bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal and Residual Stress Modelling of the Selective Laser Sintering Process
Authors: Ibraheem Ameer K. , Derby Brian , Withers Phillip J.
Published: April 2011

The production of functional tool steel components by selective laser sintering requires an understanding of the effects of the laser processing parameters on the microstructure evolution during the fabrication process. This would allow the production of tools that have predictable and reproducible microstructure, good mechanical properties and low residual stresses. In this paper, finite element modelling has been carried out to investigate the temperature distribution and residual stresses during laser sintering of hot-work tool steel powders. The effects of the laser power and scanning rate on the selective laser sintering process have been investigated. Thermal residual stresses accumulated during the process have been predicted and compared with strain measurements made using neutron diffraction.
Surface Over-Melt During Laser Polishing of Indirect-SLS Metal Parts
Authors: Ramos J. A. , Bourell D. L. , Beaman J. J.
Published: April 2011

Laser polishing of indirect-SLS parts made from 420 stainless powder infiltrated with bronze has been achieved using CO2 and Nd:YAG lasers. Two mechanisms have been previously proposed for the reduction in surface roughness, namely: shallow surface melting (SMM) and surface over-melt (SOM). In SMM reflow of the molten surface minimizes the peak-valley height driven by capillary pressure and liquid curvature. On the other hand, during SOM the melting depth is such that the entire surface becomes liquid and formation of surface periodical structures dominates driven by a surface tension gradient. This surface morphology was identified by means of optical and scanning electron microscopy (SEM). The onset of this regime is dictated by the energy density (i.e., ratio of laser power to scan speed and beam diameter) as well as the initial roughness Ra value prior to laser surface polishing. In contrast with SMM, onset of the latter mechanism increases the roughness Ra with speed reduction. A thermo-physical model is presented, signaling good agreement with roughness Ra and characteristic surface wavelength results obtained for varying laser beam scan speeds. Understanding the surface over-melt mechanism is critical for determining the optimum polishing conditions that minimize roughness.
Biochemical IC Chips Fabricated by Hybrid Microstereolithography
Authors: Ikuta Koji , Maruo Shoji , Hasegawa Tadahiro , Adachi Takao , Takahashi Atsushi , Ikeda Kota
Published: April 2011

The world's first microstereolithography named “IH process” was developed by Ikuta et al. in 1992. Several types of micro stereo lithography including Hybrid-IH process, Super-IH process and Two-photon IH process, have been also developed. Three-dimensional (3D) resolution has reached to 140 nm in the two-photon IH process. The super-IH process and the two-photon process enable direct writing of movable micromechanisms without assembling process or sacrificial layer technique. The hybrid-IH process provides various types of composite devices with other functional elements such as actuators and sensors. These IH processes can be widely used for making polymeric microdevices. We have applied these techniques to create new micro chemical device named “Biochemical IC Chip” proposed by Ikuta et al. in 1994. IH process enables to make the biochemical IC chip including real 3D micro fluidic channels. Various kinds of Biochemical IC chip such as micro pumps, switching valves, reactors, concentrators, have already been fabricated. In chip cell-free protein synthesis has been demonstrated by using biochemical IC chips. The biochemical IC chips will open new bioscience and medicine based on innovative technology. In this paper, we introduce several types of IH process and its application to biochemical IC chips.
Damage and Failure Mechanisms in High Pressure Silicon-Glass-Metal Microfluidic Connections
Authors: Shim Dong-Jin , Sun Hong-Wei , Vengallatore Srikar T. , Mark Spearing S.
Published: April 2011

The characteristics and mechanisms of damage and failure in microfluidic joints consisting of Kovar metal tubes attached to silicon using borosilicate glass seals have been investigated. These joints are representative of seals for the MIT microrocket which is a silicon-based MEMS device. A key concern in such joints is the occurrence of cracks in silicon and glass due to residual stresses caused by a large thermal excursion during processing and the dissimilar coefficients of thermal expansion of the constituent materials. Joints with two types of glass compositions and joint configurations were fabricated, tested, and inspected. Axial tension tests were performed to investigate load carrying capability and the effect of thermally-induced cracks. Finite element models were used to obtain residual stresses due to the fabrication, and the location of the cracks from the experiments were found to coincide with the locations of the maximum principal stresses. The current work shows that the certain types of thermally-induced cracks are more detrimental to joint strength than others and a good bond between the Kovar tube and the silicon sidewall can help increase joint strength via shear load transfer.
Nanostructured Materials for Microfluidic Sensing Application
Authors: Kariuki Nancy N. , Moussa Laura , Menard Tanya , Hassan Asif , Han Li , Crew Elizabeth , Luo Jin , Zhong Chuan-Jian
Published: April 2011

Nanostructured thin films were assembled on interdigited microelectrode (IME) arrays as sensitive interfacial materials of an electrochemical detector, which can be integrated into microfluidic sensor devices. The goal is to produce sensor devices at extremes of miniaturization. The IME were created on glass wafers using conventional lithographic techniques. Open channels were etched on quartz or glass, and covered by PDMS materials, which were created using soft-lithography. The capability of chemical recognition was provided by the ligand framework structures of the nanostructured thin films on the electrode surface. A model system for such nanostructures involved the use of monolayer-capped gold nanoparticles of ∼2 nm core sizes which were assembled by carboxylic acid functionalized alkyl thiol linkers. The detection of dopamine was studied as a redox probe to test the feasibility of the microfluidic device. Results of cyclic voltammetric and chronoamperometric experiments are presented. Implications of the findings to the development of sensitive, selective, rapid and portable microanalytical devices for chemical/biological sensing are also discussed.
Thermal Effects in Plasma Treatment of Patterned PDMS for Bonding Stacked Channels
Authors: Zou Jin , Wong Peter Y.
Published: April 2011

This paper presents the results of a study to identify the effects of preheating for plasma oxidation (ashing) of patterned Polydimethylsiloxane (PDMS) for Bio-MEMS applications. PDMS creates an irreversible seal to itself as well as strong seals with glass, silicon, and silicon nitride. This process activates the surface by producing hydroxyl groups that last for several minutes to allow bonding. Several channels can be stacked to create 3D systems for microfluidic applications using PDMS alone or in combination with other materials to develop hybrid systems. For PDMS, bonding temperatures typically occur at room temperature. This research investigates the effect of preheating the materials prior to ashing. The investigators successfully demonstrate good bonding of PDMS to slides with a work adhesion on the order of 100 mJm-2. Preheating the samples at 65°C results in significant increase in work adhesion depending on mixture. The effects of processing temperature and chemical components on bond quality and work of adhesion are reported.
Electrical Characterization of BCB for Electrostatic Microelectromechanical Devices
Authors: Modafe Alireza , Ghalichechian Nima , Kleber Benjamin , Ghodssi Reza
Published: April 2011

Electrical properties and thickness of insulating dielectric films directly affect electrical energy loss and electrical breakdown limit in electric micromachines. A thick, low-k film exhibits low parasitic capacitive effects that help with the reduction of electrical energy loss. The electrical performance can be deteriorated due to degradation of the electrical properties of the insulating dielectric material caused by process, device structure, and moisture. In this paper, we introduce the application of CYCLOTENE, a spin-on, low-k, BCB-based polymer in electric micromachines as insulating layer and interlevel dielectric. A novel approach using interdigitated capacitors for electrical characterization of CYCLOTENE and the effect of moisture absorption is introduced in this paper. The dielectric constant of CYCLOTENE is extracted from two steps of capacitance measurements, giving an average value of 2.49 with a standard deviation of 1.5 %. The dielectric constant increases by 1.2 % after a humidity stress of 85 %RH at 85 °C. The measured I-V characteristics of CYCLOTENE show a dependency of the breakdown strength and leakage current on the geometrical dimensions of the device under test. A breakdown strength of 225 V/μm for 2 μm finger spacing and 320 V/μm for 3 μm finger spacing, and a leakage current of a few to tens of pA are measured. The I-V characteristics degrades drastically after a humidity stress of 85 %RH at 85 °C, showing a breakdown strength of 100 V/μm for 2 μm finger spacing and 180 V/μm for 3 μm finger spacing. Based on the results of this study, it is expected that the electrical efficiency of an electric micromachine is improved using BCB-based polymers with negligible dependency on moisture absorption. On the other hand, the maximum performance that depends on the maximum operating voltage is adversely affected by the degradation of the breakdown voltage after moisture absorption.
Mechanical Properties of Metallic Thin Films: Tensile Tests vs. Indentation Tests
Authors: Zhang Nian , Xie Changjin , Tong Wei
Published: April 2011

The existing interpretations of indentation test data (either theoretical or numerical approaches) have been largely based on isotropic plasticity models of polycrystalline materials while most of the metallic thin films widely used in many microelectronic and MEMS applications are strongly textured with a few grains or only a single grain running through the thickness of the films. The multicrystalline nature of the thin films on correlating their indentation and tensile properties is the focus of our investigation. Using multicrystalline aluminum and copper alloy thin sheets as model material systems, both tensile tests and indentation tests were performed and the testing results were compared based on a 3D crystal plasticity finite element analysis. The correlation between the indentation data and the tensile test data (at an effective or equivalent strain) is critically examined for these two multicrystalline materials.
Effect of Mo Doping and Heat Treatment on Microstructure and Electrochemical Performance of Vanadium Oxide Nanotubes
Authors: Mai Liqiang , Chen Wen , Jiang Congsheng , Xu Qing , Peng Junfeng , Zhu Quanyao
Published: April 2011

Mo doped vanadium oxide nanotubes (VONT) were formed via a rheological phase reaction followed by self-assembling process and were heated at 400 □ in an inert atmosphere. The nanotubes were characterized by SEM, HRTEM, XRD, FTIR, electrochemical investigation, etc. In contrast to the undoped VONTs, the interlayer distance between oxide layers in the (V0.99Mo0.01)xONTs increases owing to replacement of some V in nanotubes by Mo with a larger ionic radius, resulting in a shorten diffusion length of Li ions and an improved electrochemical performance. The electrochemical performance of (V0.99Mo0.01)xONTs is further enhanced by removing the residual organic template by heating in an inert atmosphere.
Photo-formed Metal Nanoparticle Arrays in Monolithic Silica-Biopolymer Aerogels
Authors: Liu Xipeng , Zhu Yu , Yao Chunhua , Risen William M.
Published: April 2011

Transparent monolithic aerogels based on silica, the bioderived polymer chitosan, and coordinated ions have been employed to serve as a three-dimensional scaffold decorated with Au, Pt and Pd ions. The coordination states of metal ions and the initial gel in one or several of the ions are established in the thickness of the monolith that is produced by supercritical CO2extraction to form the aerogels. Also in this work, it has been found that the Au(III) aerogels can be imaged photolytically in the two planar dimensions. The spatially controlled photolysis produces nanoparticles, (Au)nin the range of from 5 to 85 nm, for example, that constitute two dimensionally imaged arrays whose volumetric concentration also varies in the third dimension. These images microarrays of nanoparticles provide a basis for localization and detection of thiols, disulfides, amino acids and protein molecules. The formation of these arrays, including the dependence of their properties on light intensity, frequency and exposure, and distribution of target molecules and ions in the initial aerogel is presented.
Sintered Tantalum and Niobium Sub-micron Powders of Solid Electrolite Capacitors
Authors: Freeman Y. Pozdeev , Gladkikh A. , Rosenberg Yu.
Published: April 2011

The results of x-ray study and electrical measurements are brought together in order to understand a difference in performance and failures of solid electrolyte capacitors made of sintered tantalum and niobium sub-micron powders. It is shown that bulk Ta and Nb exhibit different abilities for the formation and decomposition of oxygen solid solution during manufacturing steps which may be critical for stability of metal/oxide interface of capacitor.
LPE Growth of Atomically Flat Ge Layer on a Mesa Pattern
Authors: Maruyama Takahiro , Matsuda Keiji , Saikawa Norikazu , Naritsuka Shigeya
Published: April 2011

Aiming at the growth of step free surface on mesas, we tried to suppress the formation of two-dimensional nucleation on grown surface by decreasing the supersaturation. When the supersaturation was enough small at the growth temperature below 400 °C, flat facets were formed on some mesas after the LPE growth for 30 min. We considered that these facets are formed on mesas with dislocation-free surface, considering the dislocation density of Ge substrate. AFM observation indicated that some triangle hollows with monolayer step in depth were present on these facets, but that the region among the hollows was atomically flat. It was also found that the amount and the size of the hollows were related to the growth temperature. Our results show the possibility that atomically flat Ge area beyond 100 μm2 will be obtained by the control of the growth condition.
Iron Oxide / Silica Nanocomposites
Authors: Kröll Michael , Pridöhl Markus , Zimmermann Guido
Published: April 2011

Nanoscaled Iron Oxide / Silica Nanocomposite particles are produced in a pyrogenic process. The iron oxide crystallites are separated from each other and covered with a silica layer. Their size can easily be controlled by adjusting the process parameters. The amount of iron oxide can also be controlled within certain limits. Due to their size these isolated magnetic particles show a superparamagnetic behaviour. The saturation magnetisation measured depends almost linearly on the size of the iron oxide crystallites showing an increase in the magnetisation with increasing particle size. Due to the composite structure the iron oxide is chemically stable. Furthermore it shows a thermal stability which is unusual for the given oxides.
Selective Ordered Mesoporous Silica Adsorbents
Authors: Lam Koon Fung , Ho Ka Yee , Yeung King Lun , McKay Gordon
Published: April 2011

Ordered mesoporous silica (OMS) adsorbents were prepared by grafting amino, carboxylic and thiol-containing functional groups onto MCM-41 for the selective removal of dye and metal pollutants from wastewater. The amino containing OMS-NH2 adsorbent has a large adsorption capacity and a strong affinity for the Acid blue 25. It can selectively remove Acid blue 25 from a mixture of dyes (i.e., Acid blue 25 and Methylene blue). The OMS-COOH is a good adsorbent for Methylene blue displaying excellent adsorption capacity and selectivity for the dye. The chemically modified OMS adsorbents were also tested for the selective removal and recovery of metals (i.e., lead and copper). The OMS-SH adsorbent can selectively remove lead from solutions containing Pb2+ and Cu2+ ions, whereas the OMS-NH2 selectively adsorbed a large quantity of copper. The selectivity of the adsorbents for lead and copper is strongly influenced by pH. Indeed, by simply adjusting the pH, OMS-NH2 can adsorb mainly lead or copper from a mixture containing both metals.
Size Effect Characterization for Nanostructured Material in Nanoindentation Test
Authors: Wei Yueguang , Du Ying , Shu Siqi , Zhu Chen
Published: April 2011

Based on the microscopic observations and measurements, the mechanics behaviors of the nanostructured material (the surface-nanocrystallized Al-alloy material) at microscale are investigated experimentally and theoretically. In the experimental research, the hardness-indent depth curves or relations are measured by using both the method of randomly selecting loading points on the specimen surface and the continuous stiffness method. In the theoretical simulation, based on both the material microstructure characteristics and the experimental features of the nanoindentation, the microstructure cell model is developed and the strain gradient plasticity theory is adopted. The material hardness-indent depth curves are predicted and simulated. Through comparison of the experimental results with the simulation results, the material parameters and the model parameters are determined.
Preparation and Mechanical Properties of Nanostructured Tungsten Carbide Alloys Strengthened by Carbon Nanotubes
Authors: Tan G. L. , Wu X. J. , Li Z. Q.
Published: April 2011

A novel approach for the synthesis of carbon nanotubes strengthened nanostructured tungsten carbide was investigated, in which nanophase tungsten powders are carburized by C2H2 instead of CO and a fraction of decomposed carbons were in situ converted to nanotubes. In this way, the composite powders of nanocrystal WC-Co and carbon nanotubes have been in situ prepared. The composite WC-Co powders were then hot pressed into bulk alloy which shows a exceptionally high microhardness up to 3307 kg/mm2. It is proposed that carbon nanotubes with extra high Young's modulus (1.8 Tpa) play both roles on strengthening the composite matrix and prohibiting growth of WC grains, which results in the great improvement of the mechanical properties of the samples. The average grain size of the prepared WC-Co hard alloys was estimated to be less than 100 nm. The effect of hot press temperature on the mechanical properties of the prepared alloys was also studied in detail.
New Advances in Molding and Printing Processes for Organic/Plastic Electronics Using Chemically Modified Stiff, Photocured Poly (dimethylsiloxane) (PDMS) Elastomers Designed for Nano-Resolution Soft Lithography
Authors: Choi Kyung M. , Rogers John A.
Published: April 2011

The development of new materials for organic/plastic electronics allows us to fabricate novel devices through unconventional approaches. The ‘soft lithography technique’ has been widely used in replicating and fabricating small features. This technique is a low cost alternative to photolithography by generating structures from masters to substrates, which employ ‘elastomeric materials’, such as highly stretchable silicon elastomer, polydimethylsiloxane (PDMS) to replicate or transfer the original features to a variety of substrates by molding and printing processes. Since the resolution of pattern transfer significantly relies on the performance of polydimethylsiloxane (PDMS) stamp materials, commercial PDMS materials have shown limitations in high fidelity pattern transfer due to their low physical toughness and high thermal expansion coefficients. For those reasons, pattern fabrications using conventional PDMS materials are unable to satisfy our set of diverse demands, especially in the area of nano-scale replication. To achieve high performance in molding and printing, here we introduce a new strategy, design and synthesis of a modified PDMS silicon elastomer that is a stiffer and photocurable element to achieve our specific task of nano-scale resolution soft lithography. We then demonstrated its unique capabilities for the case of nano-features (300 nm wide) with narrow and tall heights (600 nm height) of photoresist, which is one of the most challenging ‘nano-patterning’ tasks in advanced soft lithography, which is often limited in its use at the nano-scale with other commercially available elastomers.
Control of Current Reversal and Separation of Particles in Inertia Ratchets
Authors: Family F. , Larrondo H.A. , Arizmendi C.M.
Published: April 2011

We have studied the deterministic dynamics of underdamped single and multiparticle ratchets associated with current reversal, as a function of both the amplitude and the frequency of an external driving force. We show that control of current reversals in deterministic inertia ratchets is possible as a consequence of a locking process associated with different mean velocity attractors. Control processes employing small perturbations on the frequency and the amplitude of the external force may be designed in view of the intermixed fractal nature of the domains of attraction of the mean velocity attractors. The range where each control parameter is capable of reversing the current is determined. Quenched noise has significant effect on the basins of attraction. In particular, with increasing disorder the direction of a packet of particles can be reversed, leading to disappearance or weakening of the negative velocity attractor. The influence of the mass of the particles is also considered in order to design control techniques capable of separating particles of different masses.
Molecular pumping and separation in a symmetric channel
Authors: Fleishman D. , Filippov A.E. , Urbakh M.
Published: April 2011

A mechanism responsible for directed transport and molecular separation in asymmetricchannel is proposed. We found that under the action of spatial harmonic oscillations of the channel, the system exhibits a directed transport in either direction, presenting multiple current reversals as the amplitude and/or frequency of the oscillations are varied. The particles of different masses may be forced to move with different velocities in the same or in the opposite directions by properly adjusting driving parameters. The directed transport can be produced in both directions even in the absence of thermal noise, the latter can speed up or slow down the transport depending on the system parameters.
Bimodal Structured Bulk Nanocrystalline Al-7.5Mg Alloy
Authors: Lee Zonghoon , Witkin David B. , Lavernia Enrique J. , Nutt Steven R.
Published: April 2011

The microstructure, mechanical properties and deformation of bimodal structured nanocrystalline Al-7.5Mg alloy were investigated. Grain refinement was achieved by cryomilling of atomized Al-7.5Mg powders, and then cryomilled nanocrystalline powders blended with 15% and 30% unmilled coarse-grained powders were consolidated by hot isostatic pressing followed by extrusion to produce bulk nanocrystalline alloys. Bimodal bulk nanocrystalline Al-7.5Mg alloys, which were comprised of nanocrystalline grains separated by coarse-grain regions, show balanced mechanical properties of enhanced yield and ultimate strength and reasonable ductility and toughness compared to comparable conventional alloys and nanocrystalline metals.
Mechanical Properties of a Cryomilled Nanostructured Al-Mg Alloy
Authors: Han B. Q. , Mohamed F. A. , Bampton C. , Lavernia E. J.
Published: April 2011

The microstructural characteristics and mechanical behavior at room temperature of a nanostructured Al-Mg alloy, with grain sizes of approximately 100 nm, manufactured by a cryomilling process were investigated in the present study. The results reveal an asymmetry of yield strength between tension and compression. On the basis of the mechanical behavior results it appears that the presence of a few micron inclusions may have a negative effect on tensile behavior of the cryomilled nanostructured Al-Mg alloy.
Dislocation Confinement and Ultimate Strength in Nanoscale Metallic Multilayers
Authors: Li Qizhen , Anderson Peter M.
Published: April 2011

In nanostructured metallic multilayers, hardness and strength are greatly enhanced compared to their microstructured counterparts. As layer thickness is decreased, three different regions are frequently observed: the first region shows Hall-Petch behavior; the second region shows an even greater dependence on layer thickness; and the third region exhibits a plateau or softening of hardness and strength. The second and third regions are studied using our discrete dislocation simulation method. This method includes the effects of stress due to lattice mismatch, misfit dislocation substructure, and applied stress on multilayer strength. To do so, we study the propagation of existing threading and interfacial dislocations as the applied stress is increased to the macroyield point. Our results show that in region 2, dislocation propagation is confined to individual layers initially. This “confined layer slip” builds up interfacial content and redistributes stress so that ultimately, the structure can no longer confine slip. The associated macroyield stress in this region depends strongly on layer thickness. In region 3, layers are so thin that confined layer slip is not possible and the macroyield stress reaches a plateau that is independent of layer thickness.
Plastic Deformation and the Role of Fault Formation in the Equation of State of Micron Size Intermetallic Alloys Under Non-Hydrostatic Pressure
Authors: Vassiliou John K. , Otto J. W. , Frommeyer G. , Davis J. J. , Pinto P.
Published: April 2011

The elastic and plastic deformation of micron size anisotropic polycrystals of Ni3Al and Cu3Au intermetallic alloys have been studied under non-hydrostatic conditions by energy-dispersive X-ray diffraction (EDX) in a diamond-anvil cell. Compression was achieved by confining the samples in a viscous fluid or directly between the diamond anvils. Deviatoric forces are introduced in the samples as a result of the increasing viscosity with pressure and the eventual glassification of the pressurizing medium or by the contact forces of the diamond anvils. Line shifts and line profiles were used to analyze elastic and plastic strains. Plastic deformation is due to the onset of non-hydrostatic stresses and the introduction of stacking faults and dislocations. A volume incompressibility due to plastic deformation and the saturation of the stacking fault probability is followed by an elastic compression of a fully plastically deformed state. The compression of this state is isotropic and independent of the presence and type of the pressurizing medium. From the measured strains at different crystallographic orientations, the uniaxial stress and the stacking fault probability as a function of the confining pressure are derived and their role in the equation of state is examined. Using finite elasticity, the equation of state is derived in the presence of uniaxial stresses causing stacking faults, defects and dislocations.
Defect diffusion in hcp Zirconium: A kinetic Monte Carlo approach
Authors: Arévalo C. , Caturla M.J. , Perlado J.M.
Published: April 2011

We have studied diffusion of defects produced during irradiation in hcp zirconium through a kinetic Monte Carlo model. The input data for these simulations is based on molecular dynamics calculations and from experiments whenever available. The initial cascade damage produced by recoils of 25 keV energy from molecular dynamics simulations has been followed for times of hours at a fixed temperature of 600K. We have calculated the number of freely migrating defects, the recombination ratio between vacancies and interstitials, the defects surviving in the bulk as well as the average cluster size for these remaining defects.
Localized Charging Effects Resulting From Focused Ion Beam Processing Of Non-Conductive Materials
Authors: Stevens-Kalceff Marion. A. , Rubanov S. , Munroe P. R.
Published: April 2011

Focused Ion Beam (FIB) systems employ a finely focussed beam of positively charged ions to process materials. Ion induced charging effects in non-conductive materials have been confirmed using Scanning Surface Potential Microscopy (SSPM). Significant localized residual charging is observed within the ion implanted micro-volumes of non-conductive materials both prior to and following the onset of sputtering. Characteristic observed surface potentials associated with the resultant charging have been modelled, giving insight into the charging processes during implantation and sputtering. The results of this work have implications for the processing and microanalysis of non-conductive materials in FIB systems.
n-wells voltage contrast imaging with a Focused Ion Beam
Authors: Roy Erwan Le , Thompson Mark
Published: April 2011

Using a focused ion beam (FIB), secondary electron (SE) imaging of n-wells under oxide from the backside of thinned integrated circuits without electrical bias was accomplished. From the backside, the n-wells were initially observed at a remaining silicon thickness ∼4.5μm, which correlates to the actual implant depth where n and p carrier concentrations are equal. When the wells were FIB imaged, contrast appeared dark relative to the p substrate. During deposition of the oxide film, the n-well brightness changed from dark relative to the p-substrate, to bright. It appears that initially during this deposition step the interaction volume of the beam reached the silicon/oxide interface to create tunneling electrons. This phenomenon dominated the capacitive effect. Then as the film thickness increased the capacitive effect prevailed. The imaging structure is analogous to a Metal-Oxide-Semiconductor (MOS) capacitor. The n- and p-MOS capacitive properties yielded a permanent imaging contrast. At an optimized oxide thickness (130nm), the n-wells appear white relative to the p-substrate with a contrast up to 85% {(Ip-substrate − In-wells)/(Ipsubstrate + In-wells)}.
Molecular Dynamics Study Of Surface Morphological Evolution By Cluster Impacts
Authors: Aoki Takaaki , Matsuo Jiro , Yamada Isao
Published: April 2011

In order to understand the characteristics of surface modification process with cluster ion irradiation, molecular dynamics simulations of Ar cluster impacting on Si surface with various surface structures were carried out. It was found that the surface morphology is dynamically deformed with only one cluster impact and the impact process of cluster is different depending on the local surface structure. For example, when an Ar2000 cluster accelerated with 20keV impacted on the convex point of the surface, the hill was compressed and the impact area was smoothed. At the impact on a concave point, a deeper crater was formed compared with the impact on a flat surface. On the other hand, the MD simulations of sequential impacts of large clusters were performed. It was found that the small tip structures on the surface could be removed easily with cluster irradiation. It was shown that surface roughness converges to 15∼20Å and this value agrees with the result obtained by single impact of cluster.
He+ ion damage in 4H-SiC studied by charge collection efficiency measurements.
Authors: Nipoti Roberta , Donolato Cesare
Published: April 2011

The nuclear microprobe facility of the Italian National Laboratories of Legnaro was used for an Ion Beam Induced Charge Collection (IBIC or IBICC) experiment which measured the charge collection of a 4H-SiC Schottky diode irradiated with 2 MeV He+ at increasing doses. The experiment was arranged so as to obtain a statistics of about 1400 events per each He+ ion from the 1st to the 500th one on the ion microprobe spot (1.5 × 1.5 μm2). These figures correspond to He+ fluence values in the range 107−1011 ions/cm2. The charge collection of the diode was almost constant from the 1st to the 10th He+ ion, i.e. up to a fluence of 109 ions/cm2, and then monotonically decreased for the subsequent ions. The SiC device collection efficiency was modelled by representing the electrical effects of the damage produced by ions as a planar interface region of given carrier recombination velocity at the depth of the damage peak. Experimental and computed data scale one to the other assuming that the interface recombination velocity and He+ fluence are linearly related.
Fabrication of Nanotips and Microbeams in Antimonide Based Semiconductor Material using Bromine Ion Beam Assisted Etching
Authors: Krejca B. , Vangala S.R. , Krishnaswami K. , Kolluru R. , Ospina M. C. , Sung C. , Goodhue W. D.
Published: April 2011

Antimonide-based compound semiconductors have emerged as the materials of choice for fabricating high-speed low-power electronics and electro-optics for applications requiring miniaturization and portability. In this work Br-IBAE is shown to be an anisotropic antimonide etching technique that is capable of generating novel structures as well as performing standard etching tasks. When etching less than optimally chemical-mechanical polished (111) InSb wafers, sharp-tipped cone structures with tip radii of the order of less than 60 nm are produced. These structures may be ideally suited for the development of field-emission devices, where small tip radii are required for useful emission currents. The anisotropic nature of the IBAE technique allows one to etch channels in the surface at angles up to 70° from perpendicular, making the fabrication of microbeams feasible. Using an angled sample holder, the first etch undercuts the masked beams from one side. The sample is then removed and realigned so as to undercut the beams from the other side. The triangular shaped microbeams are left suspended from either one or both ends. Using a combination of atomic force microscopy and mechanical engineering beam analysis techniques, the elastic parameters of the material can be measured. The microbeams can be aligned along various directions on the surface to investigate anisotropic characteristics. This is particularly important for determining the mechanical characteristics of materials that can only be grown in thin epitaxial layers, such as quaternary antimonide-based compound semiconductors.
Formation of High Quality β-FeSi2 by Pre-Amorphization-Enhanced Diffusion
Authors: Murakami Y. , Kenjo A. , Sadoh T. , Yoshitake T. , Miyao M.
Published: April 2011

Effects of Ar+ ion irradiation on solid-phase growth of β-FeSi2 have been investigated. Si substrates were amorphized with Ar+ ions (20 keV) before Fe (15 nm) deposition to form Fe(15 nm)/a-Si/c-Si stacked structures. As a reference, Fe/c-Si stacked structures were prepared. In the initial stage of annealing at 800 °C, β-FeSi2 formation was enhanced for pre-amorphized samples, which was due to the enhanced diffusion of silicidation species. In the long time annealing, β-FeSi2 formation proceeded by thermal equilibrium diffusion, and the formation rate was not affected by pre-amorphization. Crystal quality of β-FeSi2 was improved by pre-amorphization. The pre-amorphization enhanced diffusion is useful for formation of high quality β-FeSi2 thin films.
Preamorphization-induced defects in shallow P+N junctions characterized by an ac magnetic field
Authors: Abdelaoui M. , Mehor H. , Idrissi M. , Benzohra M. , Olivié F.
Published: April 2011

Germanium implantation into silicon substrate is currently used to preamorphisize the crystalline structure in order to avoid boron channeling effects in shallow P+N junction manufacturing. Nevertheless, after boron doping and rapid thermal annealing, different defects are formed within the structure, such as end of range defects which are created at the amorphous/crystalline interface. Our study concerns two types of shallow P+N junctions. These junctions were fabricated using low energy boron implantation at 3 KeV with a dose of 2×1015 cm-2 into high-energy germanium preamorphized n-type crystalline silicon substrates at 2.2 MeV with a dose of 1015 cm-2. In the first type, the preamorphization was performed at ambient temperature. In the second, the preamorphization was performed at liquid nitrogen temperature. Boron doping was followed by a Rapid Thermal Annealing (RTA) step for 15 s at 950 °C. Deep Level Transient Spectroscopy (DLTS) technique was used to characterize the defects formed in each structure. The impact of an ac magnetic field on the reverse current has been studied at a given bias, when sweeping the sample temperature. The measurements were performed under a low frequency (less than 1 kHz) magnetic field of a Vrms value of 2000 G, with sample temperature varying between 80 and 260 K. The results show a high activity of defects at low frequencies (1 and 10 Hz) for the nitrogen preamorphized sample. Moreover, this activity is observed at about 200 K which corresponds to the peak of the DLTS spectra of such sample. However, the ambient preamorphized sample characterized by a lower concentration of defects seems to be insensitive to the ac magnetic field. Therefore, it appears that the preamorphization-induced defects influence strongly the response of the junction to an applied ac magnetic field.
Ge Nanocrystal Formed Directly by High-Dose-Ion-Implantation and the Related UV-VIS Photoluminescence
Authors: Zeng Yingqiu , Lu Tiecheng , Zou Ping , Zhu Sha , Wang Lumin , Shen Liru
Published: April 2011

The investigation of nanocrystalline Ge (nc-Ge) directly prepared with high dose Ge ion implantation of 1×1016, 1×1017, 5×1017and 1×1018cm-2respectively without subsequent annealing is presented in this paper. The specimens were measured by means of GIXRD, LRS and PL. The results show the nc-Ge, which possesses strong compressive stress, can be fabricated when the implanting dose of Ge ions is over the threshold dose∼1×1017cm-2. The content and size of nc-Ge will enlarge with increasing dose. The nc-Ge formation mechanism may be the Ge atoms in the amorphous Ge (a-Ge) clusters, which are formed through the aggregation of implanted Ge ions, obtain energy from the instant local annealing zone induced by the incident Ge ion and reconstruct to nc-Ge existing in a-Ge clusters. The PL results indicate the strong PL peaks centered at about 295, 400 and 570 nm can be observed in implanted samples. The intensity of these PL peaks increases with increasing dose. The related PL mechanism in Ge-ion-implanted SiO2film has also been discussed.
Facile Fabrication of Nanoparticles in the Nanospace of Ultrathin TiO2-Gel Films: Composition, Morphology and Catalytic Activity
Authors: He Junhui , Kunitake Toyoki
Published: April 2011

In this article, we present in-situ synthesis of nanoparticles of various compositions and morphologies in the nanospace of ultrathin TiO2-gel films using low temperature H2 and O2 plasmas as reductant and oxidant, respectively. Parameters that influence the formation of nanoparticles were investigated and discussed. Reversible chemical transformation was found to give monodisperse nanoparticles. Catalytic activities of Pd monometallic and Ag-core/Pd-shell bimetallic nanoparticles were tested for hydrogenation of methyl acrylate. The much enhanced catalytic activity is attributed mainly to a large ratio of the surface Pd atoms.
Size and critical thickness evolution during growth of stacked layers of InAs/InP(001) quantum wires studied by in situ stress measurements
Authors: Fuster David , González María Ujué , González Luisa , González Yolanda , Ben Teresa , Ponce Arturo , Molina Sergio I.
Published: April 2011

Size and spatial distribution homogeneity of nanostructures is greatly improved by making stacks of nanostructures separated by thin spacers. In this work we present in situ and in real time stress measurements and reflection high energy electron diffraction (RHEED) observations and ex situ transmission electron microscopy (TEM) characterization of stacked layers of InAs quantum wires (QWr) separated by InP spacer layers, d(InP), of thickness between 3 and 20 nm. For d(InP) < 20 nm, the amount of InAs involved in the newly created QWr from the 2nd stack layer on, exceeds that provided by the In cell. Our results suggest that in those cases InAs 3D islands formation starts at the P/As switching and lasts during further InAs deposition. We propose an explanation for this process that is strongly supported on TEM observations. The results obtained in this work imply that concepts like the existence of a critical thickness for 2D-3D growth mode transition should be revised in correlated QWr stacks of layers.
Optical properties of InGaAs QDs grown in a GaAs matrix by MOCVD, emitting at 1300 nm at room temperature
Authors: Todaro M. T. , De Giorgi M. , Tasco V. , De Vittorio M. , Passaseo A. , Cingolani R.
Published: April 2011

We investigate the optical properties of InGaAs QDs emitting at 1330 nm, directly grown by Metal Organic Chemical Vapor Deposition (MOCVD) in a GaAs matrix, without indium in the barrier. The PL characterization of this new kind of QDs, shows very narrow lineshape at room temperature and a strong reduction of the temperature dependent quenching of the emission (a factor of 3 from 30 K to 300 K).

The quantum external efficiency obtained by inserting such QDs into light emitting diode structures, despite the low dot density (1.6*109 cm−2), is 0.03%. This value corresponds to an individual QD efficiency about 30% higher than that reported in the literature for state of art InGaAs/InGaAs QD LEDs.
2-D Photonic Quasicrystal in Metallic Microcavity
Authors: Zhang J. Y. , Tam H. L. , Wong W. H. , Pun Y. B. , Xia J. B. , Cheah K. W.
Published: April 2011

Photonic microcavity promises to be one of the photonic devices that can have immediate applications such as super bright LED and low threshold laser. Most photonic crystal structures currently used on microcavity are cubic or hexagonal, whose folding symmetry is no greater than 6. In this work, we fabricated 2-D photonic microcavity with Penrose quasicrystal pattern and measured the angular resolved transmission and photoluminescence spectra of the microcacity. From the experimental result it is found that isotropic photonic band gap exists in the microcavity with the Penrose quasicrystal pattern.
Design and Fabrication of Dispersion Controlled and Polarization Maintaining Photonic Crystal Fibers for Optical Communications Systems
Authors: Kawanishi Satoki , Yamamoto Takashi , Kubota Hirokazu , Tanaka Masatoshi , Yamaguchi Syun-ichiro
Published: April 2011

Recent progress on photonic crystal fibers (PCFs) is reviewed aiming at their application to high performance optical communications sytems. The optical properties, for example dispersion characteristics, can be set by selecting the appropriate combination of air hole diameter and air hole pitch. A noteworthy characteristic of PCFs is their strong birefringence, which suggests optical components with better polarization maintaining characteristics.

This paper describes the characteristics of dispersion controlled PCFs and polarization maintaining PCFs. It describes theoretical analyses and experimental results of fabricated PCFs that have short wavelength zero dispersion at 810 nm, polarization maintaining capability with birefringence of 1 × 10−3, polarization maintaining dispersion flattened functions, and absolute single polarization state support with polarization dependent loss of 1 dB/m at 1550 nm. A supercontinuum generation experiment with PM-PCF in the 1550 nm region is shown with symmetrical spectral broadening to over 40 nm. The potential of PCFs will be discussed with reference to the next generation optical communications systems.
Understanding the Electro-thermal and Phase-transformation Processes in Phase-change Materials for Data Storage Applications
Authors: Wright C. D. , Armand M. , Aziz M. M. , Senkader S. , Yu W.
Published: April 2011

Attempts at the practical utilization of Sb-Te based alloys beyond optical data storage have been made recently by employing these materials in both scanning probe type memories, and in electrical memory devices - namely Phase-Change Random Access Memory (PC-RAM). We have developed models to simulate the electrical, thermal, and phase-change characteristics of this important class of material. In this paper we describe the physical basis of our models and present simulation results for different memory configurations and operating conditions.
Memory Effects In Manganese Perovskites
Authors: Noginova N. , Chelule G. , Loutts G. B.
Published: April 2011

Manganese doped perovskites are promising materials for non-magnetic data storage. Systems with low doping concentration, such as Mn:YAlO3 are high-quality optical crystals, demonstrating significant photorefractive effect. Optically and electrically induced quasi-permanent change in low-field conductivity was observed in the materials with high concentration of manganese such as single crystals and films of LaGa1−xMnxO3 (x= 0.1–1). These memory effects can last for a long time at room temperature and can be easily erased by heating up to 230 C. We explain our experimental results by photoinduced or thermoinduced local phase transition with the oxidation of Mn ions.
Optical Properties and Phase Transformation Kinetics of Ge-Sb-Te-(N) Alloy Thin Films Investigated by Ellipsometry
Authors: Kim Sang Youl
Published: April 2011

The recent research works of optical properties and crystallization kinetics of phase change Ge-Sb-Te-(N) alloy by using ellipsometry are reviewed.

The complex refractive index spectra of phase-change Ge2Sb2+xTe5thin films and those of the nitrogen Ge2Sb2Te5thin films have been determined.

The crystallization behavior of amorphous Ge2Sb2Te5thin films investigated by in situ ellipsometry revealed that the crystallization process of Ge2Sb2Te5near 140°C is a two-step process. The kinetic exponent of the Johnson-Mehl-Avrami equation was about 4.4 for the first stage and 1.1 for the second stage. Ex situ study confirmed the cascaded crystallization behavior of phase-change Ge2Sb2Te5films.

A passive type single wavelength ellipsometer adopting a DOAP (division-of-amplitude photopolarimeter) configuration with nanosecond time resolution is developed to monitor the phase transformation of Ge2Sb2Te5caused by a high power nanosecond laser pulse in real time. The two-step process - the fast nucleation-dominant stage followed by the slow anomalous grain growth stage is confirmed.

Based on the recent analysis of the ellipsometric isotherm at moderately elevated temperature, we found for the first time that the fast nucleation dominant crystallization of Ge2Sb2Te5can be better explained by a modified JMA equation that illustrates the nucleation dominated process where the creation rate of a new nucleus is proportional to the density of preexisting nuclei and growth rate is negligible.
Kinetics of Crystal Nucleation and Growth in Thin Films of Amorphous Te Alloys measured by Atomic Force Microscopy
Authors: Kalb J. , Spaepen F. , Wuttig M.
Published: April 2011

Both the crystal nucleation rate and the crystal growth velocity of sputtered amorphous Ag0.055In0.065Sb0.59Te0.29 and Ge4Sb1Te5 thin films used for optical data storage were determined as a function of temperature. Crystals were directly observed using ex-situ atomic force microscopy, and their change in size after each anneal was measured. Between 140°C and 185°C, these materials exhibited similar crystal growth characteristics, but differed in their crystal nucleation characteristics. These observations provide an explanation for the different re-crystallization mechanisms observed upon laser-induced crystallization of amorphous marks.