bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of extra-atomic relaxation in determining Si 2p binding energy shifts at silicon/silicon oxide interfaces
Authors: Zhang K. Z. , Greeley J. N. , Banaszak Holl Mark M. , McFeely F. R.
Published: July 2002

The observed binding energy shift for silicon oxide films grown on crystalline silicon varies as a function of film thickness. The physical basis of this shift has previously been ascribed to a variety of initial state effects (Si–O ring size, strain, stoichiometry, and crystallinity), final state effects (a variety of screening mechanisms), and extrinsic effects (charging). By constructing a structurally homogeneous silicon oxide film on silicon, initial state effects have been minimized and the magnitude of final state stabilization as a function of film thickness has been directly measured. In addition, questions regarding the charging of thin silicon oxide films on silicon have been addressed. From these studies, it is concluded that initial state effects play a negligible role in the thickness-dependent binding energy shift. For the first ∼30 Å of oxide film, the thickness-dependent binding energy shift can be attributed to final state effects in the form of image charge induced stabilization. Beyond about 30 Å, charging of the film occurs.
Radiation temperatures of soda-lime glass in its shock-compressed liquid state
Authors: Kobayashi T. , Sekine T. , Fat’yanov O. V. , Takazawa E. , Zhu Q. Y.
Published: July 2002

A radiation pyrometer in conjunction with a two-stage light gas gun has been used to measure shock temperatures of soda-lime glass in the pressure range 54–109 GPa. This pyrometer consists of two parts, i.e., an optical multichannel analyzer which measures the radiation spectrum over the visible range (∼450 nm window) and a four-channel photomultiplier tube system which records the time-varying behavior of shock temperatures. The measured radiation spectra are compared with the Planck function to estimate the shock temperatures and emissivities. Obtained spectra are well fit by the Planck function with moderate emissivities, indicating that relatively homogeneous thermal radiation is the main component of radiation. Obtained shock temperatures range from 2800 (100) to 5700 (300) K and they seem to represent shock temperatures of liquefied soda-lime glass (melt). The Hugoniot is well described by a linear relation, us=0.14(21)+1.92(5)up km/s. It is deduced that the radiation from liquids under shock compression, in contrast to the radiation from solids under shock compression, is more thermal and fits the Planck function well, even at lower temperatures. This is because the radiation spectrum of solids under compression often shows nonthermal radiation due to heterogeneous deformation, while the radiation spectrum of liquids under compression could not have such a nonthermal component.
Magnetic properties of DyCo10V2
Authors: Zhang C. , Kou X. C. , Zhao Z. G. , Brück E. , Buschow K. H. J. , de Boer F. R.
Published: July 2002

The easy magnetization direction of DyCo10V2 is parallel to the c axis at room temperature. The magnetization hysteresis loops of magnetically aligned samples were measured from 5 to 300 K with fields applied parallel and perpendicular to the alignment direction. For samples field-cooled to below the compensation temperatures, shifts of the loop centers into the range of negative magnetizations were observed. These features and the occurrence of negative remanences are explained in terms of the magnetization reversal when passing the compensation temperature upon cooling. From measurements of the temperature dependence of the magnetization, it was derived that a spin-reorientation transition takes place at about TSR=41 K.
A Monte–Carlo approach to domain boundary precipitation in binary alloys
Authors: Liu J.-M.
Published: July 2002

A Monte–Carlo approach on the second phase precipitation in polycrystalline binary alloys is developed. The approach starts from the kinetic spin-exchange Ising model and the Q-state Potts model, and a coupling algorithm for simulation of both phase precipitation and domain growth is developed. The simulation on a simplified system with slow domain boundary migration reveals precipitation phenomena on the domain boundaries. The effect of domain boundaries on the morphology and kinetics of the second phase precipitates is investigated. It is shown that the scaling concept and the Lifshitz–Slyozov–Wagner law are broken in the present system.
Investigation of interference between absorption lines by wavelength modulation spectroscopy
Authors: Bullock A. M. , Dharamsi A. N.
Published: July 2002

Wavelength modulation spectroscopy is used to demonstrate that extremely weak absorption lines can be measured even when these lines suffer from interference from the wings of adjacent stronger lines. It is shown that the use of detection at several harmonics allows such interference to be examined clearly and conveniently. The results of experimental measurements on a weak magnetic dipole driven, spin-forbidden line in the oxygen A band, which experiences interference from the wings of a pair of adjacent lines towards the blue and red regions of line center, are presented. A comparison of the experimental results to theory is given.
Parametric interaction of the electric and acoustic fields in a sapphire monocrystal transducer with a microwave readout
Authors: Locke C. R. , Tobar M. E. , Ivanov E. N. , Blair D. G.
Published: July 2002

A sapphire monocrystal configured with a parametric microwave readout can potentially monitor the motion of its internal acoustic resonances at the precision governed by quantum mechanical fluctuations. The mechanism of transductance is due to parametric interaction between the electric and acoustic field within the crystal. This mechanism has been tested for the first time, and the theory has been verified by observing the pump frequency dependence of the acoustic quality factor. Because of the extremely low acoustic losses (Q>107) and electrical losses (Q>104), measurements were sensitive enough to attain positive verification at room temperature.
Magnetic domains and coercivity in FeCo soft magnetic alloys
Authors: Yu R. H. , Basu S. , Zhang Y. , Xiao J. Q.
Published: July 2002

The temperature dependence of coercive field Hc of the FeCo-based soft magnetic alloy associated with the microstructure has been investigated and correlated with microstructural features, such as structural ordering, second phases, and the grain size. An increase in the structural ordering parameter, determined by neutron diffraction, reduces the coercive field Hc. Lorenz microscopy observation indicates that the second phases and the grain boundaries act as pinning sites for the magnetic domain wall movement, thus increase the coercive field Hc.
Microstructure evolution and magnetic properties of overquenched Pr8Fe86B6 ribbons during annealing
Authors: Wang Zuocheng , Zhou Shouzeng , Zhang Maocai , Qiao Yi , Gao Xuexu , Zhao Qing , Wang Run , Gong Wei
Published: July 2002

Microstructure evolution and magnetic properties of overquenched Pr8Fe86B6 ribbons during annealing have been investigated. The results showed that, in as-quenched state, the microstructure of the ribbons consists of a mixture of amorphous phase (Am)+Pr2Fe14B+a-Fe, Am+a-Fe and only amorphous phase, respectively, for the wheel speed of 22, 26, and 30 m/s. Depending on the overquenched precursor, the microstructure evolution of the ribbons during annealing can be classified into: (1) Am+Pr2Fe14B+a-Fe→Pr2Fe14B+a-Fe; (2) Am+α-Fe→Am′+a-Fe→a-Fe+Pr2Fe23B3+Pr2Fe14B→Pr2Fe14B+a-Fe; and (3) Am→Am+a-Fe→Pr2Fe23B3+a-Fe→Pr2Fe14B+a-Fe. In all cases, the microstructure of optimally annealed ribbon samples consist of magnetically hard Pr2Fe14B and soft magnetic a-Fe phases. The magnetic properties achieved by optimal annealing were found to be strongly dependent upon the initial quenching rate of the unannealed precursor. A fairly significant drop in both Hci and Br was observed with the increase of quenching rate of the precursors.
Hard x-ray magnetic circular dichroism in GdNi5 and TbNi5 single crystals
Authors: Galéra Rose Marie , Rogalev Andrei
Published: July 2002

X-ray magnetic circular dichroism experiments have been performed at the R L2,3 (R=rare earth) and Ni K edges on single crystals of GdNi5 and TbNi5 ferromagnetic compounds. The spectra present huge and well-structured dichroic signals at both the R L2,3 and the Ni K edges. Structures due to the quadrupolar (2p→4f) transitions are clearly observed at the Tb L2,3 edges in TbNi5. For GdNi5 the dichroic signal presents a structure at 8 eV above the edge at both the Gd L2 and L3 edges. At the Ni K edge, though Ni is not magnetic in the RNi5 series, large intensities, up to 0.4%, are measured. The present results show the strong influence of the rare earth on the Ni K edge dichroic spectra.
Study of exchange anisotropy in NiFe/NiMn and NiFe/IrMn exchange coupled films
Authors: Pokhil Taras , Mao Sining , Mack Anthony
Published: July 2002

Exchange anisotropy in NiFe/NiMn and NiFe/IrMn exchange coupled films was studied as a function of temperature using vibrating sample magnetometry. The exchange field was measured using three different methods: (1) as a shift of the hysteresis loop measured in an external field applied parallel to the exchange field direction; (2) calculated from the initial susceptibility in the field applied perpendicular to the exchange field; and (3) calculated from the shift of minor reversible hysteresis loops measured in external fields applied in a few different directions close to the perpendicular to the exchange field. The values of the exchange field in NiFe/NiMn samples measured using methods 2 and 3 were similar and approximately twice as high as the values measured using method 1. For the NiFe/IrMn samples methods 2 and 3 gave exchange field values slightly exceeding the values obtained using method 1. The results are explained using a model in which it is assumed that the interfacial interactions between antiferromagnetic and ferromagnetic layers induce unidirectional and uniaxial anisotropy in the ferromagnetic layer. The temperature dependence of induced interfacial uniaxial anisotropy was calculated from the experimental data. For the NiFe/NiMn samples, the temperature dependence of the induced uniaxial anisotropy was significantly different from that of the unidirectional anisotropy.
Raman scattering and its hydrostatic pressure dependence in ZnGeP2 crystal
Authors: Shirakata Sho
Published: July 2002

Polarized Raman spectra in ZnGeP2 crystal have been measured. The symmetry of vibrations has been assigned for every mode but one. The angular dispersion of the extraordinary phonon has been measured, and the result is described by the Loudon–Poulet approximation. Hydrostatic pressure dependence of Raman shift has been measured up to 6 GPa using oriented samples. Pressure coefficients of fifteen Raman peaks have been obtained. Based on the high-pressure study, phonon modes in ZnGeP2 have been examined in terms of phonons in the GaP crystal which is the isoclectronic binary analog of ZnGeP2.
Fabrication of exchange-biased spin valves with CoFeB amorphous layers
Authors: Feng T. , Childress J. R.
Published: July 2002

Amorphous Co72Fe8B20 is a soft ferromagnetic material with a high electrical resistivity and is, therefore, unique for use as the active layer in giant magnetoresistance (GMR) spin-valve structures. CoFeB/Cu/CoFeB/FeMn spin-valve structures were prepared by magnetron sputtering with varying FeMn thickness, deposition sequence, CoFeB deposition rate, Cu deposition rate, applied magnetic field, and annealing treatment, and their magnetic and magnetotransport properties were investigated by superconducting quantum interference device magnetometry and four-terminal magnetoresistance measurements. FeMn, above a critical thickness of 100 Å, is found to be a suitable biasing layer only if deposited on top of CoFeB. Optimum CoFeB and Cu thicknesses and deposition rates were also determined. A modest GMR ratio of 1.2% in a field range 10 Oe<H<15 Oe is achieved at T=10 K in a CoFeB (40 Å)/Cu(30 Å)/CoFeB(20 Å)/FeMn(100 Å) structure. However, we expect that the size of the GMR effect can be tailored independently by suitable engineering of the CoFeB/Cu interface.
Transverse magneto-optical Kerr effect at the 2p threshold of 3d magnets
Authors: Weber N. , Bethke C. , Hillebrecht F. U.
Published: July 2002

The transverse magneto-optical Kerr effect (T-MOKE) was investigated for thin epitaxial films of Fe grown on Ag(100) in the region of the 2p excitation threshold. The experimental reflectivity and asymmetry spectra are compared to those derived from the complex dielectric function tensor. The T-MOKE asymmetry is a mixture of both the real and imaginary parts of the off-diagonal elements of the dielectric function tensor, depending sensitively on the relative magnitudes between the real and imaginary parts of the diagonal elements. We demonstrate the possibility to determine the exchange coupling between a ferromagnetic thin film and an adsorbed monolayer by T-MOKE.
Off-track bit error rate modeling
Authors: Qin Yuan , Fernandez-de-Castro Juan , Giusti Jim
Published: July 2002

Traditionally, channel generated bit error rates (BERs) at a certain signal to noise ratio (SNR) have been modeled by a Gaussian distribution function. This approach has been suitable for a peak detection channel as the analysis is performed in only one bit. In the case of a partial response maximum likelihood (PRML) channel, one data bit is determined by multiple code bits. There is a burst of errors detected if any one of the involved code bits gives an error. The chi-square distribution function, which is a sum of several independent Gaussian-squared distributions, is another method to model BERs of a PRML channel. Particularly, different PRML codes could be modeled by a chi-square distribution with different degrees of freedom. In this paper, the relationship of SNR to BER is generated using the chi-square method. The measured on-track rms SNR, read sensitivity function, and media magnetization are the input parameters. Old data and adjacent track interference are considered as random variables. At specified track pitch and read write misregistration, the probability distributions of these random variables are defined by the read sensitivity function and media magnetization. For a given interference, the off-track SNR is calculated. Error rate at a given interference is then derived from off-track SNR by using the SNR to BER relationship defined by a chi-square distribution. The BER at a specific track pitch and read–write misregistration is computed by integrating the error rate at a given interference with the probability distribution of the interference. This model describes the statistical nature of the BER in magnetoresistance head applications and provides very good correlation to experimental data.
Spin-stand measurements of time and temperature dependence of magnetic recordings
Authors: Dhagat P. , Indeck R. S. , Muller M. W.
Published: July 2002

Spin-stand experiments were performed to study the effect of temperature and demagnetizing fields on the stability of magnetic recordings. Tracks of varying linear bit densities were written on a low Mrδ medium that was heated in situ to different temperatures. The readback amplitude, which reflects the changes in the magnetization of the recordings, was observed from 32 ms to 12 h after the tracks were written. The readback amplitude was found to decay with time. The rate of decay increased at higher densities due to higher demagnetizing fields. A further increase in the decay rate was observed at higher temperatures. This increase in decay rate exceeded that predicted by proportional temperature scaling.
Simulations of fast switching in exchange coupled longitudinal thin-film media
Authors: Hannay J. D. , Chantrell R. W. , Richter H. J.
Published: July 2002

We have developed a Langevin dynamic simulation of high speed switching in longitudinal thin-film media. The model assumes a randomly placed set of grains with a particle size distribution which interact via magnetostatic and exchange fields. The dynamic properties of the material are simulated using the Langevin dynamic formalism which is essentially the Landau–Lifshitz–Gilbert equation of motion augmented by a random field whose properties are determined by the fluctuation–dissipation theorem. We have simulated pulsed-field magnetization and remanence curves which are obtained by applying a field pulse to a system in the remanent magnetization state. Calculations of the time dependence of the magnetization, and the time dependence of the coercivity have been made. The high frequency dynamic behavior of the systems is found to be strongly dependent on the value of the exchange coupling between the grains.
Neutron diffraction study of Nd3Co
Authors: Adachi Yoshiya , Lu Ying , Umehara Izuru , Sato Kiyoo , Ohashi Masayoshi , Ohoyama Kenji , Yamaguchi Yasuo
Published: July 2002

The ferromagnetic compound Nd3Co has Curie temperature TC=25 K and the spin reoriented temperatures TR1=8.5 K and TR2=14 K. Neutron powder-diffraction measurements of Nd3Co were carried out at 50 K above TC and at 2.1 K below TR1. The magnetic structure at 2.1 K was determined, whose unit cell has the volume of 2a×b×2c. The values of magnetic moment on Nd atoms in 4c and 8d sites were 2.47 and 3.08 μB, respectively. This magnetic model is consistent with the results of magnetization curves of a single crystalline Nd3Co.
Electronic structure of PrBa2Cu3O7 and YBa2Cu3O7: A local spin density approximation with the on-site Coulomb interaction study
Authors: Qian M. C. , Hu W. Y. , Zheng Q. Q. , Lin H. Q.
Published: July 2002

Using the self-consistent linear muffin-tin orbitals and the atomic sphere approximation method, the band structure calculations for PrBa2Cu3O7 and YBa2Cu3O7 are performed in the regime of the local spin density approximation with the on-site Coulomb interaction (LSDA+U). The strong electron-electron correlation effects are considered for both the Pr 4f and Cu 3d states. Comparing with the LSDA calculations, the LSDA+U calculations show that, while the essential feature of energy band of YBa2Cu3O7 is preserved, the electronic structure of PrBa2Cu3O7 is quite different. For the bands arisen from the CuO2 planes, a gap with a value of 0.5 eV is opened, indicating the insulating or semiconducting character of the CuO2 planes. The pdσ bands associated with the CuO chains are across the Fermi level, revealing the metallic character of the CuO chains.
X-ray photoelectron spectroscopy study of low-temperature molybdenum oxidation process
Authors: Castañeda S. I. , Montero I. , Ripalda J. M. , Dı́az N. , Galán L. , Rueda F.
Published: July 2002

The low-temperature oxidation during deposition by evaporation of molybdenum thin films has been investigated. Analysis by x-ray photoelectron spectroscopy and x-ray diffraction reveals that small differences in the substrate temperature during deposition may give rise to important changes in the final composition and structure of the molybdenum oxide. Changes in binding energy and line shape of the Mo 3d5/2−Mo 3d3/2 doublet attributed to oxygen incorporation have been studied. Two principal steps can be distinguished, with a transition temperature of ∼310 °C. Up to substrate temperatures of ∼310 °C, the superficial Mo remains almost unaffected, with some oxygen dissolved. At ∼310 °C, mixing of Mo0 metal and molybdenum oxide (Moδ+0<δ<4) clusters or islands is observed. Finally, above this temperature a surface layer of molybdenum oxide, Mo6+, is formed. In addition, an abrupt change in d100 interplanar parameter of Mo is observed.
Migration energy for the silicon self-interstitial
Authors: Hallén Anders , Keskitalo Niclas , Josyula Lalita , Svensson Bengt G.
Published: July 2002

The generation of vacancy-related point defects in low dose 1.3 MeV proton irradiated high purity silicon has been investigated. The dose rate was varied to give a total dose of 5×109 cm−2 at irradiation temperatures from 70 to 295 K. The inverse dose rate effect, i.e., a decrease in the production of room temperature stable vacancy related defects for increasing dose rates, is also shown to be thermally activated and involve long range migration of the silicon self-interstitial. The inverse dose rate effect is utilized to obtain a value of 0.065±0.015 eV for the migration energy of the Si interstitial at room temperature and below. This is an experimental estimate of the interstitial migration energy and the low value suggests that ionization enhanced diffusion is important for the motion of Si interstitials.
Ferroelectricity in thin films: The dielectric response of fiber-textured (BaxSr1−x)Ti1+yO3+z thin films grown by chemical vapor deposition
Authors: Streiffer S. K. , Basceri Cem , Parker C. B. , Lash S. E. , Kingon Angus I.
Published: July 2002

We have investigated the dielectric response of a series of {100} fiber-textured (BaxSr1−x)Ti1+yO3+z samples deposited by liquid-source metalorganic chemical vapor deposition onto Pt/SiO2/Si, as a function of the two most commonly varied microstructural parameters: film thickness and Ti nonstoichiometry y. We find that the overall behavior of these samples is adequately described by mean-field, Landau–Ginzburg–Devonshire theory as for bulk ferroelectrics. However, we quantify the impact of three separable factors for these films that greatly alter the dielectric susceptibility as a function of temperature, compared to that found for bulk ceramic samples at the same Ba/Sr ratio of 70/30: (i) Ti nonstoichiometry; (ii) the apparent interface effect; and (iii) the plane equibiaxial stress state resulting from thermal expansion mismatch strains. When these factors are properly taken into consideration, we show that these fine grained thin films behave in a manner entirely consistent with expectations based on bulk behavior. Implications can therefore be drawn concerning the nature of size effects in this ferroelectric system.
Elastic constants of face-centered-cubic cobalt
Authors: Gump J. , Xia Hua , Chirita M. , Sooryakumar R. , Tomaz M. A. , Harp G. R.
Published: July 2002

The wave vector dependence of Rayleigh and higher order Sezawa elastic waves in single crystalline epitaxial face-centered-cubic (fcc) Co layers are measured by Brillouin light scattering at room temperature. The dispersion of the mode velocities allows the independent elastic constants to be determined for this cubic phase of cobalt. These results compare very favorably to previous determinations of the elastic constants measured above 700 K from the high-temperature fcc phase of pure Co. Deviations from theoretical estimates are discussed.
Surface oxidation activates indium tin oxide for hole injection
Authors: Milliron D. J. , Hill I. G. , Shen C. , Kahn A. , Schwartz J.
Published: July 2002

Oxygen plasma treatment of indium tin oxide (ITO) results in a change in work function and electron affinity by ∼0.5 eV. This change correlates with the measured increase in injected current in simple “hole-only” organic devices with O-plasma treated ITO electrodes. Neither addition nor removal of surface hydroxyl functionality accounts for the observed work function and electron affinity changes. X-ray and ultraviolet photoelectron spectroscopies show a new type of oxygen species is formed. Oxidation of surface Sn-OH to surface Sn-O• units is proposed to account for the observed changes in O-plasma treated ITO; this proposal can explain a wide variety of previously described ITO surface activation results.
The tunneling magnetoresistance of Co35(SiO2)65 nanogranular films
Authors: Xu Q. Y. , Ni G. , Sang H. , Du Y. W.
Published: July 2002

A series of Co35(SiO2)65 (volume fraction) nanogranular films were prepared by ion-beam sputtering at room temperature. A tunneling magnetoresistance (TMR) of about 4% at room temperature was observed. With applied magnetic field of about 1.5×103 Oe parallel to the plane of substrates during fabrication, the TMR ratio of the sample increased up to about 5% at room temperature. The results of ferromagnetic resonance showed that the isolated Co particles embedded in the SiO2 matrix were pancake-like in shape. Thus the discrepancy of TMR between the applied magnetic field parallel and perpendicular to the plane of the sample may be due to shape-induced anisotropy.
Pinhole imaging in magnetic tunnel junctions
Authors: Allen D. , Schad R. , Zangari Giovanni , Zana Iulica , Yang D. , Tondra Mark , Wang Dexin
Published: July 2002

Magnetic tunnel junctions may experience failure due to local short cuts in the insulating layer of such devices. The thicknesses of the insulating layers need to be reduced, which will likely make this problem more prevalent. To develop low resistance magnetic tunnel junctions, the density of pinholes must be analyzed. Using the electrodeposition of copper, we have developed a method for the imaging of pinholes. With the selective nucleation of copper at pinhole sites, structures are formed which can be visualized by conventional microscopy techniques. The potential applied for electrodeposition might cause dielectric breakdown of weak spots in the insulator layer. Variation of the applied voltage will allow identification of such sources of device failure.
High frequency electromagnetic interference shielding response of mixtures and multilayer films based on conducting polymers
Authors: Joo J. , Lee C. Y.
Published: July 2002

The electromagnetic interference (EMI) shielding efficiency (SE) is measured for conductive polyaniline and its mixtures containing conducting powders. The frequency ranges of the EMI SE is 10 MHz–1 GHz by using the ASTM D4935-89 technique. The EMI SE of hydrochloric acid doped polyaniline containing silver (Ag) powder is ∼46 dB at room temperature, which indicates that the materials can be commercially applied to shielding against electromagnetic (EM) radiation. The theoretical SE is calculated by using measured dc conductivity, which is compared to the experimental data. We observe that the SE increases with increasing dc conductivity. A model to account for the increase of the SE through the chemical doping and mixing process is presented. The theory for the calculation of the EMI SE of multilayer films based on conducting polymers is discussed in terms of boundary conditions for electric and magnetic fields of EM plane waves. The high frequency (⩾300 MHz) EMI shielding response of the monolayer and multilayer films with the same thickness is theoretically compared. The frequency dependence of SE of monolayer films shows a constant behavior at low frequency and an oscillating behavior with a single period at high frequency. The SE of multilayer films, consisting of the high H and low L conducting layers with the same thickness as that of monolayer films in total, shows a constant behavior at low frequency (⩽10 GHz) and an oscillating behavior with two major periods at high frequency (>10 GHz). The SE of H–L–H layers is smaller than that of H–H–H layers at low frequency. However, there exist frequency ranges where the SE of H–L–H layers is larger than that of H–H–H layers (for example, from 35–70 GHz). The result suggests that the coherent multiple reflections at the internal interfaces of H–L–H layers contribute to an increase of SE. We observe that the effect of coherent multiple reflections decreases as the thickness of the layer increases.
Finite-temperature coercivity of multilayers of hard and soft magnets
Authors: Ma Yu-qiang , Chui S. T.
Published: July 2002

We discuss results of finite-temperature Monte Carlo simulation for the switching field of multilayers of hard and soft magnets. The maximum of the energy product as a function of the soft layer thickness is very weak and becomes weaker as the temperature is increased. However, the maximum becomes more pronounced for the energy product cost as a function of the soft layer thickness. The effect of the dipolar interaction is significant but does not change the qualitative trend of the coercive field as a function of the soft layer thickness.
Electronic quenching, rotational relaxation, and radiative lifetime of NH(A 3Π, v′=0, N′)
Authors: Hofzumahaus A. , Stuhl F.
Published: July 2002

Using ArF (193 nm) laser photolysis of NH3, excited triplet NH(A 3Π, v′=0, N′) radicals were generated with a hot rotational distribution (N′max=8–13). From the decays of the excited radicals, the average lifetime for this rotational distribution was determined to be 465±14 (3σ) ns. The values of the rate constants for the electronic quenching by NH3, NO, CH4, H2, CO, Xe, O2, CO2, Ar, N2, and He were found to decrease in the given order. Rotational relaxation was found to be so efficient to compete with the electronic quenching. The electronic quenching of rotationally relaxed NH(A 3Π, v′=0, Trot=300 K) by NH3 and H2 was observed to be 1.6 and 1.5 times faster than that of the unrelaxed system. The trend in the rate data can be described by Parmenter’s correlation for most molecules studied, hence indicating attractive forces being effective during the quenching process.
The energy weighted maximum overlap model for the electronic structure of molecules
Authors: Jo/rgensen Karl Anker , Dalgaard Esper
Published: July 2002

In this paper we discuss the energy weighted maximum overlap model (EWMO) for the electronic structure of molecules. A derivation of the model within the context of density functional theory is presented. This derivation is based on variational operator approximations rather than neglect of integrals. Examples from photoelectron spectroscopy and electron spin resonance are included in order to illustrate the formalism.
Analysis of multiexponential decay by a linear programming method: Application to light scattering spectroscopy
Authors: Zimmermann K. , Delaye M. , Licinio P.
Published: July 2002

A linear programming (LP) method is applied to the analysis of multiexponential decay (in other words, to the Laplace inversion problem). This LP method is first tested on computer generated data (with and without noise) and then applied to the analysis of intensity correlation functions as measured by light beating spectroscopy. These examples show that the distribution of exponentials describing the multiexponential decay (i.e., its Laplace transform) can be correctly recovered by the LP method even when this distribution displays fine structures (e.g., close delta peaks superimposed on smooth distributions). A statistical study of the sequences of residuals is proposed which leads to an evaluation of the ‘‘goodness of fit’’ and to a practical choice of the maximum resolution retrievable for the exponential distribution. The capabilities of the LP method are discussed in view of the results previously obtained by other methods such as cumulants analysis or various least-squares procedures.
Reexamination of the location of VO2+ in ZnSO4⋅7H2O by EPR and ZFR
Authors: Bramley Richard , Strach Steven J.
Published: July 2002

The single crystal EPR spectra of VO2+ doped ZnSO4⋅7H2O have been reexamined. The angular behavior confirms the orthorhombic structure and the ion is found to replace zinc–water units. Accurate values of the hyperfine principal values were determined by zero-field EPR (ZFR). One previous publication had incorrect locations of the crystallographic axes, with magnetically inequivalent VO2+ sites wrongly identified as physically inequivalent, and another had suggested a different crystal structure.
A theory of dense liquids based on Monte Carlo simulations of very small clusters
Authors: Brawer S. A.
Published: July 2002

A theory of dense, monatomic liquids with short-range interactions is presented. The calculation involves Monte Carlo simulations of a set of different clusters. Each cluster is defined as a central atom and a fixed number of neighbors (generally 10–16), the neighbors constrained to be within distance R0 of the central atom, R0 being the radius of the first coordination sphere. The remainder of the fluid, external to the cluster, is replaced by a mean external force acting on the particles of the cluster. The key element in the theory is an assumption about the dependence of the external force on the positions of the particles of the cluster. The approximation is made that the external force acting on a particular atom (say c) depends only on some atoms of the cluster, namely the atom c and its immediate neighbors. Then the mean external force can be calculated self-consistently from the clusters themselves, so that the short-range order of the fluid is determined self-consistently from clusters. Numerical calculations demonstrate the validity of this approximation, at least for one particular model fluid with short-range repulsive forces.
Formation of complex defects involving molecular oxygen by electron-hole reactions in x-irradiated KClO4 and KBrO4, studied by ESR and IR spectroscopy
Authors: Bjerre Nis , Byberg J. R.
Published: July 2002

Complex defects of composition [XO−2, O2], X=Cl, Br, produced by UV or x-irradiation of solid KClO4 and KBrO4 at 26 K are characterized by ESR and IR spectroscopy. [XO−2, O2] is shown to arise during x-irradiation in a reaction between self-trapped electrons in the form of XO2−4 defects, and self-trapped holes in the form of (XO4)−2 defects. The previously described hole defect [XO2, O2] is shown to arise from oxidation of [XO−2, O2] by reaction with (XO4)−2. Thus all the abundant defects observed in x-irradiated KClO4 and KBrO4 stem from self-trapping of electrons and holes and from simple reactions of the self-trapped electrons and holes. The observed equivalence of optical excitation of the anions with electron-hole recombination may be a general property of polyatomic solids.
Temperature dependence of the infrared active translational modes of solid carbon disulphide
Authors: Ishi Kimihiro , Takahashi Shin-ichi
Published: July 2002

Two infrared active translational modes of solid CS2, B1u(Γ−3) and B2u(Γ−2) were precisely measured from the temperature of liquid helium to the melting point. Remarkable temperature dependencies of the absorption bandwidths were obtained and explained by means of the perturbation theory of the anharmonic crystal. The results suggest ways in which the lattice vibration energy is dissipated or transferred.
Three-body contributions to the thermodynamic properties of supercritical argon
Authors: Leder Frederic
Published: July 2002

Numerical calculations of the thermodynamic properties of argon were performed using Zwanzig perturbation theory in which the reference radial distribution functions were derived from the Percus–Yevick equation in conjunction with an accurate pair potential (HFD–C). Three-body contributions were approximated by an Axilrod–Teller induced triple dipole potential and the Kirkwood superposition approximation to the triple radial distribution function. Agreement with experimental data is very good over a range of densities up to twice the critical density and to a temperature approaching the critical. Deviation of the model from experiment is evident near the critical point, due to onset of macroscopic fluctuations.
Preparation and structure of the 1:2 π-molecular complex of phenothiazine with pyromellitic dianhydride
Authors: Brierley C. , Barton R. , Robertson B. , Anthonj R. , Karl N.
Published: July 2002

Single crystals of the black 1:2 donor–acceptor complex of phenothiazine with pyromellitic dianhydride, PTZ:(PMDA)2, were grown by plate sublimation at ∼163 °C from the zone-refined components. The l:1 complex is produced at lower temperatures. Crystals of the 1:2 complex are monoclinic, P21/c, Z=4, a=7.689(3), b=12.953(5), c=28.14(2) Å, β=104.30(2)° at T=19 °C. The structure was refined from 2863 x-ray diffraction reflection intensities for which I>2.0σ(I) to R=0.064 and Rw=0.057. The structure consists of continuous ... DADA ... polar stacks as does the l:1 complex, but the stacks, which are parallel to the a axis, are separated in the c direction by the extra PMDA molecule. The overlap of adjacent molecules in the stack in the 1:2 complex is more closely related to the overlap of adjacent molecules in the π-molecular complex of PMDA with anthracene. The resultant angle between the stack axis and the normal to the planar molecules is 27.1°. The geometry of the individual molecules in the l:2 complex is not significantly different from those in the l:1 complex.
Light scattering polydispersity analysis of molecular diffusion by Laplace transform inversion in weighted spaces
Authors: Bertero M. , Brianzi P. , Pike E. R. , de Villiers G. , Lan K. H. , Ostrowsky N.
Published: July 2002

Previous work on the use of singular systems for the inversion of photon correlation functions obtained in the analysis of molecular polydispersity by laser light scattering is extended to allow the imposition of a ‘‘profile’’ function, having the measured mean and polydispersity index, to localize the recovered solution and improve its resolution. This profile function is used to construct an appropriate orthonormal basis in a weighted L2 space in which to expand the solution and also a basis of vectors for expanding the experimental data.
Thermal and IR-induced conformer interconversion processes for 2-fluoroethylamine in several low-temperature matrix media and ab initio 4-31G, 4-31G(N*), and 6-31G** calculations
Authors: Lotta T. , Murto J. , Räsänen M. , Aspiala A. , Särkkä P.
Published: July 2002

IR-induced conformer interconversion processes have been found to occur for 2-fluoroethylamine in solid Ar, Kr, Xe, and N2 matrices but not in solid CH4. Using information obtained from the photoprocesses as well as from thermal processes and ab initio calculations, it was possible to find out the conformers present, to evaluate the conformer energies and torsional barrier heights, and to unravel the occurring processes. The total IR process consists of two parallel first-order C–C rotations, Gg→Tg and Gt→Tt. The influence of the host molecules upon the rates and barrier heights, the efficiency of different spectral regions in initiating the process, and the thermal processes were studied. The latter occur as C–C rotations opposite to the photoprocesses and as conformational equilibria involving rotations around the C–N bond. Extensive ab initio calculations were carried out on the 4-31G, 4-31G(N*), and 6-31G** levels. Geometries of the conformers were fully optimized at these levels, and torsional potential energy barrier heights and vibrational frequencies [at the 4-31G(N*) level] were calculated; the latter confirmed the experimental conformer assignment. IR-induced conformer changes were observed also for 2-chloro- ethylamine in Ar. The mechanism of the photorotamerizations of alcohols and amines is discussed and the importance of C–C torsional barriers is emphasized. A linear relationship between the logarithm of the first-order rate constant and the ab initio 4-31G calculated barrier height of the C–C torsion has been found (including several alcohols, 2-fluoroethylamine, and two aldehydes).
A laser-induced fluorescence and information-theory investigation of energy transfer processes in benzene–argon collisions
Authors: Lyman John L. , Müller G. , Houston P. L. , Piltch M. , Schmid W. E. , Kompa K. L.
Published: July 2002

This paper reports the results of an extensive study of the internal energy-transfer processes that occur in benzene–argon collisions. We used laser-induced fluorescence and information theory for determining the energy-transfer rates between internal states of benzene in the ground electronic state (1A1g). The method provides an estimate for the rate of rotational relaxation. It gives a measure of the fraction of molecules that absorb the laser radiation at a frequency near the center of the ν18 absorption band of benzene. The use of information theory gives estimates for all of the vibrational energy transfer rates. These fit the experimental data reasonably well. However, some of the data do deviate from the information theory model. This suggests that the statistical assumptions of the model are not sufficiently restrictive. One such restriction may be in the number of vibration quanta changing per collision..
Highly negative crystal ions in a Thomas–Fermi ab initio theory with exchange
Authors: Kucharczyk M. , Olszewski S.
Published: July 2002

The existence of solutions describing highly negative ions together with the charge distribution and the electron affinity of these ions are examined in the case of the ions bound with the other atomic species, for example in a crystal lattice. The examination is done on the basis of a Thomas–Fermi statistical theory with exchange. The electrons obey the Fermi statistics and no empirical parameters are used in calculations. It is shown that solutions for the statistical ions whose nuclear charge is Z may exist in the presence of the amount of the negative charge equal at least to (3/2)Z. A similar existence of solutions for highly negative ions is obtained on the basis of a modified Englert–Schwinger statistical theory of the atomic systems.
Low-temperature X-band EPR study of Mn2+-, Cu2+-, and Co2+-doped NH4I single crystals
Authors: Chand Prem , Upreti G. C. , Misra Sushil K. , Bartkowski M.
Published: July 2002

X-band EPR of Mn2+,Cu2+, and Co2+ ions doped in ammonium iodide single crystals have been studied at low temperatures. The Mn2+ and Cu2+ spectra show the presence of only one type of complex for each with features similar to those observed at room temperature with no unusual changes. The results on Co2+ ion, reported here for the first time, reveal the presence of three equivalent Co2+ complexes having tetragonal symmetry with their tetragonal axes orthogonal to each other. The charge-compensation mechanism and possible vacancy complexes are discussed, and the spin-Hamiltonian parameters reported.
Theoretical a
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o and low-temperature ESR study of the cyclohexane cation
Authors: Lunell S. , Huang M. B. , Claesson O. , Lund A.
Published: July 2002

The cyclohexane cation has been studied theoretically using ab initio MO-LCAO-UHF calculations, as well as experimentally, by means of low-temperature ESR measurements in a CF3CCl3 matrix between 4 and 140 K. It is found that the most stable conformation of the free cation is a distorted chair conformation with Cs symmetry, with one carbon atom being separated from the others by bonds that are approximately 0.1 Å larger than the remaining C–C bonds. The symmetrical chair conformation of C2h symmetry is predicted by the calculations to lie approximately 6 kcal/mol above this lowest state. The possibility of a change of ground state because of matrix interactions is discussed in connection with the temperature dependence of the spectra.
Resonance Raman scattering of the excited triplet (3B+2u ) electronic state of naphthalene in fluid media
Authors: Fisher M. R. , Tripathi G. N. R.
Published: July 2002

Resonance Raman spectra of the photoexcited lowest triplet (3B+2u) state of naphthalene (N-h8 and N-d8), observed in solution by time-resolved technique, are reported. Eight Raman bands (396, 496, 741, 958, 1337, 1395, 1440, and 2676 cm−1) have been observed in N-h8 and ten (479, 690, 754, 1005, 1142, 1281, 1356, 2491, 2638, and 2714 cm−1) in N-d8. Vibrational assignments are briefly discussed.
Chemisorption of hydrogen into a graphite–potassium intercalation compound C8K studied by means of positron annihilation
Authors: Murakami Hideoki , Sano Mizuka , Kanazawa Ikuzo , Enoki Toshiaki , Kurihara Toshikazu , Sakurai Yoshiharu , Inokuchi Hiroo
Published: July 2002

The positron-annihilation spectrum for C8K obtained from the Doppler broadening of the 511 keV annihilation radiation is composed of two Gaussian bands: one due to annihilation with electrons in the interlayer region, the other mainly due to annihilation with electrons in the graphitic layers. Upon introduction of hydrogen to C8K, both bands sharpened, which indicates a conversion of hydrogen atoms to hybride ions through charge transfer from the graphitic layers and the formation of positron–hydride ion complexes in the interlayer region. (AIP)
Solvation thermodynamics of water in aqueous solutions. III. Ionic solutions
Authors: Ben-Naim A.
Published: July 2002

The solvation process of water in aqueous solutions of some simple electrolytes is studied. It is found that electrolytes at high concentrations cause the solvation free energy of water to be more negative than in pure liquid water. The initial effect, at very low concentrations, varies markedly from one electrolyte to another. The general trend is that increasing the size of the ions makes the effect of the solute on the solvation free energy of water more positive. Some tentative calculations of the effect of solutes on the entropies and the enthalpies of solvation of water are also presented.
Ab initio effective core potentials for molecular calculations. Potentials for the transition metal atoms Sc to Hg
Authors: Hay P. Jeffrey , Wadt Willard R.
Published: July 2002

Ab initio effective core potentials (ECP’s) have been generated to replace the Coulomb, exchange, and core-orthogonality effects of the chemically inert core electron in the transition metal atoms Sc to Hg. For the second and third transition series relative ECP’s have been generated which also incorporate the mass–velocity and Darwin relativistic effects into the potential. The ab initio ECP’s should facilitate valence electron calculations on molecules containing transition-metal atoms with accuracies approaching all-electron calculations at a fraction of the computational cost. Analytic fits to the potentials are presented for use in multicenter integral evaluation. Gaussian orbital valence basis sets are developed for the (3d,4s,4p), (4d,5s,5p), and (5d,6s,6p) orbitals of the first, second, and third transition series atoms, respectively. All-electron and valence-electron atomic excitation energies are also compared for the low-lying states of Sc–Hg, and the valence-electron calculations are found to reproduce the all-electron excitation energies (typically within a few tenths of an eV).
Ab initio effective core potentials for molecular calculations. Potentials for main group elements Na to Bi
Authors: Wadt Willard R. , Hay P. Jeffrey
Published: July 2002

A consistent set of ab initio effective core potentials (ECP) has been generated for the main group elements from Na to Bi using the procedure originally developed by Kahn. The ECP’s are derived from all-electron numerical Hartree–Fock atomic wave functions and fit to analytical representations for use in molecular calculations. For Rb to Bi the ECP’s are generated from the relativistic Hartree–Fock atomic wave functions of Cowan which incorporate the Darwin and mass–velocity terms. Energy-optimized valence basis sets of (3s3p) primitive Gaussians are presented for use with the ECP’s. Comparisons between all-electron and valence-electron ECP calculations are presented for NaF, NaCl, Cl2, Cl2−, Br2, Br2−, and Xe2+. The results show that the average errors introduced by the ECP’s are generally only a few percent.
Asymptotic properties of two-particle and single-particle density matrices in N-electron atoms and molecules
Authors: Dawson K. A. , March N. H.
Published: July 2002

The asymptotic form of the single-particle density matrix in an N-electron atom is known to be determined by the overlap of the ground state wave functions of the N and (N−1) electron systems. We discuss the generalization of this result to the two particle density matrix. The connection with recent work by Patil on the asymptotic form of the wave function for two-electron atomic ions, and its generalization, is pointed out.