bluuebunny/crossref_metadata_2025 huggingface dataset:
Profile control in dry development of high-aspect-ratio resist structures
Authors: Stern M. B. , Palmateer S. C. , Horn M. W. , Rothschild M. , Maxwell B. E. , Curtin J. E.
Published: July 2002

Anisotropic etching for dry development of thick resist layers in oxygen-based plasmas has been developed for two particular applications: trilayer resist for planarization of steep binary optics structures, and top surface imaged (silylated) resists for deep submicron lithography. To reduce linewidth degradation during etching of high-aspect-ratio resist structures, lateral etching and bow are minimized in two different reactors, a conventional parallel-plate reactive ion etching (RIE) system and a low-pressure, high-ion-density helicon etcher. In the conventional RIE system, C5H8, a polymer-forming gas is added to the O2 feed gas to form a sidewall inhibition layer. In the helicon reactor, very low temperatures (−100 °C) are used to suppress sidewall etching. Different optimization conditions are found for trilayer resist etching and pattern transfer of silylated resist in the helicon reactor.
Quantitative two-dimensional dopant profiles obtained directly from secondary electron images
Authors: Venables D. , Maher D. M.
Published: July 2002

Doping-dependent contrast in secondary electron images of p/n junctions in silicon obtained in a field-emission scanning electron microscope was observed and characterized. The optimum experimental conditions for observing this ‘‘electronic’’ contrast were established by investigating the effect of microscope and material parameters on the magnitude of the contrast. The contrast between the bright p-type areas and the darker n-type areas was maximized at an accelerating voltage of ∼1 kV, and when a through-the-lens detector configuration was employed. Secondary electron contrast profiles of boron doped p+/n junctions in silicon showed a good correlation with secondary ion mass spectroscopy depth profiles of the atomic concentration down to the 1017 cm−3 level. However, similar results were not obtainable for n+/p junctions. It is demonstrated that this contrast effect may be exploited for obtaining two-dimensional dopant profiles directly from secondary electron images of p+/n junctions provided that the technique is empirically calibrated against a one-dimensional dopant profiling method.
Characterization of a simplified gas distribution for wafer cost reduction in a plasma metal etcher
Authors: Chou C. , Saravanan K. , Kava J. , Siegel M.
Published: July 2002

A perforated gas distribution plate (GDP) is currently the preferred method to provide uniform gas flow in plasma etch systems. Anodized gas distribution plates are consumable in metal etch systems because they are subject to erosion due to the high pressure Cl2 chemistry and the high velocity of the gas flow. This can result in potentially higher particle levels, higher cost of consumables, and lower mean number of wafers between wet cleans. A new simplified gas distribution plate (SGD) has been developed to replace the existing GDP. The ceramic SGD is less susceptible to corrosion and leads to a longer lifetime, resulting in reduction of the cost of consumables. An orthogonal design of experiments on the bulk etch of Al–Cu/TiW film stack etching was conducted. The plasma chamber lid was designed as one of the variables in this orthogonal design with GDP and SGD as the two levels. BCl3, Cl2, N2, CF4, pressure, backside He cooling, and power were the other variables in this orthogonal design at three levels. This allowed the effect of gas distribution and the other variables on nonuniformity of etch, metal etch rate, selectivity to photo-resist, and the profile to be studied. N2 flow, rf power, BCl3 flow and backside He cooling had a significant effect on the nonuniformity of the process in the range analyzed. The selectivity of the aluminum to photo-resist was significantly affected by power, Cl2 flow, pressure, and backside He cooling. The mode of gas distribution was found to have no significant effect on the nonuniformity of the process, metal etch rate, selectivity to photo-resist, and the profile.
High resolution patterning of thin magnetic films to produce ultrasmall magnetic elements
Authors: Khamsehpour B. , Wilkinson C. D. W. , Chapman J. N. , Johnston A. B.
Published: July 2002

Lithographic and dry etching techniques have been used to fabricate submicron and micron sized elements from magnetic thin films. Through a combination of electron beam lithography and reactive ion etching using CF4/O2 followed by CH4/H2/O2, well defined elements with lateral dimensions as small as 24 nm have been produced. The films were deposited on thin electron-transparent Si3N4 membranes so that the structural and micromagnetic properties of the elements could be studied by transmission electron microscopy. Lorentz microscopy on micron sized permalloy elements has confirmed that the magnetic integrity is maintained after patterning and a comparison with similar sized elements produced using a lift off route is given.
Molecular beam epitaxial growth of Eu-doped CaF2 and BaF2 on Si
Authors: Fang X. M. , Chatterjee T. , McCann P. J. , Liu W. K. , Santos M. B. , Shan W. , Song J. J.
Published: July 2002

The growth of Eu-doped CaF2 and BaF2 thin films on Si(100), (110), and (111) substrates has been realized by molecular beam epitaxy using elemental Eu evaporation. Very bright blue emissions from Eu-doped CaF2 and yellow emissions from Eu-doped BaF2 were obtained in the wavelength range of 400–850 nm at 10 K. Depending on the Si substrate orientation, the zero-phonon line of Eu2+ in the CaF2 thin films was shifted by different amounts relative to that of bulk CaF2 due to residual strain in these epilayers.
Field emission characteristics of diamondlike carbon films synthesized by pulsed laser deposition process using a Au-intermediate layer
Authors: Chuang F. Y. , Wang W. C. , Cheng H. F. , Sun C. Y. , Lin I. N.
Published: July 2002

The characteristics of the diamondlike carbon (DLC) films deposited on Au-coated silicon substrate are observed to vary markedly with the substrate temperature. Large relative proportion of sp3-bonds had pronouncedly improved the electron emission properties of the DLC films. A low turn on field as 7 V/μm and a large emission current density as 2000 μA/cm2, at 20 V/μm, were achieved for DLC/Au/Si films deposited at 200 °C. Too high a substrate temperature (i.e., 600 °C) induced graphitization that degraded the field emission behavior. The DLC/Au/Si films grow in a similar behavior as DLC/Mo/Si films, but possess substantially better field emission characteristics. The scanning electron microscopic and secondary ion mass spectroscopics analyses implied that the main factor is the improvement on the interfacial structure through the interdiffusion between DLC, Au, and Si layers.
Thin film phosphor prepared by physical vapor deposition for field emission display application
Authors: Lee Yun Hi , Song Man Ho , Ju Byeong Kwon , Shin Dong Ki , Oh Myung Hwan
Published: July 2002

We fabricated very thin ZnO:Zn film using rf magnetron sputtering and ZnS:Pr,Ce layer by electron-beam evaporation for color field emission display application. Also, in order to investigate the influence of surface conductive layer onto the phosphor films upon the emission characteristics, we prepared the layered structures having an additional conducting layer of 2–6-nm-thick Sn-doped In2O3 film. Cathodoluminescence spectrum of sputtered ZnO:Zn (250 nm) film shows two broad peaks centered around 540 and 600 nm, respectively. The spectra characteristics of ZnS:Pr,Ce,F films show white spectrum that covered a whole visible wavelength. One of the effects of an additional surface layer of indium tin oxide on ZnO and ZnS phosphor is the shift of spectrum toward shorter wavelength as well as low voltage emission, as compared to our phosphor film without the surface conductive layer.
Effects of vacuum conditions on low frequency noise in silicon field emission devices
Authors: Trujillo Johann T. , Chakhovskoi Andrei G. , Hunt Charles E.
Published: July 2002

The effects of pressure on emission current noise have been studied. Field emission currents from 50×50 arrays and single emitter silicon devices were observed over a range of pressures. The current fluctuations were analyzed in both the time and frequency domain. Signal to noise ratios between 0.9 and 6.9 were observed and appear to be more dependent on operation time and current than on pressures. At higher pressures, emission currents are reduced and the current is cut off completely above a threshold pressure which is somewhere in the 10 s of Torr. Plasmas were observed in the mTorr range. The total current from a 50×50 tip array was measured to be only one order of magnitude greater than that for a single tip, suggesting that only 4–10 of the emitters in the array were functional. Spectral density coefficients of low frequency measurements range from 1.37 to 1.81. Some pressure dependence is suggested in the lower pressure ranges. The single emitter exhibited burst noise with a cutoff frequency of about 10 Hz.
Technique for fabricating self-aligned gates onto silicon field emitter arrays
Authors: Zhu Chang-Chun , Guan Hui , Liu Weidong , Li Tian-Ying , Sin Johnny K. O.
Published: July 2002

A technique for fabricating self-aligned gate structures onto pre-existing silicon field emitter arrays is introduced in detail in this article. The gate-controlled field emission characteristics of the resulting devices are also described.
Magnetic nanostructures studied by scanning probe microscopy and spectroscopy
Authors: Wiesendanger R. , Bode M. , Kleiber M. , Löhndorf M. , Pascal R. , Wadas A. , Weiss D.
Published: July 2002

Scanning tunneling microscopy and spectroscopy (STM/STS) were applied to study the nanostructural and nanoelectronic properties of ultrathin magnetic films, from individual adatoms and clusters (zero-dimensional systems) to three-dimensional bulklike islands. Complementary investigations of the nanomagnetic structure of ultrathin films were performed by magnetic force microscopy (MFM). Quantum magnetic structures were prepared by electron-beam lithography and nanosphere lithography and analyzed by STM/STS as well as by MFM. Magnetization switching of single-domain Co dots induced by the MFM tip is demonstrated, and its potential application for quantum magnetic storage is shown. Finally, tunneling spectroscopy performed with magnetic probe tips yields new information about the spin-resolved nanoelectronic properties of magnetic nanostructures.
Modifying chemical vapor deposited diamond films for field emission displays
Authors: Habermann T. , Göhl A. , Nau D. , Wedel M. , Müller G. , Christ M. , Schreck M. , Stritzker B.
Published: July 2002

A systematic investigation of deposition parameters and post-treatments was performed for the development of field emission displays based on flat chemical vapor deposited diamond films. The lowest onset field strengths were obtained for films grown at the highest substrate temperature, highest methane content, and with negatively biased substrate. Intentionally damaging the films by implantation with 50 keV and 100 keV carbon ions as well as with 4.4 MeV silicon ions usually resulted in an enhanced field emission. The emission followed the Fowler–Nordheim law up to 0.5 mA/mm2, and a current carrying ability of more than 100 mA/mm2 was detected. Considerably improved emission was achieved by short and long-term processing at higher current levels.
Remote plasma chemical vapor deposition silicon oxynitride thin films: Dielectric properties
Authors: Hernández Vélez M. , Sánchez Garrido O. , Gutiérrez F. Fernández , Falcony C. , Martı́nez Duart J. M.
Published: July 2002

Silicon oxynitride thin films have been deposited using remote plasma chemical vapor deposition from SiCl4+NH3+O2 gas mixtures. The stoichiometry of the deposited films varies from that corresponding to the silicon oxide to a stoichiometry very close to silicon nitride when the NH3/O2 gas ratio is changed in the plasma. The approximate compositions of the films were determined by Rutherford backscattering spectroscopy and nuclear reaction analysis, and the local bonding arrangements were determined by infrared spectroscopy. Analysis of metal–insulator–semiconductor devices under the effect of and external sinusoidal electric field (dielectric spectrometry) indicates the presence of traps centers in the Si–SiO2 interface. Correlations between the local bonded structures in the oxynitride and the conduction and polarization processes detected in the films are also discussed.
Focused ion beam implantation for opto- and microelectronic devices
Authors: König H. , Mais N. , Höfling E. , Reithmaier J. P. , Forchel A. , Müssig H. , Brugger H.
Published: July 2002

Focused ion beam implantation is a powerful technology for the fabrication of opto- and microelectronic devices. Optoelectronic devices like gain coupled distributed feedback lasers and nonabsorbing waveguides can be defined in semiconductor heterostructures by the band gap shift due to highly spatially resolved implantation induced thermal intermixing. Single mode emitting devices were fabricated with emission wavelengths of 1 and 1.55 μm in the material systems GaInAs/(Al)GaAs and GaInAsP/InP, respectively. Band gap shifts of more than 65 meV could be reached in GaInAsP quantum film structures which simplifies the integration of nonabsorbing waveguide sections with, e.g., lasers, modulators, and detectors. In highly doped semiconductor layers semi-insulating areas could be defined by focused ion implantation. Depletion lengths down to 50 nm can be controlled and were demonstrated on current injection restricted resonant tunneling devices. By using this technique collector-up heterobipolar transistors were fabricated which exhibit current amplification factors up to 45.
Directional and ionized physical vapor deposition for microelectronics applications
Authors: Rossnagel S. M.
Published: July 2002

The manufacturing of interconnect features on semiconductor wafers has evolved from lift-off-based evaporation to reactive ion etching metallization and now to Damascene technology. Physical sputter deposition has been widely used for blanket metal film deposition, but is impractical for high aspect topographies. Filtered, or directional sputter techniques, such as long throw or collimation, have been used for some high aspect ratio applications, but suffer from poor efficiency, high cost, and/or poor scaling. Ionized sputter deposition, which uses in-flight ionization of sputtered metal atoms and subsequent film deposition by means of a substrate potential, has been developed as a technique to extend physical vapor deposition into higher aspect ratios.
Epitaxial silicon grown on CeO2/Si(111) structure by molecular beam epitaxy
Authors: Jones J. T. , Croke E. T. , Garland C. M. , Marsh O. J. , McGill T. C.
Published: July 2002

Using electron beam evaporation, a Si/CeO2/Si(111) structure has been grown in a molecular beam epitaxy machine. In situ low energy electron diffraction, cross sectional transmission electron microscopy, selected area diffraction, and atomic force microscopy have been used to structurally characterize the overlying silicon layer and show it to be single crystalline and epitaxially oriented. Rutherford backscattering and energy dispersive x-ray analysis have been used to confirm the presence of a continuous 23 Å CeO2 layer at the interface. Rutherford backscattering and x-ray photoemission spectroscopy show an additional presence of cerium both at the exposed silicon surface and incorporated in low levels (∼1%) within the silicon film, suggesting a growth mechanism with cerium riding atop the silicon growth front leaving behind small amounts of cerium incorporated in the growing silicon crystal.
Fabrication of x-ray mask from a diamond membrane and its evaluation
Authors: Noguchi H. , Kubota Y. , Okada I. , Oda M. , Matsuda T. , Motoyoshi A. , Ohki S. , Yoshihara H.
Published: July 2002

We have prepared a diamond membrane x-ray mask using our novel fabrication techniques which include fluidized bed pretreatment, stress control of diamond film, and chemical-mechanical polishing (CMP), and we have evaluated its important properties for practical use in detail. Surface roughness of diamond film was improved from 55.7 to 1.5 nm Ra using the CMP technique. The transmittance of visible light increased considerably due to the reduction of incident light scattering at the diamond surface, and the transmittance of 2.2-μm-thick smooth diamond film was 92% at 633 nm. In-plane distortion-induced synchrotron radiation irradiation was Max(x,y)=(13,10) nm with a dosage of 12.8 kJ/cm2. In final evaluation, that is, of lithographic performance, we confirmed that a 0.2 μm gate array pattern can be successfully transferred.
Surface chemistry of II–VI semiconductor ZnSe studied by time of flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy
Authors: Zhao J. , Na M. H. , Lee E. H. , Chang H. C. , Gardella J. A. , Luo H.
Published: July 2002

The composition and chemical state of the native oxide of single-crystalline ZnSe and the effect of HCl (18.5%)/H2O wet etching have been studied by time of flight secondary ion mass spectrometry (TOF-SIMS) and x-ray photoelectron spectroscopy (XPS). TOF-SIMS depth profile measurements show that the oxide layer of ZnSe is removed by etching in this solution for one minute, followed by a subsequent one minute rinse in deionized H2O. XPS depth profile measurements of the untreated ZnSe surface show that Se oxide only exists at the topmost surface (within the top 10% of the oxide layer). The change of Zn Auger parameter with depth of the untreated ZnSe specimen indicates that the remaining oxygen is chemically associated to Zn. High resolution XPS measurements of the etched ZnSe show no detectable Se oxide at the surface. Meanwhile, the Zn Auger parameter is similar to that of the unetched ZnSe after its oxide layer being removed by Ar+ sputtering. Both experiments show longer wet etching times result in Zn deficiency and more Cl contamination at the sample surface.
Fabrication of Cu interconnects of 50 nm linewidth by electron-beam lithography and high-density plasma etching
Authors: Hsu Y. , Standaert T. E. F. M. , Oehrlein G. S. , Kuan T. S. , Sayre E. , Rose K. , Lee K. Y. , Rossnagel S. M.
Published: July 2002

The feasibility of building Cu interconnects with a linewidth as small as 50 nm embedded in insulating SiO2 has been explored using the damascene process. Fine line test structures, designed for evaluating effects of small linewidth on metal line electric resistivity, were written on a poly(methylmethacrylate) resist layer and then transferred to the underlying SiO2 layer by high-density plasma etching. Using a CHF3 etching gas and an inductive power of 400 W, we were able to produce 50-nm-wide and 150-nm-deep trenches in SiO2. These trenches were then filled with a thin (5–10 nm) TaSiN or TaN liner and a thick Cu layer by the ionized physical vapor deposition technique. The field Cu was removed by a chemical-mechanical polishing process, leaving narrow damascene Cu in the oxide trenches. Direct current resistance measurements have indicated a wide distribution of resistivity in these fine lines. The low end of the distribution is close to the effective resistivity of a perfect Cu line. The high values are indicative of severe necking or other imperfections induced during the fabrication process.
Small aperture fabrication for single quantum dot spectroscopy
Authors: Park D. , Marrian C. R. K. , Gammon D. , Bass R. , Isaacson P. , Snow E.
Published: July 2002

A simple fabrication method for submicron diameter metallic apertures using negative electron beam resist and metal lift-off has been developed. In general, the lift-off process is beneficial for semiconductor quantum dot spectroscopy, since the original surface condition of the substrate is not altered or destroyed as it may be in a conventional dry or wet etching processes to form apertures in a subtractive process. With an optimum combination of process parameters, such as higher pre- and postexposure bake temperatures for longer times, longer developing time and with optimal mixtures of developers, high aspect ratio resist posts were obtained. Using 20 kV single dot e-beam exposure, a reentrant profile can be obtained directly. While this profile is not obtained with 50 kV single dot e-beam exposure, a higher aspect ratio (∼7:1) and sub-100 nm diam resist posts are possible. High vertical sidewall 100 nm diam resist posts are obtained using 50 kV area e-beam exposures. Taking advantage of these characteristics: high aspect ratio, high vertical resist sidewall, and resist undercut at the bottom of post, sub-100 nm diam apertures in 100 nm thick metallic films are obtained by evaporation of metal on the sample and dissolving the resist post in solvent. For sub-100 nm apertures, a significant improvement in aperture edge smoothness was achieved by applying an oxygen plasma.
Easy and reproducible method for making sharp tips of Pt/Ir
Authors: Lindahl J. , Takanen T. , Montelius L.
Published: July 2002

We have investigated a simple yet powerful method for making sharp scanning tunneling microscopy tips of Pt/Ir. It consists of three electrochemical polish/etch steps, not requiring any special micropolishing. The tips, as seen by high-resolution transmission electron microscopy, are sharper than 20 Å. Furthermore, they are smooth, without mini tips and covered with an oxide layer not much thicker than the native one (as seen from a freshly cut wire) when all three steps are applied.
Observations on the formation and ashing of giant folds in high dose ion-implanted resists
Authors: Vinogradov Georgy K. , Menagarishvili Vladimir M.
Published: July 2002

A kinetics of surface transformations and ashing of high energy high dose As+ implanted resists was studied. Continuous bulk polymer structures, having minimum cross-sectional dimensions 10–30 times larger than the initial resist thickness, were found. These structures, named as giant folds, are formed as a result of heating and melting of the normal polymer resist sublayer and its interaction with a mechanically deformed implanted resist layer. The giant folds are responsible for the most difficult to remove surface remaining features of ion implanted resists processed in downstream gas discharge ashers. It is shown that the main problem of dry ashing of ion implanted resists of this type is the flow patterns of the normal resist sublayer, not the hard implanted surface layer itself.
Low-voltage electron emission from chemical vapor deposition graphite films
Authors: Obraztsov A. N. , Pavlovsky I. Yu. , Volkov A. P.
Published: July 2002

Thin film cold cathodes composed of a graphite-type carbon coating on Si substrate have been fabricated and tested. Electrons from the cathodes were emitted into vacuum when the average electric field exceeded 1.5 V/μm. The emission current density was more than 1 mA/cm2 and emission site density was higher than 107 cm2 at the electric field of 4 V/μm. The current–voltage dependencies were studied at different temperatures from 77 to 600 K and found to be typical for the field emission. We propose a mechanism of electron emission from carbon cold cathodes, based on the enhancement of electric field due to surface morphology and on the modification of electronic properties of carbon atoms localized on the surface of graphite-type material.
Study of factors limiting electron mobility in InSb quantum wells
Authors: Chung S. J. , Goldammer K. J. , Lindstrom S. C. , Johnson M. B. , Santos M. B.
Published: July 2002

We observe a significant increase in InSb quantum-well mobility when remote doping of Al0.09In0.91Sb barriers is accomplished by three layers, rather than one layer, of Si δ doping. At 7 K, the electron mobility in single quantum-well structures grown on GaAs substrates is as high as 280 000 cm2/V s with an electron density of 2.33×1011 cm−2. The density of oriented abrupt steps and square-mound features on the sample surface correlates with the electron mobility in the well.
Reflectance difference spectroscopy and magneto-optical analysis of digital magnetic heterostructures
Authors: Bonanni A. , Prechtl G. , Heiss W. , Schinagl F. , Holl S. , Krenn H. , Sitter H. , Stifter D. , Hingerl K.
Published: July 2002

We report on the investigation of CdTe/Cd0.75Mg0.25Te quantum wells grown by molecular-beam epitaxy and containing a digital distribution of magnetic MnTe fractional monolayers in the well. The influence of electronic confinement and of exciton primary localization on the formation of ferromagnetic ordering on the scale of small spin clusters (polarons) has been investigated by performing selective excitation of the exciton luminescence. The calculated temperature dependence of the free magnetic polarons binding energy F is found to qualitatively agree with the photoluminescence excitation data and the ferromagnetic clusters result to be more stable in these magnetic structures of reduced dimensionality, with respect to the three-dimensional case. The magneto-optical Kerr effect is discussed in the case of reflectance difference spectroscopy (RDS) and from the angular dependence of the RDS spectra in magnetic field, signals due to interband Faraday rotation and signals originating from crystal anisotropy could be distinguished. The Faraday rotation in these structures is found to follow the Curie–Weiss law with a transition temperature of −6 K corresponding to the nominal ion spin concentration in the magnetic barriers.
Characterization of AlSb/InAs surfaces and resonant tunneling devices
Authors: Nosho B. Z. , Weinberg W. H. , Barvosa-Carter W. , Bracker A. S. , Magno R. , Bennett B. R. , Culbertson J. C. , Shanabrook B. V. , Whitman L. J.
Published: July 2002

We have studied the evolution of AlSb-on-InAs(001) surfaces and interfaces grown by molecular-beam epitaxy using in situ scanning tunneling microscopy. We find that forming InSb-like interfacial bonds on an InAs(001)-(2×4) surface creates surface roughness because the surface In coverage inherent to the (2×4) reconstruction is insufficient to form a complete InSb(001)-(1×3)-like surface layer. This morphological roughness can be eliminated by depositing additional In to compensate for the different compositions of the reconstructions. We have also grown three different 5-monolayer-thick films of AlSb on the InSb-like interface to study the effect of growth conditions on the film surface morphology. The AlSb surface can be improved by either raising the growth temperature or by growing the film using migration-enhanced epitaxy. Finally, we present electrical characterization of InAs/AlSb/GaSb resonant interband tunneling devices fabricated with different growth procedures. The possible effects of various growth procedures on interfacial quality and device properties are discussed.
Luminescence properties of CdS quantum dots on ZnSe
Authors: Kobayashi M. , Nakamura S. , Kitamura K. , Umeya H. , Jia A. , Yoshikawa A. , Shimotomai M. , Kato Y. , Takahashi K.
Published: July 2002

The luminescence properties of self-assembled CdS quantum dots (QDs) were studied. CdS QD structures formed on ZnSe buffer layers without capping layers showed intense photoluminescence (PL). The PL peak position could be controlled by changing the amount of CdS deposited. Introduction of the capping layer enhanced the PL intensity. The buffer layer material selected also affected the luminescence properties of the CdS QDs, and brighter PL with the higher transition energy was observed by replacing the ZnSe buffer layer with ZnSSe. A light emitting diode structure based on CdS QDs sandwiched in the pn junction of ZnSe was fabricated and bright blue or green luminescence from current injection was observed at 77 K as well as at room temperature.
Stability of low-temperature amorphous silicon thin film transistors formed on glass and transparent plastic substrates
Authors: Yang C.-S. , Smith L. L. , Arthur C. B. , Parsons G. N.
Published: July 2002

This article describes the formation of amorphous silicon thin film transistors (TFTs) on glass and flexible transparent plastic substrates using rf plasma enhanced chemical vapor deposition and a maximum processing temperature of 110 °C. Silane diluted with hydrogen was used for the preparation of the amorphous silicon, and SiH4/NH3/N2 or SiH4/NH3/N2/H2 mixtures were used for the deposition of the silicon nitride gate dielectric. The amorphous silicon nitride layers were characterized by transmission infrared spectroscopy and current-voltage measurements; the plastic substrates were 10 mil thick (0.25 mm) polyethylene terephthalate sheets. Transistors formed using the same process on glass and plastic showed linear mobilities ranging from 0.1 to 0.5 cm2/V s with ION/IOFF ratios⩾107. To characterize the stability of the transistors on glass, n- and p-channel transconductances were measured before and after bias stressing. Devices formed at 110 °C show evidence of charge trapping near the a-Si/SiNx interface and the creation of dangling-bond defects. The defect dynamics are consistent with the defect pool model. Under +10 and +25 V bias stress, the rates of creation of low energy defects are only moderately larger than those for high temperature devices; the devices show markedly higher rates of defect creation under higher positive bias. Current-voltage analysis of low temperature dielectrics shows very low leakage, but positive bias stress shows a significantly higher electron trapping rate near the a-Si:H/SiNx interface, indicating problems with low temperature dielectric formation. The magnitude of the rates of defect creation and trapping in these nonoptimized devices suggests that amorphous silicon TFTs with stability approaching that of typical large area active matrix electronic devices could be formed at low temperatures compatible with transparent flexible polymeric substrates.
Structural and magnetic properties of molecular beam epitaxy grown GaMnAs layers
Authors: Sadowski J. , Domagała J. Z. , Ba̧k-Misiuk J. , Koleśnik S. , Sawicki M. , Świa̧tek K. , Kanski J. , Ilver L. , Ström V.
Published: July 2002

GaMnAs layers with Mn contents from 0.05% to 7% were grown by low temperature molecular beam epitaxy. At substrate temperatures lower than 300 °C and in this composition range a uniform ternary GaMnAs compound can be grown without MnAs precipitation. Reflection high energy electron diffraction intensity oscillations recorded during GaMnAs growth were used to calibrate the composition of the GaMnAs films with high accuracy (better than 0.1%). Films containing more than 1% Mn exhibit a ferromagnetic phase transition with Curie temperatures from a few up to 70 K depending on the composition and other growth parameters. In contrast to previous reports we have observed this transition also in the case of layers grown at very low substrate temperatures (below 200 °C).
Stress and defects in silicate films and glasses
Authors: Phillips J. C.
Published: July 2002

Both silicate films of technological interest and commercial silicate glasses exemplify atomic networks with low defect densities. Although the films and glasses are prepared differently, they appear to exhibit many similar chemical trends. Here these trends are discussed in detail for the glasses, and features of the very large glass database which may be relevant to films are identified.
Noise in scanning capacitance microscopy measurements
Authors: Zavyalov V. V. , McMurray J. S. , Williams C. C.
Published: July 2002

Scanning capacitance microscopy (SCM) is a powerful tool for two-dimensional (2D) dopant/carrier profiling. Currently noise limits the accuracy of 2D dopant profiles obtained by SCM. In an effort to reduce noise, a systematic analysis of different SCM noise sources is provided. The main noise sources during SCM measurements are capacitance sensor noise and oxide–semiconductor surface induced noise. For adequate tip size, the dominant noise in SCM measurements is caused by variations in the quality of surface. On as-polished surfaces, nonstationary noise is observed. This noise is likely caused by the variations in the density of oxide traps. Tip induced charging of these traps and local variations or fluctuations in discharge time during SCM imaging cause the noise level and noise pattern to be different from image to image. Heat treatment under ultraviolet irradiation or in a hydrogen ambient is found to be an effective way to reduce or even eliminate this type of SCM noise. Stationary surface noise is mostly created by the variations in the oxide thickness. This type of noise correlates with topographic roughness and is very consistent during SCM measurements. By reducing the topographic roughness, the stationary surface noise may be reduced to the level of ∼10−2 of the depletion SCM signal for typical experimental conditions. It is shown that the capacitance sensor noise depends on the capacitance sensor tuning parameters and under proper conditions can be reduced to a negligible level for standard probe tips used in SCM measurements.
Pituitary Development: Regulatory Codes in Mammalian Organogenesis
Authors: Scully Kathleen M. , Rosenfeld Michael G.
Published: July 2002

During mammalian pituitary gland development, distinct cell types emerge from a common primordium. Appearance of specific cell types occurs in response to opposing signaling gradients that emanate from distinct organizing centers. These signals induce expression of interacting transcriptional regulators, including DNA binding–dependent activators and DNA binding–independent transrepressors, in temporally and spatially overlapping patterns. Together they synergistically regulate precursor proliferation and induction of distinct cell types. Terminal cell type differentiation requires selective gene activation strategies and long-term active repression, mediated by cell type–specific and promoter-specific recruitment of coregulatory complexes. These mechanisms imply the potential for flexibility in the ultimate identity of differentiated cell types.
Neuroanatomy of Magnetoreception: The Superior Colliculus Involved in Magnetic Orientation in a Mammal
Authors: Němec Pavel , Altmann Jens , Marhold Stephan , Burda Hynek , Oelschläger Helmut H. A.
Published: July 2002

The neural substrate subserving magnetic orientation is largely unknown in vertebrates and unstudied in mammals. We combined a behavioral test for magnetic compass orientation in mole rats and immunocytochemical visualization of the transcription factor c-Fos as a marker of neuronal activity. We found that the superior colliculus of the Zambian mole rat (
Cryptomys anselli
) contains neurons that are responsive to magnetic stimuli. These neurons are directionally selective and organized within a discrete sublayer. Our results constitute evidence for the involvement of a specific mammalian brain structure in magnetoreception.
Interaction of the Response Regulator ARR4 with Phytochrome B in Modulating Red Light Signaling
Authors: Sweere Uta , Eichenberg Klaus , Lohrmann Jens , Mira-Rodado Virtudes , Bäurle Isabel , Kudla Jörg , Nagy Ferenc , Schäfer Eberhard , Harter Klaus
Published: July 2002

The
Arabidopsis thaliana
response regulator 4, expressed in response to phytochrome B action, specifically interacts with the extreme amino-terminus of the photoreceptor. The response regulator 4 stabilizes the active Pfr form of phytochrome B in yeast and in planta, thus elevates the level of the active photoreceptor in vivo. Accordingly, transgenic
Arabidopsis
plants overexpressing the response regulator 4 display hypersensitivity to red light but not to light of other wavelengths. We propose that the response regulator 4 acts as an output element of a two-component system that modulates red light signaling on the level of the phytochrome B photoreceptor.
Parallel Single-Cell Monitoring of Receptor-Triggered Membrane Translocation of a Calcium-Sensing Protein Module
Authors: Teruel Mary N. , Meyer Tobias
Published: July 2002

Time courses of translocation of fluorescently conjugated proteins to the plasma membrane were simultaneously measured in thousands of individual rat basophilic leukemia cells. We found that the C2 domain—a calcium-sensing, lipid-binding protein module that is an essential regulator of protein kinase C and numerous other proteins—targeted proteins to the plasma membrane transiently if calcium was released from internal stores, and persistently in response to entry of extracellular calcium across the plasma membrane. The C2 domain translocation time courses of stimulated cells clustered into only two primary modes. Hence, the reversible recruitment of families of signaling proteins from one cellular compartment to another is a rapid bifurcation mechanism for inducing discrete states of cellular signaling networks.
Collisions and Gravitational Reaccumulation: Forming Asteroid Families and Satellites
Authors: Michel Patrick , Benz Willy , Tanga Paolo , Richardson Derek C.
Published: July 2002

Numerical simulations of the collisional disruption of large asteroids show that although the parent body is totally shattered, subsequent gravitational reaccumulation leads to the formation of an entire family of large and small objects with dynamical properties similar to those of the parent body. Simulations were performed in two different collisional regimes representative of asteroid families such as Eunomia and Koronis. Our results indicate that all large family members must be made of gravitationally reaccumulated fragments; that the post-collision member size distribution and the orbital dispersion are steeper and smaller, respectively, than for the evolved families observed today; and that satellites form frequently around family members.
"Heavy Electron" Photoelectron Spectroscopy: Rotationally Resolved Ion Pair Imaging of CH
3
+
Authors: Liu Xianghong , Gross Richard L. , Suits Arthur G.
Published: July 2002

We applied the velocity map imaging technique under high-resolution conditions to study ion pair products of the vacuum ultraviolet photodissociation of methyl chloride. We obtained rotationally resolved kinetic energy release spectra that directly provide vibrational frequencies and rotational constants of the fundamental carbocation, CH
3
+
. The technique is analogous to photoelectron spectroscopy, with the chloride anion playing the role of a “heavy electron.” The approach shows promise as a general probe of ionic species not amenable to study by traditional methods.
Emergence of Modern Human Behavior: Middle Stone Age Engravings from South Africa
Authors: Henshilwood Christopher S. , d'Errico Francesco , Yates Royden , Jacobs Zenobia , Tribolo Chantal , Duller Geoff A. T. , Mercier Norbert , Sealy Judith C. , Valladas Helene , Watts Ian , Wintle Ann G.
Published: July 2002

In the Eurasian Upper Paleolithic after about 35,000 years ago, abstract or depictional images provide evidence for cognitive abilities considered integral to modern human behavior. Here we report on two abstract representations engraved on pieces of red ochre recovered from the Middle Stone Age layers at Blombos Cave in South Africa. A mean date of 77,000 years was obtained for the layers containing the engraved ochres by thermoluminescence dating of burnt lithics, and the stratigraphic integrity was confirmed by an optically stimulated luminescence age of 70,000 years on an overlying dune. These engravings support the emergence of modern human behavior in Africa at least 35,000 years before the start of the Upper Paleolithic.
Partitioning of the Matrix Fraction of the Golgi Apparatus During Mitosis in Animal Cells
Authors: Seemann Joachim , Pypaert Marc , Taguchi Tomohiko , Malsam Jörg , Warren Graham
Published: July 2002

The Golgi apparatus is partitioned during mitosis in animal cells by a process of fragmentation, dispersal, and reassembly in each daughter cell. We fractionated the Golgi apparatus in vivo using the drug brefeldin A or a dominant-negative mutant of the Sar1p protein. After these treatments, Golgi enzymes moved back to the endoplasmic reticulum, leaving behind a matrix of Golgi structural proteins. Under these conditions, cells still entered and exited mitosis normally, and their Golgi matrix partitioned in a manner very similar to that of the complete organelle. Thus, the matrix may be the partitioning unit of the Golgi apparatus and may carry the Golgi enzyme–containing membranes into the daughter cells.
Multiple Glassy States in a Simple Model System
Authors: Pham K. N. , Puertas A. M. , Bergenholtz J. , Egelhaaf S. U. , Moussaı̈d A. , Pusey P. N. , Schofield A. B. , Cates M. E. , Fuchs M. , Poon W. C. K.
Published: July 2002

Experiments, theory, and simulation were used to study glass formation in a simple model system composed of hard spheres with short-range attraction (“sticky hard spheres”). The experiments, using well-characterized colloids, revealed a reentrant glass transition line. Mode-coupling theory calculations and molecular dynamics simulations suggest that the reentrance is due to the existence of two qualitatively different glassy states: one dominated by repulsion (with structural arrest due to caging) and the other by attraction (with structural arrest due to bonding). This picture is consistent with a study of the particle dynamics in the colloid using dynamic light scattering.
Manipulating the Quantum State of an Electrical Circuit
Authors: Vion D. , Aassime A. , Cottet A. , Joyez P. , Pothier H. , Urbina C. , Esteve D. , Devoret M. H.
Published: July 2002

We have designed and operated a superconducting tunnel junction circuit that behaves as a two-level atom: the “quantronium.” An arbitrary evolution of its quantum state can be programmed with a series of microwave pulses, and a projective measurement of the state can be performed by a pulsed readout subcircuit. The measured quality factor of quantum coherence
Q
ϕ
≅ 25,000 is sufficiently high that a solid-state quantum processor based on this type of circuit can be envisioned.
Formation of the Three-Ring Structure Around Supernova 1987A
Authors: Tanaka T. , Washimi H.
Published: July 2002

From a magnetohydrodynamic simulation, we reproduce a three-ring structure in the circumstellar space of the supernova (SN) 1987A observed by the Hubble Space Telescope. When a star develops from a red supergiant (RSG) to a blue supergiant (BSG) just before the SN explosion, a wind-wind interaction occurs between the slow stellar wind from the RSG and the subsequent fast stellar wind from the BSG. This process is simulated numerically under an assumption that the density and velocity distributions around the RSG are anisotropic owing to the existence of toroidal magnetic field and coronal holes. The three rings with observed size and position are reproduced by the magnetic pinch effect and amplification of initial density asymmetry through the dynamical interaction.
Functional Annotation of a Full-Length
Arabidopsis
cDNA Collection
Authors: Seki Motoaki , Narusaka Mari , Kamiya Asako , Ishida Junko , Satou Masakazu , Sakurai Tetsuya , Nakajima Maiko , Enju Akiko , Akiyama Kenji , Oono Youko , Muramatsu Masami , Hayashizaki Yoshihide , Kawai Jun , Carninci Piero , Itoh Masayoshi , Ishii Yoshiyuki , Arakawa Takahiro , Shibata Kazuhiro , Shinagawa Akira , Shinozaki Kazuo
Published: July 2002

Full-length complementary DNAs (cDNAs) are essential for the correct annotation of genomic sequences and for the functional analysis of genes and their products. We isolated 155,144 RIKEN
Arabidopsis
full-length (RAFL) cDNA clones. The 3′-end expressed sequence tags (ESTs) of 155,144 RAFL cDNAs were clustered into 14,668 nonredundant cDNA groups, about 60% of predicted genes. We also obtained 5′ ESTs from 14,034 nonredundant cDNA groups and constructed a promoter database. The sequence database of the RAFL cDNAs is useful for promoter analysis and correct annotation of predicted transcription units and gene products. Furthermore, the full-length cDNAs are useful resources for analyses of the expression profiles, functions, and structures of plant proteins.
Phosphorelay and Transcription Control in Cytokinin Signal Transduction
Authors: Sheen Jen
Published: July 2002

The past decade has seen substantial advances in knowledge of molecular mechanisms and actions of plant hormones, but only in the past few years has research on cytokinins begun to hit its stride. Cytokinins are master regulators of a large number of processes in plant development, which is known to be unusually plastic and adaptive, as well as resilient and perpetual. These characteristics allow plants to respond sensitively and quickly to their environments. Recent studies have demonstrated that cytokinin signaling involves a multistep two-component signaling pathway, resulting in the development of a canonical model of cytokinin signaling that is likely representative in plants. This Viewpoint outlines this general model, focusing on the specific example of
Arabidopsis
, and introduces the STKE Connections Maps for both the canonical module and the specific
Arabidopsis
Cytokinin Signaling Pathway.
High Mutation Frequencies Among
Escherichia coli
and
Salmonella
Pathogens
Authors: LeClerc J. Eugene , Li Baoguang , Payne William L. , Cebula Thomas A.
Published: July 2002

Here it is reported that the incidence of mutators among isolates of pathogenic
Escherichia coli
and
Salmonella enterica
is high (over 1 percent). These findings counter the theory, founded on studies with laboratory-attenuated strains, that suggests mutators are rare among bacterial populations. Defects in methyl-directed mismatch repair underlie all mutator phenotypes described here. Of nine independently derived hypermutable strains, seven contained a defective
mutS
allele. Because these mutant alleles increase the mutation rate and enhance recombination among diverse species, these studies may help explain both the rapid emergence of antibiotic resistance and the penetrance of virulence genes within the prokaryotic community.
Anthropoid Origins
Authors: Kay Richard F. , Ross Callum , Williams Blythe A.
Published: July 2002

Recent fossil discoveries have greatly increased our knowledge of the morphology and diversity of early Anthropoidea, the suborder to which humans belong. Phylogenetic analysis of Recent and fossil taxa supports the hypotheses that a haplorhine-strepsirrhine dichotomy existed at least at the time of the earliest record of fossil primates (earliest Eocene) and that eosimiids (middle Eocene, China) are primitive anthropoids. Functional analysis suggests that stem haplorhines were small, nocturnal, arboreal, visually oriented insectivore-frugivores with a scurrying-leaping locomotion. A change from nocturnality to diurnality was the fundamental adaptive shift that occurred at the base of the tarsier-eosimiid-anthropoid clade. Stem anthropoids remained small diurnal arborealists but adopted locomotor patterns with more arboreal quadrupedalism and less leaping. A shift to a more herbivorous diet occurred in several anthropoid lineages.
Ion-Surface Interactions--From Channeling to Soft-Landing
Authors: Kleyn A. W.
Published: July 2002

When ions collide with surfaces—as might happen when one tries to make films of useful materials by some methods—the collision is violent and may lead to breakup or rearrangement of the substance being deposited. In his Perspective, Kleyn discusses results reported in the same issue by Miller
et al
. (
p. 1447
) in which materials in the form of “molecular parachutes” have been softly placed on surfaces, a technique that may permit fabrication of new classes of surface compounds.
β-Catenin as Oncogene--The Smoking Gun
Authors: Peifer Mark
Published: July 2002

Three reports [Korinek
et al.
(
p. 1784
), Morin
et al
. (
p. 1787
), and Rubinfeld
et al
. (
p. 1790
)] in this issue provide new evidence about the molecular pathway that goes awry in colon cancer and melanoma. The protein β-catenin, previously known to be associated with the colon-cancer-causing adenomatous polyposis coli protein, is shown to be an oncogene in its own right. In his Perspective, Peifer discusses the normal functions of these proteins in mammals and flies and how their dysfunction can lead to cancer.