bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogenated amorphous silicon thin films deposited by triode assisted reactive sputtering
Authors: Soukup R. J. , Kantor K. J.
Published: July 2002

Thin films of hydrogenated amorphous silicon have been deposited for solar cell and other device applications. If device quality thin films can be deposited by triode assisted sputtering, more control over film properties can be achieved than with the more thoroughly studied glow discharge and magnetron sputtering techniques. The results reported here are on films with many properties which are equivalent to those of device quality materials. These hydrogenated amorphous silicon films were all intrinsic and were deposited under a variety of H2:Ar ratios and substrate temperatures. The best results were on films deposited at 240 °C and hydrogen contents in the range of 11%–20%. The films were characterized by means of thermal evolution studies to determine hydrogen content, Fourier transform infrared transmission spectroscopy to determine the H2 bonding modes, van der Pauw dark conductivity and photoconductivity measurements, ultraviolet/visible light absorption to determine the band gap, scanning electron microscopy studies to determine film surface quality, and Auger and secondary ion mass spectroscopy in order to determine the surface and bulk impurity levels. Films grown to a thickness of about 1 μm had light to dark conductivity ratios greater than 5×104, band gaps of 1.78 eV and they exhibited the monohydride bonding configuration, all of which are results characteristic of device quality films.
Ag segregation and epitaxial Cr growth on Ag(100)
Authors: Krembel C. , Hanf M. C. , Peruchetti J. C. , Bolmont D. , Gewinner G.
Published: July 2002

The crystallographic and electronic structure of Cr films deposited on an Ag (100) crystal is studied by angle resolved photoemission. Both valence band and photoelectron forward scattering data show that body-centered-cubic Cr grows epitaxially on Ag (100) held at room temperature during deposition. Yet the Cr film is not uniform and exhibits a poor long range order. As soon as bilayer islands are formed and up to coverages as high as ∼60 layer equivalent (LE), the growth of Cr films is invariably accompanied by surface segregation of Ag. Apparently monolayer islands formed initially are free of segregated Ag. This is confirmed by a study of the flat well-ordered Cr monolayer formed when one LE is deposited on the substrate heated at ∼440 K [C. Krembel, M. C. Hanf, J. C. Peruchetti, D. Bolmont, and G. Gewinner, J. Magn. Magn. Mater. 93, 529 (1991); C. Krembel, M. C. Hanf, J. C. Peruchetti, D. Bolmont, and G. Gewinner, Phys. Rev. B 44, 8407, 11472 (1991)]. In spite of the higher substrate temperature during deposition we could not find any evidence for the presence of segregated Ag on top of the ordered Cr monolayer. Possible reasons for this peculiar behavior, namely that Ag segregation takes place on bi- or multilayers of Cr but not on the monolayer, are discussed.
Step doubling and related transitions on vicinal surfaces
Authors: Einstein T. L. , Jung T. M. , Bartelt N. C. , Williams Ellen D. , Rottman Craig
Published: July 2002

We discuss two types of step-height doubling transitions on vicinal surfaces. In one type, exemplified by Ge(111)-[12̄1], a phase transition can occur since the symmetry between alternate terraces is broken at low temperatures. There is evidence in both experiment and in Monte Carlo simulations that this transition can have Ising character. In the second type, exemplified by Si(001)-[110], one subset of terraces is always favored, so that no symmetry is broken. If an actual phase transition occurs (rather than a smooth crossover), it is expected to be first order, implying a coexistence region in a temperature-misorientation phase diagram. Finally, the coalescence of steps into steps of height more than two atomic layers is briefly considered.
Local site identification for NO on Ni(111) in vibrationally distinct adsorption states
Authors: Asensio M. C. , Woodruff D. P. , Robinson A. W. , Schindler K-M. , Gardner P. , Ricken D. , Bradshaw A. M. , Conesa J. C. , González-Elipe A. R.
Published: July 2002

Vibrational spectroscopy of NO on Ni(111) shows two distinct N–O stretching bands for adsorption on the clean surface at different coverages which have been attributed to tilted and perpendicular bridging species at low and high coverage, respectively, while an even higher vibrational energy seen when NO is coadsorbed with oxygen has been attributed to atop NO. We have investigated the local adsorption geometry of these species with scanned energy mode photoelectron diffraction from the N and O 1s states, a method previously found to be very sensitive to site changes and capable of quantitative site identification. We find essentially identical photoelectron diffraction spectra from all three species, indicating that there are no site changes to within a few hundredths of an Ångstrom unit. Moreover, a quantitative analysis using double scattering model calculations indicates that in all cases the adsorption site is actually a threefold coordinated hollow and not bridge or atop.
Soft x-ray transmission of thin film diamond: Applications to detectors and high pressure gas cells
Authors: Fischer D. A. , Phillips W.
Published: July 2002

Thin film diamond windows are emerging as a high technology answer for a variety of soft x-ray window applications for detectors and high pressure gas cells. This innovation provides a soft x-ray window with no measurable diffusion of gas between the high pressure (≳1 atm) and vacuum sides of the thin film diamond. Applications are discussed for soft x-ray fluorescence detectors as well as a high pressure in situ catalytic reactor for soft x-ray materials characterization at a synchrotron radiation source. We have measured the soft x-ray absolute transmission function of a thin film (0.3 to 0.5 μm) diamond window for the energy range between 275 and 750 eV using a gold photodiode at the National Synchrotron Light Source. The photodiode will be illustrated and the quantitative measurement technique fully outlined. X-ray transmission is found to be superior to other window technologies such as polymers or thin film beryllium and because of the inate high strength and thermal conductivity of diamond it has become the material of choice.
Study of the abrasion property of diamondlike films synthesized on iron
Authors: Nakayama Masatoshi , Shibahara Masanori , Namba Yoshikatsu
Published: July 2002

The iron materials coated by the diamondlike carbon (DLC) films are expected to have a wide range of application, however, for these substrate materials some difficulties are still remained compared to that of Si. Hard, flat, and strong adhesive DLC films can be synthesized on Mo coated iron substrates by the ionized deposition technique with the aid of the pretreatment of Ar ion bombardment. The DLC films on iron indicate Vickers hardness of more than 5000 kg/mm2. The abrasion test using B4C powder shows that no corrosion can be observed on the DLC films coated on iron materials. The surface properties of the strongly adhering DLC coated substrates are almost the same as those of the DLC films and these properties are independent of the base materials of the substrates.
Ion scattering study of the adatom induced missing-row reconstructions of Ni(110) and Au(113)
Authors: Jiang Q. T. , Statiris P. , Gustafsson T. , Häberle P. , Zehner D. M.
Published: July 2002

Using medium-energy ion scattering with channeling and blocking, we have investigated the (1×2) reconstructions of Ni(110) and Au(113) (stabilized by submonolayer amounts of K and Ca, respectively). Our data contain evidence that the two surface structures correspond to missing-row type reconstructions. Monte Carlo simulations show that the first interlayer spacing of the (1×2)-Au(113) surface undergoes a large contraction (−18.6%), while the first interlayer spacing of (1×2)-Ni(110) undergoes a small, unexpected expansion (+3%). Although the symmetry of Au(113) allows a lateral registry shift, none is found. Our structural models are discussed in terms of the energy balance between competing surface electronic charge densities.
Determination of the activation energy for the dissociation of the carbon–iodine bond in methyl iodide adsorbed on Ni(100) surfaces
Authors: Tjandra Sariwan , Zaera Francisco
Published: July 2002

The chemistry of methyl iodide on Ni(100) surfaces has been studied by using x-ray photoelectron spectroscopy (XPS). Methyl iodide adsorption is molecular below 100 K, but the C–I bond begins to cleave around 120 K and is completely broken by 160 K. The activation energy for the C–I bond scission was estimated to be about 3.5 kcal/mol based on results from isothermal XPS experiments.
Trends in the bonding of CO to the surfaces of Pt3M alloys (M=Ti, Co, and Sn)
Authors: Ross Philip N.
Published: July 2002

Studies of the surface composition and CO chemisorption on the [111] and [100] oriented single crystals of the isostructural [face-centered-cubic (fcc)] alloys of bulk stoichiometry Pt3M (M=Ti, Co, and Sn) are reviewed. In principle, the study of these alloys is ideal for separating ensemble effects from electronic effects in adsorbate bonding, since the surfaces of these ordered alloys formed by bulk truncation have the M atoms in fixed positions without any M–M pair sites. Also by varying M from Ti to Co to Sn one can examine the effect of the d and s–p orbital contributions to the intermetallic bond on the binding energy of CO. In practice, one must account for surface segregation, and the formation of surfaces that do not have the ideal structure and composition. The strength of the intermetallic bond is found to play a major role in determining the composition of the surface. In the very exothermic alloys Pt3Ti and Pt3Sn, the thermodynamic tendency for the atom with the lower surface energy to be at the surface determines which of the two bulk planes forms the surface plane in the [100] orientation, either pure Pt(Pt3Ti) or 50% M(Pt3Sn). In CoPt3 where the intermetallic bonding is relatively weak, the lower surface energy of Pt produces pure Pt planes on both the [111] and [100] orientations. Photoemission and thermal desorption studies show that the intermetallic bonding in all three alloys has only a small effect on the binding energy of CO, a decrease in adsorption energy of 20 kJ/mol. The surprising invariance of adsorption energy on Pt3M surfaces having such a large variation in the d-orbital configuration of the M atom is attributed to the predominance of s–p orbital contributions to the intermetallic bond in these alloys.
Study of particle emission in vacuum from film deposits
Authors: Logan Joseph S. , McGill James J.
Published: July 2002

This study was carried out to determine how much material can be accumulated on vacuum process chamber walls and shields before excessive particle generation occurs, and how the chamber wall materials influence particle generation. Samples of aluminum, stainless steel, titanium, and anodized aluminum were coated with successive layers of sputtered SiO2. Between each layer deposit, samples were transferred in vacuum to proximity with a particle counter and allowed to cool down. Particles were found to be emitted from the surfaces for times as long as 30 min, typically, before emission rates dropped to zero. The total numbers of particles emitted in a fixed time period increased with the accumulated film layers, until massive delamination was observed. Titanium was found to give the lowest particle rates for a given accumulated thickness, followed by stainless steel, and then aluminum. Anodized aluminum was found to give extremely high particle emissions. Residual stress measurements were made by measuring the bending of the samples. Stress was found to be in the range of 100 to 400 MPa compressive for all the samples. Particle data were taken every 20 s, and size distribution was calculated by the instrument, from a minimum particle size of 0.5 μm. In most cases, the particle size distribution peaked in the 2–5 μm range. The reason for this is not clear. Stress calculated for the titanium samples was somewhat higher than for the stainless steel (390 versus 120 MPa) but the particle emission rates were lower, suggesting better interfacial adhesion on titanium.
Plasma uniformity and power deposition in electron cyclotron resonance etch tools
Authors: Stevens J. E. , Huang Y. C. , Jarecki R. L. , Cecchi J. L.
Published: July 2002

We present measurements of the propagation and absorption of the 2.45 GHz waves which produce the plasma in an electron cyclotron resonance (ECR) etch tool. Measurements verify that the absorption occurs within the Doppler-broadened resonance location where ‖ω− ωce‖ ≲ k∥vte and B≲950±25 G. A ray tracing calculation is used to model power deposition in the ECR source region. Plasma radial uniformity improves when the microwaves are allowed to propagate several wavelengths (≳5) before absorption occurs. An explanation for this improved source uniformity is the fact that whistler waves refract toward regions of lower density which, when combined with ECR absorption at the low-density location, forces the profile toward radial uniformity. This effect explains previous observations of flat density profiles in configurations where the magnetic field at the microwave window is raised well above the resonant field. Etch rate uniformity is found to be closely correlated to the ion current density uniformity across the wafer surface in our system.
Characterization of electron cyclotron resonance plasmas optimized for the deposition of polycrystalline diamond films
Authors: Youchison D. L. , Eddy C. R. , Sartwell B. D.
Published: July 2002

Optical emission spectroscopy, Langmuir probes, and B-field probes have been used to characterize electron cyclotron resonance plasmas used in the deposition of polycrystalline diamond films. These plasmas were generated at 1.33 Pa using selected ratios of CO:H2 and CH4:O2:H2 that produced the highest quality films (i.e., high degree of faceting and an intense Raman peak at 1332 cm−1). Electron temperature, ion density, plasma potential and B-field profiles obtained at optimum growth conditions are presented. The best diamond films were produced on silicon (100) substrates biased to +40 V dc and maintained at a constant temperature of 500 °C. These substrates were placed downstream of an electron cyclotron resonance (ECR) layer (the region of high plasma density created by resonant microwave absorption at the 87.5 mT B-field contour), characterized by a Te near 1 eV and ion densities near 4×1012 cm−3. Actinometry was used to quantify the optical emission spectra. In the CO:H2 system, quality films were obtained for line intensity ratios of Hγ/Ar=4.0, Hγ/C2=1.1, CH/C2=1.9, CO/C2=0.73, and O/C2=0.89. Nearly identical films were produced in the CH4:O2:H2 system, with line intensity ratios of Hγ/Ar=4.2, Hγ/C2=1.2, CH/C2=1.5, CO/C2=0.78, O/C2=0.99. These results indicate that feedgas composition is less important than the critical ratios of C/O/H2 in an ECR plasma.
Rolling friction in a linear microactuator
Authors: Ghodssi R. , Denton D. D. , Seireg A. A. , Howland B.
Published: July 2002

In order to design a precise and repeatable microelectromechanical system, friction and wear must be minimized in the surfaces of the microstructure. Rolling bearings are known to exhibit lower friction over sliding contact bearings in precision macromechanical systems. Rolling friction can be characterized on a microscale to facilitate the design of precision microelectromechanical systems. We have designed a test specimen utilizing stainless steel microballs (285 μm in diameter) in contact with silicon micromachined v-groove surfaces (310 μm wide, 163 μm deep, 10 000 μm long). Different thin films are deposited on the surface of the silicon v grooves and their frictional properties are investigated experimentally. We have shown that at zero applied normal force, the adhesion is dominant and as the applied normal force is increased, the friction coefficient reaches an asymptotic value below 0.01. The measured frictional forces represent the total resistance at the onset of rolling motion for the bearing which is generated at all the contacting surfaces. The measured values for the coefficient of friction will allow designers to select optimum lubricant surfaces to be used in microroller bearings using microballs and silicon micromachined V-groove surfaces.
In situ surface-enhanced Raman spectroscopic study of CO oxidation by NO and O2 over rhodium-coated gold surfaces
Authors: Tolia Anish A. , Weaver Michael J. , Takoudis Christos G.
Published: July 2002

Surface-enhanced Raman spectroscopy (SERS) is used as an in situ probe to study gas–solid catalytic reactions. The oxidation of CO by NO, and O2 is studied on electrochemically deposited overlayers of Rh on roughened gold substrates. A multichannel charge coupled device detector is used to obtain time-resolved SER spectra at actual reaction conditions of atmospheric pressure and temperatures up to 623 K. The gas-phase composition is simultaneously monitored with a quadrupole mass spectrometer. Correlations are made between real time measurements of adsorbed species and reaction intermediates on Rh surfaces by SERS and changes in the gas phase composition detected by mass spectrometry. For example, disappearance of adsorbed CO from the surface can be directly correlated to changes in rates of the CO oxidation reaction. Reaction intermediates of the CO and NO reaction on the Rh overlayers are observed. NO adsorption yields spectral features at 315 and 530 cm−1 attributed to the dissociation products of NO viz. adsorbed nitrogen and oxygen, respectively. There seems to be no evidence of molecularly adsorbed NO, suggesting the possibility of substantial dissociation of NO. Adsorbed reaction intermediates such as NO2, isocyanate, and cyanide species, are also observed during the CO/NO reaction at reaction temperatures. The temperature dependency of the dissociation products and reaction intermediates has also been studied. The results strongly suggest a dissociative mechanism for the CO/NO reaction at these conditions.
Thermal desorption of ultraviolet–ozone oxidized Ge(001) for substrate cleaning
Authors: Zhang X.-J. , Xue G. , Agarwal A. , Tsu R. , Hasan M.-A. , Greene J. E. , Rockett A.
Published: July 2002

X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), and reflection high-energy electron diffraction (RHEED) have been used to show that 30 min exposures of a degreased and deionized-water-rinsed Ge(001) wafer to ultraviolet (UV)–ozone in laboratory air is sufficient to remove C contamination and form a nonpermeable passive amorphous GeO2 layer with a thickness of ≂1.8 nm. Subsequent annealing in ultrahigh vacuum (UHV) at ≥390 °C for ≥30 min resulted in desorption of the oxide layer and the exposure of a clean well-ordered Ge(001)2×1 surface. No impurities, including C and O, were detected by either XPS or AES. EELS spectra from the clean surface showed well-defined peaks corresponding to transitions involving dangling bonds, surface states, and surface plasmons. Shorter UV–ozone exposures (i.e., <30 min) often resulted in residual C contamination while incomplete oxide removal was obtained at lower oxide desorption temperatures. Ge overlayers deposited by molecular beam epitaxy at temperatures between 200 and 450 °C on UV–ozone processed substrates were found by a combination of plan-view and cross-sectional transmission electron microscopy to be highly perfect single crystals with abrupt film/substrate interfaces and no detectable dislocations or extended defects.
Wave propagation and plasma uniformity in an electron cyclotron resonance plasma
Authors: Samukawa Seiji
Published: July 2002

This study examined microwave propagation and plasma uniformity in the mode of introduced microwaves and the discharged gases. TE11-mode microwaves are almost all absorbed close to the electron cyclotron resonance (ECR) region. Conversely, TM01-mode microwaves are mainly absorbed upstream from the ECR region. Accordingly, in the case of TE11-mode microwave, the plasma uniformity strongly depends on the magnetic field profiles and the position of the resonance region. TM01-mode microwave plasma is generated uniformly at any magnetic field and any position. Moreover, the microwave propagation states are changed on the discharged gases. TE11-mode microwaves are gradually absorbed upstream from the ECR region in CHF3 gas plasma, whereas N2 gas plasma causes microwave absorption close to the ECR region. Then, the CHF3 plasma results in a uniform ion current density, in comparison with the result for N2 gas plasma. This is considered to be due to electron temperature differences in the plasmas.
Influence of ion beam modification on the oxidation behavior of intermetallic compound Ni3Al(0.1B)
Authors: Liu Xianghuai , Zheng Zhihong , Huang Wei , Lin Zixin , Wang Xi , Yang Genqing , Zou Shichang , Taniguchi S. , Shibata T.
Published: July 2002

Ion implantation, ion beam mixing, and ion beam enhanced deposition (IBED) were employed to improve oxidation resistance of intermetallic compound Ni3Al(0.1B) in pure flowing oxygen at temperature of 1100 K. X-ray diffraction and scanning electron microscopy were used to examine the composition and structure of the scales after oxidation. Improved resistance to oxidation of Ni3Al(0.1B) was observed in Ta+-implanted, ion beam mixed Si layers, and IBED films coated specimens. The possible mechanisms for these effects were discussed.
Proposal of a sputter-ion pump structure
Authors: Suetsugu Yusuke
Published: July 2002

A new sputter-ion pump structure is proposed, wherein magnets reside within the Penning cell assembly. Magnetic fields in the cell assembly are calculated and found to have the necessary intensity to ignite and sustain a Penning discharge. This structure has a possibility of realizing a compact ion pump although it has some problems, such as a somewhat high fringing magnetic field, and limit of baking temperature.
Plasma and processing effects of electrode spacing for tungsten etchback using a bipolar electrostatic wafer clamp
Authors: Marx William F. , Ra Yunju , Yang Richard , Chen Ching-Hwa
Published: July 2002

A tungsten etchback process has been developed using a bipolar electrostatic clamp (ESC) in a parallel-plate, single wafer etcher with a 13.56 MHz power applied to the top electrode. The transfer of a SF6/N2 etchback process from a mechanically clamped to a bipolar electrostatically clamped system was not straightforward. Initially, the ESC system produced more tungsten residue and a lower etch rate than a mechanically clamped system. By optimizing the rf grounding circuit of the ESC, the residue was reduced. A Langmuir probe study demonstrated that the ion current profile varied strongly with electrode spacing for SF6 but not for gases such as Cl2 or Ar. Both the tungsten residue and the anomaly in the ion current profile were eliminated by the proper choice of electrode spacing. Energetic electrons have been proposed as the cause of the unusual ion current profile. Process results have been optimized with the new electrode spacing, allowing the fabrication of submicrometer tungsten plugs on 200 mm wafers. The tungsten plug recess, which is controllable by wafer temperature and process conditions, is typically 0.1 μm.
Increased precision in strain measurement of diamond by microRaman spectroscopy
Authors: Alexander W. Brock , Holloway Paul H. , Simmons Joseph , Ochoa Romulo
Published: July 2002

MicroRaman spectroscopy has been used to measure stress in diamond with improved precision. Stress was induced by rf sputter deposited tungsten films of 1- and 9-μm thickness. Preliminary data showed a systematic error in the diamond Raman peak position of about 0.05 cm−1/scan, which led to inaccurate and imprecise stress measurement. A new technique, using a reference 5520-Å krypton line only 10.5 cm−1 from the Raman diamond line, results in an order of magnitude increase in measurement precision. Using this calibration, diamond peak position could be measured with a precision of ±0.03 cm−1 which corresponds to ±11 MPa of stress. This is an easy and inexpensive means to improve stress measurements in diamond by microRaman spectroscopy.
Advanced electron beam source for ultrahigh vacuum (molecular beam epitaxy) and high vacuum applications of thin film deposition
Authors: Moore J. W. , Tsujimoto N. K.
Published: July 2002

A new electron beam source designed specifically for cutting edge technology has been developed. The source is tailored for today’s demanding applications providing precise control of very low deposition rates for research and molecular beam epitaxy processes while retaining the ability to operate at high power levels for production systems. Applications consist of the evaporation of all metals, subliming materials, and dielectric materials in both high and ultrahigh vacuum environments. Evaluation of the sources performance during deposition will be displayed, together with a discussion about new design features. In addition the latest advances in solid state power supplies and controllers for electron beam deposition processes will be reviewed.
Structural and surface characterization of ultrafine iron carbide particles generated by laser pyrolysis. I. High temperature He treatment
Authors: Sethuraman Anantha R. , Stencel John M. , Rubel Aurora M. , Cavin Burl , Hubbard Camden R.
Published: July 2002

Three samples of passivated ultrafine iron carbide particles, synthesized by laser induced pyrolysis of gaseous precursors, were examined by x-ray diffraction, x-ray photoelectron spectroscopy, and thermogravimetry/mass spectroscopy at temperatures as high as 600 °C under a He atmosphere. The approximate 6–7 nm diam particles began to sinter at temperatures between 300 and 400 °C and formed a complex mixture of carbide, oxide and metallic phases. Preservation of the carbide structure on heating was dependent on the purity of the carbide, and the concentration of oxygen and carbon in the particles. A topotactic transformation from Fe7C3 to Fe0.98O was observed and is discussed relative to the as-synthesized/passivated particles composition and structure. This topotaxy leads to the selective formation of γ-Fe2O3 from specific ultrafine particle carbides.
Real-time monitoring of homoepitaxial and heteroepitaxial processes by p-polarized reflectance spectroscopy
Authors: Dietz N. , Miller A. , Bachmann K. J.
Published: July 2002

In this communication we describe a simple, inexpensive technique for the real-time monitoring of epitaxial processes based on the reflection of a parallel-polarized light that impinges onto the surface of the substrate close to the Brewster angle for the substrate material. In the case of heteroepitaxy, a quarter-wavelength modulation of the intensity of the reflected light is observed, which contains information concerning the evolution of the optical properties as well as a record of the growth rate for the entire duration of film deposition. Changes in the amplitude of this signal provides information about deviations in bulk dielectric properties of the growing film caused by absorption and inhomogeneities in the refractive index of the film as well as changes in the surface roughness. Furthermore, under the conditions of pulsed chemical beam epitaxy (PCBE), the reflected intensity contains a periodic oscillation that is superimposed on the polarized reflectance spectroscopy (PRS) signal with an Å scale period and is maintained over thousands of Å of film growth. The periodicity of this fine structure matches the period of the sequence of precursor pulses of the PCBE process. Also, an amplitude modulation of the superimposed oscillation is observed which may be understood on the basis of the results of PRS studies of homoepitaxial growth. Under the conditions of homoepitaxy, the quarter-wavelength oscillations in the PRS signal cease to exist since the epitaxial film and the substrate have the same dielectric function. However, the fine structure can still be observed and may be utilized for both analysis of the growth mechanism and in conjunction with the observation of heteroepitaxial growth for the same material, the real-time monitoring of the growth rate.
Auger electron spectroscopy as a real-time compositional probe in molecular beam epitaxy
Authors: Chambers S. A. , Tran T. T. , Hileman T. A.
Published: July 2002

We describe the use of dynamical Auger electron spectroscopy to determine the stoichiometry of compound materials grown by molecular beam epitaxy (MBE). A small, high-speed Auger electron spectrometer has been incorporated into a custom-built MBE system in such a way that Auger measurements can be carried out during growth without blocking any of the atomic or molecular beams. The same electron beam used to generate reflection high-energy electron diffraction patterns is used to excite Auger transitions. The sensitivity of the method is determined by measuring and modeling the angular dependence of Mg KLL and O KLL Auger emission from clean MgO(001). We have tested the technique for MgO(001) homoepitaxy and heteroepitaxy of CrxMo1−x on MgO(001). With careful calibration, film composition can be rapidly determined to within a few percent both during and after growth by this method. In addition to the successes achieved with the technique thus far, potential difficulties are discussed.
Characterization of a slot antenna microwave plasma source for hydrogen plasma cleaning
Authors: Korzec D. , Werner F. , Brockhaus A. , Engemann J. , Schneider T. P. , Nemanich R. J.
Published: July 2002

A new large volume microwave plasma source has been used for the production of a hydrogen plasma. The source consists of an annular waveguide cavity with axial slots on the inner side which acts as a field applicator to sustain a plasma at 2.45 GHz. The plasma is contained in a fused silica bell jar of 16 cm in diameter and 20 cm in height. The distance between the slots corresponds to a waveguide wavelength. The source is able to generate a highly dissociated (up to 90%) hydrogen plasma for cleaning purposes. Stable operation of the plasma source is shown for a pressure range of 0.1–1.3 mbar and a power range of 600–2000 W. The plasma can be ignited over the entire examined pressure range, and the power needed for discharge ignition is below 1.7 kW. The minimum ignition power is 1050 W for a pressure of 0.7 mbar. A double Langmuir probe and optical emission spectroscopy were used to characterize the hydrogen plasma as a function of microwave power, pressure, and position. The results indicated a typical ion density of 1.5×1011 cm−3 which is an order of magnitude less than that obtained for argon under similar conditions. The typical electron temperature is 2.5 eV for microwave power of 2 kW and pressure of 0.7 mbar.
Synchrotron radiation photoelectron emission microscopy of chemical-vapor-deposited diamond electron emitters
Authors: Shovlin J. D. , Kordesch M. E. , Dunham D. , Tonner B. P. , Engel W.
Published: July 2002

A variety of natural and chemical-vapor-deposited diamond surfaces have been imaged using a photoelectron emission microscope and synchrotron radiation in the 4–18 and 250–350 eV ranges. Both images and spatially resolved total electron yield curves were acquired simultaneously. Near-edge spectra at the carbon 1s edge show a resonance due to graphite; the image intensity varies uniformly in proportion to the C 1s edge intensity. In the 4–18 eV range, no sharp features related to negative electron affinity electron emission were observed below 7 eV in the electron yield curves on any of the specimens. The image contrast was not strongly dependent on the illumination energy. Natural type IIa diamond showed severe charging effects.
Surface analysis at low to ultrahigh vacuum by ion scattering and direct recoil spectroscopy
Authors: Hammond M. S. , Schultz J. A. , Krauss A. R.
Published: July 2002

The surface analytical methods designated as mass spectroscopy of recoiled ions (MSRI) and direct recoil spectroscopy (DRS) are characterized by the incidence of energetic ions on the sample and the detection of scattered primary beam particles or recoil-sputtered surface atoms that are energy and/or mass analyzed. The use of time-of-flight for energy analysis of scattered primary particles and recoiled surface atoms creates a powerful technique for structural and elemental analysis of surfaces. Time-of-flight ion scattering and recoil spectroscopy are emerging as viable surface analysis tools with particular strength for in situ monitoring during low pressure (<few mTorr) thin film processing. DRS has the distinct advantage over most other surface spectroscopies of being able to measure surface hydrogen. MSRI is particularly useful for elemental and isotopic surface analysis and, in several important cases (e.g., N), is considerably more sensitive than secondary ion mass spectroscopy. This review covers the latest applications of MSRI and DRS in a variety of thin film growth and nucleation studies, highlighting the many advantages presented by these unique spectroscopies.
Effects of atomic chlorine wall recombination: Comparison of a plasma chemistry model with experiment
Authors: Meeks E. , Shon J. W. , Ra Y. , Jones P.
Published: July 2002

Results from a plasma chemistry model provide predictions of spatially and temporally averaged plasma properties. Application of the model to chlorine-etch process conditions, typical of a high plasma-density transformer coupled plasma reactor, provides plasma composition dependence on reactor operating parameter such as power and pressure. Model results also show the dependence of species concentrations on the atomic-chlorine recombination rate at reactor walls. Comparison of model predictions to measured composition trends as determined by Langmuir probe, actinometry, and ion-energy analysis reveals a critical wall-recombination probability of about 0.1 for chlorine atoms on a chlorinated anodized-aluminum surface. At or above this critical value, the model reproduces the experimentally observed trends, while employing a recombination probability below this value results in predictions that are inconsistent with the data. The model determines gas-phase and surface-species compositions in plasma-etch reactors through the solution of species, mass, electron-energy, and surface-site conservation equations. The use of well mixed reactor approximations reduces the computational expense of detailed kinetics calculations and allows investigation into the dependence of plasma chemistry on uncertain kinetic parameters. The dominance of surface reaction rates in determining plasma properties is expected to be equally important in more complex two-dimensional inductively coupled plasma models due to the highly diffuse nature of these low-pressure reactors.
Magnetic properties of pseudomorphic ferromagnetic alloy films on Cu(100)
Authors: Mankey G. J. , Wu S. Z. , Schumann F. O. , Huang F. , Kief M. T. , Willis R. F.
Published: July 2002

We report the variation of the thickness dependence of the Curie temperature for a range of ultrathin ferromagnetic alloy films. By simultaneously depositing Fe or Co and Ni on Cu(100) we produce pseudomorphic alloys with controlled stoichiometry. An analysis of the Curie temperature versus thickness curves with an empirical finite size scaling formula reveals that the Curie temperature in the thick film limit increases monotonically with Co or Fe concentration. We compare the bulk alloy Curie temperatures to those of the alloy films extrapolated from the few monolayers limit.
Effect of the substrate state on the formation of diamond film in a low temperature microwave-plasma-enhanced chemical vapor deposition system
Authors: Kim S. H. , Park Y. S. , Jung S. K. , Kang D. H. , Lee J.-W.
Published: July 2002

Diamond films were deposited on substrates using a low temperature microwave-plasma-enhanced chemical vapor deposition system. Low temperature (below 500 °C) deposition can be achieved only by making the substrate position remote from the plasma under the normal deposition condition. The substrate was untreated or was pre-treated by 30 μm diamond powder. Among various substrates (untreated silicon, pre-treated silicon, pre-treated quartz, untreated glass, and pre-treated glass), pre-treated quartz and pre-treated glass enhance the diamond formation, while untreated glass gives only graphite formation even under the same deposition conditions. We understand that the better formation of diamond on pre-treated glass and pre-treated quartz was due to the existence of a diamond particle on the substrates. We also deposited diamond films on pre-treated glass at various CH4 concentrations. The largest grain size can be acquired at 3% of CH4 concentration and the growth rate of the film increases with increasing CH4 concentration.
Electron-beam controlled radio frequency discharges for plasma processing
Authors: Kushner Mark J. , Collison Wenli Z. , Ruzic David N.
Published: July 2002

During plasma etching and deposition of semiconductor materials, it is desirable to have separate control over the magnitude and energy of the ion flux onto the substrate. This control is difficult to achieve in reactive ion etching discharges since the radio frequency (rf) voltage applied to the substrate both generates the ions and accelerates the ions into the substrate. High plasma density devices such as electron cyclotron resonance and inductively coupled plasma reactors achieve this control by having separate power sources for ionization and ion acceleration. In this article, we present results from a computational study of an electron beam controlled rf discharge in which the production and acceleration of ions are similarly separately controlled. Ionization is dominantly produced by injection of an electron beam into the reactor. Ion acceleration is determined by a separate rf bias applied to the substrate. The limits of e-beam voltage, current, and rf bias voltage for which this separate control can be achieved will be discussed.
Measuring and modeling stresses in Al metallization
Authors: Li Z. H. , Wu G. Y. , Gu Y. , Chen W. R. , Wang Y. Y.
Published: July 2002

Stresses in passivated and unpassivated Al films with different thicknesses have been measured with x-ray diffraction. The stress strongly depends on the thickness of a film and is different from conventional elastic or plastic theory. A novel model based on plastic deformation and dislocation theories has been developed to explain it. In the model it is assumed that interaction between Al and the dielectric near their interface increases the yield strength of the Al film. Results calculated through the model are consistent with experimental results.
Electric field effects on force curves for oxidized silicon tips and ice surfaces in a controlled environment
Authors: Slaughterbeck C. R. , Kukes E. W. , Pittenger B. , Cook D. J. , Williams P. C. , Eden V. L. , Fain S. C.
Published: July 2002

A scanning force microscope and environmental chamber are described for use in studying the surface properties of ice that is grown from vapor. This microscope uses a modulated optical deflection scheme to minimize low frequency noise, and a thermal feedback system which can stabilize the ice temperature to within 0.4 mK. The ice crystal can be examined in its own vapor plus other controlled gaseous environments. Initial results show that, in the range of −8 to −10 °C and negative tip voltages, necks form between the oxidized silicon tip and the ice sample after contact with the surface.
Ultrastructural characterization of colloidal metal films for bioanalytical applications by scanning force microscopy
Authors: Fritzsche Wolfgang , Sokolov Konstantin , Chumanov George D. , Cotton Therese M. , Henderson Eric
Published: July 2002

Colloidal metal films (CMFs) are prepared by the attachment of silver, gold, or platinum (or other metal) particles to a glass slide modified by silanization with 3-mercaptopropyl silane. The covalent attachment of the metal particles occurs through the metal–sulfur bond. In these samples the local electromagnetic field is enhanced near the surface of the CMF due to excitation of plasmon resonances. This phenomenon can be used for a variety of analytical applications. Because the optical properties are strongly dependent on the morphology of the film, its structural characterization becomes of great importance. To further characterize CMFs we have used scanning force microscopy (SFM). Initial studies revealed lateral dimensions of the particles as well as the particle density. Height measurements were made using the three-dimensional topographic image of the surface yielded by SFM, and were used to evaluate the selective deposition of a silica spacer layer onto the metal particles. Comparative SFM measurements in water and air using different imaging modes were performed to investigate the mechanical stability of CMFs against the forces exerted by the scanning tip.
Experimental and theoretical study of vibrations of a cantilevered beam using a ZnO piezoelectric sensor
Authors: Jooste B. R. , Viljoen H. J. , Rohde S. L. , van Rensburg N. F. J.
Published: July 2002

Piezoelectric sensors can measure vibrations of solid structures very accurately. A model of a cantilevered beam, with a ZnO film on one side is presented. Both viscous and internal damping are considered. The output of the sensor is modeled and matched with experimental results by adjusting the damping parameters. A theoretical formulation for damage is introduced. Experimental results for a damaged beam confirm the shift in frequencies to lower values. The model is used to identify the extent of the damage.
Zirconium silicate thin films for antireflection coatings
Authors: Barrie J. D. , Fletcher E. L.
Published: July 2002

Antireflection coatings are used to enhance the performance of a wide variety of optical devices. Laser and nonlinear optical devices are among the most demanding for antireflection coating applications, requiring both excellent optical properties and good durability. In this article, we report on the optical properties of zirconium silicate based thin films and their application as antireflection coatings for a number of components used in laser applications. These films have been demonstrated to be easily and reproducibly prepared, to have readily tailored indices of refraction, and to withstand the high optical intensities found in device applications. Films with indices of refraction in the range of 1.6–1.9 have been prepared using rf planar magnetron sputtering, allowing optimized antireflection coatings to be deposited on a variety of materials, including GaP, GaAs, and AlGaAs.
Deposition mechanism and electrical properties of low pressure chemically vapor deposited W as a gate electrode
Authors: Kim Kijoon , Sone J. H. , Kim S.-O. , Park J. S. , Kim Hyeong Joon
Published: July 2002

We have investigated the feasibility that low pressure chemically vapor deposited W (LPCVD-W) could be used as a gate electrode material of metal–oxide semiconductor (MOS) field effect transistors. Smooth W thin films with good adhesion to SiO2 were deposited in a relatively short time by the pulsing injection method, in which the source gas WF6 was periodically injected into the low pressure chemical vapor deposition (LPCVD) reactor. Right after the WF6 flow was stopped, instantly the ratio of SiH4 to WF6 increased rapidly, enhancing the additional nucleation between the initially formed W islands. This additional nucleation presumably made it possible to form a continuous W thin film on the oxide surface at the initial stage of deposition. The phase of deposited W films changed from α-W to W5Si3 at the SiH4/WF6 ratio of 2–3. We have optimized the process conditions in order to deposit a reliable W gate electrode for the application of MOS capacitors. MOS structure capacitors were fabricated using a LPCVD-W gate electrode and their electrical properties were characterized. It was found that the 20-Å-thick Si3N4 layer protected SiO2 from a chemical attack by WF6. The composite gate dielectric of SiO2 and Si3N4 layers showed low leakage current and good dielectric breakdown strength distribution. The deposition was carried out at the temperature range of 300–750 °C and various SiH4/WF6 ratios of 0.6–14. Transmission electron microscopy and scanning electron microscopy were used to analyze the phase and the film morphology of LPCVD-W on the SiO2 substrate, respectively.
Use of surface photoabsorption to analyze the optical response of GaAs(001) surfaces
Authors: Eryiğit Resul , Marschel Peter K. , Herman Irving P.
Published: July 2002

The dielectric functions of Ga- and As-terminated GaAs(001) surfaces are determined by using a three-layer model and experimentally available surface photoabsorption (SPA) data, and are compared to those previously obtained from reflectance-difference spectroscopy. Using the SPA-derived dielectric functions, approaches for optimizing conditions in SPA experiments for GaAs and other materials are presented.
Metal vapor sources for scientific research and thin film technology: Review
Authors: Zolkin Alexander S.
Published: July 2002

Continuous and pulse sources of metal vapor for application in physics, chemistry, and technologies are described. The maximum temperature and vapor pressure are: T0⩽2800 K, P0⩽105 Pa. Source classification. The first group includes the sources involving the expansion of vapor into vacuum from the saturated state (or close to it). These sources are united by the common constructional feature, namely, the use of a single heater which limits experimental possibilities due to the difficulty of independent change of the characteristics of vapor expansion, i.e., pressure and temperature. The second group includes the sources in which vapor is superheated before expansion. These sources allow to handle the characteristics of vapor expanding into vacuum. The application of two-temperature sources in scientific research and in technologies allows one to control the metal gas dynamic flow, produce atomic, cluster beams, or vapor jets without microdroplet phase in it. The goal of the review is to demonstrate how to create a reliable metal vapor source with high intensity j≈1022–1023atom/cm2 s and more with high optical density n>1015atom/cm2.
Structure and mechanical properties of dual-ion-beam deposited CNxTiy/TiN multilayers
Authors: Zhao X.-A. , Ong C. W. , Tsang Y. C. , Choy C. L. , Chan P. W.
Published: July 2002

CN x Ti y /TiN multilayers have been synthesized using dual-ion-beam deposition. X-ray photoelectron spectra of C 1s, Ti 2p, N 1s, and Si 2p electrons were investigated against the depth from the film surface. The results confirm the layered structure of the films. The Ti atoms contained in a CNxTiy layer sandwiched between two TiN layers are expected to come from interlayer diffusion of Ti atoms enhanced by ion beam irradiation during deposition. As a consequence, a CNxTiy layer contains a C–N phase, a Ti–N phase, and a T–C phase. The C–N phase contains 27 at. % nitrogen, less than the level required to form the hypothetical β-C3N4 phase, indicating that the multilayer structure containing TiN layers does not favor for increasing N content in the C–N phase of the CNxTiy layers. The Ti–N and Ti–C phases are about stoichiometric. The TiN layers comprise mainly a Ti–N phase, and a small fraction of the Ti–C phase, which are both stoichiometric. However, the bonding between C and N is weak. The hardness H and elastic modulus E of the films were investigated by nanoindentation experiments. The single-layer CN0.3 is the softest (H=11.4 GPa), and the single-layer TiN is the hardest (H=22 GPa) among the samples in the series. H and E increase with increasing TiN volume fraction, as well as the number of interfaces. They also increase with increasing substrate temperature, possibly due to stronger interlayer diffusion of Ti atoms at higher temperature.