bluuebunny/crossref_metadata_2025 huggingface dataset:
ANALYSIS OF MUCILAGE SECRETION AND EXCRETION INMICRASTERIAS(CHLOROPHYTA) BY MEANS OF IMMUNOELECTRON MICROSCOPY AND DIGITAL TIME LAPSE VIDEO MICROSCOPY1
Authors: Oertel Anke , Aichinger Nicole , Hochreiter Romana , Thalhamer Josef , Lütz‐Meindl Ursula
Published: July 2004

Two different, independent, and alternative modes of mucilage excretion were found in the unicellular green algaMicrasterias denticulataBréb. under constant culture conditions. The cells were capable of either excreting mucilage over all their cell surface or they extruded mucilage from one of their polar ends, which enabled directed movement such as photoorientation or escape from unfavorable environmental conditions. By means of a polyclonal antibody raised againstMicrasteriasmucilage, the secretory pathway of Golgi derived mucilage vesicles from their origin to their discharge was analyzed by means of conventional and energy filtering TEM. Depending on the stage of the cell cycle, mucilage vesicles were subjected to maturation processes. This may occur either after they have been pinched off from the dictyosomes (e.g. during cell growth) or when still connected to trans‐Golgi cisternae, as in the case of interphase cells. Only fully grown mature vesicles contained mucilage in its final composition as indicated by antibody labeling. After fusion of mucilage vesicles with vacuoles, no immunolabeling was found in vacuoles, indicating that the vesicle content was digested. Mucilage vesicles fused with the plasma membrane in areas of cell wall pores but were also able to excrete mucilage at any site directly through the respective cell wall layer. This result disproves earlier assumptions that the pore apparatus in desmids are the only mucilage excreting areas at the cell surface. Both mechanisms, excretion through the pores and through the cell wall, lead to formation of mucilage envelopes covering the entire cell surface.
UV‐EXCITED BLUE AUTOFLUORESCENCE OF PSEUDO‐NITZSCHIA MULTISERIES (BACILLARIOPHYCEAE)1
Authors: Orellana Mónica V. , Petersen Timothy W. , Van Den Engh Ger
Published: July 2004

A flow cytometer coupled to a scanning monochromator and a fluorescence microscope were used to characterize the fluorescence spectrum of Pseudo‐nitzschia multiseries (Hasle) Hasle, a pennate diatom that produces the neurotoxin domoic acid, a lethal amnesic. In this research, we characterize the fluorescence spectrum of P. multiseries in vivo over the wavelength range of 360 to 850 nm and show that this diatom autofluoresces blue when excited with UV light (350–365 nm). The autofluorescence characterization of Pseudo‐nitzschia may provide new methods for rapid in situ monitoring of diatom populations and reiterates the usefulness of flow cytometry in the analysis and study of marine phytoplankton.
CONTRASTING EFFECTS OF METHIONINE SULFOXIMINE ON UPTAKE AND ASSIMILATION OF AMMONIUM IN ULVA INTESTINALIS (CHLOROPHYCEAE)1
Authors: Barr Neill G. , Tijsen Rob J. , Rees T. Alwyn V.
Published: July 2004

Ammonium is assimilated in algae by the glutamine synthetase (GS)–glutamine:2‐oxoglutarate aminotransferase pathway. In addition to the assimilation of external ammonium taken up across the cell membrane, an alga may have to reassimilate ammonium derived from endogenous sources (i.e. nitrate reduction, photorespiration, and amino acid degradation). Methionine sulfoximine (MSX), an irreversible inhibitor of GS, completely inhibited GS activity in Ulva intestinalis L. after 12 h. However, assimilation of externally derived ammonium was completely inhibited after only 1–2 h in the presence of MSX and was followed by production of endogenous ammonium. However, endogenous ammonium production in U. intestinalis represented only a mean of 4% of total assimilation attributable to GS. The internally controlled rate of ammonium uptake (Vi) was almost completely inhibited in the presence of MSX, suggesting that Vi is a measure of the maximum rate of ammonium assimilation. After complete inhibition of ammonium assimilation in the presence of MSX, the initial or surge (Vs) rate of ammonium uptake in the presence of 400 μM ammonium chloride decreased by only 17%. However, the amount that the rate of ammonium uptake decreased by was very similar to the uninhibited rate of ammonium assimilation. In addition, the decrease in the rate of ammonium uptake in darkness (in the absence of MSX) in the presence of 400 μM ammonium chloride matched the decrease in the rate of ammonium assimilation. However, in the presence of 10 μM ammonium chloride, MSX completely inhibited ammonium assimilation but had no effect on the rate of uptake.
Contact potential difference measurements of doped organic molecular thin films
Authors: Chan Calvin , Gao Weiying , Kahn Antoine
Published: July 2004

The possibility of nonequilibrium conditions in doped organic molecular thin films is investigated using a combination of ultraviolet photoemission spectroscopy (UPS) and contact potential difference measurements. Surface or interface photovoltage is of particular concern in materials with large band gap and appreciable band (or energy level) bending at interfaces. We investigate here zinc phthalocyanine (ZnPc) and N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′biphenyl-4,4″ diamine (α-NPD) p-doped with the acceptor molecule, tetrafluorotetracyanoquinodimethane (F4-TCNQ). In both cases, we observe an upward movement of the vacuum level away from the metal interface with respect to the Fermi level, consistent with the formation of a depletion region. We show that photovoltage is not a significant factor in these doped films, under ultraviolet illumination during UPS. We suggest that the carrier recombination rate in organic films is sufficiently fast to exclude any photovoltage effects at room temperature.
Self-aligned silicides for Ohmic contacts in complementary metal–oxide–semiconductor technology: TiSi2, CoSi2, and NiSi
Authors: Zhang S.-L. , Smith U.
Published: July 2004

Metal silicides continue to play an indispensable role during the remarkable development of microelectronics. Along with several other technological innovations, the implementation of the self-aligned silicide technology paved the way for a rapid and successful miniaturization of device dimensions for metal–oxide–semiconductor field-effect transistors (MOSFETs) in pace with the Moore’s law. The use of silicides has also evolved from creating reliable contacts for diodes, to generating high-conductivity current paths for local wiring, and lately to forming low-resistivity electrical contacts for MOSFETs. With respect to the choice of silicides for complementary metal–oxide–semiconductor (CMOS) technology, a convergence has become clear with the self-alignment technology using only a limited number of silicides, namely TiSi2, CoSi2, and NiSi. The present work discusses the advantages and limitations of TiSi2, CoSi2, and NiSi using the development trend of CMOS technology as a measure. Specifically, the reactive diffusion and phase formation of these silicides in the three terminals of a MOSFET, i.e., gate, source, and drain, are analyzed. This work ends with a brief discussion about future trends of metal silicides in micro/nanoelectronics with reference to potential material aspects and device structures outlined in the International Technology Roadmap for Semiconductors.
Power supply with arc handling for high peak power magnetron sputtering
Authors: Christie D. J. , Tomasel F. , Sproul W. D. , Carter D. C.
Published: July 2004

High power pulsed magnetron sputtering (HPPMS) can generate a dense plasma with high target material ion content, using essentially conventional magnetron sputtering equipment. However, process arcs, which generate macroparticles and target damage, are not avoidable due especially to imperfections in vacuum system hardware and target materials. Arc handling is required for practical application of HPPMS. An experimental power supply capable of peak powers up to 3 MW, peak currents to 3000 A, at discharge voltages reaching 2 kV has been designed and built. It has voltage ring-up capability for pulse by pulse plasma ignition. This power supply technology enables the practical application of a whole range of sputtering processes, based on pulsing magnetrons operating at high peak powers. Power supply performance for typical pulses and for arc handling at peak currents into the kiloamp range is shown with temporal current and voltage characteristics of the discharge for typical pulses and for arcing operation.
Laser-etched silicon pillars and their porosification
Authors: Mills David , Kolasinski Kurt W.
Published: July 2004

Mesoscale silicon pillars are formed when silicon wafers are irradiated by a nanosecond excimer laser operating at 308 nm and incident fluence of ∼3 J cm−2. The morphology of the pillars responds to the chemical composition of the gas phase above the Si surface. Postprocessing can also be used to change the structure of the pillars. We demonstrate using Raman spectroscopy that the pillars can be covered with a nanocrystalline porous layer as the result of chemical etching. A stain etchant produces brilliant reddish-orange photoluminescent films. Porous pillars of this type are interesting candidates for use as drug and DNA delivery vehicles.
Photoexcited electrodeposition of Cu structures on p-Si(001)
Authors: Scheck C. , Liu Y.-K. , Evans P. , Schad R. , Bowers A. , Zangari G. , Williams J. R. , Issacs-Smith T. F.
Published: July 2004

Selective growth of metals on semiconductors has recently raised considerable interest due to its possible application in the direct formation of conduction paths and contacts on semiconductors. We produced small structures by photoexcited electroless plating of Cu on p-type Si(001). The p-type substrate forms a Schottky barrier with the solution which inhibits the plating process. Local illumination creates minority carriers which become available to discharge metal ions. Illumination was done by converging a 1–5 mW laser beam to a 1–2 μm focus diameter on the substrate in the plating solution using an optical microscope. The dimensions of the dots are determined by the diffusion length of the excited minority carriers. We analyzed the diameter of the growing dots as a function of the laser light wavelength and intensity, illumination duration, composition of the solution and charge carrier lifetime in the substrate. The lateral dimensions of the structures produced are found to decrease with reduced laser wavelength or intensity but are independent of the duration of illumination. Shorter minority carrier lifetimes in the semiconductor substrate lead to a further reduction of structure dimensions. The effect of spontaneous background precipitation on the Si surface is studied as a function of the solution composition. The optical reflectivity can be related to the fractal surface roughness.
Direct trim etching process of Si/SiO2 gate stacks using 193 nm ArF patterns
Authors: Tan K. M. , Yoo W. J. , Ma H. H. H. , Li F. , Chan L.
Published: July 2004

A polysilicon gate of 30 nm length is successfully fabricated by direct trimming of a gate stack that consists of organic BARC, polycrystalline silicon (poly-Si) and SiO2. It is achieved by patterning the gate stack using a 193 nm photoresist process and trimming the poly-Si gate with HBr/Cl2 plasma chemistry in an inductively coupled plasma (ICP) etcher. HBr is found to be more effective than Cl2 as a trimming etchant since it can achieve a higher trimming rate. A maximum trimming rate of 32 nm/min is obtained with gas chemistry of 80% HBr and 20% Cl2 at 40 mTorr, ICP power of 700 W, and rf bias power of 0 W. In general, the trimming rate increases with an increase in ICP power from 200 to 800 W and decrease in pressure from 70 to 10 mTorr. The inclusion of SF6 and O2 to the plasma and the longer trimming time are found to be very effective in reducing the poly-Si footprint which is observed after the trimming process.
Efficient electrical spin injection in GaAs: A comparison between AlOx and Schottky injectors
Authors: Van Dorpe P. , Van Roy W. , Motsny V. F. , Borghs G. , De Boeck J.
Published: July 2004

We demonstrate electrical spin injection in GaAs from ferromagnetic metals through tunneling. We use and compare an AlOx insulating layer as well as the native Schottky barrier at the metal–semiconductor interface as tunnel barriers. The injected spin polarization has been measured by analyzing the electroluminescence polarization using the oblique Hanle effect technique. The observed bias dependence of the measured spin polarization is sensitive to both the type of injector and the doping profile in the semiconductor. Hot electron spin relaxation due to the D’yakonov–Perel spin relaxation mechanism has been identified as the cause of the different bias dependence in two AlOx-based injectors with different doping levels of the active region while a change in the electron transit times in the highly doped interfacial region has been found as the cause of the bias dependence in the Schottky-based injectors.
Correlated structural and magnetization reversal studies on epitaxial Ni films grown with molecular beam epitaxy and with sputtering
Authors: Zhang Zhengdong , Lukaszew R. A. , Cionca C. , Pan X. , Clarke R. , Yeadon M. , Zambano A. , Walko D. , Dufresne E. , te Velthius Suzanne
Published: July 2004

We have studied the correlation between film structure and the azimuthal dependence of the magnetization reversal in (001) and (111) epitaxial Ni films grown on MgO substrates using two different deposition techniques: molecular beam epitaxy (MBE) and dc magnetron sputtering. The films were grown and in situ annealed under identical conditions. The magnetization reversal was investigated using MOKE. The coercive field in the sputtered (001) Ni films exhibits fourfold azimuthal symmetry as expected for crystalline films of good epitaxial quality, while MBE (001) Ni grown films exhibit an additional uniaxial symmetry superimposed to the fourfold symmetry. We performed high-resolution XRD studies as well as cross sectional TEM studies in order to establish similarities and differences in the structure of the films. Both types of films exhibit epitaxial growth and very good crystalline quality with no indication of strain. The main difference between the films is the different magnetic anisotropy. We postulate that this difference may be due to different interfacial structure and/or morphology due to the possible formation of a NiO interfacial layer only present or highly ordered in the MBE grown films. Polarized neutron reflectivity measurements performed on some of the films are correlated with the interfacial structure and magnetic anisotropy.
Photoinduced decomposition of alkyl monolayers using 172 nm vacuum ultraviolet light
Authors: Shirahata Naoto , Oda Kotaro , Asakura Shuuichi , Fuwa Akio , Yokogawa Yoshiyuki , Kameyama Tetsuya , Hozumi Atsushi
Published: July 2004

The photoinduced stability of two alkyl monolayers on Si has been investigated using a Xe2 excimer lamp radiating 172 nm vacuum ultraviolet (VUV) light. The photoinduced stability of 1-octadecene monolayer (ODM) was compared with that of alkylsilane monolayer. 1-octadecene was employed as a starting precursor of alkyl monolayer on Si. The alkylsilane monolayer was formed from otadecyltrimethoxysilane monoalyer (OTSM) onto the SiO2/Si substrate. The decomposition of ODM was investigated under VUV irradiation conducted at 10 and 105 Pa. The VUV light decomposed ODM at both 10 and 105 Pa. The photodecomposition rate at 105 Pa was smaller than that at 10 Pa. The decomposed methyl and ethyl groups from the alkyl chain formed carboxyl groups. The carboxyl coverage on the surface of Si increased with increasing VUV irradiation time ranging from 0 to 60 s at 10 Pa, and decreased after 60 s. In contrast, the Si–O component in x-ray photoelectron Si 2p spectrum drastically increased after the VUV irradiation time of 60 s. The Si–O component indicated complete covering of Si surface. Similar decomposition rates between ODM and OTSM were observed for the VUV irradiation time ranging from 0 to 45 s conducted at 10 Pa. After 45 s, the photodecomposition rate of ODM was smaller than that of OTSM. The effectiveness of VUV light for the micropatterning of ODM was also investigated.
Study of rough growth fronts of evaporated polycrystalline gold films
Authors: Munuera C. , Aznárez J. A. , Rodrı́guez-Cañas E. , Oliva A. I. , Aguilar M. , Sacedón J. L.
Published: July 2004

The scaling exponents of interface width and coarsening of evaporated gold films with thickness from 30 to 1800 nm were obtained from two-dimensional measurements on scanning tunneling microscopy (STM) images and are presented here. The lateral size of protrusion on the surface of the films increases with a constant scaling exponent n≈1/3. The interface width grows in two stages. The final stage starts at ≈60 nm and corresponds to a time scaling exponent of β≈1/3 with a constant slope morphology. Scaling exponents are compared with those from models for high thickness epitaxial growth and for polycrystalline film growth, all predict a constant slope morphology. To help the choice among the three compatible models, STM results are compared with transmission electron microscopy (TEM) images where low contrast structures can be observed on large crystalline plates. As a result it may be interpreted that the structures observed correspond either to a mound growth or to an array of columns with low grain boundaries between them. Other smaller crystalline components are observed in polycrystalline areas and can be assigned to columnar tops. The practically unimodal Gaussian distribution of local heights, indicates that the surface morphologies arising from these two bulk structural components are not very different and suggests that both morphologies are controlled by the same atomic surface diffusion phenomena.
Preparation of ternary alloy libraries for high-throughput screening of material properties by means of thick film deposition and interdiffusion: Benefits and limitations
Authors: Rar A. , Specht E. D. , George E. P. , Santella M. L. , Pharr G. M.
Published: July 2004

Several techniques have been investigated for making alloy libraries for combinatorial materials development. In this investigation, we demonstrate a method for Ni–Fe–Cr ternary alloy library preparation by deposition of three layers of different metals with a linear thickness gradient rotated by 120° for each layer. The layers were interdiffused and alloyed by annealing in vacuum. The resulting specimens were analyzed and compared with the well-known phase diagram for this system by means of rapid x-ray diffraction mapping with synchrotron radiation.
Use of reactive gases with broad-beam radio frequency ion sources for industrial applications
Authors: Schneider St. , Jolly T. W. , Kohlstedt H. , Waser R.
Published: July 2004

Broad-beam ion sources are used for a number of important industrial etching and deposition applications, and the use of inductively coupled plasmas has greatly increased the feasibility of using beams of reactive gases, especially of chlorine and oxygen, but also of CO, CO2, CF4, CHF3, SF6, etc. In order to gain more understanding of the factors that affect the composition of beams of these gases, we have used a Hiden energy-dispersive quadrupole mass spectrometer to analyze the flux of ions and energetic particles produced by an Oxford Instruments 15 cm rf ion source. For all of the above gases, we have analyzed the effects of changing the operating conditions on the composition of the ion beam, and the fractional production of multiply charged ions; on the plasma potential (and the consequential divergence of the ion beam) and on the spread in energy of the ion beam. We discuss how these factors influence the correct use of the ion source in etching applications with these gases. It is important that the design of the ion source should be optimized for the process gases that are used. The source was originally optimized for use on argon. We discuss the effect of the design on the source’s performance with the different gases, and we consider whether design changes would be appropriate for optimum performance on different gases.
Simultaneous dynamic stiffness and extension profiles of single titin molecules: Nanomechanical evidence for unfolding intermediates
Authors: Forbes Jeffrey G. , Wang Kuan
Published: July 2004

Striated muscle is the primary source of biomechanical force in organisms from worms to man, and is organized as a composite material from nanometer to meter scales. At nanometer scale, an array of cytoskeletal proteins are required to regulate the size, assembly and function of the sarcomere, as well as transmit force and provide elasticity for restoring the structure. One such protein is the giant protein titin (Mr 3–4×106), which spans half of the muscle sarcomere length. The passive elasticity of muscle at a physiological range of stretch arises primarily from the extension of titin. We have measured both the extension force and the dynamic stiffness of native titin with the atomic force microscope. We found that the stiffness of a single molecule of titin varied between 1 and 4 pN/nm over an extension of >1 μm. Regions showing globular domains unfolding in the sawtooth pattern of force versus extension curve exhibit periodic spikes in the stiffness. The results of this study show that simultaneous stiffness and force measurements of single molecules can provide new information on the elastic behavior and structural transitions of elastic proteins and their physiological roles in muscle elasticity.
Mechanisms of silicon nitride etching by electron cyclotron resonance plasmas using SF6- and NF3-based gas mixtures
Authors: Reyes-Betanzo C. , Moshkalyov S. A. , Ramos A. C. S. , Swart J. W.
Published: July 2004

The results of a study of SiNx, SiO2, and Si etching in a high-density electron cyclotron resonance plasma using mixtures containing SF6, NF3, N2, O2, and Ar are presented. Higher selectivities of SiNx etching over SiO2 (up to ∼100) were achieved with NF3, while higher selectivities over Si (up to 5–10) were obtained with SF6-based mixtures. Plasma and surface processes responsible for etching are analyzed, and mechanisms of nitride etching in NF3-based plasmas are proposed.
Au/CuPc interface: Photoemission investigation
Authors: Lozzi Luca , Santucci Sandro , La Rosa Salvatore
Published: July 2004

The growth of ultrathin gold films on copper phthalocyanine film has been studied by means of photoemission spectroscopy. Different photon energies have been used in order to investigate the diffusion of Au atoms inside the organic film. The evolution of the Au 4f peaks suggests the formation of small clusters. The valence-band spectra, acquired using different photon energies, indicate that these clusters diffuse inside the organic film. The growth of these clusters influences the electronic properties of the organic film. In fact, the core levels of the organic films show a charge transfer from the Au particles to the CuPc molecules, determining a shift of some components of the organic core levels. Spatially resolved photoemission spectra evidence the homogeneity of the gold film, which is not influenced by the CuPc surface defects.
Functional profile coatings and film stress
Authors: Liu Chian , Conley R. , Macrander A. T.
Published: July 2004

In recent years, we have developed a profile-coating technique to obtain functional thickness-profiled thin films and multilayers. This technique uses linear motion of the substrate in a dc magnetron sputter system and a contoured mask to obtain the desired profile perpendicular to the substrate-moving direction. The shape of the contour is determined according to the desired profile and knowledge of the film-thickness distribution at the substrate level. Applications of this technique include laterally graded multilayers and elliptical x-ray Kirkpatrick–Baez (KB) mirrors. An elliptical shape is essential for aberration-free optics. The use of profile coating to make x-ray-quality elliptical KB mirrors overcomes the obstacle of polishing asymmetrical mirror surfaces and provides the x-ray community with a practical way to obtain monolithic KB mirrors for microfocusing. Previously, we have used gold as a coating material and cylindrical Si mirrors as substrates to obtain elliptical KB mirrors. More recently, we have used flat Si substrates to fabricate elliptical KB mirrors. Substantially thicker and steeper gradients of Au films are needed to obtain an elliptical profile from a flat substrate. The Au films may relax to droplets when the stress in the film is too large. The challenges and solutions for this problem will be discussed.
Surface analysis of oxygen free electrolytic-copperX-band accelerating structures and possible correlation to radio frequency breakdown events
Authors: Harvey S. E. , Le Pimpec F. , Kirby R. E. , Marcelja F. , Adamson K. , Garwin E. L.
Published: July 2004

X-band accelerator structures meeting the next linear collider design requirements have been found to suffer vacuum surface damage caused by rf breakdown, when processed to high electric-field gradients. Improved understanding of these breakdown events is desirable for the development of structure designs, fabrication procedures, and processing techniques that minimize structure damage. rf reflected wave analysis and acoustic sensor pickup have provided breakdowns localization in rf structures. Particle contaminations found following clean autopsy of four rf-processed traveling wave structures have been catalogued and analyzed. Their influence on rf breakdown, as well as that of several other material-based properties, are discussed.
Real time optical characterization of gas flow dynamics in high-pressure chemical vapor deposition
Authors: Woods Vincent , Born Harald , Strassburg Martin , Dietz Nikolaus
Published: July 2004

While low-pressure chemical vapor deposition (CVD) methods offer excellent pathways for many compound semiconductors, these growth techniques possess limitations in the growth of high quality compounds with large thermal decomposition pressure such as InN and related materials. To study and extend the growth towards elevated pressures a high-pressure CVD system with integrated real time optical characterization techniques has been established. The built-in real time monitoring techniques allow the characterization of gas flow kinetics, precursor decomposition kinetics, as well as the crucial steps of nucleation and film formation. In this contribution, we report the characterization of process parameter under which the thin film growth process can be maintained under laminar flow condition. Laser light scattering has been proven as the most robust optical tool to characterize the onset of turbulence. Hence, it allows the mapping the pressure and flowing regime under which laminar flow can be maintained.
Ethanol reactions over Au–Rh/CeO2 catalysts. Total decomposition and H2 formation
Authors: Sheng P. Y. , Idriss H.
Published: July 2004

The reaction of ethanol has been investigated on the surface of Au–Rh/CeO2 by temperature programmed desorption (TPD), infrared spectroscopy and in steady state conditions. Most of adsorbed ethanol is found in the form of ethoxides (ν O–C at 1045 and 1096 cm−1). Heating the surface resulted in the transformation of ethoxides to carbonates (ν COO at 1561 and 1347 cm−1) without the presence of stable acetaldehyde or formaldehyde species. By 673 K all surface species has been desorbed. The relative instability of these carbonates when compared to CeO2 or Rh/CeO2 indicates that Au is enhancing the rate of oxidation. Most of CO2 formed during TPD is resulting from carbonate decomposition. Catalytic reactions showed that both CO2 and H2 can be formed with high yield over a wide temperature range.
Development of a continuous generation/supply system of highly concentrated ozone gas for low-temperature oxidation process
Authors: Ichimura Shingo , Nonaka Hidehiko , Morikawa Yoshiki , Noyori Tsuyoshi , Nishiguchi Tetsuya , Kekura Mitsuru
Published: July 2004

A system is described which can continuously generate/supply highly concentrated (HC) ozone gas to satisfy the future need for practical low-temperature oxidation. This system comprises four ozone vessels, each with independent temperature control. The system can supply a constant flow of HC ozone gas by allocating one of four modes of operation, i.e., accumulation/storage, vaporization (supply), evacuation, and cooling, to each of the ozone vessels so that all the modes can be simultaneously addressed. The maximum flow rate is 60 sccm with a flux stability of ±1.1%, and an ozone concentration of over 99.5 vol % can be achieved at the system outlet. The system was applied to the formation of an ultrathin SiO2 film on a 4 in. diameter silicon wafer substrate.
Observation of bulk HfO2 defects by spectroscopic ellipsometry
Authors: Takeuchi Hideki , Ha Daewon , King Tsu-Jae
Published: July 2004

Spectroscopic ellipsometry was used to investigate the oxidation of pure Hf films on silicon for the formation of HfO2 (hafnium oxide) gate-dielectric films in advanced complementary metal-oxide-semiconductor field-effect transistors. Absorption coefficients near the absorption edge were extracted using the data inversion method, in which the optical constants for short wavelengths were calculated using the film thickness determined from long-wavelength data. The extracted optical band gap of 5.7 eV matches well with published data, and a curve shift due to crystallization was detected. In addition, an extra absorption peak corresponding to electron transition from the valence band to a defect energy level was observed in the range 4.5–5.0 eV above the valence-band edge. The 1.2 eV energy difference between the conduction-band edge and the edge of this extra peak is close to the electron trap energy level reported elsewhere. The intensity of the detected peak was clearly correlated with leakage current and near-interface trap densities. Based on the annealing condition dependence of the extra absorption peak, the defects are likely oxygen vacancies within the HfO2 film.
Intercomparison of silicon dioxide thickness measurements made by multiple techniques: The route to accuracy
Authors: Seah M. P.
Published: July 2004

A pilot project has been launched under the auspices of the Consultative Committee for Amount of Substance to evaluate the quantification for SiO2 on (100) and (111) Si in the thickness range 1.5–8 nm. Wafers and methodologies have been carefully prepared. Forty-five sets of measurements have been made in different laboratories using eight methods: medium energy ion scattering spectrometry (MEIS), nuclear reaction analysis (NRA), Rutherford backscattering spectrometry (RBS), elastic backscattering spectrometry (EBS), x-ray photoelectron spectroscopy (XPS), ellipsometry, grazing incidence x-ray reflectometry (GIXRR), neutron reflectometry (NR), and transmission electron microscopy. The results have been assessed, against the National Physical Laboratory (NPL) XPS data, using d(respondee)=md(NPL)+c. All show excellent linearity. The main sets correlate with the NPL data with average root-mean-square scatters of 0.13 nm with half being <0.1 nm. Each set allows the relative scaling constant, m, and the zero thickness offset, c to be determined. Each method has 0<c<1 nm and it is these offsets, measured here, that have caused many problems in the past. Each technique has a different accuracy for m and consistent results have been achieved. XPS has poor accuracy for m but a high precision and, critically, has zero offset if used correctly. Achieving a consistent scaling constant and zero offset for XPS requires reference conditions that dramatically improve data consistency and validity. A combination of XPS and other methods allows an accurate determination of the XPS scaling constant, m=0.986±0.004. XPS may then have an uncertainty approaching 2%, traceable via other methods. NR, GIXRR, MEIS, NRA, RBS, and EBS have small offsets which, if they can be controlled, will enable these methods also to be used with high accuracy.
Measurement of energy flux at the substrate in a magnetron sputter system using an integrated sensor
Authors: Ekpe Samuel D. , Dew Steven K.
Published: July 2004

Knowledge of the energy flux in a sputter deposition system is important for predicting and controlling the properties of the growing film. The use of discrete sensors such as thermocouples for heat measurement has a potential contact problem due to the temperature jump between the surface of the wall and the surrounding gas especially at very low pressures. Embedded sensors such as a microfabricated polysilicon thin film thermistor eliminates the problem associated with thermal connection. In this study, the fabricated sensor is calibrated using ohmic self-heating before the deposition plasma is switched on, and also after the plasma is switched off (passive mode). At low pressures (up to 20 mTorr), pressure has an insignificant effect on the thermal resistance of the sensor. For substrate temperatures up to 250 °C, the sensor response is linear with input power. For a 3 in magnetron system, values of steady state energy flux measured with the sensor range from 5 to 46 mW/cm2 for aluminum (Al) and 14 to 114 mW/cm2 for copper (Cu) depending on the process conditions. These values compare well with those determined theoretically. Magnetron power was varied between 75 and 300 W, gas pressure 5–10 mTorr, and substrate–target distance 10.8–21 cm.
Anneal behavior of reactively sputtered HfN films
Authors: Lannon J. , Pace C. , Goodwin S. , Solomon S. , Bryant P.
Published: July 2004

This article reports electrical and thermo-physical properties of reactively sputtered HfNx films with respect to thermal annealing. All metal nitride films were sandwiched between sputtered Si3N4 films. The resulting reduction in electrical resistivity with anneal is explained by a combination of Rutherford backscattering spectrometry and secondary ion mass spectroscopy analyses. The physical mechanisms responsible for the observed anneal behavior are discussed.
Buckling of Si and Ge(111)2×1 surfaces
Authors: Nie Shu , Feenstra R. M. , Lee Ji Young , Kang Myung-Ho
Published: July 2004

Voltage-dependent scanning tunneling microscopy is used to determine the buckling of π-bonded chains on Si and Ge(111)2×1 surfaces. Images are acquired over a wide range of voltages, and are compared with theoretical constant-density contours generated from first-principles electronic-structure calculations. The theoretical predictions for 〈21̄1̄〉 corrugation shifts are quite different for positive and negative buckling; experimental results for Si are found to agree with the former and those for Ge agree with the latter. In addition to an expected shift in 〈21̄1̄〉 corrugation between small-magnitude positive and negative voltages, a further shift is also seen in both experiment and theory between small and large positive voltages.
X-ray elastic constants of chromium nitride films deposited by arc-ion plating
Authors: Hanabusa Takao , Miyagi Kazuhiro , Kusaka Kazuya
Published: July 2004

Thin films have been successfully utilized to improve the property of mechanical components. However, it is generally known that mechanical properties, such as elastic constants and tensile strength of thin films, are different from those of bulk material, and they are not known in the present state. In many times, x-ray stress measurement revealed a very high compressive residual stress state in the film when bulk elastic constants were used in the stress calculation. The purpose of this research is to investigate the elastic constants of chromium nitride (CrN) films. The film was deposited on austenitic stainless steel (JIS: SUS304) substrates by the arc-ion-plating (AIP) method under the following conditions: the pressure of nitrogen atmosphere was maintained at 2.63 Pa, the substrate temperature of about 573 K, the arc discharge current of 100 A, the bias voltage between −300 and −100 V, and the substrate rotating rate at 3 rpm. The lattice strain of CrN films was measured by x-ray method at various loading stages and the x-ray elastic constants of CrN films were evaluated.
Local oxidation of metal and metal nitride films
Authors: Farkas N. , Tokash J. C. , Zhang G. , Evans E. A. , Ramsier R. D. , Dagata J. A.
Published: July 2004

Oxide growth on sputter-deposited thin films is studied on the local scale by atomic force microscope (AFM)-assisted lithography. We investigate the group IV reactive metals Zr, Hf, Ti, and their nitrides. The nitrogen content of the deposition plasma affects the film crystal structure and electrical resistivity, which in turn alter the local oxidation rates. Mass transport plays an important role, producing features with heights ranging from a few nanometers up to hundreds of nanometers. The heights of the largest features are one to two orders of magnitude greater than observed in other material systems, and the growth is well controlled. We use various techniques to investigate the solid-state reaction and transport mechanisms involved in this oxidation driven by a highly localized electric field. Our results demonstrate the potential of AFM lithographic techniques for characterizing oxidation processes across a wide range of time and length scales.
Effect of purge pressure on desorbing water removal rate
Authors: Hinkle L. D.
Published: July 2004

The need for a high purity gas supply for vacuum systems and related processing equipment has driven the requirements for the design and operation of components in gas delivery subsystems. Water has been widely regarded as a major contaminant species in such subsystems. For designs that follow generally accepted practices for construction, sealing, and layout, the primary cause of water contamination is associated with ambient atmospheric exposure during maintenance or repair. The subsequent removal of this adsorbed water, and in particular, how this process can be accelerated has been the subject of much interest. While the enhancement of molecular desorption through various methods has received considerable attention, the effective removal of water vapor after desorption is also worthy of attention. This is especially true when considering the typical geometry of gas distribution and delivery subsystems. It is shown that at typical purge pressures, a water molecule desorbing from a surface is likely to be adsorbed again. Thus, desorption may be required multiple times for the molecule to be removed from the subsystem. However, if the purge flow is operated at modest vacuum, the desorbing molecule remains in the purge stream considerably longer and travels farther downstream before being readsorbed; thus improving the removal rate. The primary focus of this investigation is to understand the dependence of the rate of water removal on the pressure of an inert gas purge. In most cases, the implementation of lower pressure purge may be accomplished with little or no change to existing equipment. In addition to the obvious savings and convenience resulting from a time reduction, considerably less purge gas is consumed.
Improved adhesion of amorphous carbon thin films on glass by plasma treatment
Authors: Takeda Satoshi , Suzuki Susumu
Published: July 2004

We investigated the effects of plasma treatment on adhesion of sputter deposited amorphous carbon thin films to glass. Prior to the deposition, the glass surface was exposed under argon (Ar), oxygen (O2), or hydrogen (H2) plasma, and subsequently the films were deposited onto the glass by direct current magnetron sputtering. The adhesion strength of the film was considerably improved by the plasma treatment. X-ray photoelectron spectroscopy analysis revealed that silicon–carbon bonds were formed at the interface between the films and plasma-treated glass, which were not observed for the film deposited onto the glass without plasma treatment, and that the number of silicon–carbon bonds was larger for the film having higher adhesion strength. These results indicate that the silicon–carbon bonds at the interface are a major factor governing the adhesion strength of the films to glass. Furthermore, it was also found that Ar and H2 plasma were more effective to create the silicon–carbon bonds at the interface than O2 plasma. This difference can be understood in terms of the difference in interactions between the introduced gas and dangling bonds associated with silicon formed by plasma treatment.
Growth behavior and interfacial reaction between carbon nanotubes and Si substrate
Authors: Hsu Chih-Ming , Lai Hong-Jen , Kuo Cheng-Tzu
Published: July 2004

The effect of the interfacial reaction of Co catalyst with a Si substrate on growth of carbon nanotubes (CNTs) was investigated. Well-aligned multiwall CNTs (MWCNTs) were synthesized and applied barrier layers by microwave plasma-enhanced chemical vapor deposition (MPECVD). Growth proceeded in a flowing mixture of H2, CH4, and N2 as precursors at a temperature of 600 °C and a −200 V substrate bias; Co was sputtered as the catalytic material. Transmission electron microscopy (TEM) and x-ray diffraction were employed to examine the growth behavior of CNTs on Si (100) substrates on which Co had been deposited by MPECVD. The TEM results indicate that discrete conical CoSi2 layers with {111} and (100) faceted interfaces were formed on a Si (100) substrate during CNTs growth. Direct evidence that the growth is by tip growth and base growth is presented. The results show that well-aligned CNTs exhibit a significant emission current. The field emission characteristics of CNTs are contributed to the relationship between the application of different barrier layers and the growth mode of CNTs.
Calibration apparatus for precise barometers and vacuum gauges
Authors: Woo S. Y. , Choi I. M. , Lee Y. J. , Hong S. S. , Chung K. H.
Published: July 2004

In order to calibrate highly accurate absolute pressure gauges, such as barometers and vacuum gauges, laser, or ultrasonic mercury manometers have been used. However, the complexity and cost of manometers have greatly reduced the use of this method in most calibration laboratories. As a substitute, a gas-operated pressure balance is used to calibrate precise gauges. In such cases, many commercially available pressure balances are unsuitable because the necessary exposure of the piston, cylinder, and masses to the atmosphere causes contamination problems and allows dust particles into the gap between the piston and cylinder. In this article, a weight-loading device is described that allows masses to be changed in situ without breaking the vacuum. This device makes it possible to add or remove weights easily during the calibration, thereby greatly reducing the time between observations. Using this device, we efficiently calibrated a precise quartz resonance barometer (Paroscientific, model 760-16B) over a pressure range of 940–1050 h Pa and a precise vacuum gauge (MKS, CDG 100 Torr) over a pressure range of 0–100 h Pa.
Interfacial analysis using time-of-flight medium energy backscattering
Authors: Geil R. D. , Rogers B. R. , Song Zhe , Weller R. A.
Published: July 2004

Time-of-flight medium energy backscattering (TOF-MEBS) is a derivative of conventional Rutherford backscattering (RBS) that uses medium energy ions and a time-of-flight detector resulting in improved surface sensitivity, increased depth resolution, and reduced target damage compared to conventional RBS. In this study, thin dielectric materials and their lower interfaces were analyzed with TOF-MEBS using 270 keV He+ projectiles. Dielectric materials systems studied included Al2O3, SiO2, and ZrO2 on silicon. Film thicknesses ranged from approximately 10 to 200 Å. Data analyses were performed by modeling the ion interactions with material structures and performing a non-linear least squared fit to the backscattering spectra. Simulation fit results were improved up to 40% for alumina and 60% for zirconia samples by including interfacial layers on the order of a few nanometers thick in the material structure models. The significant improvement to fits resulting from the addition of extremely thin interfacial layers demonstrates the technique’s applicability to ultra-thin film characterization.
Effect of low substrate deposition temperature on the optical and electrical properties of Al2O3 doped ZnO films fabricated by ion beam sputter deposition
Authors: Seong J. W. , Kim K. H. , Beag Y. W. , Koh S. K. , Yoon K. H.
Published: July 2004

Aluminum (2 wt %) doped zinc oxide (AZO) films are prepared by ion beam sputtering method on glass substrates with very low substrate deposition temperature below 150 °C. The results of Hall effect measurements showed the decrease in resistivity (2.6×10−3–7.3×10−4 Ω cm) came from an increase in mobility and carrier concentration as substrate deposition temperature increased. We confirmed the decrease of resistivity, which resulted from the formation of oxygen deficiency (ZnO1−x) as substrate deposition temperature increased. The increase of Hall mobility and carrier concentration was also influenced by increases in crystallinity and grain growth of AZO films as substrate deposition temperature increased. The optical transmission of AZO increased from 70% to 80% with increasing substrate deposition temperature. The surface morphology analysis by atomic force microscopy showed the decrease of surface roughness might be related to the development of optical properties.
Thickness uniformity of large-area double-sided thin films simultaneously deposited with biaxial substrate rotation
Authors: Tao B. W. , Deng X. W. , Zhang Y. , Li Y. R.
Published: July 2004

We have theoretically analyzed the thickness distribution of large-area double-sided thin films deposited with biaxial substrate rotation. The films were deposited from different physical vapor deposition sources (such as point, round-plate, cylinder, and conic sources) and have different thickness distribution characters. The calculated results show that the biaxial rotation is a suitable technique for simultaneous deposition on both sides from most sources if particles transfer diffusively.
Reactive etching of platinum-manganese using a pulse-time-modulated chlorine plasma and a H2 plasma post-etch corrosion treatment
Authors: Kumagai Shinya , Shiraiwa Toshiaki , Samukawa Seiji
Published: July 2004

Highly anisotropic and corrosion-less PtMn etching was achieved for the first time by using a pulse-time-modulated (TM) chlorine electron-cyclotron-resonance plasma. It was found that PtMn etching rate, in the case of the TM plasma, increased considerably compared with that in the case of a conventional continuous-wave plasma. The formation of etching residue and post-etch corrosion products was reduced by increasing the pulse-off time of the TM plasma. Moreover, surface analysis showed that the residual chlorine concentration decreases during the TM plasma etching. In addition, hydrogen-plasma post-exposure treatment after the etching process could decrease the residual chlorine concentration and suppress post-etch corrosion product formation. It is concluded from these results that when combining TM chlorine plasma etching and the hydrogen-plasma post-exposure treatment one can successfully pattern highly anisotropic vertical etched profiles with sub-micron width and no critical-dimension loss.
Interfacial reaction effect on the ohmic properties of a Pt/Pd/Au contact on p-type GaN
Authors: Kim Han-Ki , Adesida I. , Seong Tae-Yeon
Published: July 2004

We have investigated the effect of interfacial reactions between a Pt(7 nm)/Pd(7 nm)/Au(15 nm) layer and p-GaN on its ohmic contact properties by using Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), and glancing angle x-ray diffraction. The annealed Pt/Pd/Au contact exhibits linear current-voltage characteristics, which indicates that a high-quality ohmic contact is formed. The Pt/Pd/Au contact shows a specific contact resistivity of 3.1×10−5 Ω cm2 when annealed at 600 °C for 2 min in flowing N2 atmosphere. Both AES and XPS results show that the diffusion of Pt and Pd into the GaN surface region results in the formation of gallide and plays an important role in forming a low resistance ohmic contact by the creation of a highly doped p+-GaN surface region.