bluuebunny/crossref_metadata_2025 huggingface dataset:
Blue second harmonic generation from aluminum nitride films deposited onto silicon by sputtering technique
Authors: Larciprete M. C. , Bosco A. , Belardini A. , Li Voti R. , Leahu G. , Sibilia C. , Fazio E. , Ostuni R. , Bertolotti M. , Passaseo A. , Potì B. , Del Prete Z.
Published: August 2006

We studied the second order optical nonlinearity of aluminum nitride films grown by sputtering onto silicon substrates. The crystalline properties of the films were investigated by x-ray diffraction measurements. Preliminary linear optical characterization of the films was carried out by spectrophotometric optical reflectance measurements at different incidence angles; thus the dispersion laws for both ordinary and extraordinary refractive indices were retrieved. Finally, second harmonic generation measurements in reflection mode were performed at a fixed angle from a fundamental beam provided by a picosecond Ti:sapphire laser system at λ=800nm. In the experiments a high blue light conversion efficiency was found for samples 1.5 and 2μm thick, and the second order nonlinear coefficient d33=11±1pm∕V was found.
Acridine orange base as a dopant for n doping of C60 thin films
Authors: Li Fenghong , Pfeiffer Martin , Werner Ansgar , Harada Kentaro , Leo Karl , Hayashi Naoki , Seki Kazuhiko , Liu Xianjie , Dang Xuan-Dung
Published: August 2006

We present a study on n doping of C60 thin films by acridine orange base [3,6-bis(dimethylamino)acridine(AOB)] combining conductivity, field effect, and Seebeck measurements. An increase of more than six orders of magnitude in conductivity is observed for a doping ratio of 6mol%, accompanied by a decrease in the activation energy from 0.64to0.15eV compared to the undoped C60. We observe a clear doping effect immediately after sample preparation, but also a further activation by annealing or illumination. The field effect and Seebeck measurements confirm n-type conduction of C60 thin films and show that deep donor states are formed in AOB-doped C60 thin films. A field effect mobility of 0.2cm2∕Vs is achieved for a doping level of 1.8mol%. Near Infrared (NIR) and Fourier transform infrared (FTIR) spectra demonstrate electron transfer from the dopant to the matrix: For C60 doped with AOB, C60− is present in NIR absorption and FTIR spectra. On the other hand, a peak corresponding to acridine orange [3,6-bis(dimethylamino)acridinium chloride (AOBH+)] is also observed in the FTIR spectrum of C60:AOB, where AOBH+ corresponds to AOB with one additional proton attached. Electrochemical data of AOB and AOBH+ in acetontrile suggest that the AOB radical cation is not stable, but is rapidly transformed into a compound with similar properties to AOBH+. Conductivities of C60 thin films doped with bis(ethylenedithio)-tetrathiafulvalene were also investigated to confirm that the doping effect of AOB in C60 does not result from a simple electron transfer from AOB to C60.
Superconductivity and the disorder effect in Ag and Al double doped MgB2
Authors: Shi Lei , Zhang Huarong , Zhou Shiming , Zhao Jiyin , Zuo Jian
Published: August 2006

A series of polycrystalline bulk samples of Mg1−2x(AgAl)xB2 (0.0%⩽x⩽1.0%) has been synthesized by a solid state reaction method. The structure, Raman spectrum, and superconducting properties have been investigated by x-ray diffraction, Raman spectroscopy, and low-temperature resistivity measurements. It is found that the Ag, Al double doping causes the expansion of crystal lattice along the a- and c-axis orientations due to the substitution inducing ionic size variation. A redshift of peak position is observed in Raman spectra, which is ascribed to the crystal cell volume change inducing the variation of the phonon frequency. The superconducting transition temperature (Tc) is degressive with the doping level (x) increase. By the Ag and Al double doping, the hole concentration is kept to be unchanged in MgB2, which eliminates the effects of the charge carrier concentration change and band filling on Tc. It is suggested that the reason of the Tc suppression caused by the double doping is the co-operating results of the disorder effect and the chemical pressure effect induced by the chemical substitution.
Formation of a pitchfork bifurcation in thermal convection flow inside an isosceles triangular cavity
Authors: Ridouane El Hassan , Campo Antonio
Published: August 2006

Transient, laminar thermal convection of air confined to an isosceles triangular cavity heated from the base and symmetrically cooled from the upper inclined walls has been investigated numerically. The system of conservation equations, subject to the proper boundary conditions, along with the equation of state assuming the air behaves as a perfect gas are solved with the finite volume method. In the conservation equations, the second-order-accurate QUICK scheme was used for the discretization of the convective terms and the SIMPLE scheme for the pressure-velocity coupling. The maximum height-to-base aspect ratio A is fixed at 0.5, while the Grashof number extends from a low Gr=103 to a high Gr=106. The influence of Gr on the flow and temperature patterns is analyzed and discussed for two opposing scenarios, one corresponding to increasing Gr and the other corresponding to decreasing Gr. It is found that two steady-state solutions are possible, excluding their solution images through a vertical mirror plane. The symmetrical solution prevails for relatively low Grashof numbers. However, as the Gr is gradually increased, a transition occurs at a critical value of Gr. Above this critical value of Gr, an asymmetrical solution exhibiting a pitchfork bifurcation arises and eventually becomes steady. The existing ranges of these unsteady and steady solutions are reported for the two opposing scenarios. Also, issues related to the observed hysteresis phenomenon are discussed in detail.
High frequency magnetic excitations in patterned NiFe∕Cu∕NiFe trilayered stripes subjected to a transverse magnetic field
Authors: Gubbiotti G. , Carlotti G. , Ono T. , Roussigne Y.
Published: August 2006

An experimental and theoretical investigation of the high frequency dynamical properties of trilayered stripes (700nm wide) subjected to an in-plane transverse magnetic field is presented. Stripes were obtained from both asymmetric NiFe(10nm)∕Cu(10nm)∕NiFe(30nm) and symmetric NiFe(30nm)∕Cu(10nm)∕NiFe(30nm) trilayers. Brillouin light scattering from spin waves has been exploited to study the spin mode excitations of these specimens. Several well resolved peaks have been observed in the spectra. These correspond to both localized and quantized spin mode excitations. Their field dependence has been measured as a function of the magnetic field intensity and compared to the theoretical curves, calculated by a micromagnetic numerical model, achieving a good agreement between experiment and theory. In particular, the mode softenings observed at certain values of the external applied field have been related to the cancellation of the static magnetization component along the wire.
Fickian crossover and length scales from two point functions in supercooled liquids
Authors: Stariolo Daniel A. , Fabricius Gabriel
Published: August 2006

Particle motion of a Lennard-Jones supercooled liquid near the glass transition is studied by molecular dynamics simulations. We analyze the wave vector dependence of relaxation times in the incoherent self-scattering function and show that at least three different regimes can be identified and its scaling properties determined. The transition from one regime to another happens at characteristic length scales. The length scale associated with the onset of Fickian diffusion corresponds to the maximum size of heterogeneities in the system, and the characteristic time scale is several times larger than the alpha relaxation time. A second crossover length scale is observed, which corresponds to the typical time and length of heterogeneities, in agreement with results from four point functions. The different regimes can be traced back to the behavior of the van Hove distribution of displacements, which shows a characteristic exponential regime in the heterogeneous region before the crossover to Gaussian diffusion and should be observable in experiments. Our results show that it is possible to obtain characteristic length scales of heterogeneities through the computation of two point functions at different times.
Vortical source-sink flow against a wall: The initial value problem and exact steady states
Authors: Johnson E. R. , McDonald N. R.
Published: August 2006

Fluid of uniform vorticity is expelled from a line source against a wall. An exact analytical solution is obtained for the nonlinear problem determining the final steady state. Sufficiently close to the source, the flow is irrotational and isotropic, turning on the vortical scale Q∕ω (for area flux Q and vorticity ω) to travel along the wall to the right (for ω>0). The flow is linearly stable with perturbations propagating unattenuated along the interface between vortical and irrotational fluid. Fully nonlinear numerical integrations of the time-dependent equations of motion show that flow started from rest does indeed closely approach the steady state. Similar exact steady solutions are obtained for a vortical source-sink pair and vortical source doublet against a wall. Time-dependent integrations show that the steady state is unchanged at arbitrarily large times for sufficiently small disturbances but is disrupted by finite perturbations.
Analysis of coupled mass transfer and sol-gel reaction in a two-phase system
Authors: Castelijns H. J. , Huinink H. P. , Pel L. , Zitha P. L. J.
Published: August 2006

The coupled mass transfer and chemical reactions of a gel-forming compound in a two-phase system were studied in detail. Tetra-methyl-ortho-silicate (TMOS) is often used as a precursor in sol-gel chemistry to produce silica gels in aqueous systems. TMOS can also be mixed with many hydrocarbons without chemical reaction, which allows for various applications in multiphase systems. In this study, TMOS was mixed with n-hexadecane and placed together with water in small cylinders. Upon contact of the mixture with the water, TMOS transfers completely to the aqueous phase where it forms a gel through a heterogeneous reaction. Nuclear magnetic resonance imaging and relaxation time measurements were employed to monitor the mass transfer of TMOS from the oleic to the aqueous phase. The longitudinal relaxation time (T1) was calibrated and used to determine the concentration of TMOS in n-hexadecane during the transfer. The mass transfer rate was obtained at various temperatures (25–45°C) and for several initial concentrations of TMOS. In the aqueous phase a sharp decrease in the transversal relaxation time (T2) is observed which is attributed to the gel reaction, in particular the formation of methanol in the initial stage. The minimum in T2 indicates the gelation point, and was found to be strongly dependent on temperature and concentration.
Quantitative magnetic force microscopy analysis of the magnetization process in nanowire arrays
Authors: Asenjo A. , Jaafar M. , Navas D. , Vázquez M.
Published: August 2006

Magnetic force microscopy (MFM) imaging is a useful technique to locally study the magnetic state of nanostructures. In this paper, we have used the MFM to characterize an ordered array of Ni nanowires embedded in porous membrane. Due to the large aspect ratio of the wires (30nm diameter and 1000nm length) they present an axial easy axis. Considering the nanowires as nearly single-domain structures and calculating the amount of wires pointing to each direction, we can obtain the average magnetization. An alternative method to analyze the MFM data is here introduced considering the distribution functions of magnetic contrast. By using this method, the magnetization process of the nanowire array is studied and the results are compared with major and minor hysteresis loops measured by superconducting quantum interference device magnetometer.
High resolution laser induced fluorescence spectroscopy of the [18.8]Φi3−XΦi3 (0,0) band of cobalt monofluoride
Authors: Steimle Timothy C. , Ma Tongmei , Adam Allan G. , Hamilton William D. , Merer Anthony J.
Published: August 2006

The fine and hyperfine interaction parameters in the [18.8]Φ3 (υ=0) and XΦ3 (υ=0) states of cobalt monofluoride, CoF, have been determined from an analysis of high-resolution laser induced fluorescence spectra of the [18.8]Φ33−XΦ33 and [18.8]Φ43−XΦ43 band systems. The previously reported pure rotational transitions of the XΦ43(υ=0) state [T. Okabayashi and M. Tanimoto, J. Mol. Spectrosc. 221, 149 (2003)] were included in the data set. The hyperfine parameters for Co59 (I=7∕2) and F19 (I=1∕2) have been interpreted using atomic data together with a proposed molecular orbital description for the [18.8]Φi3 and XΦi3 states. A comparison of the hyperfine parameters in the XΦ3 state of cobalt monohydride, CoH, with those of the XΦ3 state of CoF reveals that the bonding in the two molecules is significantly different. It is shown that, in a situation where the Ω substates of a multiplet degenerate electronic state are analyzed separately, the Fermi contact parameter b can be determined with fair accuracy from the apparent centrifugal distortion of the hyperfine structure.
Linear stability of ice growth under a gravity-driven water film
Authors: Shapiro Evgeniy , Timoshin Sergei
Published: August 2006

In this paper we consider linear stability of ice growth under a gravity-driven water film on a sloping wall. First, we derive an analytic solution of the stability problem in the long-wave limit, which shows that the presence of the ice layer generates an additional wave mode. Further, using a long-wave solution as an initial guess, we find the additional wave mode in the numerical solution of the complete Orr-Sommerfeld problem and investigate its behavior numerically for a wide range of problem parameters. We show that the ice mode can become unstable even at moderate Reynolds numbers, and that the ice layer alters the behavior of the mode corresponding to the waves on the liquid film surface. We also demonstrate that the presence of the ice layer stabilizes wave disturbances on the water surface and that, depending on the angle of the incline, the critical Reynolds number of the surface mode can be either increased or decreased.
Numerical simulations of the interaction of internal waves with a shelf break
Authors: Venayagamoorthy S. K. , Fringer O. B.
Published: August 2006

The energetics of the interaction of internal gravity waves with a shelf break is investigated by means of high-resolution two-dimensional numerical simulations, with an emphasis on understanding the partitioning of the internal wave energy over the course of the interaction process and the subsequent dynamics of the onshore propagating internal waves. Some of the energy is dissipated as a result of the instabilities associated with breaking, while the remaining energy is either reflected back away from or transmitted onto the shelf. We employ an analysis of the distribution of the energy flux across the shelf break taking into account the contributions from nonhydrostatic as well as nonlinear effects to quantify the percentage of energy flux that is transmitted onto the shelf, as well as the percentages of reflected and dissipated energy fluxes, from an incoming wave field. For a given frequency of an incoming wave, we vary the amplitude of the wave to vary the incident energy flux, and we simulate conditions ranging from subcritical to supercritical slopes by varying the topographic slope angle. The results show that the cumulative transmitted energy flux is a strong function of the ratio of the topographic slope γ, to wave characteristic slope s, while the reflected energy flux is a strong function of both γ∕s as well as the nonlinearity. The energy flux calculations indicate that the internal boluses that form as a result of the interaction of the incident wave with the slope are very energetic, especially for critical to supercritical slopes. These nonlinear internal waves are plausible candidates for effectively transporting mass onshore, not withstanding their contribution to diapycnal mixing as well.
Chemical-free synthesis of electrically connected gold nanotubes/nanoparticles from solution-infiltrated anodized aluminum oxide template
Authors: Lee Myungsoon , Hong Seongcheol , Kim Don
Published: August 2006

Gold nanotubes/nanoparticles are synthesized by two-step thermal decomposition of HAuCl4 infiltrated into anodized aluminum oxide (AAO) membrane without any catalysts, reducing agents, or surfactants. The Au nanotubes deposited in AAO nanochannel (60nm in diameter) are composed of single crystalline Au nanoparticles (10±2nm in diameter). The Au nanotubes are electrically conducting with an apparent electrical resistivity of 3.9Ωcm, which was about 106 times larger than that of the bulk metal, 2.2×10−6Ωcm, at room temperature.
Gate-metal formation-related kink effect and gate current on In0.5Al0.5As∕In0.5Ga0.5As metamorphic high electron mobility transistor performance
Authors: Hsu M. K. , Chen H. R. , Chiou S. Y. , Chen W. T. , Chen G. H. , Chang Y. C. , Lour W. S.
Published: August 2006

In 0.5 Ga 0.5 As ∕ In 0.5 Al 0.5 As metamorphic high electron mobility transistos were fabricated with different gate-metal formations: mesa type or air type and without or with a buried gate. Only air-type devices with a buried gate show no kink effect. Experimental results indicate that gate-feeder metal and annealing process give effects on gate current and noise figure. The peak gate current of 12 (120)μA∕mm for air-type (mesa-type) devices before annealing is improved to 8 (55)μA∕mm after annealing. At 1.8GHz, associated gain of 25dB is obtained at Fmin=1.24dB for air-type devices after annealing, while 23dB is obtained at Fmin=1.25dB before annealing.
Nonlinear dynamics of a two-dimensional viscous drop under shear flow
Authors: Zhang J. , Miksis M. J. , Bankoff S. G.
Published: August 2006

The dynamics of a viscous drop moving along a substrate under the influence of shear flow in a parallel-walled channel is investigated. A front tracking numerical method is used to simulate a drop with moving contact lines. A Navier slip boundary condition is applied to relax the contact line singularity. Steady state solutions are observed for small Reynolds and capillary number. Unsteady solutions are obtained with increasing Reynolds or capillary number. For large values of the parameters, the interface appears to rupture, but for intermediate parameter values, time periodic drop interface oscillations are possible as the drop is moving along the bottom channel wall. These different states are identified in the Reynolds number–capillary number plane for a specific range of physical parameters. The effects of density and viscosity ratio are also illustrated.
The electronic ground-state energy problem: A new reduced density matrix approach
Authors: Cancès Eric , Stoltz Gabriel , Lewin Mathieu
Published: August 2006

We present here a formulation of the electronic ground-state energy in terms of the second order reduced density matrix, using a duality argument. It is shown that the computation of the ground-state energy reduces to the search of the projection of some two-electron reduced Hamiltonian on the dual cone of N-representability conditions. Some numerical results validate the approach, both for equilibrium geometries and for the dissociation curve of N2.
Dissociative electron attachment to furan, tetrahydrofuran, and fructose
Authors: Sulzer Philipp , Ptasinska Sylwia , Zappa Fabio , Mielewska Brygida , Milosavljevic Alexandar R. , Scheier Paul , Märk Tilmann D. , Bald Ilko , Gohlke Sascha , Huels Michael A. , Illenberger Eugen
Published: August 2006

We study dissociative electron attachment to furan (FN) (C4H4O), tetrahydrofuran (THF) (C4H8O), and fructose (FRU) (C6H12O6) using crossed electron/molecular beams experiments with mass spectrometric detection of the anions. We find that FN and THF are weak electron scavengers and subjected to dissociative electron attachment essentially in the energy range above 5.5eV via core excited resonances. In striking contrast to that, FRU is very sensitive towards low energy electrons generating a variety of fragment ions via a pronounced low energy feature close to 0eV. These reactions are associated with the degradation of the ring structure and demonstrate that THF cannot be used as surrogate to model deoxyribose in DNA with respect to the attack of electrons at subexcitation energies (<3eV). The results support the picture that in DNA the sugar moiety itself is an active part in the initial molecular processes leading to single strand breaks.
Mass transfer to reactive boundaries from steady three-dimensional flows in microchannels
Authors: Kirtland Joseph D. , McGraw Gregory J. , Stroock Abraham D.
Published: August 2006

This paper presents a numerical study of the effect of transverse secondary flows on mass transfer to reactive boundaries in microchannels. The geometry considered is relevant to surface catalyzed reactions, fuel cells, biochemical sensors, and other microreactor applications. The 3D flows that we consider approximate flows that are experimentally achievable through topographical patterning of one wall of a microchannel, as in the Staggered Herringbone Mixer (SHM) and similar geometries. We simulate a mass transfer process using passive tracers to model reactive solute molecules in a Stokes flow (Reynolds number, Re=0) over a range of Péclet number, 102⩽Pe⩽105, with instantaneous kinetics at the reactive boundary. Our simulation allows for the evaluation of the local Sherwood number produced by a uniaxial Poiseuille flow and several chaotic and nonchaotic 3D flows. In chaotic flows, the local Sherwood number evolves in a simple manner that shares features with the classic Graetz solution for transfer from a uniaxial pipe flow: an entrance region with cube-root scaling in the Graetz number and a constant asymptotic value. This “Modified Graetz” behavior also differs in important ways from the standard case: the entrance length is Pe independent and the asymptotic rate of transfer is Pe dependent and potentially much greater than in the uniaxial case. We develop a theoretical model of the transfer process; the predictions of this model compare well with simulation results. We use our results to develop a correlation for the mass transfer in laminar channel flows, to elucidate the importance of chaos in defining transfer in these flows, and to provide design rules for microreactors with a single reactive wall.
Determination of energetics and kinetics from single-particle intermittency and ensemble-averaged fluorescence intensity decay of quantum dots
Authors: Tang Jau , Marcus R. A.
Published: August 2006

Quantification of energetics and kinetics for the band-edge exciton states of quantum dots and the long-lived dark state is important for better understanding of the underlying mechanism for single-particle intermittency and ensemble fluorescence intensity decay. Based on a multistate diffusion-reaction model by extending our previous studies, we analyze experimental data from ensemble measurements and fluorescence intermittency of single quantum dots and determine important molecular-based quantities such as Stokes shift, free energy gap, activation energy, reorganization energy, and other kinetic parameters.
Drop coalescence through planar surfaces
Authors: Aryafar H. , Kavehpour H. P.
Published: August 2006

A high-speed digital camera is used to investigate the important parameters of drop coalescence at a planar interface. A series of experiments have been performed to observe coalescing drops at the interface between two immiscible fluids. A variety of fluids have been used to fully investigate the effects of physical properties of fluids involved in this phenomenon. It has been shown that the important dimensionless parameter in this process is the Ohnesorge number, Oh=μ∕ρRσ, which dictates the regime of coalescence. We have also shown that for Oh>1, drops fully coalesce but when Oh<1, drops partially coalesce and a secondary drop is created. We show the dependence of the ratio of secondary drop radius to the primary drop on the regime of coalescence (inertia or viscous). Using the scaling arguments, we developed a relationship between the drop ratio and the Ohnesorge number that shows good agreement with our experimental results.
Initial stage of the overgrowth of InP on InAs∕InP(001) quantum dots: Formation of InP terraces driven by preferential nucleation on quantum dot edges
Authors: Saint-Girons G. , Patriarche G. , Michon A. , Beaudoin G. , Sagnes I. , Smaali K. , Troyon M.
Published: August 2006

This letter reports on the growth mechanism of the InP cap layer over InAs∕InP quantum dots (QDs) fabricated by metal organic vapor phase epitaxy (MOVPE). QD edges are shown to act as preferential nucleation sites for the InP cap layer, leading to the formation of InP domains around the nanostructures. As∕P exchange reactions are at the origin of the planarization of the top of the QDs under P-rich ambient, thus leading to a final QD height equal to the local thickness of the InP cap layer. The possibility to use As∕P exchange reactions to homogenize the height distribution of MOVPE grown InAs∕InP QDs is discussed on the basis of these observations.
High electrical conductivity of layered cobalt oxide Ca3Co4O9 epitaxial films grown by topotactic ion-exchange method
Authors: Sugiura Kenji , Ohta Hiromichi , Nomura Kenji , Hirano Masahiro , Hosono Hideo , Koumoto Kunihito
Published: August 2006

Epitaxial film of a layered cobalt oxide, Ca3Co4O9, was fabricated on a (0001) face of an α-Al2O3 substrate by a topotactic ion-exchange method using a γ-Na0.8CoO2 epitaxial film as a precursor. High-resolution x-ray diffraction and atomic force microscope measurements revealed that the film was high-quality (001)-oriented Ca3Co4O9 with stepped and terraced surface morphology. The film exhibits a high electrical conductivity of 2.95×102Scm−1 and a large Seebeck coefficient of ∼+125μVK−1, which leads to the thermoelectric power factor (TPF) of 4.5×10−4Wm−1K−2 at 300K, potentially usable as a building block of the multilayered film structure with an enhanced TPF value.
On the existence of Einstein oscillators and thermal conductivity in bulk metallic glass
Authors: Zhou Zhenhua , Uher Ctirad , Xu Donghua , Johnson W. L. , Gannon W. , Aronson M. C.
Published: August 2006

Low-temperature specific heat and thermal conductivity of bulk metallic glasses are measured to identify the primary vibrational modes associated with their unique structures. An Einstein-type localized vibrational mode with an Einstein temperature of 112K is found in bulk metallic glass Ni59.5Nb33.6Sn6.9. This localized vibrational mode causes resonant scattering of phonons and results in the localization of phonons which leaves the phonon hopping conduction the limiting mechanism of thermal transport in bulk metallic glass Ni59.5Nb33.6Sn6.9 at high temperature.
Exchange biasing and electric polarization with YMnO3
Authors: Martí X. , Sánchez F. , Hrabovsky D. , Fàbrega L. , Ruyter A. , Fontcuberta J. , Laukhin V. , Skumryev V. , García-Cuenca M. V. , Ferrater C. , Varela M. , Vilà A. , Lüders U. , Bobo J. F.
Published: August 2006

We report on the growth and functional characterizations of epitaxial thin films of the multiferroic YMnO3. We show that using Pt as a seed layer on SrTiO3(111) substrates, epitaxial YMnO3 films (0001) textured are obtained. An atomic force microscope has been used to polarize electric domains revealing the ferroelectric nature of the film. When a Permalloy layer is grown on top of the YMnO3(0001) film, clear indications of exchange bias and enhanced coercivity are observed at low temperature. The observation of coexisting antiferromagnetism and electrical polarization suggests that the biferroic character of YMnO3 can be exploited in novel devices.
Effective work function modification of atomic-layer-deposited-TaN film by capping layer
Authors: Choi K. , Alshareef H. N. , Wen H. C. , Harris H. , Luan H. , Senzaki Y. , Lysaght P. , Majhi P. , Lee B. H.
Published: August 2006

We demonstrate that the metallic capping layer has a strong impact on the effective work function (EWF) of the metal gate. Specifically, the EWF of atomic-layer-deposited (ALD)-TaN could be increased from 4.5to4.8eV with chemical-vapor-deposited-TiN capping, which is sufficient amount of work function modification for silicon on insulator based devices. A strong interdiffusion of Ti atoms into the ALD-TaN film is observed and correlated well with the changes in the EWF change. Ti capping experiments confirm that the Ti interdiffusion can actually modify the EWF of Ti/ALD-TaN stack.
Elastic modulus of polystyrene film from near surface to bulk measured by nanoindentation using atomic force microscopy
Authors: Miyake Koji , Satomi Noriaki , Sasaki Shinya
Published: August 2006

Using atomic force microscopy with a spherical indenter, we evaluated the surface and bulk elastic modulus of thick and thin polystyrene films. The elastic modulus of the thick films at penetration depths of more than 10nm was equivalent to that of bulk measured by a tensile test. In the thin films, the estimated values were greatly affected by the substrate material at penetration depths of more than 7nm. When the penetration depth was less than 5nm, however, the elastic modulus of both thin and thick films was slightly smaller than that of the bulk values.
III-nitride transistors with capacitively coupled contacts
Authors: Simin G. , Yang Z.-J. , Koudymov A. , Adivarahan V. , Yang J. , Asif Khan M.
Published: August 2006

Al Ga N ∕ Ga N heterostructure field-effect transistor design using capacitively coupled contacts (C3HFET) is presented. Insulated-gate [C3 metal-oxide-semiconductor HFET (C3MOSHFET)] has also been realized. The capacitively coupled source, gate, and drain of C3 device do not require annealed Ohmic contacts and can be fabricated using gate alignment-free technology. For typical AlGaN∕GaN heterostructures, the equivalent contact resistance of C3 transistors is below 0.6Ωmm. In rf-control applications, the C3HFET and especially the C3MOSHFET have much higher operating rf powers as compared to HFETs. C3 design is instrumental for studying the two-dimensional electron gas transport in other wide band gap heterostructures such as AlN∕GaN, diamond, etc., where Ohmic contact fabrication is difficult.
Low-voltage and high-gain pentacene inverters with plasma-enhanced atomic-layer-deposited gate dielectrics
Authors: Koo Jae Bon , Yun Sun Jin , Lim Jung Wook , Kim Seong Hyun , Ku Chan Hoe , Lim Sang Chul , Lee Jung Hun , Zyung Taehyoung
Published: August 2006

The pentacene thin-film transistors with the plasma-enhanced atomic-layer-deposited 150nm thick Al2O3 or 120nm thick ZrO2 have been operated at gate voltages between −3 and 3V. The inverter with a ZrO2 gate dielectric shows a gain of 49 and a full swing from supply voltage (Vdd) to 0V, operating at input voltages (Vin) from 0to−1V and at Vdd of −1V. The hysteresis observed in the voltage transfer characteristic of the inverter depends on the scan range of Vin applied to the driver transistor, regardless of the Vdd applied to the load transistor.
Defect reduction in nonpolar a-plane GaN films using in situ SiNx nanomask
Authors: Chakraborty Arpan , Kim K. C. , Wu F. , Speck J. S. , DenBaars S. P. , Mishra U. K.
Published: August 2006

We report on the use of in-situ SiNx nanomask for defect reduction in nonpolar a-plane GaN films, grown by metal-organic chemical vapor deposition. High-resolution x-ray diffraction analysis revealed that there was a monotonic reduction in the full width at half maximum, both on-axis and off-axis, with the increase in the SiNx thickness. Atomic force microscopy images revealed a significant decrease in the root-mean-square roughness and the density of submicron pits. Cross-section and plan-view transmission electron microscopy on the samples showed that the stacking fault density decreased from 8×105to3×105cm−1 and threading dislocation density decreased from 8×1010to9×109cm−2. Room temperature photoluminescence measurement revealed that the band-edge emission intensity increased with the insertion of the SiNx layer, which suggests reduction in the nonradiative recombination centers.
Ultrafast-laser-induced parallel phase-change nanolithography
Authors: Lin Y. , Hong M. H. , Chong T. C. , Lim C. S. , Chen G. X. , Tan L. S. , Wang Z. B. , Shi L. P.
Published: August 2006

A phase-change nanolithography technique is developed to fabricate up to millions of two-/three-dimensional nanostructures (∼50nm) over a large area at a high speed by combining femtosecond laser, microlens array, and wet etching process. Near-field scanning optical microscopy, electrical force microscopy, and atomic force microscopy were used to characterize optical and electrical properties of crystalline and amorphous states, respectively. Different reactions of both amorphous and crystalline areas in phase-change film to alkaline solution are demonstrated. Multiphoton absorption and ultrashort pulse contribute to nanostructure generation. This method opens up a route for nanodevice fabrication with phase-change material.
Effect of doping and disorder on the half metallicity of full Heusler alloys
Authors: Galanakis I. , Özdoğan K. , Aktaş B. , Şaşıoğlu E.
Published: August 2006

Heusler alloys containing Co and Mn are amongst the most heavily studied half metallic ferromagnets for future applications in spintronics. Using state-of-the-art electronic structure calculations, we investigate the effect of doping and disorder on their electronic and magnetic properties. Small degrees of doping by substituting Fe or Cr for Mn scarcely affect the half metallicity. A similar effect is also achieved by mixing the sublattices occupied by the Mn and sp atoms. Thus the half metallicity is a robust property of these alloys.
Soft x-ray spectra from laser heated lithium targets
Authors: Nica Petru-Edward , Miyamoto Shuji , Amano Sho , Inoue Takahiro , Shimoura Atsusi , Kaku Kakyo , Mochizuki Takayasu
Published: August 2006

The extreme ultraviolet emission characteristics of laser-produced lithium plasma are experimentally and theoretically investigated. Taking into account the target oxidation, the ion fractional populations are analyzed and the averaged plasma parameters are obtained. Theoretical results show an insignificant influence of oxygen on the temperature dependence of the lithium ion fractional number. A comparison between the theoretical spectrum for stationary and homogenous plasma and experiments shows a reasonable agreement.
Twist angle effects on the dynamic response of in-plane-switching liquid crystal displays
Authors: Sun Yubao , Ma Hongmei , Zhang Zhidong , Zhu Xinyu , Wu Shin-Tson
Published: August 2006

Twist angle effects on the response time of in-plane-switching liquid crystal displays are analyzed. The authors propose a device configuration whose top and bottom boundary liquid crystal layers are symmetric to each other with respect to the electric field direction. The analytical results of this device configuration indicate that the response time is improved at least four times faster than that of a conventional in-plane-switching twisted-nematic mode and normal in-plane-switching mode.
Improved light outcoupling for top-emitting organic light-emitting devices
Authors: Chen Shufen , Jie Zhonghai , Zhao Zhenyuan , Cheng Gang , Wu Zhijun , Zhao Yi , Quan Baofu , Liu Shiyong , Li Xue , Xie Wenfa
Published: August 2006

Light outcoupling for the top-emitting organic light-emitting device (TEOLED) with the structure of Si∕SiO2∕Ag∕Ag2O∕4,4′, 4″-tris(3-methylphenylphenylamino)triphenylamine/4, 4′-bis[N-(1-naphthyl-1-)-N-phenyl-amino]-biphenyl/tris-(8-hydroxyquinoline) aluminum (Alq3)∕LiF∕Al∕Ag is improved by optimizing the semitransparent Al∕Ag cathode and employing a ZnS top-capping layer. To both provide a fine electron injection and reduce Al absorption in the visible area, Al thickness is adjusted to 0.3nm. With another 32-nm-thick ZnS film as a refractive index-matching layer onto the optimized Al (0.3nm)∕Ag (18nm) electrode, the maximum luminance and efficiency for the TEOLED based on Alq3 emission reach 145474cd∕m2 (13V) and 12.2cd∕A (5V), respectively.
Identification of acceptor states in Li-doped p-type ZnO thin films
Authors: Zeng Y. J. , Ye Z. Z. , Lu J. G. , Xu W. Z. , Zhu L. P. , Zhao B. H. , Limpijumnong Sukit
Published: August 2006

We investigate photoluminescence from reproducible Li-doped p-type ZnO thin films prepared by dc reactive magnetron sputtering. The LiZn acceptor state, with an energy level located at 150meV above the valence band maximum, is identified from free-to-neutral-acceptor transitions. Another deeper acceptor state located at 250meV emerges with the increased Li concentration. A broad emission centered at 2.96eV is attributed to a donor-acceptor pair recombination involving zinc vacancy. In addition, two chemical bonding states of Li, evident in x-ray photoelectron spectroscopy, are probably associated with the two acceptor states observed.
Influence of AlN layers on the interface stability of HfO2 gate dielectric stacks
Authors: Agustin Melody P. , Alshareef Husam , Quevedo-Lopez Manuel A. , Stemmer Susanne
Published: August 2006

The influence of thick (∼10nm) AlN overlayers on the interface structure and reactions in Si gate stacks with HfO2 dielectrics was investigated. Annealing caused a reduction of the interfacial SiO2 at the Si interface. At high temperatures (∼1000°C) a silicide reaction was observed at the HfO2∕Si interface. No reactions were observed for stacks processed similarly but with WN or TiN overlayers instead of AlN. The reaction mechanisms, in particular, the role of oxygen deficiency of the HfO2, and the consequences for the electrical properties are discussed.
High capacity oxide/ferroelectric/oxide stacks for on-chip charge storage
Authors: Zhong S. , Alpay S. P. , Mantese J. V.
Published: August 2006

A thermodynamic model coupled with an electrostatic analysis of dielectric-ferroelectric-dielectric sandwich structures shows that high capacitance densities can be achieved when the total dielectric thickness reaches a critical fraction. For such cases, the induced polarization in the linear dielectrics (e.g., SiO2, Ta2O5, HfO2, Al2O3, and ZrO2) increases the overall permittivity until the internal electric field in the ferroelectric layer suppresses the spontaneous polarization of the ferroelectric. Beyond this critical fraction, the ferroelectric layer can no longer induce polarization in the dielectric layers. We specifically determine the critical fraction required for Ba1−xSrxTiO3 (0<x⩽0.2) and Pb1−xZrxTiO3 (0<x⩽0.5) solid solutions.
Femtosecond pulse excited two-photon photoluminescence and second harmonic generation in ZnO nanowires
Authors: Zhang C. F. , Dong Z. W. , You G. J. , Zhu R. Y. , Qian S. X. , Deng H. , Cheng H. , Wang J. C.
Published: August 2006

With femtosecond pulse excitation at the wavelength near 800nm, we observed three upconverted emission peaks from ZnO nanowires. The ultraviolet peak at about 385nm and the green emission band centered at about 515nm were attributed to the near band edge emission and defect level emission, respectively, while the intermediate peak was assigned to the second harmonic generation. From the quadratic dependence of the emission intensity on the excitation pulse energy, it is confirmed that the 385nm photoluminescence was mainly generated via two-photon absorption in ZnO nanowires under very intense light-matter interaction.
Thermal emission by metallic photonic crystal slabs
Authors: Wan Jones T. K. , Chan C. T.
Published: August 2006

Ordinary metallic photonic crystals have photonic band gaps, in which the density of states is strongly modified. Thermal emission of photons can be suppressed or enhanced accordingly. We consider that the thermal emission characteristics of metallic photonic crystal slab vary with different thicknesses, which in the thick limit approaches that of a photonic crystal and in the thin limit approaches that of a textured surface. We find that a thick tungsten photonic crystal suppresses emission in a specific range, while a thin slab suppresses low frequency emission.
Pulsed laser ablation of preferentially orientated ZnO:Co diluted magnetic semiconducting thin films on Si substrates
Authors: Zhang Y. B. , Liu Q. , Sritharan T. , Gan C. L. , Li S.
Published: August 2006

ZnO:Co thin films with room-temperature ferromagnetism have been synthesized on (001) Si substrates by pulsed laser deposition using a Zn0.95Co0.05O ceramic target. Single-phase wurtzite thin films with (002) preferential orientation were grown at 450°C in vacuum. There is no indication of Co nanocluster formation. However, copious edge dislocations appear to have formed during the film growth. A saturation magnetization of 1.04μB∕Co and a coercivity of 25Oe were obtained at room temperature. In addition to O vacancies, the Zn interstitial induced by edge dislocations may also contribute to the ferromagnetic properties in this oxide-diluted magnetic semiconductor.
One-dimensional organic giant dielectrics
Authors: Saha S. K. , Chakravorty D.
Published: August 2006

Organic dielectric gate in organic thin film transistor is a great challenge due to lack of suitable materials with high permittivity value. Here we report the observation of giant dielectric response (ε∼105) as a result of Gor’kov–Eliashberg effect in conducting polypyrrole nanorods synthesized by chemical route in nanoporus template. These nanorods are essentially comprised of metallic chain segments interrupted by chemical defects, cross-linking and entanglement of the chains. Dielectric modulus spectra of the samples show a (KWW) exponent β equal to 1. This unusual result is ascribed to the structural order in the metal segment of the aligned polypyrrole chain.
Extremely stable field emission from AlZnO nanowire arrays
Authors: Xue X. Y. , Li L. M. , Yu H. C. , Chen Y. J. , Wang Y. G. , Wang T. H.
Published: August 2006

Extremely stable electric field emission from well-aligned AlZnO nanowire arrays is realized. The emission current density is up to 6.5mA∕cm2, and no current saturation is observed. The turn-on field is 2.9V∕μm as d (distance between the nanowire emitters and anode) is 0.64mm. After aging for two days, the emission current is extremely stable with the fluctuations of±0.4%. The high stability arises from the high crystal quality with few surface states of the nanowires and the in situ fabrication of cathodes. The field emission behaviors are in excellent agreement with Fowler–Nordheim theory, and the relationship between the field enhancement factor β and d follows a universal equation. Our results imply that AlZnO nanowire arrays are promising candidates for field emission displays.
Strain-induced wrinkling on SiGe free standing film
Authors: Fedorchenko Alexander I. , Wang An-Bang , Mashanov Vladimir I. , Huang Wu-Ping , Cheng Henry H.
Published: August 2006

This study reports both experimental and theoretical investigation on the strain-induced wrinkling on Si1−xGex∕Si free standing film. Clear periodical pattern is observed and attributed to the strain relaxation of the SiGe film. With increasing lateral length of the film, both wavelength and amplitude increase. Nonlinear Von Karman plate theory is employed to model the structure. From the analysis, it shows that the formation of the wrinkling pattern is a trade-off between bending energy and stretching energy. Based on the modeling, it is found that wavelength decreased with increasing Ge content, while vice versa for the amplitude.
Comparison of the electronic structures of Zn1−xCoxO and Zn1−xMgxO nanorods using x-ray absorption and scanning photoelectron microscopies
Authors: Chiou J. W. , Tsai H. M. , Pao C. W. , Krishna Kumar K. P. , Ray S. C. , Chien F. Z. , Pong W. F. , Tsai M.-H. , Chen C.-H. , Lin H.-J. , Wu J. J. , Yang M.-H. , Liu S. C. , Chiang H. H. , Chen C. W.
Published: August 2006

X-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy (SPEM) measurements have been performed for Zn1−xCoxO and Zn1−xMgxO to elucidate the effects of the doping of Co and Mg, which have very different electronegativities, on the electronic structures of ZnO nanorods. The intensities of O K-edge near-edge features in the XANES spectra of Zn1−xCoxO and Zn1−xMgxO nanorods are found to be lower than those of ZnO, which suggests that both Co and Mg substitutions of the Zn ions enhance the effective charge on the O ion. The valence-band SPEM measurements show that Mg doping does not increase the density of near-Fermi-level states, which implies that Mg doping will not improve field emission of ZnO nanorods. It is surprising to find that both Co and Mg substitutions of Zn increase the numbers of O 2p dominated valence-band states, despite that Co and Mg have larger and smaller electronegativities than that of Zn.
Role of structural defects on ferromagnetism in amorphous Cr-doped TiO2 films
Authors: Wang Y. X. , Liu Hui , Li Z. Q. , Zhang X. X. , Zheng R. K. , Ringer S. P.
Published: August 2006

Amorphous CrxTi1−xO2 films with different Cr concentrations of 0⩽x⩽0.16 were prepared by cosputtering method at room temperature. All as-deposited samples show hysteresis behavior from 2to340K and the Curie temperatures are well above 390K. The saturation magnetization is about 3.21×10−1μB∕Cr for x=0.05 at 340K and decreases with increasing Cr dopant. After annealing at temperature above 300°C, the films crystallized into anatase structure and lost their ferromagnetic property. The results indicate that the ferromagnetism in amorphous Cr-doped TiO2 films is intrinsic and the structural defects play an important role in the ferromagnetism of Cr:TiO2 system.
Temperature dependence of the electrical activity of localized defects in InGaN-based light emitting diodes
Authors: Pavesi M. , Manfredi M. , Rossi F. , Meneghini M. , Zanoni E. , Zehnder U. , Strauss U.
Published: August 2006

Traps govern the temperature dependence of current in III-nitride quantum heterostructures, but frequently electrical measurements result unable to identify how many and what kind of defects take part in the conduction. The present work shows how a combined electrical and optical characterization in temperature can detect localized defects involved in injection mechanisms in InGaN∕AlGaN∕GaN blue light lmitting diodes. At least two different traps assisting the carrier injection by tunneling and playing an active role below and above 175K, respectively, are identified in or nearby the active layers.
Nonlinear propagation of broadband intense electromagnetic waves in an electron-positron plasma
Authors: Marklund M. , Eliasson B. , Shukla P. K.
Published: August 2006

A kinetic equation describing the nonlinear evolution of intense electromagnetic pulses in electron-positron (e-p) plasmas is presented. The modulational instability is analyzed for a relativistically intense partially coherent pulse, and it is found that the modulational instability is inhibited by the spectral pulse broadening. A numerical study for the one-dimensional kinetic photon equation is presented. Computer simulations reveal a Fermi-Pasta-Ulam-type recurrence phenomenon for localized broadband pulses. The results should be of importance in understanding the nonlinear propagation of broadband intense electromagnetic pulses in e-p plasmas in laser-plasma systems as well as in astrophysical plasma settings.
Enhancement of molecular modes by electronically resonant multipulse excitation: Further progress towards mode selective chemistry
Authors: Hauer Jürgen , Buckup Tiago , Motzkus Marcus
Published: August 2006

We show that molecular vibrations induced by resonant excitation pulses can be enhanced by pulse trains, compared to Fourier-limited pulses of equal pulse energy. As a proof-of-principle, a low frequency mode of Nile Blue at 600cm−1 is observed and amplified in a pump and probe experiment. In addition to previous experiments in our group, an increased population transfer to the excited electronic state is identified as an important element of the underlying physical mechanism. These results suggest an enhancement on the level of individual molecules rather than a macroscopic effect.