bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluorine atom subsurface diffusion and reaction in photoresist
Authors: Greer Frank , Fraser D. , Coburn J. W. , Graves David B.
Published: December 2003

Kinetic studies of fluorine and deuterium atoms interacting with an OiR 897 10i i-line photoresist (PR) are reported. All experiments were conducted at room temperature. Films of this PR were coated on quartz-crystal microbalance (QCM) substrates and exposed to alternating fluxes of these atoms in a high vacuum apparatus. Mass changes of the PR were observed in situ and in real time during the atom beam exposures using the QCM. A molecular-beam sampled differentially pumped quadrupole mass spectrometer (QMS) was used to measure the species desorbing from the PR surface during the F and D atom exposures. During the D atom exposures, hydrogen abstraction and etching of the PR was observed, but no DF formation was detected. However, during the F atom exposures, the major species observed to desorb from the surface was DF, formed from fluorine abstraction of deuterium from the photoresist. No evidence of film etching or fluorine self-abstraction was observed. The film mass increased during F atom exposure, evidently due to the replacement of D by F in the film. The rate of DF formation and mass uptake were both characterized by the same kinetics: An initially rapid step declining exponentially with time (e−t/τ), followed by a much slower step following inverse square root of time (t−1/2) kinetics. The initially rapid step was interpreted as surface abstraction of D by F to form DF, which desorbs, with subsequent F impacting the surface inserted into surface C dangling bonds. The slower step was interpreted as F atoms diffusing into the fluorinated photoresist, forming DF at the boundary of the fluorinated carbon layer. The t−1/2 kinetics of this step are interpreted to indicate that F diffusion through the fluorinated carbon layer is much slower than the rate of F abstraction of D to form DF, or the rate of F insertion into the carbon dangling bonds left behind after DF formation. A diffusion-limited growth model was formulated, and the model parameters are consistent with values reported in related systems. The implications of these results for plasma etch applications with respect to radical diffusion through surface-passivating films is discussed.
C
60
bonding to graphite and boron nitride surfaces
Authors: Reinke P. , Feldermann H. , Oelhafen P.
Published: December 2003

The present study focuses on the interaction of C60 with the surfaces of highly oriented pyrolitic graphite (HOPG) and sp2-bonded boron nitride (BN). The nanocrystalline BN film was deposited by mass selected ion beams and features an sp2-bonded surface layer, which covers a cubic phase BN film. The first part of the experiment is the sequential deposition of C60, which is monitored by photoelectron spectroscopy in the x-ray (XPS) and ultraviolet (UPS) regime. The growth of the C60 layer on HOPG is close to a layer-by-layer growth mode, but on the BN surface island growth is favored. No charge transfer or chemical reaction (e.g., carbide formation) between the fullerene layer, and the underlying substrate is observed in either case. In the second part of the experiment the samples are heated at a rate of 10 K/min while simultaneously recording the UPS VB spectra. The complete desorption of C60 from the HOPG surface occurs in a small temperature interval between 510–530 K. For the sp2 BN surface the majority of C60 desorbs around 493 K, about half a monolayer (ML) remains, and the C60 concentration decreases gradually with increasing temperature; less than a tenth of a ML can be detected even at 1000 K. The first desorption event at 493 K is attributable to the multilayer desorption from islands. The remaining C60 directly in contact with the BN surface is then removed in a large temperature interval between 500 and 1000 K which indicates the presence of a multitude of adsorption sites. The presence of C60 on the BN film surface also induces a band bending and related B 1s and N 1s core level shifts. An upward band bending is present in the C60 overlayer, which indicates that defects are responsible for the pinning of the Fermi level at the interface.
The effect of discrete attractive fluid–wall interaction potentials on adsorption isotherms of Lennard-Jones fluid in cylindrical pores
Authors: Zhang Xianren , Cao Dapeng , Wang Wenchuan
Published: December 2003

The dependence of the adsorption isotherm and phase behavior of Lennard-Jones (LJ) fluid in cylindrical pores on the fluid–wall interaction was investigated using a discrete attractive potential model and the density functional theory. The discrete attractive potential contains two parts, a deep well (dw) and a tail. The results show that the chemical potential corresponding to capillary condensation has a weak dependence on the deep well potential near the pore wall, but exhibits a strong dependence on the tail potential near the pore center. On the contrary, the chemical potential of the formation of the first monolayer is strongly dependent on the deep well potential but almost independent of the tail potential. The shape of the adsorption isotherm plotted as density versus chemical potential is determined by the shape of the fluid–wall interaction, namely εtail–εdw, rather than either the deep well potential or the weak tail potential separately. The critical temperature exhibits similar behavior in its dependence on εtail–εdw. There exists a region where layer transition and capillary condensation intersect. Adsorption isotherms, coexistence curves, and critical temperatures in this region exhibit distinct phase behaviors from other regions.
Dynamics of electronic excitation in collisions of alkali atoms with noble-gas atoms using atomic core potentials
Authors: Reyes A. , Micha D. A.
Published: December 2003

The electronic excitation of the valence electron of alkali atoms in collisions with noble gas atoms has been studied with a procedure that combines l-dependent pseudopotentials including two and three-body polarization terms and a first principles description of the dynamics based on the eikonal approximation of atomic motions and time-dependent molecular orbitals. We discuss the effects of the atomic basis set size on the calculations. We present results for interaction potentials and couplings, the time-dependence of atomic populations, and state-to-state integral cross sections in the keV range. Our results for Li–He, Li–Ne, Na–He, and Na–Ne are in very good agreement with other theoretical and experimental data.
Dynamics of spin–orbit recoupling in collisions of alkali atoms with noble-gas atoms using atomic core potentials
Authors: Reyes A. , Micha D. A.
Published: December 2003

Spin–orbit recoupling in alkali-rare-gas atom colliding pairs is developed within a first principles description of the quantum dynamics introducing l-dependent pseudopotentials and including two and three-body polarization terms and the spin–orbit interatomic potential. The treatment combines an eikonal (or short wavelength) approximation for the nuclear motion and time-dependent molecular orbitals to provide interatomic potentials, their nonadiabatic couplings, and state populations during interactions. The time evolution of recoupling of angular momenta in alkali-rare-gas atom thermal collisions is described and computational aspects of spin–orbit coupling in terms of pseudopotentials are presented. Results for potentials arising from the spin–orbit splitting of the P2 states of Li and Na are presented along with cross sections for fine-structure transitions at 400 K and 450 K. The agreement with experiment and other theories is very good.
Effect of an external electric field on the charge transport parameters in organic molecular semiconductors
Authors: Sancho-Garcı́a J. C. , Horowitz G. , Brédas J. L. , Cornil J.
Published: December 2003

Internal reorganization energies and interchain transfer integrals are two key parameters governing the charge-transport properties of organic semiconducting materials. Here, in order to model some aspects of device operation in field-effect transistors based on conjugated oligomers, we investigate via semiempirical quantum-chemical calculations the way these two parameters are modified when a static electric field in the range 106–108 V/cm is applied along the long axis of pentacene and sexithienyl molecules. For the highest fields, a pronounced redistribution of the charges along the oligomer chains occurs, which is accompanied by significant geometric distortions. However, these charge redistribution effects are found not to impact significantly the transport parameters.
Absolute entropy and free energy of fluids using the hypothetical scanning method. II. Transition probabilities from canonical Monte Carlo simulations of partial systems
Authors: White Ronald P. , Meirovitch Hagai
Published: December 2003

A variant of the hypothetical scanning (HS) method for calculating the absolute entropy and free energy of fluids is developed, as applied to systems of Lennard-Jones atoms (liquid argon). As in the preceding paper (Paper I), a probability Pi approximating the Boltzmann probability of system configuration i, is calculated with a reconstruction procedure based on adding the atoms gradually to an initially empty volume, where they are placed in their positions at i; in this process the volume is divided into cubic cells, which are visited layer-by-layer, line-by-line. At each step a transition probability (TP) is calculated and the product of all the TPs leads to Pi. At step k, k−1 cells have already been treated, where among them Nk are occupied by an atom. A canonical metropolis Monte Carlo (MC) simulation is carried out over a portion of the still unvisited (future) volume thus providing an approximate representation of the N−Nk as yet untreated (future) atoms. The TP of target cell k is determined from the number of visits of future atoms to this cell during the simulation. This MC version of HS, called HSMC, is based on a relatively small number of efficiency parameters; their number does not grow and their values are not changed as the number of the treated future atoms is increased (i.e., as the approximation improves); therefore, implementing HSMC for a relatively large number of future atoms (up to 40 in this study) is straightforward. Indeed, excellent results have been obtained for the free energy and the entropy.
Laser spectroscopy of NiI: Ground and low-lying electronic states
Authors: Tam W. S. , Leung J. W.-H. , Hu Shui-Ming , Cheung A. S-C.
Published: December 2003

High-resolution laser-induced fluorescence spectrum of a jet-cooled NiI molecule has been recorded in the near infrared and visible regions. The NiI molecule was produced by reacting laser-ablated nickel atom and methyl iodide (CH3I). Three electronic states have been identified that include the X 2Δ5/2 and two low-lying [13.9] 2Π3/2 and [14.6] 2Δ5/2 excited states. Molecular transition bands (v′,0) of the [13.9] 2Π3/2−X 2Δ5/2 system with v′=0, 4–9, and the (v′,0) bands of the [14.6] 2Δ5/2−X 2Δ5/2 system with v′=0–6 were observed and analyzed. Spectra of isotopic molecules confirmed the assignment of vibrational quantum number of the observed bands. Least squares fit of rotational transition lines yielded accurate molecular constants for the states studied. The bond length r0 measured for the X 2Δ5/2 is 2.3479 Å and the equilibrium bond length, re, for the [13.9] 2Π3/2 and [14.6] 2Δ5/2 are, respectively, 2.4834 and 2.5081 Å. With the use of a molecular orbital energy level diagram, we have examined the electronic configurations that give rise to the X 2Π3/2 ground state for NiF, NiCl, and NiBr, but the X 2Δ5/2 state for NiI. This work represents the first spectroscopic study of the NiI molecule.
One-photon mass-analyzed threshold ionization spectroscopy of 2-bromopropene (2-C3H5Br): Analysis of vibration and internal rotation in the cation
Authors: Lee Mina , Kim Myung Soo
Published: December 2003

Vibrational spectrum of 2-C3H5Br cation in the ground electronic state was obtained by one-photon mass-analyzed threshold ionization (MATI) spectroscopy using coherent vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. From the MATI spectra, ionization energy of 2-C3H5Br to the ionic ground state has been determined to be 9.4377±0.0006 eV. Vibrational assignments have been made by comparing with the vibrational frequencies and Franck-Condon factors calculated at the B3LYP and BP86 levels with the 6-311++G(3df,3pd) basis set. Several low-frequency bands have been assigned to the torsional motion of the methyl group in the cation. Energies of the torsional states and relative transition intensities to these states have been reproduced well by a one-dimensional rotor model. The torsional barrier and internal rotational constant have been determined to be 80.0 and 5.13 cm−1, respectively.
Comment on “Strontium clusters: Many-body potential, energetics, and structural transitions” [J. Chem. Phys. 115, 3640 (2001)]
Authors: Doye Jonathan P. K. , Calvo Florent
Published: December 2003

Parallel tempering simulations for Sr34 and Sr61 indicate that, contrary to Wang et al.’s predictions [J. Chem. Phys. 115, 3640 (2001)], there are no solid–solid transitions for these clusters, in which symmetrical polytetrahedral structures become most stable. These results have implications for the structural interpretation of the magic numbers observed experimentally for strontium clusters.
Core-hole Hamiltonians and corrected equivalent core model for systems with equivalent atoms
Authors: Kryzhevoi Nikolai V. , Dobrodey Nickolay V. , Cederbaum Lorenz S.
Published: December 2003

Core ionization in systems with several equivalent atoms gives rise to a set of near-degenerate core-hole states each associated with the removal of an electron from one of the delocalized orbitals. The energy splitting between the core-hole states is the intrinsic feature of core ionized systems and should not be neglected. The conventional equivalent core model (ECM) predicts strictly degenerate core-hole states because the core-hole is thought of as completely localized on one of the equivalent centers. This failure as well as several others inherent to the ECM are successfully removed in the framework of the corrected ECM presented in this paper. Two approaches are available in accordance with the two representations of the core-hole, either delocalized or localized. The Z+1 approximation is an excellent starting point in the localized representation. It must be modified, however, when the delocalized picture is used. To this end we introduce a (Z+Q) system where Q is the magnitude of point charges added to the nuclear charges of equivalent atoms which share the loss of an electron upon core ionization. Systematic corrections improving the conventional ECM are obtained by establishing a connection between the ECM and core-hole Hamiltonians. The core-hole Hamiltonians, being ideally suited for description of core ionization, are derived both in the delocalized and localized representations. Numerical results are presented for N2.
The Kramers’ restricted complete active space self-consistent-field method for two-component molecular spinors and relativistic effective core potentials including spin–orbit interactions
Authors: Kim Yong Seok , Lee Yoon Sup
Published: December 2003

The Kramers’ restricted complete active space self-consistent-field (KR-CASSCF) method based upon two-component molecular spinors and relativistic effective core potentials including spin–orbit interactions is implemented, employing the two-step approach, in which the expansion coefficients of configurations and molecular spinors are determined alternately. The present approach allows the influence of spin–orbit interactions to be taken into account in the optimization of one-electron wave function space. Test calculations were performed for the Hg atom, Au− anion, and Tl+ cation with the closed-shell electronic configuration, the ground state potential energy curves of homo-nuclear diatomic molecules, As2, Sb2, and Bi2, over a wide range of inter-nuclear distances, and the bond fission of a polyatomic molecule CH3I. The results show that the KR-CASSCF method properly describes the dissociation of molecules for the fine-structure states. It is also evident that molecular properties are affected by optimized spinors for systems containing heavy atoms such as Bi2 and CH3I at the CASSCF level of theory.
Comparative assessment of a new nonempirical density functional: Molecules and hydrogen-bonded complexes
Authors: Staroverov Viktor N. , Scuseria Gustavo E. , Tao Jianmin , Perdew John P.
Published: December 2003

A comprehensive study is undertaken to assess the nonempirical meta-generalized gradient approximation (MGGA) of Tao, Perdew, Staroverov, and Scuseria (TPSS) against 14 common exchange-correlation energy functionals. Principal results are presented in the form of statistical summaries of deviations from experiment for the G3/99 test set (223 enthalpies of formation, 86 ionization potentials, 58 electron affinities, 8 proton affinities) and three additional test sets involving 96 bond lengths, 82 harmonic vibrational frequencies, and 10 hydrogen-bonded complexes, all computed using the 6-311++G(3df,3pd) basis. The TPSS functional matches, or exceeds in accuracy all prior nonempirical constructions and, unlike semiempirical functionals, consistently provides a high-quality description of diverse systems and properties. The computational cost of self-consistent MGGA is comparable to that of ordinary GGA, and exact exchange (unavailable in some codes) is not required. A one-parameter global hybrid version of the TPSS functional is introduced and shown to give further improvement for most properties.
Kohn–Sham density-functional study of the adsorption of acetylene and vinylidene on iron clusters, Fen/Fen+ (n=1–4)
Authors: Chrétien Steeve , Salahub Dennis R.
Published: December 2003

This is the first paper in a series dealing with the formation of benzene from acetylene on iron clusters, Fen/Fen+ (n=1–4). In the present study, we have performed all-electron Kohn–Sham density-functional theory calculations on the adsorption of acetylene and vinylidene on small iron clusters. Many starting structures were fully optimized without geometric and symmetric constraints for at least three different spin states (numbers of unpaired electrons) using gradient corrected functionals. Vibrational analyses have been performed on all the optimized structures. There is a large number of low-lying electronic states within a window of 50 kJ/mol above the lowest-energy structure for each cluster size and charge state. Various types of coordination and numbers of unpaired electrons are encountered in these electronic states. According to our energetic error bar, all of these states are possible candidates for the ground state of a given complex. Inclusion of corrections beyond the gradient of the density in generalized gradient approximation functionals for correlation stabilizes electronic states with high magnetic moment and destabilizes the low spin states. Electronic states corresponding to the adsorption of an acetylene or a vinylidene molecule on only one iron atom are also more stable when higher corrections are included in the correlation functional. Finally, we have excluded the participation of the vinylidene molecule in the reaction mechanism of the formation of benzene from acetylene on small iron clusters.
Kohn–Sham density-functional study of the formation of benzene from acetylene on iron clusters, Fe/Fen+ (n=1–4)
Authors: Chrétien Steeve , Salahub Dennis R.
Published: December 2003

This is part of a series dealing with the formation of benzene from acetylene on iron clusters, Fenq+ (n=1–4, q=0,1). In this paper, we show that the formation of benzene from acetylene on Fe and Fen+ (n=1–4) is favorable from a thermodynamic point of view. We explain the variation of the rate constants observed for the successive adsorption of acetylene molecules on an iron cation and the experimental observations about the cyclodimerization of acetylene molecules in Fe(C2H2)2+ by referring to the spin conservation principle. Our results indicate that the complexes resulting from the cyclodimerization of Fen(C2H2)2+/Fe(C2H2)2 and Fen(C2H2)3+/Fe(C2H2)3(n=1–4) contain an n-C4H4 ligand (formation of a metallacycle) rather than a cyclobutadiene molecule. However, it is possible to observe the formation of cyclobutadiene from Fe(C2H2)2+ and Fe2(C2H2)3+ only if spin–orbit coupling is significant. A post-self-consistent-field method that includes a multideterminantal treatment is needed to get a quantitative energetic description of the various steps of the reaction. Finally, we discuss various difficulties met in this study and possible ways to deal with them.
Adsorption of rod-like polyelectrolytes onto weakly charged surfaces
Authors: Cheng Hao , Olvera de la Cruz Monica
Published: December 2003

We study the adsorption of strongly charged rod-like polyelectrolytes onto weakly oppositely charged surfaces in salt solutions by equating the chemical potentials between the bulk and adsorbed polyelectrolytes, and between the free and condensed ions along the rods. Lateral correlations between adsorbed polyelectrolytes lead to nonoverlapping cells of radius R, which we study as a function of salt concentration (s), surface charge densities (σ), and polyelectrolyte charge density (1/b). We find a minimum in R and a maximum in the absolute value of the effective charge density of the surface-polyelectrolyte-ion system with increasing salt concentration. Charge inversion disappears in our model as the concentration of salt increases further. The critical salt concentration (sc) for polyelectrolyte adsorption scales as σα with α≈1.8. We find differences between weakly and strongly charged polyelectrolyte adsorption. While sc decreases as b increases in weakly charged polyelectrolytes, it increases almost linearly with b in strongly charged polyelectrolytes. Similar adsorption trends are found in divalent salt solutions. More rods are adsorbed to neutralize the surface due to more rod charge neutralization in divalent salt solutions than in monovalent salt solutions. However, at high salt concentrations it is more difficult to totally desorb the chains (R=∞) in monovalent salt than in divalent salt solutions.
Effect of a static electric field on the vibrational and electronic properties of a compressed CO adlayer on Pt(110) in nonaqueous electrolyte as probed by infrared reflection–absorption spectroscopy and infrared-visible sum-frequency generation spectroscopy
Authors: Vidal F. , Busson B. , Tadjeddine A. , Peremans A.
Published: December 2003

The CO–Pt(110) in nonaqueous electrolyte electrochemical interface was studied by infrared reflection–absorption spectroscopy (IRAS) and infrared (IR)-visible sum-frequency generation (SFG) nonlinear vibrational spectroscopy over a wide range of applied potentials (−1.7⩽Φ⩽1 V/NHE). The integrated intensities of the IRAS and SFG peaks associated with resonant excitation of the atop CO internal stretch vibration (AIR and ASFG) showed distinct variations with Φ. The influence of vibrational and electronic properties on the observed variations is discussed. Potential dependent dynamical charge transfer is not sufficient to explain the observed value of ∂AIR/∂Φ. It is shown that screening factors due to dipolar interactions between molecules within the compressed adsorbed layer must be taken into account in order to explain the variations of the IRAS and SFG data and that the observed behavior differences of AIR and ASFG with the potential are not necessarily related to changes in the Raman cross section of the adsorbate.
Synthesis of colloidal nanoparticles during femtosecond laser ablation of gold in water
Authors: Kabashin A. V. , Meunier M.
Published: December 2003

Femtosecond laser radiation has been used to ablate a gold target in pure deionized water to produce colloidal gold nanoparticles. We report evidence for two different mechanisms of material ablation in the liquid environment, whose relative contributions determine the size distribution of the produced particles. The first mechanism, associated with thermal-free femtosecond ablation, manifests itself at relatively low laser fluences F<400 J/cm2 and leads to very small (3–10 nm) and almost monodispersed gold colloids. The second one, attributed to the plasma-induced heating and ablation of the target, takes place at high fluences and gives rise to a much larger particle size and broad size distribution. The fabricated nanoparticles exhibit plasmon-related optical absorption peak and are of significance for biosensing applications.
Mechanical properties of sputtered silicon nitride thin films
Authors: Vila M. , Cáceres D. , Prieto C.
Published: December 2003

Silicon nitride thin films were prepared by reactive sputtering from different sputtering targets and using a range of Ar/N2 sputtering gas mixtures. The hardness and the Young’s modulus of the samples were determined by nanoindentation measurements. Depending on the preparation parameters, the obtained values were in the ranges 8–23 and 100–210 GPa, respectively. Additionally, Fourier-transform infrared spectroscopy, Rutherford backscattering spectroscopy, and x-ray diffraction were used to characterize samples with respect to different types of bonding, atomic concentrations, and structure of the films to explain the variation of mechanical properties. The hardness and Young’s modulus were determined as a function of film composition and structure and conditions giving the hardest film were found. Additionally, a model that assumes a series coupling of the elastic components, corresponding to the Si–O and Si–N bonds present in the sample has been proposed to explain the observed variations of hardness and Young’s modulus.
Effect of high pressure isostatic annealing on oxygen segregation in Czochralski silicon
Authors: Binetti Simona , Le Donne Alessia , Emtsev Vadim V. , Pizzini Sergio
Published: December 2003

The effect of single-step annealing at 450, 650, and 1000 °C under gigapascal hydrostatic pressures on oxygen segregation from Czochralski silicon samples was investigated. It was shown that the effect of applied pressure on the oxygen segregation processes begins to be detectable at 650 °C and significant at 1000 °C. Not only was the effect of the applied pressure clearly evidenced, but also that of the dopants. In the first case the presence of a gap level associated to self-interstitial clusters could be argued, whereas in the second case both the oxide particles segregation and the dislocation formation were demonstrated to be enhanced by the pressure and by the type of doping. Furthermore, visible and ultraviolet photoluminescence emission at cryogenic temperatures were observed from silicon dioxide particles or from oxide nuclei contained in the silicon matrix.
Frequency dependence of a field-induced force between two high dielectric spheres in various fluid media
Authors: Wang Zhiyong , Shen Rong , Niu Xiaojuan , Lu Kunquan , Wen Weijia
Published: December 2003

The frequency dependence of the interaction force f between two identical SrTiO3 spheres has been investigated in various carrying media with different dielectric constants under ac electric field strengths E0. We note that the force f is proportional to E02 and increases with the frequency regardless of the carrying media. The force however, is found to be stronger than that expected theoretically when the interspherical gap is small. The experimental results demonstrate that it is the conductivity that dominates the interaction force at low frequency, while dielectric polarization becomes more important at high frequency, and reveal that stronger interaction force between high dielectric spheres may be obtained in higher dielectric fluids when the frequency of the ac field is high enough. Some anomalous behaviors of f versus frequency are found when the two spheres are nearly touched.
Ab initio molecular dynamics study of polarization effects on ionic hydration in aqueous AlCl3 solution
Authors: Ikeda Takashi , Hirata Masaru , Kimura Takaumi
Published: December 2003

The solvation shell structure and dynamics of Al3+ and Cl− in an aqueous solution of 0.8 M AlCl3 are studied under ambient conditions by using an ab initio molecular dynamics method. The solvation structures obtained from our ab initio simulations are in good agreement with the experimental ones for both Al3+ and Cl−. A detailed analysis of intramolecular geometry of hydration waters and dipole moments of the ingredients shows that the polarization has substantial effects on the structures and dynamics of both the cation and anion hydration shells. Implications for metal hydrolysis of Al3+ will also be given.
Directional nickel-induced fielded aided lateral crystallization of amorphous silicon
Authors: Izmajlowicz M. A. T. , Flewitt A. J. , Milne W. I. , Morrison N. A.
Published: December 2003

For application to active matrix liquid crystal displays (AMLCDs), a low temperature (<900 K) process for the production of polycrystalline silicon is required to permit the use of inexpensive glass substrates. This would allow the integration of drive electronics onto the display panel. Current low temperature processes include excimer laser annealing and solid phase crystallization, both of which are currently unsuitable for the fabrication of low cost, large area devices. The addition of small amounts of metal (e.g., Ni) to the amorphous silicon has been shown to significantly reduce the solid phase crystallization temperature. The rate of this solid phase metal induced crystallization can also be increased as a result of the presence of an electric field. The work presented here reports directional crystallization of amorphous silicon thin films during heat treatment in the presence of an electric field. Models are proposed for metal induced crystallization with and without an applied electric field in which a reaction between Ni and Si to produce NiSi is the rate-limiting step. The crystallization rate is increased through the application of an electric field that leads to the drift of Ni ions to the growth front. The model and experimental data reveal that the crystallization rate increases exponentially with temperature and linearly with electric field strength.
In situ determination of surface composition, polarity, crystallographic relationship, and periodicity of GaN films by mass spectroscopy of recoiled Ions and direct recoiled spectroscopy
Authors: Carreño L. A. , Boney C. , Bensaoula A.
Published: December 2003

Applicability of time-of-flight (TOF) mass spectroscopy of recoiled ions (MSRI) and direct recoiled spectroscopy (DRS) as in situ techniques for both optimization and characterization of thin film materials is presented in this article. TOF DRS/MSRI were used to monitor the growth process of GaN and (Ga,Mn)N by chemical-beam epitaxy. We show that all important growth parameters can be optimized real time and that under our experimental conditions, all epilayers are metal polar, as confirmed ex situ by wet etching. The surface periodicities of c-sapphire and the final GaN and (Ga,Mn)N epilayers were determined and found to be parallel to each other, but with a 30° in-plane relative rotation between them—as reported by several researchers. Finally, analysis of the Ga and Mn azimuthal surface signals supports that for all concentrations (0.5% to 2.5%) in our studies, the Mn atoms are substitutional into the GaN crystal structure.
Formation of misfit dislocations in strained-layer GaAs/InxGa1−xAs/GaAs heterostructures during postfabrication thermal processing
Authors: Liu X. W. , Hopgood A. A. , Usher B. F. , Wang H. , Braithwaite N. St. J.
Published: December 2003

It is demonstrated that relaxation of GaAs/InxGa1−xAs/GaAs strained-layer heterostructures can be brought about by postfabrication thermal processing. Misfit dislocations are introduced into the structure during thermal processing, even though the thickness of the strained layer is well below the critical value predicted by the Matthews–Blakeslee model. The misfit dislocations are observed to be of both 60° mixed type and 90° pure edge type. As no relaxation occurs at the lower temperatures encountered during fabrication by molecular-beam epitaxy, it can be inferred that the critical condition for the formation of misfit dislocations is not only a function of strained-layer thickness and composition, but also of temperature. This observation cannot be accounted for by differential thermal expansion or diffusion across the strained-layer interfaces, but the temperature-dependent Peierls force may offer an explanation. The high temperature required to produce relaxation of these structures suggests that they are sufficiently thermally stable for most practical applications.
Acoustic-based measurements of material absorption coefficients: Relationship between laser pulse duration and stress confinement time
Authors: Choi Bernard , Jansen E. Duco , Welch Ashley J.
Published: December 2003

Ideally, to use photoacoustics to determine the absorption coefficient μa of a medium, the laser pulse duration τp is much shorter than the stress confinement time τsr required for a laser-induced stress wave to propagate a distance equal to the light penetration depth δ. However, without prior knowledge of δ (equal to 1/μa), it is not clear whether a given photoacoustic measurement is indeed performed under stress-confined conditions. The purpose of this study was to explore the effects of τp and τsr upon efforts to obtain estimates of μa using photoacoustics. A numerical model was developed to simulate stress signals and investigate how measurements of μa are related to the ratio τ=τp/τsr. Experimental photoacoustic measurements at several values of τ were performed to estimate μa of water, and a deconvolution model was applied to correct the measured μa without prior knowledge of τ. Under the conditions simulated in this study, τp must be less than ∼0.1τsr for optimal photoacoustic measurements of μa. Since it is difficult to achieve such conditions at midinfrared wavelengths for accurate soft tissue characterization due to strong water absorption bands, a numerical deconvolution technique was implemented to overcome this limitation of conventional photoacoustics, resulting in up to a 30% improvement in photoacoustic-based estimates of the sample μa.
Electrochromic conductive polymer fuses for hybrid organic/inorganic semiconductor memories
Authors: Möller Sven , Forrest Stephen R. , Perlov Craig , Jackson Warren , Taussig Carl
Published: December 2003

We demonstrate a nonvolatile, write-once-read-many-times (WORM) memory device employing a hybrid organic/inorganic semiconductor architecture consisting of thin film p-i-n silicon diode on a stainless steel substrate integrated in series with a conductive polymer fuse. The nonlinearity of the silicon diodes enables a passive matrix memory architecture, while the conductive polyethylenedioxythiophene:polystyrene sulfonic acid polymer serves as a reliable switch with fuse-like behavior for data storage. The polymer can be switched at ∼2 μs, resulting in a permanent decrease of conductivity of the memory pixel by up to a factor of 103. The switching mechanism is primarily due to a current and thermally dependent redox reaction in the polymer, limited by the double injection of both holes and electrons. The switched device performance does not degrade after many thousand read cycles in ambient at room temperature. Our results suggest that low cost, organic/inorganic WORM memories are feasible for light weight, high density, robust, and fast archival storage applications.
NO adsorption on Rh(100). I. Structural characterization of the adlayers
Authors: Bondino F. , Comelli G. , Baraldi A. , Vesselli E. , Rosei R. , Goldoni A. , Lizzit S. , Bungaro C. , de Gironcoli S. , Baroni S.
Published: December 2003

A detailed experimental and theoretical investigation of the structure of nitric oxide adsorption layers formed at 140 K on Rh(100) has been carried out by means of x-ray photoelectron spectroscopy, x-ray photoelectron diffraction, near-edge x-ray absorption fine structure, and ab initio calculations. At saturation, a single NO species is present. Both theory and experimental results indicate a bridge adsorption site for NO in this phase, with the molecules standing upright on the surface. At low NO coverage, the presence of a different molecular species is experimentally revealed and it is fully characterized by ab initio calculations. This species has been identified with a NO molecule with the molecular axis almost parallel to the surface, lying above a Rh(100) hollow site with the two atoms in asymmetric bridge sites.
NO adsorption on Rh(100). II. Stability of the adlayers
Authors: Bondino F. , Comelli G. , Baraldi A. , Vesselli E. , Rosei R. , Goldoni A. , Lizzit S.
Published: December 2003

The composition, stability, and thermal evolution of nitric oxide on Rh(100) have been characterized by means of synchrotron radiation fast x-ray photoelectron spectroscopy and low-energy-electron diffraction. At 140 K, there is a single NO chemisorbed species (α2–NO) at saturation, forming a disordered phase which develops in an ordered p(4√×√)R45° structure after heating the layer to 373 K. A further annealing induces desorption and a progressive dissociation of the NO molecules, which is completed above 425 K, where a c(2×2) phase consisting of coadsorbed N and O atoms is observed. At low NO coverage, a different NO molecular species (α1–NO), characterized by ≈1.7 eV lower N1s binding energy, is detected on Rh(100). α1–NO is observed to undergo dissociation under the photon beam. The N1s line shape modifications due to irradiation by 500 eV photons were monitored in real time by using fast photoemission. The different stability of the α1–NO and α2–NO species is discussed.
Coupling characteristics of localized phonons in photonic crystal fibers
Authors: Khelif A. , Djafari-Rouhani B. , Laude V. , Solal M.
Published: December 2003

Photonic crystal fibers are candidates for enhanced elasto-optical interactions. The acoustic properties of such structures are investigated theoretically by the finite-difference time-domain method, and a full acoustic band gap is found. The transmission spectrum of acoustic waves through a photonic crystal fiber containing one or two coupled cavities is found to be very sensitive to the geometrical and physical parameters of the structure, as well as to the relative position of the two defects.
Electrical reliability of tunneling magnetoresistive read heads
Authors: Bae Seongtae , Judy Jack H. , Tsu I-Fei , Davis Marshall
Published: December 2003

The electrical reliability of tunneling magnetoresistive (TMR) read heads has been studied in terms of dielectric breakdown characteristics of tunnel barrier and electrical failures under constant biasing current. The TMR read heads showed both “intrinsic breakdown” characteristics, which is caused by the high electric field, and “extrinsic breakdown” characteristics, which is caused by defects or pinhole-induced breakdown especially in a very thin dielectric layer. The dielectric breakdown voltage (Vbd) of real TMR read head is revealed to be strongly dependent on the duration of the applied voltage step (or applied voltage ramping speed), the initial junction resistance (R×A, A: Junction area) related to pinholes in a dielectric tunnel barrier, the tunnel barrier thickness, the ambient substrate temperature during breakdown test, and the applied voltage polarities. Different from typical metallic giant magnetoresistive spin-valve read heads, TMR read heads have a weaker reliability on sensing current density and exhibit two types of electrical failures: (1) Electrical short induced by tunnel barrier breakdown, and (2) electrical open induced by possible void formation in the metallic layers, which are used for free and pinned layers in exchange biased TMR read heads. The quasi-static transfer curves of head gimble assemble TMR read head was measured under various biasing currents. Transfer curve exhibited a strong dependence on the number of measurements above the threshold bias current, which is considered to be due to the current-induced voltage breakdown in the tunnel barrier.
Interfacial slip on a transverse-shear mode acoustic wave device
Authors: Ellis Jonathan S. , Hayward Gordon L.
Published: December 2003

This article describes a mathematical relationship between the slip parameter α and the slip length b for a slip boundary condition applied to the transverse-shear model for a quartz-crystal acoustic wave device. The theory presented here reduces empirical determination of slip to a one-parameter fit. It shows that the magnitude and phase of the slip parameter, which describes the relative motion of the surface and liquid in the transverse-shear model, can be linked to the slip length. Furthermore, the magnitude and phase of the slip parameter are shown to depend on one another. An experiment is described to compare the effects of liquid-surface affinity on the resonant properties of a transverse-shear mode wave device by applying different polar and nonpolar liquids to surfaces of different polarity. The theory is validated with slip values determined from the transverse-shear model and compared to slip length values from literature. Agreement with literature values of slip length is within one order of magnitude.
Formation and electric property measurement of nanosized patterns of tantalum oxide by current sensing atomic force microscope
Authors: Kim Young-ho , Zhao Jianwei , Uosaki Kohei
Published: December 2003

Nanosized patterns of tantalum oxide were fabricated on a tantalum substrate by applying a potential pulse utilizing current sensing atomic force microscopy (CSAFM). The dimensions of the dots were strongly dependent on the bias applied, scan rate, and potential pulse duration. By controlling these variables, the minimum size nanodots with full width at half maximum of 35 nm was achieved. Immediately after pattern formation, the electrical properties of the Ta oxide nanodots were measured using CSAFM. The charge transport at the CSAFM tip and the nanosized Ta oxide dot can be described by Poole–Frenkel type conduction. The relative dielectric constant of the nanosized Ta2O5 dots was calculated to be 17.8–24.3, showing that the quality of the oxide was high. In addition, by controlling the substrate bias applied, pulse duration, and tip scan speed, nanosized Ta oxide lines with the desired dimensions were prepared.
Structural study of self-assembled Co nanoparticles
Authors: Chushkin Y. , Ulmeanu M. , Luby S. , Majkova E. , Kostic I. , Klang P. , Holý V. , Bochnı́ček Z. , Giersig M. , Hilgendorff M. , Metzger T. H.
Published: December 2003

We studied the ordering of colloidal Co nanoparticles on various types of substrates by grazing-incidence small-angle x-ray scattering, transmission electron microscopy, and scanning electron microscopy. Particles of 5–6 nm radius were deposited by spin coating in order to obtain uniform distribution of the particles over a large surface area. Only by the grazing-incidence small angle x-ray scattering technique could the distribution of particles on a large surface area be analyzed in detail. For quantitative analysis of the spectra the distorted-wave Born approximation approach was applied. From simulations of the spectra the particle radius, the spherical shape, the mean spacing between the particles, and the type of ordering were determined. The distribution of the particles on the surface can be described by a hexagonal close-packed structure with local order. This corresponds to the transmission electron microscopy data obtained for the same type of substrate. The parameters that affect the ordering of Co nanoparticles are discussed.
Improving the coherence of a low-energy electron beam by modulation
Authors: Pesty F. , Garoche P.
Published: December 2003

In a standard low-energy electron generator the beam is formed by particles traveling close to the axis of symmetry. However some electron trajectories are unstable and strongly dependent on the initial conditions. Numerical ray tracing shows that ultimate beam coherence is limited by these trajectories that pass far from the symmetry axis. This contribution can be partly eliminated by modulating the initial conditions and selecting the modulated response. This is exemplified with a low-energy electron beam used for electron diffraction, where the beam current modulation produces a modulated diffraction pattern that displays noteworthy improvement (sevenfold) in wave vector resolution.
Photoemission investigation of the electronic structure of lanthanum–calcium oxoborate
Authors: Nelson A. J. , Adams J. J. , Schaffers K. I.
Published: December 2003

Lanthanum calcium oxoborate is a nonlinear optical material that belongs to the calcium-rare-earth (R) oxoborate family, with general composition of Ca4RO(BO3)3 (R3+=La,Sm,Gd,Lu,Y). X-ray photoemission was used to study the valence band electronic structure and surface chemistry of this material. High resolution photoemission measurements of the valence band electronic structure and La 3d and 4d, Ca 2p, B 1s, and O 1s core lines were used to evaluate the surface and near surface chemistry. The results provide measurements of the valence band electronic structure and surface chemistry of this rare-earth oxoborate.
Structural evolution in Ar+ implanted Si-rich silicon oxide
Authors: Brusa R. S. , Karwasz G. P. , Mariotto G. , Zecca A. , Ferragut R. , Folegati P. , Dupasquier A. , Ottaviani G. , Tonini R.
Published: December 2003

Silicon-rich silicon oxide films were deposited by plasma-enhanced chemical vapor deposition. Energy was released into the film by ion bombardment, with the aim of promoting formation of Si nanoclusters and reordering the oxide matrix. The effect of the initial stoichiometry, as well as the evolution of the oxide films due to the ion bombardment and to subsequent thermal treatments, has been studied by depth-resolved positron annihilation Doppler spectroscopy, Raman scattering and Fourier transform infrared spectroscopy. As-deposited films were found to contain an open volume fraction in the form of subnanometric cavities that are positively correlated with oxygen deficiency. No Si aggregates were observed. The ion bombardment was found to promote the formation of amorphous Si nanoclusters, together with a reduction of the open volume in the matrix and a substantial release of hydrogen. It also leaves electrically active sites in the oxide and produces gas-filled vacancy defects in the substrate, with the concentrations depending on the implantation temperature. Thermal treatment at 500 °C removes charge defects in the oxide, but vacancy defects are not completely annealed even at 1100 °C. In one case, heating at 1100 °C produced cavities of about 0.6 nm in the oxide. Transformation of Si nanoclusters into nanocrystals is observed to occur from 800 °C.