bluuebunny/crossref_metadata_2025 huggingface dataset:
Concurrent measurement of adhesive and elastic surface properties with a new modulation technique for scanning force microscopy
Authors: Krotil H.-U. , Stifter Th. , Marti O.
Published: July 2002

The combination of two well-established dynamic scanning force microscopy (SFM) modes is incorporated for SFM in combined dynamic X mode or CODY Mode® SFM. A vertical modulation of low frequency and large amplitude is superimposed with a second vertical modulation of high frequency and low amplitude leading to a combination of pulsed force mode SFM, force modulation, and phase sensitive SFM. SFM in the new mode allows the simultaneous mapping of a number of physical surface properties including adhesive force and elasticity over one scan. The new SFM technique is nondestructive and alteration or even destruction of the sample surface is reduced to a minimum. A polymer blend (two homopolymers spin coated on silicon from a tetrahydrofuorane solution of a mixture of poly-2-vinylpyridin and polytertbutylmethacrylate) was used as a sample for comparative measurements between pulsed force mode, force modulation mode and the new SFM mode.
Al/Al2O3/Al single electron transistors operable up to 30 K utilizing anodization controlled miniaturization enhancement
Authors: Nakamura Y. , Klein D. L. , Tsai J. S.
Published: July 2002

We have developed a method, anodization controlled miniaturization enhancement (ACME), to make ultrasmall tunnel junctions. Anodization of electron-beam fabricated Al/Al2O3/Al tunnel junctions reduces their effective areas and capacitances, which realizes single electron transistors operating at high temperatures up to nearly 30 K. The limit of the increase in the charging energy is attributed to the initial scattering in the junction sizes.
Temperature profile of fiber tips used in scanning near-field optical microscopy
Authors: Stähelin M. , Bopp M. A. , Tarrach G. , Meixner A. J. , Zschokke-Gränacher I.
Published: July 2002

We have measured the temperature profile of aluminum coated fiber tips used for illumination-mode scanning near-field optical microscopy as a function of the optical input power with a micron sized thermocouple. The temperature coefficients vary from 20 K/mW for tips with a large cone angle to 60 K/mW for the narrow long ones. Temperatures of up to ≊470 °C have been measured close to the aperture with an optical input power of several mW before thermal damage of the coating occurred. The temperature profiles are analyzed theoretically taking into account the optical absorption, the thermal conductivity of the tip, as well as the heat loss to the environment.
Anomalous electron emission from LiNbO3 crystals
Authors: Kugel V. D. , Rosenman G.
Published: July 2002

Our experimental data show that a rather thin layer with inverted polarization at the +c-face strongly suppresses the pyroelectrically induced electron emission from LiNbO3 crystals. We assume that the microscopic electric field of pyroelectric positive surface charges increases a potential barrier to polarons moving toward the vacuum. The pyroelectrically induced electron emission provides a novel method of detecting thin surface layers with inverted polarization.
Using doping superlattices to study transient-enhanced diffusion of boron in regrown silicon
Authors: Jones K. S. , Elliman R. G. , Petravić M. M. , Kringho/j P.
Published: July 2002

A boron-doped silicon superlattice consisting of three boron spikes separated by 1700 Å of undoped silicon has been grown by molecular beam epitaxy and used to study the evolution of point defects following an amorphizing implant of Si+. After MBE growth, the wafer was implanted at 77 K with either 146 or 292 keV Si+ at a dose of 5×1015/cm2. These implants produced amorphous layer depths that coincided with the depths of either the middle B peak or just below the deepest B peak. The samples were then annealed at 800 °C in an Ar ambient. Secondary-ion-mass spectrometry and transmission electron microscopy were used to monitor the diffusion of the boron spikes upon annealing and the evolution of the extended defects upon annealing, respectively. For the lower-energy sample, an enhancement in the B diffusivity of over 500× was observed for both the surface B spike and the deepest B spike. The higher-energy implant shows conclusively that the back flow of interstitials into the regrown region is coming from the end-of-range damage just below the amorphous/crystalline interface. These results show that for these implant conditions the end-of-range damage does not act as a barrier to flow of interstitials to the surface. In addition it is noted that boron in the regrown silicon does not cluster whereas the boron below the amorphous crystalline interface does. Both of these features must be accounted for when modeling boron diffusion in regrown silicon.
Encapsulation of Ag films on SiO2 by Ti reactions using Ag–Ti alloy/bilayer structures and an NH3 ambient
Authors: Alford T. L. , Adams Daniel , Laursen T. , Manfred Ullrich B.
Published: July 2002

Thin encapsulated silver films have been prepared on oxidized silicon by nitridation of ∼200-nm-thick Ag–19 at. % Ti alloy films and Ag(120 nm)/Ti(22 nm) at 300–700 °C in an ammonia ambient. The encapsulation process has been studied in detail by Rutherford backscattering, and scanning Auger and secondary-ion-mass spectrometry, which showed that Ti-nitride and Ti-oxide-silicide formation take place at the surface and the Ag–Ti/SiO2 interface, respectively. Four-point-probe analysis of the alloy films suggests that the resistivity is controlled by the residual Ti concentration. Resistivity values of ∼4 μΩ cm were measured in encapsulated Ag alloy films with initial low Ti concentrations. The annealed bilayer structure had minimal Ti accumulations in Ag and the resistivity values were comparable to that of the as-deposited Ag (∼3 μΩ cm).
Viscous drag measurements utilizing microfabricated cantilevers
Authors: Oden P. I. , Chen G. Y. , Steele R. A. , Warmack R. J. , Thundat T.
Published: July 2002

The influence of viscous drag forces on cantilevers is investigated using standard atomic force microscope (AFM) cantilevers. Viscosity effects on several geometrically different cantilevers manifest themselves as variations in resonance frequencies, quality factors, and cantilever response amplitudes. With this novel measurement, a single cantilever can be used to measure viscosities ranging from η=10−2 to 102 g/cm s.
A low-noise single-domain fluxgate sensor
Authors: Deak J. , Miklich A. H. , Slonczewski J. , Koch R. H.
Published: July 2002

In order to gain a better understanding of the noise mechanisms and limitations of fluxgate magnetometers, fluxgates with single and multidomain tubular permalloy cores were fabricated and tested. Under similar excitation conditions, single-domain fluxgates show approximately two orders of magnitude better resolution than similarly sized multidomain fluxgates, indicating that domain wall motion is the mechanism that limits conventional multidomain fluxgate resolution. Noise in a single-domain fluxgate was shown to decrease to 10−11 Trms/√Hz at 1 Hz as the drive and a superimposed circumferential magnetic field were increased. Results suggest that further noise reductions are possible.
High resolution fluorescence imaging with cantilevered near-field fiber optic probes
Authors: Talley Chad E. , Cooksey Gregory A. , Dunn Robert C.
Published: July 2002

High resolution near-field fluorescence and topology images of intact neurons are reported using a cantilevered near-field fiber optic probe. A bend is introduced into a normal geometry near-field tip, allowing the probe to be used in a tapping-mode arrangement, similar to tapping-mode atomic force microscopy. Features with a full width at half-maximum of 140 nm are observed in the near-field fluorescence image, demonstrating the subdiffraction limit spatial resolution possible with the cantilevered near-field probe design. Characteristics of the cantilevered tips include resonances between 30 and 60 kHz, Q factors greater than 100, and measured spring constants of 300 to 400 N/m.
Correlation of real time spectroellipsometry and atomic force microscopy measurements of surface roughness on amorphous semiconductor thin films
Authors: Koh Joohyun , Lu Yiwei , Wronski C. R. , Kuang Yalei , Collins R. W. , Tsong T. T. , Strausser Y. E.
Published: July 2002

We have correlated the results of real time spectroellipsometry (SE) and ex situ atomic force microscopy (AFM) measurements of surface roughness on amorphous semiconductor thin films. Roughness layer thicknesses deduced from real time SE, using a conventional approach based on the Bruggeman effective medium theory, closely obey a relationship of the form: ds(SE)≊1.5 drms(AFM)+4 Å, for 10≤dS(SE)<100 Å, where drms(AFM) is the root-mean-square roughness from AFM. The slope and intercept of this relationship provide insights into the origin and interpretation of the optically deduced roughness layer thicknesses.
Reflection properties and defect formation in photonic crystals
Authors: Özbay E. , Temelkuran B.
Published: July 2002

We have investigated the surface reflection properties of a layer-by-layer photonic crystal. By using a Fabry–Perot resonant cavity analogy along with the reflection-phase information of the photonic crystal, we predicted defect frequencies of planar defect structures. Our predictions were in good agreement with the measured defect frequencies. Our simple model can also predict and explain double defect formation within the photonic band gap.
Molecular Rydberg states in hydrogen negative ion discharges
Authors: Hiskes J. R.
Published: July 2002

The presence of Rydberg states in a negative-ion discharge that are generated by electron collisional excitation will increase the concentration of negative ions on the order of 1% or less, compared to the concentration generated via dissociative attachment to ground-state vibrationally excited molecules.
Precursor-mediated adsorption of tertiarybutylarsine on GaAs (001)-(4×6)
Authors: Cui Jie , Ozeki Masashi , Ohashi Masafumi
Published: July 2002

The scattering property of tertiarybutylarsine (TBAs) on a GaAs(001)-(4×6) surface at room temperature was studied by supersonic-molecular-beam scattering. Polar angle measurements show that the scattering signal is due to thermal desorption of trapped molecules combined with a direct-inelastic scattering. The measurement of the sticking coefficient shows a precursor-mediated adsorption behavior. The time decay curve can be divided into two components with activation energies of 6.9 and 8.3 kcal/mol, revealing that TBAs molecules can physisorb into two different potential wells on the GaAs (001)-(4×6) surface.
Novel impurity-free interdiffusion in GaAs/AlGaAs quantum wells by anodization and rapid thermal annealing
Authors: Yuan Shu , Kim Yong , Jagadish C. , Burke P. T. , Gal M. , Zou J. , Cai D. Q. , Cockayne D. J. H. , Cohen R. M.
Published: July 2002

A novel impurity-free interdiffusion technique utilizing pulsed anodization and subsequent rapid thermal annealing at temperatures near 900 °C was reported. Enhanced interdiffusion was observed in the presence of an anodized GaAs capping layer in GaAs/AlGaAs quantum well structures. Transmission electron microscopy studies show evidence of interdiffusion. Photoluminescence spectra from interdiffused samples show large blue shift and no significant linewidth broadening. Possible mechanism of interdiffusion was discussed.
Growth and properties of c-axis textured La0.7Sr0.3MnO3−δ films on SiO2/Si substrates with a Bi4Ti3O12 template layer
Authors: Gu J. Y. , Kwon C. , Robson M. C. , Trajanovic Z. , Ghosh K. , Sharma R. P. , Shreekala R. , Rajeswari M. , Venkatesan T. , Ramesh R. , Noh T. W.
Published: July 2002

c -axis textured La0.7Sr0.3MnO3−δ (LSMO) films were fabricated on SiO2/Si(001) substrates using a Bi4Ti3O12 (BTO) template layer. Electrical and magnetic properties of LSMO were investigated. The LSMO/BTO layer of this structure has no in-plane alignment. Even though a ferromagnetic transition temperature, TC, is as high as that of the epitaxial LSMO film (360 K), a resistivity peak temperature, TP, is about 140 K lower than TC. The resistivity behavior as a function of temperature for LSMO/BTO/SiO2/Si films is found to be dominated by grain boundary effects. Low field sensitive magnetoresistance which suggests spin tunneling through the grain boundaries is also observed at room temperature.
Size quantization effects in InAs self-assembled quantum dots
Authors: Schmidt K. H. , Medeiros-Ribeiro G. , Garcia J. , Petroff P. M.
Published: July 2002

We study size quantization effects in InAs self-assembled quantum dots (QDs) that are embedded in GaAs. Using capacitance, photoluminescence and photovoltage spectroscopy, we correlate the measured quantized level energies with the quantum dot sizes and densities obtained from transmission electron microscopy. With increasing dot size, we observe a strong redshift of the QD features in all our data. In the capacitance spectra, a band gap renormalization of the two-dimensional wetting layer system appears when the first excited QD state crosses the wetting layer ground state. The relative size dependence and absolute energetic position of the QD transitions determined with photoluminescence provide some information about the influence of lateral confinement and height of the QD.
Luminescences from localized states in InGaN epilayers
Authors: Chichibu S. , Azuhata T. , Sota T. , Nakamura S.
Published: July 2002

Optical spectra of the bulk three-dimensional InGaN alloys were measured using the commercially available light-emitting diode devices and their wafers. The emission from undoped InxGa1−xN(x<0.1) was assigned to the recombination of excitons localized at the potential minima originating from the large compositional fluctuation. The emission from heavily impurity-doped InGaN was also pointed out related to the localized states.
Measurement of electron affinity in boron-doped diamond from capacitance spectroscopy
Authors: Liu Kun , Zhang Bo , Wan Mingfang , Chu J. H. , Johnston C. , Roth S.
Published: July 2002

Boron-doped diamond film sample has been grown on (100) silicon substrate using the microwave enhanced chemical vapor deposition method. It is found that the sample has very good material qualities and an excellent (100) surface morphology. Au/diamond Schottky was fabricated on the (100) surface to study electron affinity of the diamond sample. By measuring frequency dependence capacitance–voltage spectroscopy of the Schottky sample in high vacuum and at room temperature, a very small electron affinity of about 0.025 eV and a work function of about 5.165 eV have been obtained for the (100) surface of the diamond sample supposing the diamond band gap energy is 5.5 eV.
Characterization of electron emission from planar amorphous carbon thin films using in situ scanning electron microscopy
Authors: Missert N. , Friedmann T. A. , Sullivan J. P. , Copeland R. G.
Published: July 2002

Electron emission characteristics combined with in situ scanning electron microscope images have been measured on a series of amorphous carbon films grown by pulsed laser deposition. Uniform, reproducible current–voltage characteristics without morphological damage are only observed with sequential voltage ramps ⩽5 V/s for anode-cathode gaps of 10–200 μm. The field threshold and emission barrier increase with laser energy density used during film growth. This dependence of emission parameters on film growth conditions appears to be correlated with the presence of conducting filaments extending through the film thickness.
InAsSbP/InAsSb/InAs laser diodes (λ=3.2 μm) grown by low-pressure metal–organic chemical-vapor deposition
Authors: Diaz J. , Yi H. , Rybaltowski A. , Lane B. , Lukas G. , Wu D. , Kim S. , Erdtmann M. , Kaas E. , Razeghi M.
Published: July 2002

We report metal–organic chemical-vapor deposition-grown double heterostructure InAsSbP/InAsSb/InAs diode lasers emitting at 3.2 μm operating at temperatures up to 220 K with threshold current density of 40 A/cm2 at 77 K and characteristic temperature up to 42 K. Output powers as high as 260 mW in pulse mode and 60 mW in continuous wave operation have been obtained from an uncoated 100 μm stripe-width broad-area laser at 77 K. Comparison with theory shows that there is no significant nonradiative recombination mechanism for these lasers at 77 K.
Phonon-boundary scattering in thin silicon layers
Authors: Asheghi M. , Leung Y. K. , Wong S. S. , Goodson K. E.
Published: July 2002

Temperature fields in microdevices made from silicon-on-insulator (SOI) wafers are strongly influenced by the lateral thermal conductivity of the silicon overlayer, which is diminished by phonon scattering on the layer boundaries. This study measures the thermal conductivity of single-crystal silicon layers in SOI substrates at temperatures between 20 and 320 K using Joule heating and electrical-resistance thermometry in microfabricated structures. Data for layers of thickness between 0.4 and 1.6 μm demonstrate the large reduction resulting from phonon-boundary scattering, particularly at low temperatures, and are consistent with predictions based on the phonon Boltzmann transport equation.
Ge nanocrystals in SiO2 films
Authors: Kobayashi Takamitsu , Endoh Toshiaki , Fukuda Hisashi , Nomura Shigeru , Sakai Akira , Ueda Yuji
Published: July 2002

SiO 2 /Ge nanocrystal/SiO2 structures have been fabricated by deposition of Ge film on a SiO2 layer and subsequent oxidation of the structure at a temperature between 800 °C and 1000 °C. Secondary ion mass spectrometry results indicate that the Ge precipitates into the bulk SiO2 at a density of 1×1012 cm−2. Raman spectra show a sharp peak at 300 cm−1 for the nanocrystallized Ge. The nanocrystal diameter is determined to be 5 nm on average. In the metal–insulator–silicon structure, electron storage occurs in the SiO2/Ge/SiO2 potential well via electron tunneling into the oxide film. Capacitance-voltage measurements indicate that flatband voltage (VFB) shifts to 0.91 V after the electron injection. The VFB shift is attributed to the charge storing for a single electron per potential well.
Electrical properties of Na-incorporated Cu(In1−xGax)3Se5 thin films
Authors: Kohara Naoki , Negami Takayuki , Nishitani Mikihiko , Hashimoto Yasuhiro , Wada Takahiro
Published: July 2002

Na-incorporated Cu(In1−xGax)3Se5(Cu(In1−xGax)3Se5:Na) films were prepared by the deposition of Cu(In1−xGax)3Se5 layers on Na2S-coated substrates. Electrical properties of the Cu(In1−xGax)3Se5:Na films were evaluated by I–V and spectral response measurements of devices with an ITO/ZnO/CdS/Cu(In1−xGax)3Se5:Na/Mo/glass structure. The Cu(In1−xGax)3Se5:Na films with x>0 showed p-type conduction, whereas for Cu(In1−xGax)3Se5 without the addition of Na2S, films with x<0.3 showed n-type conduction. The addition of Na was found to have a strong influence on the electrical properties of Cu(In1−xGax)3Se5 films as well as Cu(In1−xGax)Se2 films.
Optical dispersion of the refractive index modulation in low Tg photorefractive polymers
Authors: Sandalphon  , Wang J. F. , Kippelen B. , Peyghambarian N.
Published: July 2002

We measure at different wavelengths the linear and nonlinear optical properties of a new chromophore for photorefractive applications by means of frequency-dependent ellipsometry experiments. We show that the optical dispersion of the refractive index modulation responsible for the high diffraction efficiency in low Tg polymers can be described by a two-level model.
Quantitative inelastic tunneling spectroscopy in the silicon metal-oxide-semiconductor system
Authors: Lye Whye-Kei , Hasegawa Eiji , Ma Tso-Ping , Barker Richard C. , Hu Yin , Kuehne John , Frystak David
Published: July 2002

A dual temperature method has been developed for subtracting the 77 K thermally smoothed background from 4.2 K inelastic electron tunneling spectra of ultrathin dielectric metal-insulator-semiconductor junctions. A mode resolving method applied to the remaining spectrum clearly identifies electrode and insulator vibrational modes. The ability to track these relative mode positions and amplitudes shows promise as a unique interface analysis and process diagnostic method. Results are reported on polycrystalline silicon gate, 1.5-nm-thick oxide devices fabricated on 1–10 Ω cm, N-type, (100) silicon substrates by a standard industrial process sequence.
Local magnetometry at high fields and low temperatures using InAs Hall sensors
Authors: Pugel E. , Shung E. , Rosenbaum T. F. , Watkins S. P.
Published: July 2002

We characterize the temperature (0.3⩽T⩽300 K), magnetic field (0⩽H⩽80 kOe), and thickness (0.1, 0.5, and 2.5 μm) dependence of the Hall response of high purity InAs epilayers grown using metalorganic chemical vapor deposition. The high sensitivity, linearity, and temperature independence of the response make them attractive for local Hall probe magnetometry, and uniquely qualified for high field applications below liquid helium temperatures. As a stringent test of performance, we use a six element micron-sized array to monitor the internal field gradient during vortex avalanches at milliKelvin temperatures in a single crystal of YBa2Cu3O7−δ.
Capture of vacancies by extrinsic dislocation loops in silicon
Authors: Herner S. B. , Gossmann H.-J. , Baumann F. H. , Gilmer G. H. , Jacobson D. C. , Jones K. S.
Published: July 2002

The capture of a flux of vacancies in Si by a band of extrinsic dislocation loops has been observed in Sb doping superlattices. Annealing Sb doping superlattices containing a band of dislocation loops in NH3 results in an injection of vacancies, which enhances the diffusion of Sb spikes located between the surface and loop band. By extracting the diffusivity in the Sb spikes on either side of the loop band, we conclude that over 90% of the injected vacancies are captured by the loops.
Measurement of the electrostrictive coefficients of modified lead magnesium niobate using neutron powder diffraction
Authors: Misture S. T. , Pilgrim S. M. , Hicks J. C. , Blue C. T. , Payzant E. A. , Hubbard C. R.
Published: July 2002

Neutron powder diffraction measurements and a constitutive model were used to determine the bulk longitudinal and transverse electrostrictive coefficients (Qijkl) for polycrystalline samples of the subject material. Effective single-crystal Qijkl were calculated from the powder neutron diffraction data. The resulting values of the three independent Qijkl, as determined from the cubic symmetry of the underlying lattice, are Q3333=2.1×10−2 m4/C2, Q3322=−0.87×10−2 m4/C2, and Q3232=1.2×10−2 m4/C2. Using these effective single-crystal values, a random ensemble average was used to predict the electromechanical performance of the polycrystalline material. Predicted values of bulk Q3333=1.86×10−2 m4/C2 and Q3322=−0.78×10−2 m4/C2 are 89% and 87%, respectively, of the effective single-crystal values for Q3333 and Q3322, while measured values of polycrystalline specimens are only ∼70% of the single-crystal values.
Accurate extraction of the diffusion current in silicon p-n junction diodes
Authors: Simoen E. , Claeys C. , Czerwinski A. , Katcki J.
Published: July 2002

An accurate method for the extraction of the reverse diffusion current component in a silicon p-n junction diode is proposed. It combines capacitance–voltage and current–voltage measurements on an array of diodes with different geometry in order to separate the peripheral and the volume leakage current components. The corrected volume capacitance is then used to calculate the depletion width as a function of the reverse bias. Extrapolation of the reverse current to zero depletion width results in the diffusion current part, both for the volume and for the peripheral component. From the temperature dependence, a thermal activation energy of 1.12 eV is obtained. The volume diffusion current density of the p-type Czochralski wafers studied, shows a pronounced substrate dependence, while the peripheral diffusion current density is constant. Finally, the implications for the extraction of the effective bulk recombination lifetime are discussed.
Electroluminescence from Si/Si oxynitride superlattices
Authors: Bai G. F. , Qiao Y. P. , Ma Z. C. , Zong W. H. , Qin G. G.
Published: July 2002

The Si/Si oxynitride superlattices, with three periods, have been grown using the two-target alternation magnetron sputtering technique. The thicknesses of Si oxynitride layers and Si layers in the superlattices are 2.0 and 1.4 nm, respectively. Visible electroluminescence (EL) from a semitransparent Au film/(Si/Si oxynitride) superlattice/p-Si structure has been observed. Each EL spectrum of the structure has a dominant peak around 640 nm, a weaker peak around 520 nm, and a shoulder around 820 nm. By comparing the EL from the semitransparent Au film/(Si/Si oxynitride) superlattice/p-Si structure with that from a semitransparent Au film/Si oxynitride film/p-Si structure, we found that the EL efficiency of the former structure is about 2–4 times of that of the latter one.
Erbium doping of LiNbO3 by the ion exchange process
Authors: Sada C. , Borsella E. , Caccavale F. , Gonella F. , Segato F. , Korkishko Yu. N. , Fedorov V. A. , Morozova T. M. , Battaglin G. , Polloni R.
Published: July 2002

Erbium-doped LiNbO3 slides are fabricated by the ion exchange process. Compositional in-depth profiles of the species involved in the exchange are obtained by secondary ion mass spectrometry. Spectroscopic properties of Er3+ ions in the matrix are determined by photoluminescence spectroscopy. Structural and spectroscopic analyses suggest the formation of two different microstructures in the exchanged region. The potential of ion exchange for a controlled doping of LiNbO3 is outlined.
On the role of interface imperfections in thermoelectric nondestructive materials characterization
Authors: Hu Jiangtao , Nagy Peter B.
Published: July 2002

This letter draws attention to a previously unnoticed artifact associated with the most common type of thermoelectric nondestructive materials characterization technique. It is shown that contact heating between the specimen to be tested and the reference electrode gives rise to a considerable offset in the measured thermoelectric voltage. The resulting bias significantly reduces the feasibility of thermoelectric measurements in nondestructive testing applications that require sensitive materials discrimination, for example, to sort metals of similar alloying content, to distinguish similar grades of heat treatment, and to detect slight variations in the thermoelectric power of metals due to hardening, texture, fatigue, etc. It is also suggested that the demonstrated intrinsic sensitivity of the thermoelectric contact technique to imperfect interfaces could be exploited for nondestructive detection of tightly compressed but metallurgically not bonded interfaces in spot welds, diffusion bonds, and other types of solid-state bonds.
Structural and optical properties of pseudomorphic InxGa1−xN alloys
Authors: Romano L. T. , Krusor B. S. , McCluskey M. D. , Bour D. P. , Nauka K.
Published: July 2002

Thick (225 nm) InxGa1−xN layers, grown on 5 μm thick GaN, were found by x-ray diffraction (XRD) measurements to be pseudomorphic up to x=0.114. Transmission electron microscopy showed that no misfit or additional threading dislocations were created at the InxGa1−xN/GaN interface. Composition of the overlayers was determined by Rutherford backscattering spectrometry and correlated to both the a and c lattice constants from XRD. It was found that Vegard’s law is applicable at these compositions, if the biaxial strain is included. Biaxial strain must also be considered to accurately determine the bowing parameter as shown by optical transmission measurements.
Local tuning of organic light-emitting diode color by dye droplet application
Authors: Hebner T. R. , Sturm J. C.
Published: July 2002

We have demonstrated that fluorescent dyes may be introduced into previously fabricated polymer thin films by local application of a dye-containing droplet. The UV fluorescence spectra of the films and the spectra of organic light-emitting diodes made from these films can be successfully tuned by this method. The technique has been implemented by ink-jet printing of the dye droplet.
Generation of a plasma waveguide in an elongated, high repetition rate gas jet
Authors: Fan J. , Clark T. R. , Milchberg H. M.
Published: July 2002

We demonstrate a pulsed gas nozzle which can produce uniform, greater than 1-cm-long gas jets with peak equivalent pressures up to several hundred Torr at a distance up to ∼3 mm from the nozzle exit. Time-resolved electron density profiles are presented for 1.2-cm-long uniform plasma waveguides produced in an axicon line focus in this jet at a repetition rate of 10 Hz.
Electrodeposition of nanoscale magnetic structures
Authors: Hofmann D. , Schindler W. , Kirschner J.
Published: July 2002

Magnetic Co clusters have been electrodeposited from an aqueous electrolyte onto Au surfaces in an electrochemical scanning tunneling microscope (STM). In a two-step electrochemical process, Co is first deposited onto a Au STM tip, then completely dissolved, and locally deposited onto the substrate underneath the STM tip due to local Co2+ oversaturation, which results in a laterally varying increase of the Co/Co2+ Nernst potential at the substrate surface. Mechanical tip–sample contacts or creation of substrate defects can be excluded. The structure size is of the order of the STM tip apex diameter, and is in detail determined by the substrate potential.
High-temperature continuous-wave 3–6.1 μm “W” lasers with diamond-pressure-bond heat sinking
Authors: Bewley W. W. , Felix C. L. , Vurgaftman I. , Stokes D. W. , Aifer E. H. , Olafsen L. J. , Meyer J. R. , Yang M. J. , Shanabrook B. V. , Lee H. , Martinelli R. U. , Sugg A. R.
Published: July 2002

Optically pumped type-II W lasers emitting in the mid-infrared exhibited continuous-wave (cw) operating temperatures of 290 K at λ=3.0 μm and 210 K at λ=6.1 μm. Maximum cw output powers for 78 K were 260 mW at λ=3.1 μm and nearly 50 mW at λ=5.4 μm. These high maximum temperatures were achieved through the use of a diamond-pressure-bonding technique for heat sinking the semiconductor lasers. The thermal bond, which is accomplished through pressure alone, permits topside optical pumping through the diamond at wavelengths that would be absorbed by the substrate.
Local electric-field-induced oxidation of titanium nitride films
Authors: Gwo S. , Yeh C.-L. , Chen P.-F. , Chou Y.-C. , Chen T. T. , Chao T.-S. , Hu S.-F. , Huang T.-Y.
Published: July 2002

Nanometer-scale patterning of TiN films grown on SiO2/Si(001) has been demonstrated using the local electric-field-induced oxidation process with a conductive-probe atomic force microscope. The chemical composition of the modified TiN region was determined by micro-Auger electron spectroscopy and was found to consist of Ti, some trace amount of N, and O, suggesting the formation of titanium oxynitride in the near surface region. The dependence of the oxide height on the sample bias voltage with a fixed scanning speed shows a nonlinear trend in the high electric field regime, indicating that the growth kinetics might be significantly different from previous studies using other film materials.
Femtosecond midinfrared-induced luminescence study of the ultrafast dynamics of split-off holes in GaAs
Authors: Burr Kent C. , Tang C. L.
Published: July 2002

The ultrafast relaxation dynamics of split-off holes in GaAs are studied using a time-resolved two-wavelength excitation luminescence technique. Following valence-to-conduction-band transitions that are excited by near-infrared femtosecond pulses, delayed midinfrared femtosecond pulses are used to promote holes from the heavy-hole band to the split-off-hole band. The subsequent conduction-to-split-off-hole luminescence indicates that the room-temperature lifetime of split-off holes in GaAs is approximately 50 fs. The accompanying changes in conduction-to-heavy-hole-and-light-hole luminescence when holes are transferred to the split-off band are also observed.
Sub-5-fs visible pulse generation by pulse-front-matched noncollinear optical parametric amplification
Authors: Shirakawa A. , Sakane I. , Takasaka M. , Kobayashi T.
Published: July 2002

Sub-5-fs pulses are generated in the visible region. A pulse-front-matched noncollinear optical parametric amplifier is operated with the full bandwidth by precompression of the seeded continuum with a customized ultrabroadband chirped mirror (UBCM) pair. The signal is compressed down to a nearly transform-limited 4.7±0.1 fs duration by a prism pair and another UBCM pair with a 5-μJ pulse energy.
High performance organic polymer light-emitting heterostructure devices
Authors: He Y. , Gong S. , Hattori R. , Kanicki J.
Published: July 2002

We report a high performance electroluminescence device based on bi-layer conjugated polymer structures consisting of a hole transporting (amine-fluorene) and an emissive (benzothiadiazole-fluorene) polymer layers prepared by the spin-coating technique on the glass substrate. Devices showed green emission with an electroluminescence peak located at around 545 nm and a full width at half maximum of about 80 nm. Our devices have also shown a high brightness (∼10 000 cd/m2 at 0.84 mA/mm2), good emission efficiency (∼14.5 cd/A) and luminous efficiency (2.26 lm/W), a large external quantum efficiency (3.8%), and a reasonable forward-to-reverse bias current rectification ratio (>103 at ±25 V).
Competition of arsenic and sulfur segregation on Fe-9%W(100) single crystal surfaces
Authors: Busch B. W. , Gustafsson T. , Uebing C.
Published: July 2002

High-resolution medium-energy ion scattering (MEIS) was used to investigate the segregation of arsenic and sulfur on the (100) oriented surface of a body-centered cubic Fe-9 wt %W(100) single crystal containing 53 wt-ppm As and 10 wt-ppm S. At temperatures ranging from 800 to 1100 °C, both segregants compete for the available surface sites. Arsenic segregation dominates at temperatures around 800 °C where maximum As surface concentrations of θAsmax=0.40 were found. S segregation is most pronounced at temperatures around 1000 °C with θSmax=0.43. MEIS shows the segregated As (S) atoms to be arranged 1.27 Å (1.22 Å) above the topmost metal layer. The metal-to-metal layer distances show an oscillatory behavior with an expansion of the first to second metal layer (+0.05 Å). With As and S on the surface, there is a strong W depletion of the topmost three metal layers.
Surface loss probabilities of the dominant neutral precursors for film growth in methane and acetylene discharges
Authors: Hopf C. , Letourneur K. , Jacob W. , Schwarz-Selinger T. , von Keudell A.
Published: July 2002

The surface loss probabilities of the dominant neutral growth species emanating from methane and acetylene discharges are investigated by depositing thin films inside a cavity. The walls of this cavity are made from silicon substrates. Particles from the plasma can enter the cavity through a slit. The surface loss probability is determined by analysis of the deposition profile inside the cavity. This surface loss probability corresponds to the sum of the probability for effective sticking on the surface and the probability for the formation of a nonreactive volatile product via surface reactions. In a methane discharge the surface loss probability is ∼0.65±0.15 and in an acetylene discharge ∼0.92±0.05, respectively. The dominant contribution in the neutral radical flux emanating from a methane discharge towards the surface consists of CH3 radicals, as known from experiments using mass spectrometry. Furthermore, it is known from literature that the upper limit for the reaction probability for CH3 is in the range of 10−2. This leads us to the conclusion that the CH3 radical is not the dominant neutral growth precursor in a methane discharge. This result refutes the widely accepted picture that CH3 radicals are the dominant neutral growth precursor in a-C:H growth from methane. From a comparison of the composition of the neutral flux towards the surface from methane and acetylene discharges, we conclude that in both cases C2Hy species are the dominant neutral precursors for film growth.
Radio-frequency amplifier with tenth-kelvin noise temperature based on a microstrip direct current superconducting quantum interference device
Authors: André Marc-Olivier , Mück Michael , Clarke John , Gail Jost , Heiden Christoph
Published: July 2002

A dc superconducting quantum interference device (SQUID) with a resonant microstrip input and a cooled heterostructure field-effect transistor as a postamplifier is used as a radio-frequency amplifier in the frequency range 90–500 MHz. At liquid He3 temperatures, gains of 24 and 20 dB and intrinsic noise temperatures of 0.06±0.02 and 0.12±0.10 K were achieved at 89.6 and 438 MHz, respectively. The system noise temperature at 438 MHz was also estimated from the Nyquist noise produced by a resonant circuit coupled to the input of the microstrip SQUID.
Focusing of high-current, large-area, heavy-ion beams with an electrostatic plasma lens
Authors: Goncharov A. A. , Protsenko I. M. , Yushkov G. Yu. , Brown I. G.
Published: July 2002

We report on measurements of the focusing of high-current, large-area beams of heavy metal ions using an electrostatic plasma lens. Tantalum ion beams were formed by a repetitively pulsed vacuum arc ion source, with energy in the 100 keV range, current up to 0.5 A, initial beam diameter 10 cm, and pulse length 250 μs. The plasma lens was of internal diameter 10 cm and length 20 cm, and had nine electrostatic ring electrodes with potential applied to the central electrode of up to 7 kV, in the presence of a pulsed magnetic field of up to 800 G. The current-density profile of the downstream, focused, ion beam was measured with a radially moveable, magnetically suppressed, Faraday cup. The tantalum ion-beam current density at the focus was compressed by a factor of up to 30. The results are important in that they provide a demonstration of a means of manipulating high-current ion beams without associated space-charge blowup.
Fabrication and electrical characterization of planar resonant tunneling devices incorporating InAs self-assembled quantum dots
Authors: Jung S. K. , Hyon C. K. , Park J. H. , Hwang S. W. , Ahn D. , Son M. H. , Min B. D. , Kim Yong , Kim E. K.
Published: July 2002

Planar-type quantum-dot devices have been fabricated and characterized. Aluminum metal electrodes with interelectrode spacing of 30 nm have been deposited on an InAs self-assembled quantum-dot wafer to form the quantum-dot devices. The current–voltage characteristics measured from the devices, in which a single quantum dot is placed in between the electrodes, exhibit negative differential resistance effects at the temperature above 77 K. They are interpreted as due to three-dimensional–zero-dimensional resonant tunneling through the InAs self-assembled quantum dot.
Dielectric properties of C60 films in the high-temperature region
Authors: Su J. S. , Chen Y. F. , Chiu K. C.
Published: July 2002

Capacitance and dissipation factor measurements of the dielectric properties on C60 thin films are performed at a temperature between 275 and 470 K. A Debye-like relaxation in the dielectric response has been observed, and the relaxation rate is thermally activated with an energy of about 467 meV which is different from the value 277 meV obtained at a temperature below 260 K. Remarkably, both the capacitance and dissipation factor curves as a function of temperature have a pronounced feature at 435 K. It confirms the fact that above 400 K a phase transition does occur in the C60 crystal except for that detected around 260 K. We interpreted the phase transition at 435 K in terms of the disappearance of one of the spherical harmonics Ylm that describe the orientational density distribution of the C60 molecules.
High electron mobility polycrystalline silicon thin-film transistors on steel foil substrates
Authors: Wu Ming , Pangal Kiran , Sturm J. C. , Wagner Sigurd
Published: July 2002

Thin-film transistors have been fabricated in polycrystalline silicon films on steel foil. The polycrystalline silicon films were formed by the crystallization of hydrogenated amorphous silicon, which had been deposited on 200-μm-thick foils of stainless steel coated with ∼0.5-μm-thick layers of SiO2. We employed crystallization temperatures (and duration) of 600 °C (6 h), 650 °C (1 h), and 700 °C (10 min). Top-gate transistors made from films crystallized at 650 °C have an average electron field-effect mobility of 64 cm2/V s, with equal values in the linear and saturated regimes. Thus steel substrates permit a substantial reduction in crystallization time over glass substrates, and afford polysilicon with high electron mobility.
Gating individual nanotubes and crosses with scanning probes
Authors: Tombler Thomas W. , Zhou Chongwu , Kong Jing , Dai Hongjie
Published: July 2002

Atomic force microscopy tips are used to apply point-like local gates to manipulate the electrical properties of individual single-walled carbon nanotubes (SWNT) contacted by Ti electrodes. Depleting a semiconducting SWNT at a local point along its length leads to orders of magnitude decrease of the nanotube conductance, whereas local gating to metallic SWNTs causes no change in the conductance of the system. These results shed light into gating effects on metal-tube contacts. Electrical properties of SWNT crosses are also investigated. Scanning-probe gating is used to identify the metallic or semiconducting nature of the nanotube components in the crosses.
Selective area deposited blue GaN–InGaN multiple-quantum well light emitting diodes over silicon substrates
Authors: Yang J. W. , Lunev A. , Simin G. , Chitnis A. , Shatalov M. , Khan M. Asif , Van Nostrand Joseph E. , Gaska R.
Published: July 2002

We report on fabrication and characterization of blue GaN–InGaN multi-quantum well (MQW) light-emitting diodes (LEDs) over (111) silicon substrates. Device epilayers were fabricated using unique combination of molecular beam epitaxy and low-pressure metalorganic chemical vapor deposition growth procedure in selective areas defined by openings in a SiO2 mask over the substrates. This selective area deposition procedure in principle can produce multicolor devices using a very simple fabrication procedure. The LEDs had a peak emission wavelength of 465 nm with a full width at half maximum of 40 nm. We also present the spectral emission data with the diodes operating up to 250 °C. The peak emission wavelengths are measured as a function of both dc and pulse bias current and plate temperature to estimate the thermal impedance.
Solar-blind AlGaN photodiodes with very low cutoff wavelength
Authors: Walker D. , Kumar V. , Mi K. , Sandvik P. , Kung P. , Zhang X. H. , Razeghi M.
Published: July 2002

We report the fabrication and characterization of AlxGa1−xN photodiodes (x∼0.70) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The peak responsivity for −5 V bias is 0.11 A/W at 232 nm, corresponding to an internal quantum efficiency greater than 90%. The device response drops four orders of magnitude by 275 nm and remains at low response for the entire near-ultraviolet and visible spectrum. Improvements were made to the device design including a semitransparent Ni/Au contact layer and a GaN:Mg cap layer, which dramatically increased device response by enhancing the carrier collection efficiency.
Bandgap closure of a flattened semiconductor carbon nanotube: A first-principles study
Authors: Mazzoni Mário S. C. , Chacham H.
Published: July 2002

We investigate, through first-principles calculations, the effects of a flattening distortion on the electronic properties of a semiconductor carbon nanotube. The flattening causes a progressive reduction of the band gap from 0.92 eV to zero. The band-overlap insulator-metal transition occurs for an interlayer distance of 4.6 Å. Supposing that the flattening of the nanotube can be produced by a force applied by a scanning microscope tip, we estimate that the force per unit length of the nanotube that is necessary to reach the insulator-metal transition is 7.4 N/m.
High ambipolar carrier mobility in self-organizing terthiophene derivative
Authors: Funahashi Masahiro , Hanna Jun-ichi
Published: July 2002

Dialkylterthiphene derivatives exhibiting self-organization of molecular alignment were synthesized and their electrical properties were studied. It was found that these materials exhibited very fast electron transport in smectic mesophases as well as hole transport, both of which were independent of electric field and temperature. The mobility for electrons and holes was 5×10−4 cm2/V s in smectic C (SmC) and was increased up to 2×10−3 cm2/V s and even more up to 1×10−2 cm2/V s in accompany with upgrade of molecular alignment from SmC to SmF and from SmF to SmG, respectively. This abrupt increase in the mobility to the extent of about one order of magnitude corresponds to that in 2-phenylnaphthalene derivatives at the phase transition from SmA to SmB and from SmB to SmE whose molecular alignments are in good correlation with those of SmC, SmF, and SmG, respectively.
Antenna configuration for uniform large-area inductively coupled plasma production
Authors: Kim S. S. , Chang H. Y. , Chang C. S. , Yoon N. S.
Published: July 2002

An antenna configuration for uniform plasma generation in a large-area inductively coupled plasma (ICP) source is presented and investigated using numerical analysis. The numerical results show that a properly tuned, segmented coil system with an external variable capacitor can allow antenna voltage, currents, and plasma uniformity to be controlled in the large-area ICP source. The key element of this concept is to induce LC-resonance in the coil system by the external capacitance variation. Through the LC-resonance, not only a small antenna voltage can be obtained, but also a selected coil current near a low plasma density regime can be significantly enhanced. Self-consistent fluid simulations for Ar and Cl2 plasmas indicate that the radial plasma spread can be optimized near the LC-resonance condition.
To the Gel’fand–Tsetlin realization of irreducible representations of classical semisimple algebras
Authors: Leznov A. N.
Published: July 2002

It is shown that the Gel’fand–Tsetlin realization of irreducible representations of the An algebra is directly connected with a linear exactly integrable system in the n-dimensional space. General solutions for this system is explicitly given.
Quantum time and spatial localization: An analysis of the Hegerfeldt paradox
Authors: Von Zuben Francis S. G.
Published: July 2002

Two related problems in relativistic quantum mechanics, the apparent superluminal propagation of initially localized particles and dependence of spatial localization on the motion of the observer, are analyzed in the context of Dirac’s theory of constraints. A parametrization invariant formulation is obtained by introducing time and energy operators for the relativistic particle and then treating the Klein–Gordon equation as a constraint. The standard, physical Hilbert space is recovered, via integration over proper time, from an augmented Hilbert space wherein time and energy are dynamical variables. It is shown that the Newton–Wigner position operator, being in this description a constant of motion, acts on states in the augmented space. States with strictly positive energy are nonlocal in time; consequently, position measurements receive contributions from states representing the particle’s position at many times. Apparent superluminal propagation is explained by noting that, as the particle is potentially in the past (or future) of the assumed initial place and time of localization, it has time to propagate to distant regions without exceeding the speed of light. An inequality is proven showing the Hegerfeldt paradox to be completely accounted for by the hypotheses of subluminal propagation from a set of initial space–time points determined by the quantum time distribution arising from the positivity of the system’s energy. Spatial localization can nevertheless occur through quantum interference between states representing the particle at different times. The nonlocality of the same system to a moving observer is due to Lorentz rotation of spatial axes out of the interference minimum.