bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic and static measurements on epitaxial Fe/Si/Fe
Authors: Kuanr Bijoy K. , Buchmeier M. , Buergler D. E. , Gruenberg P. , Camley R. , Celinski Z.
Published: July 2003

Strong antiferromagnetic interlayer exchange coupling across an insulating spacer is in increasing demand for high-density magnetic recording. We report here on the interlayer exchange coupling of epitaxial Fe(8 nm)/Si(t)/Fe(10 nm) trilayers as a function of Si thickness studied by ferromagnetic resonance (FMR), Brillouin light scattering, and magneto optic Kerr effect (MOKE) measurement techniques. A very strong antiferromagnetic (AFM) interlayer exchange coupling (>6 erg/cm2) was observed at a spacer Si thickness of 0.7 nm. The bilinear J1 and biquadratic J2 coupling constants were determined from (i) the fitting of the angular variation of the resonance field (Hres) in FMR experiments, (ii) the field variation of the frequencies of the Damon–Eshbach surface modes (both optic and acoustic) in BLS measurements, and (iii) the fitting of longitudinal MOKE hysteresis loops. We obtain a higher Hres along the easy axis than along the hard axis and the magnetizations of the two Fe films are canted. The eightfold-like symmetry of Hres as a function of the angle observed at room temperature is due to the competition between the Fe fourfold anisotropy and AFM interfacial coupling energy. This behavior vanishes at low temperatures due to a strong increase of AFM coupling (especially J2) in comparison to fourfold in-plane anisotropy. From the fitting of the temperature dependent FMR data, we obtain the temperature variation of the bilinear and biquadratic exchange coupling constants. We distinguish the existence of canted magnetization states at resonance by fitting the experimental Hres versus θH data to the model calculation.
Kinetic Monte Carlo simulations of the autocatalytic adsorption effect: CO on ZnO
Authors: Stephan J. , Burghaus U.
Published: July 2003

An increase in the coverage dependent adsorption probability with increasing coverage, i.e., an autocatalytic adsorption phenomenon, has frequently been observed. We present a time dependent (kinetic) Monte Carlo simulation scheme which can also account for this phenomenon. The scheme is tested for different adsorption scenarios and is compared with experimental results of CO adsorption on polar ZnO surfaces [T. Becker et al., J. Chem. Phys. 113, 6334 (2000)].
Experimental study on a new sterilization process using plasma source ion implantation with N2 gas
Authors: Yoshida M. , Tanaka T. , Watanabe S. , Takagi T. , Shinohara M. , Fujii S.
Published: July 2003

Plasma source ion implantation (PSII) with negative high voltage pulses has been applied to the sterilization process as a technique suitable for sterilization of three-dimensional work pieces. Pulsed high negative voltage (0–10 μs pulse width, 900 pulses/s, −9 to −16 kV) was applied to the electrode in this process at a gas pressure of 2–7 Pa of N2. This process has been found to be capable of generating glow discharge plasma around a stainless electrode, on which quartz glass samples with biological materials are placed. We found that the PSII process reduced the numbers of active Bacillus pumilus cells using N2 gas plasma generated by pulsed dc voltages. The number of bacteria survivors was reduced by 105×with 5–10 min exposure. The state of cells on quartz glass was observed by scanning electron microscopy with and without exposure. We found that the ion energy is the most important processing parameter. The technique is demonstrated to be an effective means of low-temperature surface sterilization, with very little damage to the target.
Atomic layer deposition of Al2O3 thin films using dimethylaluminum isopropoxide and water
Authors: Cho Wontae , Sung Kiwhan , An Ki-Seok , Sook Lee Sun , Chung Taek-Mo , Kim Yunsoo
Published: July 2003

Dimethylaluminum isopropoxide (DMAI), (CH3)2AlOCH(CH3)2, a precursor originally developed for the metalorganic chemical vapor deposition of alumina, was adopted as a new precursor for growing aluminum oxide thin films on HF-treated Si(001) substrates by atomic layer deposition (ALD). This precursor is stable for a prolonged period of storage time under inert atmosphere (such as in nitrogen or argon) and does not react vigorously in air, and therefore is easy to handle and safe, without causing hazards. The self-limiting ALD process by alternate surface reactions of DMAI and H2O was confirmed by thicknesses of the grown aluminum oxide films measured as functions of the DMAI pulse time and the number of DMAI-H2O cycles. A maximum growth rate of ∼1.06 Å/cycle was achieved in the substrate temperature range ∼120–150 °C. Growth of stoichiometric Al2O3 thin films without appreciable carbon incorporation was verified by Rutherford backscattering spectrometry. Atomic force microscopy images showed atomically flat and uniform surfaces. In particular, a cross-sectional high-resolution transmission electron microscopy image of an Al2O3 film shows that there is no distinguishable interfacial oxide layer between the Al2O3 film and the Si substrate. These results prove the validity of DMAI as a new ALD source for aluminum oxide.
Characterizing topography-induced contrast in photoelectron emission microscopy
Authors: Siegrist K. , Williams E. D. , Ballarotto V. W.
Published: July 2003

As part of an ongoing study to quantify the imaging response of the photoelectron emission microscope (PEEM), we have investigated the effect of sample topography on PEEM contrast. Both numerical simulations and well characterized samples were used to investigate topography-induced contrast. As expected, numerical simulations show that the lateral field strength that is present at a step edge is the same order of magnitude as the perpendicular accelerating field strength (103 V/mm) used for imaging. Consequently, electrons emitted near a step edge can be displaced from the image collection volume and thus generate image contrast. Simulations have also shown, in agreement with experiments, that the lateral field strength increases as the step height increases and as a result edge contrast increases with step height. In addition, we have found that for a metal line entrenched in a charged oxide, the edge contrast is observed to increase significantly. We attribute this effect to a constant lateral surface field. Furthermore, we show that edge contrast due to topography can be distinguished from a constant lateral surface field by varying the accelerating field strength.
Bias voltage dependence of apparent local barrier height at constant tip–sample separation
Authors: Yagyu Shinjiro , Yoshitake Michiko
Published: July 2003

The bias voltage dependence of the apparent local barrier height (LBH) corresponding to the “work function” on a nanometer-scale was measured by scanning tunneling microscopy on an Au (111) surface with an Au tip. There have been reports of the bias voltage dependence of the LBH under constant current (CC) conditions. However, under CC, a change in the bias voltage causes a change in the tip–sample separation. In this situation, the measured results contain both effects (the bias voltage and the separation). Therefore, to accurately measure the effect of the bias voltage on the LBH, the separation effects must be eliminated. We measured the bias voltage dependence of the LBH at a constant separation (CS) using the current on the current–voltage (I–V) curve and compared the results with CC. For CS measurements, in the ohmic range (the I–V curve is linear), the LBH does not depend on the bias voltage within the experimental error. Beyond the ohmic range, the LBH decreases with increased bias voltage. In contrast, CC measurement results are clearly affected by both effects. In the region where the separation effect can be neglected, the CC result corresponds to the CS result.
Indium tin oxide films with low resistivity and low internal stress
Authors: Takayama Shinji , Sugawara Toshifumi , Tanaka Akira , Himuro Tokuji
Published: July 2003

Indium tin oxide (ITO) films prepared by dc magnetron sputtering were annealed in air, vacuum, and oxygen gas atmospheres. The electrical properties and internal stresses of these annealed ITO films were systematically investigated. It was found that, among the above postannealing treatments, oxygen gas annealing significantly reduced both the resistivity and the internal stress in ITO films at fairly low temperatures of 100–150 °C. Resistivities and internal stresses as low as 7×10−4 Ω cm and 38 MPa, respectively, were obtained by annealing in oxygen gas atmosphere at 100 °C. It was also revealed that the (111) crystal orientation becomes dominant and that whole grains grow dramatically as a result of postoxygen annealing, even at 100 °C.
Correlation between microstructural and magnetic properties in Fe/KCoF3 bilayers
Authors: Malkinski L. , O’Keevan T. , Camley R. E. , Celinski Z. , He J. , Zhou W. L. , Hecker M. , Schneider C. M. , Szade J. , Skrzypek D.
Published: July 2003

Molecular beam epitaxy was used to grow a ferromagnet/antiferromagnet (Fe/KCoF3) system. A series of structural, surface, and magnetic characterization techniques were used to understand the correlation between microstructural and magnetic properties in this exchange bias system. Depending on deposition conditions, the fluoride grew either in a single crystal or a polycrystalline form, which was initially confirmed by reflection high energy electron diffraction patterns and x-ray studies. The crystalline form of the KCoF3 significantly affected the magnetic properties, in particular the exchange bias and the magnetocrystalline anisotropy of the Fe layer. Transmission electron microscopy (TEM) studies were carried out to shed more light on the microstructure of the fluoride and on the interface between Fe and KCoF3 layers. Single crystals KCoF3 layers grown at elevated temperature on (001) Fe template have a (001) orientation. On the other hand, the cross-sectional TEM images of the polycrystalline fluoride deposited at room temperature show columnar structure of the grains with a column diameter of about 10 nm. In addition, planar defects were observed in the Fe layer due to the slight mismatch between Fe and KCoF3 lattices. These defects and grain boundaries in the antiferromagnet are responsible for considerable modification of magnetic properties of the structures with polycrystalline fluoride compared to those with the single crystal KCoF3. Magnetic anisotropy and the exchange bias were measured using ferromagnetic resonance and superconducting quantum interference device magnetometry, respectively. The exchange bias and blocking temperature in the samples with polycrystalline fluoride were significantly reduced, however, the low-temperature fourfold anisotropy was enhanced by a factor of 3 for the samples with 1-nm-thick Fe and polycrystalline fluoride compared to the samples with the same thickness of Fe but single crystal fluoride.
Inductively coupled Cl2/Ar plasma: Experimental investigation and modeling
Authors: Efremov A. M. , Kim Dong-Pyo , Kim Chang-Il
Published: July 2003

Electrophysical and kinetic characteristics of Cl2/Ar plasma were investigated to understand the influence of the addition of Ar on the volume densities and fluxes of active particles, both neutral and charged. Our analysis combined both experimental methods and plasma modeling. It was found that addition of Ar to Cl2 leads to deformation of the electron energy distribution function and an increase of the electron mean energy due to the “transparency” effect. Direct electron impact dissociation of Cl2 molecules represents the main source of chlorine atoms in the plasma volume. The contributions of stepwise dissociation and ionization involving Ar metastable atoms were found to be negligible. Addition of Ar to Cl2 causes the decrease of both electron and ion densities due to a decrease in the total ionization rate and the acceleration of heterogeneous decay of charged particles.
Self-assembly and magnetism in core-shell microspheres
Authors: Bizdoaca E. L. , Spasova M. , Farle M. , Hilgendorff M. , Liz-Marzan L. M. , Caruso F.
Published: July 2003

We report on the fabrication and characterization of magnetic composite colloids with a defined shape, composition and multilayer shell thickness. They consist of a core of a polystyrene microsphere (640 nm diameter) coated with consecutive shells of Fe3O4 nanoparticles (12 nm diameter), polyelectrolytes and Au nanoparticles (15 nm). The homogeneity of the coating was confirmed by transmission electron microscopy. Composite core-shell microspheres were self-assembled into periodically ordered chains up to 2 mm in length by magnetophoretic deposition. The self-organization was visualized by optical and atomic force microscopy. Magnetic properties were determined by angular dependent ferromagnetic resonance (FMR) and superconducting quantum interference device magnetometry between 5 and 300 K. The FMR reveals long-range magnetic order at 300 K due to dipolar coupling and an easy axis in plane along the chains. We find a magnetic moment that is reduced in comparison with the magnetite bulk value.
Effects of growth temperature on the properties of atomic layer deposition grown ZrO2 films
Authors: Scarel G. , Ferrari S. , Spiga S. , Wiemer C. , Tallarida G. , Fanciulli M.
Published: July 2003

Zirconium dioxide films are grown in 200 atomic layer deposition cycles. Zirconium tetrachloride (ZrCl4) and water (H2O) are used as precursors. A relatively high dielectric constant (κ=22), wide band gap, and conduction band offset (5.8 and 1.4 eV, respectively) indicate that zirconium dioxide is a most promising substitute for silicon dioxide as a dielectric gate in complementary metal–oxide–semiconductor devices. However, crystallization and chlorine ions in the films might affect their electrical properties. These ions are produced during atomic layer deposition in which the ZrCl4 precursor reacts with the growth surface. It is desirable to tune the composition, morphology, and structural properties in order to improve their benefit on the electrical ones. To address this issue it is necessary to properly choose the growth parameters. This work focuses on the effects of the growth temperature Tg. ZrO2 films are grown at different substrate temperatures: 160, 200, 250, and 350 °C. Relevant modification of the film structure with a change in substrate temperature during growth is expected because the density of reactive sites [mainly Si+1–(OH)−1 bonds] decreases with an increase in temperature [Y. B. Kim et al., Electrochem. Solid-State Lett. 3, 346 (2000)]. The amorphous film component, for example, that develops at Si+1–(OH)−1 sites on the starting growth surface, is expected to decrease with an increase in growth temperature. The size and consequences of film property modifications with the growth temperature are investigated in this work using x-ray diffraction and reflectivity, and atomic force microscopy. Time of flight-secondary ion mass spectrometry is used to study contaminant species in the films. From capacitance–voltage (CV) and current–voltage (IV) measurements, respectively, the dielectric constant κZrO2 and the leakage current are studied as a function of the film growth temperature.
Epitaxial growth of thin Ag and Au films on Si(111) using thin copper silicide buffer layers
Authors: Pedersen Kjeld , Morgen Per , Pedersen Thomas G. , Li Zheshen , Hoffmann Søren V.
Published: July 2003

Synchrotron radiation photoemission experiments show that a thin copper silicide layer formed by depositing the equivalent of six layers of Cu on Si(111) serves as an excellent buffer for additional growth of Ag and Au overlayers. Introduction of this buffer below a Ag film leads to enhanced quantization effects in the valence band spectra and the appearance of a Ag(111) surface state. Without the buffer layers this surface state shifts above the Fermi level due to strain in the film. Strong coupling is observed between the quantized Ag sp band and the Cu d band but the coupling to the Cu sp band found for Ag on bulk Cu is absent. In the case of Au overlayers the copper silicide layer prevents the reaction between Si and Au that otherwise results in the formation of a reacted layer on top of the Au film. Introduction of the buffer layer leads to Au film properties characteristic of the (111) surface such as a surface component in the core level spectra and a surface state just below the Fermi level.
Large remanent polarization of cerium-modified bismuth–titanate thin films for ferroelectric random access memories
Authors: Kim Kyoung-Tae , Kim Chang-Il , Kang Dong-Hee , Shim Il-Wun
Published: July 2003

Cerium-substituted Bi4Ti3O12 (Bi3.4Ce0.6Ti3O12) thin films were prepared by using metal-organic decomposition method. Ferroelectric cerium-substituted Bi4Ti3O12 thin films were fabricated by spin coating onto a Pt/Ti/SiO2/Si substrate. The structure and morphology of the films were characterized using x-ray diffraction and scanning electron microscopy. The Bi3.4Ce0.6Ti3O12 (BCeT) thin films, which were annealed from 550 to 700 °C for 1 h, showed a perovskite phase and dense microstructure. The BCeT thin films annealed at temperature as low as 550 °C become crystallized and exhibit a polycrystalline structure with ferroelectric properties. The 200-nm-thick BCeT thin films annealed at 700 °C showed a large remanent polarization (2Pr) of 62.1 μC/cm2 at an applied voltage of 10 V and exhibited a fatigue-free behavior up to 5×1010 switching cycles at a frequency of 100 kHz. These experimental results are thought to be promising to use cerium-substituted Bi4Ti3O12 thin films as capacitors of ferroelectric access memory applications.
Scanning tunneling microscopy studies of the Cu:Si(5 5 12) system
Authors: Woodworth P. H. , Moore J. C. , Baski A. A.
Published: July 2003

The growth of Cu on the stable Si(5 5 12) clean surface has been studied as a function of coverage and temperature using scanning tunneling microscopy. Similar to previously studied group IB metals, Cu produces overlayer “nanowires” at lower growth temperature (<500 °C), where the 5.4 nm periodicity of the (5 5 12) surface is maintained. At higher temperatures (>500 °C), however, the underlying Si surface is disrupted and Cu induces faceting to the nearby (113) plane. At coverages above approximately 0.5 ML, the surface rearranges to form sawtooth facets composed of wide (113) planes opposed by narrow (111) segments. The (113) planes show a Cu-induced 2×2 surface reconstruction that incorporates a large number of domain boundaries. We have also studied the O2 reactivity of the Cu-induced (113)/(111) sawtooths. At temperatures above 650 °C, the sawtooths are gradually etched away to produce trapezoidal islands. The density of these islands decreases with increasing temperature, providing a possible route for the controlled fabrication of such nanostructures.
Energetic neutral fluxes towards surfaces in a magnetically enhanced reactive ion etch-like reactor
Authors: Sabisch Winfried , Kratzer Matthias , Brinkmann Ralf Peter
Published: July 2003

In very large scale integrated microelectronics fabrication magnetically enhanced reactive ion etch (MERIE) reactors are established for many dry etch processes of conducting or dielectric materials. Angularly and energetically resolved distributions of the surfaces incident particles (ions and neutrals) as well as the fluxes of ions and neutrals play an essential role for feature scale profile evolution. The focus of this work is set on the calculation of the neutral to ion fluxes ratio. Therefore the MERIE reactor’s boundary sheath is simulated by the technology-oriented computer aided design simulation tool hybrid plasma sheath model (HPSM). HPSM consists of a self-consistent coupling of a fluid dynamical part to a Monte Carlo part. The sheath and presheath regions are described in one unified model. Energetic neutrals impinging the surface can be monitored in addition to the positive ion species. Simulations with parameters in the range of about 100 mTorr, rf voltages of a few 100 V, magnetic fields of about 90 G, and plasma powers of about 1000 W are presented. The simulations show that the flux of the energetic neutrals compared to the flux of the ions is not neglectable and that the neutral flux makes an important contribution to the energy budget of the surface impinging particles.
Microhollow cathode discharges
Authors: Schoenbach K. H. , Moselhy M. , Shi W. , Bentley R.
Published: July 2003

By reducing the dimensions of hollow cathodes into the hundred micrometer range, stable, direct current, high (atmospheric) pressure glow discharges in rare gases, rare gas–halide mixtures and in air could be generated. The electron energy distribution in these microdischarges is non-Maxwellian, with a pronounced high-energy tail. The high electron energy together with the high gas density, which favors three-body collisions, is the reason for an efficient excimer generation in these microplasmas. Excimer efficiencies from 1% to 9% have been measured for argon, xenon, argon fluoride, and xenon chloride direct current excimer emitters, with a radiant excimer emittance of up to 2 W/cm2 for xenon. Adding small amounts of oxygen to argon has allowed us to generate vacuum ultraviolet line radiation at 130.5 nm with an efficiency approaching 1%. Pulsing xenon discharges with nanosecond electrical pulses has led to an increase in intensity to 15 W/cm2 and to a simultaneous increase in efficiency to more than 20%. Operating the discharges in an abnormal glow mode has allowed us to generate microdischarge arrays without individual ballast. Applications of these plasma arrays are excimer lamps and plasma reactors.
Using chemical probes to investigate properties of monolayer metal thin films
Authors: Khan Neetha A. , Chen Jingguang G.
Published: July 2003

In this study, we have compared the results of using chemical probes on model surfaces to investigate reactivity of monolayer Ni films on Pt(111), W(110), and Ru(0001) single crystal surfaces. Using H2, cyclohexene, and ethylene as probe molecules, we have studied the metal–H bond strength, the hydrogenation of cyclohexene, and the bonding and decomposition of ethylene. The Ni/Pt(111) and Ni/W(110) surfaces exhibit a low-temperature desorption of hydrogen at monolayer Ni coverages [also at 0.4 ML for the Ni/W(110) surfaces]. In contrast, the presence of monolayer Ni on Ru(0001) does not induce the low-temperature desorption state of hydrogen on the Ni/Ru(0001) surface. This desorption at low temperature is an indication of a weaker metal–H bond, which will affect the hydrogenation activity of the surfaces. For example, on the 1 ML Ni/Pt(111) and the 0.4 ML Ni/W(110) surfaces, a low-temperature hydrogenation pathway is detected. Previous high-resolution electron energy loss spectroscopy results indicate that cyclohexene is weakly π bonded to the Ni/Pt(111) surface, but it is strongly bonded to the Ni/W(110) surface. These results further confirm the importance of weakly bonded hydrogen for the enhancement of the hydrogenation pathway. Finally, the 1 ML Ni/Pt(111) surface is relatively inactive toward ethylene decomposition, while the 1 ML Ni/Ru(0001) surface remains active toward the dissociation of ethylene.
Scanning tunneling microscopy imaging of charged defects on clean Si(100)-(2×1)
Authors: Brown G. W. , Grube H. , Hawley M. E. , Schofield S. R. , Curson N. J. , Simmons M. Y. , Clark R. G.
Published: July 2003

We have used scanning tunneling microscopy (STM) to image charged defects on the clean (100)-(2×1) surface of p-type silicon. In the absence of “C”-type defects, band bending can occur during STM imaging, allowing near surface charge to influence the state density contributing to the tunnel current. As in the case of cleavage faces of III–V semiconductor crystals, the charge-induced band bending produces long range enhancements superimposed on the periodic surface lattice. The charged defects observed in this work are of the types commonly observed elsewhere in clean Si(100)-(2×1) STM studies, however, not all defects of a given type appear charged. This would indicate subtle differences in defect structure that are not obvious at higher sample bias. This work demonstrates the ability to observe charged features on the clean Si(100) surface, which will be important for current and future research focused on producing atomic scale electronic structures.
Reduction of etching damage in lead–zirconate–titanate thin films with inductively coupled plasma
Authors: Lim Kyu-Tae , Kim Kyoung-Tae , Kim Dong-Pyo , Kim Chang-Il
Published: July 2003

In this work, we etched lead–zirconate–titanate (PZT) films with various additive gases (O2 and Ar) in Cl2/CF4 plasmas, while mixing ratio was fixed at 8/2. After the etching, the plasma induced damages are characterized in terms of hysteresis curves, leakage current, retention properties, and switching polarization. When the electrical properties of PZT etched in O2 or Ar added to Cl2/CF4 were compared, the value of remanent polarization in O2 added to Cl2/CF4 plasma is higher than that in Ar added plasma. The maximum etch rate of the PZT thin films was 145 nm/min for 30% Ar added Cl2/CF4 gas having mixing ratio of 8/2 and 110 nm/min for 10% O2 added to that same gas mixture. In order to recover the ferroelectic properties of the PZT thin films after etching, we annealed the etched PZT thin films at 550 °C in an O2 atmosphere for 10 min. From the hysteresis curves, leakage current, retention property, and switching polarization, the reduction of the etching damage and the recovery via the annealing turned out to be more effective when O2 was added to Cl2/CF4 than Ar. X-ray diffraction showed that the structural damage was lower when O2 was added to Cl2/CF4 and the improvement in the ferroelectric properties of the annealed samples was consistent with the increased intensities of the (100) and the (200) PZT peaks.
Product development and yield enhancement through failure analysis of integrated circuits with scanning capacitance microscopy
Authors: Tangyunyong P. , Nakakura C. Y.
Published: July 2003

The application of scanning capacitance microscopy (SCM) to failure analysis of integrated circuits is described. Both top-down (parallel to the wafer surface) and cross-sectional SCM measurements were performed on product lots containing yield-limiting failures identified with electrical testing. The SCM images of functioning devices were compared with those of failed devices to note any differences in free carrier distributions. Using this approach, the root causes of failures in two different product lots—one bulk Si technology and one silicon-on-insulator technology—were identified. These two examples are described in detail, as well as the subsequent corrective actions taken to improve yield.
Surface modification of aligned carbon nanotube arrays for electrochemical sensing applications
Authors: Soundarrajan Prabhu , Patil Ajeeta , Dai Liming
Published: July 2003

The excellent optoelectronic, mechanical, and thermal properties of carbon nanotubes have made them very attractive for a wide range of potential applications. However, many applications require the growth of aligned carbon nanotubes with surface modification. We have developed a simple pyrolytic method for large-scale production of aligned carbon nanotube arrays perpendicular to the substrate. These aligned carbon nanotube arrays can be transferred onto various substrates of particular interest (e.g., polymer films for organic optoelectronic devices) in either a patterned or non-patterned fashion. The well-aligned structure further allows us to prepare aligned coaxial nanowires by electrochemically depositing a concentric layer of an appropriate conducting polymer onto the individual aligned carbon nanotubes. This approach is particularly attractive, as it allows surface characteristics of the aligned carbon nanotubes to be tuned to meet specific requirements for particular applications while their alignment structure can be largely retained. These aligned carbon nanotubes with tunable surface characteristics are of great significance to various practical applications. In this paper, we demonstrate the use of the conducting-polymer-coated aligned carbon nanotubes for electrochemical sensing applications.
Effects of graphite content on carbon nitride films prepared by hot carbon filament chemical vapor deposition
Authors: Aizawa Shinichiro , Aono Masami , Kitazawa Nobuaki , Watanabe Yoshihisa , Shimizu Osamu , Suda Yoshihisa
Published: July 2003

Carbon nitride (CNx) thin films were prepared by a hot carbon filament chemical vapor deposition. Several kinds of carbon coils, which are composed of graphite and glassy carbon, were applied as filaments. The carbon coil was heated at about 2073 K in a nitrogen atmosphere of 100 Pa. Effects of the graphite content of the filament on the film microstructure, surface morphology and the nitrogen content in the CNx films were studied by using field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS). FE-SEM observations show that the CNx films change from densely columnar to noncolumnar structures with increasing graphite content. AFM observations reveal that the average roughness of the film surface increases with increasing graphite content. It is found from the XPS analysis that the nitrogen content does not depend strongly on the graphite content. The filament with the low graphite content is suitable for preparing CNx films with a dense structure and smooth surface.
Progress in spectroscopic ellipsometry: Applications from vacuum ultraviolet to infrared
Authors: N. Hilfiker James , Bungay Corey L , Synowicki Ron A. , Tiwald Thomas E. , Herzinger Craig M. , Johs Blaine , Pribil Greg K. , Woollam John A.
Published: July 2003

Spectroscopic ellipsometry (SE) is a noncontact and nondestructive optical technique for thin film characterization. In the past 10 yr, it has migrated from the research laboratory into the semiconductor, data storage, display, communication, and optical coating industries. The wide acceptance of SE is a result of its flexibility to measure most material types: dielectrics, semiconductors, metals, superconductors, polymers, biological coatings, and even multilayers of these materials. Measurement of anisotropic materials has also made huge strides in recent years. Traditional SE measurements cover the ultraviolet, visible, and near infrared wavelengths. This spectral range is now acquired within seconds with high accuracy due to innovative optical configurations and charge coupled device detection. In addition, commercial SE has expanded into both the vacuum ultraviolet (VUV) and midinfrared (IR). This wide spectral coverage was achieved by utilizing new optical elements and detection systems, along with UV or Fourier transform IR light sources. Modern instrumentation is now available with unprecedented flexibility promoting a new range of possible applications. For example, the VUV spectral region is capable of characterizing lithographic materials for 157 nm photolithography. The VUV also provides increased sensitivity for thin layers (e.g., gate oxides or self-assembled monolayers) and allows investigation of high-energy electronic transitions. The infrared spectral region contains information about semiconductor doping concentration, phonon absorption, and molecular bond vibrational absorptions. In this work, we review the latest progress in SE wavelength coverage. Areas of significant application in both research and industrial fields will be surveyed, with emphasis on wavelength-specific information content.
Electrical contact behavior of Ni/C60/4H–SiC structures
Authors: Lu Weijie , Mitchel W. C. , Landis G. R. , Crenshaw T. R. , Collins W. Eugene
Published: July 2003

A C60 interfacial layer between a Ni film and SiC improves the Ohmic contact properties significantly. The C60 film is deposited by the Langmuir–Blodgett method prior to the Ni film deposition on SiC using dc sputtering. High quality Ohmic contacts of Ni/C60/4H–SiC are formed after annealing at 800 °C in Ar for 2 h with a specific contact resistivity of 1.17×10−6 Ω cm2 on SiC with a doping concentration of 1.8×1019 cm−3. Raman spectra reveal that Ohmic contacts are formed after C60 is decomposed and converted to graphitic states. The formation of Ohmic contacts and the graphitic structures in the annealed film of Ni/C60/SiC are similar to that of Ni/C/SiC, for which the Ni catalytic graphitization effects play the determining role in forming Ohmic contacts on SiC. Scanning electron microscopy images show a direct relationship between the graphitized morphological features on the films and Ohmic contact behavior.
Simplified model for calculating the pressure dependence of a direct current planar magnetron discharge
Authors: Buyle G. , Depla D. , Eufinger K. , Haemers J. , De Gryse R. , De Bosscher W.
Published: July 2003

A simplified model for the direct current planar magnetron discharge allowing one to simulate the pressure dependence over a wide range is presented. For sufficiently strong magnetic fields, the high energy electrons (HEE), the electrons that are responsible for the ionization, move predominantly in arch shaped regions in between interactions with the discharge gas. This allows one to model the discharge as being built up by arches. The influence of the interactions of the HEE on their motion is modeled by calculating the probabilities for transfer of HEE among the arch shaped regions. In this way the ionization distribution of the electrons emitted at a certain position at the target surface can be calculated. The results of this approach agree well with Monte Carlo results. This modeling of the HEE motion combined with simple schemes for determining the ionization and target erosion forms the core of the simplified model. The model is made self-consistent through iteration. It appears that for a given magnet system and discharge voltage a self-consistent solution is only possible for one particular pressure. This is the pressure for which the discharge voltage corresponds with the theoretical minimum discharge voltage needed to sustain the discharge at that pressure. The model reproduces the experimentally observed increase of the discharge voltage and widening of the erosion profile with decreasing pressure. According to the model the main cause for this pressure dependence is not the decreased confinement of electrons in the magnetic trap but the increased recapture of secondary electrons by the target.
Low temperature pulsed etching of large glass substrates
Authors: Dubost L. , Belinger A. , Perrin J. , Boswell R. W.
Published: July 2003

Glass plates of 20 cm diameter have been etched by SF6 in a pulsed capacitively coupled 13.56 MHz discharge. The plates were mechanically clamped to the cooled substrate holder and allowed to heat due to ion bombardment. The average rf power was set at 220 W and the pulse frequency varied up to 200 kHz for duty cycles between 10% and 100%. For a pressure of 50 mTorr, pulse frequencies around 100 kHz and duty cycles below 30%, the etch rate was about double that of the continuous case and the glass plate temperature was between 90 and 100 °C about 30° below the continuous case. These results show that large plates of glass can be etched rapidly at 0.16 μm per minute at temperatures below the cross linking temperature of a photoresist mask.
X-ray photoemission spectra and x-ray excited Auger spectrum investigation of the electronic structure of Pd3(PS4)2
Authors: Grasso V. , Silipigni L.
Published: July 2003

Information on the bonding states of the compositional atoms and on the occupied energy states of the Pd3(PS4)2 crystals have been obtained by investigating the Pd 3d and P and S 2p core levels and the valence band region with the x-ray photoemission spectroscopy. In particular, as far as core levels are concerned, each XPS spectrum, apart from the spin-orbit splitting, exhibits a single-peak structure suggesting the absence of nonequivalent sites for the compositional atoms. The analysis of the chemical shifts in the core-level binding energies of the constituents emphasizes their cation or anion-type behavior. As to the valence band (VB) XPS spectrum, two regions are distinguished and interpreted on the basis of the comparison with the VB XPS spectra of other palladium and (PS4)3− compounds and of some thiophosphates. Confirmation of an involvement of the Pd 4d in the bonding is also given by the analysis of the spectral shape of the x-ray induced Pd M45VV Auger transition.
Thermal stability and hydrogen atom induced etching of nanometer-thick a-Si:H films grown by ion-beam deposition on Si(100) surfaces
Authors: Biener J. , Lutterloh C. , Wicklein M. , Dinger A. , Küppers J.
Published: July 2003

Amorphous hydrogenated silicon (a-Si:H) films in the thickness range 0.1–4.5 nm were deposited on Si(100) surfaces at 350 K using the ion-beam-deposition method. The thermal stability of these a-Si:H films was studied by temperature programmed desorption spectroscopy. The films are stable up to 500 K, where a-Si:H starts to decompose via evolution of hydrogen (H2) and silane (SiH4). Approximately 99% of the hydrogen initially bound to the Si network was detected in the hydrogen channel. The hydrogen evolution peaks at ∼780 K caused by the decomposition of monohydride groups; the presence of SiH2 groups is indicated by hydrogen desorption below 700 K. The silane desorption states at 625 and 750 K reveal the existence of two different types of silyl (SiH3) groups. Etching of a-Si:H by impinging gas-phase H atoms was investigated in the temperature range from 150 to 700 K by in situ mass spectrometry. Silane was the sole etch product observed. The formation of silane proceeds via direct abstraction of silyl precursor groups by impinging hydrogen atoms, SiH3(a)+H(g)→SiH4(g); the silyl abstraction probability increases by a factor of 6 with increasing substrate temperature between 150 and 525 K. However, the steady-state erosion rate is controlled by the supply of silyl groups by successive hydrogenation of the Si network with the formation of SiH2 as bottleneck of the silyl supply.
Photoluminescence of Mg-doped GaN grown by metalorganic chemical vapor deposition
Authors: Qu B. Z. , Zhu Q. S. , Sun X. H. , Wan S. K. , Wang Z. G. , Nagai H. , Kawaguchi Y. , Hiramatsu K. , Sawaki N.
Published: July 2003

Two Mg-doped GaN films with different doping concentrations were grown by a metalorganic chemical vapor deposition technique. Photoluminescence (PL) experiments were carried out to investigate the optical properties of these films. For highly Mg-doped GaN, the PL spectra at 10 K are composed of a blue luminescence (BL) band at 2.857 eV and two excitonic luminescence lines at 3.342 eV and 3.282 eV, in addition to a L2 phonon replica at 3.212 eV. The intensity of the L1 line decreases monotonously with an increase in temperature. However, the intensity of the L2 line first slowly increases at first, and then decreases quickly with an increase in temperature. The two lines are attributed to bound excitonic emissions at extended defects. The BL band is most likely due to the transition from deep donor Mg–VN complex to Mg shallow acceptor. From the temperature dependence of the luminescence peak intensity of the BL band, the activation energy of acceptor Mg was found to be 290 meV.
Etching silicon by SF6 in a continuous and pulsed power helicon reactor
Authors: Herrick A. , Perry A. J. , Boswell R. W.
Published: July 2003

The etch rate of silicon by SF6 in a helicon reactor has been measured along with simultaneous actinometric measurements of the concentration of atomic fluorine in the gas phase for a variety of gas flow rates resulting in pressures in the mTorr range. A bias rf power was applied to the substrate to investigate the effect of ion energy on the etch rate. The etch rate was found to be proportional to the fluorine concentration and independent of the bias for the higher gas flow rates. However, at lower flow rates, the situation was more complicated and no simple model can explain the measurements. Measurements of the etch rate were also made in the afterglow of a repetitively pulsed discharge so that the directed ion energy would be reduced to the thermal motion after the rapid collapse of the plasma potential. A simple model was developed to explain the temporal etching phenomena in terms of the lifetime of the atomic fluorine.
Influence of working gas pressure on structure and properties of WO3 films reactively deposited by rf magnetron sputtering
Authors: Takahashi T. , Tanabe J. , Yamada N. , Nakabayashi H.
Published: July 2003

Tungsten trioxide (WO3) films with thickness of 0.9–6.7 μm have been deposited on glass-slide substrates, using rf magnetron sputtering in an atmosphere of mixture 80% Ar and 20% O2. The as-deposited films had a dark metallic color, like the W target, at a working gas pressure PW of 1 mTorr. Yellow films resulted at a PW of 3 mTorr. With a further increase of PW, the film color changed to pale yellow. From the x-ray diffraction patterns, the as-deposited films were polycrystalline crystallizing in the monoclinic crystal structure with high c-axis orientation perpendicular to the film plane. The optical transmittance of the films deposited at a PW of 1 mTorr is nearly zero. However, the transmittance of the films deposited at other PW are larger than 70% in the wavelength, λ, ranging from 500 to 900 nm. With decreasing λ to 400 nm, the transmittance decreases steeply to zero. The λ at this absorption edge is longer than that in TiO2 and comes in the visible region. The surface morphology of the films depends on PW. This different morphology may be attributed to the effect of the substrate heating by plasma emission because of the high plasma density at higher PW. The morphology of the films may also depend on the crystallinity of the WO3 films. As PW increased, the surfaces of the films became rougher but the grain sizes of the films did not always become larger. The WO3 films deposited in this study may be used for the underlayer of TiO2 photocatalyst.
Thermal behavior of hafnium-based ultrathin films on silicon
Authors: Pezzi R. P. , Morais J. , Dahmen S. R. , Bastos K. P. , Miotti L. , Soares G. V. , Baumvol I. J. R. , Freire F. L.
Published: July 2003

We report here on the thermodynamical stability of ultrathin, hafnium-based dielectric films, namely hafnium oxide (HfO2), silicate (HfSixOy), and aluminum silicate (AlHfxSiyOz), deposited on silicon. These materials are promising candidates to replace the well established silicon oxide and oxynitride as gate dielectric materials in advanced Si-based complementary metal–oxide–semiconductor technology. Since there are mandatory requirements on the gate dielectric material, hafnium oxide is currently being modified, by adding silicon and aluminum into the matrix, increasing its thermal stability, and improving its electrical properties. Diffusion-reaction during thermal processing was investigated using isotopic substitution together with ion beam techniques such as Rutherford backscattering spectrometry, narrow nuclear resonance profiling, and nuclear reaction analysis. The chemical changes in the films were accessed by x-ray photoelectron spectroscopy.
Valence-band x-ray photoelectron spectroscopic studies of different forms of sodium phosphate
Authors: Asunskis Amy L. , Gaskell Karen J. , Asunskis Daniel J. , Sherwood Peter M. A.
Published: July 2003

This article reports the valence-band x-ray photoelectron spectroscopy (XPS) of various forms of sodium phosphate. Valence-band spectra are compared to spectra generated from cluster and band-structure calculations. Five different forms of sodium phosphate are studied as follows, Na4P2O7, Na5P3O10, Na4P4O12, Na2H2P2O7, and NaH2PO2. Core-level XPS studies are of little use for differentiating between such similar compounds while valence band photoemission has been found to be particularly effective at identifying subtle differences in surface chemistry. The results indicate that the valence-band region clearly distinguishes between these different phosphates and that these differences can be predicted by spectra generated from both cluster and band-structure calculations.
Real-time control of ion density and ion energy in chlorine inductively coupled plasma etch processing
Authors: Chang Cheng-Hung , Leou Keh-Chyang , Lin Chaung , Lin Tsan-Lang , Tseng Chih-Wei , Tsai Chuen-Horng
Published: July 2003

In this study, we have experimentally demonstrated the real-time closed-loop control of both ion density and ion energy in a chlorine inductively coupled plasma etcher. To measure positive ion density, the trace rare gases-optical emission spectroscopy is used to measure the chlorine positive ion density. An rf voltage probe is adopted to measure the root-mean-square rf voltage on the electrostatic chuck which is linearly dependent on sheath voltage. One actuator is a 13.56 MHz rf generator to drive the inductive coil seated on a ceramic window. The second actuator is also a 13.56 MHz rf generator to power the electrostatic chuck. The closed-loop controller is designed to compensate for process drift, process disturbance, and pilot wafer effect and to minimize steady-state error of plasma parameters. This controller has been used to control the etch process of unpatterned polysilicon. The experimental results showed that the closed-loop control had a better repeatability of plasma parameters compared with open-loop control. The closed-loop control can eliminate the process disturbance resulting from reflected power. In addition, experimental results also demonstrated that closed-loop control has a better reproducibility in etch rate as compared with open-loop control.
Valence-band x-ray photoelectron spectroscopic studies of vanadium phosphates and the formation of oxide-free phosphate films on metallic vanadium
Authors: Asunskis Daniel J. , Sherwood Peter M. A.
Published: July 2003

The valence-band and core-level x-ray photoelectron spectroscopy (XPS) of vanadium phosphates are reported, and the valence-band spectra interpreted by various calculation models. The spectral interpretation of the vanadium phosphates is used to show that an oxide-free vanadium phosphate film corresponding to VO(H2PO4)2 can be prepared on vanadium metal. Three types of vanadium phosphate were investigated to provide an understanding of the XPS data for vanadium phosphates, and to demonstrate the differences between these phosphates and vanadium oxides. The three phosphates formed, VO(H2PO4)2, VOHPO4.0.5H2O, and VOPO4⋅2H2O were prepared by reaction of vanadium with phosphoric acid under a variety of conditions. The article focuses upon the valence-band region which shows significant differences between different types of vanadium phosphates as well as clear differences between the phosphates on the one hand and oxides on the other hand. The valence-band spectra are effectively interpreted by the multiple scattered-wave Xα calculations and band structure calculations.