bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature-programed time-of-flight secondary ion mass spectrometry study of 1-butyl-3-methylimidazolium trifluoromethanesulfonate during glass-liquid transition, crystallization, melting, and solvation
Authors: Souda Ryutaro , Günster Jens
Published: September 2008

For this study, time-of-flight secondary ion mass spectrometry was used to analyze the molecular orientation of 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([bmim][OTf]) and its interaction with the adsorbed Na and LiI species at temperatures of 150–300K. A glassy [bmim][OTf] film crystallizes at around 230K, as observed from the increase in the [bmim]+ yield. LiI and Na adsorbed on the glassy film are solvated, whereas they tend to form islands on a crystalline film. The crystalline surface inertness is ascribable to the termination with the CF3 and C4H9 groups, whereas the exposure of polar SO3 and imidazole groups at the glassy film results in the solvation. Surface layering occurs during solvation of LiI on the glassy film in such a way that the [bmim]+ ([OTf]−) moiety is exposed to the vacuum (oriented to the bulk). The LiI adsorbed on the glassy film is incorporated into the bulk at temperatures higher than 200K because of the glass-liquid transition. No further uptake of LiI is observed during crystallization, providing a contrast to the results of normal molecular solids such as water and ethanol. The surface layers of the crystal melt at temperatures below the bulk melting point, as confirmed from the dissolution of adsorbed LiI, but the melting layer retains a short-range order similar to the crystal. The [bmim][OTf] can be regarded as a strongly correlated liquid with the combined liquid property and crystal-type local structure. The origin of this behavior is discussed.
Magnetic field-induced reverse transformation in B2-type NiCoMnAl shape memory alloys
Authors: Kainuma R. , Ito W. , Umetsu R. Y. , Oikawa K. , Ishida K.
Published: September 2008

Effects of the addition of Co to the NiMnAl alloy on the martensitic and magnetic properties were investigated. The magnetic properties of the parent (P) phase drastically changed from paramagnetic to ferromagnetic, while the magnetization in the martensite (M) phase slightly decreased with increasing Co composition. Consequently, in the Ni40Co10Mn33Al17 alloy with the B2 ordered structure, the martensitic transformation from a ferromagnetic P to a weak magnetic M phase was obtained. The martensitic transformation temperatures in this alloy decreased by about 30K with the application of a magnetic field of 7T and a metamagnetic phase transformation was confirmed.
Evanescent wave magnetometers with ultrathin (∼100μm) cells
Authors: Zhao K. F. , Wu Z.
Published: September 2008

We studied the performance of an evanescent wave magnetometer with a coated cell of adjustable length. The cell length varies from a few millimeters to less than 100μm. Two kinds of antirelaxation coatings are used: octadecyltrichlorosilane (OTS) and dichlorooctamethyltetrasiloxane (Surfasil). Sub-kilohertz linewidth can be achieved for a 100μm thick OTS-coated cell. Magnetometers with coated ultrathin cells have superior performance in inhomogeneous magnetic fields, and can achieve a spatial resolution of better than 25μm.
Femtosecond spectral interferometry of optical activity: Theory
Authors: Rhee Hanju , Ha Jeong-Hyon , Jeon Seung-Joon , Cho Minhaeng
Published: September 2008

Optical activities such as circular dichroism (CD) and optical rotatory dispersion (ORD) are manifested by almost all natural products. However, the CD is an extremely weak effect so that time-resolved CD spectroscopy has been found to be experimentally difficult and even impossible for vibrational CD with current technology. Here, we show that the weak-signal and nonzero background problems can be overcome by heterodyned spectral interferometric detection of the phase and amplitude of optical activity free-induction-decay (OA FID) field. A detailed theoretical description and a cross-polarization scheme for selectively measuring the OA FID are presented and discussed. It is shown that the parallel and perpendicular electric fields when the solution sample contains chiral molecules are coupled to each other. Therefore, simultaneous spectral interferometric measurements of the parallel and perpendicular FID fields can provide the complex susceptibility, which is associated with the circular dichroism and optical rotatory dispersion as its imaginary and real parts, respectively. On the basis of the theoretical results, to examine its experimental possibility, we present numerical simulations for a model system. We anticipate the method discussed here to be a valuable tool for detecting electronic or vibrational optical activity in femtosecond time scale.
Study of hardness and deformation of brittle materials with a density functional theory
Authors: Zhou Shujia , Zhou Xiangyang , Zhao Yusheng
Published: September 2008

We investigated controlling parameters of hardness in brittle materials by exploring the correlation between hardness and shear mode cracking. Density functional theory was used to calculate the unstable stacking energies (shear resistance to irreversible deformation) and the surface energies (tension resistance to fracture) for comparison. We found that both the unstable stacking energies and the surface energies had a monotonic relationship with hardness in Ge, Si, 3C-SiC, cBN, and diamond. In particular, both the relationship between hardness and the unstable stacking energy and the relationship between hardness and surface energy are better characterized as power law than linear relationships. Moreover, the surface energy has a better correlation with hardness than the unstable stacking energy. Both the theoretical stress for a crack to form and the stress intensity factor for a crack to propagate, which depend on surface energies, have better correlation with hardness than the stress intensity factor for a crack to emit a dislocation, which depends on unstable stacking energies. The implication of these results for fracture and deformation mechanism during hardness measurement is also discussed.
Role of electron energy loss in modification of C60 thin films by swift heavy ions
Authors: Bajwa Navdeep , Ingale Alka , Avasthi D. K. , Kumar Ravi , Tripathi A. , Dharamvir Keya , Jindal V. K.
Published: September 2008

This paper presents a comparative study of the effects of irradiation by swift heavy ions (SHIs) with Se values ranging from 80 to 1270 eV/Å and fluence ranges varying between 1010 and 1014 ions/cm2 incident on thin films of C60. The control over Se is exercised through the choice of ion species for irradiation (O, Ni, and Au). Structural changes in C60 were investigated quantitatively using Raman spectroscopy. The results indicate that at low fluences polymer formation takes place whereas at high fluences there is complete fragmentation of C60, resulting in amorphous carbon formation. Measured values of band gap and in situ resistivity decrease with fluence. This result is consistent with the structural modifications observed by Raman spectroscopy. The composition of the polymer fraction formed (e.g., the content of two dimensional polymerized network of C60 molecules) as well as that of a-C (e.g., the content of nanographite) also vary with Se of the ion used. A phenomenological model, taking into account the ion track, enables us to explain the trend of polymer formation as well as fragmentation of C60, with increasing fluence of SHI. The cross section for damage (fragmentation of C60 molecules) has two values—one effective at low fluences and the other at high fluences. By arriving at a quantitative formula giving the fraction of polymer/damaged C60 molecules at any given fluence, we are able to predict the fluence and ion species required for a given amount of polymerization/damage or vice versa. Effort has been made to correlate Se and Sn values to the damage cross sections using data from this work along with those from other experiments using keV and MeV ions.
Influence of SiO2 surface energy on the performance of organic field effect transistors based on highly oriented, zone-cast layers of a tetrathiafulvalene derivative
Authors: Miskiewicz Pawel , Kotarba Sylwia , Jung Jaroslaw , Marszalek Tomasz , Mas-Torrent Marta , Gomar-Nadal Elba , Amabilino David B. , Rovira Concepcio , Veciana Jaume , Maniukiewicz Waldemar , Ulanski Jacek
Published: September 2008

In this paper we present that the surface energy of silicon dioxide employed as the dielectric in bottom gate organic field effect transistors has large impact on the device performance. By the use of the zone-casting simple solution processing technique, we ensured reproducibility of active layer preparation confirmed by the atomic force microscopy and x-ray diffraction that showed high crystalline quality. Electrical measurements revealed that charge carrier mobility based on highly ordered zone-cast tetrakis-(octadecylthio)-tetrathiafulvalene layer was increased 30 times to 0.2 cm2/V s, when dielectric surface energy decreased from 51.8 to 40.1 mN/m.
Photoemission from single-walled carbon nanotubes
Authors: Nojeh Alireza , Ioakeimidi Katerina , Sheikhaei Samad , Pease R. Fabian W.
Published: September 2008

Carbon nanotubes have promising electron emission characteristics. We report on photo-electron emitters made from sparse collections of single-walled carbon nanotubes resting on a silicon dioxide surface. A 266 nm ultraviolet laser was used. The measured emission current suggests a level of optical power absorption of approximately an order of magnitude higher than what is expected purely based on the surface area of the nanotubes; it appears that a more efficient mechanism is at work. We also present simulation results and discuss whether optical antenna effects could provide an insight.
Lieb–Thirring estimates for non-self-adjoint Schrödinger operators
Authors: Bruneau Vincent , Ouhabaz El Maati
Published: September 2008

For general nonsymmetric operators A, we prove that the moment of order γ≥1 of negative real parts of its eigenvalues is bounded by the moment of order γ of negative eigenvalues of its symmetric part H=12[A+A∗]. As an application, we obtain Lieb–Thirring estimates for non-self-adjoint Schrödinger operators. In particular, we recover recent results by Frank et al. [Lett. Math. Phys. 77, 309 (2006)]. We also discuss moment of resonances of Schrödinger self-adjoint operators.
Mesoscopic order and the dimensionality of long-range resonance energy transfer in supramolecular semiconductors
Authors: Daniel Clément , Makereel François , Herz Laura M. , Hoeben Freek J. M. , Jonkheijm Pascal , Schenning Albertus P. H. J. , Meijer E. W. , Silva Carlos
Published: September 2008

We present time-resolved photoluminescence measurements on two series of oligo-p-phenylenevinylene materials that self-assemble into supramolecular nanostructures with thermotropic reversibility in dodecane. One set of derivatives form chiral helical stacks, while the second set form less organized “frustrated” stacks. Here we study the effects of supramolecular organization on the resonance energy transfer rates. We measure these rates in nanoassemblies formed with mixed blends of oligomers and compare them with the rates predicted by Förster theory. Our results and analysis show that control of supramolecular order in the nanometer length scale has a dominant effect on the efficiency and dimensionality of resonance energy transfer.
Electrical characteristics and conduction mechanisms of metal-insulator-metal capacitors with nanolaminated Al2O3–HfO2 dielectrics
Authors: Ding Shi-Jin , Xu Jun , Huang Yue , Sun Qing-Qing , Zhang David Wei , Li Ming-Fu
Published: September 2008

Electrical characteristics of metal-insulator-metal capacitors with various Al2O3–HfO2 nanolaminates are investigated. The results indicate that the breakdown field decreases with increasing the HfO2 individual-layer (IL) thickness. Concerning the same dielectric composition, the insulator with a thinner HfO2 IL also exhibits a significant improvement in the electrical breakdown and leakage characteristics. This is attributed to enhanced crystallization of the thicker HfO2 ILs. The insulator with alternate 1nm Al2O3 and 5nm HfO2 exhibits a breakdown field of 3.85MV∕cm at 125°C, and a leakage current of 9.6×10−8A∕cm2 at 1MV∕cm and 200°C. Further, it is revealed that the conduction mechanism in the high field range is dominated by the Poole–Frenkel emission with intrinsic trap energy of 1.91eV.
Columnar mesophases of hexabenzocoronene derivatives. I. Phase transitions
Authors: Marcon Valentina , Vehoff Thorsten , Kirkpatrick James , Jeong Cheol , Yoon Do Y. , Kremer Kurt , Andrienko Denis
Published: September 2008

Using atomistic molecular dynamic simulations we study the transitions between solid herringbone and liquid crystalline hexagonal mesophases of discotic liquid crystals formed by hexabenzocoronene derivatives. Combining a united atom representation for the side chains with the fully atomistic description of the core, we study the effect of side chain substitution on the transition temperatures as well as molecular ordering in the mesophases. Our study rationalizes the differences in charge carrier mobilities in the herringbone and hexagonal mesophases, which is predominantly due to the better rotational register of the neighboring molecules.
Predicting conformational entropy of bond vectors in proteins by networks of coupled rotators
Authors: Dhulesia Anne , Bodenhausen Geoffrey , Abergel Daniel
Published: September 2008

In this article, a formal expression for the conformational entropy of a bond vector in a protein is derived using the networks of coupled rotators model for the description of internal dynamics. Analytical relationships between NMR order parameters and conformational entropies are derived, and the possibility to extract the latter from NMR experiments is discussed. These results are illustrated in the case of the calcium-binding protein calbindin.
A comparison of quantum and quasiclassical statistical models for reactions of electronically excited atoms with molecular hydrogen
Authors: Aoiz F. J. , González-Lezana T. , Sáez Rábanos V.
Published: September 2008

A detailed comparison of statistical models based on the quasiclassical trajectory (SQCT) and quantum mechanical (SQM) methods is presented in this work for the C(D1)+H2, S(D1)+H2, O(D1)+H2 and N(D2)+H2 insertion reactions. Reaction probabilities, integral (ICS) and differential (DCS) cross sections at different levels of product’s state resolution are shown and discussed for these reactions. The agreement is in most cases excellent and indicates that the effect of tunneling through the centrifugal barrier is negligible. However, if there exists a dynamical barrier, as in the case of the N(D2)+H2 reaction, some of the SQM results can be slightly different than those calculated with the SQCT model. The rationale of the observed similarities and discrepancies can be traced back to the specific topologies of the potential energy surfaces for each of the reactions examined. The SQCT model is sensitive enough to show the relatively small inaccuracies resulting from the decoupling inherent to the centrifugal sudden approximation when used in the SQM calculations. In addition, the effect of ignoring the parity conservation is also examined. This effect is in general minor except in particular cases such as the DCS from initial rotational state j=0, which requires, in order to reproduce the sharp forward and backward peaks, the explicit conservation of parity.
Dynamic aspects of the liquid-liquid phase transformation in silicon
Authors: Jakse N. , Pasturel A.
Published: September 2008

First principles molecular dynamics simulations are used to characterize dynamic properties of supercooled liquid silicon across the liquid-liquid phase transition. Our results evidence the presence of a boson peak in the terahertz frequency range for the low-density liquid and support the scenario of a fragile-to-strong transition. The analysis of the collective excitations shows that its origin is due to a coupling of the longitudinal and transverse acoustic modes localized on the nanometer scale and can be attributed to collective vibrations of connected tetrahedra.
ZnO film thickness effect on surface acoustic wave modes and acoustic streaming
Authors: Du X. Y. , Fu Y. Q. , Tan S. C. , Luo J. K. , Flewitt A. J. , Milne W. I. , Lee D. S. , Park N. M. , Park J. , Choi Y. J. , Kim S. H. , Maeng S.
Published: September 2008

Surface acoustic wave (SAW) devices were fabricated on ZnO thin films deposited on Si substrates. Effects of ZnO film thickness on the wave mode and resonant frequency of the SAWs have been investigated. Rayleigh and Sezawa waves were detected, and their resonant frequencies decrease with increase in film thickness. The Sezawa wave has much higher acoustic velocity and larger signal amplitude than those of Rayleigh mode wave. Acoustic streaming for mixing has been realized in piezoelectric thin film SAWs. The Sezawa wave has a much better efficiency in streaming, and thus is very promising for application in microfluidics.
Infrared predissociation spectroscopy of cluster cations of protic molecules, (NH3)n+, n=2–4 and (CH3OH)n+, n=2,3
Authors: Hachiya Masaki , Matsuda Yoshiyuki , Suhara Ken-ichiro , Mikami Naohiko , Fujii Asuka
Published: September 2008

Infrared predissociation spectroscopy is carried out for the structure investigation of unprotonated cluster cations of protic molecules such as ammonia and methanol, which are generated through vacuum-ultraviolet one-photon ionization of their jet-cooled neutral clusters. The observed spectral features show that the cluster cations have the proton-transferred type structures, where a pair of a protonated cation and a neutral radical, NH4+⋯NH2 or CH3OH2+⋯OCH3, is formed. Theoretical calculations at the MP2 and B3LYP levels support the formation of the proton-transferred type structures for the cluster cations, and indicate that they are formed by proton-transfer following the photoionization of the neutral clusters.
Optical properties of GaN/AlGaN quantum wells grown on nonpolar substrates
Authors: Badcock T. J. , Dawson P. , Kappers M. J. , McAleese C. , Hollander J. L. , Johnston C. F. , Rao D. V. Sridhara , Sanchez A. M. , Humphreys C. J.
Published: September 2008

In this paper we report on the optical properties of a series of GaN/AlGaN multiple quantum well structures grown on a-plane (112¯0) GaN, which had been deposited on r-plane (11¯02) sapphire substrates, compared to a reference GaN template of the same orientation. The low temperature photoluminescence spectrum of the template layer is dominated by two emission bands, which we attribute to recombination involving excitons in the bulk of the layer and electrons and holes trapped at basal-plane stacking faults, designated X1 and X2, respectively. The photoluminescence spectra from the quantum well structures show similar emission bands except that both X1 and X2 shift to higher energy with decreasing quantum well thickness. The shift to higher energy is due to the effects of quantum confinement on carriers trapped at the stacking faults that intersect the quantum wells, as well as those excitons that are localized within the quantum wells. This assignment is based partly on excitation spectroscopy that reveals exciton transitions associated with electrons from the n=1 and n=2 quantum well confined states.
Field emitter density control effect on emission current density by Ag–Cu alloy coating on carbon nanotubes
Authors: Lee Seung Youb , Choi Won Chel , Jeon Cheolho , Park Chong-Yun , Yang Ji Hoon , Kwon Myeung Hoi
Published: September 2008

We have investigated the morphological evolution and improvement in field emission properties of carbon nanotube (CNT) emitters coated with an Ag–Cu alloy (ACa). Vertically aligned multiwalled CNTs (MWCNTs) were synthesized by direct current-plasma enhanced chemical vapor deposition. The MWCNTs were then coated with ACa by dc-magnetron sputtering and then annealed. Scanning electron microscopy revealed an increase in the size of the ACa droplets on the CNTs after thermal annealing, and a decrease in the emitter density with increasing deposition time. The emitter density was controlled by the amount of ACa with high surface tension and annealing. A lower turn-on voltage (1.18 V/μm) and higher emission current density of 588.9 μA/cm2 at 5.0 V/μm were achieved from the sample containing ACa droplets with an average radius of 500 nm.
On electromechanical stability of dielectric elastomers
Authors: Díaz-Calleja R. , Riande E. , Sanchis M. J.
Published: September 2008

This paper studies the competition between electric and mechanical force fields simultaneously applied to a polar elastomer that can lead to electric breakdown. The analysis of the system, performed assuming that the free energy of the elastomer is simply the addition of polarizing and stretching energies leads to the classical “thermodynamic” (in this case “electromechanical”) stability.
Structural and dynamical aspects of the phase transition in the new thiourea thiazolium bromide inclusion compound
Authors: Pajzderska A. , Wąsicki J. , Małuszyńska H. , Czarnecki P. , Toupet L. , Collet E.
Published: September 2008

A new thiourea thiazolium bromide inclusion compound is presented here. Detailed investigations of its phase transition were performed by differential scanning calorimetry, x-ray diffraction, and dielectric and nuclear magnetic resonance spectroscopy methods, completed by calculation of the steric hindrances for molecular reorientations and simulations of the second moment of the nuclear magnetic resonance line by the Monte Carlo method. A second order ferrielectric structural phase transition has been detected at 190.5K as thiazolium cations collectively reorient inside channels. The dynamics is discussed in terms of inequivalent energy barriers associated with cation rotation as the symmetry breaking occurs. Oscillations of thiourea molecules and NH2 groups have been also observed.
Single-laser-shot detection of nitric oxide in reacting flows using electronic resonance enhanced coherent anti-Stokes Raman scattering
Authors: Chai Ning , Naik Sameer V. , Laurendeau Normand M. , Lucht Robert P. , Roy Sukesh , Gord James R.
Published: September 2008

Single-laser-shot electronic resonance enhanced coherent anti-Stokes Raman scattering (ERE-CARS) spectra of nitric oxide (NO) were generated using the 532 nm output of an injection-seeded Nd:YAG (yttrium aluminum garnet) laser as the pump beam, a broadband dye laser at approximately 591 nm as the Stokes beam, and a 236 nm narrowband ultraviolet probe beam. Single-laser-shot ERE-CARS spectra of NO were acquired in an atmospheric-pressure hydrogen/air counterflow diffusion flame. The single-shot detection limit in this flame was found to be approximately 30 ppm, and the standard deviation of the measured NO concentration was found to be approximately 20% of the mean.
Low cost patterning of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) films to increase organic photovoltaic device efficiency
Authors: Emah J. B. , Curry R. J. , Silva S. R. P.
Published: September 2008

A low-cost lithographic technique to pattern poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) films with 10 nm deep features of 700 nm periodicity is demonstrated. The use of these patterned films in poly(3-hexylthiophene):[6,6]-phenylC61-butyric acid methyl ester organic photovoltaic devices leads to an increase in short circuit current (Jsc), fill factor, and power conversion efficiency (PCE) with only a slight reduction in open circuit voltage. Patterning the PEDOT:PSS at 150 °C increases Jsc from 2.44 to 3.03 mA/cm2 improving the PCE from 0.63% to 0.81% with similar increases due to patterning also being obtained at other temperatures.
Calibration of the isomer shift for the 77.34 keV transition in A197u using the full-potential linearized augmented plane-wave method
Authors: Wdowik U. D. , Ruebenbauer K.
Published: September 2008

The isomer shift calibration constant has been calculated for the 77.34 keV Mössbauer transition connecting the ground state of the A197u nucleus with the first excited state of this nucleus. The full-potential linearized augmented plane-wave method was used in the fully relativistic approach, albeit without taking into account the spin-orbit coupling. The final assignment of the calibration constant was based on calculations performed for AuCN, AuCl3, AuBr3, KAuCl4, KAuBr4, and metallic gold. It is found that the calibration constant takes on the following value α=+0.0665(4) mm s−1 a.u.3. The error quoted is due to the linear regression fit, and the real error might be as large as 10%. The spectroscopic electric quadrupole moment for the ground state of the A197u nucleus was calculated as the by-product. It was found that this moment equals Qg=+0.566(1)b in fair agreement with the accepted value based on the muonic hyperfine spectroscopy results. The error quoted is again due to the linear regression fit and the real error might be as large as 10%. The final assignment of the value for the quadrupole moment is based on the calculations for the following compounds: AuCl, AuBr, AuI, AuCN, and AuMn2. Results for the magnetically ordered Au2Mn were applied to determine the sign of the quadrupole moment.
Efficient ejection of H3+ from hydrocarbon molecules induced by ultrashort intense laser fields
Authors: Hoshina Kennosuke , Furukawa Yusuke , Okino Tomoya , Yamanouchi Kaoru
Published: September 2008

The ejection processes of hydrogen molecular ion H3+ from 12 kinds of hydrocarbon molecular species, methanol, ethanol, 1-propanol, 2-propanol, acetone, acetaldehyde, methane, ethane, ethylene, allene, 1,3-butadiene, and cyclohexane, induced by intense laser fields (∼1014W∕cm2) have been investigated by time-of-flight mass spectroscopy. The observation of the H3+ production with the kinetic energy range of 3.5–5.0eV from doubly ionized ethylene, allene, 1,3-butadiene, and cyclohexane, which have no methyl groups, showed the existence of the ultrafast hydrogen migration processes that enables three hydrogen atoms to come together to form H3+ within a hydrocarbon molecule.
Identifying critical residues in protein folding: Insights from ϕ-value and Pfold analysis
Authors: Faísca P. F. N. , Travasso R. D. M. , Ball R. C. , Shakhnovich E. I.
Published: September 2008

We apply a simulational proxy of the ϕ-value analysis and perform extensive mutagenesis experiments to identify the nucleating residues in the folding “reactions” of two small lattice Gō polymers with different native geometries. Our findings show that for the more complex native fold (i.e., the one that is rich in nonlocal, long-range bonds), mutation of the residues that form the folding nucleus leads to a considerably larger increase in the folding time than the corresponding mutations in the geometry that is predominantly local. These results are compared to data obtained from an accurate analysis based on the reaction coordinate folding probability Pfold and on structural clustering methods. Our study reveals a complex picture of the transition state ensemble. For both protein models, the transition state ensemble is rather heterogeneous and splits up into structurally different populations. For the more complex geometry the identified subpopulations are actually structurally disjoint. For the less complex native geometry we found a broad transition state with microscopic heterogeneity. These findings suggest that the existence of multiple transition state structures may be linked to the geometric complexity of the native fold. For both geometries, the identification of the folding nucleus via the Pfold analysis agrees with the identification of the folding nucleus carried out with the ϕ-value analysis. For the most complex geometry, however, the applied methodologies give more consistent results than for the more local geometry. The study of the transition state structure reveals that the nucleus residues are not necessarily fully native in the transition state. Indeed, it is only for the more complex geometry that two of the five critical residues show a considerably high probability of having all its native bonds formed in the transition state. Therefore, one concludes that, in general, the ϕ-value correlates with the acceleration/deceleration of folding induced by mutation, rather than with the degree of nativeness of the transition state, and that the “traditional” interpretation of ϕ-values may provide a more realistic picture of the structure of the transition state only for more complex native geometries.
Plasmon enhanced fluorescence microscopy below quantum noise limit with reduced photobleaching effect
Authors: Mondal Partha Pratim , Gilbert Richard J. , So Peter T. C.
Published: September 2008

We propose a plasmon enhanced fluorescence microscopy technique below the quantum noise limit. This is achieved by exciting fluorescent molecules with photon number squeezed (PNS) light and using nanoparticles as an enhancer for overcoming the low absorption cross section. PNS light has an inherent sub-Poissonian photon distribution for which the variance Δn<⟨n⟩. PNS light has the added advantage of antibunching, which eliminates photobleaching due to higher order photon interactions. We anticipate that single molecule studies will benefit from such a radiation source.
Highly delocalized orbiting resonances
Authors: García-Vela A.
Published: September 2008

The Ne–Br2(B,v) intermolecular resonances embedded in the continuum of the v=26 vibrational manifold have been characterized. The nature of these states as long-lived, strongly overlapping orbiting resonances supported by centrifugal barriers originated in rotational excitation of Br2 within the complex has been confirmed. The orbiting resonances are found to be highly delocalized in space, both in the radial and angular coordinates, giving rise to long-lived, large-sized Ne-Br2 complexes.
Mössbauer spectroscopy studies of carbon-encapsulated magnetic nanoparticles obtained by different routes
Authors: Bystrzejewski M. , Grabias A. , Borysiuk J. , Huczko A. , Lange H.
Published: September 2008

Carbon-encapsulated magnetic nanoparticles (CEMNPs) are nanomaterials with a core-shell structure. Their intrinsic properties result both from the unique nature of the encapsulated magnetic phases and the high chemical stability of the external carbon shells. CEMNPs may find many prospective applications, e.g., in magnetic data storage, catalysis, xerography, magnetic resonance imaging, and in biomedical applications. Herein, we present detailed structural studies of such nanostructures by Mössbauer spectroscopy, x-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy. CEMNPs have been obtained by three different techniques: carbon arc, combustion synthesis, and radio frequency thermal plasma. The evaluation of the phase composition of the products was strongly limited due to the broadening and overlapping of the lines in XRD diffraction patterns. The presence of the semicrystalline phases, which could not been identified by XRD, was established by Mössbauer spectroscopy. Furthermore, the magnetic core phase composition was evaluated quantitatively. The products were purified before structural analyses to remove the nonencapsulated particles. The purification caused significant changes in the mass and the saturation magnetization. The Mössbauer spectra of the purified products were compared with the literature data concerning the as-produced CEMNPs.
Frequency dependence of negative differential capacitance in Schottky diodes with InAs quantum dots
Authors: Lin S. D. , Ilchenko V. V. , Marin V. V. , Panarin K. Y. , Buyanin A. A. , Tretyak O. V.
Published: September 2008

The frequency dependence of negative differential capacitance (NDC) in Schottky diodes with InAs quantum dots (QDs) is studied. The measured peak capacitances of NDC decay rapidly as the testing frequencies are higher than a few kilohertz. A kinetic model considering the testing signal is proposed and the capture rates of QDs are extracted. The simulation result is quantitatively consistent with the experimental data when the charging effect in QDs is included.
Different equation-of-motion coupled cluster methods with different reference functions: The formyl radical
Authors: Kuś Tomasz , Bartlett Rodney J.
Published: September 2008

The doublet and quartet excited states of the formyl radical have been studied by the equation-of-motion (EOM) coupled cluster (CC) method. The Sz spin-conserving singles and doubles (EOM-EE-CCSD) and singles, doubles, and triples (EOM-EE-CCSDT) approaches, as well as the spin-flipped singles and doubles (EOM-SF-CCSD) method have been applied, subject to unrestricted Hartree–Fock (HF), restricted open-shell HF, and quasirestricted HF references. The structural parameters, vertical and adiabatic excitation energies, and harmonic vibrational frequencies have been calculated. The issue of the reference function choice for the spin-flipped (SF) method and its impact on the results has been discussed using the experimental data and theoretical results available. The results show that if the appropriate reference function is chosen so that target states differ from the reference by only single excitations, then EOM-EE-CCSD and EOM-SF-CCSD methods give a very good description of the excited states. For the states that have a non-negligible contribution of the doubly excited configurations one is able to use the SF method with such a reference function, that in most cases the performance of the EOM-SF-CCSD method is better than that of the EOM-EE-CCSD approach.
Gas indiffusion contribution to impedance in tin oxide thick films
Authors: Ponce M. A. , Malagu C. , Carotta M. C. , Martinelli G. , Aldao C. M.
Published: September 2008

The ac electrical resistance and capacitance of SnO2 thick films under vacuum and air atmosphere were analyzed using the Cole–Cole plot. To fit the experimental results, a simple circuit model that considers a capacitance and a resistance in parallel was employed. An explanation for the resistance variation considering spherical grains with different characteristics is proposed. A careful analysis of the resulting depletion layers and doping levels gives evidence for gas diffusion into the grains.
Dopant distribution in high fluence Fe implanted GaN
Authors: Azarov A. Yu. , Jensen J. , Hallén A. , Aggerstam T.
Published: September 2008

Undoped wurtzite GaN epilayers implanted at room temperature with 50–325 keV Fe+ ions in the fluence range of 1015–1017 ions/cm2 are studied by a combination of Rutherford backscattering/channeling spectrometry and time-of-flight elastic recoil detection analysis. The results show an enhanced Fe concentration close to the surface for high ion fluences (>1×1016 cm−2), which increases with the ion fluence. Annealing at 800 °C for 30 min has a negligible effect on the Fe distribution in the material bulk, but further increases the Fe concentration near the surface. Our findings can be understood by radiation enhanced diffusion during ion implantation and an increased Fe diffusivity in the near surface region with distorted stoichiometry, or formation of secondary phases and precipitates for the highest doses. The simulation shows that, if enhanced diffusion is the reason for Fe buildup at the surface, both radiation enhanced diffusion and the thermal diffusion of Fe atoms near the surface, need to be at least five times larger than ordinary bulk diffusion to explain the increased Fe surface concentration.
Optical emission spectroscopy of atmospheric pressure microwave plasmas
Authors: Jia Haijun , Fujiwara Hiroyuki , Kondo Michio , Kuraseko Hiroshi
Published: September 2008

The optical emission behaviors of Ar, He, and Ar+He plasmas generated in air using an atmospheric pressure microwave plasma source have been studied employing optical emission spectroscopy (OES). Emissions from various source gas species and air were observed. The variations in the intensities and intensity ratios of specific emissions as functions of the microwave power and gas flow rate were analyzed to investigate the relationship between the emission behavior and the plasma properties. We find that dependence of the emission behavior on the input microwave power is mainly determined by variations in electron density and electron temperature in the plasmas. On the other hand, under different gas flow rate conditions, changes in the density of the source gas atoms also significantly affect the emissions. Interestingly, when plasma is generated using an Ar+He mixture, emissions from excited He atoms disappear while a strong Hα signal appears. The physics behind these behaviors is discussed in detail.
Direct observation/characterization of spatial distribution of current leakage spots in zinc oxide/aluminum nitride thin film precursor field effect transistor structures using conducting atomic force microscopy
Authors: Dey Shirshendu , Jejurikar Suhas M. , Adhi K. P. , Dharmadhikari C. V.
Published: September 2008

Charge transport across pulsed laser deposited zinc oxide (ZnO)/aluminum nitride (AlN)/Si(100) thin film structures has been studied using conducting atomic force microscopy at different stages of sample preparation. The spatial coverage of current leakage spots could be directly imaged, characterized, and shown to exhibit hysteresis against applied bias voltage. Current-voltage (I-V) measurements on both AlN and ZnO/AlN/Si(100) structure exhibited asymmetric nonlinear behavior with a large zero current region. Further analysis of I-V and current-force data suggests Fowler–Nordheim like behavior under Hertzian contact as a dominant mechanism for electron transport.
Hot optical phonon decay in carbon nanotubes
Authors: Pennington G. , Kilpatrick S. J. , Wickenden A. E.
Published: September 2008

We simulate hot optical phonon decay in small diameter (<0.7 nm) carbon nanotubes, solving the phonon Boltzmann transport equation using Monte Carlo methods incorporating the full phonon spectrum and phonon-phonon scattering. Results indicate decay times inversely proportional to the lattice temperature with negligible dependence on hot phonon polarization/wave vector or nanotube diameter and chirality. Nonequilibrium optical phonons with energies of ∼0.2 eV decay by emitting two ∼0.1 eV optical phonons, corresponding to out-of-plane polarization modes in graphitic materials. Modes polarized perpendicular to the nanotube axis may allow manipulation of hot phonon effects by the near environment of the nanotube.
Enhanced nonradiative Auger recombination in p-type modulation doped InAs/GaAs quantum dots
Authors: Jang Y. D. , Badcock T. J. , Mowbray D. J. , Skolnick M. S. , Park J. , Lee D. , Liu H. Y. , Hopkinson M. , Hogg R. A. , Andreev A. D.
Published: September 2008

The photoluminescence efficiency and carrier recombination time of p-type modulation doped InAs/GaAs quantum dots (QDs) have been measured as a function of doping density. At 10 K the carrier lifetime decreases from 1200 to 350 ps over the doping range of 0 and 30 acceptors/QD. This behavior is attributed to an enhancement of the Auger-type recombination due to the presence of extrinsic holes in the QDs. The hole density dependence of the Auger process is found to be weaker than in bulk semiconductors and quantum wells (QWs).
Relaxation processes of point defects in vitreous silica from femtosecond to nanoseconds
Authors: Cannizzo A. , Leone M. , Gawelda W. , Portuondo-Campa E. , Callegari A. , van Mourik F. , Chergui M.
Published: September 2008

We studied ultrafast relaxation of localized excited states at Ge-related oxygen deficient centers in silica using femtosecond transient-absorption spectroscopy. The relaxation dynamics exhibits a biexponential decay, which we ascribe to the departure from the Frank–Condon region of the first excited singlet state in 240 fs, followed by cooling in ∼10 ps. At later times, a nonexponential relaxation spanning up to 40 ns occurs, which is fitted with an inhomogeneous distribution of nonradiative relaxation rates, following a chi-square distribution with one degree of freedom. This reveals several analogies with phenomena such as neutron reactions, quantum dot blinking, or intramolecular vibrational redistribution.
Jump processes on leaves of multibranching trees
Authors: Albeverio Sergio , Karwowski Witold
Published: September 2008

The p-adic numbers have found applications in a wide range of diverse fields of scientific research. In some applications the algebraic properties of p-adics enter as an indispensable ingredient of the theory. Another class of applications has to do with hierarchical treelike systems. In this context the applications are based on the well known correspondence between p-adics and the trees with p branches emerging from every branching point. Then the algebraic structure does not enter and p-adics are used merely as a labeling system for the tree branches. We introduce a space of sequences denoted by SB suitable for labeling the trees with varying number of branches emerging from the branching points. We introduce a non-Archimedean metric in SB and describe the basic topological properties of SB. We also demonstrate that the known constructions of the stochastic processes on p-adics carry over to the stochastic processes on SB and hence on the corresponding trees.
Multiple impact regimes in liquid environment dynamic atomic force microscopy
Authors: Melcher John , Xu Xin , Raman Arvind
Published: September 2008

A canonical assumption in dynamic atomic force microscopy is that the probe tip interacts with the sample once per oscillation cycle. We show this key ansatz breaks down for soft cantilevers in liquid environments. Such probes exhibit “drum roll” like dynamics with sequential bifurcations between oscillations with single, double, and triple impacts that can be clearly identified in the phase of the response. This important result is traced to a momentary excitation of the second flexural mode induced by tip-sample forces and low quality factors. Experiments performed on supported biological membranes in buffer solutions are used to demonstrate the findings.
X-ray nanospectroscopic characterization of a molecularly thin ferromagnetic Ti1−xCoxO2 nanosheet
Authors: Kotani Yoshinori , Taniuchi Toshiyuki , Osada Minoru , Sasaki Takayoshi , Kotsugi Masato , Guo F. Z. , Watanabe Yoshio , Kubota Masato , Ono Kanta
Published: September 2008

We investigated the local electronic structures of a molecularly thin ferromagnetic Ti0.8Co0.2O2 nanosheet by means of x-ray nanospectroscopy with spectroscopic photoemission and low energy electron microscopy. By analyzing the Co 2p x-ray absorption and photoemission spectra, the chemical state of doped Co ions in individual Ti0.8Co0.2O2 nanosheet was found to be Co2+ low-spin state, which is consistent with previous magnetization data and first-principles calculation [M. Osada et al., Phys. Rev. B 73, 153301 (2006)]. Furthermore, we employed photoelectron emission microscopy to image the variation in chemical states in Ti0.8Co0.2O2 nanosheets with different stacking structures and clarified the identical Co2+ low-spin state in monolayer and overlapped cases.
Mechanical and electrical evaluation of parylene-C encapsulated carbon nanotube networks on a flexible substrate
Authors: Chen Chia-Ling , Lopez Ernesto , Jung Yung-Joon , Müftü Sinan , Selvarasah Selvapraba , Dokmeci Mehmet R.
Published: September 2008

Carbon nanotube networks are an emerging conductive nanomaterial with applications including thin film transistors, interconnects, and sensors. In this letter, we demonstrate the fabrication of single-walled carbon nanotube (SWNT) networks on a flexible polymer substrate and then provide encapsulation utilizing a thin parylene-C layer. The encapsulated SWNT network was subjected to tensile tests while its electrical resistance was monitored. Tests showed a linear-elastic response up to a strain value of 2.8% and nearly linear change in electrical resistance in the 0%–2% strain range. The networks’ electrical resistance was monitored during load-unload tests of up to 100 cycles and was hysteresis-free.
A line-of-sight electron cyclotron emission receiver for electron cyclotron resonance heating feedback control of tearing modes
Authors: Oosterbeek J. W. , Bürger A. , Westerhof E. , de Baar M. R. , van den Berg M. A. , Bongers W. A. , Graswinckel M. F. , Hennen B. A. , Kruijt O. G. , Thoen J. , Heidinger R. , Korsholm S. B. , Leipold F. , Nielsen S. K.
Published: September 2008

An electron cyclotron emission (ECE) receiver inside the electron cyclotron resonance heating (ECRH) transmission line has been brought into operation. The ECE is extracted by placing a quartz plate acting as a Fabry–Perot interferometer under an angle inside the electron cyclotron wave (ECW) beam. ECE measurements are obtained during high power ECRH operation. This demonstrates the successful operation of the diagnostic and, in particular, a sufficient suppression of the gyrotron component preventing it from interfering with ECE measurements. When integrated into a feedback system for the control of plasma instabilities this line-of-sight ECE diagnostic removes the need to localize the instabilities in absolute coordinates.
Magnetic core test stand for energy loss and permeability measurements at a high constant magnetization rate and test results for nanocrystalline and ferrite materials
Authors: Burdt Russell , Curry Randy D.
Published: September 2008

A test stand was developed to measure the energy losses and unsaturated permeability of toroidal magnetic cores, relevant to applications of magnetic switching requiring a constant magnetization rate of the order of 1–10 T/μs. These applications in pulsed power include linear induction accelerators, pulse transformers, and discharge switches. The test stand consists of a coaxial transmission line pulse charged up to 100 kV that is discharged into a magnetic core load. Suitable diagnostics measure the voltage across and the current through a winding on the magnetic core load, from which the energy losses and unsaturated permeability are calculated. The development of the test stand is discussed, and test results for ferrite CN20 and the nanocrystalline material Finemet FT-1HS are compared to demonstrate the unique properties of a nanocrystalline material. The experimental data are compared with published data in a similar parameter space to demonstrate the efficacy of the experimental methods.
A new generalized model for elliptical arc flexure hinges
Authors: Chen Guimin , Shao Xiaodong , Huang Xinbo
Published: September 2008

Flexure hinges have been used in many engineering areas where high precision and sensitivity are required. Many kinds of flexure profiles were proposed during the past decade. Therefore, a general closed-form solution for flexure hinges of different profiles that incorporates the profile selection and parameter design will be of great benefit to the hinge design. The present work brings circular, right-circular, and elliptical profiles together by proposing a generalized flexure hinge model, which we call elliptical arc flexure hinges (whose maximum eccentric angle ϕm ranges from 0 to π/2) to distinguish from the existing elliptical flexure hinge (ϕm=π/2). Based on the theories of mechanics of materials, all the elements in the compliance matrix for elliptical arc flexure hinges are deduced by introducing the eccentric angle of ellipse as the integral variable. These compliance equations simply boil down to four integrals, thus simplifying the compliance calculation. These equations also apply to elliptical (ϕm=π/2), circular (a=b), and right-circular (ϕm=π/2 and a=b) hinges. These compliance equations were checked by comparing them with the results of finite element analysis, the existing equations, and experiment results. The comparison results show that these generalized equations are concise and adequate for most design purposes.