bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Yield Criterion on Numerical Simulation Results Using a Stress-Based Failure Criterion
Authors: Sakash Aaron , Moondra Sumit , Kinsey Brad L.
Published: July 2006

Determining tearing concerns in numerical simulations of sheet metal components is difficult since the traditional failure criterion, which is strain-based, exhibits a strain path dependence. A stress-based, as opposed to a strain-based, failure criterion has been proposed and demonstrated analytically, experimentally in tube forming, and through numerical simulations. The next step in this progression to the acceptance of a stress-based forming limit diagram is to demonstrate how this failure criterion can be used to predict failure of sheet metal parts in numerical simulations. In this paper, numerical simulation results for dome height specimens are presented and compared to experimental data. This procedure was repeated for various yield criteria to examine the effect of this parameter on the ability to predict failure in the numerical simulations. Reasonable agreement was obtained comparing the failure predicted from numerical simulations and those found experimentally, in particular for the yield criterion which has been shown to best characterize the material used in this study.
Use of Inverse Solutions for Residual Stress
Measurements
Authors: Schajer Gary S. , Prime Michael B.
Published: July 2006

For most of the destructive methods used for measuring residual stresses, the relationship between the measured deformations and the residual stresses are in the form of an integral equation, typically a Volterra equation of the first kind. Such equations require an inverse method to evaluate the residual stress solution. This paper demonstrates the mathematical commonality of physically different measurement types, and proposes a generic residual stress solution approach. The unit pulse solution method that is presented is conceptually straightforward and has direct physical interpretations. It uses the same basis functions as the hole-drilling integral method, and also permits enforcement of equilibrium constraints. In addition, Tikhonov regularization is shown to be an effective way to reduce the influences of measurement noise. The method is successfully demonstrated using data from slitting (crack compliance) measurements, and excellent correspondence with independently determined residual stresses is achieved.
Polynomial Interpolated Taylor Series Method for Parameter Identification of Nonlinear Dynamic System
Authors: Wong Simon C. , Barhorst Alan A.
Published: July 2006

This research work is in the area of structural health monitoring and structural damage mitigation. It addresses and advances the technique in parameter identification of structures with significant nonlinear response dynamics. The method integrates a nonlinear hybrid parameter multibody dynamic system (HPMBS) modeling technique with a parameter identification scheme based on a polynomial interpolated Taylor series methodology. This work advances the model based structural health monitoring technique, by providing a tool to accurately estimate damaged structure parameters through significant nonlinear damage. The significant nonlinear damage implied includes effects from loose bolted joints, dry frictional damping, large articulated motions, etc. Note that currently most damage detection algorithms in structures are based on finding changed stiffness parameters and generally do not address other parameters such as mass, length, damping, and joint gaps. This work is the extension of damage detection practice from linear structure to nonlinear structures in civil and aerospace applications. To experimentally validate the developed methodology, we have built a nonlinear HPMBS structure. This structure is used as a test bed to fine-tune the modeling and parameter identification algorithms. It can be used to simulate bolted joints in aircraft wings, expansion joints of bridges, or the interlocking structures in a space frame also. The developed technique has the ability to identify unique damages, such as systematic isolated and noise-induced damage in group members and isolated elements. Using this approach, not just the damage parameters, such as Young’s modulus, are identified, but other structural parameters, such as distributed mass, damping, and friction coefficients, can also be identified.
Ostwald ripening of manganese silicide islands on Si(001)
Authors: Krause M. R. , Stollenwerk A. , Licurse M. , LaBella V. P.
Published: July 2006

The deposition of Mn onto Si(001) in the submonolayer regime has been studied with scanning tunneling microscopy to gain insight into the bonding and energetics of Mn with Si. The as-deposited Mn films at room temperature are unstructured. Upon annealing to 300–700 °C three-dimensional islands of Mn or MnxSiy form while between the islands the Si(001)-(2×1) reconstruction becomes visible. With increasing annealing time the density of islands per surface area decreases while the average height of the remaining islands increases. The large islands grow in size at the expense of the small ones, which can be understood in the context of Ostwald [Z. Phys. Chem. 34, 495 (1900)] ripening theory. The average island height shows a time dependence of H∼t1∕4, indicating that surface diffusion is the growth limiting process.
End-pointing chamber clean by calorimetric probing of process effluent
Authors: Chen Ing-Shin , Neuner Jeffrey W. , Welch James J. , Chen Philip S. H. , DiMeo Frank
Published: July 2006

The semiconductor industry employs gas-phase cleaning widely to remove materials deposited on the chamber walls during thin-film deposition processes. Chamber clean end-pointing—i.e., terminating the process when the chamber is clean—is desirable to manage cost of ownership and environmental impact. Existing end-pointing methods tend to rely on changes of plasma characteristics as the in situ plasma removes the deposit in time. Chamber clean technology is moving towards remote generation of plasma species for cleaning. In this arrangement, the chamber is located downstream from the plasma source. Because the etching reaction occurs ex situ, there are no relevant changes occurring in the plasma characteristics, and the effectiveness of many existing methods decreases. We report the development of a calorimetric probe for chamber clean end-pointing. The probe has an all solid-state construction and is engineered to be immersed in the process effluent during end-pointing operation. When the probe is operated at constant temperature, the probe power is closely related to the energy flux carried by the effluent, which in turn correlates with chamber conditioning. We examine probe response to NF3 plasma and etching of silicon specimens in a laboratory setting, and demonstrate successful end-pointing for both in situ and remote chamber clean on production tools. The probe results compare favorably with other coinstalled end-pointing solutions.
High-voltage parallel writing on iron nitride thin films
Authors: Farkas N. , Ehrman J. D. , Evans E. A. , Ramsier R. D. , Dagata J. A.
Published: July 2006

We report large area patterning of sputter-deposited FeN thin films by a high-voltage parallel writing technique that was recently developed to modify ZrN surfaces. Systematically patterned 15–100-nm-thick FeN films consisting of features with well-defined sizes and shapes are obtained by applying high dc voltages between a stamp and the samples. During the process the oxide dissolves, exposing the substrate beneath. This controlled breakdown eliminates the need for any postexposure etching. The single-step imprinting method presented here provides an emerging route to fabricate isolated FeN geometrical structures on silicon substrates for magnetic applications.
Role of defects at nanoscale ZnO and Cu(In,Ga)Se2 semiconductor interfaces
Authors: Strzhemechny Y. M.
Published: July 2006

Current understanding and control of semiconductor contacts increasingly require measurements sensitive to defects and chemical changes at nanoscale interfaces. We offer examples illustrating dramatic macroscopic effects occurring in semiconductor systems as a result of nanoscale interface phenomena. In some cases, there is interplay of several competing defect-driven mechanisms. Elucidating them and finding the leading ones require careful experimental approach. For single-crystalline ZnO, we study the role of near-surface defects on the formation of Au Schottky contacts. Among the factors degrading the rectifying characteristics of such contacts one should consider the following. High concentrations of shallow donors in the surface and subsurface regions lead to barrier thinning, resulting in increased tunneling. Alternatively, the presence of deep defects near contact interface promotes tunneling by defect-assisted hopping. Nanoscale electronic and chemical studies show that independent reduction of both shallow donors and deep defects significantly improves the rectifying performance of the Au∕ZnO contacts. We find that processing of ZnO with remote O and H plasmas allows for controllable tailoring of chemical and physical properties of the surface. By the same token, nanoscale compositional and electrostatic variations between grain boundaries and grain interiors in thin polycrystalline films of Cu(In,Ga)Se2, absorber layers in record-setting solar cells, show how nanoscale arrangement of near-surface stoichiometric defects may improve the overall photovoltaic efficiency. Confirming the theory, we find a 50% reduction in Cu composition from grain interior to boundary and a p-type potential barrier that acts to reduce majority-carrier hole recombination. These examples emphasize the practical significance of nanoscale chemical and electronic features at electronic material interfaces.
Real-time spectroscopic ellipsometry studies of the growth of amorphous and epitaxial silicon for photovoltaic applications
Authors: Levi D. H. , Teplin C. W. , Iwaniczko E. , Yan Y. , Wang T. H. , Branz H. M.
Published: July 2006

In situ monitoring of material properties during thin-film deposition provides researchers with a valuable tool for maximizing solar cell performance, while also enabling efficient exploration of deposition parameter space. This article describes how our research team has utilized in situ real-time spectroscopic ellipsometry (RTSE) to maximize our productivity in two related projects. We are using hot wire chemical vapor deposition (HWCVD) for low-temperature (90–235 °C) deposition of very thin films of amorphous hydrogenated silicon for amorphous Si∕crystal-Si heterojunction (SHJ) solar cells. We are also using HWCVD for low-temperature (200–440 °C) deposition of epitaxial films of silicon on crystal-Si substrates. We utilize RTSE as both an in situ diagnostic and a postgrowth analysis tool for SHJ solar cells and epi-Si films grown by HWCVD. Using input from RTSE analysis we have achieved a photovoltaic energy conversion efficiency of 17.1% on an Al-backed p-type float-zone c-Si wafer. Epi-Si films have been grown as thick as 500 nm utilizing parameter optimization based on RTSE analysis.
Laser processing of polymer nanocomposite thin films
Authors: Sellinger A. T. , Leveugle E. M. , Gogick K. , Zhigilei L. V. , Fitz-Gerald J. M.
Published: July 2006

Current biotechnology and sensor research has enhanced the drive to establish viable methods for depositing high-quality polymer thin films. In this research, thin films of poly(methyl methacrylate) (PMMA) were prepared by matrix-assisted pulsed-laser evaporation (MAPLE). Up to 2wt% of carbon nanotubes were subsequently added to MAPLE target systems for deposition of polymer nanocomposite films. Targets were ablated using a 248nm (KrF) laser at fluences ranging from 0.045to0.75J∕cm2. In addition, polymer concentration in MAPLE targets was varied between 1 and 5wt% relative to the matrix solvent, in this case toluene. Films were deposited on Si substrates at room temperature in an Ar atmosphere. Molecular-dynamics simulations of MAPLE were utilized for interpretation of experimental observations. Particularly, the ejection of large clusters consisting of both PMMA and toluene molecules was studied and related to the observed morphology of the deposited films.
Unintentional doping and compensation effects of carbon in metal-organic chemical-vapor deposition fabricated ZnO thin films
Authors: Li Xiaonan , Asher Sally E. , Limpijumnong Sukit , Zhang S. B. , Wei Su-Huai , Barnes Teresa M. , Coutts Timothy J. , Noufi Rommel
Published: July 2006

Carbon is a typical impurity in thin films fabricated by metal-organic chemical-vapor deposition (MOCVD). The role of carbon in undoped and nitrogen-doped ZnO thin films was studied experimentally and theoretically to understand the possible compensation effects. ZnO thin films are fabricated by low-pressure MOCVD using diethylzinc, nitric oxide (for nitrogen-doped films), or oxygen precursors (for undoped films). Compared with sputtering-fabricated ZnO film, the carbon concentration in the MOCVD-fabricated ZnO film is very high. Furthermore, the MOCVD-fabricated ZnO:N film has an even higher carbon concentration than the undoped ZnO. Considering the signal observed previously by Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy, it is possible that the incorporated carbon has formed complexes with doped nitrogen. The first-principles calculations predict that the formation energy for carbon interstitial (Ci) is relatively high. However, due to the large binding energy between Ci and NO (nitrogen substitute on oxygen site), the formation energy of the carbon-nitrogen (CN) defect complex is lower than that of the Ci. As a result, with nitrogen doping, the carbon-impurity concentration would be high. In the insulator or p-type ZnO films, the CN defect complexes have 1+ charge state. Therefore, the existence of carbon in the ZnO:N film could be another possible passivation factor to the nitrogen acceptor, in addition to hydrogen.
Role of low-level impurities and intercalated molecular gases in the α particle radiolysis of polytetrafluoroethylene examined by static time-of-flight secondary-ion-mass spectrometery
Authors: Fisher Gregory L. , Szakal Christopher , Wetteland Christopher J. , Winograd Nicholas
Published: July 2006

The structural degradation of polytetrafluoroethylene (PTFE) upon irradiation with MeV alpha (α) particles is accompanied by the proliferation of hydrogenated and oxygen-functionalized fluorocarbon species. In this article, we explore the origin of monoxide- and dioxide-functionalized fluorocarbon species that emerge upon α particle irradiation of PTFE. Samples of neat PTFE were irradiated to α doses in the range of 107–5×1010rad using 5.5MeV He2+4 ions produced in a tandem accelerator. Static time-of-flight secondary-ion-mass spectrometry (TOF-SIMS), using a 20keV C60+ source, was employed to probe chemical changes as a function of α particle irradiation. Chemical images and high-resolution mass spectra were collected in both the positive and negative polarities. Residual gas analysis, utilized to monitor the liberation of molecular gases during α particle irradiation of the PTFE in vacuum, is discussed in relationship to the TOF-SIMS data.
Para-sexiphenyl thin films grown by hot wall epitaxy on KCl(001) substrates
Authors: Andreev A. Yu. , Montaigne A. , Hlawacek G. , Sitter H. , Teichert C.
Published: July 2006

Here, we use atomic force microscopy (AFM) to study the morphology and growth kinetics of para-sexiphenyl layers deposited by hot wall epitaxy on crystalline KCl(001) substrates. It is shown that the growth process is quite complex and can be divided preliminarily into two steps. The initial growth stage is characterized by the formation of long needlelike crystallites built of “lying” molecules and oriented mainly into the ⟨110⟩ directions in accordance with the substrate’s fourfold symmetry. If the coverage increases, terraced crystalline mounds composed of monolayers of upright standing molecules start to develop between the needles. The mound formation is due to repeated two-dimensional nucleation of para-sexiphenyl molecules. By means of phase imaging in the AFM tapping mode, it could be further demonstrated that both needlelike crystallites and flat terraced mounds grow directly on the substrate surface, i.e., there is no wetting layer formed during the deposition of para-sexiphenyl on KCl(001).
Metal organic chemical vapor deposition of ZrO2 thin films using the single precursor zirconium 3-methyl-3-pentoxide, Zr(mp)4
Authors: Cho Wontae , Jang Hong Suk , An Ki-Seok , Lee Young Kuk , Chung Taek-Mo , Kim Chang Gyoun , Kim Yunsoo , So Byung-Soo , Hwang Jin-Ha , Jung Donggeun
Published: July 2006

Thin films of zirconium dioxide, ZrO2, have been deposited on silicon substrates by metal organic chemical vapor deposition using the single precursor zirconium 3-methyl-3-pentoxide, {Zr[OC(CH3)(C2H5)2]4, Zr(mp)4}, with no additional oxygen source, and the chemical vapor deposition reaction mechanism was also investigated. Zr(mp)4 is a liquid at room temperature and shows an excellent one-step weight loss and a low residual weight less than 3% in its thermogravimetric analysis. The deposition rate was found to be ∼13Å∕min at the substrate temperature of 300 °C with the activation energy of 33.5kJ∕mol, which was obtained at the moderate precursor temperature of 70 °C and 50 sccm of the N2 carrier gas. By gas chromatography/mass spectrometry and nuclear magnetic resonance analyses of the thermally decomposed vapor phase products collected during the deposition of ZrO2 films, it was clearly found that the ZrO2 films are grown via β-hydrogen elimination processes of the Zr(mp)4 single precursor. An x-ray photoelectron spectroscopy investigation of the ZrO2 films revealed an almost negligible carbon incorporation, which indicates that, except for the β-hydrogen elimination processes, no additional decomposition and/or recombination processes contributed to the growth of the ZrO2 films. The morphology, crystallinity, and electrical properties of the ZrO2 films were characterized by x-ray diffraction, scanning electron microscopy, and capacitance-voltage measurements.
Effect of probe tip size on atomic force microscopy roughness values for very smooth samples
Authors: Gondran Carolyn F. H. , Michelson Diane K.
Published: July 2006

Two-dimensional geometric models and experimental data are used to evaluate the effect of tip shape artifacts on atomic force microscopy images, roughness values, and power spectra. The effects of tip size are studied as a function of the surface feature height, spacing, and width. The models demonstrate that the need for sharp tips is dictated by the sample roughness and the size and spacing of surface features. In addition, the magnitude and direction of the error in the measured roughness parameters are related to artifact-induced changes in the skew in the distribution of the data points about the surface mean. Significantly, it is shown that either higher or lower roughness values can be measured using a smaller sized tip, depending on the surface character. These model results are supported by sample data obtained with 2 and 10 nm radii of curvature tipped probes on films used in semiconductor research and development. Sharp-tipped probes are clearly beneficial for imaging the surface microstructure of low-k materials. Tip size has a marked impact on the roughness values obtained on a somewhat smoother metal film sample. However, the high-k sample studied was smooth enough that no benefit was realized with the use of a sharper-tipped probe.
ISAC target vacuum system
Authors: Yosifov Dimo , Sekachev Igor
Published: July 2006

The Isotope Separator and Accelerator (ISAC) facility at TRIUMF has been in full operation since 1999. The ISAC east and west targets use proton beam from the cyclotron to produce various radioactive isotopes, which are then ionized and extracted. The ions are then passed through the mass separator and selected ions are transferred to the low energy experiments or injected into a radio frequency quadrupole accelerator. The accompanying radioactive contamination from the production of radioactive ions requires a complex vacuum system. The main target vacuum space consists of two semiseparate (primary and secondary) volumes pumped by turbo-molecular pumps. The primary volume uses four pumps while the secondary volume uses two pumps. Two hermetic rotary vane pumps are used as backing pumps. The nominal vacuum in both volumes is about 1.33×10−4Pa(1.0×10−6Torr). The pressure is monitored by two cold cathode and two hot filament ion gauges. The cold cathode gauges are used to interlock the system, which is critical during the bake out of the target and beam production. The exhaust gas from the vacuum pumps can be radioactive. Three gas storage tanks (decay tanks) are used for temporary storage of the radioactive exhaust and its controlled release to the atmosphere. Gas-species insensitive membrane gauges are used for monitoring the pressure in the storage tanks. This article describes the details of the ISAC target vacuum system as well as some procedures related to the handling of the exhaust gas with traces of radioactive contamination produced by the targets.
Characteristics of atomic layer deposited TiO2 films and their photocatalytic activity
Authors: Pheamhom Rodjana , Sunwoo Changshin , Kim Do-Heyoung
Published: July 2006

Titanium dioxide thin films were grown by atomic layer deposition (ALD) at 100–250 °C with tetrakis-dimethyl-amido titanium, using H2O2 as a counter-reactant. We have explored the effects of deposition temperature and the reactant pulse and purge times on the film growth rate to optimize the ALD process of TiO2. The film growth rate decreased with growth temperature below 175 °C, but was saturated to 0.28Å∕cycle at 175–250 °C. All the as-deposited films were highly pure, and the root-mean-square roughness was less than 2.5% of the film thickness. The films deposited at 150 °C and above were polycrystalline with an anatase structure, whereas those deposited at 125 ° C were amorphous. There was no change of crystal structure after annealing the crystalline films at temperatures of 450–650 °C. All the crystalline films were shown to have a photocatalytic activity in decomposing methylene blue in an aqueous solution. The films prepared at higher deposition temperatures were shown to have a better photocatalytic activity in decomposing methylene blue.
Synthesis of Au nanotubes with SiOx nanowires as sacrificial templates
Authors: Lu M. Y. , Chang Y. C. , Chen L. J.
Published: July 2006

Gold nanotubes with SiOx nanowires as sacrificial templates have been synthesized. SiOx nanowires were functionalized by 3-aminopropyl trimethoxysilane that generates a charged surface. The attachment of negatively charged Au nanoparticles was followed. The coverage of Au nanoparticles was initially less than 30%. Further coverage was achieved by the reduction of gold hydroxide to grow the continuous nanoshell on Au nanoparticles, which serve as nucleation sites. The final coverage of Au nanoshells on SiOx nanowires depends strongly on the relative amount of SiOx nanowires in gold hydroxide solution. Both transmission electron microscope and scanning electron microscope images revealed the formation of Au nanotubes with the removal of SiOx nanowires by etching in a dilute HF solution.
Aspect ratio dependent etching lag reduction in deep silicon etch processes
Authors: Lai S. L. , Johnson D. , Westerman R.
Published: July 2006

Microelectromechanical system (MEMS) device fabrication often involves three dimensional structures with high aspect ratios. Moreover, MEMS designs require structures with different dimensions and aspect ratios to coexist on a single microchip. There is a well-documented aspect ratio dependent etching (ARDE) effect in deep silicon etching processes. For features with different dimensions etched simultaneously, the ARDE effect causes bigger features to be etched at faster rates. In practice, ARDE effect has many undesired complications to MEMS device fabrication. This article presents a physical model to describe the time division multiplex (TDM) plasma etch processes and thereafter the experimental results on ARDE lag reduction. The model breaks individual plasma etch cycles in the TDM plasma etch processes into polymer deposition, polymer removal, and spontaneous silicon etching stages. With the insights gained from the model and control over the passivation and etch steps, it has been demonstrated that ARDE lag can be controlled effectively. Experiments have shown that a normal ARDE lag can be changed to an inverse ARDE lag. Under optimized conditions, the ARDE lag is reduced to below 2%–3% for trenches with widths ranging from 2.5 to 100μm, while maintaining good etch profile in trenches with different dimensions. Such results are achieved at etch rates exceeding 2μm∕min.
Modeling of InAs∕GaAs self-assembled heterostructures: Quantum dot to quantum ring transformation
Authors: Filikhin I. , Vlahovic B. , Deyneka E.
Published: July 2006

A single subband model for InAs∕GaAs quantum dots (QDs) and quantum rings (QRs), where the energy dependence of the electron effective mass is defined by the Kane formula, is used. Model assumptions lead to the nonlinear Schrödinger equation in a three-dimensional space. Geometrical parameters of the model are based on the fabrication of QRs from a QD procedure for which the experimental capacitance-gate voltage (CV) data are available. The confinement state energies of QDs (QRs) are calculated. Obtained results for single electron energy levels reveal a good agreement with the CV spectroscopy experiments.
Computational fluid dynamic model of a tapered Holweck vacuum pump operating in the viscous and transition regimes. I. Vacuum performance
Authors: Giors S. , Colombo E. , Inzoli F. , Subba F. , Zanino R.
Published: July 2006

Holweck molecular drag pumps are used as high-pressure stages in hybrid turbomolecular vacuum pumps, where they can operate in the transition and the viscous regime. In this article we develop a Navier-Stokes model of a Holweck pump with tapered pumping channels, applying slip-flow boundary conditions, to predict vacuum performances with and without gas flow. The commercial computational fluid dynamic code FLUENT is used to solve the model equations and to predict the pressure profile along the grooves. A specifically designed experiment is presented, whose arrangement provides the boundary conditions as input to the model and whose results are used to validate it.
High temperature outgassing tests on materials used in the DIII-D tokamak
Authors: Holtrop K. L. , Hansink M. J.
Published: July 2006

This article is a continuation of previous work on determining the outgassing characteristics of materials used in the DIII-D magnetic fusion tokamak [K. L. Holtrop, J. Vac. Sci. Technol. A 17, 2064 (1999)]. Achievement of high performance plasma discharges in the DIII-D tokamak requires careful control of impurity levels. Among the techniques used to control impurities are routine bakes of the vacuum vessel to an average temperature of 350°C. Materials used in DIII-D must release only very small amounts of impurities (below 2×10−6mole) at this temperature that could be transferred to the first wall materials and later contaminate plasma discharges. To better study the behavior of materials proposed for use in DIII-D at elevated temperatures, the initial outgassing test chamber was improved to include an independent heating control of the sample and a simple load lock chamber. The goal was to determine not only the total degassing rate of the material during baking, but to also determine the gas species composition and to obtain a quantitative estimate of the degassing rate of each species by the use of a residual gas analyzer. Initial results for aluminum anodized using three different processes, stainless steel plated with black oxide and black chrome, and a commercially available fiber optic feedthrough will be presented.
Adsorption of sulfur dioxide on Zircaloy-4 at 300K
Authors: Stojilovic N. , Ehrman J. D. , Ramsier R. D.
Published: July 2006

We investigate the interaction of sulfur dioxide (SO2) with Zircaloy-4 (Zry-4) surfaces after adsorption at 300K. A shift in the Zr(MNN) feature toward lower energies of about 3eV is observed following saturation exposures, indicating oxidation of Zr by dissociated oxygen. Temperature programed desorption experiments indicate irreversible adsorption. Relatively short Ar-ion sputtering removes sulfur from the near-surface region without significantly affecting the oxygen Auger signal. Annealing of the SO2∕Zry-4 system results in dissolution of oxygen into the bulk, leaving sulfur in the near-surface region.
Production of a hafnium silicate dielectric layer for use as a gate oxide by solid-state reaction
Authors: Johnson-Steigelman H. T. , Brinck A. V. , Chang J. P. , Lyman P. F.
Published: July 2006

The formation of hafnium silicate films (HfSixOy) for use as gate oxides with a large dielectric constant by solid-state reaction of Hf metal and SiO2 was investigated. Thin, fully reacted silicate films could be formed, and were thermally stable in vacuum to temperatures in excess of 800°C. Evidence was found that the interface between a hafnium silicate layer and the silicon substrate is stable against SiO2 formation.
Fabrication of micropatterned mesoporous silica film on a flexible polymer substrate through pattern transfer and subsequent photocalcination
Authors: Hozumi Atsushi , Kizuki Takashi , Inagaki Masahiko , Shirahata Naoto
Published: July 2006

A microfabrication method for mesoporous silica (MPS) film on a flexible polymer substrate is proposed. The method consists of three processes. First, by using a spatially defined microtemplate consisting of dual self-assembled monolayers (SAMs) with alternating trifluorocarbon (CF3) and amino (NH2) groups, a mesostructured silica/surfactant composite (MSSC) film was site-selectively deposited on the CF3-terminated SAM regions through hydrophobic and van der Waals interactions between the surfactant molecules and the hydrophobic SAM surface. Next, in order to transfer these prefabricated MSSC micropatterns to a poly(ethyleneterephthalate) (PET) substrate, the sample was pressed firmly against the PET surface for 60min at 90°C under a pressure of 4MPa. Due to the weak adhesion between the MSSC film and the CF3-terminated SAM surface, the deposited MSSC micropatterns readily peeled off the SAM surface and were transferred to the PET substrate while preserving both the morphology and the nanostructures of the micropatterns, as evidenced by atomic force microscopy (AFM), scanning electron microscopy, energy dispersion x-ray spectroscopy, and x-ray diffractometry (XRD). Finally, to remove the surfactant molecules and obtain well-defined nanopores, a photochemical approach, known as “photocalcination,” using UV light of 185 and 254nm wavelengths was employed. Fourier transform infrared spectroscopy XRD, and AFM confirmed that the surfactant molecules were completely eliminated from the MSSC micropatterns without distorting either their finely patterned microstructures or their well-ordered periodic nanostructures. Through this technique, well-shaped 5μm wide MPS micropatterns were fabricated on the flexible PET substrates. These embedded MPS micropatterns adhered tightly to the PET substrates and no peeling was observed in a Scotch® tape peeling test.
Fe(001) thin films for x-ray diffraction and terahertz emission studies
Authors: Meserole C. A. , Fisher G. L. , Hilton D. J. , Jia Q. X. , Averitt R. D. , Funk D. J. , Taylor A. J.
Published: July 2006

Our interests in growing thin films of iron (Fe) are twofold. First, Fe(001) films are ideal targets for an ultrafast x-ray diffraction instrument designed to understand complex behavior, such as melting or solid-solid phase transitions, in shock-loaded materials. Second, we have discovered that thin iron films generate picosecond, broadband terahertz frequencies after intense femtosecond pulse excitation by a Ti:sapphire laser. Excluding film thickness, the criteria for samples used in both experiments are identical due to the similarities of the experiments. Iron films are grown in ultrahigh vacuum (UHV) conditions on (001)-oriented magnesium oxide (MgO) substrates. We have investigated the effects of substrate preparation on the film quality and have found that films grown in UHV on UV/ozone-cleaned and annealed MgO(001) have a better crystal quality than films grown on as-received MgO(001). However, both substrate preparation methods produce continuous, (001)-oriented thin films of iron.
Wafer level microarcing model in 90nm chemical-vapor deposition low-k via etch on 300mm silicon-on-insulator substrate
Authors: Cong Hai , Low Chun Hui , Pradeep Yelehanka Ramachandramurthy , Zhang Xin , Chandima Perera , Liu Wu Ping , Tan Juan Boon , Hsia Liang Choo
Published: July 2006

In SiOCH (C-doped SiO2) via etch application, high polymer deposition chemistry is needed for better selectivity to both photoresist and underlying barrier materials. To prevent etch stop, high ion energy plasma is required to achieve a good process window. C4F6∕CH3F, etc., was used as via main etch chemistry for better selectivity and striation performance. However, wafer level microarcing (WLMA) was observed at the wafer edge around the guard ring. This WLMA phenomenon is different from that of the magnetically enhanced reactive ion etching or capacitively coupled plasma low-gap reactor. By process optimization, we managed to develop a process that is production-ramp worthy. We have also compared the rf parameters during via etch process on both silicon-on-insulator and bulk Si substrates, which shows no significant difference. The electrical and defect scan results suggest that it is free from WLMA.
Particle-in-cell simulations of planar and cylindrical Langmuir probes: Floating potential and ion saturation current
Authors: Iza Felipe , Lee Jae Koo
Published: July 2006

Particle-in-cell and hybrid electron-Boltzmann simulations of planar and cylindrical Langmuir probes are compared with various probe theories. Floating potentials for planar and cylindrical probes are calculated and significant deviations from the typical approximation used for argon discharges of ∼5Te are shown. The interpretation of simulated ion saturation currents by the orbital motion limited and the Laframboise theories result in an overestimation of the ion density. On the other hand, the cold-ion theory underestimates the ion density. These deviations are related to the overestimation and underestimation, respectively, of the ion orbital motion around cylindrical probes. The best agreement is obtained when the probe theory suggested by Tichy et al. is used. This theory incorporates ion orbital motion as in the Laframboise theory, collisional orbital motion destruction as suggested by Zakrzewski and Kopiczynski, and ion scattering as given by Chouet al.
Reactive magnetron sputtering deposition and columnar growth of nc-TiC∕a-C:H nanocomposite coatings
Authors: Galvan D. , Pei Y. T. , De Hosson J. Th. M.
Published: July 2006

Ti C ∕ a - C : H coatings were deposited using closed-field unbalanced reactive magnetron sputtering deposition from Ti targets. Different acetylene gas flow and substrate bias values were employed to vary the coatings’ compositions and microstructures. The application of an external negative substrate bias increased the deposition rate of the plasma-enhanced chemical vapor deposition process from the reactive atmosphere. The sputtering of carbonaceous species from the poisoned targets surface was a minor source of C flux to the substrates. The application of an external substrate bias during deposition yielded films with a featureless cross-sectional structure, but the dominant parameter controlling the columnar growth was the chemical composition of the films. An explanation of this effect was formulated based on the microstructures observed and the deposition technique employed.
Time-of-flight secondary ion mass spectrometry measurements of a fluorocarbon-based self-assembled monolayer on Si
Authors: Ohlhausen J. A. , Zavadil K. R.
Published: July 2006

Low surface energy coatings and films are needed to minimize stiction, high friction, and wear of the oxide-terminated silicon-based microelectromechanical systems (MEMSs) to ensure reliable device function. One common approach is to deposit self-assembled monolayer (SAM) films of molecules possessing a reactive silane head group and low energy pendant chain to cover the complex structures used in MEMS devices. The composition of these films is difficult to characterize and quantify. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is an excellent tool for characterizing these types of films because of its ability to detect small quantities of surface species at high spatial resolution and surface sensitivity; however, interpretation of the spectral data generated is complex and challenging. We are using the combination of x-ray Photoelectron Spectrometry and ToF-SIMS to detect and quantify a fluorocarbon-based SAM on Si coupons and on MEMS devices. Unexpected fragmentation caused by the interaction of the primary ion beam with the fluorocarbon chain in contact with the Si surface creates ions whose presence is not intuitive. We can account for these ion fragments and use them to aid in quantifying the film composition. Our methods include the use of coverage-dependent fragmentation signatures along with the application of multivariate statistical techniques to establish the covariance in these signatures.
Formation of large-area nanostructures on Si and Ge surfaces during low energy ion beam erosion
Authors: Ziberi B. , Frost F. , Rauschenbach B.
Published: July 2006

In this contribution results on self-organized patterns formed during low energy Xe+ ion beam erosion on Si and Ge surfaces are presented. It was found that the evolution of surface patterns depends on ion incidence angle, erosion time, and ion energy. In the case without sample rotation ripple patterns form on the Si and Ge surfaces with a wavelength λ<100nm, for ion energies Eion⩽2000eV at near normal ion incidence (αion∼5°) and at room temperature. The experimental results of a decreasing ripple wavelength with ion incidence angle on Si coincide with the Bradley-Harper [J. Vac. Sci. Technol. A 6, 2390 (1988).] theory of ripple formation. While the independency of λ from the ion flux suggests that thermally activated surface diffusion can be ruled out as the dominant relaxation mechanism. Experiments reveal that the wavelength of ripples increases with ion energy. With sample rotation at 75° ion incidence angle dot patterns form on the surface with a mean size λ<50nm.
Observation of crystallite formation in ferromagnetic Mn-implanted Si
Authors: Awo-Affouda C. , Bolduc M. , Huang M. B. , Ramos F. , Dunn K. A. , Thiel B. , Agnello G. , LaBella V. P.
Published: July 2006

Mn-implanted Si was investigated using transmission electron microscopy to gain insight into the structure of the implanted region. Diffraction contrast images, selected area diffraction patterns, and high resolution images of the samples were acquired before and after postimplant annealing at 800°C. The images of the annealed samples revealed the formation of nanometer size precipitates distributed throughout the implanted region. Analysis of the selected area diffraction pattern determined that the most prominent lattice spacing of the crystallites is 2.15Å. This spacing indicates that the most probable phase of the crystallites is MnSi1.7 and this is consistent with the Mn:Si binary phase diagram. This phase is paramagnetic at room temperature with a Curie temperature of 47K and cannot readily account for the high Curie temperature of the material.
Surface and bulk electronic structures of Heusler-type Fe2VAl
Authors: Miyazaki Hidetoshi , Soda Kazuo , Yagi Sinya , Kato Masahiko , Takeuchi Tsunehiro , Mizutani Uichiro , Nishino Yoichi
Published: July 2006

Surface and bulk electronic structures of Heusler-type (L21 type) Fe2VAl have been investigated by photoelectron spectroscopy, in particular, for the valence band and V 2p core level regions, in order to elucidate the changes in the valence band electronic structures for the surface and bulk regions. In the valence band spectrum, the intensity at the Fermi level EF is increased for the surface-sensitive low photon energy excitation in comparison to the bulk-sensitive high photon energy excitation. It is also found that the intensity around a binding energy of 0.4eV is enhanced for large photoelectron takeoff angles for the bulk-sensitive photoelectron spectrum. The V 2p core level spectrum shows a surface-derived shoulder structure on the low binding energy side of the main feature, which suggests that the valence electron concentration around V may be large in the surface layers in comparison to the bulk. These facts suggest that a pseudogap is formed around EF in the bulk electronic structure, as predicted by band calculations, and that it is destroyed in the surface layers by the V 3d states as well as the Fe 3d states emerging in midpseudogap of the bulk electronic structure.
Annealing temperature effects on the structure of ferromagnetic Mn-implanted Si
Authors: Bolduc M. , Awo-Affouda C. , Ramos F. , LaBella V. P.
Published: July 2006

The dependence of the magnetization of Mn-implanted Si on the postimplant annealing temperature is studied. p-type Si wafers were implanted with 300keV Mn+ ions at 350°C to a fluence of 1×1016cm−2 and then annealed at 500–900°C for 5min. Ferromagnetic hysteresis loops were obtained at 10K using a superconducting quantum interference device magnetometer. The saturation magnetization increases with the postimplant annealing temperature, reaching an optimum field strength of 0.2emu∕g at 800°C. An out diffusion of Mn is observed at higher temperatures that coincides with a decrease in the saturation magnetization. The calculated point-defect profile that was generated by the implantation process peaks around the Mn-depleted region, suggesting that the residual implant damage may play a role in the ferromagnetic behavior of Mn-implanted Si.
Compliant system of polyimide microwires for cryogenic detector applications
Authors: Allen C. A. , Franz D. E. , Moseley S. H.
Published: July 2006

We have developed a system of highly compliant, low thermal conductance electrical interconnects for cryogenic detector applications. The arrays of microwires are metallic, thin-film electrical leads supported by a layer of polyimide, capable of spanning the thermally isolated gap between the detector array and the low temperature heat sink in cryogenic detector assemblies. The low thermal conductance of the microwires enables detector thermal isolation without the need for conventional hard wiring, such as soldered manganin (an alloy of nickel, manganese, aluminum, iron, and copper) or stainless steel. Designed for compactness, an array of 30 microwires can be designed to fit on a silicon chip less than one-half of 1cm2 in total surface area. We describe techniques for fabrication of arrays of polyimide microwires with several different types of conductive traces, both superconducting and normal metals. Mechanical elongation of 20% beyond the design length resulted in an increase in aluminum microwire resistance of only 1%, and no stress to the polyimide. Cryogenic elongation yielded no change in electrical or mechanical properties. The thermal conductivity of a single, aluminum microwire is found to be 3.8×10−8W∕K at 4.4K and 1.1×10−8W∕K at 2.2K.
Cu
Pc
:
C
60
blend film: A photoemission investigation
Authors: Lozzi L. , Granato V. , Picozzi S. , Simeoni M. , La Rosa S. , Delly B. , Santucci S.
Published: July 2006

The electronic structure of thin blend films composed of copper phthalocyanine (CuPc) and fullerene (C60) have been studied by x ray, soft-x-ray photoemission spectroscopy, and by theoretical simulations. Samples with different C60∕CuPc concentration ratios were prepared by thermal evaporation in ultrahigh vacuum conditions. A strong shift of the highest occupied molecular orbital (HOMO) of CuPc towards the Fermi level and of the HOMO C60 states towards higher binding energy was observed. The comparison between valence band structures and core level line shape indicates that the central part of the CuPc molecule is lightly modified by the presence of the C60 molecule. The theoretical analysis, performed using density functional theory, confirms this small interaction between the two molecules, with a small charge density localized between the two molecules and a structural modification of the CuPc molecule.
Fabrication of high precision demultiplexer using embossing technique with thermal curable polymers
Authors: Choi C.-H. , Lee M.-W. , O B.-H. , Lee S.-G. , Park S.-G. , Lee E.-H.
Published: July 2006

Photonic devices based on polymer materials have been fabricated mainly by using conventional lithography and etch processes. However, the fabrication method through these processes is complex and expensive. We fabricated 1310∕1550nm demultiplexer using an embossing technique, which was able to reduce the fabrication cost. The mold is an elastomeric polydimethylsiloxane (PDMS) and resists used as the core and the cladding layers are ZP 51 (ChemOptics) and ZP 49 (ChemOptics), respectively, which are thermal curable polymers. The fabrication process is summarized as follows: (1) manufacturing the photoresist master by lithography process, (2) forming the PDMS mold from the master, and (3) replicating the device using the mold. There is no observation of any noticeable pattern difference between the master and the replica in microscaled dimension. In this work, we also investigated the durability of a PDMS mold for mass production and successfully fabricated the 50th replica with the same mold. The replicated device was measured by the laser source and the charge-coupled device camera.
Pressure dependence of laminar-turbulent transition in gases
Authors: Hinkle L. D. , Muriel A. , Novopashin S. A.
Published: July 2006

The transition between the laminar and turbulent flow regimes is traditionally addressed using the continuum formulation of the Navier-Stokes equations and dimensionless parameters such as the Reynolds number. However, a detailed understanding of the transition mechanisms has remained elusive. Theoretical approaches based on molecular and quantum mechanical models have been proposed but have yet to be thoroughly tested experimentally. In an effort to test a quantum-based model, specific apparatus and experiments have been designed to evaluate particular features of the laminar-turbulent transition. Hysteresis plots of flow versus differential pressure are used to examine the flow transition that occurs inside a tube with a divergent entrance. The hysteresis plots generated in these tests show several notable features and quantitative trends. The primary focus of this article is on the observed dependence of the laminar-turbulent transition behavior on the absolute pressure. Whereas the continuum-based model does not predict a pressure dependence of the laminar-turbulent transition, a molecular-based model indicates a pressure effect on the transition to turbulent flow.