bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion Beam Induced Surface Modulations from Nano to Pico: Optimizing Deposition During Erosion and Erosion During Deposition
Authors: MoberlyChan Warren John , Schalek Richard
Published: April 2011

Ion beams of sufficient energy to erode a surface can lead to surface modulations that depend on the ion beam, the material surface it impinges, and extrinsic parameters such as temperature and geometric boundary conditions. Focused Ion Beam technology both enables site-specific placement of these modulations and expedites research through fast, high dose and small efficient use of material. The DualBeam (FIB/SEM) enablesin situmetrology, with movies observing ripple formation, wave motion, and the influence of line defects. Nanostructures (ripples of >400nm wavelength to dots spaced <40nm) naturally grow from atomically flat surfaces during erosion, however, a steady state size may or may not be achieved as a consequence of numerous controlled parameters: temperature, angle, energy, crystallography. Geometric factors, which can be easily invoked using a FIB, enable a controlled component of deposition (and/or redeposition) to occur during erosion, and conversely allow a component of etching to be incurred during (ion-beam assisted) deposition. High angles of ion beam inclination commonly lead to “rougher” surfaces, however, the extreme case of 90.0° etching enables deposition of organized structures 1000 times smaller than the aforementioned, video-recorded nanostructures. Orientation and position of these picostructures (naturally quantized by their atomic spacings) may be controlled by the same parameters as for nanostructures (e.g. ion inclination and imposed boundary conditions, which are flexibly regulated by FIB). Judicious control of angles during FIB-CVD growth stimulates erosion with directionality that produces surface modulations akin to those observed for sputtering. Just as a diamond surface roughens from 1-D ripples to 2-D steps with increasing angle of ion sputtering, so do ripples and steps appear on carbon-grown surfaces with increase in angle of FIB-CVD. Ion beam processing has been a stalwart of the microelectronics industry, is now a vital tool for research of self-organizing nanostructures, and promises to be a focus for future picotechnology.
Self-Organized Swelling of a Metal-Capped Polymer Thin Bilayer
Authors: Kwon S. Joon , Park Jae-Gwan
Published: April 2011

Self-organized swelling of a metal-polymer bilayer directed by a corrugated mold was reported. The corrugated pattern by the elastomeric mold was observed from the earlier stages of swelling. The temporal evolution of the self-organized pattern was analyzed theoretically, and the experimental data were well matched with the analysis. The maximum harmonic number for the corrugated wave number was also analyzed. With a relatively large line width, irregular self-organized patterns were observed.
Nanohole and Nanopillar Arrays on GaAs and GaSb Using Nanosphere Lithography and Bromine Ion Beam Assisted Etching
Authors: Qian Xifeng , Li Jin , Goodhue William D.
Published: April 2011

Nanosphere lithography (NSL) has been successfully used to nanopattern silicon and glass substrate surfaces using a spin process in conjunction with the chemical functionalized polystyrene nanospheres. Here, we report for the first time the formation of periodic arrays of nanohole and nanopillar on GaAs and GaSb substrates using a combination of NSL, electron beam (E-Beam) evaporation and Bromine Ion Beam Assisted Etching (Br-IBAE). When 250 nm diameter nanospheres were used as a template or mask, periodic arrays of approximate 55 nm hexagonal nanoholes and 39 nm hexagonal nanopillars were obtained from double-layer nanosphere templates, while arrays of approximate 65nm triangular nanohole and 53nm triangular nanopillar were obtained from single-layer nanosphere templates. The high uniformity of these nanohole and nanopillar arrays demonstrates the technique¡¦s potential for applications in the fabrication of novel high performance opto- and electronic devices in the important GaAs and GaSb III-V direct bandgap semiconductors.
Monitoring nanoprobe diffusion in osmotically-stressed hydrogels
Authors: Boukari Hacene , de Silva Candida , Nossal Ralph , Horkay Ferenc
Published: April 2011

We have developed an optical chamber for studying the effect of swelling or shrinking of a gel on the translational diffusion of fluorescent nanoprobes embedded in the gel. On one side of the chamber, the gel is in contact with a hydrating or dehydrating polymeric solution through a porous membrane, allowing control of the rate of hydration or dehydration of the gel. On the other side, a laser beam is focused into the gel to excite the fluorescence of the nanoprobes, which is continuously monitored to reveal possible structural changes of the stressed gel. Using fluorescence correlation spectroscopy we measure correlation functions of the nanoprobes at various times following the contact of the gel with the hydrating or dehydrating solution, and determine changes of both the average concentration and the apparent diffusion time of the nanoprobes as the gel is shrinking or swelling. We have tested the chamber using the fluorophore, TAMRA (MW = 430 Da), embedded in a poly(vinyl-alcohol) gel that is being dehydrated by a solution of poly(vinyl-pyrrolidone) (28% w/w). As expected TAMRA moves slower as the gel shrinks. However, the changes in the diffusion time of TAMRA as a function of the PVA concentration of the shrinking gel appear to be different than those measured on TAMRA diffusing in PVA gels prepared at different PVA concentrations but with the same cross-link density.
Analytical Approach to Quantifying the Non-Affine Behavior of Fiber Networks
Authors: Hatami-Marbini Hamed , Picu Catalin
Published: April 2011

Fiber networks deform nonaffinely due to their inhomogeneous structure. The degree of nonaffinity depends on many factors such as the spatial distribution and properties of fibers, the nature of the applied load, the type of joints and the length scale of observation. The “homogenized” response on given scale depends on the non-affine mechanics on all sub-scales. Here, a method is developed to map the non-affine mechanics of a regular network with a large density of defects into an equivalent continuum, which is then used to determine the homogenized elastic properties of the network. This semi-analytic method establishes a relationship between the structure of the network and its overall elastic properties. Furthermore, we develop a method to quantify the nonaffine strains in a random network and use it to study the dependence of the degree of non-affinity to the scale of observation as well as the dependence on the network architecture.
Electrical Impedance Analysis of Phospholipid Bilayer Membranes for Enabling Engineering Design of Bio-based Devices
Authors: Sarles Stephen A. , Sundaresan Vishnu B. , Leo Donald J.
Published: April 2011

Recent research at Virginia Tech have shown that active transporter proteins reconstituted into suspended bilayer lipid membranes (BLMs) formed across an array of pores in synthetic substrates can convert chemical energy available in adenosine triphosphate (ATP) into electricity. Experimental results from this work show that this system—called BioCell—is capable of 1.7μW of electrical power per square centimeter of BLM area and per 15μL of ATPase enzyme. In support of such a system, the lipid membrane, as host to active biological proteins and channels, must be formed evenly across a porous substrate, remain stable and yet fluid-like for protein folding and activation, and provide sufficient electrical insulation. We report on the formation and characterization using electrical impedance spectroscopy (EIS) of BLMs formed across two types of porous substrates: polycarbonate filters and single-aperture silicon substrates. Equivalent electrical circuits describing the lipid membranes and their supporting substrates are approximated to fit the measured responses. The results show that BLMs formed in some but not all of the 400nm pores of the filters, while the formation of BLMs on the single-aperture silicon substrates was much more consistent.
Electrostatic Field Calculations for Electrophoresis Using Surfaces
Authors: Ramasamy Perumal Radha , Elmaghrabi Raafat M , Halada Gary
Published: April 2011

The distribution of electric field in and near the surface of the electrophoretic cell determines the motion of proteins in the buffer and along the surface. This is a complicated problem, influenced by buffer ion concentration, electrode configuration, and surface and substrate conductivities. Steady state calculations approximating the experimental geometry were made for different arrangements of electrodes using MAFIA (Computer Simulation Technologies) program and ESTAT programs. Electric field distributions in both conducting surfaces like ITO (Indium Tin Oxide) (Kevley Technologies), gold and aluminum and non conducting surfaces were studied. In order to measure the EOF of the buffer neutrally charged fluorescent Poly-Styrene beads of 1 μm diameter were included in the buffer and imaged using confocal microscope. It was observed that the electric filed was highly modified by various factors like the conducting nature of the surface, position of the electrodes, salt concentration in the buffer and distance from the separation surface.
Effects of Changes in Structural Hydration of Multiphasic Heterogeneous Calcium Phosphate Powders Created via Auto-Ignition Combustion Synthesis
Authors: Vollmer Nina Louise , Burkes Douglas , Moore John , Ayers Reed
Published: April 2011

Calcium phosphate (CaP) materials are commonly used in bone tissue engineering applications since they closely resemble the chemistry of bone and teeth. The inorganic component of mineralized tissue is multiphasic in nature-thus to better replicate those tissues, CaP materials should also be multiphasic. Combustion synthesis is a process that creates multiphasic CaP (HCaP) with low energy input over a relatively short time. The structure and chemistry of HCaP synthesized via auto-ignition combustion synthesis (AICS) varies greatly with respect to structural hydration. Product hydration was accomplished by modifying hydrogen and oxygen content in the combustion reaction by changing the amount of fuel, urea [ ] pre-reaction, and heating or sintering products post-reaction. The reaction equation for this specific system is given below. Calcium nitrate [ ], and ammonium nitrate [ ] are the components that form HCaP. Urea acts as an ignition source and fuel. Changes in the amount of urea dictate the amount of excess hydrogen to form water within the reaction. Excess products formed include water, carbon dioxide, and nitrogen. Salts of the reactants were mixed with 10 milliliters of de-ionized water in a Pyrex beaker, heated on a hot plate for 20 minutes or until the reactants began to foam, and then placed in a muffle furnace at 1000°C until the foam ignited in a combustion reaction. This was noted by the progression of a combustion wave throughout the foam. Post-AICS, products were heated at 105°C for 8 hours and 24 hours and massed to determine water content of the product. Subsequently, the products were sintered at 1000°C for 8 hours and massed again. The primary products formed using AICS are hydroxyapatite (HA), á-tricalcium calcium phosphate (TCP) and hydrated forms of tricalcium phosphate (HTCP). During low temperature heating, 105°C, water content decreases as time increases and the products began to densify. Initial results indicate that surface porosity decreases during the powder densification. XRD shows that peak intensity increases after low temperature heating, indicating an increase in crystallinity and grain orientation. XRD confirms that both crystalline and amorphous phases occur in the hydroxyapatite (HA), á-TCP and HTCP products. The amount of structural hydration has an effect on CaP, and these effects are noted by an increase in density and decrease in porosity as structurally bound water is removed from the system. Future research will be dedicated to determining hydration ratio (amount of urea in the reaction to the amount of water within the products) and a Ca:P ratio that result in optimal powder porosity, ductility and grain size generating a multiphasic HCaP implant biomaterial that accurately replicates natural bony tissue.
Fluorescent and Magnetic Resonance Imaging by Rare Earth Doped Nanoparticles with Garnet Structure
Authors: Asakura Ryo , Sakane Hiroshi , Noda Kunihiro , Isobe Tetsuhiko , Morita Masahito , Inubushi Toshiro
Published: April 2011

Yb3+ doped Y3Al5O12 (YAG:Yb3+) nanoparticles are prepared from yttrium acetate tetrahydrate, ytterbium acetate tetrahydrate and aluminum isopropoxide in 1,4-butanediol by autoclave treatment at 300 °C for 2 h. Moreover, Gd-YAG:Yb3+ nanoparticles are prepared from the mixture of YAG:Yb3+ colloidal solution and gadolinium acetate tetrahydrate by the same autoclave treatment as YAG:Yb3+. Properties of structure, near infrared photoluminescence and magnetic resonance contrast enhancement are characterized for as-prepared and calcined YAG:Yb3+ and Gd-YAG:Yb3+ nanoparticles.
Stable, Hydrophilic Nitrilotriacetic Acid-Capped Gold Monolayer Protected Clusters
Authors: Sosibo Ndabenhle M. , Tshikhudo Robert T. , Revaprasadu Neerish
Published: April 2011

A one step synthesis and functionalization of robust, hydrophilic monolayer protected clusters of gold (Au-MPCs) containing a nitrilotriacetic acid (NTA) is described. The 14 nm Au-MPCs were prepared by the attachment of two bifunctional thioalkylated-poly(ethylene glycol) ligands on the nanoparticles, one containing a nitrilotriacetic acid (NTA) terminal group, while the second hydroxyl (OH) terminated ligand was used as a co-stabilizer to promote the stability of the MPCs. The resulting PEGylated NTA functionalized Au MPCs, which are characterized by TEM, UV-vis and agarose gel electrophoresis are attractive probes for many target species e.g. hexahistidine-tagged proteins. Importantly, the NTA functionality on MPCs ligand shell can be varied.
Synthesis of Cu-In-S Fluorescent Nanocrystals
Authors: Watanabe Kosuke , Uehara Masato , Nakamura Hiroyuki , Maeda Hideaki
Published: April 2011

CuInS2 (CIS) fluorescent nanocrystals (NCs) were obtained by heating organic metal complex. The photoluminescence (PL) originated from the donor-acceptor, and the quantum yield (QY) was achieved at 6%. Furthermore, we doped some metal ions (Zn2+, Cd2+ or Ag+) by the post heat-treatment in the organic coordinating solvent in order to tune the band gap of NCs. By this post treatment, the alteration of NCs structure was suggested, such as changing into an alloying and composite structure. In Zn-doping, the PL wavelength was widely tuned from 535 to 650 nm by alloying between CIS and ZnS. Moreover, PL intensity was increased with these structure alterations. In particular, the materials doped with Zn or Cd achieved respective QY of 25% and 40%.
Fabrication and Characterization of Individually Controlled Multi-Pixel Carbon Nanotube Cathode Array Chip for Micro-RT Application for Cancer Research
Authors: Wang Sigen , Liu Zhijun , An Lei , Zhou Otto , Chang Sha
Published: April 2011

Carbon nanotubes (CNTs) have attracted considerable attention as future field emission electron sources for a variety of applications due to their high aspect ratio and robust structure. One application is multi-pixel beam array x-ray micro-RT (radiotherapy) for small animal irradiation. The x-ray pixel beam array is produced by a CNT pixel cathode array. One challenge in the micro-RT fabrication is how to fabricate individually addressable multi-pixel CNT cathode array on wafer with high pixel beam packing density and high emission current. We report here the development of a new CNT field emission multi-pixel cathode array chip, a vital component of the multi-pixel beam x-ray micro-RT system under development. The CNT field emission cathode array has up to 25 (5 × 5) individually addressable cathode pixels, each is 1 mm in diameter and with center-to-center distance of 2 mm. The fabrication is a two-step process: first a Cr/Cu electrical contact was fabricated on Si substrates with a 5 μm SiO2 dielectric layer using photolithography; and second the CNTs were selectively deposited on 1 mm-diameter predefined Cr/Cu contact dots by using a combined photolithography/electrophotoresis technique. The electron pixel beams produced from the multi-pixel arrays are uniform and individually controllable and can be used for micro-RT application.
Electronic Transport in Co-deposited Hydrogenated Amorphous/Nanocrystalline Thin Films
Authors: Adjallah Y. , Blackwell C. , Anderson C. , Kortshagen U. , Kakalios J.
Published: April 2011

Mixed-phase hydrogenated amorphous silicon thin films containing nanocrystalline silicon inclusions have been synthesized in a dual chamber co-deposition system. A PECVD deposition system produces small crystalline silicon particles (3-5 nm diameter) in a flow-through reactor, and injects these particles into a separate capacitively-coupled plasma chamber in which hydrogenated amorphous silicon is deposited. Raman spectroscopy is used to determine the volume fraction of nanocrystals in the mixed phase thin films, while infra-red spectroscopy characterizes the hydrogen bonding structure as a function of nanocrystalline concentration. At a moderate concentration of 5 nm silicon crystallites, the dark conductivity and photoconductivity are consistently found to be higher than in mixed phase films with either lower or higher densities of nanocrystalline inclusions.
Characterization of the Mobility Gap in μc-Si:H Pin Devices
Authors: Pieters Bart Elger , Schicho Sandra , Stiebig Helmut
Published: April 2011

For the mobility gap of hydrogenated micro-crystalline silicon (μc-Si:H) a value near 1.1 eV is commonly found, similar to the bandgap of crystalline silicon. However, in other studies mobility gap values have been reported to be in the range of 1.48-1.59 eV. Indeed, for accurate modeling of μc-Si:H solar cells it is paramount that key parameters like the mobility gap are accurately determined. In this work we will discuss a method to determine the mobility gap of μc-Si:H using the dark current activation energy of μc-Si:H pin devices, and apply this method to μc-Si:H solar cells with varying crystalline volume fraction. We found the mobility gap is around 1.2 eV to 1.26 eV for μc-Si:H solar cells with a crystalline volume fraction between 50 % and 70 %. For a highly crystalline solar cell we found a mobility gap of 1.07 eV.
Doping Effects in Co-deposited Mixed Phase Films of Hydrogenated Amorphous Silicon Containing Nanocrystalline Inclusions
Authors: Blackwell C. , Pi Xiaodong , Kortshagen U. , Kakalios J.
Published: April 2011

Hydrogenated amorphous silicon films containing silicon nanocrystalline inclusions (a/nc-Si:H) that have been n-type doped have been synthesized using a dual-plasma co-deposition system. We report the structural and electronic properties of n-type doped a/nc-Si:H as a function of phosphine doping level and nanocrystalline concentration. The volume fraction of nanocrystals in the doped a/nc-Si:H thin films is measured using Raman spectroscopy, and the hydrogen binding configurations are characterized using infra-red absorption spectroscopy. In undoped a/nc-Si:H, the inclusion of low and moderate nanocrystalline concentrations results in an increase in the dark conductivity, compared to a-Si:H films grown without nanocrystalline inclusions. In contrast, the addition of even a low concentration of silicon nanoparticles in doped a/nc-Si:H thin films leads to a decrease in the dark conductivity and photoconductivity, compared to pure a-Si:H films.
Seeding Solid Phase Crystallization of Amorphous Silicon Films with Embedded Nanocrystals
Authors: Anderson Curtis , Kortshagen Uwe
Published: April 2011

Silicon nanocrystals with diameters up to 30 nm are used as nucleation seeds for fast solid phase crystallization of amorphous silicon films. Purely amorphous films required an incubation time of up to 12 hours at 600°C prior to the onset of nucleation, while films with nanocrystals embedded between layers of amorphous silicon grew immediately upon annealing in a quartz tube furnace. Structural characterization was performed by heated-stage transmission electron microscopy and Raman spectroscopy.
Transient Photoconductivity Study of the Distribution of Gap States in 100°C VHF-deposited Hydrogenated Silicon Layers
Authors: Brinza Monica , Adriaenssens Guy J. , Rath Jatindra K. , Schropp Ruud E.I.
Published: April 2011

The energy distribution of gap states has been examined by means of transient photocurrent measurements in a series of 100°C VHF-deposited Si:H samples that spans the amorphous to microcrystalline transition. The ‘amorphous’ distribution, consisting of a continuous background and a prominent dangling-bond-induced peak, remains largely intact across the transition. The transport path located at the conduction band edge in a-Si:H, some 0.63 eV above the dangling bond D− energy, moves down to ∼0.55 eV above the corresponding D− level in the microcrystalline samples.
Multilayered a-SiC:H device for Wavelength-Division (de)Multiplexing applications in the visible spectrum
Authors: Vieira Manuela , Fernandes Miguel , Louro Paula , Vieira Manuel Augusto , Barata Manuel , Fantoni Alessandro
Published: April 2011

A multiplexer is a device that combines two or more signals onto a single output without losing their specificity. In this paper we present results on the use of multilayered a-SiC:H heterostructures either as wavelength-division multiplexing or demultiplexing device (WDM). The WDM is a glass/ITO/a-SiC:H (p-i-n)/ a-SiC:H(-p) /Si:H(-i)/SiC:H (-n)/ITO double heterostructure which faces the modulated light incoming together from different beams, each one with a specific wavelength and period. By reading out, at different applied bias, the photocurrent generated by all the incoming optical carriers, the information is multiplexed or demultiplexed and can be transmitted and recovered again. The devices were characterized through spectral response measurements, under different electrical bias and frequencies. Results show that in the multiplexing mode the output signal is balanced by the wavelength of each incoming optical carrier and modulated by their frequencies. In the demultiplexing mode the photocurrent is controlled by the applied voltage and optical bias allowing to regain the transmitted information. An electrical model is presented to explain the device operation.
Magnetic Resonance in Hydrogenated Nanocrystalline Silicon Thin Films
Authors: Su Tining , Ju Tong , Yan Baojie , Yang Jeffrey , Guha Subhendu , Taylor P. Craig
Published: April 2011

We have investigated the localized electronic states in mixed-phase hydrogenated nanocrystalline silicon thin films (nc-Si:H) with electron-spin-resonance (ESR). The dark ESR signal most likely arises from defects at the grain boundaries or within the crystallites. With illumination with photon energies ranging from 1.2 eV to 2.0 eV, there is no evidence of photo-induced carriers trapped in the bandtail states within the amorphous region. Dependence of the light-induced ESR (LESR) upon the exciting photon energy reveals that, at different excitation photon energies, different regions dominate the optical absorption. This behavior may have potential consequences for understanding the light-induced degradation in nc-Si:H.
Blue and Yellow Electroluminescence of MOSLED Made on Si-rich SiOx Film with Detuning Buried Si Nanoclusters Size
Authors: Lin Gong-Ru , Liu Chi-Wee , Hsieh Chin-Hua , Chou Li-Jen , Lin Gong-Ru
Published: April 2011

We have demonstrated the blue and yellow electroluminescence of MOSLEDs made on Si-rich SiOx film with buried Si nanoclusters of different sizes. The situation of dehydrogenation of Si nanocrystals within the SiOx film becomes more pronounced then the re-growth of SiO2 matrix along with the prolongation of annealing time period. A linear variation on the O/Si composition ratio of the Si-rich SiOx film related to the deposition recipe is reported, giving rise to the precipitation of Si nanocrystals with different size. With such synthesis conditions, the SiOx films result in relatively strong photoluminescence at blue and yellow colors. From the comparison of the I–V curves we can conclude that there is a linear decrease on the threshold voltage of the SiOx based MOSLEDs by decreasing the thickness of the SiOx layer. According to EL pattern, we could demonstrate that the yellow- and blue-light pattern can be observed at 5.5 and 7.25 MV/cm, respectively.
Hysteresis Phenomenon in Sequential Lateral Solidification poly-Si Thin Film Transistor at low temperature (213K)
Authors: Choi Sung-Hwan , Park Sang-Geun , Lee Won-Kyu , Ha Tae-Jun , Han Min-Koo
Published: April 2011

We have investigated temperature dependence on the hysteresis phenomenon of SLS poly-Si TFT on a glass substrate, extremely at low temperature (213K). The p-type sequential lataral solidification (SLS) polycrystalline Silicon (poly-Si) TFT was fabricated on glass substrate. As the temperature was reduced, it was observed that hysteresis phenomenon was increased, whereas the hysteresis was suppressed at high temperature. This could be explained by a difference of initially electron and hole trapped charges into gate insulator is much larger in low temperature than in high temperature. And we have verified that drain current was changed with a different previous gate starting voltage even at same bias condition by experimental results due to the hysteresis phenomenon of SLS poly-Si TFT. Hysteresis of SLS poly-Si TFT should be improved for a pixel element of high quality AMOLED display.
Luminescent Colloidal Silicon Nanocrystals Prepared by Nanoseconds Laser Fragmentation and Laser Ablation in Water
Authors: Svrcek Vladimir , Mariotti Davide , Hailstone Richard , Fujiwara Hiroyuki , Kondo Michio
Published: April 2011

The surface states of silicon nanocrystals (Si-ncs) considerably affect quantum confinement effects and may determinate final nanocrystals properties. Colloidally dispersed Si-ncs offer larger freedom for surface modification compared to common plasma enhanced chemical vapor deposition or epitaxial synthesis in a solid matrix. The Si-ncs fabrication and elaboration in water by pulsed laser processing is an attractive alternative for controlling and engineering of nanocrystal surface by environmentally compatible way. We report on the possibility of direct silicon surface ablation and Si-ncs fabrication by nanosecond pulsed laser fragmentation of electrochemically etched Si micrograins and by laser ablation of crystalline silicon target immersed in de-ionized water. Two nanosecond pulsed lasers (Nd:YAG, and excimer KrF) are successfully employed to assure fragmentation and ablation in order to produce silicon nanoparticles. Contrary to the fragmentation process, which is more efficient under Nd:YAG irradiation, the laser ablation by both lasers led to the fabrication of fine and room temperature photoluminescent Si-ncs. The processing that has natural compatibility with the environment and advanced state of fabrication technologies may imply new possibilities and applications.
Monolithic 3D Integration of Single-Grain Si TFTs
Authors: Mofrad Mohammad Reza Tajari , Ishihara Ryoichi , Derakhshandeh Jaber , Baiano Alessandro , van der Cingel Johan , Beenakker Cees
Published: April 2011

Vertical stacking of transistors is a promising technology which can realize compact and high-speed integrated circuits (ICs) with a short interconnect delay and increased functionality. Two layers of low-temperature fabricated single-grain thin-film transistors (SG TFTs) have been monolithically integrated. NMOS mobilities are 565 and 393 cm2/Vs and pMOS mobilities are 159 and 141 cm2/Vs, for the top and bottom layers respectively. A three-dimensional (3D) inverter has also been fabricated, with one transistor on the bottom layer and the other on the top layer. The inverters showed an output voltage swing of 0 to 5 V with a switching voltage of around 2 V.
Determination of the Core-structure of Shockley Partial Dislocations in 4H-SiC
Authors: Chen Yi , Zhang Ning , Huang Xianrong , Caldwell Joshua D , Liu Kendrick X , Stahlbush Robert E , Dudley Michael
Published: April 2011

Synchrotron x-ray topographs taken using basal plane reflections indicate that the electron-hole recombination activated Shockley partial dislocations in 4H silicon carbide bipolar devices appear as either white stripes with dark contrast bands at both edges or dark lines. In situ electroluminescence observations indicated that the mobile partial dislocations correspond to the white stripes in synchrotron x-ray topographs, while immobile partial dislocations correspond to the dark lines. Computer simulation based on ray-tracing principle indicates that the contrast variation of the partial dislocations in x-ray topography is determined by the position of the extra atomic half planes associated with the partial dislocations lying along their Peierls valley directions. The chemical structure of the Shockley partial dislocations can be subsequently determined unambiguously and non-destructively.
Factors Influencing the Growth Rate, Doping, and Surface Morphology of the Low-Temperature Halo-Carbon Homoepitaxial Growth of 4H SiC with HCl Additive
Authors: Melnychuk Galyna , Lin Huang De , Kotamraju Siva Prasad , Koshka Yaroslav
Published: April 2011

In this work, a possibility to further suppress silicon vapor condensation and formation of Si clusters in order to improve the growth rate and morphology during the low-temperature halo-carbon epitaxial growth of 4H-SiC was investigated. While a pronounced dissociating of Si clusters was clearly demonstrated, the enhancement of the growth rate and morphology was less significant then expected. In addition, the homogeneity of the growth rate and doping along the gas flow direction indicated that a significant and non-equal depletion of Si and C growth species takes place at sufficiently high HCl supply. HCl flow-dependent formation of polycrystalline Si and SiC deposits in the upstream portion of the hot zone was shown to be the source of this depletion.
Effect of SiC Power DMOSFET Threshold-Voltage Instability
Authors: Lelis Aivars , Habersat D. , Green R. , Ogunniyi A. , Gurfinkel M. , Suehle J. , Goldsman N.
Published: April 2011

We have performed bias-stress induced threshold-voltage instability measurements on fully processed 4-H SiC power DMOSFETs as a function of bias-stress time, field, and temperature and have observed similar instabilities to those previously reported for lateral SiC MOSFET test structures. This effect is likely due to electrons tunneling into and out of near-interfacial oxide traps that extend spatially into the gate oxide. As long as the threshold voltage is set high enough to preclude the onset of subthreshold drain leakage current in the blocking state, then the primary effect of this instability is to increase the on-state resistance. For well-behaved power DMOSFETs, this would increase the power loss by no more than a few percent.
Performance Characteristics of 65nm PFETs Using Molecular Implant Species for Source and Drain Extensions
Authors: Tan Chung Foong , Teo L. W. , Yin C-S. , Lee J. G. , Liu J. , See A. , Zhou M. S. , Quek E. , Chu S. , Hatem C. , Variam N. , Arevalo E. , Gupta A. , Mehta S.
Published: April 2011

We investigated the performance of 65nm pFETs whereby the source and drain extensions (SDE) were implanted with Carborane, (C2B10H12) a novel form of molecular species. The high atomic mass of this molecule (146 a.m.u.) and the number of boron atoms transported per ion enables the productivity at low energy required for manufacturing of ultra shallow junctions for advanced scaling. In this investigation, Carborane was implanted at 13 keV to produce a Boron profile near equivalent to that produced by the reference BF2 implant. Results of electrical measurements did not exhibit any compromise in the I-V characteristics in terms of Id-Vg and Id-Vd and Ion-Ioff. External resistance and Vt roll-off shifted slightly with respect to the reference devices. This is attributed to a deeper junction with Carborane due to slight offset in the profile matching. It will be shown that with fully matched profiles, a perfect match of the device characteristics can be achieved.
Doping of Sub-50nm SOI Layers
Authors: Pawlak Bartek J. , Duffy Ray , van Dal Mark , Voogt Frans , Weemaes Robbert , Roozeboom Fred , Zalm Peer , Bennett Nick , Cowern Nick
Published: April 2011

Doping of thin body Si becomes very essential topic due to increasing interest of forming source/drain regions in fully depleted planar silicon-on-isolator (SOI) devices or vertical Fin field-effect-transistors (FinFETs). To diminish the role of the short-channel-control-effect (SCE) the Si layers thicknesses target the 10 nm range. In this paper many aspects of thin Si body doping are discussed: dopant retention, implantation-related amorphization, thin body recrystallization, sheet resistance (Rs) and carrier mobility in crystalline or amorphized material, impact of the annealing ambient on Rs for various SOI thicknesses. The complexity of 3D geometry for vertical Fin and the vicinity of the extended surface have an impact on doping strategies that are significantly different than for planar bulk devices.
Boron Enhanced H Diffusion in Amorphous Si Formed by Ion Implantation
Authors: Johnson Brett Cameron , Atanacio Armand J. , Prince Kathryn E. , McCallum Jeffrey C.
Published: April 2011

Boron enhanced H diffusion in amorphous Si (a-Si) layers formed by ion implantation is observed using secondary ion mass spectroscopy (SIMS). Constant concentrations of B were achieved using multiple energy B implantations into thick a-Si layers. The evolution of single H implanted profiles centered on the uniformly B-implanted regions was studied for partial anneals at temperatures in the range 380 – 640 °C. Boron enhanced diffusion is observed and the enhanced diffusion coefficient shows trends with temperature typically associated with a Fermi level shifting dependence. A modified form of the generalized Fermi level shifting model is considered in light of these results.
Intrinsic and Dopant-Enhanced Solid Phase Epitaxy in Amorphous Germanium
Authors: Johnson Brett Cameron , Gortmaker Paul , McCallum Jeffrey C.
Published: April 2011

The kinetics of intrinsic and dopant-enhanced solid phase epitaxy (SPE) are studied in thick amorphous germanium (a-Ge) layers formed by ion implantation on <100> Ge substrates. The SPE rates for H-free Ge were measured with a time-resolved reflectivity (TRR) system in the temperature range 300 – 540 °C and found to have an activation energy of (2.15 ± 0.04) eV. Dopant enhanced SPE was measured in a-Ge layers containing a uniform concentration profile of implanted As spanning the concentration regime 1 – 10 × 1019 cm3. The generalized Fermi level shifting model shows excellent fits to the data.
Atomistic Modeling of {311} Defects and Dislocation Ribbons
Authors: Trzynadlowski Bart , Dunham Scott , Ahn Chihak
Published: April 2011

Ab-initio calculations of dislocation and {311} defect structures in silicon were performed in order to investigate the formation energies as functions of geometry, including the effects of applied strain, with a simple model. Predictions were made concerning the size at which a {311} defect becomes less favorable than a dislocation loop, and it was shown that this is affected by applied strain.
An Alternative Approach to Analyzing the Interstitial Decay from the End of Range Damage During Millisecond Annealing
Authors: Camillo-Castillo Renata , Law Mark E , Jones Kevin S
Published: April 2011

Flash-assist Rapid Thermal Processing (RTP) presents an opportunity to investigate annealing time and temperature regimes which were previously not accessible with conventional annealing techniques such as Rapid Thermal Annealing. This provides a unique opportunity to explore the early stages of the End of Range (EOR) damage evolution and also to examine how the damage evolves during the high temperature portion of the temperature profile. However, the nature of the Flash-assist RTP makes it is extremely difficult to reasonably compare it to alternative annealing techniques, largely because the annealing time at a given temperature is dictated by the FWHM of the radiation pulse. The FWHM for current flash tools vary between 0.85 and 1.38 milliseconds, which is three orders of magnitude smaller to that required for a RTA to achieve similar temperatures. Traditionally, the kinetics of the extended defects has been studied by time dependent studies utilizing isothermal anneals; in which specific defect structures could be isolated. The characteristics of Flash-assist RTP do not allow for such investigations in which the EOR defect evolution could be closely tracked with time. Since the annealing time at the target temperature for the Flash-assist RTP is essentially fixed to very small times on the order of milliseconds, isochronal anneals are a logical experimental approach to temperature dependent studies. This fact presents a challenge in the data analysis and comparison. Another feature of Flash-assist RTP which makes the analysis complex is the ramp time relative to the dwell time spent at the peak fRTP temperature. As the flash anneal temperature is increased the total ramp time can exceed the dwell time at the peak temperature, which may play a significantly larger role in dictating the final material properties. The inherent characteristics of Flash-assist RTP have consequently required the development of another approach to analyzing the attainable experimental data, such that a meaningful comparison could be made to past studies. The adopted analysis entails the selection of a reference anneal, from which the decay in the trapped interstitial density can be tracked with the flash anneal temperature, allowing for the kinetics of the interstitial decay to be extracted.
Phase Change in (GeTe)1-x(Sb2Te3)x Investigated by Hard X-ray Photoemission Spectroscopy
Authors: Kobayashi Keisuke , Kim Jung-Jin , Matsunaga Toshiyuki , Kifune Kouichi , Ikenaga Eiji , Kobata Masaaki , Ueda Shigonori , Kojima Rie , Yamada Noboru
Published: April 2011

The mechanism of the fast reversible change between the amorphous and crystalline phases in (GeTe)1−x(Sb2Te3)x (GST) has not yet been fully understood. The crystalline phase has been identified as having a NaCl-type cubic structure with random occupation of the A sites by Ge, Sb and vacancies, and 100% occupation of B sites by Te. This fact calls our attention to a possible close relation to the inherent crystal bonding instability observed for the average five valence electrons (<5>) family. We present here the results of systematic hard X-ray photoemission experiments on GST films with various compositions in both the amorphous and crystalline phases, and discuss that a similar chemical bonding instability does indeed play an essential role in the phase change mechanism in GST. We propose a model for the fast phase change, in which 6 fold to 3 fold transition of p-like bonding play an essential role, in this class of materials.
Universal glass dynamics in PCM nano-glasses
Authors: Karpov I. V. , Mitra M. , Kau D. , Spadini G. , Karpov V. G. , Kryukov Y. A.
Published: April 2011

The classical double well potential (DWP) model known to explain many phenomena in glasses, is extended to the nano glasses of chalcogenide phase change memory (PCM). We describe simple analytical expressions for the temporal drift of PCM reset parameters. The threshold voltage Vth and the amorphous state resistance R are shown to drift with the time (t) as deltaVth ∝ ν propotional to ln t and R proportional to t power alpha respectively in broad intervals spanning many decades in time. These dependencies saturate at long enough times that can be shorten with temperature increase. All the available data on the PCM drift are shown to be fully consistent with DWP model.
Characterization of RF magnetron sputtered Se-doped Ge2Sb2.3Te5 thin films
Authors: Wagner Tomas , Gutwirth Jan , Orava Jiri , Prikryl Jan , Bezdicka Petr , Bartos Miroslav , Vlcek Milan , Frumar Miloslav
Published: April 2011

RF magnetron sputtering technique has been used to deposit new films potentially applicable in phase-change memories. Ge2Sb2Te5 seems to be promising material, but it is not clear whether it is optimum composition for such application. We studied different deposition condition and deposition of films doped by excess of Sb and doped also by Se, which equally replaces Te atoms compare to Ge2Sb2Te5. The sputtering target composition for our study was Ge2Sb2.3Te4Se1. Sputtered films contained less Se than target. Deposited films were characterized as-deposited and after thermal treatment in temperature range 30 − 300 °C.
In pursuit of “super”high-k ternary oxides: aqueous CSD and material properties
Authors: Hardy An , Van Elshocht Sven , D'Haen Jan , De Gendt Stefan , Van Bael Marlies K. , Heyns Marc , D'Olieslaeger Marc , Mullens Jules
Published: April 2011

Important material properties of dielectric oxide films fabricated by aqueous chemical solution deposition, such as crystallization, topography, contamination and interfacial layer were evaluated and related to the films' dielectric properties.

Functional ultrathin films (<20 nm thickness) of zirconia, barium zirconate and strontium niobate were deposited. The films were all subjected to the same thermal treatment, based on the high similarity of their precursors' thermal decomposition behavior. The evolution of the films' chemical purity as a function of temperature and the effect of annealing on the interfacial SiO2 layer was studied by grazing angle ATR-FTIR. The films' crystallization behavior was dependent on film thickness and composition as shown by high temperature XRD. C-V characterization of the films demonstrated a k-value in the same order of magnitude as for the ZrO2 reference material. This is lower than the bulk material's value, thus leaving room for further optimization of the current materials or alternatively selection of other material compositions.
The Study of Hafnium Silicate by Various Nitrogen Gas Annealing Treatment
Authors: Suh Dong Chan , Chung Kwun Bum , Cho Mann-Ho , Cho Young Dae , Ko Dae-Hong
Published: April 2011

Post annealing of Hf-silicate thin film grown by ALD was done with different kind of nitrogen gas and order of annealing. Annealing conditions are as follows: (1) NO gas only, (2) NH3 gas only, (3) NO gas + NH3 gas, and (4) NH3 + NO gas. With these conditions, the physical and electrical properties of nitrided Hf-silicate films were analyzed. Content of nitrogen is decreased with post NO gas annealing. In case of NH3, content of nitrogen is much higher than NO case. Most nitrogen atoms were distributed between Si substrate and Hf-silicate film for NO gas annealing. However, with NH3 gas annealing, nitrogen atoms were distributed in the whole Hf-silicate film evenly. Leakage current was decreased with post NO gas annealing and flat band voltage was also decreased.
Photo-induced Deposition of Nanostructured Thin Films by UV-exposure of Heteroleptic Ti-alkoxide Solutions
Authors: Musgraves J. David , Potter B.G. , Boyle Timothy J.
Published: April 2011

Photodeposited physical relief structures have been formed via the UV-irradiation of solutions of the heteroleptic titanium alkoxide, (OPy)2Ti(TAP)2. Raman studies of the films produced confirm the photoinitiation of hydrolysis and condensation reactions in the molecular structure, leading to the development of an insoluble solid phase. Using a shadow mask technique, these films were deposited directly from solution with microscale patterning and their structure and properties were studied as a function of both irradiation conditions (UV-fluence and intensity) as well as precursor solution chemistry (water content). Variations in nanostructure are visible in scanning electron micrographs, with a higher solution water content producing a more condensed, i.e. less porous, film.
Correlation Between Microstructure and Optical Properties of ZnO Based Nanostructures Grown by MOCVD
Authors: Falyouni Farid , Barjon Julien , Sallet Vincent , Lusson Alain , Garry Guy , Galtier Pierre
Published: April 2011

The correlation between structural properties of ZnO sharp conical needles grown by Metallorganic Chemical Vapor Deposition (MOCVD) on sapphire substrate and their optical signature measured by low temperature cathodoluminescence (CL) is investigated. Transmission Electron Microscopy (TEM) shows the excellent structural properties of these needles from their base up to the end of the tip. In order to probe the emission of the needles along their length, UV CL mapping has been performed at low temperature on a single needle previously characterized by TEM. A clear blue shift of 25meV is observed for the excitonic emission close to the needle tip. This shift is too high to be fully attributed to quantum confinement. Although, it qualitatively agrees with previous observations which assigned it to a surface contribution becoming dominant upon size shrinking, the effect is less pronounced. The results are discussed in term of surface quality and other possible contributions associated to a decrease of the n-dopant concentration and to quantum confinement effect close to the tip.
Characterization of Nanoparticles by Light Scattering
Authors: Nobbmann Ulf , Morfesis Ana
Published: April 2011

Metal oxide nanoparticles are increasingly being used to prepare new nanocrystaline materials. By controlling formulations of multicomponent metal oxides; crystal shape, structure and surface properties important in the design of new materials are gaining acceptance for many applications. Metal oxide composites are being used to design new electronic, magnetic and optical properties into material structures. Often these are formulated and processed in slurries or aqueous suspensions. A key parameter of controlling the design of such colloidal nanoparticle systems is their particle size. There are different methods by which a particle size can be obtained. Comparing stated dimensions from one method with those from another must be approached with caution: distributions in terms of volume, number or scattering intensity usually produce vastly differing results – despite expressing the exact same physical situation. Another fundamental colloidal characteristic is the zeta potential. This parameter effectively quantifies electrostatic stabilization, and can be used in formulation development to avoid instability as a result of particle-particle attraction.

Both size and zeta potential are easily measured by light scattering. Small amounts of aggregates are quickly detected by dynamic light scattering (DLS). The zeta potential is rapidly measured by electrophoretic light scattering (ELS). As an example of a typical metal oxide, data for TiO2 nanoparticles are presented.

Light scattering is a versatile measurement technique and ideally suited as a metrology of choice for size and stability quantification of nano-sized materials.