bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy-level alignment at interfaces between metals and the organic semiconductor 4,4′-N,N′-dicarbazolyl-biphenyl
Authors: Hill I. G. , Rajagopal A. , Kahn A.
Published: July 2002

We have used ultraviolet photoemission spectroscopy to study the formation of interfaces between the organic semiconductor, 4,4′-N,N′-dicarbazolyl-biphenyl (CBP), and the metals Au, Ag, and Mg. Each interface was studied by depositing the organic on the metal, and by depositing the metal on the organic. The two methods produced inequivalent interfaces, except in the case of Au/CBP. The position of the highest occupied molecular orbital relative to the Fermi level and the magnitude of the interface dipole were measured for each interface. The barrier to electron injection from each metal was estimated using the magnitude of the measured optical gap. An interface dipole, of magnitude nearly independent of the metal work function, was formed when CBP was deposited on a metal surface. The position of the Fermi level within the CBP gap was found to vary strongly with the metal work function.
Hole transport in strained Si1−xGex alloys on Si1−yGey substrates
Authors: Bufler F. M. , Meinerzhagen B.
Published: July 2002

Hole transport at 300 K in (001)-strained Si1−xGex alloys grown on unstrained Si1−yGey is theoretically analyzed considering the full band structure and new, accurate mobility experiments. Ohmic in-plane and out-of-plane drift mobilities are computed over the whole range of x and y. Velocity-field characteristics and transient overshoot effects are studied for fields along the 〈100〉 and 〈110〉 directions in technologically relevant configurations with Monte Carlo simulation. Overshoot peaks around 2×107 cm/s are found in strained Si and Ge-rich SiGe for 100 kV/cm and the 〈100〉 direction.
Interface charge relaxation in ZnS:Mn based alternating-current thin-film electroluminescent devices
Authors: Goldenblum A. , Oprea A.
Published: July 2002

The relaxation process of accumulated carriers on the anode interface of a metalinsulator-semiconductor-insulator-metal structure is investigated. It is studied by measuring the dependence of the transferred charge on the time interval between the voltage trapezoidal pulses. The presence of two independent relaxation channels is evidenced. This aspect of the relaxation process is incorporated in a model that describes the entire charge transfer process. A good fit between the computed data and the experimental ones is found for different maximum voltage and rising slope values. A possible mechanism for the relaxation of the interface accumulated carriers is discussed.
Mechanical and structural properties of Ni/Ti multilayers and films: An application to neutron supermirrors
Authors: Senthil Kumar M. , Böni P. , Clemens D.
Published: July 2002

Multilayers containing Ni and Ti have been investigated for their applications in neutron-optical devices. These multilayers exhibit low neutron reflectivity when sputtered in Ar owing to large interface roughness and interdiffusion. While attempting to improve the interface smoothness by reactive sputtering of Ni in partial pressures of Ar and air, stress and embrittlement develops. Stress and x-ray diffraction measurements on Ni films and multilayers reveal a transition that is attributed to the occupancy of the interstitial sites by nitrogen and oxygen atoms. After identifying appropriate sputtering conditions so as to keep both macroscopic and local stresses within a tolerable limit, we have successfully prepared several supermirrors having 600–1200 layers yielding critical angles of reflection from 3.65 to 4.15 times that of bulk Ni.
Pressure dependence of electrical and optical characteristics of Alq3 based organic electroluminescent diodes
Authors: Destruel P. , Jolinat P. , Clergereaux R. , Farenc J.
Published: July 2002

Organic electroluminescent diodes based on thin organic layers are one of the most promising next-generation systems for the backlighting of liquid crystal screens. In the literature, conduction has been interpreted in terms of tunneling or as a space charge limited process. To clarify this point we carried out an experimental study of the electrical and optical characteristics, as a function of the applied voltage, for different hydrostatic pressures. Results show that tunneling is the dominant mechanism which controls the organic light emitting diodes efficiency.
Deep trap in InGaAs grown by gas source molecular beam epitaxy
Authors: Takanashi Yoshifumi , Kondo Naoto
Published: July 2002

The deep-level transient spectroscopy (DLTS) measurement method is used to investigate the deep traps in In0.53Ga0.47As grown by gas source molecular beam epitaxy. An electron trap with activation energy of 0.28 eV is detected and a capture cross section is estimated to be 8.03×10−22 cm2 by measuring the dependence of DLTS spectrum on the majority carrier pulse width. The concentration of this trap is determined from the peak value of the DLTS signal to be 3.7×1014 cm−3.
Intersubband terahertz lasers using four-level asymmetric quantum wells
Authors: Kinsler P. , Harrison P. , Kelsall R. W.
Published: July 2002

We demonstrate the potential for laser operation at far-infrared wavelengths (30–300 μm, 1–10 THz) by using intersubband emission in four-level GaAs/AlGaAs asymmetric (stepped) quantum wells. Achieving population inversion in these devices depends critically on the lifetimes of the nonradiative intersubband transitions, and so we have performed detailed calculations of electron–electron and electron–phonon scattering rates. Our four-subband structures show potential for the realization of room temperature lasing, unlike previously considered three-subband structures which did not give population inversions except at impractically low electron densities and temperatures. Auger-type electron–electron interactions involving the highly populated ground subband effectively destroyed the population inversion in three level systems, but in these four subband structures the inversion is maintained by strong phonon-mediated depopulation of the lower laser level. The largest population inversions are calculated at low temperatures (<30 K), but for the structures with higher emission energies, room temperature (300 K) operation is also predicted.
Diffusion during metalorganic vapor-phase epitaxy on V-groove patterned substrates
Authors: Wüllner D. , Chahoud M. , Schrimpf T. , Bönsch P. , Wehmann H.-H. , Schlachetzki A.
Published: July 2002

We studied the diffusion process in metalorganic vapor-phase epitaxy of InGaAs on V-groove patterned InP substrates. A model, recently developed for selective-area growth on planar patterned substrates, enabled us to analyze growth rate distribution and to determine diffusion lengths of growing species. Atomic force microscopy (AFM) and photoluminescence measurements have been employed to measure the growth rate and composition of the ternary alloy. A new technique based on composition sensitive etching combined with etch rate measurements by cross-section AFM reveals the reduced solidifying probability of Ga on {111}A planes as the origin of compositional variations.
Structure and properties of magnetic inhomogeneities of the “static soliton” type in (001) plates with a combined anisotropy
Authors: Vakhitov Robert M. , Kucherov Vladimir Ye.
Published: July 2002

The article looks into the conditions for origination and stability areas of magnetic inhomogeneities of the static soliton type in a (001) crystal plate with a combined anisotropy. It has been shown that static solitons can localize upon defects of certain types and at some values of material parameters. It has been found that the soliton stability area is bounded by the two sets of limit values of material parameters: with one set the soliton is unstable relative to a collapse, with the other—the soliton diffuses. It has been discovered that the soliton stability area substantially differs from the one that was theoretically predicted in the model, which did not account for finiteness of the sample and availability of defects therein.
Coupling between the ionic cyclotron motion and the circular ionic drift motion in a cylindrical ion cyclotron resonance cell
Authors: Lee Sung Ho
Published: July 2002

In this work, we have first constructed a special cylindrical ion cyclotron resonance cell and investigated the ionic motion in the cell experimentally as well as theoretically. Due to the field symmetry in the cell, the ionic cyclotron motion is coupled with a well-defined circular drift motion in the plane perpendicular to the magnetic field and a trapping oscillation parallel to the magnetic field. The effective cyclotron frequency ωeff could be given as ωc−ωd−ωd2/2ωc which can be attributed to the influence of the Coriolis and the centrifugal accelerations caused by the circular drift motion with ωd. This is in contrast to the case for conventional ion drift cell with parallelepiped geometry where the effective cyclotron frequency is given in terms of the electric field gradients. Thus, this newly developed cylindrical cell can be used not only as an ion trap but also as a simulator for studying some fundamental processes such as the Coriolis and centrifugal couplings in classical dynamics.
Electron diffraction and Raman studies of the effect of substrate misorientation on ordering in the AlGaInP system
Authors: Halsall M. P. , Dunbar A. D. F. , Bangert U.
Published: July 2002

We report a systematic study of the effect of substrate orientation on the ordering in the AlGaInP system, including the Al0.52In0.48P lattice-matched ternary case. Four AlGaInP/GaAs/AlInP samples were grown by metalorganic vapor phase epitaxy under identical growth conditions on [100] substrates orientated 0°, 2°, 10° and 15° either towards the [110] or the [111] axis. The ordering in both the AlInP and the AlGaInP layers was studied by electron diffraction and the Raman scattering technique. The tendency for ordering decreased with increasing misorientation and is less for (AlxGa1−x)0.52In0.48P than for AlInP. The AlInP was found to spontaneously order even when grown after a completely disordered AlGaInP layer. The Raman results show features correlated to the electron diffraction results and hence we conclude that this technique constitutes a reliable nondestructive means of characterizing this system.
Pure nuclear Bragg reflection of a periodic Fe56/Fe57 multilayer
Authors: Deák L. , Bayreuther G. , Bottyán L. , Gerdau E. , Korecki J. , Kornilov E. I. , Lauter H. J. , Leupold O. , Nagy D. L. , Petrenko A. V. , Pasyuk-Lauter V. V. , Reuther H. , Richter E. , Röhloberger R. , Szilágyi E.
Published: July 2002

Grazing incidence nuclear multilayer diffraction of synchrotron radiation from a periodic stack of alternating Fe56 and Fe57 layers was observed. Resonant layer fraction, substrate size, flatness, and surface roughness limits were optimized by previous simulations. The isotopic multilayer (ML) sample of float glass/Fe57(2.25 nm)/[Fe56(2.25 nm)/Fe57(2.25 nm)]×15/Al(9.0 nm) nominal composition was prepared by molecular beam epitaxy at room temperature. Purity structure and lateral homogenity of the isotopic ML film was characterized by magnetometry, Auger electron, Rutherford backscattering, and conversion electron Mössbauer spectroscopies. The isotopic ML structure was investigated by neutron and synchrotron Mössbauer reflectometry. Surface roughness of about 1 nm of the flat substrate (curvature radius >57 m) was measured by scanning tunneling microscopy and profilometry. A pure nuclear Bragg peak appeared in synchrotron Mössbauer reflectometry at the angle expected from neutron reflectometry while no electronic Bragg peak was found at the same position by x-ray reflectometry. The measured width of the Bragg peak is in accordance with theoretical expectations.
Growth of Si1−xGex(011) on Si(011)16×2 by gas-source molecular beam epitaxy: Growth kinetics, Ge incorporation, and surface phase transitions
Authors: Taylor N. , Kim H. , Spila T. , Eades J. A. , Glass G. , Desjardins P. , Greene J. E.
Published: July 2002

Single crystal Si1−xGex(011) layers with x⩽0.35 have been grown on double-domain Si(011)“16×2” surfaces from Si2H6/Ge2H6 mixtures at temperatures Ts=400–950 °C. D2 temperature programmed desorption was used to show that the structure of the Si(011)“16×2” surface unit cell, more correctly written as [217 21] since the unit cell vectors are nonorthogonal, is composed of 16 adatoms and eight π-bonded dimers with a dangling bond density half that of the 1×1 surface. Si1−xGex(011) overlayers are “16×2” when xxc(Ts). The value of xc decreases from ≃ 0.10 at Ts=475 °C to 0.08 at 550 °C to 0.06 at 650 °C. Both the “2×8” and “16×2” Si1−xGex(011) surface reconstructions gradually and reversibly transform to 1×1 at Ts between 650 and 725 °C. Film growth kinetics exhibit three distinct regimes. At low temperatures (Ts≲500 °C), the film deposition rate RSiGe decreases exponentially with 1/Ts in a surface-reaction-limited growth mode for which the rate-limiting step is hydrogen desorption from Si and Ge monohydride phases. RSiGe becomes essentially constant with Ts in the intermediate impingement-flux-limited range, Ts=500–650 °C. At Ts>650 °C, RSiGe increases again with Ts due initially (Ts≃650–725 °C) to an increase in the steady-state dangling bond coverage as the surface reconstruction gradually transforms to 1×1. The continued increase in RSiGe at even higher Ts is associated with strain-induced roughening. Ge/Si ratios in as-deposited films are linearly proportional to the incident Ge2H6/Si2H6 flux ratio JGe2H6/JSi2H6 and nearly independent of Ts indicating that the reactive sticking probabilities of Si2H6 and Ge2H6 have very similar temperature dependencies. RSiGe(JGe2H6/JSi2H6,Ts) in both the surface-reaction-limited and flux-limited regimes is well described by a simple kinetic model incorporating second-order dissociative chemisorption and second-order hydrogen desorption as rate-limiting steps.
Enhancement of a rectifying characteristic of InGaP diodes by hydrogenation
Authors: Lee J. Y. , Kwon Y. H. , Kim M. D. , Kim H. J. , Kang T. W. , Hong C. Y. , Cho H. Y.
Published: July 2002

The effect of hydrogenation on electrical properties of InGaP epitaxy layers grown on GaAs has been investigated. It is found that hydrogenation using an infrared lamp heating at 200 °C can give rise to good rectifying characteristics on the Au/n-InGaP Schottky diode as well as to the passivation of defects. For the hydrogenated sample, the breakdown voltage increases to 35 from 4 V, the leakage current decreases by three orders of magnitude, and the saturation current increases about 100 times, relative to those for the untreated one. This characteristic is thought to result from the increase of the diode barrier height during hydrogenation. That is, the atomic hydrogen which diffuses into InGaP neutralizes the Si donor dopant as well as deep levels near the surface, resulting in the increase of the barrier height and the reduction of recombination centers.
Effects of buried oxide on electrical performance of thin-film silicon-on-insulator metal–oxide–semiconductor field-effect transistor
Authors: Lee Jong-Wook , Oh Min-Rok , Koh Yo-Hwan
Published: July 2002

Local oxidation of silicon-isolated thin-film silicon-on-insulator (SOI) device characteristics have been investigated in terms of stress in the buried-oxide interface by both simulation and experiment. A bonded SOI wafer with a 400 nm buried oxide and a separation by implanted oxygen SOI wafer with a 100 nm buried oxide are used for device fabrication. In the 100 nm buried-oxide case, boron atoms are accumulated at the silicon side in the interface between the silicon film and oxide (i.e., including the buried oxide and field oxide) due to a highly stressed oxide so that the increased boron concentration increases the threshold voltage of the edge channel. Therefore, it is found that there is no drain current hump in the subthreshold region of thin-film SOI n-channel metal–oxide–semiconductor field-effect transistors with 100 nm buried oxide. From the simulation, it is demonstrated that the 100 nm buried oxide has higher compressive stress than the 400 nm counterpart after the local oxidation of silicon process.
New barium ferrite particles: Spherical shape
Authors: Hong Y. K. , Jung H. S.
Published: July 2002

Pure and ZnTi-doped spherical barium ferrite particles were prepared using two different methods: semicoprecipitation and ultrasonic spray pyrolysis. The ultrasonic spray pyrolysis method was more effective in controlling particle shape. Particle size was in between 0.27 and 0.3 μm. Coercivity and saturation magnetization were in the range of 1000 to 5000 Oe and 49 to 53 emu/g, respectively. Crystallization of amorphous Ba–Fe–O spherical precursors occurs at a lower temperature than Ba–Fe–Zn–Ti–O precursors. ΔM measurement shows that magnetic interaction in spherical barium ferrite tape is weaker than hexagonal platelet barium ferrite.
Magnetic domain pinning in patterned magneto-optical material
Authors: Wu Te-Ho , Wu J. C. , Huang Y. W. , Chen Bing-Mau , Schieh Han-Ping D.
Published: July 2002

Pinning magnetic domains with defined shapes have been made for magneto-optical thin film material. The pinning array of holes on the substrate was fabricated using electron beam lithography. The domain pinning behaviors were studied by applying an external magnetic field perpendicular to the film plane and imaged by atomic force microscopy in their remanent state. Magnetic domains were found to be pinned inside the hole arrays and reproduced the shapes of the holes. The coercivity in the patterned region is larger than in the nonpatterned region. Moreover, the coercivity inside the hole sites is larger than the land sites.
Using Fourier transform infrared grazing incidence reflectivity to study local vibrational modes in GaN
Authors: Sun W. H. , Chen K. M. , Yang Z. J. , Li J. , Tong Y. Z. , Jin S. X. , Zhang G. Y. , Zhang Q. L. , Qin G. G.
Published: July 2002

Both Fourier transform infrared (FTIR) grazing incidence reflectivity and FTIR transmission methods have been used to study GaN films grown on α-Al2O3 (0001) substrates by atmospheric pressure metal-organic chemical vapor deposition and low pressure metal-organic chemical vapor deposition. The results show that in the frequency range from 400 to 3500 cm−1 the signal-to-noise ratio of the FTIR grazing incidence measurement is far higher than that of the FTIR transmission measurement. Some new vibrational structures appearing in the former measurement have been discussed. The features around 1460 and 1300 cm−1 are tentatively assigned to scissoring and wagging local vibrational modes of CH2 in GaN, respectively.
Thermosetting enhancement of the light-induced polar orientation stability of molecules in polymers
Authors: Si Jinhai , Kitaoka Kenji , Mitsuyu Tsuneo , Ye Peixian , Hirao Kazuyuki
Published: July 2002

Two kinds of polymers with disperse red 19 pendant groups, a thermal-imidization polyimide and a thermal-crosslinking polyurethane, were used in thermal-assisted optical poling to improve the photostability of the optically induced polar orientation of molecules. During the seeding process, samples heated in an oven were irradiated simultaneously by the coherent superposition of the 1064 nm fundamental and the 532 nm second-harmonic light of a nanosecond-pulsed Nd:YAG laser. The second-order optical nonlinearity of the polymer films seeded at elevated temperatures kept stable at room temperature even under illumination of the intense 1064 nm fundamental light. The nonlinear optical coefficient d33 was estimated to be 6.9 pm/V for the azopolyimide film and 12.7 pm/V for the azopolyurethane film, respectively. Experimental results indicated that the optically aligned azodye molecules were fixed by the thermosetting polymer matrix during the thermal-assisted optical poling process.
Shoulder at the 887 cm−1 infrared band in neutron irradiated Si
Authors: Londos C. A. , Sarlis N. V. , Fytros L. G.
Published: July 2002

Infrared spectroscopy was used to study the 887 cm−1 band in neutron irradiated Czochralski-grown silicon arising in the spectra upon annealing of the 830 cm−1 band of the VO defect. Our analysis showed the presence of a 884 cm−1 shoulder in the region of the 887 cm−1 infrared band. The 887 cm−1 band is generally attributed to the VO2 defect formed by the capture of a mobile VO center by an oxygen interstitial impurity. In our study the shoulder at 884 cm−1 is tentatively correlated with the V3O defect. Semiempirical calculations carried out for the vibrational frequency of V3O structure gave a value at 883 cm−1 thus corroborating the latter assignment. This new picture of the spectra in the range of the 887 cm−1 band could explain some so far unaccounted for experimental findings previously reported in literature.
Zn
0.85
Cd
0.15
Se
active layers on graded-composition InxGa1−xAs buffer layers
Authors: Müller B. H. , Lantier R. , Sorba L. , Heun S. , Rubini S. , Lazzarino M. , Franciosi A. , Napolitani E. , Romanato F. , Drigo A. V. , Lazzarini L. , Salviati G.
Published: July 2002

We investigated the structural and optical properties of Zn0.85Cd0.15Se epilayers for blue optical emission on lattice-matched InxGa1−xAs buffer layers. Both the II–VI layers and the III–V buffers were grown by molecular beam epitaxy on GaAs(001) wafers. A parabolic In concentration profile within the graded-composition InxGa1−xAs buffers was selected to control strain relaxation and minimize the concentration of threading dislocations. Dislocation-free II–VI growth was readily achieved on the graded buffers, with a Rutherford backscattering yield ratio reduced by a factor of 3 and a deep-level emission intensity reduced by over two orders of magnitude relative to those observed following direct II–VI growth on GaAs. The surface morphology of the materials, however, was found to replicate the crosshatched pattern of the underlying InxGa1−xAs substrates.
Spin-disorder resistivity in Fe–Ni and Mn–Ni alloys
Authors: Jen S. U. , Liou S. S.
Published: July 2002

Two series of fcc Fe100−xNix and Mn100−xNix alloys were prepared for the purpose of testing the theory of spin-disorder scattering. The original theory, as proposed by deGennes and Friedel, was valid in a strict sense only for pure metals. For a binary alloy A1−xBx, we have modified the theory so that the average local spin S̄ for the alloy is defined and well incorporated in the whole scheme. Experimentally speaking, we have measured the high-temperature (from 300 to 1100 K) electrical resistivity ρ and the low-temperature (at 5 K) saturation magnetization MS of the alloys. From the resistivity measurement, the spin-disorder resistivity at or above the Curie temperature ρmag was found, and from the magnetization measurement, S̄ could be determined for each alloy. In our theory, we can express the quantity ρmag/S̄(S̄+1) as a function of the nickel concentration x explicitly. Then, the ρmag/S̄(S̄+1) data from the Fe–Ni and Mn–Ni alloys were plotted versus x, and then fitted by the modified theory. Note, the former alloy is on the straight line of the Slater–Pauling curve and the latter shows marked deviations. We have reached a conclusion that |JsdFe|>|JsdNi|>|JsdMn|, where |JsdFe|, |JsdNi|, and |JsdMn| are the magnitudes of the s-d exchange interactions between the spin s of the 4s electron and the local spin Si at the iron, nickel, and manganese sites, respectively.
Resistance noise as a technique for measuring finite-size effects in single-layer Cu_Mn spin-glass films
Authors: Fenimore P. W. , Weissman M. B.
Published: July 2002

We present measurements of the spin-freezing temperature as a function of film thickness in single-layer thin films of Cu_Mn and Cu_MnAu. The noise measurements are used to characterize the temperature of the spin freezing in Cu_Mn and the cooperativity of the spin dynamics. As expected, the thicker films show cooperative spin dynamics near the spin-glass temperature. The measured spin-glass freezing temperatures as a function of film thickness are consistent with three-dimensional finite-size scaling. This article demonstrates that measurements of the resistance noise are a convenient alternative to magnetic measurements when studying dimensional effects in spin glasses.
Electron emission from ferroelectric ceramics with a special design patterned front electrode
Authors: Boscolo I. , Scurati A. , Stellato M.
Published: July 2002

Electron emission from a ceramic disk is due to spontaneous polarization switching induced by a high-voltage pulse applied to the surface electrodes. With a conventional front electrode, emission was erratic as a function of samples and decayed with shot number. On the contrary, when the front electrode consisted of a pattern of unconnected patches contained within a ring, emission was stable. The physics of the two configurations is investigated and a possible interpretation of the two different behaviors is given.
Effects of hydrogen in the annealing environment on photoluminescence from Si nanoparticles in SiO2
Authors: Withrow S. P. , White C. W. , Meldrum A. , Budai J. D. , Hembree D. M. , Barbour J. C.
Published: July 2002

The role of hydrogen in enhancing the photoluminescence (PL) yield observed from Si nanocrystals embedded in SiO2 has been studied. SiO2 thermal oxides and bulk fused silica samples have been implanted with Si and subsequently annealed in various ambients including hydrogen or deuterium forming gases (Ar+4%H2 or Ar+4%D2) or pure Ar. Results are presented for annealing at temperatures between 200 and 1100 °C. Depth and concentration profiles of H and D at various stages of processing have been measured using elastic recoil detection. Hydrogen or deuterium is observed in the bulk after annealing in forming gas but not after high temperature (1100 °C) anneals in Ar. The presence of hydrogen dramatically increases the broad PL band centered in the near infrared after annealing at 1100 °C but has almost no effect on the PL spectral distribution. Hydrogen is found to selectively trap in the region where Si nanocrystals are formed, consistent with a model of H passivating surface states at the Si/SiO2 interface that leads to enhanced PL. The thermal stability of the trapped H and the PL yield observed after a high temperature anneal have been studied. The hydrogen concentration and PL yield are unchanged for subsequent anneals up to 400 °C. However, above 400 °C the PL decreases and a more complicated H chemistry is evident. Similar concentrations of H or D are trapped after annealing in H2 or D2 forming gas; however, no differences in the PL yield or spectral distribution are observed, indicating that the electronic transitions resulting in luminescence are not dependent on the mass of the hydrogen species.
On the decay of end effects in conduction phenomena: A sandwich strip with imperfect interfaces of low or high conductivity
Authors: Benveniste Y.
Published: July 2002

The rate of decay of end effects in steady state heat conduction in a symmetric sandwich strip with anisotropic constituents and imperfect interfaces between the layers is studied. Two kinds of imperfect interfaces are considered: an imperfect interface which models a thin interphase of low conductivity and an imperfect interface which models a thin interphase of high conductivity. In the former case, the normal component of the heat flux is continuous at the interface, whereas the temperature field undergoes a discontinuity which is proportional to the normal component of the heat flux. In the latter case, the temperature field is continuous at the interface and the normal component of the heat flux exhibits a discontinuity proportional to a surface differential operator of the temperature, called the surface Laplacian. The characteristic rate of decay of end effects is given by the smallest real and positive root of a transcendental equation. This rate decreases as the discontinuity in the temperature or the heat flux across the interface increases, in either kind of the imperfect interface. Exact duality relations are shown to exist between the decay rate of end effects in strips with imperfect interfaces of low conductivity, and that in strips with imperfect interfaces of high conductivity.
Evolution of mosaic structure in Si0.7Ge0.3 epilayers grown on Si(001) substrates
Authors: Li J. H. , Peng C. S. , Mai Z. H. , Zhou J. M. , Huang Q. , Dai D. Y.
Published: July 2002

In this article, we report a study of mosaic structures in partially relaxed Si0.7Ge0.3 epilayers grown on Si(001) substrates by x-ray double- and triple-axis diffractometry. The samples have different layer thicknesses and hence different degrees of strain relaxation. Our results show that, at early stages of strain relaxation, the films contain mosaic regions laterally separated by perfect regions. This is because the mosaic structure caused by a misfit dislocation is effectively localized in a lateral range of the layer thickness. Therefore, far from the dislocations, the film is virtually a perfect crystal. With the increase in the degree of strain relaxation, and consequently in the dislocation density, the mosaic regions of the layer expand while the perfect regions shrink and finally vanish completely. Moreover, our results indicate that the conventional method of estimating dislocation density from the x-ray rocking curve width fails in our case.
On the constant composition and thickness of the chlorinated silicon surface layer subjected to increasing etching product concentrations during chlorine plasma etching
Authors: Bogart K. H. A. , Donnelly V. M.
Published: July 2002

The influence of etching products on the surface layer formed during chlorine (Cl2) plasma etching of unmasked crystalline p-type Si(100) was investigated using vacuum sample-transfer and angle-resolved x-ray photoelectron spectroscopy (XPS). Varying the Cl2 flow rate from 10.0 to 0.4 sccm at a constant pressure of 4 mTorr controlled the etching product concentration. Gas-phase Cl, Cl2, and SiCly (y=0–3) were monitored (∼1 cm above the wafer) by optical emission spectroscopy. For a positive ion density of 7×1010 cm−3 and an average ion energy of ∼140 eV, the Si etching rate decreased linearly with Cl2 flow from 2850 Å/min at 10.0 sccm to 1920 Å/min at 0.4 sccm. From these rates, mass balance, and the Si area, the ratio of product-to-etchant (SiCly-to-Cl) flux to the wafer varied from 0.078 to 11 at 10.0 and 0.4 sccm, respectively. After etching, Cl was present in the Si(100) surface layer as SiClx (x=1–3) at XPS Si (2p3/2) binding energies of 99.9, 101.0, and 102.0 eV, respectively, relative to Si at 99.1 eV. The amounts of the three silicon chlorides and the total Cl (derived from its 2p peak) were nearly independent of the product-to-etchant flux ratio. Depth profiles were obtained from an inversion of the observed take-off angle dependences of the XPS signals. For the Cl2 flow rates investigated, the chlorinated surface layer was ∼16 Å thick, with Cl falling off in a graded fashion. The Cl areal density, integrated throughout the layer, was similar for all experimental conditions and averaged 2.63±0.15×1015 Cl/cm2. The stoichiometry of the chlorosilyl layers was also independent of Cl2 flow rate and averaged [SiCl]:[SiCl2]:[SiCl3]=[1.0]:[0.45±0.09]:[0.33±0.02]. Reaction pathways are presented to interpert both the constancy of the chlorinated surface layer and the decrease in etching rate as the Cl2 flow rate was decreased from 10.0 to 0.4 sccm.
Electric signal detection at the early stage of laser ablation in air
Authors: Lu Y. F. , Hong M. H.
Published: July 2002

A tiny metal probe was used to detect electric signals induced at the early stage of laser ablation in air. It is found that the electric signals result from probe ablation, plasma–probe interaction, and plasma-induced electric field. The recorded signals strongly depend on the probe positions. For a probe placed out of the plasma–probe interaction region, the detected electric signal is a negative peak in the nanosecond range, due to the plasma-induced electric field. The peak arrival time corresponds to the total amount of ion emission from the substrate surface, and therefore, does not vary with the probe position. The signal amplitude is inversely proportional to the square of the probe distance, consistent with the distance dependence of the field intensity from an electric dipole. The signal amplitude increases with the laser fluence while the peak arrival time reduces, reflecting the earlier plasma generation at a higher laser fluence. Both peak width and its arrival time of the electric signals increase with laser fluence and tend to saturate above 6.4 J/cm2. The electric signals were analyzed for laser ablation of different substrate materials. The electric signal detection was also applied to monitor the laser cleaning of organic contamination in real time. The mechanism of the electric signal generation and the process of electron and ion emission are briefly discussed.
Cathodoluminescence, microstructure, and morphology of tensile-strained AlxGa(1−x)N epitaxial films grown by gas source molecular beam epitaxy
Authors: Van Nostrand J. E. , Hengehold R. L. , Leedy K. D. , Grant J. T. , Brown J. L. , Xie Q.-H.
Published: July 2002

Tensile-strained AlxGa(1−x)N (0⩽x⩽0.4) alloys are deposited on 2-μm-thick GaN on Al2O3(0001) by gas source molecular beam epitaxy using ammonia as the nitrogen source. The evolution of the surface morphology of AlxGa(1−x)N epitaxial films as a function of mole fraction is studied using atomic force microscopy. Surface roughness initially increases with Al mole fraction, but then decreases with a corresponding onset of defects. Extended ridge-like defects are observed along the 〈0010〉 of the AlxGa(1−x)N for high Al mole fractions. Band-edge and subband-edge emission at 6 K is investigated using cathodoluminescence. Strong emission, ascribed to donor-bound excitons, shallow donor to shallow-acceptor pair emission, and deep emission associated with the “yellow” band of GaN are observed. The energy level of emission from donor-bound excitons is found to exhibit a linear dependence on Al more fraction, suggesting a lack of band bending in this material system. Finally, microstructure is investigated using a triple axis x-ray diffraction system. X-ray results are combined with x-ray photoelectron spectroscopy data to determine the extent of relaxation of AlxGa(1−x)N epitaxial films. For 0.5 μm AlxGa(1−x)N films deposited on thick GaN on Al2O3(0001), a “critical” Al mole fraction of x=0.20 is determined, beyond which significant film relaxation and extended defect formation is observed.
Quasiparticle diffusion, edge losses, and back-tunneling in superconducting tunnel junctions under x-ray irradiation
Authors: Cristiano R. , Esposito E. , Frunzio L. , Nappi C. , Ammendola G. , Parlato L. , Pepe G. , Kraus H. , Walko P.
Published: July 2002

The efficiency of the charge collecting mechanism of a radiation detector based on superconducting tunnel junctions depends strongly on the competition between tunneling and losses of quasiparticles in the electrodes of the junction. In this article we discuss the loss of quasiparticles, both in the bulk and at the edges of the electrodes. The quasiparticle loss taking place during their diffusion in the junction limits the amount of charge carriers tunneling and thereby the energy resolution of the detector. A charge amplification process caused by multiple tunneling of quasiparticles is beneficial to higher signal to noise ratios. Such multiple tunneling is always present in the case of junctions based on symmetrical electrodes. In this article we present a theory for the detector response which takes into account both multiple tunneling and the diffusion of quasiparticles. A model is presented for the spectral response of the detector based on four parameters one of which is the degree of back-tunneling present in the device. Analytical solutions of the model for rectangular and circular junctions are discussed. The predictions of the theory are compared with an experimental pulse height spectrum obtained on a Nb/Al2O3/Nb junction.
Nonlinear I–V characteristics of a mesoscopic conductor
Authors: Wang Baigeng , Wang Jian , Guo Hong
Published: July 2002

We present a general theoretical formulation, based on nonequilibrium Green’s functions, for nonlinear dc transport in multiprobe mesoscopic conductors. The theory is gauge invariant and is useful for the predictions of current–voltage characteristics and the nonequilibrium charge pileups inside the conductor. We have provided a detailed comparison between the gauge invariant scattering matrix theory and our theory. We have also given several examples where the I–V curve can be obtained analytically. The effects of exchange and correlation have been considered explicitly.
Generalized plane strain analysis of superconducting solenoids
Authors: Markiewicz W. Denis , Vaghar Mohammad Reza , Dixon Iain R. , Garmestani Hamid
Published: July 2002

A stress analysis of superconducting solenoids is presented which includes a generalized plane strain (GPS) condition for the axial strain. The GPS condition is introduced on the assumption that the deformation of a solenoid from a right circular cylinder is small. The GPS assumption results in an analytic solution for all three components of stress and strain in a solenoid. The work is presented in the context of the historical development of stress analysis for solenoids. The general stress equations for a magnetic solenoid are formulated. The relationship between a right cylinder deformation and the generalized plane strain condition is examined for the physical conditions in the central region of a solenoid magnet. The general analytic solutions of the stress equations are given for the cases of magnetic and thermal loading. The constant coefficients are determined for cases of common interest in solenoid magnet design. The analytic results are compared with numerical analysis results for an example solenoid consisting of a single coil with external reinforcement. In particular, the degree to which the axial strain is a constant and satisfies the GPS assumption is examined for the example solenoid. The analysis reveals features of the axial stress in solenoids, including the Poisson’s ratio induced axial stress and the axial stress distribution between coil and reinforcement during cooldown and operation. The strong agreement between the GPS and numerical analysis results shows that the assumptions contained in the GPS analysis accurately represent the conditions in the central region of a solenoid magnet.
Co
1−x
Cr
x
/
Pt
multilayers as perpendicular recording media
Authors: Takano Kentaro , Zeltzer G. , Weller D. K. , Fullerton Eric E.
Published: July 2002

We have investigated Co1−xCrx/Pt multilayers as potential perpendicular media capable of high-density magnetic recording. The films exhibited strong perpendicular anisotropy, coercivity values ranging from 0.3 to 6.9 kOe, and a range of coercive squareness (S*) from 0.21 to 0.96. Magnetic and atomic force microscopy were used to correlate the grain and magnetic domain structures. The degree of intergranular exchange is clearly dependent on the deposition temperature and, to a lesser extent, Cr content. Co1−xCrx/Pt multilayers are ferromagnetic at room temperature for x>30%, which is not observed in thick Co1−xCrx films. Initial recording results determined a SONR ratio of 23 dB for a [Co(4 Å)/Pt(5 Å)]10 multilayer recorded at 10 kiloflux changes per millimeter using a standard longitudinal ring head.
Effect of underlayer roughness, grain size, and crystal texture on exchange coupled IrMn/CoFe thin films
Authors: Pakala M. , Huai Y. , Anderson G. , Miloslavsky L.
Published: July 2002

The exchange bias field (Hex) between a ferromagnetic and antiferromagnetic film has been found to be sensitive to interface roughness, crystalline texture, and grain size. In order to isolate the effects of these three parameters, we deposited Si/UL/CoFe4/IrMn5/Ta5nm (top) and Si/UL/IrMn5/CoFe4/Ta5nm (bottom configuration) exchange coupled multilayers on three underlayers, namely Cu, Ru, and [Cu1/Ru1nm]n with thickness between 5 and 100 nm. With an increase in Cu (fcc) underlayer thickness, roughness and grain size increased rapidly up to 0.9 nm rms and 48 nm, respectively. For the Ru (hcp) underlayer, roughness increased gradually to 0.3 nm while the grain size increased to 30 nm. In case of Cu/Ru (hcp+fcc), the roughness observed is between that of Cu and Ru for comparable thickness. However, the grain size is much smaller compared to Ru and Cu. For both top and bottom exchange coupled films, Hex (200–300 Oe) is observed above a critical underlayer thickness (⩾5 nm for Ru and ⩾15 nm for Cu and Cu/Ru). In the top configuration, above the critical underlayer thickness, Hex decreases from 295 to 180 Oe with an increase in underlayer (UL) thickness due to the rougher interface. However, Hex did not change with roughness for the bottom case. The difference in Hex dependence on roughness for top and bottom cases can be explained in terms of magnetostatic effects on domain formation in the antiferromagnetic layer. In both cases, above the critical UL thickness, no correlation between Hex and the grain size and texture was found. After annealing at 225 °C for 1 h, high interfacial exchange energy (Jk∼0.22 ergs/cm2) for the top configuration is obtained for films deposited on UL which have large grain size. In the bottom case, a high Jk (∼0.3 ergs/cm2) is obtained for films with good fcc-IrMn(111) texture, corresponding to growth on Cu/Ru underlayers.
Spectroscopic properties of nonlinear NdSc3(BO3)4
Authors: Gruber John B. , Reynolds Thomas A. , Keszler Douglas A. , Zandi Bahram
Published: July 2002

NdSc 3 ( BO 3 ) 4 (NdSB) can be grown as a nonlinear optical crystal having hexagonal (huntite) structure. The crystal has important spectroscopic properties suitable for various applications in photonics. The observed crystal-field splitting of the energy levels of Nd3+(4f3) has been identified based on analyses of the fluorescence, absorption, and excitation spectra obtained at 13, 80, and 300 K. A detailed crystal-field splitting calculation in which initial crystal-field parameters Bnm are established from lattice–sum calculations gives good agreement to the observed splitting. Experimental branching ratios and fluorescence lifetimes are reported and are compared with calculated values. The spectroscopic properties of Nd3+ in NdSB are also compared with values obtained for Nd3+ as a dopant in the nonlinear crystal YAl3(BO3)4.
Dielectric relaxation processes in Cd2Nb2O7 compound
Authors: Ang Chen , Guo Ruyan , Bhalla A. S. , Cross L. E.
Published: July 2002

This article reports a study on the dielectric relaxation processes of Cd2Nb2O7 compound. Three dielectric relaxation modes I, II, and III were reexamined. By using the Cole–Cole equation fitting of the frequency dependence of dielectric constant and loss, we obtained more precise relaxation time data, compared to the data reported in the literature. The results indicate that the relaxation time for mode I follows the Arrhenius law with one slope rather than two slopes as reported in the literature in the frequency range of 102–105 Hz. However, the parameters obtained from the Arrhenius law fit are not physically reasonable. More physically reasonable parameters can be obtained by fitting the relaxation time to the empirical Vogel [Z. Phys. 22, 645 (1921)]–Fulcher [J. Am. Ceram. Soc. 8, 339 (1925)] relation with essentially the same fitting quality. A comparison of Cd2Nb2O7 with well known triglycine sulphate (TGS) is made. The similarity between the dielectric response of Cd2Nb2O7 and TGS is emphasized. The physical mechanism of the relaxation modes is briefly discussed. With increasing dc bias, the three relaxation modes were suppressed and eventually eliminated. This indicates that the dielectric responses of Cd2Nb2O7 at zero dc bias are the sum effect of several dielectric modes with relaxation polarization superimposed on the ferroelectric–paraelectric phase transition.
Granular CoPt/C films for high-density recording media
Authors: Panagiotopoulos I. , Stavroyiannis S. , Niarchos D. , Christodoulides J. A. , Hadjipanayis G. C.
Published: July 2002

Granular CoPt/C films, consisting of nanoparticles of the face-centered-tetragonal (fct) CoPt phase embedded in a carbon matrix, have been made by cosputtering from CoPt and C targets using a tandem deposition mode. The as-made films have a disordered face-centered-cubic structure and low coercivity (below 100 Oe). The granular structure is obtained after an aging heat treatment, which is followed by a drastic increase in coercivity to values up to 9 kOe due to the formation of the highly anisotropic fct phase. Transmission electron microscope studies showed the size of the CoPt particles to increase from 5 nm in the as-made state to 7–12 nm in the optimally annealed state. The measured coercivities are much lower than the value expected for noninteracting, randomly distributed single-domain particles. The large discrepancy is attributed to interparticle interactions, particle-size effects, and mainly to a lower anisotropy of the fct phase because of incomplete ordering.
Magnetic domain structures in arrays of submicron Co dots studied with magnetic force microscopy
Authors: Demand M. , Hehn M. , Ounadjela K. , Stamps R. L. , Cambril E. , Cornette A. , Rousseaux F.
Published: July 2002

The magnetic properties of submicron circular epitaxial Co dot arrays fabricated by electron beam lithography have been studied as a function of thickness using high resolution magnetic force microscopy. As a function of thickness, in-plane single domain, vortex, or perpendicular multidomain phases have been identified. The evolution of the domain structures with dot thickness agrees well with theory.
The effect of aspect ratio on the magnetic anisotropy of particle arrays
Authors: Farhoud M. , Smith Henry I. , Hwang M. , Ross C. A.
Published: July 2002

Arrays of evaporated nickel particles with a variety of diameters (75–122 nm) and aspect ratios are fabricated in order to study the effect of the particles’ geometry on their magnetic behavior, interactions and switching mechanism. Hysteresis loops generated by simulating single-domain particles with out-of-plane magnetization are compared to the experimentally obtained data.
Structure and magnetic properties of Y2Co17−xMnx (x=0–8) compounds
Authors: Sun Zhi-gang , Zhang Hong-wei , Liang Bing , Wang Jing-yun , Shen Bao-gen , Liu J. P.
Published: July 2002

X-ray diffraction (XRD) and magnetization measurements were employed to investigate the effect of Mn substitution for Co on the structure and magnetic properties of Y2Co17−xMnx compounds with x=0–8. XRD patterns show that all samples are single phase with a hexagonal Th2Ni17-type structure. The substitution of Mn for Co in Y2Co17−xMnx compounds leads to a monotonic increase in unit cell volume. The saturation magnetization remains nearly constant for x⩽3, then decreases quickly with increasing Mn content; this can be explained by the change of the 3d energy band structure and an electron transfer process. The Curie temperature TC is found to decrease rapidly with increasing Mn concentrations. X-ray diffraction measurement on magnetically aligned Y2Co17−xMnx compounds exhibit an easy-plane type of magnetic anisotropy at room temperature for x=0 and an easy-axis type of magnetic anisotropy at room temperature with x=1–7. Substitution of Mn for Co leads to a change of the magnetocrystalline anisotropy of the Co sublattice from the basal plane to the c axis and strongly increases the uniaxial anisotropy of Y2Co17−xMnx. The magnetocrystalline anisotropy field HA is found first to increase and then decrease with increasing Mn concentration, attaining a maximum value of 20.6 kOe at x=3.