bluuebunny/crossref_metadata_2025 huggingface dataset:
Momentum conservation for hot electrons at the Au/Si(111) interface observed by ballistic-electron-emission microscopy
Authors: Bell L. D.
Published: July 2002

Ballistic-electron-emission microscopy (BEEM) spectroscopy was performed at room temperature and at 77 K on Au/Si(111) structures. Au thickness was varied in the range 75–300 Å. At 77 K a direct signature of parallel momentum conservation is observed in the BEEM spectra of samples with thick Au layers. The change in spectral shape which was observed as a function of both Au thickness and temperature places restrictions on allowable values of inelastic and elastic mean-free paths. The observations also suggest the presence of multiple reflections of the injected electrons within the Au layer. An independent indication of these multiple reflections is observed in the dependence of BEEM current on Au thickness in Au/Si(100) structures. Calculations provide good agreement with observed BEEM spectra and attenuation length data.
Field-emission barrier height of an alloy tip: Possible effect of surface segregation
Authors: Nakane Tetsuhiro , Sano Kazuya , Sakai Akira , Magosakon Akihiro , Yanagimoto Kengo , Sakata Toyo
Published: July 2002

We have investigated the influence of surface segregation on the field-emission characteristics of alloy emitters. Our tip material is a Ni-0.8 at. % Au alloy where gold segregates to the surface. Emission barrier height was obtained from the slope of the Fowler–Nordheim plot assuming the field proportionality constant estimated from the best image voltage in the field-ion imaging. Upon annealing the alloy tip at 700 K, the barrier height is found to decrease by ∼0.5 eV. As no lowering of the barrier height was observed in an annealed Ni tip, the observed reduction of the barrier height is attributable to the surface enrichment of gold due to its partial segregation. Our findings thus support the claim by Yoshihara and Yoshitake [J. Vac. Sci. Technol. A 13, 2407 (1995)] that the surface segregation can be used as a method for improving the emission characteristics of field emitters.
Working surface science model of CoMoS hydrodesulfurization catalysts
Authors: de Jong Arthur M. , (San) de Beer V. H. J. , Rob van Veen J. A. , (Hans) Niemantsverdriet J. W.
Published: July 2002

Model catalysts, consisting of a conducting substrate with a thin SiO2 or Al2O3 layer on top of which the active catalytic phase is deposited, were applied to study the sulfidation of Co–Mo catalysts and to test their catalytic behavior in the hydrodesulfurization of thiophene. CoMoS, the highly active cobalt promoted MoS2 in which Co is thought to decorate the edges of MoS2 slabs, can be synthesized by sulfiding nitrilotriacetic acid complexes of cobalt and molybdenum. These complexes are deposited on SiO2/Si(100) and Al2O3/Si(100) model supports by spin coating. X-ray photoelectron spectroscopy measurements on these Co–Mo catalysts provide detailed insight into the mechanism of sulfidation. It appears that Mo is sulfided first and then the Co; this is imperative to form the CoMoS phase. Thiophene hydrodesulfurization studies of CoMoS model catalysts yield activities and product distributions consistent with those obtained from their high surface area counterparts, proving that these models are realistic. They offer, therefore, a great potential for fundamental surface science studies of catalytic phases and of adsorption, desorption, and reactions of gases as well.
Reactive sputtering of titanium diboride and titanium disilicide
Authors: Maya L. , Vallet C. E. , Fiedor J. N.
Published: July 2002

Nanocomposite films of titanium nitride in either boron nitride or silicon nitride matrices were prepared by reactive sputtering of titanium diboride or titanium disilicide targets in a nitrogen plasma. These films were expected to have high dielectric constants and in the case of the silicon nitride matrix high hardness. The films were characterized by a variety of physicochemical techniques including photoelectron spectroscopy, Rutherford backscattering spectroscopy, RBS, and transmission electron microscopy. The films derived from titanium diboride incorporated oxygen as an inadvertent impurity in the form of titanium monoxide and dioxide. A silicon oxynitride underlayer is suggested by the RBS analysis of the silicon nitride based film, apparently arising from exposure of the native oxide on silicon to the nitrogen plasma. Capacitance measurements of the films showed moderately high dielectric constants of about 30–60 and a hardness of 11 GPa for the silicon nitride nanocomposite.
Insight into the dry etching of fence-free patterned platinum structures
Authors: Milkove K. R. , Wang C. X.
Published: July 2002

An investigation was undertaken to characterize the time progression of the Pt etch process during the dry etching (DE) of fence-free patterned structures. The goal of this study was to clarify the mechanism of fence-free Pt etching. In particular an explanation was sought that could account for the origin of the extremely shallow sidewall angles typically reported in the literature for fence-free Pt etching. The experiment consisted of coprocessing two oxidized Si wafers possessing identical 250 nm thick Pt film layers, but different photoresist (PR) mask thicknesses. Etching was suspended at 20%, 40%, 60%, and 80% of the full etch process in order to cleave off small pieces of wafer for analysis by scanning electron microscopy (SEM). Using Cl2-based DE conditions known to produce fence-free etching for 250 nm thick film layers, we found that a severe fence actually coats the PR mask during the first 20% of the etch process! As the etch continues the fence structure evolves, achieving a maximum height and width followed by progressive recession until disappearing completely prior to process endpoint. SEM micrographs clearly reveal how the existence of these transient fence structures account for the formation of shallow Pt sidewalls. The data also shows that the final profile of an etched Pt structure possesses a functional dependence on the initial thickness and slope of the PR mask as well as on the initial thickness of the Pt layer. Finally, we believe that the observed behavior of the transient fence provides the strongest evidence to date supporting the existence of a chemically assisted physical sputtering component associated with the DE of Pt films in halogen-based plasmas.
Fe–N gradient films and epitaxial Fe16N2 single-crystal films
Authors: Tian M. B. , Jiang E. Y. , Sun D. C.
Published: July 2002

Fe–N gradient films and epitaxial Fe16N2 single-crystal films were prepared with a facing-target sputtering system. The Rutherford backscattering spectrum, x-ray diffraction, and selected area electron diffraction indicate that the gradient films possess some composition and structure gradient. The α′′-Fe16N2, γ-Fe4N, ε-FexN(2<x⩽3), and ζ−Fe2N phases are present in the gradient films at different depths. The α′′-Fe16N2 single-crystal films correspond to a deformed body-centered tetragonal structure with parameters of a=b=5.72 Å and c=6.29 Å. They grew epitaxially on a NaCl(100) substrate with an orientation relationship of α′′-Fe16N2(001)∥NaCl(001) and α′′-Fe16N2[100]∥NaCl[100]. Perfect electron diffraction patterns with perfect symmetry in the [1̄11], [011], and [001] directions can be observed distinctly by a rotational double tilting sample stand. By controlling N2 partial pressure, substrate temperature, and crystal orientation, α′′-Fe16N2 single-crystal films can be successfully grown epitaxially.
Comparison of the standards for high and ultrahigh vacuum at three national standards laboratories
Authors: Jousten K. , Filippelli A. R. , Tilford C. R. , Redgrave F. J.
Published: July 2002

A preliminary phase of an international comparison of standards for high and ultrahigh vacuum was carried out by the National Institute of Standards and Technology (NIST), the National Physical Laboratory-Teddington (NPL-UK), and the Physikalisch-Technische Bundesanstalt (PTB). A spinning rotor gauge (SRG), a Bayard-Alpert gauge (BAG) and an extractor gauge (EXG) were chosen as transfer standards. The comparison was carried out in a star-like pattern with PTB as pilot laboratory. The argon pressures generated by the standards at 9×10−4 Pa were compared by measuring the accommodation coefficient of the SRG, the argon pressures from 3×10−7 Pa to 9×10−4 Pa by measuring the sensitivity of the two ionization gauges. The accommodation coefficients determined at NIST and PTB indicate a difference between the pressures generated by the NIST and PTB standards of (PNIST−PPTB)/PPTB=(0.09±0.11)% (standard or one-sigma uncertainty). For the pressures between 3×10−7 Pa and 9×10−4 Pa the results obtained at NIST and PTB had a mean difference of 〈(PNIST−PPTB)/PPTB〉=(0.24±0.12)%, with a maximum difference of (1.2±0.6) at the lowest pressure. The NIST-PTB differences are all within the combined uncertainties of the two standards. Large transfer standard instabilities and inconsistent results in a first NPL-PTB comparison prompted a repeat set of measurements. An average of the two sets of SRG measurements indicates a significant difference between NPL and PTB standards of (PNPL−PPTB)/PPTB=(1.31±0.14)%. The two sets of ionization gauge measurements effectively repeated, but the results for the individual gauges are inconsistent. The EXG results indicate no significant pressure dependence in the difference between the standards for pressures below 9×10−4 Pa. The BAG results indicate a significant increase in the difference between the standards as the pressure is reduced, with (PNPL−PPTB)/PPTB becoming as large as 5% or 6% at the lower pressures. Several potential problems with the BAG operation were identified, which might indicate that more confidence should be placed in the EXG results. However, there is no reliable evidence that the BAG comparison results were actually affected, and the results for each gauge are so internally consistent that neither can be rejected. Further work should be directed towards resolving this discrepancy.
Observation of the reaction of gas-phase atomic oxygen with Ru(001)-p(1×1)-D at 80 K
Authors: Weiss M. J. , Hagedorn C. J. , Weinberg W. H.
Published: July 2002

The interaction of gas-phase atomic oxygen with chemisorbed deuterium on Ru(001) has been investigated by means of temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). Exposure of gas-phase atomic oxygen to the p(1×1) deuterium overlayer at a surface temperature of 80 K results primarily in the adsorption of oxygen atoms. Thermal desorption spectra measured after large atomic oxygen exposures show the desorption of D2O between 150 and 190 K as well as a large decrease in the activation energy for the recombinative desorption of deuterium. HREEL spectra demonstrate the presence of D2O following atomic oxygen exposure at 80 K and, together with TPD spectra, suggest the presence of chemisorbed OD. Since OD and D2O are formed at low surface temperatures, an Eley-Rideal-like mechanism is suggested in which oxygen atoms from the gas phase react with deuterium adatoms prior to being thermally accommodated to the surface.
A cylindrical magnetron sputtering system for depositing metal–aluminium nitride cermet solar coatings onto batches of tubes
Authors: Zhang Qi-Chu , Zhao K. , Zhang B.-C. , Wang L.-F. , Shen Z.-L. , Lu D.-Q. , Xie D.-L. , Zhou Z.-J. , Li B.-F.
Published: July 2002

A cylindrical direct current (dc) magnetron sputtering system of commercial scale for coating glass tubes with metal–aluminium nitride (M–AlN) cermet solar selective surfaces is described. The stainless steel–aluminium nitride (SS–AlN) cermet material has been investigated as a solar absorbing layer. During the deposition of a SS–AlN cermet layer, both an Al metal target and stainless steel target are sputtered simultaneously in a gas mixture of argon and nitrogen. The nitrogen partial pressure is set sufficiently high at the aluminum target side to ensure that a nearly pure AlN ceramic sublayer is deposited onto the surrounding tubes by dc reactive sputtering. The excellent nitriding resistance of stainless steel leads to a nearly pure SS sublayer being deposited onto the tubes. Tube planetary rotation results in a deposited multi-layered system consisting of alternating SS and AlN sublayers. This multi-sublayer system can be considered as a macro-homogeneous cermet layer with the metal volume fraction determined by controlling the thicknesses of SS and AlN sublayers. Varying the SS target current achieves different SS volume fractions in the cermet layers. Following this procedure the SS–AlN cermet solar selective coatings with a double cermet layer structure were deposited onto 32 borosilicate glass tubes of 37 mm outside diameter and 1.2 m long. A solar absorptance of 0.94–0.95 and emittance of 0.04–0.05 at room temperature has been achieved.
Study of the desorption mechanism of alkylsiloxane self-assembled monolayers through isotopic labeling and high resolution electron energy-loss spectroscopy experiments
Authors: Kluth G. Jonathan , Sander Melissa , Sung Myung M. , Maboudian Roya
Published: July 2002

Recently it has been proposed that alkylsiloxane self-assembled monolayers on oxidized Si(100) decompose through C–C bond cleavage [G. J. Kluth, M. M. Sung, and R. Maboudian, Langmuir 13, 3775 (1991)]. To verify this desorption picture, pentadecyltrichlorosilane precursors with four deuterated carbon atoms at the end of the molecule have been synthesized. High-resolution electron energy-loss spectroscopy shows that the monolayers are stable in vacuum up to 750 K. Above 750 K the C–D stretch disappears, while the C–H stretch remains, indicating that the end of the chain desorbs before the entire chain. From these observations it is concluded that the chains decompose primarily through C–C bond cleavage, resulting in the desorption of hydrocarbon fragments and a reduction in chain length.
Properties of various sputter-deposited Cu–N thin films
Authors: Wang Dao-yuan , Nakamine Norio , Hayashi Yasunori
Published: July 2002

Compositions and structures of sputter-deposited Cu–N films are strongly dependent on the total sputtering pressure and on the content of nitrogen gas. The Cu–N films obtained can be classified into four categories: metallic Cu-rich Cu3N films with a positive temperature coefficient of resistivity (TCR), semiconducting Cu-rich Cu3N films, semiconducting stoichiometric Cu3N films, and semiconducting N-rich Cu3N films with a negative TCR. The current–voltage curves of various Cu–N films are presented. The metallic conduction and semiconductor conduction are two main electrical conduction mechanisms for various Cu–N films. The decomposition temperature of various Cu–N films has been determined to be around 604–614 K using both thermogravimetry and dynamical measurement of electrical resistance during heating in a vacuum furnace. The great scattering of data over the electrical resistivity of Cu3N reported up to now is mainly due to the nonstoichiometry of the Cu3N. The optical band gap of stoichiometric Cu3N is determined to be around 1.8–1.9 eV, but it decreases with the decrease in the degree of stoichiometry.
Diamond-like bonds in amorphous hydrogenated carbon films induced by x-ray irradiation
Authors: Sato Fumio , Saito Nobuo , Hirano Yoshiyuki , Jayatissa Ahalapitiya H. , Takizawa Kuniharu , Kawado Seiji , Kato Takanori , Sugiyama Hiroshi , Kagoshima Yasushi , Ando Masami
Published: July 2002

Diamond-like carbon films have been irradiated with x-rays from a synchrotron radiation source. Raman measurements showed that the fraction of tetrahedrally coordinated (sp3) bond in the film increased with the increase of x-ray irradiation time, whereas it decreased as the annealing temperature increased. It was confirmed by electron spin resonance measurements that the number of spins did not change by x-ray irradiation. These results indicated that the transition from sp2 to sp3 bond takes place by nonthermal Coulomb repulsive rearrangement of atoms after inner-shell electron excitation.
General technological modeling method for the design of transparent conductive In2O3 electrodes
Authors: Golan G. , Axelevitch A. , Rabinovitch E.
Published: July 2002

Highly conductive transparent indium oxide (In2O3) thin films were prepared by DC magnetron sputtering using pure indium oxide targets in a pure argon (Ar) atmosphere. A linear programming method for the design and optimization of the process was used. The physical model of the sputtering process was based on randomly selected sections of the parameter space. The processing model was optimized by the “steep rise” method, using the mathematical model gradient to obtain optimal parameters. The active independent factors of the sputtering process were Ar pressure during the process, substrate temperature, target voltage and deposition time. As a result of the optimization process, the transparent conductive indium oxide thin films had the following characteristics: Transmittance (T) was 90.7% at λ=550 nm on glass substrates with an uncoated external T=91.1% and resistivity of up to 0.043 Ω cm for a 250 nm film thickness. Thus, the linear model method for the design and optimization of this multiparameter physical process was effective.
Preparation of high quality RuO2 electrodes for high dielectric thin films by low pressure metal organic chemical vapor deposition
Authors: Lee Jong Myeong , Shin Ju Cheol , Hwang Cheol Seong , Kim Hyeong Joon , Suk Chang-Gil
Published: July 2002

Pure and conducting RuO2 thin films were deposited on a Si substrate at 250–450 °C using Ru(C11H19O2)3 as a precursor by low pressure metal organic chemical vapor deposition (MOCVD). At a lower deposition temperature, the smoother and denser RuO2 thin films were deposited. The amount of O2 addition did not seriously affect the properties of the RuO2 thin film. The RuO2 thin films which were crack free and well adhered onto the substrates showed very low resistivity of 45–60 μΩ cm. At a lower deposition temperature and a smaller amount of O2 addition, RuO2 thin films showed better step coverage, indicating that MOCVD RuO2 thin films from Ru(C11H19O2)3 can be applied for an electrode of high dielectric thin films for a capacitor of ultralarge scale integrated dynamic random access memory.
Transparent barrier coatings on polyethylene terephthalate by single- and dual-frequency plasma-enhanced chemical vapor deposition
Authors: da Silva Sobrinho A. S. , Latrèche M. , Czeremuszkin G. , Klemberg-Sapieha J. E. , Wertheimer M. R.
Published: July 2002

Transparent barrier coatings on polymers are receiving much attention in industry, for pharmaceutical, food and beverage packaging applications. Plasma-enhanced chemical vapor deposition (PECVD) is among several competing techniques which can produce thin layers of inorganic glassy barrier materials. In this article we describe the performance of silicon compounds (SiO2 and Si3N4) on 13 μm polyethylene terephthalate (PET) substrates, the barrier coatings being deposited in a dual-frequency (microwave/radio frequency) pilot-scale PECVD reactor for continuously moving flexible webs up to 30 cm in width. The volatile silicon compound used for SiO2 deposition is HMDSO (C6H18Si2O), while SiH4 serves to deposit Si3N4. Coating thicknesses, d, in the range 8 nm⩽d⩽200 nm, are measured using a variety of techniques, namely stylus profilometry, continuous wavelength optical interferometry, x-ray fluorescence, variable angle spectroscopic ellipsometry, and transmission electron microscopy, while film compositions are determined by x-ray photoelectron spectroscopy. Oxygen transmission (OTR) and water vapor transmission (WVTR) measurements are carried out with MOCON “Oxtran” and “Permatran-W” instruments, respectively. As also reported by other workers, we typically find OTR values of about 0.5 scc/m2 day and WVTR about 0.3 g/m2 day, for barrier thicknesses exceeding a “critical” value (dc, about 15 nm), but the minimum permeation values depend upon the concentration of defect sites in the coating (mostly related to substrate microroughness). In order to confirm this correlation, we have developed a technique combining reactive ion etching through the PET, followed by optical and transmission electron microscopies, to characterize the types and number densities of coating defects. On the basis of these, we find good agreement between measured and calculated values of OTR.
High temperature oxidation of (Ti1-XAlX)N coatings made by plasma enhanced chemical vapor deposition
Authors: Kim Byoung-June , Kim Young-Cheol , Nah Jae-Woong , Lee Jung-Joong
Published: July 2002

(Ti 1-X Al X ) N coatings were deposited by the plasma enhanced chemical vapor deposition method using a gas mixture of TiCl4, AlCl3, NH3, H2 and Ar, and the oxidation behavior at high temperatures as well as the oxidized structure of the coatings were examined. The oxidation rate of the coatings at temperatures below 1000 °C was found to fit well to a parabolic time dependence. It has also been found that up to 900 °C (Ti1-XAlX)N coatings at X⩾0.25 showed considerably improved oxidation resistance compared to TiN, due to the formation of a dense α-Al2O3 layer at the surface of the coatings. At X<0.25, however, this dense protective layer could not form, and the coatings were fully oxidized after a short period of time. When the temperature reached 900 °C, Fe in the substrate diffused out through the coating by pipe diffusion as well as through the cracks that were produced by thermal stresses, and oxidized rapidly at the surface of the coating.
Stabilization of long travel-single bellows-horizontal manipulators
Authors: Smentkowski V. S. , Linsebigler A. L.
Published: July 2002

Long travel, single bellows, horizontal manipulators are required for many experiments in surface science. Unfortunately, the gravitational forces exerted on long travel, single bellows, horizontal manipulators cause stability problems. The stability problems include, but are not limited to unwanted sample vibrations and nonreproducible sample positioning. We have designed, built, and tested a simple add on device that efficiently alleviates such problems. The device that will be described can be used with any manipulator, regardless of age. The cost to implement this device (machining and parts) is minimal.
Design and installation of a low particulate, ultrahigh vacuum system for a high power free-electron laser
Authors: Dylla H. F. , Biallas G. , Dillon-Townes L. A. , Feldl E. , Myneni G. R. , Parkinson J. , Preble J. , Siggins T. , Williams S. , Wiseman M.
Published: July 2002

A high-average power (kW) infrared (IR) free-electron laser (FEL) is currently being commissioned for the Jefferson Laboratory FEL User Facility. The IR FEL is driven by a unique superconducting rf linac which is recirculated to recover electron beam power that is not radiated in the FEL. The design and installation of the vacuum system for the FEL involved particular attention to minimizing particulate contamination which could cause problems with the superconducting acceleration cavities and the high power FEL optics. Particulate contamination levels of all vacuum components were monitored during the cleaning process using laser scattering. Cleaning, transport, and installation procedures were developed to minimize the contamination of the complete system. We will summarize a data base we compiled of particulate contamination levels of the various components installed in the FEL vacuum system.
Morphology and excited state dynamics in thin organic molecular films probed by femtosecond time-resolved photoemission spectroscopy
Authors: Mäkinen A. J. , Xu S. , Zhang Z. , Diol S. J. , Gao Y. , Mason M. G. , Muenter A. A. , Mantell D. A. , Melnyk A. R.
Published: July 2002

We have studied the lifetimes of the excited electron states of thin N,N′bis(phenethyl)perylene-3,4:9,10-bis(dicarboximide) (DPEP) films, prepared in situ, using femtosecond time-resolved photoemission spectroscopy. DPEP is an organic compound similar to photoreceptor materials widely used in many imaging applications. By controlling the evaporation conditions, we have been able to grow films of different morphologies, and found that the relaxation dynamics depends on the morphology. We have investigated two distinct films characterized by very different absorption spectra. We have found that for the film with absorption maximum at 500 nm, a typical lifetime is 55 fs at 2.1 eV above the highest occupied molecular orbital level. For the other film with absorption maximum at 630 nm, the relaxation rate is almost twice as fast, resulting in a lifetime of 30 fs at the same energy. We attribute the extremely short lifetimes to a rapid internal conversion process from S2 and S1 levels to the vibrational manifolds of S1 and S0 states and the vibrational relaxation of the latter. The dependence of the lifetimes on the morphology can be explained by the formation of extended states in the better-ordered DPEP film and by fast transitions within these states.
Secondary ion mass spectrometry of deep trench capacitors in dynamic random access memory
Authors: Parks C. C. , Glawischnig H. , Levy M. , Stengl R. , Dieseldorff Chr.
Published: July 2002

Secondary ion mass spectrometry (SIMS) supported the development of deep trench capacitors in dynamic random access memory. SIMS is done efficiently by analyzing thousands of cells in parallel and the approach described in this article is scaleable to the multi-Gbit generation. By projecting out fundamental values using geometrical formalisms, the behavior of contaminants and dopants in sub-micrometer geometries is understood without the need for small-area measurements. This array-profiling approach is used to quantify and partition halogen, alkali, and transition-metal contaminants among deep trench and other processing sectors. The deposition of self-limiting layers of arsenic during polysilicon fill of the deep trench is explored in detail. The doping of the trench sidewalls, either through angle ion implants or by drive in of doped-glass deposition, is quantified.
Redistribution and activation of implanted S, Se, Te, Be, Mg, and C in GaN
Authors: Wilson R. G. , Zavada J. M. , Cao X. A. , Singh R. K. , Pearton S. J. , Guo H. J. , Pennycook S. J. , Fu M. , Sekhar J. A. , Scarvepalli V. , Shu R. J. , Han J. , Rieger D. J. , Zolper J. C. , Abernathy C. R.
Published: July 2002

A variety of different possible donor and acceptor impurities have been implanted into GaN and annealed up to 1450 °C. S+ and Te+ produce peak electron concentrations ⩽5×1018 cm−3, well below that achievable with Si+. Mg produces p-type conductivity, but Be+- and C+- implanted samples remained n type. No redistribution was observed for any of the implanted species for 1450 °C annealing. Much more effective damage removal was achieved for 1400 °C annealing of high-dose (5×1015 cm−2) Si+ implanted GaN, compared to the more commonly used 1100 °C annealing.
Investigation of resonant photoemission in Gd with x-ray linear dichroism
Authors: Mishra S. R. , Cummins T. R. , Waddill G. D. , Gammon W. J. , van der Laan G. , Goodman K. W. , Tobin J. G.
Published: July 2002

The constructive summing of direct and indirect channels above the absorption threshold of a core level can cause a massive increase in the emission cross section, leading to a phenomenon called “resonant photoemission.” Using novel magnetic linear dichroism in angular distribution photoelectron spectroscopy experiments and theoretical simulations, we have probed the nature of the resonant photoemission process in Gd metal. It now appears that temporal matching as well as energy matching is a requirement for true resonant photoemission.
Challenges in plasma etching and patterning for fabrication of new systems and devices
Authors: Engelhardt M. , Weinrich V. , Nagel N. , Hartner W.
Published: July 2002

Besides plasma etching of through-wafer interconnects in wafer stacks for vertical integration of chips [M. Engelhardt et al., Proceedings of the 23rd Annual Tegal Plasma Seminar (1997)] fabrication of Pt storage nodes with nontapered sidewalls is one of the most challenging tasks of plasma process technology today. In this work the fabrication of vertical Pt profiles was achieved by plasma processing with resist mask. In this novel approach, the buildup of thin redepositions of Pt onto the sidewalls of the resist, obtained as a result of processing in pure Ar plasmas, is utilized to achieve a sidewall steepness of the patterned Pt film which is determined by the steepness of the preetch resist profile. After pattern transfer and resist stripping, the portion of the redepositions protruding above the fabricated storage node was completely removed by chemical mechanical polishing.
Intermediate structures appearing in the phase transition of Si(111)-7×7 to (√3×√3)R30° induced by HBO2 molecular irradiation
Authors: Miyake K. , Kaikoh T. , Hata K. , Morita R. , Yamashita M. , Shigekawa H.
Published: July 2002

We have investigated the breakdown process of the 7×7 structure during its transition to the (√3×√3)R30° phase induced by HBO2 irradiation. The 7×7 structure was destroyed over the wide area before the nucleation of the (√3×√3)R30° phase. Even when the (√3×√3)R30° structure nucleated in the disordered area, disordered structure existed between the domains of the 7×7 and (√3×√3)R30° structural phases. The observed results are completely different from the (√3×√3)R30° formation processes induced by other group III atoms, where (√3×√3)R30° phases are formed as adjacent to the 7×7 structural domains. The surface B atom concentration in the 7×7, disordered, and (√3×√3)R30° regions were estimated to be about one, three, and six per 7×7 unit cell. The disordered structure remained on the surface even after annealing the sample at 750 and 900 °C. And the B concentration in the disordered region did not change. These results indicate that the disordered structure is an intrinsic nature of the B-induced reconstruction, and suggest the existence of the relationship between the B atom concentration and the stability of the 7×7 structure.
Thallium overlayers on Si(111): Structures of a “new” group III element
Authors: Vitali Lucia , Leisenberger Friedrich P. , Ramsey Michael G. , Netzer Falko P.
Published: July 2002

The structure and growth of Tl overlayers on Si(111)7×7 surfaces have been investigated using ultraviolet photoelectron spectroscopy, low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and scanning tunneling microscopy (STM). At low coverages Tl adsorption occurs almost exclusively on the faulted half of the (7×7) unit cell and forms small, two-dimensional clusters. With increasing Tl coverage the whole surface becomes covered while the (7×7) surface periodicity is maintained as evidenced by LEED and STM. After deposition of the first 2 monolayers (ML) the high mobility of Tl adatoms leads to the condensation of few, but large islands. At the surface of the second monolayer of Tl an interesting network of bright contrast lines is observed, which appears to be induced by the (7×7) substrate periodicity lying two layers below and which may be caused by the surface strain mediated by the (7×7) unit cell boundaries. The surface phase diagram of Tl–Si(111) at elevated temperatures contains a (1×1) structure at 1 ML coverage and an approximate (6×6) phase. The latter is due to an incommensurate structure of the second Tl layer on top of the (1×1) ML.
Electromigration induced dynamics of surface dislocations and atomic steps
Authors: Shimoni N. , Biham O. , Millo O.
Published: July 2002

Electromigration induced dynamics of surface dislocations in flame annealed gold films is studied using scanning tunneling microscopy. The emergence of new dislocations appears to be strongly correlated with the onset of current stressing, and their direction is correlated with that of the current. The emergence rate decreases with time elapsed from flame annealing. We also investigate the time evolution of dislocations, which, in most cases, are found to be more robust against electromigration as compared to the normal atomic steps.
Monte Carlo simulations of the kinetics of catalytic reactions on nanometer-sized particles, with diffusion over facet boundaries
Authors: Persson H. , Thormählen P. , Zhdanov V. P. , Kasemo B.
Published: July 2002

Using the Monte Carlo technique, we comprehensively investigate the steady-state kinetics of the 2A+B2→2AB reaction on a nanometer-sized catalyst particle. The attention is focused on the adsorbate-diffusion-mediated interplay of reaction kinetics occurring on different facets. This effect is explored for different ratios of the rate constants for adsorption, desorption, reaction, and diffusion. The results obtained demonstrate that the reaction kinetics can be uniquely different on nanometer particles compared to those on macroscopic single-crystal surfaces.
Ionization gauge errors at low pressures
Authors: Kendall B. R. F.
Published: July 2002

Factors affecting the accuracy of ionization gauge measurements at low pressures are reviewed. In hot-cathode gauges these include electron-stimulated desorption at the electron collector, forward and reverse x-ray effects, the potential of the gauge envelope, outgassing, and various controller-related errors. In cold-cathode gauges they include nonlinearities below the “magnetron knee,” plasma instabilities, and background currents. Case studies are given to illustrate many of these sources of error and their elimination. The case studies were gathered in the course of long-term stability measurements on over 30 ionization gauges at pressures ranging from the 10−8 to 10−11 Torr ranges. The investigation included Bayard–Alpert (both conventional and modulated), extractor, inverted magnetron, double inverted magnetron, and magnetron gauges. Errors caused by outgassing from virtual leaks in all-metal seals are also considered. By far the largest and most unpredictable source of error proved to be electron-stimulated desorption in hot-cathode gauges, avoidable by operating the grid at a sufficiently high temperature. It is concluded that, with proper precautions, better then 10% reproducibility in the 10−10 Torr range is easily achievable over periods of many months with either hot-cathode or cold-cathode gauges. Over shorter periods, reproducibility of better than 1% is obtainable with well-designed hot-cathode gauges.
Composition and structure of HCl-isopropanol treated and vacuum annealed GaAs(100) surfaces
Authors: Tereshchenko O. E. , Chikichev S. I. , Terekhov A. S.
Published: July 2002

The GaAs(100) surfaces chemically treated in HCl-isopropanol solution and annealed in vacuum were studied by means of Auger electron spectroscopy, x-ray photoelectron spectroscopy, high-resolution electron energy-loss spectra, and Low-energy electron diffraction (LEED). Chemical treatment and sample transfer into ultrahigh vacuum were performed under nitrogen atmosphere. The HCl-isopropanol treatment removes gallium and arsenic oxides from the surface, with about 2 monolayers of excess arsenic being left on it. The residual carbon contaminations were around 0.2–0.4 ML and consisted of the hydrocarbon molecules. These hydrocarbon contaminations were removed from the surface together with the excess arsenic by vacuum annealing at 300–420 °C. With increased annealing temperature, a sequence of six reconstructions were identified by LEED: (1×1), (2×4)/c(2×8), (2×6), (3×6), (4×1) and c(8×2) in the temperature intervals of 250–400, 420–480, 480–500, 500–520, 520–560 and 560–600 °C, respectively. All surface reconstructions were irreversible. The structural properties of chemically prepared GaAs(100) surfaces were found to be similar to those obtained by molecular-beam epitaxy-growth and by decapping of As-capped epitaxial layers.
Energy transfer into the growing film during sputter deposition: An investigation by calorimetric measurements and Monte Carlo simulations
Authors: Drüsedau Tilo P. , Bock Torsten , John Thomas-Maik , Klabunde Frank , Eckstein Wolfgang
Published: July 2002

The power density at the substrate during sputter deposition was measured by a calorimetric method. In combination with measurements of the atomic deposition rate, the total amount of the energy input per incorporated atom was determined. The measured values range from 18 eV for aluminum to about 1000 eV maximum per atom for carbon. There is, for all elements investigated, a general trend for a linear increase of the energy per atom with increasing sputtering argon pressure over the range from 0.2 to 7 Pa. The energy per atom decreases with increasing power of the sputtering discharge. The application of a negative bias to the substrate reduces the total energy per atom to the values measured at low pressure of 0.4 Pa or below. The total energy flux in the low pressure range (0.4 Pa or less) can be well described by contributions due to plasma irradiation, the heat of condensation of the deposited atoms, their kinetic energy, and the kinetic energy of the reflected argon neutrals. The latter two components are a priori calculated by TRIM.SP Monte Carlo simulations. There is good agreement between the a priori calculated and the measured values. The combination of experimental and theoretical data result in empirical rules for the energies of the sputtered and reflected species, which allow an estimate of the energy input during sputter deposition for every elemental target material in the low pressure range. In a first approximation, the energy per incorporated atom is proportional to the ratio between target atomic mass and sputtering yield.
Recommended practices for measuring the performance and characteristics of closed-loop gaseous helium cryopumps
Authors: Welch Kimo M. , Andeen Bruce , de Rijke Johan E. , Foster Christopher A. , Hablanian Marsbed H. , Longsworth Ralph C. , Millikin William E. , Sasaki Y. Tito , Tzemos Constantinos
Published: July 2002

This article establishes a set of uniform procedures for quantitatively characterizing closed-loop gaseous helium cryopumps. Topics include a listing of technical definitions and hardware illustrations of cryopumps; safety considerations in the use of cryopumps; methods and procedures for determining the speed, ultimate pressure, capacity, cool-down time, impulsive gas load tolerance, regeneration time, thermal radiation tolerance, and maximum throughput tolerance of cryopumps; and, a method of measuring the vibration characteristics of cryopumps.
Fine control of deposition film compositions using radio-frequency reactive sputtering with periodic gas additions
Authors: Kimura Shoji , Honda Takuya , Fukushi Daigo
Published: July 2002

Thin films of titanium nitride are prepared on metallic substrates using rf reactive sputtering. A pure titanium target and argon plasma are used with reactive gas of nitrogen in the sputter. The pressure of Ar is 0.53 Pa, and the input power 300 W. The reactive gas is periodically added to a constant plasma supporting Ar flow as a form of square waves, and this is called the modulation method. Wide atomic ratios of N to Ti, 0.3 to unity, are obtained by changing the duty ratio or period, where the stoichiometric ratio of TiN is unity. The variation of the atomic ratio is slower than that of the continuous nitrogen gas addition and this promises easy handling for producing a film with a particular atomic ratio. Moreover, the deposition rates are maintained within a factor of 30% decrease. These results indicate possible application to bulky material preparations such as functionally gradient materials (FGMs) and FGM-like intermediate layers for composite materials.
Enhancement of the etch rate of LiNbO3 by prior bombardment with MeV O2+ ions
Authors: Leech Patrick W. , Ridgway Mark C.
Published: July 2002

The implantation of LiNbO3 with 5 MeV O2+ ions has been examined as a means of increasing the rate of subsequent reactive ion etching in CF4/CHF3 plasmas. The etch rate of LiNbO3 implanted at a dose sufficient to amorphize the substrate (1×1015–5×1015 ions cm−2) was ⩽3 times higher than in unimplanted substrates. The measured etch rates in CF4/CHF3 plasmas were essentially independent of the implant dose below 3×1014 ions cm−2 but increased significantly at and above 1×1015 ions cm−2. This transition was correlated with the onset of amorphization. In an Ar plasma, the etch rate of LiNbO3 was unaffected by prior million electron volt implantation and was an order of magnitude lower than in the CF4/CHF3 plasmas. These results have suggested that the damage induced by million electron volt implantation acted to accelerate the process of ion-enhanced chemical etching in LiNbO3 but had no significant influence on the process of physical sputtering in an Ar plasma.
High aspect ratio SiO2 etching with high resist selectivity improved by addition of organosilane to tetrafluoroethyl trifluoromethyl ether
Authors: Chinzei Y. , Feurprier Y. , Ozawa M. , Kikuchi T. , Horioka K. , Ichiki T. , Horiike Y.
Published: July 2002

Measurements of the ion species generated in the planar type neutral loop discharge of tetrafluoroethyl trifluoromethyl ether (CF3–O–CHF–CF3;HFE 227) demonstrate the presence of CFx+ species and CFx radicals, in a comparable manner to plasmas of more established gases such as C4F8, C2F6 or CHF3. However, as the etch selectivity of boron phosphorus silica glass (BPSG) to resist is quite poor in HFE 227 plasmas, organosilane Si(CH3)xH4−x additive gases are investigated as a source of Si to improve the BPSG/resist selectivity. The addition of 10% trimethylsilane to HFE 227 is capable of providing selectivity close to 5, which is desirable for the fabrication of deep holes. It is shown that the HFE 227/trimethylsilane plasma chemistry also preserves the resist hole pattern and does not cause hole expansion during the etching process. These latter observations are attributed to the deposition of polymer precursors induced by the trimethylsilane addition which reduces the top resist surface etch rate and balances the removal rate of the resist sidewalls. As a result, 0.15 μm diam holes with an aspect ratio of 15 are successfully fabricated. Mass spectrometry measurements of fluorocarbon radicals and ionic species imply that the high aspect ratio feature can be fabricated by having mostly CF3+ ions and lower density of fluorocarbon radicals. Furthermore, the microloading-free etching of contact holes is achieved at a bias voltage of −500 V for diameters down to 0.15 μm holes. The limit of the etching performance of the HFE 227/10% trimethylsilane plasma etch chemistry is investigated using very fine patterns defined by electron beam lithography. Trenches of 20 nm in width and mesh holes of 70 nm can be fabricated.
Influence of substrate temperature on the properties of indium oxide thin films
Authors: Adurodija F. O. , Izumi H. , Ishihara T. , Yoshioka H. , Motoyama M. , Murai K.
Published: July 2002

Pure indium oxide (In2O3) and SnO2-doped In2O3 (5 and 10 wt %) films were deposited on glass at different substrate temperatures (Ts) ranging from room temperature (RT=25 °C) to 350 °C using pulsed laser deposition. At low Ts (RT to 100 °C), pure In2O3 films yielded the lowest resistivity of (1.8–2.5)×10−4 Ω cm and the resistivity increased sharply with an increase in Ts, and the rise in the resistivity of pure In2O3 films resulted mainly from a decrease in carrier concentration and Hall mobility. For SnO2-doped In2O3 films, the resistivity decreased from 3.5×10−4 to 1.3×10−4 Ω cm with increasing Ts from RT to 350 °C and the reduction in the resistivity is associated with thermal activation of Sn leading to an increase in carrier concentration. Amorphous films were obtained at RT, but from Ts of 100 °C, the films appeared polycrystalline with orientation in the 〈111〉 plane. From atomic force microscopy, minimum surface roughness (Ra)⩽1.3 nm was obtained at RT and Ts>200 °C. Between 100 and 150 °C, Ra was maximum (2.5–4.9 nm). The films also exhibited high optical transmittance (>85%) to visible light.
New C–F interatomic potential for molecular dynamics simulation of fluorocarbon film formation
Authors: Tanaka J. , Abrams C. F. , Graves D. B.
Published: July 2002

A new interatomic potential of fluorocarbon systems has been developed. This potential is based on Brenner’s reactive empirical bond-order potential [D. W. Brenner, Phys. Rev. B 42, 9458 (1990)] for hydrocarbon systems which is a variation of Tersoff potential [J. Tersoff, Phys. Rev. Lett. 56, 632 (1986)]. A set of empirical correction functions was determined so as to reproduce the accurate atomization energies of many types of fluorocarbon molecules. To check the transferability of Tersoff–Brenner potential to ion sputtering problems, molecular dynamics simulations were conducted. We thereby studied carbon sputtering by argon ions for the first time and obtained reasonable sputtering yield compared with experimental data. The fluorocarbon film formation on an amorphous carbon surface exposed to CFx+ (x=1,2,3) bombardments was also simulated with the new C–F potential. (The ion energy was 100 eV.) CF+ impacts continued to grow carbon-rich fluorocarbon film, but CF2+ ions formed a fluorocarbon film that was then etched down. And CF3+ ion impacts turned the deposition into etching more rapidly than CF2+. The composition of etching products changed according to the state of fluorocarbon films, and this change should be included in boundary conditions of macrolevel simulations.
Compact wide-range cold-cathode gauges
Authors: Kendall B. R. F. , Drubetsky E.
Published: July 2002

Cold-cathode ionization gauges offer many advantages for routine high-vacuum measurements. They are simple and robust. Thermal outgassing and electron-stimulated desorption, both significant problems in hot-cathode gauges, are negligible. There are no x-ray effects to cause errors at low pressures. For many applications it would be useful to reduce the physical size of cold-cathode gauges and especially to reduce the volume in which the associated stray magnetic field is significant. We describe experiments to explore the role of the operating voltage and magnetic field strengths on the performance of cold-cathode gauges. The results allowed the design and development of compact wide-range gauges having internal volumes as low as 5–15 cm3, while maintaining a high sensitivity of 10 A Torr−1 at 10−6 Torr. The magnets are little more than one third the volume used in most conventional designs. This, combined with the use of a double inverted magnetron layout, reduces the external magnetic fields by more than an order of magnitude. At 15 cm from the center of the compact gauge, the external field is comparable with the Earth’s magnetic field. For ultrahigh vacuum applications, an internal field emitter provides quick starting. If necessary, an Americium 241 source or a carbon film cold emitter can be used for essentially instant starting. Testing in nitrogen has covered pressures from the mid-10−11 Torr range to above 10−2 Torr.
Transverse elastic waves in periodically layered infinite, semi-infinite, and slab media
Authors: Camley R. E. , Djafari-Rouhani B. , Dobrzynski L. , Maradudin A. A.
Published: July 2002

The propagation of transverse elastic waves both perpendicular and parallel to the laminations of infinite and semi-infinite periodically layered media is studied. The displacement fields and the dispersion relations for such waves are obtained analytically, and the latter are solved numerically to yield the corresponding dispersion curves. It is shown that a semi-infinite medium layered periodically parallel to its stress-free surface can support shear horizontal surface acoustic waves that have no counterpart in a homogeneous medium. Finally, the dynamical elastic Green’s function for a semi-infinite medium layered periodically parallel to its stress-free surface is obtained, and its possible application to Brillouin scattering studies of the surface acoustic waves on such a medium is discussed.