bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of bond strength of plasma-sprayed hydroxyapatite/titanium composite coatings on titanium: Partial nitriding of titanium deposits by rf thermal plasma
Authors: Inagaki M. , Yokogawa Y. , Kameyama T.
Published: July 2003

The bond strength of plasma-sprayed HA/Ti composite coatings on Ti substrate was significantly improved by the partial nitriding of Ti deposits in the coatings during plasma spraying. HA/Ti composite coatings were deposited on titanium substrates by a rf thermal plasma-spraying method with rf input powers of 12–27 kW. The ratio of HA and Ti powders supplied into the plasma was precisely controlled by two microfeeders so as to change the coating composition from Ti rich to HA rich toward the upper layer. When sprayed in plasma gas with 0.8% N2 added, the bond (tensile) strength of the obtained HA/Ti composite coatings sprayed at 12 kW was 41.4 MPa. On the contrary, the bond strength of coatings sprayed with pure Ar at 12 kW was 33.6 MPa despite the other processing parameters being almost the same. When sprayed with 1.8% N2 added at 27 kW, the bond strength reached 65.3 MPa. X-ray diffraction patterns of Ti coatings without HA showed that titanium nitrides were formed in the titanium deposits sprayed with plasma gas containing N2. Scanning electron microscopic observation showed that these nitrided Ti deposits had an acicular texture. Transmission electron microscopic observation showed that Ti2N was formed at the interface between two nitrided Ti splats, while electron diffraction analyses showed that an α-titanium lattice was formed inside of the nitrided Ti splats.
Properties of Co-deposited indium tin oxide and zinc oxide films using a bipolar pulse power supply and a dual magnetron sputter source
Authors: Hwang Man-Soo , Seob Jeong Heui , Kim Won Mok , Seo Yong Woon
Published: July 2003

Multilayer coatings consisting of metal layers sandwiched between transparent conducting oxide layers are widely used for flat panel display electrodes and electromagnetic shield coatings for plasma displays, due to their high electrical conductivity and light transmittance. The electrical and optical properties of these multilayer films depend largely on the surface characteristics of the transparent conducting oxide thin films. A smoother surface on the transparent conducting oxide thin films makes it easier for the metal layer to form a continuous film, thus resulting in a higher conductivity and visible light transmittance. Indium tin oxide (ITO) and zinc oxide (ZnO) films were co-deposited using a dual magnetron sputter and a bipolar pulse power supply to decrease the surface roughness of the transparent conducting oxide films. The symmetric pulse mode of the power supply was used to simultaneously sputter an In2O3 (90 wt %) : SnO2 (10 wt %) target and a ZnO target. We varied the duty of the pulses to control the ratio of ITO : ZnO in the thin films. The electrical and optical properties of the films were studied, and special attention was paid to the surface roughness and the crystallinity of the films. By co-depositing ITO and ZnO at a pulse duty ratio of ITO:ZnO=45:45 using a dual magnetron sputter and a bipolar pulse power supply, we were able to obtain amorphous transparent conducting oxide films with a very smooth surface which had a Zn-rich buffer layer under a In-rich surface layer. All of the films exhibited typical electrical and optical properties of transparent conducting oxide films deposited at room temperature.
Infrared thermal annealing device
Authors: Gladys M. J. , Clarke I. , O’Connor D. J.
Published: July 2003

A device for annealing samples within an ultrahigh vacuum (UHV) scanning tunneling microscopy system was designed, constructed, and tested. The device is based on illuminating the sample with infrared radiation from outside the UHV chamber with a tungsten projector bulb. The apparatus uses an elliptical mirror to focus the beam through a sapphire viewport for low absorption. Experiments were conducted on clean Pd(100) and annealing temperatures in excess of 1000 K were easily reached.
Edison’s vacuum technology patents
Authors: Waits Robert K.
Published: July 2003

During 1879 Thomas Edison’s Menlo Park, New Jersey laboratory developed the means to evacuate glass lamp globes to less than a mTorr in 20 min and in mid-1880 began production of carbon-filament incandescent lamps. Among Edison’s nearly 1100 U.S. patents are five for vacuum pump improvements, and at least eight others that are vacuum-related; all applied for between 1880 and 1886. Inspired by an 1878 article by De La Rue and Müller [Philos. Trans. R. Soc. London, Ser. A 169, 155 (1878)] on studies of glow discharges, Edison devised a combination pump using the Geissler pump as a rough pump and the Sprengel pump for continuous exhaustion. Edison’s patents described means to control the mercury flow and automate the delivery of the mercury to banks of up to a hundred pumps. Other patents described various means to remove residual gases during lamp processing.
Structural and mechanical properties of diamond-like carbon films deposited by direct current magnetron sputtering
Authors: Broitman E. , Hellgren N. , Czigány Zs. , Twesten R. D. , Luning J. , Petrov I. , Hultman L. , Holloway B. C.
Published: July 2003

The microstructure, morphology, and mechanical properties of diamond-like carbon (DLC) films deposited by direct current magnetron sputtering were investigated for microelectromechanical systems applications. Film properties were found to vary markedly with the ion energy (Eion) and ion-to-carbon flux ratio (Jion/JC). Cross-sectional high-resolution transmission electron microscopy revealed an amorphous microstructure. However, the presence of nanometer-sized domains at Eion∼85 eV was detected. Film stresses, σ, which were compressive in all cases, ranged from 0.5 to 3.5 GPa and depended on the flux ratio as well as ion energy. The hardness (H), Young’s moduli (ε), and elastic recovery (R) increased with Eion to maximum values of H=27 GPa, ε=250 GPa, and R=68% at Eion=85 eV and Jion/JC=4.4. However, near edge x-ray absorption fine structure and electron energy-loss spectrum analysis showed that the sp2/sp3 content of the films does not change with Eion or Jion/JC. The measured change in mechanical properties without a corresponding change in sp2/sp3 ratio is not consistent with any previously published models. We suggest that, in the ranges 5 eV ⩽Eion⩽85 eV and 1.1 ⩽Jion/JC⩽6.8, the presence of defective graphite formed by subplanted C and Ar atoms has the dominant influence on the mechanical properties of DLC films.
Development of sputtering systems for large-area deposition of CuIn1−xGaxSe1−ySy thin-film solar cells
Authors: Dhere Neelkanth G. , Gade Vivek S. , Jahagirdar Anant H. , Kadam Ankur A. , Patil Harshad P. , Kulkarni Sachin S.
Published: July 2003

CuIn 1−x Ga x Se 1−y S y (CIGS) thin-film modules are expected to become cheaper than crystalline silicon modules within 5 yr. At present, commissioning and reaching full production of thin film modules is delayed because of nonavailability of turnkey manufacturing plants. Very few universities are conducting research on development of PV plants. CIGS thin-film solar cells are being prepared routinely at Florida Solar Energy Center (FSEC) on glass and metallic foil substrates for terrestrial and space applications. Earlier, the substrate size was limited to 3×3 cm2. This article presents results of development of large-area sputtering systems for preparation of large (15.2×15.2 cm2) CIGS thin-film solar cells. The facilities have the potential of serving as a nucleus of a pilot plant for fabrication of CIGS minimodules. Initial problems of bowing of the brass diaphragm, restriction of effective water flow and consequent heating of the target material were resolved by increasing the thickness of the backing plate and redesigning the structural members. Thickness uniformity was improved by modifying the magnetic field distribution in the middle 15 cm portion of the 10.2×30.5 cm2 magnetron sputtering sources by selectively removing nickel-coated soft-iron pieces at the rear. This resulted in Mo layer thickness uniformity of ±3% over 10.2×10.2 cm2. The magnetic field was boosted at extremities to avoid precipitous ∼15% drop beyond 10.2 cm. With this, thickness uniformities of ±2.5% for Mo and ±4.5% for ZnO over 12.7×10.2 cm2 have been achieved however with a continuing drop beyond 12.7 cm width. Modifying the magnetic field to achieve better distribution by preferentially removing soft irons pieces and also boosting of the magnetic field at the ends are two new concepts introduced and successfully utilized in this study. Scaling up of the large-area uniform deposition of metallic precursor layers was a challenging task. The efforts were directed towards obtaining similar thickness and uniformity that have provided very good photovoltaic efficiencies of 10.4% (Air mass AM 1.5) in small area CIGS thin film solar cells on stainless steel foils in earlier research. Preliminary results on large area CIGS solar cells are encouraging.
dc field-emission analysis of GaAs and plasma–source ion-implanted stainless steel
Authors: Hernandez C. , Wang T. , Siggins T. , Bullard D. , Dylla H. F. , Reece C. , Theodore N. D. , Manos D. M.
Published: July 2003

Field-emission studies have been performed on a GaAs wafer and a sample of its stainless-steel (SS) support electrode that are part of a photocathode gun for the 10 kW Upgrade infrared free electron laser at Jefferson Lab. The objective of the studies presented here is to characterize the effect of both the cleanliness of the wafer and the plasma–source ion-implanted layer on the electrode to suppress field emission. Field emission is the limiting factor to achieve the required 6 MV/m at the surface of the wafer. Potential field emitters are first located on the surface of 1 in. diameter samples with a dc scanning field-emission microscope at 60 MV/m, then each emitter is characterized in a scanning electron microscope equipped with an energy dispersive spectrometer. The GaAs wafer was hydrogen cleaned before the study. The results show three emitters caused by indium contamination during wafer handling. The GaAs wafer thus shows good high-voltage characteristics and the need to maintain cleanliness during handling. The SS sample is hand polished with diamond paste to a 1 μm surface finish, then implanted with N2/SiO2 in a plasma–source ion-implantation chamber in preparation for the field-emission studies.
Microstructural and optical properties of aluminum oxide thin films prepared by off-plane filtered cathodic vacuum arc system
Authors: Zhao Z. W. , Tay B. K. , Lau S. P. , Xiao C. Y.
Published: July 2003

Transparent, amorphous, surface smooth, and hard aluminum oxide thin films were deposited on Si (100) and quartz substrates by an off-plane filtered cathodic vacuum arc (FCVA) system. We systematically studied the optical properties, such as transmittance and optical constants, of the aluminum oxide thin films deposited under various oxygen partial pressures. Experimental results show that the optical properties for aluminum oxide thin films are strongly dependent on oxygen partial pressure; the higher oxygen partial pressure causes much more oxygen to incorporate into the film thus inducing more modification of film properties. At proper oxygen partial pressure, the stoichiometric alumina film is obtained, which is smooth and dense. Additionally, it also displays good optical properties with a refractive index of ∼1.7 at 550 nm. The properties exhibited by the alumina thin films manifest the potential applications for alumina thin films in optical coatings and for FCVA technology in deposition of metal oxide optical films.
Comparison of silicon dioxide layers grown from three polymethylsiloxane precursors in a high-density oxygen plasma
Authors: Qi Y. , Xiao Z. G. , Mantei T. D.
Published: July 2003

We have compared the elemental composition, growth rates, and hardness of silicon dioxide layers grown from hexamethyldisiloxane (HMDSO), octamethylcyclotetrasiloxane (OMCTS), and tetramethylcyclotetrasiloxane (TMCTS) in a high-density electron cyclotron resonance oxygen plasma. Hard colorless coatings could be grown from each precursor; coating composition, growth rates, and hardness depended strongly on the ratio of oxygen to precursor flow. At the highest O2/precursor flow ratios (4:1 for HMDSO and 8:1 for OMCTS and TMCTS), the coatings were SiO2-like with oxygen-to-silicon ratios close to 2:1 and carbon percentages as low as 12% for HMDSO, 3.4% for OMCTS, and 1.4% for TMCTS. Growth rates were 0.7–1.1 μm/min, initially increasing with the O2/precursor flow ratio; final coating thicknesses after 5 min were 3.5 μm to 5.5 μm. Coating hardness values generally increased with increasing O2/precursor flow ratio, attaining 6 GPa, 7.4 GPa, and 8.7 GPa for HMDSO, OMCTS, and TMCTS, respectively.
Laser desorption time-of-flight mass spectrometry of fluorocarbon films synthesized by C4F8/H2 plasmas
Authors: Shibagaki K. , Maeda T. , Takada N. , Sasaki K. , Kadota K.
Published: July 2003

Molecular structures of fluorocarbon films synthesized by C4F8/H2 plasmas were analyzed by laser desorption time-of-flight mass spectrometry (LD-TOFMS). Mass peaks of positive and negative ions with m/z up to 250 were observed in the mass spectra. Most of these ions were assigned as atomic hydrogen, atomic fluorine, carbon clusters, hydrocarbon clusters, fluorocarbon clusters, and hydrofluorocarbon clusters. The mass spectra changed sensitively with the partial pressure of H2. The LD-TOFMS analysis showed that the films changed from a polytetrafluoroethylene-like film into crosslinked carbon- and hydrogen-rich one by the addition of H2. The change in the chemical composition of the mass spectrum was consistent with the analyses by conventional x-ray photoelectron spectroscopy and Fourier transform infrared absorption spectroscopy. It is emphasized that LD-TOFMS can be used for the analysis of the degree of polymerization, which is an advantage of LD-TOFMS over the conventional analysis methods.
Determination of Ti+-flux and Ar+-flux of ionized physical vapor deposition of titanium from multiscale model calibration with test structures
Authors: Jacobs W. , Kersch A. , Ruf A. , Urbansky N.
Published: July 2003

In this article we determine physical parameters characterizing the ionized physical vapor deposition of titanium in a Hollow Cathode Magnetron by comparing experimental results obtained from suitable submicron test structures with a multiscale model. The model includes the reactor scale, the plasma sheath and presheath scale, and the feature scale. The reactor scale model delivers the energy and angular distribution of the neutral sputtered particles from the reactor geometry and an energy dependent collision model. The sheath and presheath model calculates the energy and angular distribution of the ions from the reactor model and a subsequent scattering model describes collisions in the presence of magnetic fields. The levelset-based feature scale simulator propagates the front according to local growth velocities which are calculated from Monte Carlo particle flux and reaction kinetics (derived from molecular dynamics calculation). The calibration is performed in two steps with help from bottle-shaped test structures as well as technologically relevant structures. First, hi-fill and ultra-hi-fill magnetron sputter processes of titanium are investigated in order to verify the transport model for the neutral particles. Second, a Hollow Cathode Magnetron sputter process of titanium is analyzed in order to verify the transport model for postionized particles. This analysis is performed for a floating substrate process and a process with rf-driven substrate bias. The postionized flux fraction of titanium in this technology is not calculated from a plasma model but treated as a free parameter. The prediction of the model and the comparison with the experimental data allow us to determine this value as 0.7±0.1 under a standard condition. The ionized flux of argon relative to the ionized flux of titanium is determined as 2. The results show that the bottom and sidewall coverage of the process depends significantly on the angular dependence of the ionized component which is essentially a result of processes in the presheath. The validity of the model covers a variety of plasma and process conditions. It can be applied to other reactor concepts and materials.
Transitional change to amorphous fluorinated carbon film deposition under energetic irradiation of mass-analyzed carbon monofluoride ions on silicon dioxide surfaces
Authors: Ishikawa Kenji , Karahashi Kazuhiro , Tsuboi Hideo , Yanai Ken-ichi , Nakamura Moritaka
Published: July 2003

We have studied both the etching of SiO2 film and the growth of an amorphous fluorinated carbon (a-C:F) film by mass-analyzed fluorocarbon ion irradiation. This experiment was done in an ultrahigh vacuum with a pressure of 10−7 Pa even during irradiation. When using a carbon monoflouride (CF1+) ion with an energy of 300 eV to irradiate, it was found that SiO2 film a few nm thick was initially etched away. Then, an a-C:F film was continuously deposited on the SiO2 surface as the ion dose exceeded about 5×1016 cm−2. Using in situ x-ray photoelectron spectroscopy analysis, it was determined that carbon accumulates on the surface at this early stage as the ion dose increases, so that this transition is resulted by the surface modification on which the CF1+ ion itself irradiates the SiO2 surface. Especially in highly ionized fluorocarbon plasmas, surface conditions such as the carbon concentration affect possibly etching performance.
X-ray diffraction study of residual stresses and microstructure in tungsten thin films sputter deposited on polyimide
Authors: Villain P. , Goudeau P. , Ligot J. , Benayoun S. , Badawi K. F. , Hantzpergue J.-J.
Published: July 2003

Structural and mechanical properties of metal/polymer systems are of great interest for technological applications since they strongly influence the quality and lifetime of these systems. The phase composition, microstructure, and residual stresses of tungsten films sputter deposited on polyimide substrates have been analyzed by x-ray diffraction. The influence of several deposition parameters is studied. In 200 nm thick films, the tungsten β phase is observed when oxygen incorporation is high. As the film thickness increases, a thermally activated β→α phase transition occurs and only the α phase exists in the 600 nm films. High compressive residual stresses are evidenced in both phases.
Mechanism of hardening in Cr–Al–N–O thin films prepared by pulsed laser deposition
Authors: Hirai M. , Suzuki T. , Suematsu H. , Jiang W. , Yatsui K.
Published: July 2003

Chromium aluminum oxynitride (Cr–Al–N–O) thin films have been prepared by pulsed laser deposition. Experiments were carried out by changing the surface area ratio of targets [SR=SAlN/(SCr2N+SAlN)] from 0% to 100%. The composition of the thin film prepared at SR=75% was determined to be Cr0.11Al0.39N0.25O0.25 by Rutherford backscattering spectroscopy. From the result of grazing angle x-ray diffractometry, the phase transition of the Cr–Al–N–O thin films was clarified to occur, when the aluminum content in cations (x) ranged from 70 to 90 at. %. In addition, the thin films having composition close to the solubility limit were observed by transmission electron microscopy to contain chromium nitride particulates below 200 nm in diameter. The Cr–Al–N–O thin film with x=25 at. %, which was the hardest over the whole x range, had Vickers hardness above 4000. In this thin film, nanometer-sized crystallites were found in the grains. Moreover, the elastic modulus was shown to be higher than those of other Cr–Al–N–O thin films.
Etch characteristics of Bi4−xEuxTi3O12 (BET) thin films using inductively coupled plasma
Authors: Lim Kyu-Tae , Kim Kyoung-Tae , Kim Dong-Pyo , Kim Chang-II
Published: July 2003

Bi 4−x Eu x Ti 3 O 12 (BET) thin films were etched by inductively coupled CF4/Ar plasma. We obtained the maximum etch rate of 78 nm/min at the gas mixing ratio of CF4 (10%)/Ar (90%). This result may suggest that sputtering by Ar ions is more effective than chemical etching by fluorine atoms for Bi4−xEuxTi3O12 (BET) etching. The variation of volume density for F and Ar atoms are measured by optical emission spectroscopy. As CF4 increased in CF4/Ar plasma, the emission intensities of F increase but Ar atoms decrease, which confirms our suggestion that the etch rate of BET thin film and emission intensity of an Ar+ ion is proportional to the volume density of Ar atoms. From x-ray photoelectron spectroscopy, the intensities of the Bi–O, the Eu–O, and the Ti–O peaks are changed with increasing CF4 concentration. By pure Ar plasma, the intensity peak of the oxygen–metal (O–M: TiO2, Bi2O3, Eu2O3) bond seemed to disappear while the intensity of the pure oxygen peak showed an opposite tendency. After the BET thin films were etched by CF4/Ar plasma, the peak intensity of the O–M bond increases slowly, but more quickly than that of peak belonging to pure oxygen atoms due to the decrease of Ar ion bombardment. These results indicate that Bi and Eu have a reaction with little F and those are removed predominantly by argon-ion bombardment. However, Ti reacts with little F radicals and is mainly removed by chemically assisted physical etching. To fabricate high-density ferroelectric random access memory devices, etch processes require stringent critical dimension control to ±0.02 μm and steep etch profiles over 70°. From the scanning electron microscopy, we had an almost perpendicular taper angle of over 85°.
Effects of adsorbates on charge exchange in Li+ ion scattering from Ni(100)
Authors: Yang Ye , Yarmoff Jory A.
Published: July 2003

Resonant charge transfer during the backscattering of 3.0 keV Li+ from hydrogen- and iodine-covered Ni(100) is probed with time-of-flight spectroscopy. Hydrogen adsorption on Ni(100) induces only a small increase of the surface work function and the neutralization probabilities for backscattered Li are not significantly affected. Iodine adsorbs with some net negative charge, so that a dipole directed into the surface is expected. Such a dipole would increase the work function thereby decreasing the neutralization probability. Iodine adsorption decreases the work function of Ni(100), however, and the neutralization probabilities for Li scattered from the iodine sites are always larger than for scattering from nickel sites. These results suggest that the local charge density associated with adsorbed iodine is not uniform.
Photocatalytic properties of TiO2/WO3 bilayers deposited by reactive sputtering
Authors: Takahashi T. , Nakabayashi H. , Yamada N. , Tanabe J.
Published: July 2003

To study the decomposition of methyl alcohol (CH3OH) by a photocatalytic reaction, TiO2/WO3 bilayers composed of TiO2 and WO3 films were deposited using reactive sputtering at the working gas pressure PW of 1 and 3–8 mTorr, respectively. The optical transmittance spectra of as-deposited TiO2/WO3 bilayers monotonically decreased with decreasing wavelength in the range of 200–900 nm. When depositing WO3 films, the adsorption edge shifted to a higher wavelength of about 400 nm with decreasing PW. These spectra may depend on the properties of WO3 films, rather than those of TiO2 films. As expected, the bilayer can adsorb much more visible light compared to TiO2 single layers. From the measurement of Fourier transform infrared transmittance spectra, CH3OH can be decomposed strongly into CO2 and H2O molecules, compared to the TiO2 single layer. When the TiO2/WO3 bilayer was irradiated with artificial sunrays for 130 min, the formation rate of CO2 molecules was about two times as fast as that in the TiO2 single layer. We found that the decomposition of CH3OH may depend on the crystallinity and optical properties of WO3 underlayers.
Combined atomic force microscope and acoustic wave devices: Application to electrodeposition
Authors: Friedt J.-M. , Francis L. , Choi K.-H. , Frederix F. , Campitelli A.
Published: July 2003

We present a combination of acoustic wave based sensors with scanning probe microscopy as a tool for better understanding the interaction of the former with the surrounding viscous medium when used for detection of analytes in liquids. Simultaneous analysis of the gold coated sensing surface with an atomic force microscope and monitoring changes in the acoustic propagation properties during copper electrodeposition provides a mean of correlating observations on the nanometer and millimeter scales. We find that the frequency shift of the quartz crystal microbalance is predominantly attributed to viscous effects in the lower mass range (below 1 μg/cm2 copper electrodeposition) and only becomes representative of the added rigid mass in the higher mass range. We observe that the sensitivity of surface acoustic wave Love-mode devices appears constant over the whole mass range analyzed (0.5–10 μg/cm2), indicating a rigid layer interaction leading to a frequency shift representative of the deposited mass.
Observation of an isotope effect in femtosecond laser-induced desorption of O2/Pd(111)
Authors: Quinn Daniel P. , Heinz Tony F.
Published: July 2003

Femtosecond laser pulses can induce desorption of oxygen adsorbed in the molecular state on Pd(111) surfaces. In this study, the behavior of the O216 and O218 isotopic species is characterized for the saturated Pd(111) surface at a base temperature of 95 K. The O216 species is found to desorb with a yield 1.8±0.3 times greater than that of the O218 species. The implications of this finding for the desorption mechanism are discussed.
Surface morphology and magnetization reversal
Authors: Lukaszew Rosa Alejandra , Zhang Zhengdong , Cionca Codrin , Stoica Vladimir , Clarke Roy
Published: July 2003

We have studied the microstructure and surface morphology in annealed and nonannealed (001) epitaxial Ni films deposited on MgO single crystalline substrates. The correlation between microstructure and the magnetic anisotropy properties of the films such as the magnetization reversal has been determined. Scanning tunneling microscopy images of the surface of the annealed films indicate self-assembled periodic stripe nano-patterning, while images of the nonannealed films show typical mounded surfaces. The azimuthal dependence of the coercive field in the nonannealed films exhibits fourfold symmetry as expected from the symmetry of the crystal. The annealed films exhibit an additional uniaxial symmetry superimposed to the fourfold symmetry. Additional structural studies to understand the origin of the surface nano-patterning observed on (001) Ni films will also be presented.
Critical tasks in high aspect ratio silicon dry etching for microelectromechanical systems
Authors: Rangelow Ivo W.
Published: July 2003

The process of pattern transfer of desired topological features into silicon plays a critical role for the production of microelectronic and photonic devices, and micro- and nanoelectromechanical systems. Any deviation from the desired shape of the pattern limits density, yield, and reliability of these devices. Gas reactivity, pressure, ion, electron, and reactant transport to the surface, and product transport away from the surface, have all been identified as important issues that control the microscopic uniformity in high aspect ratio etching. When etch-inhibiting chemistry by the gas chopping deep reactive ion etching (RIE) was employed, it caused enormous complications in the scaling of etching rates, with increasing aspect ratio. Using an energy-resolving quadrupole mass spectrometer assembled into the cathode, specially designed test features, and etching simulation models, we establish the link between etch process parameters such as pressure, rf power, etching gas chemistry, temperature, and the physical and chemical process parameters like energy and angular distribution of ions and neutrals, radical sticking, and surface charging. The most significant effects like RIE lag, notching, bowing, faceting, microtrenching, profile shape dependence, etc. will be discussed in this article. 2003 American Vacuum Society.
Study of a magnetic cluster/superconducting matrix interface: Co/Nb system
Authors: Dupuis V. , Jamet M. , Favre L. , Tuaillon-Combes J. , Melinon P. , Perez A.
Published: July 2003

In a previous work on 3 nm diameter Co clusters embedded in a Nb matrix, we suggested a core-shell model to account for the cluster structure. In this model, clusters are made up of a pure face-centered-cubic Co core surrounded with a “magnetically dead” CoNb alloyed interface. In the present work, we focus on the structure of this interface using different x-ray based analysis techniques to correlate structure and magnetism in such a nanogranular (Co)Nb system. As a model for the cluster/matrix interface, in situ measurements are also performed on a Co/Nb bilayer grown under an ultrahigh vacuum. No epitaxial growth of Nb on Co is achieved at room temperature. Therefore, we can conclude that magnetoelastic effects are too weak to explain the large magnetic anisotropy previously obtained with the microsuperconducting quantum interference device technique on a single Co cluster embedded in a Nb matrix. On the other hand, interface anisotropy, estimated from the Néel model, is in good agreement with the experimental value suggesting interface driven magnetic properties in this system.
p-type semiconducting Cu2O–CoO thin films prepared by magnetron sputtering
Authors: Suzuki Shingo , Miyata Toshihiro , Minami Tadatsugu
Published: July 2003

The preparation by magnetron sputtering of p-type semiconducting thin films consisting of a multicomponent oxide composed of Cu oxide and Co oxide is described. The electrical, optical, and crystallographical properties of films deposited by rf magnetron sputtering using (Cu2O)1−x–(CoO)x powder targets were strongly dependent on not only the deposition condition but also the calcination condition as well as the CoO content of the targets. These properties drastically changed in films prepared with a CoO content around 90 mol %. All prepared films, i.e., CoO content in the range from 0 to 100 mol %, were found to be p type, or positive hole conductors, as evidenced from the Seebeck effect: Resistivities in the range from 103 to 10−3 Ω cm. A hole concentration on the order of 1016 cm−3 and a mobility on the order of 10−1 cm2/V s were obtained in an amorphous multicomponent oxide film prepared with a CoO content of 50 mol %. Fabricated thin-film pin heterojunction diodes consisting of a p-type high-resistance multicomponent oxide combined with undoped ZnO and n-type Al-doped ZnO exhibited a rectifying current–voltage characteristic.
High-rate deposition of ZnO thin films by vacuum arc plasma evaporation
Authors: Miyata Toshihiro , Ida Satoshi , Minami Tadatsugu
Published: July 2003

Transparent and conductive Al- or F-doped ZnO (AZO or FZO) thin films were prepared by a vacuum arc plasma evaporation method using oxide fragments. A resistivity of 5.8×10−3 Ω cm was obtained in an AZO film deposited with an Al2O3 content of 10 wt %. However, it was found that doping Al into ZnO films was very difficult because of the large difference in decomposition energy (vapor pressure) between Al2O3 and ZnO. In FZO film depositions, the electrical and optical properties could be controlled by varying the ZnF2 content. Highly conductive and transparent FZO films were prepared on low-temperature substrates with the introduction of O2 gas during the deposition. A low resistivity of 7.4×10−4 Ω cm and an average transmittance above about 78% in the visible wavelength range were obtained in a FZO film deposited at a substrate temperature of 100 °C. A high deposition rate of 180 nm/min was obtained in films deposited on large area substrates with a cathode plasma power of 6.0 kW.
Raman and photoluminescence of ZnO films deposited on Si (111) using low-pressure metalorganic chemical vapor deposition
Authors: Ye Jiandong , Gu Shulin , Zhu Shunmin , Chen Tong , Liu Wei , Qin Feng , Hu Liqun , Zhang Rong , Shi Yi , Zheng Youdou
Published: July 2003

The highly c-oriented ZnO films were epitaxially grown on n-type Si (111) substrate at the temperature range of 340–460 °C using the low-pressure metalorganic chemical vapor deposition method. All films exhibit a pronounced (002) peak for ZnO, indicative of the strong c-axis oriented characteristic. The ZnO film grown at 400 °C shows the best structural quality along with the largest lateral grain size, well supported by the narrowest full width at half maximum of ZnO (002) peak about 0.19° in x-ray diffraction. However, the temperature dependence of the vibrational modes at 436 and ∼563 cm−1 in Raman spectra revealed a low density of oxygen vacancies in the films grown at low temperatures, which is supposed to determine the photoluminescence (PL) properties. At low temperatures, the narrow ultraviolet (UV) near band emission dominated the PL spectrum with a very weak low energy tail near the band. High temperature (up to 460 °C) would cause serious oxygen deficiency, resulting in the weak broad UV band with obvious blue band emission.
Ionic densities and ionization fractions of sputtered titanium in radio frequency magnetron sputtering
Authors: Okimura Kunio , Nakamura Tadashi
Published: July 2003

Ionic densities of sputtered titanium (Ti) in rf magnetron sputtering were measured using an optical absorption method. Measurements of ionic densities of sputtered Ti were made by varying pressure of Ar gas, applied rf power and distance from the target. The densities of Ti atoms were measured using an atomic absorption method for deriving ionization fraction of sputtered Ti. At the rf power of 200 W, ionic densities of Ti were found to be lower than 1.0×1010 cm−3 indicating that ionization fractions were of the order of several percentages at Ar pressures lower than the pressure of several Pascals that is used in conventional sputtering. The ionic density increased with increasing pressure and reached a maximum value of 4.8×1010 cm−3 at the Ar pressure of 21 Pa for z=15 mm where z is axial distance with origin at the Ti target surface. Also, both ionic and atomic densities of sputtered Ti increased monotonically with increasing rf power resulting in an almost constant value of ionization fraction at the Ar pressure of 7 Pa. Probe measurements indicated that fractions of Ti ion were around 30%–40% of the total ionic density which at pressures higher than several Pa was mainly made up of Ar ion. The ionization rate of electron impact for Ti and Ar is discussed based on measurements made by the authors.
Standards for surface analysis: ASTM committee E-42 on surface analysis
Authors: Czanderna A. W.
Published: July 2003

Surface analysis is of critical importance to most of the Divisions of the American Vacuum Society and has been one of the most dynamic scientific and technological growth areas for the last 30 yr. The ASTM Committee E-42 on Surface Analysis was formed in 1976 to help advance the quality of surface analysis by developing appropriate standards (reference materials, reference data, and reference procedures), and by leading round robin comparisons, preparing publications, and holding symposia and workshops. A major function of the committee has been the development of standards and reference procedures. This article is a description of the organization of Committee E-42, and a summary of recent activities by this volunteer group with an emphasis on the processes used, a description of standards published, and standards that are being developed by Committee E-42 and other international organizations.
Thermal plasma fabricated lithium niobate-tantalate films on sapphire substrate
Authors: Kulinich S. A. , Yoshida T. , Yamamoto H. , Terashima K.
Published: July 2003

We report the deposition of LiNb1−xTaxO3 (0⩽x⩽1) films on (001) sapphire substrates in soft vacuum using a radio frequency thermal plasma. The growth rate, crystallinity, c-axis orientation, and surface roughness were examined as functions of substrate temperature, precursor feed rate, and substrate surface condition. The film Nb/Ta ratio was well controlled by using an appropriate uniform mixture of lithium-niobium and lithium-tantalum alkoxide solutions. The epitaxy and crystallinity of the films were much improved when the film growth rate was raised from 20 to 180–380 nm/min, where the films with the (006) rocking curve full width at half maximum values as low as 0.12°–0.2° could be produced. The film roughness could be reduced by using a liquid precursor with higher metal concentrations, achieving the root-mean-square value on the order of 5 nm. The refractive indices of the films are in good correspondence with their composition and crystallinity.
Surface morphology and dynamic scaling in growth of iron nitride thin films deposited by dc magnetron sputtering
Authors: Wang X. , Zheng W. T. , Gao L. J. , Wei L. , Guo W. , Bai Y. B. , Fei W. D. , Meng S. H. , He X. D. , Han J. C.
Published: July 2003

Iron nitride films were deposited by dc magnetron sputtering using an Ar/N2 gas mixture. The structure, roughness, and surface morphology of the films were investigated using x-ray diffraction, grazing incidence x-ray scattering (GIXS), and atomic force microscopy (AFM). It was found that the morphologies and structures of the films were influenced by the N2 fraction. The perpendicular fluctuations in the height h(x,t) of the surface were also analyzed by AFM and GIXS in the light of dynamical scaling approach. The surfaces of the films typically exhibited self-affining structures both in space and in time. The two dependent nontrivial exponents, roughness exponent α and growth exponent β, were determined. For the iron nitride films grown at N2 fraction of 5%, 10%, and 30%, α≈0.65, 0.56, and 0.39, and β≈0.53±0.02, 0.38±0.02, and 0.29±0.03, respectively. The scaling relationship α+α/β≈2 is obeyed in all samples, which is in agreement with Kardar–Parisi–Zhang universality. The discrepancies between the theoretical foundations of dynamic scaling and experimental results have been discussed as well.
Oxygen environmental Auger electron spectroscopy: Eliminating the electron beam effects on Al2O3 during Auger analysis
Authors: Guo Hansheng , Maus-Friedrichs W. , Kempter V. , Ji Y.
Published: July 2003

The charging phenomena and charge compensation under electron beam irradiation have been studied on alumina using Auger electron spectroscopy (AES). Electron-beam effects, observed in AES as oxygen depletion, contamination from residual gas, and charge-up, can be efficiently reduced in an oxygen environment of ⩽5×10−8 Torr O2. The oxygen environmental Auger electron spectroscopy reveals an inherent relation between the oxygen depletion and the charge-up of alumina: Oxygen depletion due to electron-stimulated desorption, preceding the other electron-beam effects, is the primary cause of the charge-up of alumina. The charging phenomena of alumina and the efficiency of the O2 environment for charge compensation can be interpreted in terms of the general energy band schema.
Investigation of SrBi2Ta2O9 thin films etching mechanisms in Cl2 /Ar plasma
Authors: Efremov A. M. , Kim D. P. , Kim C. I.
Published: July 2003

An investigation of the SrBi2Ta2O9 (SBT) etching mechanism in a Cl2/Ar plasma was carried out. Experiments showed that an increase of the Ar mixing ratio under constant pressure and input power conditions leads to increasing an etch rate of SBT, which reaches a maximum value when the Ar is 80% of the gas. The modeling of volume kinetics using the measured electron temperature and electron density indicated monotonic changes of both densities and fluxes of active species such as chlorine atoms and positive ions. Nevertheless, an analysis of surface kinetics in the framework of an ion-assisted etching mechanism confirms the possibility of nonmonotonic etch rate behavior due to the concurrence of physical sputtering and chemical etching activated by ion bombardment.
C 4 F 8 dissociation in an inductively coupled plasma
Authors: Radtke M. T. , Coburn J. W. , Graves David B.
Published: July 2003

A study of the dissociation of a small concentration of cyclic-C4F8 (c-C4F8) in a predominately argon, low pressure inductively coupled plasma is reported. Measurements of electron density, plasma potential, and electron energy distribution function (EEDF) were made at several pressures and over a range of dilute Ar/C4F8 plasmas using a Langmuir probe. The c-C4F8 concentration in the plasma was estimated using appearance potential mass spectrometry and ion mass spectrometry. Optical emission spectroscopy was used to estimate the gas temperature and total neutral number density. Volume-averaged total dissociation rate coefficients for c-C4F8 ionization and total dissociation into neutrals were calculated using reported cross sections and the measured EEDFs. Rate coefficients inferred by both methods were in agreement within experimental uncertainties and approximations of the model, indicating that the dissociation cross sections are accurate.
Potential application of tungsten carbides as electrocatalysts
Authors: Hwu Henry H. , Chen Jiangguang G.
Published: July 2003

The reactions of methanol, water, and carbon monoxide over clean and modified tungsten carbide surfaces are studied by using temperature programmed desorption, high-resolution electron energy loss spectroscopy, and Auger electron spectroscopy. The carbide-modified W(111) surface is highly active toward the decomposition of methanol, with 55% going to complete decomposition, 31% to CO, and 14% to CH4. Additionally, the C/W(111) surface exhibits strong activity toward the dissociation of water. Furthermore, the desorption of CO from C/W(111) occurs at a relatively low temperature of ∼330 K. When modified by the presence of submonolayer Pt, the decomposition pathways of methanol are significantly altered. The presence of low-coverage Pt onto C/W(111) effectively inhibits the production of CH4, an undesirable side product in direct methanol fuel cells. The Pt-modified C/W(111) surface also remains active toward the dissociative of water. When C/W(111) is modified by oxygen, the surface retains significant activity toward water and methanol, and at the same time lower the CO desorption temperature to 242 K. Finally, the investigations on carbide-modified W(110) reveal minor structure sensitivity in terms of product selectivities, while the overall activity values of methanol and water on the two C/W surfaces are nearly identical. The results on the C/W(111), Pt/C/W(111), O/C/W(111), and C/W(110) surfaces are compared to those on the Ru(0001) and Pt(111) surfaces.
High-frequency noise measurements in spin-valve devices
Authors: Stutzke N. A. , Burkett S. L. , Russek S. E.
Published: July 2003

High-frequency magnetic noise in magnetoresistive devices being developed for read-sensor and magnetic random access memory applications may present fundamental limitations on the performance of submicrometer magnetic devices. High-frequency magnetic noise (HFN) arises from intrinsic thermal fluctuations of the device magnetization. High-frequency noise spectroscopy provides a powerful tool to characterize the dynamics and response of small multilayer magnetic devices. In this study, the noise characteristics of micrometer-dimension spin valves have been investigated at frequencies in the range 0.1–6 GHz. At frequencies below this range 1/f noise dominates. HFN measurements, as a function of bias current and longitudinal magnetic field, are obtained for IrMn exchange-biased spin valves using a 50 GHz spectrum analyzer, low-noise amplifier, and a microwave probing system. The magnetic noise is obtained by taking the difference between the noise spectrum of the device in a saturated and unsaturated state. The data can be fit to simple models that predict the noise power to be proportional to the imaginary part of the free-layer magnetic susceptibility. There are some important differences between the high-frequency noise measurements and direct measurements of the device susceptibility (both at the device and wafer level). The noise measurements show a smaller damping parameter (a smaller ferromagnetic resonance linewidth) and additional features due to the presence of nonuniform modes.
Substrate temperature effects on surface reactivity of SiFx (x=1, 2) radicals in fluorosilane plasmas
Authors: Williams K. L. , Fisher E. R.
Published: July 2003

Control of substrate temperature (TS) during plasma etching and film deposition using fluorinated silicon gases has profound effects on etch and deposition rates as well as the overall composition of deposited materials. How TS directly affects individual species and reactions at the plasma–surface interface, however, is not fully understood. Using the imaging of radicals interacting with surfaces technique, we have measured the effect of TS on SiF and SiF2 surface reactivity in SiF4 and SiF4:H2 plasmas under a variety of plasma conditions. At TS=300 K, there is significantly more SiF2 than SiF emanating from the surface. This is expected as SiF2 is a known etch product. Interestingly, higher substrate temperatures result in significant increases in surface scatter for both molecules. These results are discussed with respect to the role that each molecule plays in etching and deposition mechanisms, as well as in comparison to results for plasma species in other plasma systems. In addition to surface interaction measurements, rotational temperatures (θR) for SiF and SiF2 were measured in a 170 W plasma as 450±50 and 752±100 K, respectively.
Correlation between crystallographic orientations and Raman spectra of TiO2 sputtered films with changing degrees of plasma exposure
Authors: Takahashi T. , Nakabayashi H. , Tanabe J. , Yamada N. , Mizuno W.
Published: July 2003

Most of the titanium dioxide (TiO2) films deposited in this study were transparent and had anatase crystal structures, while some of the films were semitransparent. The anatase phase of the as-deposited films was revealed in the Raman spectra with a Raman shift of 145 cm−1 and x-ray diffraction patterns. When the films were deposited at the working gas pressure (PW) of 3 mTorr with increasing plasma exposure, the highest intensity of the peak which had a Raman shift of 145 cm−1 steeply increased with preferential enhancement of the crystallographic orientation of the A(220) plane, where A shows the anatase phase of TiO2. However, in the films deposited at the PW of 1 mTorr with decreasing plasma exposure, such Raman peak intensity gradually decreased at the condition that the preferential crystallographic orientation changed from A(220) to A(101). This implies that the change in the Raman peak intensity may be closely related to the change in the A(220) peak intensity. When the TiO2 crystallites became larger regardless of the PW, the A(220) peak was significantly higher than other peaks. It was found that the Raman peak intensity of the as-deposited TiO2 films was strongly affected by the degree of the plasma exposure, which was related to the substrate position during film deposition.
Chemical vapor deposition-formed p-type ZnO thin films
Authors: Li X. , Yan Y. , Gessert T. A. , Perkins C. L. , Young D. , DeHart C. , Young M. , Coutts T. J.
Published: July 2003

We have fabricated nitrogen-doped zinc oxide (ZnO) films that demonstrate p-type behavior by using metalorganic chemical vapor deposition. In our experiment, diethylzinc is used as a Zn precursor, and NO gas is used to supply both O and N to form a N-doped ZnO (ZnO:N) film. With these precursors, we have routinely reached an N concentration in the ZnO films of about 1–3 at. %. When the N concentration level is higher than 2 at. %, the films demonstrate p-type characteristics. The carrier concentration of the films varies from 1.0×1015 to 1.0×1018 cm−3, and mobilities are mainly in the 10−1 cm2 V−1 s−1 range. The lowest film resistivity achieved is ∼20 Ω cm.