bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Dislocation Behavior during Bulk Crystal Growth of SiC
Authors: Ohtani Noboru , Katsuno Masakazu , Nakabayashi Masashi , Tsuge Hiroshi , Fujimoto Tatsuo , Yashiro Hirokatsu , Sawamura Mitsuru , Aigo Takashi , Hoshino Taizo
Published: April 2011

It is well-known that SiC crystal deficiencies are delaying the realization of outstandingly superior SiC power electronics. Efforts to date have centered on eradicating micropipes, and 4H-SiC substrates with extremely low micropipe densities have been achieved. Nevertheless, SiC substrates and epilayers still contain several types of dislocations in densities on the order of thousands per square centimetres, which are nearly 100-fold micropipe densities. While not nearly as detrimental to SiC device performance as micropipes, it has recently been demonstrated that dislocations existing in SiC crystals degrade several characteristics of SiC devices, e.g., the forward bias characteristics of SiC pin diodes and the gate oxide reliability of SiC MOSFETs.

This paper reports several dislocation processes occurring during the growth of hexagonal SiC bulk crystals. Particularly, we focus on the dislocation formation and propagation processes in SiC crystals. We have investigated dislocation processes in 4H-SiC bulk crystals grown by the physical vapor transport (PVT) growth method, using defect selective etching and transmission electron microscopy (TEM).

It was found that foreign polytype inclusions introduced a high density of dislocations at the polytype boundary. In the polytype-transformed areas of the crystal, very few medium size hexagonal etch pits due to threading screw dislocations were observed, indicating that the polytype transformation ceased the propagation of threading screw dislocations. The oval-shaped etch pit arrays observed on the etched vicinal (0001)Si surface, indicative of the dislocation multiplication in the basal plane, showed characteristic distribution around micropipes and low angle grain boundaries. Based on the results, we will argue the dislocation behavior in PVT grown SiC crystals, suggesting that dislocation interaction and conversion are relevant processes to understanding the behavior.
Do You Really Expect To Grow Epilayers On That? A Rationale For Growing Epilayers On Roughened Surfaces
Authors: Sumakeris Joseph John , Hull Brett A. , O'Loughlin Michael J. , Ha S. , Skowronski Marek , Palmour John W. , Carter Calvin H.
Published: April 2011

We describe surface preparation and epilayer growth techniques that readily reduce the density of Vf drift inducing basal plane dislocations in epilayers to less than 10 cm-2 and permit the fabrication of bipolar SiC devices with very good Vf stability. The optimal process route requires etching the substrate surface prior to epilayer growth to enhance the natural conversion of basal plane dislocations into threading edge dislocations during epilayer growth. The surface of this relatively rough “conversion” epilayer is subsequently repolished prior to growing the device structure. We provide details on processing parameters and potential problems as well as describe devices produced using this low basal plane dislocation growth processes.
SIMS Analysis of Nitrogen in Silicon Carbide Using Raster Change Technique
Authors: Wang Larry , Park Byoung-Suk
Published: April 2011

Today's state of the art silicon carbide (SiC) growth can produce semi-insulating crystals with a background doping around 5×1015 atoms/cm3 or lower. It is essential to have an accurate measurement technique with low enough detection limit to measure low level nitrogen concentration. Current SIMS detection limit of low E15 atoms/cm3 will provide accurate determination for nitrogen doping level of 5E16 at/cm3 or higher. In order to determine the lower nitrogen concentration, it is necessary to provide a better detection limit and to separate the contribution of background nitrogen properly. The “raster changing” method provides an accurate way to determine and remove contribution of background nitrogen to the signal, because secondary ion intensities and matrix ion intensities can be analyzed at the same location of the sample by changing the primary beam raster size during a profile. In this study we have succeeded in applying the raster changing method to (a) N in the SiC substrate located under an SiC epi layer, and (b) the detection of N as low as 3E14/ cm3 a bulk-doped SiC substrate.
Growth Mechanism and Dislocation Characterization of Silicon Carbide Epitaxial Films
Authors: Dhanaraj Govindhan , Chen Yi , Chen Hui , Vetter William M , Zhang Hui , Dudley Michael
Published: April 2011

SiC homo-epitaxial layers were grown in a chemical vapor deposition process using silicon tetrachloride and propane precursors with hydrogen as a carrier gas. Growth rates were found to increase as temperatures increased at high carrier gas flow rate, while at lower carrier gas flow rate growth rates were observed to decrease as temperature increased. Based on the equilibrium model, “thermodynamically controlled growth” accounts for the growth rate reduction. The grown epitaxial layers were characterized using various techniques. Reduction in the threading screw dislocation (SD) density in the epilayers was observed. Suitable models were developed for explaining the reduction in the screw dislocation density as well as the conversion of basal plane dislocations (BPD) into threading edge dislocations (TED).
Atomic Structure of Non-Basal-Plane SiC Surfaces: Hydrogen Etching and Surface Phase Transformations
Authors: Soubatch Serguei , Lee Wai Y. , Hetzel Martin , Virojanadara Chariya , Coletti Camilla , Saddow Stephen E. , Starke Ulrich
Published: April 2011

A-plane (11-20) and diagonal cut (1-102) and (-110-2) surfaces of 4H-SiC have been investigated using atomic force microscopy (AFM), low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). After hydrogen etching the surfaces show large, flat terraces. On SiC(11-20) steps down to single atomic heights are observed. On the diagonal cut surfaces steps run parallel and perpendicular to the [-1101] direction, yet drastically different morphologies for the two isomorphic orientations are found. All surfaces immediately display a sharp LEED pattern. For SiC(1-102) and SiC(-110-2) the additional significant presence of oxygen in the AES spectra indicates the development of an ordered oxide. All three surfaces show an oxygen free, well ordered surface after Si deposition and annealing. A transformation between different surface phases is observed upon annealing.
Thermal Interactions of Ni on Stepped 6H-SiC Surfaces: Implications for Thin Film Microstructure
Authors: Woodworth Andrew , Raghavan Srikanth , Stinespring Charter D
Published: April 2011

Ni films are important as both Schottky junctions and Ohmic contacts for high temperature SiC devices. Ni/SiC Schottky junctions are observed to become Ohmic upon annealing. This transition has been attributed to changes in film microstructure. The experiments reported here compare the thermal behavior of Ni films deposited on standard 6H-SiC (0001) surfaces with films deposited on periodically stepped surfaces. The former were prepared by wet chemical etching and are typical of those used in device fabrication. The latter were prepared by high temperature hydrogen etching. Ni films ranging from monolayer to nominal device thickness (~50 nm) were annealed on both surfaces. Analysis of these surfaces by in-situ Auger electron spectroscopy (AES) and ex-situ atomic force microscopy (AFM) provided elemental, chemical and morphological information. The results show that the morphology and microstructure of annealed films are dependent on initial film thickness and substrate surface conditions.
Fabrication and Characterization of 5 kV IGBTs on 4H-SiC
Authors: Jonas Charlotte Elizabeth , Zhang Qingchun , Ryu Sei-Hyung , Agarwal Anant , Palmour John
Published: April 2011

P-channel planar IGBT devices were made on 4H-SiC. Punch-through buffer and drift layers were designed to block 5 kV were grown on 4H-SiC n-type substrate. Ion implantion was used for all selective doping such as n-well, p+, n+, JFET region and terminations. Gate oxidation was thermally grown and annealed. Blocking voltage of 5.7 kV was demonstrated. IGBTs exhibit VTH of -12 V, VT = -3.1 V, Rdiff,on = 400 mΩcm2 at Vg = -34 V at room temperature. Ron decreased to 108 mΩcm2 at Vg = -30 V at 300°C.
Template Routes to Non-Oxide Ceramic Nano- and Micro-Structures
Authors: Kusari Upal , Bao Zhihao , Ye Cai , Ahmad Gul , Sandhage Kenneth H , Sneddon Larry G
Published: April 2011

Non-oxide ceramic materials like boron carbide and silicon carbide are technologically relevant as advanced high temperature materials, while boron nitride is a thermally robust low-k insulating material with electronic applications. Efficient routes to boron carbide, boron nitride, and silicon carbide ceramic nanostructures have been developed which employ molecular and polymeric precursors, including the boron carbide precursor 6, 6'-bis(decaboranyl)hexane, the boron nitride precursor polyborazylene, and a commercially available silicon carbide precursor allylhydridopolycarbosilane(AHPCS), in conjunction with colloidal silica and biological silica “diatom” templates. Layered submicron-sized ordered void structures with three-dimensional periodicity and tunable length scales were fabricated by the melt infiltration of the precursors into ordered colloidal silica bead templates. Pyrolytic ceramic conversion followed by dissolution of the silica beads by chemical treatment with aqueous HF or NaOH generated highly uniform ceramic structures with thicknesses up to 50μm and ordered voids ranging in diameter from 50-150 nm. Following on earlier work by Sandhage who generated polymer and oxide ceramic structures, vacuum filtration of the ceramic precursor solutions through bioclastic silica diatom frustule templates generated polymer coated replicas of their 3-D micro- and nanostructures. Subsequent pyrolysis and dissolution of the frustules in 48% HF yielded free-standing ceramic structures with fine features on length scales of 60-200 nm. This technique therefore provides a large scale route to nano- and micro structured non-oxide ceramic materials. Structural control of the end products was achieved by changing the concentration of the precursor solution, pore size and/or the frustule template. Characterization by XRD, DRIFT, SEM, TEM and possible uses of these uniform nano- and micro-structured ceramics will be discussed.
Pattern Evolution of Self-Assembled Quantum Dots Under Biaxial Stresses
Authors: Pang Yaoyu , Huang Rui
Published: April 2011

A stressed epitaxial film can undergo surface instability. The stress field and the interface interaction have profound effects on the dynamics of surface evolution that leads to self-assembled quantum dots. In this paper, by using a nonlinear evolution equation, we investigate pattern evolution of self-assembled quantum dots under general biaxial stresses. It is found that the shape of quantum dots and their spatial ordering are strongly influenced by the relative magnitudes of the biaxial stresses. Linear perturbation analysis and nonlinear numerical simulations are conducted to elucidate the effect of stress anisotropy on the process of self-assembly that selects different patterns.
Use of sub-10 nm Diameter Upconversion Nanophosphors as Bio-labels
Authors: Lim Shuang Fang , Riehn Robert , Tung Chih-Kuan , Tank David , Ryu William S. , Yao Nan , Austin Robert H.
Published: April 2011

We have synthesized rare-earth doped sub-10 nm diameter upconverting yttrium oxide based nanophosphors by flame spray pyrolysis. We have investigated the emitted visible fluorescence of the sub-10nm nanophosphors under both infrared excitation and electron excitation, and observed comparable narrow band emission spectra. The viability of the nanoparticles for biological imaging was confirmed by imaging the digestive system of the nematode worm C. elegans in the upconversion mode. We have surface functionalized the nanophosphors making them suitable for bio labeling.
First-principles Study of Adsorption Energetics of Alkanethiols on GaAs(001)
Authors: Voznyy Oleksandr , Dubowski Jan J.
Published: April 2011

Adsorption of alkanethiols on GaAs (001) surface under low coverage conditions was studied using density functional calculations in a periodic supercell approach. The study of physisorbed precursor and transition to chemisorption revealed that hydrogen atoms stay on the surface upon S-H bond cleavage and significantly affect desorption products and energies, in agreement with available experimental data. Binding of thiols to GaAs is found to be comparable or stronger than that of thiols to noble metals surfaces. Calculated thiolate-surface binding energies are found to be higher for Ga-rich than for As-rich surfaces, and are strongly dependent on surface reconstruction, adsorption site and coverage. This dependence is explained by the violation or fulfillment of electron counting rule, rehybridization of surface atom orbitals and strain relaxation upon addition of extra electrons brought by adsorption.
Design of a Novel Electrically Conducting Biocompatible Polymer with Degradable Linkages for Biomedical Applications
Authors: Guimard Nathalie Kathryn , Sessler Jonathan L. , Schmidt Christine E.
Published: April 2011

Upon the discovery of the first conducting polymer in 1976, the replacement of metal-based semiconductors in many applications with conducting polymers was inevitable. Perhaps more surprisingly these materials showed promise in many biomedical applications. The finding that electrical fields and charges modulate shape, size, and proliferation of a number of cell types including nerve and bone, has prompted biomedical engineers to focus on the development of conducting polymer scaffolds for tissue regeneration and neural probes. A number of polymers have been studied for these applications, including polypyrrole (PPy), polythiophene, and polyaniline. One serious limitation to the use of conducting polymers in biological systems is their inability to degrade. Therefore, it has been proposed to design and synthesize a biocompatible, biodegradable, semiconducting polymer, which could broaden the scope of applications for conducting polymers. For instance, these unique polymers could potentially be implemented in temporary tissue and neural scaffolds, drug delivery, short-term electrodes, and tethers between nanotubes. Therefore, the goal of this investigation is to synthesize a polymer that is degradable, while maintaining conductivity. Initially, the incorporation of pyrrole oligomers into a biodegradable polymer was attempted; however, to overcome difficulties associated with the instability of these oligopyrroles, a novel polymer design has been proposed which incorporates thiophene oligomers. Oligothiophenes (OTs) are apt to be more conductive than oligopyrroles due to a smaller band gap between the valence and conductance bands. Additionally, OTs share many of the advantageous properties of oligopyrroles, including cell compatibility, but are more stable. The proposed novel co-polymer consists of quaterthiophene oligomers tethered together by aliphatic ester linkages, which would potentially render the co-polymer conductive by means of inter and intra chain oligo overlap and degradable via cleavage of the ester bond by esterases in the body. The synthesis of the novel copolymer, poly-dialcohol dimethyl quaterthiophene-co-adipic acid (PAMQAA) has been completed successfully and corroborated by NMR and MALDI. Initial characterization indicates PAMQAA has the following properties: Mw = 11,240-64,080 g/mol, PI = 1.2-1.4, degradation temperature = ∼160°C. Currently PAMQAA is being characterized to assess its Tg, Tm, conductivity, degradability, and biocompatability. Polymer modifications could allow further optimization of properties, such as the rate of degradation and conductivity, to target better the application of interest.
Integration of Biomolecules with Inorganic Ferroelectrics: A Novel Approach to Nanoscale Devices
Authors: Reiss Brian , Auciello Orlando , Ocola Leonidas E. , Firestone Millicent Anne
Published: April 2011

In this work, we investigate the feasibility of using a surface-tethered heptapeptide sequence as the basis for a ferroelectric-actuated component in a nanofluidic device. The fluorescently-labeled peptide sequence, (CISLLHSTC) is shown by fluorescence microscopy to selectively coat the PZT patterned channel floors. The peptide binding strength to PZT is determined over a range of flow rates in the patterned channel by imaging the fluorescence intensity of the coated channel and monitoring the output spectroscopically. The peptide is found to be stripped from the PZT at flow rates exceeding 5mL/h. Initial results demonstrating the possibility of covalently integrating the short peptide sequence to larger biological components such as antibodies are also presented.
Development of Novel Nanostructured Tissue Engineering Scaffold Materials through Self-assembly for Bed-side Orthopedic Applications
Authors: Zhang Lijie , Ramsaywack Sharwatie , Fenniri Hicham , Webster Thomas J.
Published: April 2011

The objective of the current study was to utilize a natural self-assembled organic biomaterial (helical rosette nanotubes (HRNs)) to improve bone growth necessary for orthopedic implant applications. The DNA base pair building blocks of HRNs can self-assemble through 18 H-bonds to form a supermacrocycle in water which then stack to form a nanotube 3.5 nm in diameter and several μm in length. The nanometric features and ability to place diverse amino acid side chains on HRNs make them intriguing materials for orthopedic applications. In this study, HRNs are combined with a biocompatible hydrogel matrix in order to obtain more robust scaffolds. Bone cell experiments in vitro demonstrated that the novel HRNs with hydrogels could greatly enhance osteoblast (bone-forming cell) adhesion even at a very low concentration (close to 0.001mg/ml). Morphology of the HRNs with hydrogel scaffolds was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Results showed that there were bundles of nanotubes in the HRNs with hydrogel scaffolds. Therefore, considering the good biocompatibility and nano bone-like structure of these scaffolds, the nanostructured hydrogel matrix with HRNs have the potential to serve as novel bone building agents for “on-the-site” orthopedic applications.
Detection of Respiratory Viruses with Plastic High Throughput Screening Devices
Authors: Zhao Zhengshan , Diaz-Quijada Gerardo A. , Peytavi Régis , LeBlanc Éric , Frenette Johanne , Boivin Guy , Zoval Jim V. , Madou Marc , Dumoulin Michel M. , Veres Teodor , Bergeron Michel G.
Published: April 2011

Microarrays have become one of the most convenient tools for high throughput screening and have catalyzed major advances in genomics and proteomics. Other important applications can be found in medical diagnostics, detection of biothreats, drug discovery, etc. Integration of microarrays with microfluidic devices can be highly advantageous in terms of portability, shorter analysis time and lower consumption of expensive biological analytes. Since fabrication of microfluidic devices using traditional materials such as glass is rather expensive, there is a high interest in employing polymeric materials as a low cost alternative suitable for mass production. We present proof-of-concept DNA arrays on a plastic platform for the detection of four important respiratory pathogens: Influenza A virus, respiratory syncytial virus, human enterovirus, and human metapneumovirus.

This was accomplished by amplifying the genetic material from the viruses and simultaneously labeling the amplicons with a fluorescent dye (Cy3) via a highly sensitive multiplex Reverse Transcription Polymerase Chain Reaction (RT-PCR). The resultant RT-PCR product was hybridized, without further purification, with an array of specific oligonucleotide probes (20 mers) that had been covalently bound to a plastic substrate. Results indicate a high signal to background ratio that is comparable to commercially available microarray glass slides. In addition, 5 minute hybridization on this plastic substrate has been demonstrated using a centrifugal microfluidic platform, paving the way to a rapid medical diagnostic device for point-of-care use that is based on a low-cost portable Micro-Total-Analysis-System (μ-TAS).
Ge/Si self-assembled Islands for Photonics Applications
Authors: Boucaud Philippe , El Kurdi Moustafa , Li Xiang , Sauvage Sébastien , Checoury Xavier , David Sylvain , Yam Navy , Fossard Frédéric , Bouchier Daniel , Fishman Guy
Published: April 2011

We first present an analysis of the band line-up in the case of SiGe/Si quantum wells and in the case of SiGe/Si self-assembled islands. The conduction and valence band diagrams are obtained from a 30 band k.p Hamiltonian which allows to describe simultaneously conduction and valence band states. The strain field is obtained from a microscopic valence force field theory. The band edge alignment is strongly dependent on the input parameters for this heterosystem. We determine the average valence band offset from photoluminescence measurements of heterostructures grown on relaxed SiGe buffer layers. A type II band line-up is calculated for all Ge compositions in the case of two-dimensional quantum wells and SiGe/Si self-assembled islands. The 30-band formalism allows the determination of the near-infrared interband recombination energy as a function of the self-assembled island structural parameters. We then present recent results obtained by embedding SiGe/Si self-assembled islands in two-dimensional photonic crystals. The photoluminescence of GeSi islands acts as an internal probe to characterize the optical properties of silicon-based two-dimensional photonic crystals designed for the near-infrared spectral range. Cavities, defect-free photonic crystals operated at the second Bragg order and two-dimensional photonic crystals fabricated on top of one-dimensional Bragg mirrors (2D + 1D) are described. We show that, in the case of 2D +1D structures, we can control the quality factor of optical modes at the second Bragg order by matching the resonance conditions and controlling the thickness of the layers. Photonic crystals with pure Ge layers are finally described.
Luminescence in Multilayers of SiGe Nanocrystals Embedded in SiO2
Authors: Avella Manual , Prieto Ángel Carmelo , Jiménez Juan , Rodríguez Andrés , Sangrador Jesús , Rodríguez Tomás , Ortiz María Isabel , Ballesteros Carmen , Kling Andreas
Published: April 2011

Luminescent multilayers of SiGe nanocrystals embedded in an oxide matrix have been fabricated by Low Pressure Chemical Vapour Deposition of a-SiGe and SiO2 in a single run followed by a Rapid Thermal Annealing treatment. The diameter of the nanoparticles, the oxide interlayer thickness and the annealing conditions have been investigated in order to get the maximum intensity of the luminescence. The structures with small nanoparticles (3-4.5 nm) separated by thick oxide barriers (≈35 nm) annealed at 900 °C for 60 s yield the maximum intensity. These samples exhibit luminescence from 80 K to room temperature. An additional treatment at 450 °C in forming gas further increases the intensity of this luminescence.
Laser Crystallization of Silicon Thin Films Using Photo Absorption Layer Formed by Spin Coating of Carbon Particles
Authors: Andoh Nobuyuki , Maki Masato , Sameshima Toshiyuki , Sano Naoki
Published: April 2011

We report crystallization of amorphous silicon films 50∼1400 nm thick formed on glass substrates by irradiation of an infrared semiconductor laser. Carbon particles with a mean diameter of 200 nm were uniformly coated on the silicon films as the optical absorption layer. Samples were irradiated with a 940-nm continuous wave (CW) semiconductor laser with a power of 20 W. A high optical absorbance 76.5% at 940 nm of the carbon particles layers resulted in annealing of silicon films by heat diffusion from the carbon particle layers. After removing the carbon particles layer, Raman scattering spectral measurements were carried out. A high scattering intensity and a sharp crystalline silicon phonon band were observed. The analysis of Raman spectra revealed a crystalline volume ratio almost 1.0. The analysis of the optical reflectivity spectra also revealed that the silicon films were crystallized in the whole thickness by the present method.
Nonlinear Optical Properties of Si Nanocrystals
Authors: Spano Rita , Cazzanelli Massimo , Daldosso Nicola , Gaburro Zeno , Ferraioli Luigi , Tartara Luca , Yu Jin , Degiorgio Vittorio , Hernandez Sergi , Lebour Youcef , Pellegrino Paolo , Garrido Blas , Jordana Emmanuel , Fedeli Jean Marc , Pavesi Lorenzo
Published: April 2011

A systematic study of nonlinear optical properties of silicon nanocrystals (Si-nc) grown by plasma enhanced chemical vapor deposition (PECVD) is reported. Nonlinear optical refraction and absorption have been measured by z-scan technique at three different time regimes and at different wavelengths to investigate both the thermal and electronic responses. For this purpose three different laser sources have been used. Different behaviors, as expected from the theory, for different pump pulse durations are observed.
Mn-incorporated ZnSe and CdSe 1-dimensional Nanostructures
Authors: Hwang Seonoh , Lee Jinyoung , Lee Hyunju , Yoon Sangwon , Park Jeunghee
Published: April 2011

Novel Mn-incorporated ZnSe and CdSe 1-dimensionl nanostructures; straight nanowires, zigzagged nanobelts, and nanohooks, were first synthesized using chemical vapor deposition method. The Mn content reaches up to 40%. They all consisted of single-crystalline wurtzite structure for all Mn content. The structure has been thoroughly investigated by high-resolution transmission electron microscopy images as well as energy-dispersive X-ray fluorescence spectroscopy. The X-ray diffraction pattern confirms the formation of the wurtzite structure, even for 40% Mn incorporation. The lattice constants of Mn-doped ZnSe and CdSe 1-D nanostructures are expanded and reduced, respectively, by the Mn doping. The Mn2+ emission at 2.1 eV, originating from the d-d (4T1 → 6A1) transition, confirms the effective paramagnetic Mn2+ doping at tetrahedral coordinate sites. These Mn-incorporated nanostructures exhibit a paramagnetic behavior.
Patterned Carbon Nanotube Thin-Film Transistors with Transfer-Print Assembly
Authors: Sangwan Vinod. K. , Hines D. R. , Ballarotto V. W. , Esen G. , Fuhrer M. S. , Williams E. D.
Published: April 2011

Conditions for the transfer printing of patterned carbon nanotube (CNT) films, along with a Au-gate, a poly methylmethacrylate (PMMA) dielectric layer and Au source-drain electrodes have been developed for the fabrication of thin-film transistors on a polyethylene terephthalate (PET) substrate. Chemical vapor deposition (CVD) grown CNTs were patterned using a photolithographic method.

Transfer printing was used to fabricate devices having both top gate and bottom gate configurations. Replacement of the SiO2 dielectric with PMMA correlates with a decreased hysteresis in the transconductance behavior. Encapsulation of the CNTs between the polymeric substrate and dielectric layer yields ambipolar behavior. Variations in device performance are also observed as a function of CNT film density and channel length, suggesting changing contributions of the metallic and semiconducting CNTs to the transport mechanism.
Single Walled Carbon Nanotube Analysis by Photoluminescence and Raman Microscopy: Rapid, Robust Acquisition and Simulation of Quantum and Chiral Maps to Ease Structural Assignments
Authors: Gilmore Adam Matthew , Adar Fran , Lee Eunah , Kaminski Ray , Whitley Andrew
Published: April 2011

This paper describes improved methods for both data acquisition and analysis that are pertinent to interpreting the structural composition of single-walled carbon nanotube (SWNT) mixtures and suspensions.

Rapid data acquisition of photoluminescence is made possible with a specially configured spectrofluorometer which uses a liquid nitrogen-cooled InGaAs array detector, imaging spectrograph, excitation reference photodiode and tunable xenon excitation source to collect seamless, instrument-corrected, excitation-emission quantum maps. The preferred instrument configuration with the InGaAs array can generate a quantum map with both high S/N levels and spectral resolution in only seconds to minutes; previous single-channel InGaAs photodiode and photomultiplier detector measurements took hours to days. The standard spectral range for excitation and emission is from 250 nm to 1700 nm with an option to extend to 2200 nm. Robust analysis of the quantum maps is facilitated by a custom global analysis program (US Patent Pending) which incorporates a powerful ‘double-convolution integral’ DCI algorithm to simultaneously model the excitation and emission spectral bands for each SWNT species. The patented DCI algorithm reduces the number of free fitting parameters for the spectral simulation by up to a factor of 1000 compared to conventional 2 D spectral simulators. The global analysis yields quantitative information on the chirality and diameter parameters of SWNT species in a given mixture. Together the acquisition hardware and analysis software constitute significant developments with respect to enhanced sensitivity and statistical significance for quantifying the components of complex SWNT mixtures.

Raman maps of SWNT's were collected from dispersions plated onto substrates such as silicon plates using multiple excitation wavelengths. Identification of the chirality of the tubes was made using the Kataura plot. In many instances single lines in the radial breathing mode region were recorded indicating the presence of a single tube. The implication for this observation is that there is more than adequate sensitivity to detect and identify single-walled tubes. More recently Raman excitation on an AFM using a gold-coated tip to induce surface enhancement has been achieved. In this configuration it will be possible to map the topology of the tubes using detailed information on their structural composition.
Covalent Bond Formation in Defected Nanopeapods Induces Local Deformations on Nanotube Walls
Authors: Yumura Takashi , Kertesz Miklos
Published: April 2011

Properties of defected nanopeapods, in which a defected C60 cage with a C1–C59 topology is encapsulated inside a (10,10) single walled carbon nanotube, have been analyzed using density functional theory (DFT) calculations. When new CC bonds are formed between the defected C60 and the nanotube, the CC network of the nanotube is perturbed near the binding site, and has butadiene and quinonoid perturbations. Such geometrical changes could play an important role in the selective functionalizations of carbon nanotubes.
Carbon Nanotube - Silicon Heterojunction Hyperspectral Photocurrent Response
Authors: Kuo Teng-fang , Straus Daniel A. , Tzolov Marian , Xu Jimmy
Published: April 2011

Carbon nanotubes (CNT) have been studied intensively for explorations of their unique electrical and mechanic properties in many applications. However, direct and functional integration of carbon nanotubes with silicon to form an electronically functional structure or device has remained a great challenge. Whereas vertically aligned bundles of nanotubes have been grown previously on silicon, the integration is mechanical, rather than electronical, in nature and the application of such mechanical integration is rather limited. In this work, we report on electronically functional integration of carbon nanotube with silicon, i.e., the formation of an electronic heterojunction by controlled growth of vertical and highly ordered array of ‘carbon nanotube - silicon’ (CNTS) heterojunctions of uniform diameter, length, and alignment. Moreover, we examine it as a hyperspectral photodiode. From the measured spectral dependence of the photocurrent, one may also extract the band gap of the nanotubes, which we find to be in agreement with that determined from conductance measurements. Mechanism of the infrared photocurrent response is elucidated by the current-voltage (I-V) and radiation intensity-photoresponse measurements. The linear intensity dependence of the photoresponse in the absorption ranges of Silicon and CNTs and the measured I-V characteristics all suggest that the photocurrent responses corresponding to the Silicon and CNT bands both originate from the intrinsic functionality of the heterojunction.
Molecular-Wetting Control by Ultrasmooth Pentacene Buffer for High-crystallinity Organic Field-Effect Transistors
Authors: Itaka Kenji , Yamashiro Mitsugu , Yamaguchi Jun , Haemori Masamitsu , Yaginuma Seiichiro , Matsumoto Yuji , Koinuma Hideomi
Published: April 2011

Organic thin film devices are of interest for a variety of forthcoming ubiquitous electronics applications. In order to build ubiquitous high-performance devices, it is necessary to fabricate crystalline thin films of various organic materials onto “ubiquitous substrates” that are dictated by applications. However, many organic thin films crystallize only on a limited selection of substrates. Unfortunately, promising organic molecules, which have a large overlap of pi-orbitals between molecules, cannot migrate freely on a substrate because of stronger cohesion between molecules than interaction between the molecule and the substrate. Therefore, enhancement of the molecule-substrate interaction, i.e. ‘molecular wettability’ should promote crystallization. We found that an ultrasmooth monolayer of pentacene (C22H14), which can be grown on many general dielectric substrates, changes the molecular wettability of a substrate for other poorly wettable organic materials. We also demonstrate that a field effect transistor (FET) using a crystalline C60 thin film on a pentacene-buffered substrate can have a mobility of 4.9 cm2/Vs, which is 5-fold higher than that of C60 FETs without the buffer. Molecular wetting-controlled substrates can thus offer a general solution to the fabrication of high-performance crystalline plastic and molecular electronics.
Self Organization in Thin Films of a Substituted Perylene Imide with a Twisted Aromatic Core
Authors: Graaf Harald , Mattheus Christine C , Schlettwein Derck
Published: April 2011

The aromatic core of perylene bisimides can be twisted by chemical substitution with chlorine in the bay-position. An example for this strategy is 1,6,7,10-tetra-chloro-N,N'-dimethyl-perylene-tetracarboxylic-bisimide, Cl4MePTCDI. This twisting leads to a decrease in directed intermolecular interactions, which causes a decrease in the electronic coupling of the molecules, interesting to be investigated in thin films of this molecular semiconductor. An amorphous solid phase was formed by physical vapor deposition. This amorphous phase showed the tendency to crystallize under ambient conditions as apparent von optical microscopy at the films. The crystallized phase was investigated by atomic force microscopy AFM and optical methods, where a formation of weak excimers was found.
Dependency of Nonvolatile Memory Behavior on Curing Temperature for Au Nanocrystals Embedded in PVK
Authors: Han Beyong-il , Lee Chang-Kyu , Kwon Jong-Sung , Na In-Chul , Park Jea-gun , Kim Young-Min
Published: April 2011

A bistable effects of Au nano-crystals embedded in poly(N-vinylcarbazole) (PVK) were observed. Subsequently we investigated dependency of the nonvolatile memory behavior on curing temperature for the Au nano-crystals embedded in the PVK. For the study, in the devices of different curing temperatures we measured current-voltage characteristics for the devices and investigated the formation of the Au nano-crystals using cross sectional transmission electron microscopy (TEM). The nonvolatile memory behavior depends on the curing temperature, which is attributed to the suitable formation of the Au nano-crystal.
An Investigation of Au-Ag Interface Formed by Cold Welding Using Focused Ion Beam/Transmission Electron Microscopy
Authors: Cao Yifang , Yao Nan , McIlwrath Kevin , Zhou Jikou , Osinkolu Gabriel , Soboyejo Winston O.
Published: April 2011

This paper reports the recent results of a transmission electron microscopy study of cold-welded and e-beam deposited Au-Ag interfaces. Dust particles were observed to be embedded between the cold-welded interfaces. These are shown to amplify the defect regions caused by surface asperities. Electron energy loss spectroscopy (EELS) analysis revealed that there was no significant diffusion zone across the cold welding interface. However, sub-micron mechanical twining structures were revealed by transmission electron microscopy (TEM) analyses. These were found to penetrate through both the cold-welded and control Au-Ag interfaces, but with different orientations.
Texture Evolution in Cu Films and Lines
Authors: Chung Chia-Jeng , Field David , Park No-Jin , Woo Christy
Published: April 2011

Grain growth in polycrystalline films is controlled by the energetics of the surface, interface and grain boundaries as well as strain energy. The unique character of damascene lines fabricated from electroplated Cu films introduces the additional considerations of bath chemistry and geometric constraints. The moderate stacking fault energy of Cu allows for the development of a substantial twin fraction for certain growth conditions. This paper discusses in-situ observation of grain growth in Cu films and lines under various processing conditions. It is shown that for thicker films and for structures constrained within damascene trenches the energetics of twin boundary formation play a large role in texture development of these structures.
Activation of Low k Dielectrc Surfaces for ALD Barrier Formation
Authors: Liu Junjun , Bao Junjing , Shi Hualiang , Ho Paul S.
Published: April 2011

Atomic layer deposition (ALD) of ultra-thin barrier layers is a key process for implementation of Cu/low k interconnects. Low k dielectric surfaces are generally characterized by weak surface bonds which have to be properly activated for barrier formation. In this study, we investigated the surface activation of low k dielectrics by atomic hydrogen, nitrogen and ammonia beams for ALD of Ta/TaN barrier layers. In-situ x-ray photoemiision spectroscopy (XPS) together with differential FTIR were used to examine the beam modification of the surface and the subsequent growth on the low k surface. The evolution of the low k surface chemistry revealed an initial transient growth region controlled mainly by the substrate surface chemistry. The initial chemisorption was found to be through formation of Ta-O bonds on organosilicates (OSG) and charge transfer complexes on aromatic SiLK. This led to a significant slower initial nucleation on the OSG low k surface without beam activation. The atomic beams, particularly the nitrogen and amine radials, were found to serve as effective reducing agents in initiating and enhancing the precursor chemisorption. This led to an improvement of the barrier film quality and an increase of the deposition rate at a temperature compatible with low k dielectrics (< 400C). In the subsequent linear growth region, atomic hydrogen species was able to reduce the chlorine content under appropriate temperature and with sufficient purge. The effect of porosity in low k dielectrics on barrier formation will be discussed.
Height Dependent Resistivity of Copper Interconnects in the Size Effect
Authors: Kitada Hideki , Suzuki Takashi , Kimura Takahiro , Nakamura Tomoji
Published: April 2011

We investigated the copper grain size dependence on the interconnect line height using the EBSD (Electron Back Scattering Diffraction) pattern method. In our grain size measurements, we excluded the twin boundaries because of its small contribution to the electron scattering. Our experiments showed that the average grain size of a 70 nm-high line was about 24% smaller than for a 190 nm-high line.

We estimated the grain boundary scattering components by the Fuchs-Sondheimer (FS) and the Mayadas-Shatzkes (MS) models including the line height dependence of the grain size parameter (d). In order to evaluate precisely the influence of height dependence of grain size in the FS and MS models, we also determined the surface scattering coefficient of the Ta/Cu and SiC/Cu interfaces by an independent experiment.

From this, we found that grain boundary scattering components became approximately 32% larger for the 70 nm-wide line when the line height dependence of the grain size was taken into consideration.
Localized Charge Trapping Memory Cells in a 63 nm Generation with Nanoscale Epitaxial Cobalt Salicide Buried Bitlines
Authors: Mueller Torsten , Kleint C. , Fitz C. , Isler M. , Riedel S. , Sachse J.-U. , Olligs D. , Boubekeur H. , Heinrichsdorf F. , Polei V. , Pritchard D. , Verhoeven M. , Lattard L. , Markert M. , Schupke C. , Tippelt B. , Teichert S. , Reisdorf R. , Ludwig C. , Stein v. Kamienski E.G. , Mikolajick T. , Nagel N.
Published: April 2011

A 63nm Twin Flash memory cell with a size of 0.0225μm2 per 2 (or 4) bits is presented. To achieve small cell areas, a buried bit line and an aggressive gate length of 100 nm are the key features of this cell together with a minimum thermal budget processing. A novel epitaxial CoSi2 process allows the salicidation of local buried bitlines with only a few tens of nanometer width.
The Optical and Electrical Properties of SiOx(x<2) Thin Films Prepared by Pulsed Laser Deposition Technique
Authors: Park Byoung Youl , Lee Sol , Bae Chang Hyun , Park Seung Min , Park Kyoungwan
Published: April 2011

SiOx (x<2) films were deposited in an O2 atmosphere using Si target in a pulsed laser deposition system. Post-annealing process was employed in an O2 atmosphere to form the nanometer-sized Si crystallites embedded in the SiO2 films. The transmission electron microscope analysis shows the existence of crystalline silicon nano-dots with diameters ranging from 2 to 4 nm. Also, the clear separation of Si and SiO2 phases can be seen in the X-ray photoemission spectra. Photoluminescence peak from the annealed films was obtained, which is attributed to the quantum confinement effect of the Si nano-dots. C-V measurements of the metal-oxide-silicon (MOS) structure containing the silicon nano-dots in the oxide layer were performed to investigate the charging/discharging behavior of the silicon nano-dots. The maximum program window of the MOS was measured to be4.1V under ±5V sweep.
The Study on Charge-trapping Mechanism in Nitride Storage Flash Memory Device
Authors: Wu Jia-Lin , Chien Hua-Ching , Chang Chi-Kuang , Liao Chien-Wei , Lee Chih-Yuan , Wang Je-Chuang , Chen Yung-Fang , Kao Chin-Hsing
Published: April 2011

In this work, the charge-trapping distributions of polysilicon-oxide-nitride-oxide-silicon (SONOS) structure are studied. The trapping energy level of SiNx films with different composition ratio deposited by low-pressure chemical vapor deposition (LPCVD) were first characterized by photoluminescence (PL) measurement. Moreover, using F-N/CHE program and charge pumping techniques, the vertical location and the lateral distribution of programmed charges are investigated in the nitride films with different composition ratio. The study offers strong evidence that the density of charge-trapping levels in the Si-rich nitride is higher than the standard nitride. A simple qualitative model and calculation explains that the trapping level distributions in the SiNx films are shallower by increasing relative Si-content. Furthermore, we have observed the nitride trap vertical location was changed by adjusted Si/N composition ratio. And the lateral distribution of hot electron programmed charges in the modified nitride is broader than that in the standard nitride because it offered more charge-trapping sites and shallower charge-trapping levels. In summary, the study can help researchers to understand the nitride charge-trapping mechanism and the analysis of optical/electrical characteristics.
Resistance Non-volatile Memory – RRAM
Authors: Ignatiev Alex , Wu Naijuan , Chen Xin , Nian Yibo , Papagianni Christina , Liu Shangqing , Strozier John
Published: April 2011

Electric-pulse induced resistance (EPIR) change effect encompasses the reversible change of resistance of a thin oxide film under the application of short, low voltage pulses. The phenomenon is widely observed in complex and binary oxides, and is the basis for development of non-volatile resistance random access memory (RRAM). A variety of analytical techniques have been employed to understand the origin of the resistance change with recent data yielding a model incorporating oxygen ion/vacancy diffusion and pile-up near the interface region of the oxide at the impervious metal interface. Further efforts are still required to fine tune the model and apply it to the optimization of RRAM device development.
A Proposal of a Parallel Resistance Model for the Conduction Mechanism of Binary Transition Metal Oxide ReRAM
Authors: Kinoshita Kentaro , Noshiro Hideyuki , Yoshida Chikako , Sato Yoshihiro , Aoki Masaki , Sugiyama Yoshihiro
Published: April 2011

A parallel resistance model (PRM), in which the total resistance, Rtotal, is given by a parallel connection of resistance of a filament, Rfila, and that of a film excluding a filament, Rexcl, was proposed to understand DC electric properties of resistive RAM (ReRAM). Here, the relationship of 1/Rtotal = 1/Rfila + 1/Rexcl is satisfied. To prove the validity of this model, the dependence of the relationship between resistance and temperature, R(T), of Pt/NiO/Pt on an area of a top electrode, S, was investigated. It was clarified that R(T) depended on S, which is the result definitely expected by the PRM. It was also clarified that smaller S is crucial to observe intrinsic properties of a filament of ReRAM.
Spectroscopic Ellipsometry Studies of Tb-doped SiO2 Thin Films
Authors: Feng Zhe Chuan , Feng Zhe Chuan , Chang Yia Chung , Li Ting Kai
Published: April 2011

The optical properties of Tb-doped SiO2 films have been studied from multi-wavelength spectroscopic ellipsometry (SE) measurements performed over the 250–1100 nm wavelength range. The SE modeling carried out with care to adhere as much to the ellipsometric fitting qualities. The refractive index dispersions, the layer thickness, and the lateral thickness variation of the films are given and discussed regarding the optical constitution of these films and the ellipsometric validity of these parameters
Preparation of Cu(In1-xGax)Se2 Thin Films and Solar Cells Using a Se-radical Beam Source
Authors: Ishizuka Shogo , Yamada Akimasa , Shibata Hajime , Sakurai Keiichiro , Fons Paul , Matsubara Koji , Niki Shigeru
Published: April 2011

We have grown device-grade Cu(In,Ga)Se2 (CIGS) thin films using a RF-cracked Se-radical beam source. A unique combination of film properties: smooth surface, large grain size and high photovoltaic performance are shown. A competitive energy conversion efficiency of 17 % has been demonstrated from a solar cell fabricated using a CIGS absorber grown with a Se-radical source. In addition to the unique combination of film properties and high photovoltaic performance, a significant improvement in the use of Se source material in comparison with the conventional Se-evaporative sources has been demonstrated.
Zn-Based Buffer Layer and High-Quality CIGS Films Grown by a Novel Method
Authors: Yamada Akira , Meng Fanying , Chiba Yoshiyuki , Kawamura Masahiro , Konagai Makoto
Published: April 2011

ZnMgO was fabricated by MOCVD and the films were applied to a buffer layer of Cu(InGa)Se2 solar cells.

A nove growth method for Cu(InGa)Se2 was described in which cracked Se was utilized.