bluuebunny/crossref_metadata_2025 huggingface dataset:
Some aspects of dissipation mechanisms in chlorine containing capacitively coupled discharges
Authors: Franz Gerhard
Published: July 2006

The temperature of gaseous neutrals in capacitively coupled discharges of chlorine, argon, and hydrogen has been measured using optical emission spectroscopy. This has been accomplished by adding small amounts of nitrogen to the ambient. The temperature can then be obtained by fitting the unresolved second rotational positive band of nitrogen. It has been found that the gaseous temperature in argon saturates for higher pressures logarithmically, whereas in chlorine, a linear behavior is observed up to the highest pressures and power inputs. Highest temperatures in chlorine have been found to be about 1100°C, whereas in hydrogen, temperatures higher than 500°C are rarely observed. Likewise, the effective collision frequency in chlorine increases significantly in the medium pressure range indicating a change in excitation/dissipation from the regime of stochastic heating to Ohmic heating, whereas the discharge in the inert gas still remains in the regime of stochastic heating. The experimental data for the collision frequency of the electrons with neutrals can be perfectly modeled for chlorine with these reduced gaseous densities.
Temperature-induced control of aspect ratio of gold nanorods
Authors: Park Hyung Ju , Ah Chil Seong , Kim Wan-Joong , Choi Insung S. , Lee Kwang-Pil , Yun Wan Soo
Published: July 2006

Aspect ratio of gold nanorods can be controlled by simply adjusting the reaction temperature in the seed-mediated synthesis of the nanorods. The gold nanorods were synthesized by the injection of gold nanoparticle seeds of around 4nm in diameter into a reaction mixture containing hydrogen tetrachloroaurate, hexadecyltrimethylammonium bromide, and ascorbic acid. Average aspect ratio of the resulting nanorod increases from 1 to about 40 with decreasing the reaction temperature from 315to276K, which can be attributed to the temperature-induced change in the shape of the micellar templates. For further understanding of the growth mechanism, silver nanoparticles were also used as seeds in the preparation of the gold nanorod.
Effects of N2 remote plasma nitridation on the structural and electrical characteristics of the HfO2 gate dielectrics grown using remote plasma atomic layer deposition methods
Authors: Choi Jihoon , Kim Seokhoon , Kim Jinwoo , Kang Hyunseok , Jeon Hyeongtag , Bae Choelhwyi
Published: July 2006

The characteristics of remote plasma atomic layer deposited HfO2 on Si, which has a very thin SiO2 interlayer with and without remote plasma nitridation (RPN), have been investigated. Small amounts of N atoms were successfully incorporated by RPN pretreatment, in which the dominant emission species were excited atomic nitrogen (N*) and excited molecular nitrogen (N2*), into a very thin SiO2 interlayer for the growth of HfO2 thin film. The thin (∼1.5nm) intermediate layer containing nitrogen, which was prepared by sequential O2 and N2 remote plasma treatment of the Si substrate, can effectively suppress growth of the unintentional interface layer. In addition, it enhances the thermal stability and the resistance to oxygen diffusion during rapid thermal annealing. The HfO2 film containing the remote plasma nitrided SiO2 interlayer annealed at 800°C showed a lower equivalent oxide thickness of ∼1.89nm and a lower leakage current density (3.78×10−7Acm−2 at ∣VG−VFB∣=2V) compared to a non-nitrided sample of the same physical thickness. Also, we compared the characteristics of HfO2 films annealed in two different ambient environments, N2 and O2.
X-ray photoelectron spectroscopy study of the nucleation processes and chemistry of CdS thin films deposited by sublimation on different solar cell substrate materials
Authors: Espinós J. P. , Martín-Concepción A. I. , Mansilla C. , Yubero F. , González-Elipe A. R.
Published: July 2006

Cadmium sulfide has been deposited by evaporation on five different substrates: CdTe, ZnO, Ag, TiO2, and partially reduced titanium oxide (i.e., TiO1.73). The deposition rate and the evolution of the Cd∕S ratio on the different substrates have been determined by x-ray photoelectron spectroscopy. The growth mode of the films has been also studied by analyzing the shape of the backgrounds behind the photoemission peaks (peak shape analysis). It has been found that, under completely equivalent conditions, the deposition efficiency (i.e., sticking coefficient) is large on CdTe and TiO1.73, but very small on ZnO and TiO2. Silver constitutes an intermediate situation characterized by a long induction period where the deposition rate is small and a later increase in deposition efficiency comparable to that on CdTe. For the initial stages of deposition, below an equivalent monolayer, it has been also found that the Cd∕S ratio is smaller than unity on TiO1.73 and ZnO but larger than unity on CdTe and Ag substrates. For sufficiently long deposition times the Cd∕S ratio on the surface reaches unity. Except for silver substrate, cadmium appears as Cd2+ and sulfur as S−2 species at the initial stages of deposition. On the silver surface, cadmium adsorbs as Cd0 at low coverage. Peak shape analysis has shown that cadmium sulfide grows according to layer-by-layer mechanism (Frank–van de Merwe model) when the substrates are CdTe and TiO1.73, but large particles are formed that do not cover the surface for ZnO and Ag substrates (Volmer-Weber growth model). These results are consistent with the different chemical affinities of the substrate towards the atoms of cadmium and sulfur produced during the evaporation of the cadmium sulfide.
Reactive vacuum vapor deposition of aluminum oxide thin films by an air-to-air metallizer
Authors: Kobayashi T. , Itoh Y. , Nakano Y. , Hirai E. , Hashimoto R. , Kamikawa S.
Published: July 2006

Reactive vacuum vapor deposition of aluminum oxide thin films by an air-to-air metallizer was examined via the direct simulation Monte Carlo method and experiments. Comparison of the calculated results with the measurements of the Al oxide thin film’s thickness showed (a) that the empirical flux of Al atoms arriving at the substrate is lower than the calculated result, probably due to the formation of Al oxide on the evaporation surface and (b) that the amount of oxygen calculated from the thickness of the film is twice the amount corresponding to the calculated flux, probably due to the effects of the decreased sticking coefficient of oxygen on the evaporating surface and sidewall, underestimated gas phase reaction, large mesh size overestimated film density, and formation of substoichiometric oxide. Aluminum oxide thin films deposited on plastic film substrates by this metallizer under strictly controlled O2 supply conditions have good transparency, an oxygen transmission rate of 2.7cc∕m2day, and an electrical resistivity of 4.4×106Ω2m. Furthermore it was found that the oxygen transmission rate was reduced greatly to 1.0cc∕m2day or less when the Al oxide coating film was laminated with another plastic film using an adhesive.
Process optimization for the sputter deposition of molybdenum thin films as electrode for AlN thin films
Authors: Martin F. , Muralt P. , Dubois M.-A.
Published: July 2006

Molybdenum thin films have been deposited on Ti/(100) Si substrates by dc sputtering. For process optimization, a design of experiments method was used with three input factors (target power, substrate temperature, and process gas flow). Deposition rate, resistivity, roughness, diffraction angle, and rocking curve width were analyzed as output responses using statistical analysis method. Subsequently, a process allowing the deposition of highly crystalline, smooth, and low resistivity Mo film was selected and tested against film thickness. The as-optimized sputtered molybdenum thin film was used as seeding electrode for the growth of highly c-axis textured AlN film by dc pulsed reactive sputtering.
Alternative method of using an electron beam for charge compensation during ultralow energy secondary-ion-mass spectroscopy experiments
Authors: Guzmán de la Mata B. , Dowsett M. G. , Morris R. J. H.
Published: July 2006

Secondary-ion-mass spectroscopy (SIMS) analysis of insulators using positive primary beams is routinely performed by compensating the induced charge with a coincident electron beam. In the case of SIMS depth profiling, the established method consists of focusing an electron beam into the SIMS crater with a current well in excess of that of the primary ion beam. In this article we used both caesium and oxygen beams to bombard float glass, and intrinsic and doped diamond samples while varying the electron beam current and the area bombarded by electrons. We have studied how the electron beam to primary ion current density ratio modifies the charging conditions. We demonstrate that, for certain insulating and highly resistive materials, defocusing of the electron beam so as to cover the whole of the sample surface and part of the sample holder is extremely effective. It is also observed that the defocused electron beam works efficiently for an electron to primary ion current density ratio less than 1. We attribute this to the enhancement of surface conductivity through the creation of carriers in the conduction band, and observe similar effects when irradiating the surface with a laser diode. The ability to use a defocused electron beam will significantly aid profiling of insulating and highly resistive materials where alignment of the coincident electron and ion beams is problematic. Defocusing of the electron beam also offers the possible advantage of reducing or eliminating localized electron beam damage of certain material surfaces prior to and during profiling.
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blue light emitting diodes with modulation-doped AlGaN∕GaN heterostructure layers
Authors: Chen Chin-Hsiang
Published: July 2006

The modulation-doped AlGaN∕GaN heterostructure layers were used to improve the output power and efficiency of nitride-based blue light emitting diodes (LEDs). It was found that the output power of LEDs with the modulation-doped AlGaN∕GaN layers measured at 20mA injection current was increased from 4.8to6mW. It was also found that the modulation-doped AlGaN∕GaN layers can effectively spread pulse current. Nitride-based blue LEDs with the modulation-doped AlGaN∕GaN layer can even endure a 3000V reverse electrostatic discharge pulse voltage.
Influence of layer thickness and compositional variations on the electrorefractive properties of a quantum well polarization-conversion modulator
Authors: Ristic Sasa , Jaeger Nicolas A. F.
Published: July 2006

We present our work done towards the development of a quantum well polarization-conversion modulator. This modulator will consist of multiple repetitions of quantum well structures exhibiting large electrorefractive effects. In them, a channel waveguide supporting only the fundamental TE-like and TM-like modes will be subjected to an applied electric field. Changes in this applied field cause the effective refractive index of one of the modes to increase and that of the other to decrease. Using these structures shows that short (∼2–3mm) modulators, with 90° polarization rotation, low chirp (∼±0.1), and low drive electric fields (∼10kV∕cm) can be achieved. In this article, numerical simulations based on the effective-mass envelope-function approximation are used to study the influence of layer thickness and compositional variations on the electrorefractive properties of these quantum well structures.
Quantum-dot nanodevices with carbon nanotubes
Authors: Ishibashi K. , Moriyama S. , Tsuya D. , Fuse T. , Suzuki M.
Published: July 2006

We review our recent work on quantum-dot devices with carbon nanotubes. We conclude that the single-wall carbon nanotube quantum dot is an artificial atom with two- or four-electron shell structures. Zeeman splitting of single particle levels was observed, which is advantageous for the spin based quantum computing device (spin qubit) because the single spin is generated by putting one electron in the shell. Single-electron devices such as single-electron inverter and single-electron exclusive-OR gates have been fabricated, and their performance has been demonstrated at liquid-helium temperature. Despite the expected room-temperature operation from the single-electron charging energy, the operation temperature of our devices was limited to ∼10K because of the low height of the tunnel barrier.
Effect of different frequency combination on ArF photoresist deformation and silicon dioxide etching in the dual frequency superimposed capacitively coupled plasmas
Authors: Lee C. H. , Kim D. H. , Lee N.-E. , Kwon G. C.
Published: July 2006

This study investigated the deformation of ArF photoresist (PR) and the etch characteristics of ArF PR and SiO2 layers in a dual frequency superimposed capacitively coupled plasma (DFS-CCP) etcher with multiple frequency sources under different frequency combinations in C4F8∕CH2F2∕O2∕Ar capacitively coupled plasma. In the DFS-CCP etcher, the high-frequency (fHF) power (13.56, 27, and 60MHz) was varied to control the plasma density while a fixed low frequency (fLF) of 2MHz was used to control the ion bombardment energy to the wafer. The morphology of the blanket ArF PR surfaces and line patterns of the ArF PR after etching showed a significant increase in the level of surface roughening and deformation with increasing HF source frequency (fHF) from 13.56to60MHz under the same Vdc and gas flow conditions. This was attributed to the increased F radical flux and possibly ion flux on the surface. The Vdc also played an important role in increasing the surface roughness and ArF PR deformation, which was presumably due to the increased ion flux and ion-bombardment energy, respectively. The etch rates of the ArF PR and silicon oxide layers increased significantly with increasing ∣Vdc∣ and fHF possibly due to the increased ion energy and ion/radical flux density, respectively. The etch selectivity of the SiO2 layer to the ArF PR was enhanced most significantly by the increase in CH2F2 flow rate due to the formation of a thicker and C-rich CFx polymer on the oxide and PR surfaces.
Etching characteristics of LaNiO3 thin films in BCl3∕Ar gas chemistry
Authors: Kim Gwan-Ha , Kim Chang-Il
Published: July 2006

La Ni O 3 (LNO) electrode was intensively studied as electrodes because LNO has a pseudocubic perovskite crystal structure with a lattice parameter of 3.84Å. But the etching process of LNO thin films must be developed in order to realize highly integrated ferroelectric random access memories. In this work, we investigated etching characteristics and mechanisms of LNO thin films using inductively coupled BCl3∕Ar plasma (ICP) system. The maximum etch rate of LNO thin films was 41.1nm∕min at a BCl3(20)∕Ar(80) gas mixing ratio. The positive ions and the ion energy distributions were measured with a quadrupole mass spectrometer (QMS). As rf power and dc bias voltage increased and working pressure decreased, the ion energy and etch rates of LNO thin films were increased. A chemically assisted physical etch of LNO was experimentally confirmed by ICP system and QMS measurements.
Replication-based fabrication for an optical device that incorporates vertically curved structures
Authors: Lee M. W. , Lim K. J. , Choi C. H. , Jo S. B. , Lee S. G. , Lee E. H. , Park S. G. , O B. H.
Published: July 2006

The replication process is a good method to fabricate passive optical devices. Silicon-based fabrication technology provides an efficient way to fabricate a replication master with an optically smooth surface roughness. As silicon-based technologies are often two-dimensional processes, the replication requires sophisticated fabrication steps for a master structure. For this, a vertically curved structure, which is essential for a passive optical device, is hard to fabricate. Special processes, such as x-ray lithography, laser ablation, and gray-scale lithography, can overcome the conventional two-dimensional fabrication process challenges. But these processes need additional steps, machines, and masks. This study demonstrates an easy way for fabricating a silicon master structure for vertically curved mirrors. This fabrication method is roughly divided into two steps. During the first step, a silicon wafer is etched using an inductively coupled plasma system to form optical waveguide structures in the master structure (45μm depth and ∼5nm surface roughness). During the second step, the vertically curved mirror structures at each end of the waveguides are formed by using photoresist reflow process. After the master fabrication, the master shape was transferred to a PDMS mold. The replication process was carried out by using UV curable polymers, and a successful vertical redirection of light by the curved structure was observed with a charge-coupled device. The measured propagation loss of the fabricated waveguide structure was 0.13dB∕cm, and the curved mirror loss was 0.35dB.
Effect of oxygen incorporation on structural and properties of Ti–Si–N nanocomposite coatings deposited by reactive unbalanced magnetron sputtering
Authors: Ding X. Z. , Zeng X. T. , Liu Y. C. , Zhao L. R.
Published: July 2006

Ti–Si–N–O nanocomposite coatings with different contents of oxygen were deposited by a combined dc/rf reactive unbalanced magnetron sputtering process in an Ar+N2+O2 mixture atmosphere. The composition, structure, mechanical, and tribological properties of the as-deposited coatings were analyzed by energy dispersive analysis of x-rays, x-ray diffraction (XRD), nanoindentation, and pin-on-disk tribometer experiments, respectively. It was found that in the range of lower oxygen content with atomic ratio of O∕N⩽0.72, the tribological properties of the Ti–Si–N–O coatings are evidently improved, in comparison with the coating without oxygen incorporation. At O∕N=0.72, the friction coefficient and wear rate of the as-deposited coatings are reduced to 20% and 45%, respectively. Meanwhile, however, their hardness was not reduced, but, on the contrary, slightly increased. With increasing oxygen content further to O∕N⩾0.72, coating hardness decreased significantly. The friction coefficient of the as-deposited coatings decreased monotonously with the increase of oxygen content in the whole composition range investigated. The wear rate of the coatings exhibited a minimum value at around O∕N=0.72. In the lower range of O∕N, wear rate decreased significantly due to the lubricant effect of oxygen incorporation, while in the higher range of O∕N, wear rate increased gradually due to the weakening of coating hardness. XRD patterns revealed that the as-deposited coatings were mainly crystallized in cubic TiN phase, accompanied with minority of rutile structure titania in the case of higher oxygen incorporation.
Irradiation effect of nitrogen ion beam on hydrogenated amorphous carbon films
Authors: Watanabe Yoshihisa , Katoh Satoru , Kitazawa Nobuaki
Published: July 2006

Hydrogenated amorphous carbon (a-C:H) thin films were deposited on silicon single crystal substrates from toluene vapor using rf plasma at room temperature. After deposition, the a-C:H films were irradiated with a nitrogen ion beam and effects of nitrogen ion beam irradiation on surface morphology and composition were studied. Nitrogen ion irradiation was performed using nitrogen ion beams of 0.2 and 1.5keV for 10min under the constant ion current density at room temperature. Surface morphology was observed by atomic force microscopy (AFM). Changes in composition and carbon-nitrogen bonding states were analyzed by x-ray photoelectron spectroscopy (XPS). Carbon structures were examined by Raman spectroscopy. AFM observations revealed that the film surface became smooth after nitrogen ion beam irradiation and a notable difference in surface roughness is hardly observed between 0.2 and 1.5keV ion irradiation. XPS studies showed that nitrogen was implanted near the surface of the a-C:H films after nitrogen ion irradiation and combined with carbon, resulting in carbon nitride formation. Depth profiles obtained by XPS showed that nitrogen ions were implanted in the a-C:H films more deeply after 1.5keV ion irradiation than 0.2keV ion irradiation. The implanted nitrogen ion behavior inside the films has been clarified, which is useful to judge the effectiveness for the formation of carbon nitride layers. Carbon structures did not change remarkably after nitrogen ion irradiation except the surface region, where carbon nitride layers are formed.
Thermochromic La1−xSrxMnO3 (x=0.1, 0.175, and 0.3) smart coatings grown by reactive pulsed laser deposition
Authors: Soltani M. , Chaker M. , Jiang X. X. , Nikanpour D. , Margot J.
Published: July 2006

Thermochromic La1−xSrxMnO3 (x=0.1, 0.175, and 0.3) (LSMO) smart coatings were synthesized on (100) silicon and (0001) sapphire substrates by means of reactive pulsed laser deposition process at relatively low substrate temperature (500°C) and without postannealing. X-ray diffraction patterns indicated that all deposited LSMO films have polycrystalline structures. The energy dispersive x-ray spectroscopy analysis indicated approximately the same La∕Sr ratio in the formed LSMO coatings as in their corresponding targets. While, the x-ray photoelectron spectroscopy analysis of the LSMO/sapphire revealed that the strontium segregate at the film surface. The thermochromism of LSMO coatings was investigated by measuring their infrared reflectance as a function of temperature (up to 160°C). It was observed that the reflectance decreased as the temperature increased. Reflectance switching of about 25% was achieved in La0.7Sr0.3MnO3∕Si at a wavelength of 5μm. The sheet electrical resistivity as a function of temperature (up to 130°C) of LSMO/sapphire was investigated by means of the standard four-point probe technique. The resistivity decreased with increasing the temperature and no metallic-to-insulator transition was observed. However, it is found that the resistivity is very sensitive to the concentration level of Sr dopant: the resistivity decreased as the concentration of Sr increased. In addition, at room temperature, a higher temperature coefficient of resistance of −2.30%∕°C was achieved in La0.9Sr0.1MnO3 thin films. Finally, these LSMO smart coatings are promising materials for optical switching and IR uncooled bolometer devices.
Direct observations of rapid diffusion of Cu in Au thin films using in situ x-ray diffraction
Authors: Elmer J. W. , Palmer T. A. , Specht E. D.
Published: July 2006

In situ x-ray diffraction was performed while annealing thin film Au∕Cu binary diffusion couples to directly observe diffusion at elevated temperatures. The temperature dependence of the interdiffusion coefficient was determined from isothermal measurements at 700, 800, and 900°C, where Cu and Au form a disordered continuous face centered cubic solid solution. Large differences in the lattice parameters of Au and Cu allowed the initial diffraction peaks to be easily identified, and later tracked as they merged into one diffraction peak with increased diffusion time. Initial diffusion kinetics were studied by measuring the time required for the Cu to diffuse through the Au thin film of known thickness. The activation energy for interdiffusion was measured to be 65.4kJ∕mole during this initial stage, which is approximately 0.4× that for bulk diffusion and 0.8× that for grain boundary diffusion. The low activation energy is attributed to the high density of columnar grain boundaries combined with other defects in the sputter deposited thin film coatings. As interdiffusion continues, the two layers homogenize with an activation energy of 111kJ∕mole during the latter stages of diffusion. This higher activation energy falls between the reported values for grain boundary and bulk diffusion, and may be related to grain growth occurring at these temperatures which accounts for the decreasing importance of grain boundaries on diffusion.
Effects of N2 addition on chemical dry etching of silicon oxide layers in F2∕N2∕Ar remote plasmas
Authors: Hwang J. Y. , Kim D. J. , Lee N.-E. , Jang Y. C. , Bae G. H.
Published: July 2006

In this study, chemical dry etching characteristics of silicon oxide layers were investigated in the F2∕N2∕Ar remote plasmas. A toroidal-type remote plasma source was used for the generation of remote plasmas. The effects of additive N2 gas on the etch rates of various silicon oxide layers deposited using different deposition techniques and precursors were investigated by varying the various process parameters, such as the F2 flow rate, the additive N2 flow rate, and the substrate temperature. The etch rates of the various silicon oxide layers at room temperature were initially increased and then decreased with the N2 flow increased, which indicates an existence of the maximum etch rates. Increase in the oxide etch rates under the decreased optical emission intensity of the F radicals with the N2 flow increased implies that the chemical etching reaction is in the chemical reaction-limited regime, where the etch rate is governed by the surface chemical reaction rather than the F radical density. The etch rates of the silicon oxide layers were also significantly increased with the substrate temperature increased. In the present experiments, the F2 gas flow, the additive N2 flow rate, and the substrate temperature were found to be the critical parameters in determining the etch rate of the silicon oxide layers.
Time-of-flight secondary ion mass spectrometry chemical imaging analysis of micropatterns of streptavidin and cells without labeling
Authors: Lee Tae Geol , Shon Hyun Kyong , Lee Kyung-Bok , Kim Jinmo , Choi Insung S. , Moon Dae Won
Published: July 2006

A bismuth cluster ion-beam-based time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been successfully used to image micropatterns of streptavidin and Chinese hamster ovary (CHO-k1) cells, as received and without any labeling. Three different analysis ion beams (Bi+, Bi3+, and Bi32+) were compared to obtain label-free TOF-SIMS chemical images of micropatterns of streptavidin, which were subsequently used for generating biotinylated cell patterns. Unlike using a Bi+ ion beam, using a Bi3+ or Bi32+ primary analysis ion beam yielded well-contrasted-TOF-SIMS images of streptavidin characteristic secondary ions. A principal component analysis of TOF-SIMS data was performed to generate a chemical image of the streptavidin itself. A chemical specific TOF-SIMS image analysis gave us a better understanding of the localization of cells at the outer boundaries of the streptavidin-patterned circles. Our work suggests that using cluster-ion analysis beams together with multivariate data analysis for TOF-SIMS chemical imaging would be an effectual method for producing label-free chemical images of micropatterns of biomolecules, including proteins and cells.
Spallation Neutron Source ring vacuum systems
Authors: Mapes M. , Hseuh H. C. , Rank J. , Smart L. , Todd R. , Weiss D.
Published: July 2006

The Spallation Neutron Source ring, which is presently being commissioned at Oak Ridge National Laboratory, is designed to accumulate high-intensity protons. Ultrahigh vacuum of 10−9torr is required in the accumulator ring to minimize beam-residual gas ionization. To reduce the secondary-electron yield and the associated electron cloud instability, the ring vacuum chambers are coated with titanium nitride (TiN). In order to minimize radiation exposure, quick-disconnect chain clamp flanges are used in some areas where radiation levels are expected to be high. This article describes the design, fabrication, assembly, and vacuum processing of the ring and beam transport vacuum systems, as well as the associated vacuum instrumentation.
Mechanism for difference in etched depth between isolated and dense via holes of SiOCH film
Authors: Momonoi Yoshinori , Yonekura Kazumasa , Izawa Masaru
Published: July 2006

We investigated the mechanism for differences in etched depth between isolated and dense via holes of a damascene structure using a SiOCH film (k=2.8). In Ar∕CHF3∕N2 and Ar∕C4F6∕N2 plasmas, the depth of an isolated (4.8μm pitch) hole was more than 40% varied from a dense (200nm pitch) hole. The difference between dense and isolated holes was found to become larger with increasing air exposure time of the wafer. The amount of H2O in the SiOCH film also increased with increasing air exposure time based on thermal desorption spectroscopy (TDS) analysis. Therefore, we investigated the effects of H2O addition to the plasmas. The investigation revealed that the etched depths of dense holes became similar to those of isolated holes with H2O addition. Based on these results, we concluded that the mechanism for the difference between isolated and dense holes was as follows. When the capping layer on SiOCH is etched, the H2O contained in SiOCH desorbs in etched holes and affects etching reactions. The etching characteristics of isolated holes are significantly affected, since the amount of desorbed H2O in isolated holes is larger than that in dense holes.
Plasma etching of proton-exchanged lithium niobate
Authors: Hu H. , Milenin A. P. , Wehrspohn R. B. , Hermann H. , Sohler W.
Published: July 2006

Plasma etching of lithium niobate with fluorine gases is limited by the redeposition LiF. This results in a low etch rate and nonvertically etched walls. Etching of proton-exchanged lithium niobate can prevent the LiF deposition to a large extent because of the greatly reduced lithium concentration in lithium niobate. We performed different inductively coupled plasma etching processes using SF6 or CHF3∕Ar on proton-exchanged lithium niobate. Negligible underetching and nearly vertically etched walls on proton-exchanged lithium niobate samples were obtained by CHF3∕Ar gas at chamber pressure of 6mTorr and 130V dc bias.
Conceptual design of a deposition system for uniform and combinatorial synthesis of multinary thin-film materials via open-boat physical-vapor deposition
Authors: Teeter Glenn
Published: July 2006

Conventional flux-distribution formulas for rotating and static substrates are used to develop a method for combinatorial physical-vapor deposition. With this method, a single deposition system may be used, without modification, to deposit either highly uniform or graded-composition thin-film materials. This is accomplished through appropriate automated sequencing of source shuttersand substrate rotation. A constrained-composition parametrization is introduced, whichdetermines relative deposition times for the film constituents with and without substraterotation. The combinatorial deposition scheme developed here is applicable to binary, ternary,or quaternary phase systems. Examples are considered for the pseudoquaternary CuInSe2–AgInSe2–CuGaSe2–AgGaSe2 chalcopyrite materials system, which has relevance to thin-film photovoltaics.
Effects of molecular environments on the electrical switching with memory of nitro-containing OPEs
Authors: Gergel-Hackett N. , Majumdar N. , Martin Z. , Swami N. , Harriott L. R. , Bean J. C. , Pattanaik G. , Zangari G , Zhu Y. , Pu I. , Yao Y. , Tour J. M.
Published: July 2006

An oligo(phenylene ethynylene) (OPE) molecule with a nitro side group has exhibited electrical switching with memory and thus has potential for use in molecular electronic devices. However, different research groups have reported different electrical behaviors for this molecule. In addition to variations among test structures, differences in local molecular environments could be partially responsible for the differences in the reported results. Thus, we tested four variations of a nitro-OPE/dodecanethiol monolayer in the same type of nanowell test device to study how the environment of the nitro-OPE affects the observed electrical behavior. We found that the density of the nitro-containing molecules in the device altered the observed electrical switching behavior. Further, we found a positive correlation between the disorder of the monolayer and the observed electrical switching behavior. This correlation is consistent with suggestions that nitro molecule switching may depend on a conformational change of the molecule, which may be possible only in a disordered monolayer.
X-ray photoemission spectroscopy characterization of electrochemical growth of conducting polymer on oxidized Si surface
Authors: Kato H. , Takemura S. , Takakuwa N. , Ninomiya K. , Watanabe T. , Watanabe Y. , Nanba N. , Hiramatsu T.
Published: July 2006

Electrochemical growth of conducting polymer polythiophene (PT) film on an oxidized Si(100) wafer was closely investigated by x-ray photoemission spectroscopy (XPS). The initial stage of polymer growth was investigated by analyzing the core-level energies and spectral profiles of the atomic components. The oxidized Si surface was also closely characterized by XPS using curve fitting of Si 2p and Si 2s core-level spectra to determine precisely covalent states of Si at surface layers. The XPS spectra of Si 2p and Si 2s of the oxidized substrate surface was composed of five peaks which correspond with Si valence values, such as Si, Si+, Si2+, Si3+, and SiO2. The core-level energy positions of those different states were determined by XPS. The Si wafer was prepared through several stages of a wet cleansing process. Scanning tunneling microscopy image of nanoscale ordered native oxide surface was obtained. The native SiO2 layers remained and was probed by Fourier transform infrared spectroscopy reflection absorption spectroscopy and XPS measurements. Electrochemical PT growth at the initial stage was implemented on the oxidized SiO2 surface on Si(100) substrate. The obtained XPS spectra of Si 2p showed that the Si2+ and Si3+ peaks associated with polymer deposition shrank. This experimental result reflects the interface linkage between the organic polymer chain and the Si oxidized layer such as S–O–Si. The bonds between organic and inorganic species such as S–Si are also suggested by analysis of the S 2p3∕2,1∕2 core-level profile.
Effect of nitrogen contents on the temperature dependence of photoluminescence in InGaAsN∕GaAs single quantum wells
Authors: Lai Fang-I , Kuo S. Y. , Wang J. S. , Kuo H. C. , Wang S. C. , Wang H. S. , Liang C. T. , Chen Y. F.
Published: July 2006

A series of InGaAsN∕GaAs single-quantum wells (SQWs) with N contents varied from 0% to 5.3% were grown by molecular-beam epitaxy using a solid As and a nitrogen plasma sources. The impact of nitrogen concentration on the optical properties, as determined by the temperature dependence of photoluminescence (PL), of a 6nm SQW was investigated. In the low-temperature region, a pronounced temperature-dependent S-shaped peak position was observed in PL spectra while increasing the nitrogen concentration. Quenching behavior reveals that the defect-related nonradiative processes might be enhanced in the highly nitrogen incorporated samples and thus influence the recombination dynamics. In addition, the evolution of the peak position of the InGaAsN∕GaAs samples was in agreement with the empirical Varshni model in the high-temperature region. A significant reduction in the temperature dependence of the emission peak position is analyzed as well, and further confirms the prediction of proposed band anticrossing model of the electronic structure of III-N-V alloys.
Dependence of the electrical properties of the ZnO thin films grown by atomic layer epitaxy on the reactant feed sequence
Authors: Lee Chongmu , Lim Jongmin
Published: July 2006

Nitrogen-doped, p-type ZnO films have been grown successfully on sapphire (0001) substrates by atomic layer epitaxy (ALE) using Zn(C2H5)2 [diethylzinc (DEZn)], H2O, and NH3 as a precursor for zinc, an oxidant, and a doping source gas, respectively. The main process parameters for the growth of p-type ZnO were the NH3 flux and the reactant feed sequence in ALE. An annealing process was performed after the ALE process. The lowest electrical resistivity of the p-type ZnO films grown by ALE was 17.9Ωcm with a hole concentration of 1.59×1017cm−3. The results indicated that the carrier concentrations and carrier mobilities in the as-grown and annealed ZnO thin films depend strongly on the NH3 pulse time and on which step of an ALE cycle the NH3 doping is conducted. For both reactant feed sequences of DEZn–NH3–H2O and H2O–NH3–DEZn, n-type ZnO was changed to p-type ZnO by annealing, but the latter led to p-type ZnO with a carrier concentration after annealing higher than that in sequence 1 for the same NH3 flow rate. In addition, a model is proposed which can explain the difference between the two feed sequences in carrier concentration and carrier mobility before and after annealing. Time-dependent Hall effect measurement results also support that the nitrogen-doped ZnO film grown by ALE and then annealed at 1000°C for 1h is a p-type semiconductor.
Spectroellipsometric analysis of CHF3 plasma-polymerized fluorocarbon films
Authors: Easwarakhanthan T. , Beyssen D. , Le Brizoual L. , Bougdira J.
Published: July 2006

Optical and morphological properties of fluorocarbon films (CFx) deposited on Si substrates from CHF3 in a reactive ion etcher were studied by spectroscopic ellipsometry (SE). The study has led for 0.3–1.5μm thick films to a thickness-independent, roughnessless, apparently nongraded two-layer model that requires the Cauchy dispersion and the Gaussian absorption for the film refractive index and extinction coefficient, and to an interface mixture of CFx, Si, and voids. The Si native oxide removal was ascertained from films formed on SiO2-sputtered Si substrate. The sample SE results were further verified by x-ray diffraction, atomic force microscopy, Fourier transform infrared, x-ray photoelectron and Auger electron spectroscopies, and capacitance studies. The film microstructure may thus be considered isotropic and homogeneous resulting from a random addition of CFx fragments including cross-links along the film depth. The films have low-dielectric constant(k≈2.2) quality index of 1.38(615nm) and are noticeably absorbent in UV while exhibiting strong transparency in visible. These films growing at a rate of 0.033μm∕min have 2%–3% thickness nonuniformity. The SE model decision making steps are described and the degree of confidence on the SE results are discussed with the support of literature results and those from and the above studies.
Characterization of a methyl radical source for ultrahigh vacuum thin film growth studies
Authors: Gold J. S. , Lannon J. M. , Ziemer K. S. , Guntu M. , Tolani V. L. , Stinespring C. D.
Published: July 2006

An ultrahigh vacuum compatible methyl radical source has been developed and characterized. The methyl radicals were generated by passing a dilute mixture of methane in argon through a microwave discharge and sampling the discharge products using a molecular beam skimmer. The resulting molecular beam was characterized using a differentially pumped mass spectrometer. In addition to methyl radicals, other species observed in the beam included methane and higher hydrocarbons whose relative amounts were affected by source operating conditions. Radical fluxes as high as 8.4×1014cm−2s−1 were produced.
Reactive ion beam etching of HfO2 film and removal of sidewall redeposition
Authors: Wang Xudi , Liu Ying , Xu Xiangdong , Fu Shaojun , Cui Zheng
Published: July 2006

Comparative studies on ion beam etching (IBE) and reactive ion beam etching (RIBE) of HfO2 film have been carried out using photoresist as the masking layer. The etching rates of HfO2 film and photoresist mask in pure Ar and Ar∕CHF3 mixture plasmas were measured as a function of ion energy, plasma composition, and ion beam incident angle. It has been found that the RIBE with Ar∕CHF3 plasma is capable of lowering the threshold energy of ion beam and increasing sputtering yield, compared to the IBE with pure Ar. The redeposition of photoresist sidewall is a major issue, due to the formation of nonvolatile etching products during sputtering of HfO2 film in both IBE and RIBE. However, the sidewall redeposition can be easily removed in HCl solutions with assistance of ultrasonic wave for RIBE with Ar∕CHF3 plasma. Alternatively, the sidewall redeposition can be eliminated by controlling the slope of photoresist sidewall or combined with ion incident angle.
Synthesis and purification of single-walled carbon nanotubes by methane decomposition over iron-supported catalysts
Authors: Kim Jong-Sik , Kim Gwan-Ha , Kim Chang-Il
Published: July 2006

This article describes the synthesis and the purification of carbon nanotubes. Large quantities of single-walled carbon nanotubes (SWNTs) with few defects and very small amount of amorphous carbon coating have been synthesized by catalytic decomposition of methane over well-dispersed iron particles supported on MgO at the temperature range from 800to1000°C. It was found that the quality of carbon nanotubes was slightly increased as increasing growth temperature while the yield was decreased to some degree. It was also found that the as-grown SWNTs can be separated easily from the support by a simple acidic treatment rather than thermal oxidation to obtain a product with high yields of SWNTs. Above 94wt% high purity SWNTs were obtained by combining two-step processes of thermal oxidation in air and acid treatment without multistep filtration. The as-grown and purified SWNTs were also characterized by field emission scanning electron microscopy, x-ray diffraction, and Raman spectroscopy.
Dry etching of TaN∕HfO2 gate-stack structure in BCl3∕Ar∕O2 inductively coupled plasmas
Authors: Shin M. H. , Park M. S. , Lee N.-E. , Kim Jiyoung , Kim Chung Ywong , Ahn Jinho
Published: July 2006

In this work, etching characteristics of TaN(200nm)∕HfO2(80nm) gate-stack structures on Si substrate were investigated by varying the process parameters such as BCl3∕(BCl3+Ar+O2) gas mixing ratio (Q), top-electrode power, dc self-bias voltage (Vdc), and overetch time in an inductively coupled plasma etcher. To understand the role of the etch gas chemistry, we measure the relative changes in the optical emission intensity of ions and radicals in the plasma as well as in the chemical binding states of the etched TaN surfaces. We used optical emission spectroscopy and x-ray photoelectron spectroscopy respectively. The results showed that BCl3∕Ar∕O2 plasma is more effective in etching the oxidized TaN than Cl2∕Ar∕O2 or HBr∕Ar∕O2 plasma. It is believed that the B radical species removes the oxygen atoms on the oxidized TaN surface more effectively by forming volatile boron-oxygen-chlorine compounds, such as trichloroboroxin (BOCl)3), boron oxychloride (BOCl), and boron dioxide. The measurement data also indicated that high etch selectivities of the TaN to the HfO2 layer could be obtained at the low Vdc, high top-electrode power, and shorter overetch time.
Oxidation threshold in silicon etching at cryogenic temperatures
Authors: Tillocher T. , Dussart R. , Mellhaoui X. , Lefaucheux P. , Maaza N. Mekkakia , Ranson P. , Boufnichel M. , Overzet L. J.
Published: July 2006

In silicon etching in SF6∕O2 plasmas, an oxidation threshold appears when the oxygen content is large enough. A SiOxFy passivation layer is formed under such conditions. This threshold is reached at lower oxygen proportions if the substrate is cooled down to cryogenic temperatures. In this article, we present a mass spectrometry study of this oxidation threshold in different experimental conditions (temperature, source rf power, self-bias) on bare silicon wafers. The presence of the threshold is clearly evident in the signals of many ions, for example, SiF3+, F+, and SOF2+. This helps us to determine the main reactions which can occur in the SF6∕O2 plasma in our experimental conditions. This threshold appears for higher oxygen proportions when either the source power or the chuck self-bias is increased. The ion bombardment transfers energy to the surface and makes the film desorb. A model, describing the oxygen coverage as a function of the parameters mentioned above, is proposed to interpret these results. Data presented in this article give another point of view of the cryogenic etching process. They contribute to explain how anisotropic profiles can be achieved at low temperature. Surfaces subjected to ion bombardment (the bottom of the structures) are below the oxidation threshold while the structures sidewalls, not subjected to ion bombardment, are in passivating regime.
Diagnosis of fusariosis in urine cytology
Authors: Su Cheng-Chuan , Hsu Hui-Jine , Wu Jiunn-Jong , Chou Chien-Wen
Published: July 2006

Fusariumis a filamentous fungus widely distributed in plants and in the soil. Most species are more common at tropical and subtropical areas. Besides being a common contaminant and a well-known plant pathogen,Fusariumsp may cause various infections in humans. However, it has not yet been reported as being the pathogen of urinary tract infection. A 67-year-old woman had extracorporeal shock wave lithotripsy and percutaneous nephrolithotomy for renal stones 7 and 6 years ago, respectively. She had had fever, chillness, urinary urgency and frequency for 6 days. Routine testing of urine showed numerous leucocytes. She was admitted under the impression of urinary tract infection. On admission, many spindle-shaped structures were found in the urine smears. This shows thatFusariumwas identified.Fusariummay be the pathogen of the urinary tract infection, particularly when urolithiasis is present.
Effect of cigarette smoking on nitric oxide, structural, and mechanical properties of mouse arteries
Authors: Guo X. , Oldham M. J. , Kleinman M. T. , Phalen R. F. , Kassab G. S.
Published: July 2006

Cigarette smoking (CS) is a major risk factor for vascular disease. The aim of this study was to quantitatively assess the influence of CS on mouse arteries. We studied the effect of short-term (6 wk) and long-term (16 wk) CS exposure on structural and mechanical properties of coronary arteries compared with that of control mice. We also examined the reversibility of the deleterious effects of CS on structural [e.g., wall thickness (WT)], mechanical (e.g., stiffness), and biochemical [e.g., nitric oxide (NO) by-products] properties with the cessation of CS. The left and right coronary arteries were cannulated in situ and mechanically distended. The stress, strain, elastic modulus, and WT of coronary arteries were determined. Western blot analysis was used to analyze endothelial NO synthase (eNOS) in the femoral and carotid arteries of the same mice, and NO by-products were determined by measuring the levels of nitrite. Our results show that the mean arterial pressure was increased by CS. Furthermore, CS significantly increased the elastic modulus, decreased stress and strain, and increased the WT and WT-to-radius ratio compared with those of control mice. The reduction of eNOS protein expression was found only after long-term CS exposure. Moreover, the NO metabolite was markedly decreased in CS mice after short- and long-term exposure of CS. These findings suggest that 16 wk of CS exposure can cause an irreversible deterioration of structural and elastic properties of mouse coronary arteries. The decrease in endothelium-derived NO in CS mice was seen to significantly correlate with the remodeling of arterial wall.