were compared to the unexposed composite and unfilled polymer samples. This study has focused on the stability of the nanotube composites when exposed to radiation and prior to hydrogen exposure. It was shown that the stability of the functional group is not constant with SWNTs produced by different processes and that radiation exposure is capable of defluorinating SWNTs in polyethylene.
Stoichiometry, crystallinity, and nano-scale surface morphology of the graded calcium phosphate-based bio-ceramic interlayer on Ti-Al-V
Authors: Long J. D. , Ostrikov K. , Xu S. , Ligatchev V.
Published: April 2011

A plasma-assisted concurrent Rf sputtering technique for fabrication of biocompatible, functionally graded CaP-based interlayer on Ti-6Al-4V orthopedic alloy is reported. Each layer in the coating is designed to meet a specific functionality. The adherent to the metal layer features elevated content of Ti and supports excellent ceramic-metal interfacial stability. The middle layer features nanocrystalline structure and mimics natural bone apatites. The technique allows one to reproduce Ca/P ratios intrinsic to major natural calcium phosphates. Surface morphology of the outer, a few to few tens of nanometers thick, layer, has been tailored to fit the requirements for the bio-molecule/protein attachment factors. Various material and surface characterization techniques confirm that the optimal surface morphology of the outer layer is achieved for the process conditions yielding nanocrystalline structure of the middle layer. Preliminary cell culturing tests confirm the link between the tailored nano-scale surface morphology, parameters of the middle nanostructured layer, and overall biocompatibility of the coating.
Compressive Behavior for Surface-Nanocrystallized Al-Alloy Material
Authors: Wei Yueguang , Zhu Chen , Wu Xiaolei
Published: April 2011

Mechanical behavior of the surface-nanocrystallized material fabricated by the ultrasonic shot peening method is investigated experimentally and theoretically. In the experimental research, based on microscopic observations, the compressive specimens are designed and machined considering the material features, and the compressive experiments are performed. Furthermore the compressive stress-strain curves are measured. In the theoretical research, a microstructure cell model is presented considering the material microscopic organization observed from experiments, and the compressive stress-strain relations are simulated. Both experimental and theoretical results display the strong size effect on the material behavior.
Material Properties and Process Compatibility of Spin-on Nano-foamed Polybenzoxazole for Copper Damascene Process
Authors: Enoki Takashi , Maejima Kenzo , Saito Hidenori , Katsumura Akifumi
Published: April 2011

We have developed nano-foamed OxD which has good properties such as dielectric constant=2.2, homogeneous distributed nano pores, smooth surface based on polybenzoxazole chemistry and nano-foaming technology. The nano-foamed OxD also has excellent thermal stability, chemical stability and etching property. The developed nano-foamed OxD is one of good candidates for copper damascene structure to achieve shrinking dimensions of future semi-conductor devices.
Synthesis of Titania coated Alumina Particles by a Hybrid Sol-gel Method
Authors: Schmidt A.D. , Majumder S.B. , Dobal P.S. , Katiyar R.S. , Agrawal D.C.
Published: April 2011

Modifying their surface with a coating of another ceramic material can dramatically alter the properties of ceramic particles. In the present work we have demonstrated that the Al2O3 particles can be successfully coated by TiO2 using a novel sol-gel technique. The nature of these coatings was predicted on the basis of scanning electron microscopy imaging in conjunction with the micro-Raman scattering measurements. The surface morphology of these particles shows that either individual or group of sub-micron alumina particles are coated with the nano-crystalline titania particles. The thickness of the titania coating could be varied by changing the precursor sol concentration. Amorphous titania was converted to anatase phase at 400°C and upon further heating it started transforming to rutile phase, and both these phases coexisted in the coated particles that were heat treated up to 800°C. The mechanical strength of the titania coating was measured qualitatively by ultrasonicating the coated powders for longer duration to observe that titania coatings are strongly adhered with the alumina particles.
Processing of Clay/Epoxy Nanocomposites with A Three-Roll Mill Machine
Authors: Yasmin Asma , Abot Jandro L. , Daniel Isaac M.
Published: April 2011

In the present study, a three-roll mill machine was used to disperse/exfoliate the nanoclay particles in an epoxy matrix. The compounding process was carried out with varying mixing time and concentrations of clay particles (1 to 10 wt.%). It was found that the longer the mixing time, the higher the degree of intercalation. Mechanical properties, XRD and TEM were used to characterize the nanocomposites. Elastic modulus was found to increase with increasing clay content, however, the tensile strength was not found to vary accordingly. Compared to conventional direct and solution mixing techniques, the compounding of clay/epoxy nanocomposites by a three-roll mill was found to be highly efficient in achieving higher levels of intercalation/exfoliation in a short period of time and also environmentally friendly.
Characterization of Metal-Oxide Nanoparticles: Synthesis and Dispersion in Polymeric Coatings
Authors: Sung Li-Piin , Scierka Stephanie , Baghai-Anaraki Mana , Ho Derek L.
Published: April 2011

Metal-oxide nanoparticles can be used to optimize UV absorption and to enhance the stiffness, toughness, and probably the service life of polymeric materials. Characterization of the nano- and microstructure dispersion of particles is necessary to optimize the structure-property relationships. Characterizations of both TiO2 particles dispersed in an acrylic-urethane matrix and TiO2 nanostructured films obtained through sol-gel synthesis are discussed. Experimental methods include microscopy (confocal, AFM) and small angle neutron scattering (SANS). Results from SANS experiments, which yield information about the cluster size of the nano-TiO2 particles and the spatial dispersion in various nanoparticle/polymer samples are presented and compared to the results of microscopy studies.
Adhesion of HVOF Sprayed Diamond-Containing Nanostructured Composite Coating
Authors: Kireitseu Maksim V. , Nemerenco Ion
Published: April 2011

In the present paper mechanical properties of HVOF sprayed diamonds-containing aluminum oxide composite coating have been investigated. Crystallographic and morphologic texture was measured. Diamonds nanoparticles may improve fracture resistance of aluminum oxide-based coating. Investigations of thermally sprayed coatings by the test revealed high accuracy, speed and reliability of the test. It is also thought that the composite coatings will have better thermal conductivity and thermal shock resistance than that of aluminum oxide-based coatings.
Synthesis of Zeolite Y Nanocrystals from Clear Solutions
Authors: Shen Y. , Manning M.P. , Warzywoda J. , Sacco A.
Published: April 2011

Synthesis of zeolite nano-sized crystals has attracted much attention because of their properties, some of which maybe different from the normal sized crystals. A synthesis adopted by Voltchev and Mintova was used as the starting point: 0.078 Na2O: 4.35 SiO2: 1.0 Al2O3: 2.35 (TMA)2O: 248 H2O. Both the silicate and aluminum starting solutions were clear. Zeolite Y nanocrystals with zeolite A nanocrystals as an impurity were obtained with a size range of 20–100 nm through this synthesis technique.
Nanoindentation Technique at Investigating of Aluminum Oxide - CrC Nanoparticles Composite Coating
Authors: Kireitseu Maksim V.
Published: April 2011

In this paper fatigue and fracture of Al-Al2O3-CrC nanostructured composite coatings was investigated by nanoindentation technique and in-situ experiments performed by a scanning electron microscope to permit examination of freshly exposed surfaces. Crystallography and morphological textures were characterized and fracture resistance was measured. CrC layer improves fracture resistance of alumina layer. CrC layer produced by pyrolitic deposition (CVD) may effectively heal pores and defects of alumina layer. It resulted in high load rating of the composite coating. Experiments reveal that in all cases, the detection of an acoustic signal corresponded to the appearance of a circular cracks seen on surface; in a very few cases, examination of surface after detection of a signal revealed presence of two ring cracks. Degree of toughening associated with crack healing is determined by a number of healed defects and an effectiveness of an individual healing.
The Improvement of Temperature Coefficient of Frequency in Thin Film Bulk Acoustic Wave Resonator using Secondary Harmonics
Authors: Yoshino Yukio , Takeuchi Masaki , Yamada Hajime , Goto Yoshihiko , Nomura Tadashi , Makino Takahiro , Arai Seiichi
Published: April 2011

We have succeeded in making an 870MHz-range thin film bulk acoustic wave (BAW) resonator that has a small temperature coefficient of frequency (TCF) using secondary harmonics. The 870MHz-range BAW resonator has been requested to have nearly zero TCF, because it will be used in an oscillator for remote keyless entry systems. The BAW resonator has composite structure that consists of Al electrodes and ZnO/SiO2. We directed our attention to the fact that ZnO and Al have negative TCF, and SiO2 has a positive one. It is theoretically possible to make zero TCF BAW resonators by optimizing the thickness ratio of ZnO and SiO2. However, using fundamental resonance, TCF is so sensitive to the thickness ratio that it cannot be easily controlled by MEMS techniques. We founds in finite element method simulation and confirmed by experiment that the TCF of secondary harmonics has a local minimum when changing the ZnO/SiO2 thickness ratio. As the result, a nearly zero TCF resonator without strict control of ZnO/SiO2 thickness ratio has been realized by adopting Al/ZnO/SiO2/ZnO/Al/SiO2 structure and combining thermal oxidized Si and sputtered SiO2. The resonator has the TCF of -1.86ppm/degree in the range of −40 to 85 degrees centigrade.
High Temperature Behavior of Polysilicon
Authors: Oh Chung-Seog , Coles George , Sharpe William N.
Published: April 2011

The polysilicon elements of thermal actuators can reach temperatures high enough to cause permanent deformation. A fundamental understanding of the constitutive behavior is necessary for intelligent design and life prediction, but mechanical testing at high temperatures is especially challenging at the micron level.

This paper describes techniques for testing freestanding thin-film polysilicon specimens in tension at temperatures up to 700°C. Strain is measured directly on the specimens by laser interferometry from platinum markers. The complete stress-strain curve can be obtained as well as strain versus time for creep tests. Initial results show that polysilicon is ductile at temperatures above 500°C and can have a high creep rate.
Nonuniformity in Selective Anodization of Silicon and its Application to Micro-Tip Fabrication
Authors: Uehara S. , Negishi N. , Matsubara T.
Published: April 2011

Characteristics of selective anodization of p+-type Si have been studied. Temporal evolution of the etching front was visualized by periodic porosity modulated anodization. The etching front proceeded inside along the bottom of mask making its angle with the mask bottom face sharper and sharper. It was also found that the etching front proceeds forming a specifically angled facet. Selective anodization was applied to form Si micro-tips. Proper time of anodization for p+-type Si substrate with an n-type circular shape mask left a Si micro-tip formed on the substrate. A high resolution SEM observation revealed that the apex of the tip was composed of {110} facets.
Channel Epitaxy of 3C-SiC on Si Substrates by CVD
Authors: Nishino S. , Okui Y. , Jacob C. , Ohshima S.
Published: April 2011

Epitaxial growth of 3C-SiC on Si substrates has been studied for many years, however an important issue is how to reduce the high density of interfacial defects. Channel epitaxy is the growth of a film on small channeled windows and is related to selective growth. Channel epitaxy of 3C-SiC grown on the seed 3C-SiC previously deposited on patterned Si substrates was achieved via CVD using hexamethyldisilane (HMDS). The proper selection of mask materials was also key to achieve channel epitaxy. Thermal oxide, silicon nitride and thin SiC masks were tried. Thin SiC was an effective mask to achieve selective growth at 1350°C. Smooth surface morphology was observed on both the channel regions and the mask regions at the growth temperature of 1350°C. Scanning electron microscopy revealed coalescence of the laterally grown regions via channel epitaxial growth of 3C-SiC.
3C-SiC Monocrystals Grown on Undulant Si(001) Substrates
Authors: Nagasawa Hiroyuki , Yagi Kuniaki , Kawahara Takamitsu , Hatta Naoki
Published: April 2011

A novel technique to reduce planar defects in 3C-SiC is to grow it on “undulant-Si” substrates, on which the surface forms countered slopes oriented in the [110] and [110] directions. In the initial stage of 3C-SiC growth, step flow epitaxy occurs on each slope of the substrate, reducing the anti-phase boundaries. Then, the stacking faults in the (111) and (111) planes are gradually annihilated by combining with counter-stacking faults, while those parallel to (111) and (111) vanish. The freestanding 3C-SiC exhibits anisotropy in its electrical properties. The origin of the anisotropy in electrical properties is discussed by referring to the results of X-ray diffraction study.
Thermal stress as the major factor of defect generation in SiC during PVT growth
Authors: Cherednichenko D. I. , Drachev R. V. , Khlebnikov I. I. , Deng X. , Sudarshan T. S.
Published: April 2011

Numerical simulations of the thermal stress distribution in a SiC boule 2” in diameter and 1” long grown by conventional PVT technique were performed based on the temperature field distribution in a resistively heated growth reactor that was simulated using the GAMBIT-2.0.4/FIDAP-8.6.2 software package. Analysis of the simulation results revealed the existence of a thermal stress, which was excessively nonuniform in distribution and whose magnitude exceeded the value of the critical resolved shear stress of 1.0 MPa by a factor of 2. The high stress initiated plastic deformation and the high temperature provoked the intense self-diffusion processes. The combination of these factors alters the mechanism of plastic deformation, significantly affecting the structural quality of the growing crystal. The influence of self-diffusion processes initiating the formation of interstitial atoms and vacancies; stacking fault formation as a result of the nonconservative motion of the basal plane dislocations; and micropipe formation from the dislocation groups piled up at silicon and carbon second phase inclusions are also discussed.
Ion Implantation Induced Deep Defects in n-type 4H-Silicon Carbide
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C. , Capano M. A.
Published: April 2011

Aluminum (Al) and argon (Ar) ions were implanted into n-type 4H-SiC epitaxial layers at 600 °C. The energy of the ions was 160 keV at a dose of 2 × 1016 cm-2. After annealing at 1600 °C for 5–60 minutes, Schottky diodes were fabricated on the ion implanted samples. Deep Level Transient Spectroscopy (DLTS) was used to characterize ion implantation induced defects. A defect at EC-0.18 eV was observed in the Al+ implanted devices annealed for five and fifteen minutes. However, annealing for 30 minutes produced an additional deeper defect at EC -0.24 eV. This defect annealed out after a sixty minute anneal. DLTS studies of Ar+ implanted devices showed six defect levels at EC -0.18 eV, EC -0.23 eV, EC -0.31 eV, EC -0.38eV, EC -0.72 eV, and EC -0.81eV. These defects are attributed to intrinsic-related defects. It is suggested that “hot” implantation of Al+ inhibits the formation of intrinsic-related defects. While “hot” implantation of Ar+ into 4H-SiC does not reduce the concentration of the vacancies and interstitials.
SiO2/SiC Interface Properties on Various Surface Orientations
Authors: Yano Hiroshi , Hirao Taichi , Kimoto Tsunenobu , Matsunami Hiroyuki
Published: April 2011

The interface properties of MOS capacitors and MOSFETs were characterized using the (0001), (1120), and (0338) faces of 4H-SiC. (0001) and (1120) correspond to (111) and (110) in cubic structure. (0338) is semi-equivalent to (100). The interface states near the conduction band edge are discussed based on the capacitance and conductance measurements of n-type MOS capacitors at a low temperature and room temperature. The (0338) face indicated the smallest interface state density near the conduction band edge and highest channel mobility in n-channel MOSFETs among these faces.
A semi-empirical model for electron mobility at the SiC/SiO2 interface
Authors: Saks Nelson S.
Published: April 2011

The mobility of electrons in inversion layers at SiC/SiO2 interfaces μinv has been characterized in 4H- and 6H-SiC using Hall effect measurements. In order to understand the cause of the low mobilities typically observed in SiC MOS devices, a semi-empirical mobility model has been developed based on a previous model for silicon inversion layers. Using this model, two scattering mechanisms, surface phonon and Coulomb scattering from high densities of electrons trapped at the SiC/SiO2 interface, are found to account reasonably well for the behavior of the mobility. The model employs a changing density of trapped electrons as a function of gate voltage to accurately model Coulomb scattering. Surprisingly, evidence of surface roughness scattering is not observed in any SiC MOS device.
Modeling the crystal growth of cubic silicon carbide by molecular dynamics simulations
Authors: Resta Nicoletta , Kohler Christopher , Trebin Hans-Rainer
Published: April 2011

The crystal growth of a seed of cubic SiC into the amorphous material has been investigated by means of classical molecular dynamics simulations. The crystallization process was studied with a set of supercells containing up to 2000 atoms, initially consisting of a 12 Å thick layer of crystalline SiC and a 18 Å thick layer of amorphous SiC at high pressure. The dynamic evolution of crystallization was then followed for several nanoseconds with the simulated annealing technique performed at constant pressure and temperature. The atomic interactions were described by the Tersoff potential. We studied the dependence of the growth process on the crystallographic orientation of the crystalline/amorphous interface by considering three different crystal planes, namely the {100}, {110}, and {111} planes. Within the pressure-temperature range considered in our simulations, we observed the crystal growth only for the {110} and the {111} orientations, but not for the {100} ones. The atomistic details of the growth mechanism are described and discussed.
Porous SiC – Prospective Applications (Invited)
Authors: Mynbaeva Marina
Published: April 2011

Possible applications for porous SiC (PSC) are addressed and related innovative aspects discussed. The formation and properties of PSC itself are considered first, since they define the area where PSC can be used. Then epitaxial growth on PSC substrates is reviewed in detail, with the emphasis on the chemical vapor deposition (CVD) technique. Next, new applications featuring the in-diffusion of V and Si into PSC for obtaining semi-insulating material and autodoping of GaN epitaxial layers from PSC substrates are presented.
A New Process for the Fabrication of SiC Power Devices and Systems on SiCOI (Silicon Carbide On Insulator) Substrates
Authors: Templier François , Daval Nicolas , Cioccio Léa Di , Bourgeat Daniel , Letertre Fabrice , Planson Dominique , Chante Jean-Pierre , Billon Thierry
Published: April 2011

Feasibility of 4H-SiC epitaxy on SiCOI substrates has been demonstrated, with high quality of obtained layers. Power Schottky diodes were designed and fabricated on these new structures, and exhibited very interesting electrical performance, particularly in reverse mode, with Vbr ∼ 1000 V. This technology is very promising for the realization of monolithic SiC power systems.
Large-Area, Device Quality GaN on Si Using a Novel Transition Layer Scheme
Authors: Rajagopal Pradeep , Gehrke Thomas , Roberts John C. , Brown J. D. , Weeks T. Warren , Piner Edwin L. , Linthicum Kevin J.
Published: April 2011

The emergence of III-nitride technology and fabrication of high quality GaN based devices is possible due to the advances in the heteroepitaxial growth of III-N thin-films on lattice-mismatched substrates. Typically, the substrate of choice is either SiC or sapphire. We have adopted 100mm Si as our substrate of choice; uniform substrates of high quality are inexpensive and plentiful due to decades of use in the microelectronics industry. Growth of device quality GaN on Si is challenged by the ∼17% lattice mismatch and an additional thermal expansion coefficient (TEC) mismatch of ∼56%. In order to accommodate this strain and TEC mismatch between Si and GaN, a novel transition layer was designed, grown and successfully optimized, ® obviating the need for either a PENDEO based overgrowth process or a SiC interlayer-based process. This growth technique (SIGANTIC®) does not require any wafer conditioning prior to growth and thus reduces the process complexity and maintains the cost effectiveness of the GaN on Si strategy. We will report on this manufacturable 100mm MOCVD heteroepitaxial process that consistently produces device quality AlGaN/GaN heterostructures with two dimensional electron gas (2DEG) mobilities typically around 1400 cm2/Vs at room temperature. Structural and electrical properties as determined by optical reflectance, atomic force microscopy, capacitance-voltage and van der Pauw Hall measurements, which are measured across the 100mm wafer, will be presented. Device results will be mentioned to show continuous wave (CW) RF operation at 2 GHz with competitive power output, gain and power added efficiency (PAE).
III-Nitride Growth on Lithium Niobate: A New Substrate Material for Polarity Engineering in III-Nitride Heteroepitaxy
Authors: Doolittle W. Alan , Namkoong Gon , Carver Alexander , Henderson Walter , Jundt Dieter , Brown April S.
Published: April 2011

Herein, we discuss the use of a novel new substrate for III-Nitride epitaxy, Lithium Niobate. It is shown that Lithium Niobate (LN) has a smaller lattice mismatch to III-Nitrides than sapphire and can be used to control the polarity of III-Nitride films grown by plasma assisted molecular beam epitaxy. Results from initial growth studies are reported including using various nitridation/buffer conditions along with structural and optical characterization. Comparisons of data obtained from GaN and AlN buffer layers are offered and details of the film adhesion dependence on buffer layer conditions is presented. Lateral polarization heterostructures grown on periodically poled LN are also demonstrated. While work is still required to establish the limits of the methods proposed herein, these initial studies offer the promise for mixing III-Nitride semiconductor materials with lithium niobate allowing wide bandgap semiconductors to utilize the acoustic, pyroelectric/ferroelectric, electro-optic, and nonlinear optical properties of this new substrate material as well as the ability to engineer various polarization structures for future devices.
Determination of AlGaN/GaN HFET Electric Fields using Electroreflectance
Authors: Kurtz S. R. , Allerman A. A. , Koleske D. D. , Baca A. G. , Briggs R. D.
Published: April 2011

A contacted electroreflectance technique was used to characterize the electronic properties of AlGaN/GaN heterostructure field-effect transistors (HFETs). By studying variations in the electroreflectance with applied electric field, spectral features associated with the AlGaN barrier, the 2-dimensional electron gas at the interface, and bulk GaN were observed. Barrier-layer composition and electric field were determined from the AlGaN Franz-Keldysh oscillations. Comparing HFETs grown on SiC and sapphire substrates, the measured AlGaN polarization electric field (0.25±0.05 MV/cm) approached that predicted by a standard model (0.33 MV/cm) for the higher mobility HFET grown on SiC.
Optical and electrical properties of semi-insulating GaN:C grown by MBE
Authors: Armitage R. , Yang Qing , Feick H. , Tzeng S. Y. , Lim J. , Weber E. R.
Published: April 2011

Semi-insulating wurtzite GaN:C of high optical quality is obtained with CCl4or CS2 doping sources in plasma-assisted molecular-beam epitaxy in Ga-rich growth conditions. The highest resistivity (107Ω-cm) is found for [C] in the low 1018cm−3range. An increasing fraction of carbon appears to form electrically inactive pair defects for higher doping levels causing the concentration of uncompensated residual donors to be higher in films with [C] in the 1019cm−3range compared with [C] in the 1018cm−3range. Blue (2.9 eV) and yellow (2.2 eV) luminescence bands are associated with carbon-related defects, and additional support is provided for the association of the blue luminescence with the carbon-acceptor deactivating pair defect. Finally, the temperature dependence of the resistivity is described within the grain-boundary controlled transport model of Salzmanet al., Appl. Phys. Lett.76, 1431 (2000).
Excitons of the Structure in Zinc-Blende InxGa1-xN and their Properties
Authors: Alexandrov Dimiter
Published: April 2011

The existence of excitons of the structure in zinc-blende InxGa1-xN is reported in this paper. The LCAO electron band structure of zinc-blende InxGa1-xN is calculated as function of both the electron wave vector and the electron radius-vector. The observed optical absorption edge in In-rich regions in InxGa1-xN is explained on the basis of this electron band structure. The excitons of the structure are found on the basis of the electron band structure of zinc-blende InxGa1-xN. The binding energy and the hydrogen like energy levels of these excitons are determined. It is found that these excitons are localized. The observed photoluminescence spectrum in In-rich regions of InxGa1-xN is explained by the excitons of the structure. It is found that destroying of these excitons occurs in their interactions with hetero-junction and that the electrons and the holes of exciton origin penetrate in the semiconductor of wider energy band gap. This phenomenon is used for explanation of the observed spectral blue shift of the electroluminescence in the quantum well structures on InxGa1-xN.
Optical Band Gap Measurements of InN Films in the Strong Degeneracy Limit
Authors: Haddad D. B. , Thakur J. S. , Naik V. M. , Auner G. W. , Naik R. , Wenger L. E.
Published: April 2011

The optical properties of InN thin films (0.5 μm thick) grown on sapphire substrates by plasma source molecular beam epitaxy deposition have been measured in order to study the effect of electron degeneracy on the band gap measurement. X-ray diffraction measurements show that the films are wurtzite polycrystalline at a growth temperature of 325 °C, whereas a completely c-axis textured growth at a temperature of 475°C. The Raman bands A1 (LO) and E2 are rather broad indicating the presence of a large number of structural defects. Hall effect measurements show that both the films are n-type with carrier concentrations of (8.0 ± 1.6) × 1020 cm−3 and (3 ± 0.6) × 1020cm−3, respectively. The optical absorption data on these samples show n dependent band gap edge and a peak corresponding to plasmon due to strong electron degeneracy. The band gap absorption data were analyzed assuming a direct band gap and incorporating the Moss-Burstein shift effect. By taking into account the non-parabolic dispersion and the band-renormalization effects for the conduction band of InN, the calculated true band gap (0.7 eV) agrees with other recent measurements on high quality InN films.
Electricaland Optical Properties of InN/Si Heterostructure
Authors: Mizuo K. , Yamaguchi T. , Saito Y. , Araki T. , Nanishi Y.
Published: April 2011

Single crystalline InN films were grown on Si substrates by radio-frequency plasma-excited molecular beam epitaxy. Electrical property of InN/Si heterojunction was investigated. We obtained rectifying characteristics in n-InN/p-Si heterostructure for the first time. Forward I-V characteristics were affected by both the buffer layer deposition and the nitridation process. Strong photoluminescence peaks for both single crystalline and polycrystalline InN films grown on the Si substrates were observed at around 0.8 eV, which were smaller than the previous reported PL emission peak of around 1.9 eV.
A Study of the Decomposition of GaN during Annealing over a Wide Range of Temperatures
Authors: Rana M. A. , Choi H. W. , Breese M. B. H. , Osipowicz T. , Chua S. J. , Watt F.
Published: April 2011

Annealing experiments were carried out on gallium nitride layers, which were grown on sapphire through Metal Organic Chemical Vapor Deposition (MOCVD). Rutherford Backscattering Spectrometry (RBS) was performed on as-grown and annealed GaN samples using a 2 MeV proton beam to study the stoichiometric changes in the near-surface region (750 nm) with depth resolution better than 50 nm. No decomposition was measured for temperatures o up to 800 °C. Decomposition in the near-surface region increased rapidly with a further increase o of temperature, resulting in a near-amorphous surface-region for annealing at 1100 °C. The depth profiles of nitrogen and incorporated oxygen in the decomposed GaN are extracted from the nanoscale RBS data for different annealing temperatures. The surface roughness of the GaN layers observed by atomic force microscopy (AFM) is consistent with RBS decomposition measurements. We describe the range of annealing conditions under which negligible decomposition of GaN is observed, which is important in assessing optimal thermal processing conditions of GaN for both conventional and nanoscale optoelectronic devices.
Spectroscopic Characterization of Ion-Implanted GaN
Authors: Chen L. , Skromme B. J.
Published: April 2011

We investigate implantation of high purity HVPE GaN with Mg, Be, C, Zn, Cd, Ca, N, O, P, As, Ne, and Ar. After annealing at 1300 °C, the material is characterized using low temperature photoluminescence (PL). The Mg acceptors exhibit much better optical activation than Be, C, Zn, Cd, or Ca acceptors implanted and annealed under the same conditions. Acceptor-bound exciton peaks and well-resolved donor-acceptor pair bands are observed for both Mg and Zn. A broad peak centered near 2.78 eV is obtained for Cd, confirming that it is deeper than Zn. Isoelectronic As or P exhibit sharp no-phonon bound exciton lines at 2.952 and 3.200 eV, respectively. Defect-related bands centered at 2.2 and 2.35 eV are studied. Both Be and C strongly enhance the yellow (2.2 eV) PL band, but no other impurities do so, including O.
Tunnel radiation in the luminescence spectra of GaN-based heterostructures
Authors: Yunovich A. E. , Kudryashov V. E. , Turkin A. N. , Leroux M. , Dalmasso S.
Published: April 2011

Tunnel effects in luminescence spectra and electrical properties of LEDs based on InGaN/GaN-heterostructures made by different technological groups were studied. The tunnel radiation in a spectral region of 1.9 - 2.7 eV predominates at low currents (J<0.2 mA). The position of the tunnel luminescence maximum orħħωmaxis approximately equal to the voltage U, orħħωmax= eU. The low energy spectral band is described by the theory of tunnel radiative recombination. Tunnel recombination mechanisms in GaN-based heterostructures are caused by high electric fields in the active InGaN/GaN - MQW layers. The energy diagram of the structures is analyzed. The probability of tunnel radiation is higher due to piezoelectric fields in InGaN quantum wells. The tunnel radiation spectral band was not observed in the more effective LEDs with modulated doped MQWs. The spectra of GaN-based LEDs are compared with tunnel radiation spectra of GaAs-, InP- and GaSb- based LEDs. The equation: orħħωmax= eU describes experimental data in various semiconductors in the range 0.5–2.7 eV.