bluuebunny/crossref_metadata_2025 huggingface dataset:
Hard x-ray absorption spectroscopy of CuO and Cu2O with a photoacoustic detector
Authors: Toyoda Taro , Masujima T. , Shiwaku H. , Ando M.
Published: July 2002

The hard x-ray spectra of CuO, Cu2O, and pure Cu metal have been measured at x-ray absorption near-edge structure (XANES) regions with a photoacoustic detector using synchrotron radiation. It is shown that the information derived from XANES is also included in the x-ray photoacoustic spectrum which reflects the heat production processes in those copper oxides and metal. However, the results showed that the increases and changes of the photoacoustic signal were different from those of the x-ray absorption coefficient at the photon energy regions.
Infrared absorption enhancement in light- and heavy-hole inverted Ga1−xInxAs/Al1−yInyAs quantum wells
Authors: Xie H. , Katz J. , Wang W. I.
Published: July 2002

We have investigated infrared absorption properties at normal incidence in p-type Ga1−xInxAs/Al1−yInyAs strained quantum wells. They are designed such that the ground state for holes is a light-hole state, which results from the effects of biaxial tensile strain in the quantum wells. We find that in this light- and heavy-hole inverted structure the infrared absorption from intervalence subband transitions can be greatly enhanced up to 8500 cm−1, which is comparable to that in the intrinsic Hg1−xCdxTe detector. This novel structure’s ability to detect infrared radiation at normal incidence makes it promising for infrared photodetection applications.
Growth of (110)-oriented CeO2 layers on (100) silicon substrates
Authors: Inoue T. , Ohsuna T. , Luo L. , Wu X. D. , Maggiore C. J. , Yamamoto Y. , Sakurai Y. , Chang J. H.
Published: July 2002

CeO2 layers epitaxially grown on (100) silicon substrates by electron-beam evaporation were investigated and proved to have (110) orientation. X-ray diffraction measurements showed the CeO2 layers consist of more than 98% volume fraction of the (110) component. Cross-sectional high-resolution transmission electron microscopy and selected-area electron diffraction clearly verified the above configuration of crystallographic orientations and that the 〈100〉 direction in the CeO2(110) plane is parallel with the 〈110〉 direction in the Si(100) plane. The cross-sectional lattice image clarified the existence of a ∼60-Å-thick intermediate amorphous layer between the CeO2 layer and the silicon substrate. Moreover, the high density of defects such as dislocations and low-angle boundaries that exist in the vicinity of the interface agree well with Rutherford backscattering and channeling measurements.
Lattice site locations of excess arsenic atoms in gallium arsenide grown by low-temperature molecular beam epitaxy
Authors: Yu Kin Man , Liliental-Weber Z.
Published: July 2002

The excess As atoms present in as-grown GaAs buffer layers grown by molecular beam epitaxy at low substrate temperature (∼200 °C) was measured by particle induced x-ray emission to be ∼4×1020 atoms/cm3. The lattice site location of these excess As atoms in the layer was studied by ion channeling methods. Our results strongly suggested that the excess As atoms are located in an interstitial position close to the substitutional As atoms with a projected displacement ∼0.3 Å into the 〈110〉 channel. These results are consistent with the 〈111〉 split interstitials model suggested from TEM results. After annealing at 600 °C these excess As atoms coalesce forming As precipitates.
Hydrogen diffusivities below room temperature in silicon evaluated from the photoinduced dissociation of hydrogen–carbon complexes
Authors: Kamiura Yoichi , Yoneta Minoru , Hashimoto Fumio
Published: July 2002

We have evaluated hydrogen and deuterium diffusivities in silicon below room temperature (220–270 K) by analyzing the kinetics of photoinduced dissociation of a chemical etching introduced hydrogen (deuterium)–carbon complex. Under sufficiently strong illumination, the annihilation rate of the complex was proportional to the phosphorus density, indicating that the rate-determining step is the diffusion of hydrogen (deuterium) to phosphorus atoms. Applying the diffusion-controlled reaction theory, we have evaluated the diffusion coefficients as 7×10−2exp(−0.54 eV/kT) cm2 s−1 for hydrogen and 5×10−3exp(−0.49 eV/kT) cm2 s−1 for deuterium, being in good agreement with the extrapolation of the high-temperature diffusion data of A. Van Wieringen and N. Warmoltz [Physica 22, 849 (1956)].
Holographic Bessel beam amplification
Authors: Lee Hee S. , Stewart B. W. , Will D. , Fenichel Henry
Published: July 2002

The generation of a diffraction-free Bessel beam from a beam that is originally Gaussian is accompanied by substantial power loss. We employed the technique of holographic intensity amplification to enhance the conversion from a Gaussian beam to a Bessel beam with conversion efficiency approaching 50%. In addition the maximum propagation distance was extended.
Exponential growth of periodic surface ripples generated in laser-induced etching of GaAs
Authors: Kumagai H. , Toyoda K. , Machida H. , Tanaka S.
Published: July 2002

The exponential growth of periodic surface ripples in laser-induced etching of GaAs was demonstrated for the first time. The etched depth of the ripple structure increased exponentially with increasing laser irradiation time because of the nonlinear effect of stimulated surface-plasma-wave scattering, while the etched depth of holographic grating increased linearly. A small-signal gain of 5.6%/min was obtained in the growth of the etched depth which was consistent with the theoretical value.
High-purity InP layer grown by metalorganic chemical vapor deposition using tertiarybutylphosphine
Authors: Imori Toru , Ninomiya Takayuki , Ushikubo Kouhei , Kondoh Kazuhiro , Nakamura Kouichi
Published: July 2002

High-purity InP layers have been successfully grown by metalorganic chemical vapor deposition (MOCVD) using tertiarybutylphosphine (TBP) as a phosphorus source. The highest quality InP layer, which was grown at a V/III ratio of 36, a growth temperature of 600 °C and a growth pressure of 760 Torr, exhibited electron mobility as high as 167 000 cm2/V s and carrier concentrations as low as 1.8×1014 cm−3 at 77 K. The film quality strongly depended on the silicon content as an impurity in TBP. Electron mobility at 77 K was dependent on the silicon content, changing its value from 10 100 cm2/V s (Si content; 0.8 ppm) to 167 000 cm2/V s (Si content; <0.03 ppm). The low-temperature (4.2 K) optical properties were also affected by silicon content as a impurity. It was found that electron mobility of 167 000 cm2/V s was the highest ever reported for InP grown by MOCVD using TBP as a phosphorus source. The quality of InP grown using TBP was equivalent to that of InP grown using phosphine (PH3).
Highly carbon-doped p-type Ga0.5In0.5As and Ga0.5In0.5P by carbon tetrachloride in gas-source molecular beam epitaxy
Authors: Chin T. P. , Kirchner P. D. , Woodall J. M. , Tu C. W.
Published: July 2002

Highly carbon-doped, highly p-type Ga0.5In0.5As and Ga0.5In0.5P epilayers were grown by gas-source molecular beam epitaxy (GSMBE) using carbon tetrachloride (CCl4). Growth temperatures slightly below conventional values were used to increase the carbon incorporation, and a short-duration post-growth anneal near the growth temperature was necessary in order to obtain the highest hole concentrations, which were p=3×1019 cm−3 for Ga0.5In0.5As and p=5×1018 cm−3 for Ga0.5In0.5P. This is the first report of significant p-type carbon doping for Ga0.5In0.5P and the highest concentration from carbon doping yet reported for both ternary compounds. Reversible acceptor passivation from hydrogen species in the growth environment is a plausible explanation for the annealing behavior.
Adhesion of polycrystalline diamond thin films on single-crystal silicon substrates
Authors: Gamlen C. A. , Case E. D. , Reinhard D. K. , Huang B.
Published: July 2002

Polycrystalline diamond films were deposited on (100) oriented silicon substrates using a microwave plasma disk reactor. Circular delaminations between the diamond thin film and the silicon substrate were produced by Vickers microindentation. While an overall relationship between mean delamination diameter and film thickness was not observed, an unexpectedly strong correlation was observed between delamination diameter and the square root of the coating grain size. A disadvantage of the Vickers microindentation technique is the damage sustained by the Vickers indenter tip after repeated loadings.
Dislocation glide at a (100) SixGe1−x/Si interface
Authors: Rajan Krishna
Published: July 2002

An unusual fourfold extended dislocation node at a SixGe1−x/Si strained layer interface has been revealed using weak-beam electron microscopy. A detailed contrast analysis shows that this node structure is the result of the constriction of Lomer–Cottrell dislocations formed by intersecting slip dislocations on {100} and {111} type planes. This mechanism necessitates the glissile behavior of dislocation nodes at the (100) epitaxial interface.
Practical low-noise integrated dc superconducting quantum interference device magnetometer with additional positive feedback
Authors: Ryhänen T. , Cantor R. , Drung D. , Koch H.
Published: July 2002

We have designed and fabricated a low-noise dc superconducting quantum interference device (SQUID) magnetometer that is integrated on a 4×4 mm2 chip. The white flux noise of the magnetometer measured in a flux-locked-loop mode using simple, direct-coupled electronics with additional positive feedback (APF) is 6.4×10−7 Φ0/√Hz. The corresponding white flux density noise is 3.9 fT/√Hz. The SQUID flux-to-voltage transfer function with APF is enhanced to 4.7 mV/Φ0 at the optimal working point, thereby significantly reducing the preamplifier contribution to the total noise. A maximum feedback field of 65 nT for frequencies up to 300 Hz and a maximum slew rate of 120 μT/s at 300 Hz have been attained using a two-pole integrator.
Nitrogen-oxygen complexes in silicon studied by photothermal ionization spectroscopy
Authors: Hu C. M. , Huang Y. X. , Ye H. J. , Shen S. C. , Qi M. W.
Published: July 2002

High-resolution photothermal ionization spectroscopy has been performed on silicon grown in a nitrogen environment by the Czochralski technique for the first time. Three shallow donors related to the complexes of nitrogen and oxygen impurities D(N-O-3), D(N-O-4), and D(N-O-5) have been observed. Previously unresolved transitions related to the excited states higher than 3p± for D(N-O)s are observed in the spectra as well. The ionization energies of D(N-O)s have been accurately determined as 36.16, 36.41, and 37.37 meV, respectively. In addition, two previously unidentified donor levels found in the absorption spectra of silicon crystal involving nitrogen and oxygen are identified as originating from the splitting of the ground state of phosphorus.
Optical absorption of ZnSe-ZnS strained layer superlattices
Authors: Yang Fang , Parbrook P. J. , Henderson B. , O’Donnell K. P. , Wright P. J. , Cockayne B.
Published: July 2002

A study of the absorption spectra of excitons in ZnSe-ZnS strained layer superlattices (SLS) with well widths ranging from 0.6 to 7.6 nm is reported. The n=1 heavy hole (hh) and light hole (1h) exciton absorptions are clearly resolved for all samples even near room temperature. A theoretical estimation of the n=1 hh exciton peak energy, which takes account of strain, quantum confinement of free carriers, and exciton binding energy enhancement by reduced dimensionality, is in excellent agreement with the experimental results. The variations in absorption linewidth and energy shift between absorption and emission band peaks, as a function of quantum well width, have also been measured: the experimental results provide evidence that the origin of the so-called ‘‘Stokes’ shift’’ lies in Anderson localization due to monolayer fluctuations in the well width. The temperature dependence of the exciton peak energy and its linewidth are interpreted in terms of electron-phonon and exciton-phonon interactions.
Influence of the composition modulation on the relaxation of In0.54Ga0.46As strained layers
Authors: Peiró F. , Cornet A. , Morante J. R. , Clark S. , Williams R. H.
Published: July 2002

TEM observation of In0.54Ga0.46As grown by MBE on InP shows a coarse tweed quasiperiodic structure related with a composition modulation. The period Λ of this modulation has been found to be dependent on the layer thickness. The elastic energy associated with the modulation induced strain, has been taken into account to explain this period dependence. The evolution of strain parallel to growth surface with epilayer thickness has been correlated with both the change on the modulation period and the presence of defects.
Measurement of local stress in silicon nitride films grown by plasma-enhanced chemical vapor deposition using micro-Raman spectroscopy
Authors: Okada Yoshio , Nakajima Shin-ichi
Published: July 2002

This letter presents the first attempt to use micro-Raman spectroscopy to evaluate the local stress in silicon nitride films deposited by plasma-enhanced chemical vapor deposition. The frequency of the Si-H stretching mode in IR absorption of the films increases linearly with increasing compressive film stress [3.6 (cm−1)/109 (dyn/cm2)]. In micro-Raman spectra, the film with a higher compressive stress shows a higher frequency shift. Micro-Raman spectroscopy was applied to determine the local stress in patterned structures. It is found that the silicon nitride film deposited over trench structures shows a higher local stress at the top corner.
Comparison of high quality (111)B and (100) AlGaAs grown by molecular beam epitaxy
Authors: Chin Albert , Martin Paul , Ballingall Jim , Yu Tan-Hua , Mazurowski John
Published: July 2002

State-of-the-art quality Al0.3Ga0.7As was achieved on both (111)B and (100) GaAs by molecular beam epitaxy. Low-temperature photoluminescence linewidths of 2.9 and 2.4 meV were obtained for (111)B and (100) Al0.3Ga0.7As, grown at 650 and 700 °C, respectively, with nearly equivalent integrated luminescence intensity. This is the narrowest linewidth ever reported for (111) AlGaAs. The low growth temperature and high material quality of (111)B Al0.3Ga0.7As is expected to be an important factor to the future development of both electronic and optical heterostructure devices.
Pairing of noble metals with phosphorus
Authors: Zimmermann H. , Khanh N. Q. , Battistig G. , Gyulai J. , Ryssel H.
Published: July 2002

Pairing of gold and platinum with phosphorus is examined. For this purpose, gold, respectively platinum, is diffused into silicon wafers, which contained phosphorus doped regions. A value of 1.0×1019 cm−3 at 900 °C is suggested for the equilibrium concentration of gold phosphorus pairs for a phosphorus concentration of 3.0×1020 cm−3. The pair-forming capability of platinum with phosphorus is found to be much smaller. The equilibrium concentration of platinum phosphorus pairs is less than 3×1017 cm−3. Deep level transient spectroscopy measurements show that gold does not penetrate a 14 μm thick phosphorus layer in 2 h and that the platinum concentration in the bulk is a factor of four smaller than in reference samples without phosphorus doping.
Electrical characteristics of oxynitrides grown on textured single-crystal silicon
Authors: Hao Ming-yin , Lee Jack C.
Published: July 2002

The electrical characteristics of oxynitrides grown on textured single-crystal silicon are discussed in this letter. This study compares the I-V, C-V, charge trapping, interface state generation, and breakdown characteristics of this new gate dielectric with those of oxides and oxynitrides grown on untextured silicon, and oxides grown on textured silicon. Textured oxynitrides were found to have enhanced conduction and significantly reduced interface state generation. Furthermore, they exhibit an improved immunity to charge trapping under high-field stress, and a significantly higher charge-to-breakdown QBD compared to the textured oxides. These properties make the textured oxynitride a promising gate dielectric for applications in electrical-erasable programmable read-only memories (EEPROMs).
Controlled spontaneous emission in room-temperature semiconductor microcavities
Authors: Huffaker D. L. , Lei C. , Deppe D. G. , Pinzone C. J. , Neff J. G. , Dupuis R. D.
Published: July 2002

Data are presented demonstrating controlled spontaneous emission in room-temperature AlGaAs-GaAs Fabry–Perot microcavities, which utilize high contrast Bragg reflectors. The reflector materials are a CaF2/ZnSe combination. A GaAs quantum well contained in the microcavities is excited using a low power He-Ne laser, and the spontaneous emission characteristics are measured in terms of spectral characteristics and radiation patterns. The measured data are compared with calculations which predict controlled spontaneous emission in such structures. We find that the dominant effects on spontaneous emission in these thin layer structures are due to cavity controlled emission into allowed optical modes and stress induced dipole orientation in the GaAs quantum well.
Passivation of ion-beam damage in metal-oxide-silicon structures by room-temperature hydrogenation
Authors: Kar S. , Srikanth K. , Ashok S.
Published: July 2002

The efficacy of room-temperature hydrogenation, by a 400-eV hydrogen beam from a Kaufman source, in the removal of ion-beam-induced defects in metal-oxide-silicon (MOS) structures was investigated. The defects were generated by exposure of thermally oxidized silicon samples to a 16-kV Si ion beam in an ion implanter. The oxide thickness was 115 or 350 Å. Experimental results obtained from admittance-voltage-frequency measurements of the MOS structures indicated significant reductions in trap density and other defects.
Self-consistent scattering matrix calculation of the distribution function in semiconductor devices
Authors: Stettler Mark A. , Lundstrom Mark S.
Published: July 2002

The scattering matrix approach is a new technique for solving the Boltzmann equation in devices. We report a self-consistent application of the technique to realistic silicon devices exhibiting strong nonlocal effects. Simulation of a hot-electron, n-i-n diode demonstrates that the new technique efficiently and accurately reproduces Monte Carlo results without the statistical noise, allowing much tighter convergence with Poisson’s equation.
Comparison of electro-optic lead-lanthanum zirconate titanate films on crystalline and glass substrates
Authors: Preston K. D. , Haertling G. H.
Published: July 2002

It has been demonstrated that electro-optically active lead zirconate titanate (PZT) and lanthanum-modified lead zirconate titanate (PLZT) films derived from a water-soluble acetate precursor system can be produced on glass substrates at a processing temperature of 600 °C through the initial application of a lanthanum-modified lead titanate (PLT) buffer layer. A comparison of the electro-optic behavior is made between films deposited onto glass and single-crystal sapphire substrates when processed under the same conditions. Memory effects were observed in PZT 0/65/35 films, while quadratic behavior was exhibited by the PLZT 9/65/35 films consistent with expected bulk behavior. However, the measured birefringent shift in the films on glass substrates was lower than that on sapphire.
Magneto-optical evidence of phase separation in amorphous U-As films
Authors: Fumagalli P. , Gambino R. J. , Plaskett T. S. , McGuire T. R.
Published: July 2002

Magneto-optical spectroscopy has been used for the first time to detect phase separation in a magnetic system. The polar Kerr rotation of amorphous UxAs1−x films was measured in the photon energy range from 0.65–3.5 eV at various fields well below the Curie temperature. At concentrations x≥55 at. % U, the Kerr spectrum is dominated by a broad, negative peak near 1.1 eV that we associate with an U5f→6d transition. For x<55 at. % U, a positive peak appears below 1 eV. The positive peak has much higher coercivity and remanence than the negative peak, indicating a phase separation. The two amorphous phases could possibly be metallic UAs and semiconducting UAs2, based on a percolation analysis of the composition dependence of the resistivity.
Laser processing of carbon-implanted Cu, Ni, and Co crystals: An attempt to grow diamond films
Authors: Lee S.-Tong , Chen Samuel , Agostinelli J. , Braunstein G. , Huang L. J. , Lau W. M.
Published: July 2002

Carbon films have been prepared by laser-pulse treatment of single crystals of copper, nickel, and cobalt, which have been previously implanted at room temperature with 50 keV carbon ions to a fluence of 1×1018 cm−2. Characterization using Raman scattering, Auger spectroscopy, and transmission electron microscopy showed that the films consisted of amorphous carbon and microcrystalline graphite but not diamond. In addition, an appreciable amount of substrate material was found present embedded in the carbon films.
New six face lithography technique for realization of contacts on μm size Y1Ba2Cu3O7−x single crystals
Authors: Charalambous Melissa , Chaussy Jacques , Lejay Pascal
Published: July 2002

We have developed a new contact technique for use on very small Y1Ba2Cu3O7−x single crystals (typical dimensions: 100×100×20 μm). A precise contact pattern (resolution ≊2 μm) is realized on the different faces of the sample. This allows the injection of a current parallel to a single crystallographic axis, without mixing of the anisotropic conduction channels. Contact resistivities are satisfactory: 1×10−5 Ω cm2 for the ab contacts, 1×10−6 Ω cm2 for the c-axis contacts. To date the technique has been used to directly measure the c-axis resistivity of the Y1Ba2Cu3O7−x compound, but other applications such as anisotropic thermal conductivity and thermoelectric power are possible.
Structure of the stepped Si/SiO2 interface after thermal oxidation: Investigations with scanning tunneling microscopy and spot-profile analysis of low-energy electron diffraction
Authors: Pietsch G. J. , Köhler U. , Jusko O. , Henzler M. , Hahn P. O.
Published: July 2002

After wet chemical oxide removal and fast transfer into ultrahigh vacuum the Si(111)/SiO2 interface structure of wafers from semiconductor-industrial processes (polishing, oxidation, annealing) is investigated with scanning tunneling microscopy (STM): Regular terrace arrays with atomic step height are visible with STM after technological ex situ preparation. The local step structure varies, kinks at step edges occur, and irregular islands are formed with increasing oxide thickness and oxidation rate. The local STM information is compared to macroscopically averaged results provided by electron diffraction (spot-profile analysis of low-energy electron diffraction).
Photocurrent study of the influence of photogenerated carriers on the EL2*-EL2 transformation in semi-insulating GaAs
Authors: Chafai M. , Jiménez J. , Alvárez A. , Bonnafé J.
Published: July 2002

The optically induced EL2*-EL2 transformation is studied by photocurrent measurements, allowing the monitorization of the free-carrier generation during the near-band-gap (NBG) recovery excitation. The efficiency recovery spectrum is found to be anticorrelated with the NBG photocurrent spectrum. This observation rules out the possibility of a free-carrier assisted process as the main mechanism accounting for the NBG induced EL2*-EL2 reverse transformation.
Growth of Si/GaAs superlattices by molecular beam epitaxy
Authors: Gillespie H. J. , Crook G. E. , Matyi R. J.
Published: July 2002

The growth and characterization of a ten period silicon/GaAs superlattice by molecular beam epitaxy is described. Reflection high energy electron diffraction of the surface reconstruction during growth of the GaAs layers showed the (4×2)→(3×2) →(3×1)→(2×4) sequence reported previously for GaAs grown on pseudomorphic silicon, although the intermediate stages were much more persistent than previously reported. X-ray diffraction revealed satellite peaks clearly visible out to the fourth order, indicating a high degree of structural perfection. Comparison of the experimental diffraction profile and that obtained using a dynamical diffraction simulation yielded average layer thicknesses of 440 and 2.7 Å for the GaAs and silicon layers, respectively. Excellent agreement between the experimental and the simulated profiles was observed.
Photoluminescence characterization of nonradiative recombination in carbon-doped GaAs
Authors: Calderon L. , Lu Y. , Shen H. , Pamulapati J. , Dutta M. , Chang W. H. , Yang L. W. , Wright P. D.
Published: July 2002

Room-temperature photoluminescence is used to investigate the basic recombination mechanisms in carbon-doped GaAs samples, with hole concentrations ranging from 3.0×1016 to 1.2×1020 cm−3. The solution of a one-dimensional, steady-state continuity equation for minority carriers indicates that in heavily carbon-doped GaAs, surface recombination is minimal, while bulk nonradiative recombination is dominant. The bulk nonradiative recombination rate depends not only on p2, which represents Auger recombination, but also on p3. By using a single p+-GaAs:C (1×1020 cm−3) base layer in an AlGaAs/GaAs heterojunction bipolar transistor, the surface recombination is minimized.
Optical second harmonic generation in Langmuir–Blodgett films of n-docosyl-2-methyl-4-nitroaniline
Authors: Howarth V. A. , Asai N. , Kishii N. , Fujiwara I.
Published: July 2002

The preparation of Langmuir–Blodgett (LB) films of n-docosyl-2-methyl-4-nitroaniline (DCMNA) is reported. LB multilayers of DCMNA are highly anisotropic showing a strong absorption for light polarized parallel to the dipping direction. Furthermore, optical second harmonic generation was observed from LB multilayers of DCMNA. The SH signal was always polarized parallel to the dipping direction; and maximum SH intensity was obtained when the direction of the fundamental wave was also polarized parallel to this direction. The SH intensity increased quadratically with the number of LB layers up to 50 layers. Preliminary x-ray diffraction studies indicate a Y-type arrangement for the molecules with a bilayer spacing of 3.77 nm and a strong tilt angle of 34° for the alkyl chains with respect to the substrate plane.
Flowing afterglow synthesis of polythiophene films
Authors: Haaland Peter , Targove James
Published: July 2002

Penning ionization of thiophene and 2,5-dichlorothiophene by metastable argon in a flowing afterglow leads to the deposition of dense, uniform polythiophene films. Homogeneous kinetics have been examined using quadrupole mass spectrometry. The films have been characterized by spectroscopic ellipsometry, optical absorption, Rutherford backscattering spectrometry, and scanning force microscopy. The polymer, which has a nonlinear optical susceptibility χ(3)=10−11 esu at 602 nm, has been deposited on Si, quartz, and metal substrates.
Magnetic coupling in amorphous Fe80−xRxB12Si8(R=Er, Gd) alloys
Authors: Krishnan R. , Lassri H. , Radwanski R. J.
Published: July 2002

We have prepared amorphous Fe-Er-B-Si and Fe-Gd-B-Si alloys and magnetization studies in fields up to 35 T at 4.2 K have been carried out on some selected samples. The results have been analyzed on the existing model proposed by Verhoef et al. for crystalline Fe and Co compounds with rare earths. The magnetic moments of Fe, Er, and Gd, as well as other parameters such as the intersublattice molecular-field coefficient (nRT), the strength of the exchange interaction etc., have been determined.
Intersubbband absorption in narrow Si/SiGe multiple quantum wells without interfacial smearing
Authors: Fujita K. , Fukatsu S. , Shiraki Y. , Yaguchi H. , Ito R.
Published: July 2002

Si/Si1−xGex multiple quantum wells with abrupt heterointerfaces have been formed by segregant-assisted growth (SAG) with Sb. Distinct well-width dependence of intersubband absorption in the narrow quantum wells has been observed. The well-width dependence of the absorption peak energy is in good agreement with a calculation based on the Kronig–Penney model where interfacial smearing is taken to be less than 0.4 nm, suggesting the integrity of Si/Si1−xGex interfaces grown by SAG.
Lateral p-n junctions and quantum wires formed by quasi two-dimensional electron and hole systems at corrugated GaAs/AlGaAs interfaces
Authors: Porod Wolfgang , Harbury Henry K. , Goodnick Stephen M.
Published: July 2002

We report the results of modeling lateral p-n junctions and p-n-p quantum wire structures at corrugated GaAs/AlGaAs interfaces, using the surface orientation dependent amphoteric nature of Si doping. We determine the potential landscape and the electron and hole charge densities within a semiclassical Thomas–Fermi screening model, and then solve the two-dimensional Schrödinger equation using finite elements for the quantized electron and hole states at the heterointerfaces. We demonstrate the formation of a one-dimensional electron system confined between two lateral p-n junctions, and discuss the advantages of this structure compared to conventional electrostatic confinement schemes for fabricating quantum wires.
Induced anisotropy in amorphous Sm-Co sputtered films
Authors: Chen K. , Hegde H. , Cadieu F. J.
Published: July 2002

The variation of the in-the-film-plane anisotropy constant, Ku, with composition and the magnitude of the field, Hs, applied in plane during the sputter deposition of amorphous SmxCo1−x, 0.08≤x≤0.40, thin films has been studied. We demonstrate here that with a large Hs, 5.0 kOe, a well defined and large in-the-film-plane anisotropy can be obtained. An exceptionally high value of Ku=3.3×106 erg/cm3 has been obtained. For the loop measured along the in-plane hard direction, the opening of the loop was undetectable, and the loop along the easy axis was a perfect rectangle. For certain conditions, the anisotropy field measured perpendicular to the film plane when corrected for demagnetization (Nd=4π) was the same as that for the in-plane measurements. It is concluded that surface induced short range ordering was the origin of the anisotropy observed in amorphous films deposited in a magnetic field. The formation mechanism is different from that of the short range ordering induced by field annealing.
Atomic resolution with an atomic force microscope using piezoresistive detection
Authors: Tortonese M. , Barrett R. C. , Quate C. F.
Published: July 2002

A new detection scheme for atomic force microscopy (AFM) is shown to yield atomic resolution images of conducting and nonconducting layered materials. This detection scheme uses a piezoresistive strain sensor embedded in the AFM cantilever. The cantilever is batch fabricated using standard silicon micromachining techniques. The deflection of the cantilever is measured directly from the resistance of the piezoresistive strain sensor without the need for external deflection sensing elements. Using this cantilever we achieved 0.1 Årms vertical resolution in a 10 Hz–1 kHz bandwidth.
Special narrowing of ultrashort laser pulses by self-phase modulation in optical fibers
Authors: Oberthaler M. , Höpfel R. A.
Published: July 2002

We demonstrate experimentally and theoretically that frequency-modulated femtosecond laser pulses can be spectrally narrowed by self-phase modulation in optical fibers. We obtain a reduction of the spectral linewidth from 10.6 down to 2.7 nm, limited only by the laser power in the fiber. Applications for extracavity conversion of femtosecond lasers to narrow-linewidth picosecond sources are discussed.
Optical power limiting of fullerenes
Authors: Wray J. E. , Liu K. C. , Chen C. H. , Garrett W. R. , Payne M. G. , Goedert R. , Templeton D.
Published: July 2002

Optical power limiting processes in C60 solutions have been measured in a double-pass geometry designed to produce high beam attenuation. Based on the concentration of C60 and measured attenuation of laser fluence, it was found that, at high intensities, more than 100 visible (532 nm) photons per C60 molecule can be absorbed during a single 7-nanosecond laser pulse. The requisite features of such efficacious attenuation mechanisms are briefly discussed and a model meeting the requirements is described.
Long-wavelength stacked SiGe/Si heterojunction internal photoemission infrared detectors using multiple SiGe/Si layers
Authors: Park J. S. , Lin T. L. , Jones E. W. , Del Castillo H. M. , Gunapala S. D.
Published: July 2002

Utilizing low temperature silicon molecular beam epitaxy growth, long-wavelength stacked SiGe/Si heterojunction internal photoemission (HIP) infrared detectors with multiple SiGe/Si layers have been fabricated and demonstrated. Using an elemental boron source, high doping concentration (≊4×1020 cm−3) has been achieved and high crystalline quality multiple Si0.7Ge0.3/Si layers have been obtained. The detector structure consists of several periods of degenerately boron doped (≊4×1020 cm−3) thin (≤50 Å) Si0.7Ge0.3 layers and undoped thick (≊300 Å) Si layers. The multiple p+-Si 0.7Ge0.3/undoped-Si layers show strong infrared absorption in the long-wavelength regime mainly through free-carrier absorption. The stacked Si0.7Ge0.3/Si HIP detectors with p=4×1020 cm−3 exhibit strong photoresponse at wavelengths ranging 2–20 μm with quantum efficiencies of about 4% and 1.5% at 10 and 15 μm wavelengths, respectively. The detectors show near ideal thermionic-emission limited dark current characteristics.
Study of density in pulsed-laser deposited amorphous carbon films using x-ray reflectivity
Authors: Huai Y. , Chaker M. , Broughton J. N. , Gat E. , Pépin H. , Gu T. , Bian X. , Sutton M.
Published: July 2002

We report the accurate determination of the absolute density of the pulsed-laser deposited amorphous carbon ultrathin films as well as the film density evolution with the substrate temperatures Ts (22–300 °C) using high-resolution x-ray reflectivity. The density values ρ for the films deposited with laser power density of 8×108 W/cm2 varied from 3.10 to 2.40 g/cm3 as the substrate temperature increased from 22 to 300 °C. This result, together with the optical band-gap values obtained by transmittance measurements, clearly indicates a diamond-like to graphite-like microstructure change near Ts=200 °C.
Formation of artificial BaTiO3/SrTiO3 superlattices using pulsed laser deposition and their dielectric properties
Authors: Tabata Hitoshi , Tanaka Hidekazu , Kawai Tomoji
Published: July 2002

We have formed strained dielectric superlattices of BaTiO3 (BTO) and SrTiO3 (STO) by a pulsed laser deposition technique. A large strain of 400–500 MPa is introduced at the interface between the BTO and STO layers. A large dielectric constant of 900 was observed with a stacking periodicity of 2 unit cells/2 unit cells. The superlattices show drastically different electrical behavior from that of the solid solution (Sr,Ba)TiO3 films. Broad maxima of the dielectric constants occur around 40–50 °C and the values remain large even for a temperature above 200 °C.
Microcavity effects in a spin-coated polymer two-layer system
Authors: Lemmer U. , Hennig R. , Guss W. , Ochse A. , Pommerehne J. , Sander R. , Greiner A. , Mahrt R. F. , Bässler H. , Feldmann J. , Göbel E. O.
Published: July 2002

We report on the design and the optical properties of a spin-coated multilayer organic microcavity. Tri(stilbene)amine blended with polysulfone as the first layer and an oxadiazole derivative (BPBD) blended with polystyrene as the second layer are sandwiched between two planar mirrors. Enhancement of the luminescence and spectrally narrow emission are observed. By means of time resolved luminescence spectroscopy we show that the spontaneous emission rate is increased in the cavity.
Mixing liquids in microseconds
Authors: Regenfuss Peter , Clegg Robert M. , Fulwyler Mack. J. , Barrantes Francisco J. , Jovin Thomas M.
Published: July 2002

An instrument is described in which two solutions can be homogeneously mixed within several microseconds. The liquids flow separately through two coaxial capillaries with conical tips and then simultaneously around a sphere (50–100 μ in diameter) which has been positioned close to the end of the outer tip. The liquids flow with velocities of ∼100 m/s through the small passages (∼5 μ wide) separating the sphere and the wall of the outer capillary and mix in the turbulent liquid flow behind the sphere. The mixed liquids are then ejected as a narrow liquid jet for observation. Design characteristics and construction techniques are presented along with a discussion of the properties of the turbulent flow field and estimates of the expected practically realizable mixing times. The experimentally determined speed of mixing indicates that we have nearly achieved the proposed lower limits of the mixing time.
Noncontact temperature measurement. II. Least squares based techniques
Authors: Khan Mansoor A. , Allemand Charly , Eagar Thomas W.
Published: July 2002

A technique for the noncontact measurement of temperatures is described. The technique is based on the measurement of the emitted intensity at multiple wavelengths and the simultaneous calculation of emissivity and temperature through the use of least squares curve fitting techniques. The technique is shown to make no assumptions regarding the emissivity of the target except that it be possible to model it with an analytic function. A theory is developed to predict the errors in the estimation of temperatures based on both linear and nonlinear least-squares techniques. It is shown that the maximum error in the predicted temperature is related to the noise in the measured intensities in a quantifiable manner. It is shown using computer simulations that the theory and algorithms developed here can predict both the temperatures and the uncertainty associated with each temperature prediction with a very high accuracy. An instrument was developed to test this theory. This instrument, referred to as the MITTMA, was used to measure absolute temperatures of various sources from 900 °C to 2300 °C with an average accuracy of approximately 0.5%.
Real-time computer-optimized electron coincidence spectrometer
Authors: Murray Andrew J. , Turton Brian C. H. , Read Frank H.
Published: July 2002

An electron coincidence spectrometer utilizing real-time optimization and control by a standard IBM 80286 personal computer is described. Details of the system hardware and software are presented together with a description of the optimization routine adopted for maintaining the tuning of the spectrometer and data acquisition. Data collected by the computer-controlled spectrometer for (e,2e) coincidence experiments are also presented.
High-temperature diffraction gratings for synchrotron radiation
Authors: Kita Toshiaki , Harada Tatsuo , Maezawa Hideki , Muramatsu Yasuji , Namba Hidetoshi
Published: July 2002

SiC-based mechanically ruled master gratings and replicas are developed for synchrotron radiation instruments. An SiC-based gold replica grating without any thermal deformation due to active cooling is used in a high-photon-flux-soft x-ray monochromator that is installed in a bending magnet beamline. An SiC-based gold master grating is used in a vacuum ultraviolet/soft x-ray monochromator installed in an undulator beamline with slight groove shape deformation. This deformation is caused by the thermal change of the gold film occurring at higher than 250–300 °C. A method for cleaning carbon-contaminated synchrotron radiation optics is tested. The ultraviolet ozone ashing method effectively cleans carbon contamination on the optics and is useful for extending the lifetime of synchrotron radiation optics.
Frequency shift on a micromachined resonator excited photothermally in vacuum
Authors: Hane K. , Iwatuki T. , Inaba S. , Okuma S.
Published: July 2002

The photothermal activation of a micromachined resonator in vacuum is reported. The resonance frequency shift was obtained at the pressures in the viscosity flow region. This effect will be useful for the development of a miniature vacuum gauge operated optically.
Determination of the position or speed of an object using pulsed laser photoacoustic beam deflection
Authors: Sell Jeffrey A.
Published: July 2002

We demonstrate here a method of measuring the position or speed of an object using photoacoustic beam deflection. Two laser beams are utilized: a pulsed one focused normally on the object and a continuous one parallel to the surface of the object. An acoustic wave generated by the pulsed laser is launched from the surface of the object and propagates through the air to the other beam where it deflects the beam. This deflection is measured by a position sensitive detector. The time-of-flight of the acoustic wave is determined from the zero crossing of the beam deflection signal. Multiplying this by the speed of sound gives the distance of the object from the probe beam.
Density fluctuation effects on electron cyclotron emission correlation measurements in optically gray plasmas
Authors: Rempel T. D. , Gandy R. F. , Wootton A. J.
Published: July 2002

Measurements of electron temperature using electron cyclotron emission (ECE) may be contaminated by density effects in plasmas with low optical depth. ECE intensity fluctuations in these plasmas will include a component dependent on density fluctuations as well. Correlation measurements, which will extract the temperature fluctuations from the dominant radiometer thermal noise, will include correlated density fluctuations in the result. In tokamak core plasmas, where normalized density fluctuations have been measured to be about 1%, this effect can be considerable (∼100%) at low levels of temperature fluctuations. However, at ‘‘relevant’’ levels, defined by the amount of anomalous heat transport, these effects are reduced, at least in TEXT-U. While exact interpretation of temperature fluctuation amplitudes is compromised, statements regarding the relevance of the inferred temperature fluctuation amplitudes can be made relatively unambiguously.
High-resolution retarding potential analyzer
Authors: Enloe C. L.
Published: July 2002

A simple electrostatic retarding potential analyzer (RPA) configuration is described that gives a true measure of charged particle energy irrespective of the angle of incidence of the particles. The device has an inherently high energy resolution (ΔE/E<0.01). The device eliminates errors in particle energy measurement usually associated with planar gridded RPAs. Electrostatic models and results from an experimental prototype are presented.
Time-resolved fluorescence lifetime imaging microscopy using a picosecond pulsed tunable dye laser system
Authors: Periasamy Ammasi , Wodnicki Pawel , Wang Xue F. , Kwon Seongwook , Gordon Gerald W. , Herman Brian
Published: July 2002

The design and implementation of a time-resolved fluorescence lifetime imaging microscope (TRFLIM) for the biomedical sciences are described. The measurement of fluorescence lifetimes offers many benefits, among which is that they are independent of local signal intensity and concentration of the fluorophore and they provide visualization of the molecular environment in a single living cell. Unlike single photon counting, which employs a photomultiplier as the detector, TRFLIM uses a nanosecond-gated multichannel plate image intensifier providing a two-dimensional map of the spatial distribution of fluorescent lifetime in the sample under observation. Picosecond laser pulses from a tunable dye laser are delivered to the fluorophore inside living cells on the stage of a fluorescent microscope. Images of the fluorescence emission at various times during the decay of the fluorescence are collected using a high-speed gated image intensifier and the lifetimes are calculated on a pixel-by-pixel basis. Lifetimes measured by TRFLIM are compared with those measured by conventional methods.
Time domain dielectric spectroscopy: An advanced measuring system
Authors: Feldman Yuri , Andrianov Alexander , Polygalov Evgeny , Ermolina Irina , Romanychev Grigory , Zuev Yuri , Milgotin Bronislava
Published: July 2002

The new time domain measurement system for dielectric measurements is described. The current model is comprised of an IBM PC-AT/486, ‘‘TDM-2,’’ a new time domain measurement system, a set of thermostabilized sample holders, and operation and analysis software. This system is designed for use in the measurement of dielectric parameters of liquid and solid materials over the frequency range 100 kHz–10 GHz. Software consists of programs of registration, accumulation and data collection, Fourier analysis, time domain treatment, analysis software: fast and reliable nonlinear curve fitting programs to determine spectroscopic parameters and correlation analysis in time domain. The system utilizes the difference method of measurement with the registration of primary signals with multiwindow nonuniform sampling. Such a system permits the overlap of a frequency range of five orders in a single measurement.
A simple extended-cavity diode laser
Authors: Arnold A. S. , Wilson J. S. , Boshier M. G.
Published: July 2002

Operating a laser diode in an extended cavity which provides frequency-selective feedback is a very effective method of reducing the laser’s linewidth and improving its tunability. We have developed an extremely simple laser of this type, built from inexpensive commercial components with only a few minor modifications. A 780 nm laser built to this design has an output power of 80 mW, a linewidth of 350 kHz, and it has been continuously locked to a Doppler-free rubidium transition for several days.
Low-voltage operation of a plasma reactor for exhaust gas treatment by dielectric barrier discharge
Authors: Jani Muaffaq A. , Takaki K. , Fujiwara T.
Published: July 2002

Low-voltage operation of a plasma reactor for exhaust gas treatment has been performed by using a multipoint-to-plane geometry device at high frequency. The plasma was produced in a narrow gap by a dielectric barrier discharge of 2–3 kV at 50 kHz. The multipoint electrode has 585 points in the shape of a quadrangular pyramid with 30°. Nitrogen oxide (NOx) removal performance of the reactor was tested for an exhaust gas from a diesel engine generator (20 kV A). The NOx components have been removed with about 100% efficiency of 0.3 mol/kW h from the exhaust gas with NOx concentration of 200 ppm.
Four parameter data fit for Langmuir probes with nonsaturation of ion current
Authors: Desideri D. , Serianni G.
Published: July 2002

The four parameter data fit for Langmuir probes is here generalized within the classical single Langmuir probe theory. The data fit accounts for the variation of the Debye sheath thickness of the probe with the applied voltage which results in a nonsaturation of the ion current. The new fitting formula has been applied to the RFX experimental data. With respect to the use of the simple exponential fit, in general a correction of the order of 20% on electron temperature and ion saturation current has been obtained.
First results from the far-infrared polarimeter system on the Madison Symmetric Torus reversed field pinch
Authors: Lanier N. E. , Anderson J. K. , Forest C. B. , Holly D. , Jiang Y. , Brower D. L.
Published: July 2002

The far-infrared laser interferometer on the Madison Symmetric Torus has recently been upgraded to allow simultaneous interferometry and polarimetry measurements. Centered around a heterodyne laser system that operates at λ≃432 μm, the diagnostic has a frequency response of 1 kHz for the polarimeter and up to 1 MHz for the interferometer. The distribution of laser power through the 11 chord system is managed with wire mesh beamsplitters. Concurrent with the system upgrade to polarimetry, a detailed study of the effect of the wire mesh beamsplitters on beam polarization was conducted. The study shows that the mesh characteristics must be included to extract the polarimetry phase measurement from the raw data. The modifications to the data analysis as well as preliminary five chord polarimetry profile data are presented.