bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytical balance-based Faraday magnetometer
Authors: Riminucci Alberto , Uhlarz Marc , De Santis Roberto , Herrmannsdörfer Thomas
Published: March 2017

We introduce a Faraday magnetometer based on an analytical balance in which we were able to apply magnetic fields up to 0.14 T. We calibrated it with a 1 mm Ni sphere previously characterized in a superconducting quantum interference device (SQUID) magnetometer. The proposed magnetometer reached a theoretical sensitivity of 3 × 10−8 A m2. We demonstrated its operation on magnetic composite scaffolds made of poly(ε-caprolactone)/iron-doped hydroxyapatite. To confirm the validity of the method, we measured the same scaffold properties in a SQUID magnetometer. The agreement between the two measurements was within 5% at 0.127 T and 12% at 24 mT. With the addition, for a small cost, of a permanent magnet and computer controlled linear translators, we were thus able to assemble a Faraday magnetometer based on an analytical balance, which is a virtually ubiquitous instrument. This will make simple but effective magnetometry easily accessible to most laboratories, in particular, to life sciences ones, which are increasingly interested in magnetic materials.
Incremental full configuration interaction
Authors: Zimmerman Paul M.
Published: March 2017

The incremental expansion provides a polynomial scaling method for computing electronic correlation energies. This article details a new algorithm and implementation for the incremental expansion of full configuration interaction (FCI), called iFCI. By dividing the problem into n-body interaction terms, accurate correlation energies can be recovered at low n in a highly parallel computation. Additionally, relatively low-cost approximations are possible in iFCI by solving for each incremental energy to within a specified threshold. Herein, systematic tests show that FCI-quality energies can be asymptotically reached for cases where dynamic correlation is dominant as well as where static correlation is vital. To further reduce computational costs and allow iFCI to reach larger systems, a select-CI approach (heat-bath CI) requiring two parameters is incorporated. Finally, iFCI provides the first estimate of FCI energies for hexatriene with a polarized double zeta basis set, which has 32 electrons correlated in 118 orbitals, corresponding to a FCI dimension of over 1038.
Theoretical volume profiles for conformational changes: Application to internal rotation of benzene ring in 1,12-dimethoxy-[12]-paracyclophane
Authors: Wiebe Heather , Louwerse Miranda , Weinberg Noham
Published: March 2017

Identification of the transition state is an important step in the study of reaction kinetics and mechanisms. However, for non-rigid chemical systems where multiple viable reaction pathways may exist, enumeration of all possible transition states quickly becomes computationally expensive, if at all feasible. As an alternative approach, we recently proposed a methodology where the volumetric properties of a flexible reaction system are used to locate its transition state ensemble through a comparison of its theoretically determined volume profile and experimental activation volumes derived from high pressure kinetic data. In this work, we apply this method to internal rotation of the benzene ring in 1,12-dimethoxy-[12]-paracyclophane. For this system, the transition state ensemble was found to be the state with the lowest volume, where the benzene ring and the flexible methylene tether are coplanar. This result was verified by comparison with a Gibbs free energy profile obtained via umbrella sampling.
High strain magnetostriction in a ferromagnet-polymer composite
Authors: Hamann Aaron , Dahlberg E. Dan
Published: March 2017

A magnetostrictive composite material exhibiting the capacity for large magnetostrictive strains was created by suspending magnetic wires in a soft polymer matrix. Magnetostrictive strains as large as 20% were found in an applied field of 600 Oe for this proof of concept composite. Our analysis indicates that reversible strains of over 6% are reasonable for this specific composite. The large values of magnetostriction are due to the mechanical rotation of the wires in the polymer matrix.
Significance of symmetry in the nuclear spin Hamiltonian for efficient heteronuclear dipolar decoupling in solid-state NMR: A Floquet description of supercycled rCW schemes
Authors: Equbal Asif , Shankar Ravi , Leskes Michal , Vega Shimon , Nielsen Niels Chr. , Madhu P. K.
Published: March 2017

Symmetry plays an important role in the retention or annihilation of a desired interaction Hamiltonian in NMR experiments. Here, we explore the role of symmetry in the radio-frequency interaction frame Hamiltonian of the refocused-continuous-wave (rCW) pulse scheme that leads to efficient 1H heteronuclear decoupling in solid-state NMR. It is demonstrated that anti-periodic symmetry of single-spin operators (Ix, Iy, Iz) in the interaction frame can lead to complete annihilation of the 1H–1H homonuclear dipolar coupling effects that induce line broadening in solid-state NMR experiments. This symmetry also plays a critical role in cancelling or minimizing the effect of 1H chemical-shift anisotropy in the effective Hamiltonian. An analytical description based on Floquet theory is presented here along with experimental evidences to understand the decoupling efficiency of supercycled (concatenated) rCW scheme.
Magnetized direct current microdischarge I. Effect of the gas pressure
Authors: Levko Dmitry , Raja Laxminarayan L.
Published: March 2017

Following Paschen's law, electrical breakdown of gaps with small pd, where p is the gas pressure and d is the interelectrode gap, requires extremely high voltages. This means that the breakdown voltage for low-pressure microdischarges is of the order of a few kilovolts. This makes impractical the generation of low-pressure dc microdischarges. The application of dc magnetic field confines electrons in the cathode-anode gap. This leads to the significant decrease in the breakdown voltage because each electron experiences many collisions during its diffusion toward the anode. However, as was obtained experimentally, magnetized low-pressure microdischarges experience numerous instabilities whose nature is still not completely understood. In the present paper, we study the influence of the magnetic field on the low-pressure microdischarges. We use the self-consistent one-dimensional Particle-in-Cell Monte Carlo collisions model, which takes into account the electron magnetization while ions remain unmagnetized. We obtain striations in the discharge. We show that these striations appear in both homogeneous and non-homogeneous magnetic fields. We find simple expression for the instability growth rate, which shows that the instability results from ionization processes.
Magnetized direct current microdischarge. II. Effect of magnetic field amplitude on the plasma
Authors: Levko Dmitry , Raja Laxminarayan L.
Published: March 2017

The influence of magnetic field amplitude on the direct current low-pressure (5 Torr) microplasma parameters is studied using one-dimensional particle-in-cell Monte Carlo collisions model with magnetized electrons and unmagnetized ions. We find that the breakdown voltage as the function of magnetic field has the local minimum. The position of this minimum corresponds to the value of magnetic field at which the electron magnetization is obtained. Also, we obtain two modes of microdischarge operation, namely, a low- and a high-current mode. These modes are separated by the magnetic field at which the electron mobility in the vicinity of the cathode becomes smaller than the ion mobility. This critical magnetic field also separates stable and unstable microplasma behaviour.
Tuning of the magnetostrictive properties of cobalt ferrite by forced distribution of substituted divalent metal ions at different crystallographic sites
Authors: Anantharamaiah P. N. , Joy P. A.
Published: March 2017

Comparative studies have been made to understand the role of different crystallographic site preferences of the substituted non-magnetic divalent metal ions in the magnetostrictive properties of cobalt ferrite, by substitution of Zn2+ and/or Mg2+ for Fe3+ in CoMgxFe2−xO4, CoZnxFe2−xO4, and CoMgx/2Znx/2Fe2−xO4 (0.0 ≤ x ≤ 0.2). Detailed Raman spectral and magnetic characterizations are made to extract the information on the tetrahedral/octahedral site preferences of Zn and Mg in the spinel lattice of cobalt ferrite. The structural, microstructural, magnetic, Raman spectral, and magnetostrictive parameters of the studied compositions show distinguishable variations for x < 0.1 and x ≥ 0.1. Co-substitution of a small amount of Mg and Zn for Fe in CoMgx/2Znx/2Fe2−xO4 (x < 0.1) showed relatively larger strain sensitivity, [dλ/dH]max (−2.6 × 10−9 mA−1 for x = 0.05), higher than that for the Mg-substituted samples (−2.05 × 10−9 mA−1 for x = 0.05) and comparable to that for the Zn-substituted samples (−2.47 × 10−9 mA−1 for x = 0.05), without much drop in the maximum value of magnetostriction, λmax (−189 ppm for x = 0.05) compared to that for the unsubstituted counterpart (−221 ppm). The results show that it is possible to obtain high strain sensitivity (at fields <50 kA/m), along with high magnetostriction strain at low magnetic fields (∼250 kA/m), by tuning the distribution of the substituted cations in the tetrahedral and octahedral sites of the cobalt ferrite lattice.
Ultrafast inhomogeneous magnetization dynamics analyzed by interface-sensitive nonlinear magneto-optics
Authors: Chen J. , Wieczorek J. , Eschenlohr A. , Xiao S. , Tarasevitch A. , Bovensiepen U.
Published: March 2017

We analyze laser-induced ultrafast, spatially inhomogeneous magnetization dynamics of epitaxial Co/Cu(001) films in a 0.4–10 nm thickness range with time-resolved magnetization-induced second harmonic generation, which probes femtosecond spin dynamics at the vacuum/Co and Co/Cu interfaces. The interference of these two contributions makes the overall signal particularly sensitive to differences in the transient magnetization redistribution between the two interfaces, i.e., ultrafast magnetization profiles in the ferromagnetic film. We conclude that the magnetization dynamics within the first several hundred femtoseconds is characteristically dependent on the Co film thickness. In films up to 3 nm thickness, we find a stronger demagnetization at the film surface compared to the Cu/Co interface, which we explain by a spin current from Co into the Cu substrate with an effective mean free path of about 3 nm. For film thicknesses larger than 3 nm, the transient magnetization profile over the Co film reverses its sign since spins can be transferred into the substrate only from the interface near region. Our work emphasizes that spatial inhomogeneities in the dynamic magnetic response to femtosecond laser excitation allow conclusions on the underlying microscopic processes.
A wave-dominated heat transport mechanism for negative differential thermal resistance in graphene/hexagonal boron nitride heterostructures
Authors: Chen Xue-Kun , Liu Jun , Peng Zhi-Hua , Du Dan , Chen Ke-Qiu
Published: March 2017

Nonlinear thermal transport in graphene/hexagonal boron nitride (h-BN) heterostructure is investigated by the nonequilibrium molecular dynamics method. It is found that negative differential thermal resistance (NDTR) will appear as the applied temperature difference increases. Detailed phonon spectra analysis reveals that the excited out-of-plane acoustic wave plays an important role in the heat transport across such interface. That is, the mechanical wave results in a significant mismatch between the lattice vibrations of graphene and h-BN domains and hinders interfacial thermal transport. In addition, NDTR can be tuned through the temperature parameter. Interestingly, the regime of NDTR becomes smaller and eventually vanishes with increasing the heterostructure length. However, NDTR is insensitive to the variation of system width. The work may be useful for nanoscale thermal managements utilizing the graphene/h-BN heterostructure.
Extremely low thermal conductivity of high density and ordered 10 nm-diameter silicon nanowires array
Authors: Kikuchi Akiou , Yao Akifumi , Mori Isamu , Ono Takahito , Samukawa Seiji
Published: March 2017

We present the fabrication and thermal conductivity of a high-density and ordered 10 nm-diameter Si nanowires (SiNWs) array for thermoelectric devices, realized through the use of a bio-template mask as well as neutral beam etching techniques. The SiNWs were embedded into spin-on-glass (SoG) to measure the thermal conductivity of the SiNWs-SoG composites. By decreasing the thickness of SiNWs-SoG composites from 100 nm to 30 nm, the thermal conductivity was drastically decreased from 1.8 ± 0.3 W m−1 K−1 to 0.5 ± 0.1 W m−1 K−1. Moreover, when the electrical conductivities of 100 nm-long SiNWs were 1.7 × 10 S m−1, 6.5 × 103 S m−1 and 1.3 × 105 S m−1, their thermal conductivities of SiNWs-SoG composites were 1.8 ± 0.3 W m−1 K−1, 1.6 ± 0.2 W m−1 K−1 and 0.7 ± 0.2 W m−1 K−1, respectively. The cross-plane thermal conductivity of the fabricated 10 nm diameter SiNWs-SoG composites was dependent on their thickness and the electrical conductivity of SiNWs, which were significantly decreased from bulk.
Local environment structure and dynamics of CO2 in the 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and related ionic liquids
Authors: Lourenço Tuanan C. , Aparicio Santiago , Costa Gabriela C. , Costa Luciano T.
Published: March 2017

Despite the innumerous papers regarding the study of the ionic liquids as a potential candidate for CO2 capture, many details concerning the structure and dynamics of CO2 in the system are still to be revealed, i.e., the correlation between the local environment structure and the dynamic properties of the substance. This present work relied on the performance of molecular dynamics both for the neat [C2mim][Tf2N] and [C2mim][Tf2N]/CO2 mixtures in an attempt to elucidate the local environment of CO2 and their effects on the dynamic properties of [C2mim][Tf2N]. A slight change in the orientation of the cation and anion could be observed, which was correlated to the cation and anion moving away from each other in order to receive the carbon dioxide. The gas molecules pushed both the cation and the anion away to create sufficient void to its accommodation. The diffusion coefficient of [C2mim]+ is higher than [Tf2N]− regardless the increase of the CO2 concentration. The addition of CO2 in the ionic liquid has shown an increase of 4-5 times for the diffusivity of ions, which was related to the decrease of cation-anion interaction strength. The transport properties’ results showed that the addition of CO2 in the ionic liquid generates the fluidization of the system, decreasing the viscosity as a consequence of the local environment structure changing. Likewise, the effect of the type of anion and cation on the system properties was studied considering [Ac]− and [BMpyr]+ ions, showing large effects by the change of anion to [Ac]− which rise from the strong [C2mim]+–[Ac]− interaction, which conditions the solvation of ions by CO2 molecules.
Colloid-polymer mixtures under slit confinement
Authors: Pérez-Ramírez Allan , Figueroa-Gerstenmaier Susana , Odriozola Gerardo
Published: March 2017

We report a NVT molecular dynamic study of colloid-polymer mixtures under slit confinement. For this purpose, we are employing the Asakura-Oosawa model for studying colloidal particles, polymer coils, and hard walls as the external confining field. The colloid-polymer size ratio, q, is varied in the range 1⩾q⩾0.4 and the confinement distance, H, in 10σc⩾H⩾3σc, σc being the colloidal diameter. Vapor-liquid coexistence properties are assessed, from which phase diagrams are built. The obtained data fulfill the corresponding states law for a constant H when q is varied. The shift of the polymer and colloidal chemical potentials of coexistence follows a linear relationship with (H−σc)−1 for H≳4σc. The confined vapor-liquid interfaces can be fitted with a semicircular line of curvature (H−σc)−1, from which the contact angle can be obtained. We observe complete wetting of the confining walls for reservoir polymer concentrations above and close to the critical value, and partial wetting for reservoir polymer concentrations above and far from it.
Exploiting the principle parametric resonance of an electric oscillator for vibratory energy harvesting
Authors: Caldwell N. B. , Daqaq M. F.
Published: March 2017

Vibratory energy harvesters typically exploit ordinary direct resonances to mechanically amplify environmental inputs before channeling a portion of their energy into an electric load using an electromechanical transduction mechanism. Nonetheless, parametric resonance which has also been recently exploited, but to a lesser extent, holds a key advantage over direct excitations in that, when the level of input excitation exceeds a certain threshold, the amplitude of growth associated with parametric pumping is not limited by the total linear damping present in the system. While all of the previous research studies using parametric resonances for energy harvesting focused on utilizing it as a means of mechanical amplification, this letter demonstrates that vibratory excitations can also be used effectively to induce parametric resonances in the harvesting circuit itself, thereby providing a direct and simple means of electric amplification. A vibratory energy harvester exploiting this phenomenon is proposed in this letter and is shown to produce a maximum of 18 mW root-mean-square power per 1 g of input acceleration.
Device-size dependence of field-free spin-orbit torque induced magnetization switching in antiferromagnet/ferromagnet structures
Authors: Kurenkov A. , Zhang C. , DuttaGupta S. , Fukami S. , Ohno H.
Published: March 2017

We study spin-orbit torque induced magnetization switching in devices consisting of an antiferromagnetic PtMn and ferromagnetic Co/Ni multilayer with sizes ranging from 5 μm to 50 nm. As the size decreases, switching behavior changes from analogue-like to stepwise with several intermediate levels. The number of intermediate levels decreases with the decreasing size and finally evolves into a binary mode below a certain threshold. The results are found to be explained by a unique reversal process of this system, where ferromagnetic domains comprising a number of polycrystalline grains reverse individually and among the domains both out-of-plane and in-plane components of exchange bias vary.
Thermo-mechanical vibration of a single-layer graphene sheet and a single-walled carbon nanotube on a substrate
Authors: Ding Dongqing , Yang Zhaoyao , Dong Shuhong , Yu Peishi , Zhao Junhua
Published: March 2017

The thermo-mechanical vibration of a single-layer graphene sheet (SLGP) and a single-walled carbon nanotube (SWCNT) on a substrate is studied by using a nonlocal elastic plate model and two nonlocal elastic beam models (including Timoshenko-beam model and Euler-beam model) with quantum effects, respectively. The effect of the van der Waals (vdW) interactions between the SLGP (or the SWCNT) and the substrate on the vibration is obtained. Checking against our molecular dynamics simulations shows that the present models are reasonable. In particular, the radial vibration of the SWCNT on the substrate with quantum effects is further derived through the continuum shell model due to the different vdW forces on each point of the SWCNT circumference. The present models show that the normalized transverse frequency decreases and the normalized radial frequency increases with increasing SWCNT radius, respectively. The radial amplitude of the SWCNT (or the amplitude of the SLGP) nonlinearly increases and the transverse amplitude of the SWCNT linearly increases with increasing temperature for a given distance, respectively. The obtained analytical solution should be of great importance for understanding the thermo-mechanical vibration of nanoelectronic devices on a substrate.
Microstructure control of macroscopic graphene paper by electrospray deposition and its effect on thermal and electrical conductivities
Authors: Xin Guoqing , Zhu Weiguang , Yao Tiankai , Scott Spencer Michael , Lian Jie
Published: March 2017

Macroscopic graphene paper is fabricated by an electrospray deposition approach, and the microstructure can be controlled from highly porous to highly compact geometries by varying deposition parameters including graphene colloid concentration and deposition rate. Free-standing graphene films can be separated from substrates via a simple water exfoliation method in which the surface properties of graphene films and substrates control film exfoliation. Specifically, water exfoliation can be achieved when the contact angle of substrates is 64° or below. Thermal and electrical conductivities of the macroscopic graphene paper upon thermal annealing are measured, enabling the establishment of the process-microstructure-property correlation beneficial for further development and property manipulation of graphene-based materials.
Comparative study of the breakdown transients of thin Al2O3 and HfO2 films in MIM structures and their connection with the thermal properties of materials
Authors: Pazos S. , Aguirre F. , Miranda E. , Lombardo S. , Palumbo F.
Published: March 2017

In this work, the breakdown transients of Al2O3- and HfO2-based metal-insulator-metal (MIM) stacks with the same oxide thickness and identical metal electrodes were compared. Their connection with the thermal properties of the materials was investigated using alternative experimental setups. The differences and similarities between these transients in the fast and progressive breakdown regimes were assessed. According to the obtained results, Al2O3 exhibits longer breakdown transients than HfO2 and requires a higher voltage to initiate a very fast current runaway across the dielectric film. This distinctive behavior is ascribed to the higher thermal conductivity of Al2O3. Overall results link the breakdown process to the thermal properties of the oxides under test rather than to dissipation effects occurring at the metal electrodes.
A silicon microwire under a three-dimensional anisotropic tensile stress
Authors: Ji Xiaoyu , Poilvert Nicolas , Liu Wenjun , Xiong Yihuang , Cheng Hiu Yan , Badding John V. , Dabo Ismaila , Gopalan Venkatraman
Published: March 2017

Three-dimensional tensile stress, or triaxial tensile stress, is difficult to achieve in a material. We present the investigation of an unusual three-dimensional anisotropic tensile stress field and its influence on the electronic properties of a single crystal silicon microwire. The microwire was created by laser heating an amorphous silicon wire deposited in a 1.7 μm silica glass capillary by high pressure chemical vapor deposition. Tensile strain arises due to the thermal expansion mismatch between silicon and silica. Synchrotron X-ray micro-beam Laue diffraction (μ-Laue) microscopy reveals that the three principal strain components are +0.47% (corresponding to a tensile stress of +0.7 GPa) along the fiber axis and nearly isotropic +0.02% (corresponding to a tensile stress of +0.3 GPa) in the cross-sectional plane. This effect was accompanied with a reduction of 30 meV in the band gap energy of silicon, as predicted by the density-functional theory calculations and in close agreement with energy-dependent photoconductivity measurements. While silicon has been explored under many stress states, this study explores a stress state where all three principal stress components are tensile. Given the technological importance of silicon, the influence of such an unusual stress state on its electronic properties is of fundamental interest.
Stress originating from nanovoids in hydrogenated amorphous semiconductors
Authors: Wang Zumin , Flötotto David , Mittemeijer Eric J.
Published: March 2017

Structural inhomogeneities in the form of voids of nanometer sizes (nanovoids) have long been known to be present in hydrogenated amorphous semiconductors (Si, Ge). The physical and electrical properties of hydrogenated amorphous semiconductors can be pronouncedly influenced by the presence and characteristics of such nanovoids. In this work, by measuring in situ the intrinsic stress developments during deposition of pure, amorphous and of hydrogenated amorphous semiconductor (Si, Ge) thin films, under the same conditions in ultrahigh vacuum and on a comparative basis, a major source of tensile stress development could be ascribed to the occurrence of nanovoids in a-Si:H and a-Ge:H. The measurements allowed a quantitative evaluation of the surface stress acting along the surface of the nanovoids: 1.1–1.9 N/m for a-Si:H and 0.9–1.9 N/m for a-Ge:H.
Optical interactions of silver nanoparticle decorated cellulose nanocrystals created from a one-pot reduction method
Authors: Dawson Nathan J. , Spinella Stephen , Peters Kyle C. , Maiorana Anthony , Qian Qian , Hepworth Victoria , Gross Richard A. , Singer Kenneth D.
Published: March 2017

Modified cellulose nanocrystals were decorated with silver nanoparticles using a one-pot reduction method. In contrast to a quasi-uniform distribution of silver nanoparticles, we report on the interactions of non-contact nanoparticle clusters with significant line broadening and red shifts in the extinction spectra. The particle size and cluster distributions were examined using a transmission electron microscope. Monte Carlo random walk (MCRW) simulations of the extinction spectrum show that the interacting silver nanospheres are organized in small, non-contact clusters. We observed that the MCRW optimization using the first-order iterative approximation to the self-consistent dipole field equations quickly approaches the observed localized clusters.
Dependence of surface plasmon-phonon-polariton in 4 H-SiC on free carrier concentration
Authors: Karakachian H. , Kazan M.
Published: March 2017

In this paper, we present a thorough study of the characteristics of the surface modes that result from coupling between plasmon electronic oscillation modes, phonon modes, and electromagnetic modes. The Fourier transform of p-polarized reflectivity measurements were carried out on different 4 H-SiC epilayers differing in their free carrier concentration. The reflectivity measurements were performed with appropriate care to record reflectivity spectra averaged over a wide range of incidence angles. The complex infrared dielectric functions of the measured samples were determined by correcting the values obtained from the conventional Kramers-Kronig conversion technique with reference to Fresnel equations for reflectivity. The obtained dielectric functions were used to compute the effect of the free carrier concentration and the resulting plasmon electronic oscillation on the dispersion spectrum, lifetime, mean propagation length of the bulk, and surface plasmon-phonon-polariton modes. The effect of the free carrier concentration on the temporal coherence of surface plasmon-phonon-polariton is investigated, showing a potential practical method for enhancing the temporal coherence of SiC based thermal sources.
Observation of two-photon photoemission from cesium telluride photocathodes excited by a near-infrared laser
Authors: Panuganti H. , Piot P.
Published: March 2017

We explore the nonlinear photoemission in cesium telluride (Cs2Te) photocathodes where an ultrashort (∼100 fs full width at half max) 800-nm infrared laser is used as the drive-laser in lieu of the typical ∼266-nm ultraviolet laser. An important figure of merit for photocathodes, the quantum efficiency, we define here for nonlinear photoemission processes in order to compare with linear photoemission. The charge against drive-laser (infrared) energy is studied for different laser energy and intensity values and cross-compared with previously performed similar studies on copper [P. Musumeci et al., Phys. Rev. Lett. 104, 084801 (2010)], a metallic photocathode. We particularly observe two-photon photoemission in Cs2Te using the infrared laser in contrast to the anticipated three-photon process as observed for metallic photocathodes.
Rotational spectra of two six-membered heterocyclic N-methyl-piperidinol compounds: Conformations by OH rotation, N-methyl inversion, and ring puckering
Authors: Thomas Javix , Mariona Eric , Xu Yunjie
Published: March 2017

Rotational spectra of two nitrogen containing six-membered heterocycles which are commonly used in syntheses of pharmaceuticals, namely, N-methyl-3-piperidinol (NMP3) and N-methyl-4-piperidinol (NMP4), were measured using a broadband chirped pulse and a cavity based Fourier transform microwave spectrometer. The possible conformers due to the OH rotation, N-methyl inversion, and ring puckering were investigated theoretically for these two heterocycles. The substituent position of the hydroxyl group with respective to the N atom in the heterocyclic ring has a strong influence on the preferred conformations. While one dominant conformer, favoring the OH⋯N close contact, was predicted for NMP3, several close energy conformers with OH pointing at different directions were predicted for NMP4. In contrast, only one conformer was identified for each compound experimentally. The 14N nuclear quadrupole hyperfine structures were observed for all rotational transitions and analyzed. In addition, rotational spectra of all 13C and 15N isotopologues of NMP4 were studied in their natural abundance, leading to a definite identification of the NMP4 conformer observed. The differences in the conformational landscapes and the OH motions in the two compounds are presented and also discussed in the context of the 1,3-diaxial interaction rule commonly used in organic chemistry.
A plastic-composite-plastic structure high performance flexible energy harvester based on PIN-PMN-PT single crystal/epoxy 2-2 composite
Authors: Zeng Zhou , Gai Linlin , Wang Xian , Lin Di , Wang Sheng , Luo Haosu , Wang Dong
Published: March 2017

We present a high performance flexible piezoelectric energy harvester constituted by a Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN-PMN-PT) single crystal/epoxy 2-2 composite flake, a polyethylene terephthalate (PET) substrate, and a PET cover, which is capable of harvesting energy from biomechanical movements. Electrical properties of the device under different epoxy volume fractions, load resistances, and strains are studied systematically. Both theoretical and experimental results show that the plastic-composite-plastic structure contributes to the flexibility of the device, and a high performance bulk PIN-PMN-PT single crystal (a thickness of 50 μm) results in its high electrical output. At a low excitation frequency of 4.2 Hz, the optimal flexible energy harvester (with ve = 21%) can generate a peak voltage of 12.9 V and a maximum power density of 0.28 mW/cm3 under a bending radius of 10.5 mm, and maintain its performance after 40 000 bending-unbending cycles. High flexibility and excellent electrical output at low operational frequency demonstrate the promise of the device in biomechanical motion energy harvesting for wireless and portable low-power electronics.
In situ transmission electron microscope formation of a single-crystalline Bi film on an amorphous substrate
Authors: Neklyudova M. , Sabater C. , Erdamar A. K. , van Ruitenbeek J. M. , Zandbergen H. W.
Published: March 2017

We have performed a range of in situ heating experiments of polycrystalline Bi films of 22–25 nm-thickness in a transmission electron microscope (TEM). This shows that it is possible to locally transform a polycrystalline thin film into a [111]-oriented single-crystalline film, whereby the unique feature is that the original thickness of the film is maintained, and the substrate used in our experiments is amorphous. The single-crystalline areas have been created by heating the Bi film to temperatures close to the melting temperature with additional heating by focusing of the electron beam (e-beam), which results in local melting of the film. The film does not collapse by dewetting, and upon subsequent cooling, the film transforms into a single-crystalline [111] oriented area. The observed phenomenon is attributed to the presence of a thin Bi-oxide layer on top of Bi film. We show that removal of the Bi-oxide layer by heating the film in a H2 gas atmosphere results in changes in the Bi film thickness and dewetting upon in situ heating in the TEM.
A niobium oxide-tantalum oxide selector-memristor self-aligned nanostack
Authors: Diaz Leon Juan J. , Norris Kate J. , Yang J. Joshua , Sevic John F. , Kobayashi Nobuhiko P.
Published: March 2017

The integration of nonlinear current-voltage selectors and bi-stable memristors is a paramount step for reliable operation of crossbar arrays. In this paper, the self-aligned assembly of a single nanometer-scale device that contains both a selector and a memristor is presented. The two components (i.e., selector and memristor) are vertically assembled via a self-aligned fabrication process combined with electroforming. In designing the device, niobium oxide and tantalum oxide are chosen as materials for selector and memristor, respectively. The formation of niobium oxide is visualized by exploiting the self-limiting reaction between niobium and tantalum oxide; crystalline niobium (di)oxide forms at the interface between metallic niobium and tantalum oxide via electrothermal heating, resulting in a niobium oxide selector self-aligned to a tantalum oxide memristor. A steady-state finite element analysis is used to assess the electrothermal heating expected to occur in the device. Current-voltage measurements and structural/chemical analyses conducted for the virgin device, the electroforming process, and the functional selector-memristor device are presented. The demonstration of a self-aligned, monolithically integrated selector-memristor device would pave a practical pathway to various circuits based on memristors attainable at manufacturing scales.
Flexible plasma linear antenna
Authors: Zhao Jiansen , Wang Shengzheng , Wu Huafeng , Liu Yue , Chang Yongmeng , Chen Xinqiang
Published: March 2017

In this work, we introduce a type of plasma antenna that was fabricated using flexible materials and excited using a 5−20 kHz alternating current (ac) power supply. The results showed that the antenna characteristics, including the impedance, the reflection coefficient (S11), the radiation pattern, and the gain, can be controlled rapidly and easily by varying both the discharge parameters and the antenna shapes. The scope for reconfiguration is greatly enhanced when the antenna shape is changed from a monopole to a helix configuration. Additionally, the antenna polarization can also be adjusted by varying the antenna shapes.
Photoluminescence enhancement of ZnO via coupling with surface plasmons on Al thin films
Authors: Dellis S. , Kalfagiannis N. , Kassavetis S. , Bazioti C. , Dimitrakopulos G. P. , Koutsogeorgis D. C. , Patsalas P.
Published: March 2017

We present that the ultra-violet emission of ZnO can be enhanced, as much as six-times its integral intensity, using an Al thin interlayer film between the Si substrate and ZnO thin film and a post-fabrication laser annealing process. The laser annealing is a cold process that preserves the chemical state and integrity of the underlying aluminum layer, while it is essential for the improvement of the ZnO performance as a light emitter and leads to enhanced emission in the visible and in the ultraviolet spectral ranges. In all cases, the metal interlayer enhances the intensity of the emitted light, either through coupling of the surface plasmon that is excited at the Al/ZnO interface, in the case of light-emitting ZnO in the ultraviolet region, or by the increased back reflection from the Al layer, in the case of the visible emission. In order to evaluate the process and develop a solid understanding of the relevant physical phenomena, we investigated the effects of various metals as interlayers (Al, Ag, and Au), the metal interlayer thickness, and the incorporation of a dielectric spacer layer between Al and ZnO. Based on these experiments, Al emerged as the undisputable best choice of metal interlayers because of its compatibility with the laser annealing process, as well as due to its high optical reflectivity at 380 and 248 nm, which leads to the effective coupling with surface plasmons at the Al/ZnO interfaces at 380 nm and the secondary annealing of ZnO by the back-reflected 248 nm laser beam.
Mechanical and electronic properties of SiC nanowires: An ab initio study
Authors: Oliveira J. B. , Morbec J. M. , Miwa R. H.
Published: March 2017

Using first-principles calculations, based on the density functional theory, we have investigated the mechanical and electronic properties of hydrogen-passivated 3C-, 2H-, 4H-, and 6H-SiC nanowires (NWs), analyzing the effects of the diameter on these properties. Our results show that the band-gap energies of the nanowires are larger than the corresponding bulk values and decrease with the increasing diameter. All nanowires investigated exhibit direct band gaps, in contrast with the indirect band gaps observed in bulk SiC. The effect of uniaxial stress on the electronic properties of SiC nanowires has also been examined, and our results reveal that the band-gap dependence on the strain is different for each nanowire polytype. In 3C-SiC nanowires, the band gaps increase (decrease) with tensile (compressive) strain. For 4H- and 6H-SiC nanowires, the influence of strain on the band gaps is more pronounced in the thicker wires. Finally, we estimated the band offsets of hypothetical NW homostructures, composed of stacking SiCNW layers with different polytypes.
Coexistence of gyromagnetic resonance and low frequency plasmonic state in the submicron Ni granular composite materials
Authors: Massango Herieta , Tsutaoka Takanori , Kasagi Teruhiro , Yamamoto Shinichiro , Hatakeyama Kenichi
Published: March 2017

Relative complex permeability and permittivity spectra of submicron Ni granular composite materials have been studied from RF to microwave frequency range for realization of the negative permittivity and permeability spectra. The Ni particles are spherical in shape with the average diameter of 170 nm; the electrical conductivity of compacted particles shows a semiconductive property. From the variation of conductivity with particle content, it was found that the Ni composite material indicates an electrical percolation at 56.0 vol. % where the conductivity shows an abrupt increase. Above the percolation threshold, a positive permittivity spectrum with conductive loss was observed up to 65.7 vol. %; the low frequency plasmonic state with the negative permittivity spectrum was found at the particle content of 66.1 vol. %. A negative permeability spectrum caused by the gyromagnetic spin resonance was also observed in the particle content above 60 vol. %. The coexistence of negative permittivity and permeability spectra was realized in the 66.1 vol. % Ni granular composite. The negative permeability spectrum was induced by the external magnetic field in the percolated 57.5 vol. % sample; a ferromagnetic resonance type permeability dispersion is enhanced by the external field.
Interpretation of the surface charge decay kinetics on insulators with different neutralization mechanisms
Authors: Zhang Boya , Zhang Guixin
Published: March 2017

Surface charge decay kinetics on corona-charged polymeric insulators were studied. In the experiment, the sample surface exposed to corona was kept open to ambient air whereas the opposite surface was in contact with a grounded plate. The resulting surface potential distribution was scanned in a raster mode using a Kelvin electrostatic probe, from which the relief map of charge density was obtained by an inverse calculation method. The developed procedure allowed for implementation of two study cases: (i) gas neutralization took place under natural conditions, with enhanced concentration of free ions, and with limited gas volume; (ii) surface charge decay occurred only due to bulk neutralization. Three mechanisms were considered responsible for surface charge decay, i.e., bulk neutralization, gas neutralization, and surface conduction. They were discussed separately with the help of numerical models, which quantified the relative importance of each mechanism on the total process of charge decay. The results of the latter case were further utilized to determine the energy distribution of electron and hole traps of the materials based on the isothermal relaxation current theory.
Observation of weak antilocalization effect in high-quality ScNiBi single crystal
Authors: Deng L. , Liu Z. H. , Ma X. Q. , Hou Z. P. , Liu E. K. , Xi X. K. , Wang W. H. , Wu G. H. , Zhang X. X.
Published: March 2017

In this paper, we have successfully grown the high-quality ScNiBi single crystals by a Bi flux method and investigated their electronic-transport properties. It was found that the ScNiBi single crystal is a gapless semiconductor with positive linear magnetoresistance (MR). Moreover, the field-dependent MR in the low-field region has demonstrated obvious weak antilocalization (WAL) effect below 50 K. The extremely large prefactor α and angle-dependent magnetoconductance ΔGxx suggest that the WAL effect originates from the contribution of a strong bulk spin-orbital coupling.
Time resolved small angle X-ray scattering experiments performed on detonating explosives at the advanced photon source: Calculation of the time and distance between the detonation front and the x-ray beam
Authors: Gustavsen R. L. , Dattelbaum D. M. , Watkins E. B. , Firestone M. A. , Podlesak D. W. , Jensen B. J. , Ringstrand B. S. , Huber R. C. , Mang J. T. , Johnson C. E. , Velizhanin K. A. , Willey T. M. , Hansen D. W. , May C. M. , Hodgin R. L. , Bagge-Hansen M. , van Buuren A. W. , Lauderbach L. M. , Jones A. C. , Graber T. J. , Sinclair N. , Seifert S. , Gog T.
Published: March 2017

Time resolved Small Angle X-ray Scattering (SAXS) experiments on detonating explosives have been conducted at Argonne National Laboratory's Advanced Photon Source Dynamic Compression Sector. The purpose of the experiments is to measure the SAXS patterns at tens of ns to a few μs behind the detonation front. Corresponding positions behind the detonation front are of order 0.1–10 mm. From the scattering patterns, properties of the explosive products relative to the time behind the detonation front can be inferred. This report describes how the time and distance from the x-ray probe location to the detonation front is calculated, as well as the uncertainties and sources of uncertainty associated with the calculated times and distances.
Analytic energy gradient of projected Hartree–Fock within projection after variation
Authors: Uejima Motoyuki , Ten-no Seiichiro
Published: March 2017

We develop a geometrical optimization technique for the projection-after-variation (PAV) scheme of the recently refined projected Hartree–Fock (PHF) as a fast alternative to the variation-after-projection (VAP) approach for optimizing the structures of molecules/clusters in symmetry-adapted electronic states at the mean-field computational cost. PHF handles the nondynamic correlation effects by restoring the symmetry of a broken-symmetry single reference wavefunction and moreover enables a black-box treatment of orbital selections. Using HF orbitals instead of PHF orbitals, our approach saves the computational cost for the orbital optimization, avoiding the convergence problem that sometimes emerges in the VAP scheme. We show that PAV-PHF provides geometries comparable to those of the complete active space self-consistent field and VAP-PHF for the tested systems, namely, CH2, O3, and the [Cu2O2]2+ core, where nondynamic correlation is abundant. The proposed approach is useful for large systems mainly dominated by nondynamic correlation to find stable structures in many symmetry-adapted states.
An analytical solution for contact resistance of staggered organic field-effect transistors
Authors: Karimi-Alavijeh Hamidreza , Katebi-Jahromi Alireza
Published: March 2017

We have developed analytical models for bias dependent contact resistance (RC) and output characteristics of staggered organic field-effect transistors (OFETS) based on a bulk resistance-approximated and mobility-modified current-crowding method. Numerical evaluations of RC and its resistive components show that the bias dependency of the bulk resistance is negligible. Consequently, the properties of the active layer interfaces determine RC and its characteristics. Effective parameters include a normally constant charge injection barrier at the organic-metal interface (Eb) and a gate induced surface carrier-concentration (PS0) at the organic-insulator boundary. The energy barrier pertains to the fabrication process, and its related resistance (rc) can be determined as the fitting parameter of the theoretical model. However, PS0 is strongly gate bias dependent and the results of the numerical model indicate that the resulting component (rch) is dominant and has a considerable effect on RC and its characteristics. More importantly, PS0 as the key parameter of the contact resistance is analytically expressible and by using a proposed mobility-modified current-crowding model, the contact resistance can be analytically formulated. Accordingly, the output characteristics of the OFETs in the triode region can be also analytically modeled using the developed relation of RC.
Measurement of thin film interfacial surface roughness by coherence scanning interferometry
Authors: Yoshino H. , Abbas A. , Kaminski P. M. , Smith R. , Walls J. M. , Mansfield D.
Published: March 2017

Coherence Scanning Interferometry (CSI), which is also referred to as scanning white light interferometry, is a well-established optical method used to measure the surface roughness and topography with sub-nanometer precision. One of the challenges CSI has faced is extracting the interfacial topographies of a thin film assembly, where the thin film layers are deposited on a substrate, and each interface has its own defined roughness. What makes this analysis difficult is that the peaks of the interference signal are too close to each other to be separately identified. The Helical Complex Field (HCF) function is a topographically defined helix modulated by the electrical field reflectance, originally conceived for the measurement of thin film thickness. In this paper, we verify a new technique, which uses a first order Taylor expansion of the HCF function to determine the interfacial topographies at each pixel, so avoiding a heavy computation. The method is demonstrated on the surfaces of Silicon wafers using deposited Silica and Zirconia oxide thin films as test examples. These measurements show a reasonable agreement with those obtained by conventional CSI measurement of the bare Silicon wafer substrates.
Nonlinear TE-polarized SPPs on a graphene cladded parallel plate waveguide
Authors: Wu Yuexiang , Dai Xiaoyu , Xiang Yuanjiang , Fan Dianyuan
Published: March 2017

We consider the transverse electric (TE) surface plasmon polaritons (SPPs) supported by a graphene parallel plate waveguide bounded by Kerr-type nonlinear media in the mid-infrared and terahertz frequencies. Through theoretical analysis of the exact dispersion relations, we reveal the existence conditions of the even mode and odd mode of nonlinear TE SPPs in this system. To be specific, if the linear permittivity of the nonlinear cladding is larger than the permittivity of the core, it only supports the even mode and two branches of the dispersion curve exist. However, when the linear permittivity of the nonlinear cladding is smaller than the permittivity of the core, both even and odd modes can be supported. Moreover, it is found that the propagation constant of even and odd modes decreases with the increasing Fermi energy of graphene.