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This paper presents an overview of experimental results of a laser-produced plasma expanding into a background gas, immersed within a large range of highly uniform magnetic fields (of up to 3 T), that are transverse to the expanding plasma. We used intensified gated imaging to capture the expansion of the plasma across and along the magnetic field lines to observe the spatiotemporal expansion dynamics for different magnetic field strengths. We observe changes in the perpendicular and parallel dynamics of the laser-produced plasmas expansion at high magnetic field. In addition, our results have also indicated the presence of electron-ion hybrid instabilities at relatively high pressures (100 mTorr) and relatively high magnetic field strengths (2 T), in accordance with theoretical calculations. [ABSTRACT FROM AUTHOR]

We have observed the behavior of striations caused by ionization waves propagating in low-pressure helium DC discharges using the non-invasive laser-collision induced fluorescence (LCIF) diagnostic. To achieve this, we developed an analytic fit of collisional radiative model (CRM) predictions to interpret the LCIF data and recover quantitative two-dimensional spatial maps of the electron density, ne, and the ratios of LCIF emission states that can be correlated with Te with the use of accurate distribution functions at localized positions within striated helium discharges at 500 mTorr, 750 mTorr, and 1 Torr. To our knowledge, these are the first spatiotemporal, laser-based, experimental measurements of ne in DC striations. The ne and 447:588 ratio distributions align closely with striation theory. Constriction of the positive column appears to occur with decreased gas pressure, as shown by the radial ne distribution. We identify a transition from a slow ionization wave to a fast ionization wave between 750 mTorr and 1 Torr. These experiments validate our analytic fit of ne, allowing the implementation of an LCIF diagnostic in helium without the need to develop a CRM. [ABSTRACT FROM AUTHOR]

In this study, we present a microspectroscopic investigation on the quasi-transverse optical phonon modes Q(TO) in some self-generated aluminum nitride (AlN) grains grown on sapphire using hydride vapor phase epitaxy. Using X-ray diffraction and transmission electron microscope, these grains were confirmed to be embedded in (0001)-AlN (c-AlN) epitaxial matrix with an appearance plane of (1011) (s-plane). Two beam bright field images further showed that the AlN grains were free of dislocation. In-plane phonon anisotropy of the AlN grains was discussed in detail using angular-dependent polarized Raman spectroscopy. The dependence of pure Raman phonons intensity on rotation angle agrees well with the calculation. The Q(TO) phonon intensity exhibited similar behavior to that of A1(TO) phonon, which can be explained by Loudon's formula. However, the observed frequency fluctuation for the Q(TO) phonon differs from that of the pure phonon modes, which cannot be directly understood from the classic Loudon's formula. A modified Loudon's formula appropriate to non-normal incidence was presented to explain the observed Q(TO) phonon frequency fluctuation. Combining with the angular-dependent Raman spectra, we proposed that a small inclination of s-plane along with the various in-plane orientations in c-AlN matrix lead to the frequency fluctuation of Q(TO) in these embedded semipolar AlN grains. [ABSTRACT FROM AUTHOR]

In the present work, polycrystalline Ni45Co5-xPdxMn37In13 (x = 0, 0.5, 1, and 3) Heusler alloys were prepared. The influences of Pd substitution for Co on crystal structure, martensitic transformation (MT), and magnetic properties have been carefully investigated for these quinary alloys. The structure measurement indicates that every sample possesses L10 martensitic structure at room temperature. With increasing of Pd content, it is found that the MT region shifts towards higher temperature, but the Curie transition region of austenitic state moves to lower temperature. Owing to the fact that the MT gradually approaches Curie point, the magnetization of austenitic phase is significantly decreased, while the one of martensitic phase almost remains unchanged. In addition, the functional properties associated with the field-induced reverse MT have been also studied in Ni45Co5-xPdxMn37In13 (x = 0, 0.5, and 1) alloys. In comparison to quaternary parent alloy, both of enhanced magnetostrain (0.3%) and isothermal entropy change (25 J/kg K) are observed in quinary Ni45Co4.5Pd0.5Mn37In13 alloy under an applied magnetic field up to 3 T. The implication of such results has been discussed in detail. [ABSTRACT FROM AUTHOR]

Graphene is fabricated by thermal decomposition of silicon carbide (SiC) and Pb islands are deposited by Pb flux in molecular beam epitaxy chamber. It is found that graphene domains and SiC buffer layer coexist. Selective growth of Pb islands on SiC buffer layer rather than on graphene domains is observed. It can be ascribed to the higher adsorption energy of Pb atoms on the 6√3 reconstruction of SiC. However, once Pb islands nucleate on graphene domains, they will grow very large owing to the lower diffusion barrier of Pb atoms on graphene. The results are consistent with first-principle calculations. Since Pb atoms on graphene are nearly free-standing, Pb islands grow in even-number mode. [ABSTRACT FROM AUTHOR]

A nanosecond pulsed atmospheric pressure dielectric barrier glow discharge in helium with 1% of argon was studied. The effects of the electric field, frequency, and gas mixture ratio on the temporal behavior of the plasma discharge were captured with an ICCD camera. Special interest was given to the timing and scale of the secondary or return stroke. It was found that the external electric field can control the occurrence of the return stroke in a dielectric barrier discharge. If the electric field is high enough, the return stroke occurs earlier than previously observed in other works. Increasing frequency leads to faster discharge initiation times for both the primary and secondary discharges. Increasing the argon ratio of the mixture leads to an increased intensity of the primary discharge, a decrease in the intensity of the secondary discharge, and a delay in the timing of the primary discharge. [ABSTRACT FROM AUTHOR]

The energy bands and electronic states of hybrid boron nitride (BN) and graphene structures are studied by first principle calculations. The electronic states change from semi-metallic to insulating depending on the number of B and N atoms as well as domain symmetry. When there are unequal numbers of B and N atoms, mid-gap states usually appear around the Fermi level and the corresponding hybrid structure possesses magnetic and semi-metallic properties. However, when the numbers of B and N atoms are equal, a band gap exists indicative of a semiconducting or insulating nature which depends on the structural symmetry. [ABSTRACT FROM AUTHOR]

The work reported in this paper aims at studying the magneto-electric field variation accounting for a thin interphase layer with different materials. Thin interphase within a solid can significantly affect the overall response of the composite material. In order to obtain this phenomenon, we replace the interphase by an imperfect interface with appropriately devised interface conditions. To get the interface conditions, a Taylor expansion of the relevant physical fields in the thin region is introduced. Those conditions do not involve the fields within the interphase, which just have relation to the material properties and the fields of the adjacent media. Finally, the influence of the thin interphase on the performance of fibrous multiferroic composites is analyzed in detail by using our method and some useful conclusions are summarized. [ABSTRACT FROM AUTHOR]

Kinetic roughening of tantalum films during the initial growth stages has been studied by atomic force microscopy, scanning electron microscopy, and dynamic scaling theory. Different from the time-independent scaling behavior for continuous film growth, an intriguing unstable kinetic roughening occurs during island coalescence. In such case, roughness exponent α increases with growth time, accompanied by lower growth exponent β and higher coarsening exponent η. Detailed analysis of film surface morphology and simple phenomenological models suggests that this unstable behavior is related to the pronounced lateral growth of surface islands, which arises from the combined effect of the formation of grain boundary and the covering of heterogeneous substrate surface. [ABSTRACT FROM AUTHOR]

Using the first-principle methods, we investigate the structural and electronic properties of the wurtzite InxGa1-xN (00.25. The densities of px and py orbitals are higher than that of pz orbital at the valence band top. This anisotropy induces the pronounced bowing of the pressure coefficient. [ABSTRACT FROM AUTHOR]

By using a two-dimensional ensemble Monte Carlo method, we have studied the terahertz-frequency response of a self-switching device (SSD), which is a semiconductor rectifier consisting of an asymmetric nanochannel. The simulations reveal that the performance can be improved by adjusting the shape and dielectric material filling of the insulating trenches that define the SSD. We show that the rectified current of the SSD has a nonmonotonic frequency dependence with a pronounced peak occurring just below the cutoff frequency. Through optimizations of the geometry, the peak current can reach twice that at low frequencies, enabling not only a higher detection sensitivity but also a degree of frequency selectivity. The effect is discussed in terms of a localized surface plasma oscillation in the asymmetric nanostructure. [ABSTRACT FROM AUTHOR]

NiFe/FeMn/NiFe trilayer prepared by dc magnetron sputtering was systematically investigated by ferromagnetic resonance technique (FMR) at room temperature. For NiFe/FeMn/NiFe trilayer, there are two distinct resonance peaks both in in-plane and out-of-plane FMR spectra, which are attributed to the two NiFe layers, respectively. The isotropic in-plane resonance field shift is negative for the bottom NiFe layer, while positive for the top NiFe layer. And, such phenomena result from the negative interfacial perpendicular anisotropy at the bottom NiFe/FeMn interface and positive interfacial perpendicular anisotropy at the top FeMn/NiFe interface. The linewidth of the bottom NiFe layer is larger than that of the top NiFe layer, which might be related to the greater exchange coupling at the bottom NiFe/FeMn interface. [ABSTRACT FROM AUTHOR]

Surface morphologies of Cu films with different thicknesses varying from 110 to 660 nm deposited on Ta-covered Si(111) substrates at 700 K by magnetron sputtering were investigated by atomic force microscopy (AFM). The global surface fluctuation image of the film was obtained directly from AFM measurement with larger scan size. Multiresolution wavelet transform approach incorporating power spectrum density analysis was proposed to extract the local surface fluctuation image. From these images, the dynamical exponents of both global and local surface fluctuations were calculated in terms of dynamic scaling theory. The multiscale surface evolution of Cu film could be characterized by a set of local exponent values αl≈0.87 and βl≈0.22, and global exponent values αg≈0.83 and βg≈0.85. The dynamic evolution of local surface fluctuations is consistent well with that predicted by linear surface diffusion-dominated growth equation, while the dynamic evolution of global surface fluctuations exhibits anomalous scaling behavior due to the presence of nonlocal bulk diffusion. [ABSTRACT FROM AUTHOR]

Based on an effective propagation constant and a frequency-dependent dielectric constant, the plane wave method is extended to calculate the complex photonic band diagram and the density of states for electromagnetic waves propagating in a two-dimensional finite structure with nonoverlapping dielectric cylinders of arbitrary radii, which may be randomly embedded in a dielectric matrix. The effective propagation constant is obtained by using the Twersky formula [J. Math. Phys. 3, 700 (1962)] and the scattering matrix method. A case study shows that an embedded defect with optimal radius in a finite photonic crystal can increase the first photonic band gap as compared to the similar structure without the defect. This work is expected to provide a useful tool in determining the photonic properties of a disorder dielectric medium with arbitrary embedded nanoparticles and nanowires. [ABSTRACT FROM AUTHOR]

The influence of the polarization-induced electric field on the wavelength and the absorption coefficient of the intersubband transitions (ISBTs) in AlxGa1-xN/GaN coupled double quantum wells (DQWs) have been investigated by self-consistent calculation. It is found that the wavelength of the ISBT between the first odd order and the second even order subbands (the 1odd-2even ISBT) can be shortened to 1.3 μm owing to the Stark shift induced by the polarization effect. The absorption coefficient of the 1odd-2even ISBT decreases by increasing the polarization field discontinuity. On the other hand, a shorter wavelength and a larger absorption coefficient of the ISBTs are obtained by decreasing the width of the central barrier of AlxGa1-xN/GaN DQWs. The results are beneficial to achieving devices operation within the optical communication wavelength range. [ABSTRACT FROM AUTHOR]

Vibration of a double-walled carbon nanotube aroused by nonlinear interlayer van der Waals (vdW) forces is studied. The interlayer vdW forces as a nonlinear function are described by the interlayer spacing. The inner and outer carbon nanotubes are modeled as two individual elastic beams. Detailed results are demonstrated for double-walled carbon nanotubes (DWCNTs) with an aspect ratios of 10 and 20, based on the simply supported, fixed, or free end conditions, respectively. Harmonic balance method is used to analyze the relation between the amplitudes of deflection and the frequencies of coaxial and noncoaxial free vibrations. Our results indicate that the nonlinear factors of vdW forces have little effect on the coaxial free vibration, and that the deflection amplitudes increase rapidly with the increasing frequency, which are almost the same with those of the linear free vibration. On the other hand, the nonlinear factors of vdW forces have a great effect on noncoaxial free vibration. The relation between the deflection amplitudes and the frequencies shows nonlinear trend, which indicates that the aspect ratio and end condition almost have no affect on the noncoaxial amplitudes of DWCNTs. [ABSTRACT FROM AUTHOR]

Silicon films were deposited on bare glass, copper- and gold-coated glass substrates at 200 °C. X-ray diffraction (XRD) showed that the films deposited on substrates with gold underlayer were polycrystalline while those deposited on bare glass and copper-coated glass had no identifiable crystalline silicon XRD peak. Raman spectroscopy was used to confirm the film’s crystalline properties. The Raman spectra indicated that films deposited on gold-coated glass substrates were composed of predominantly crystalline silicon with small amounts of amorphous silicon. Atomic force microscopy (AFM) was used to study the topography and adatom diffusion on the surface. AFM micrographs showed that the polycrystalline silicon films had grain size up to 95 nm. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The polarity of GaN films grown on nitrided (0001) sapphire substrates by low-pressure metalorganic vapor phase epitaxy was controlled by trymethyl-aluminum (TMA1) preflow prior to the growth of GaN buffer layer. The TMA1 preflow served as forming a few monolayers of A1 to modify the nitrided sapphire surface. The effects of the TMA1 preflow on GaN epilayer polarities were investigated by coaxial impact collision ion scattering spectroscopy. It was shown that, by increasing the TMA1 preflow time, the polarities of GaN epilayers were changed from a N polarity to a mixed polarity, and finally to a pure Ga polarity when the preflow time was over than 5 s. A schematic model of "two monolayers of AI" was proposed to understand the related mechanisms. The effects of the TMA1 preflow on the epilayer quality were also evaluated by high-resolution x-ray diffraction. [ABSTRACT FROM AUTHOR]

A highly reliable interface of an ultrathin CuSiN self-aligned barrier between Cu film and nanoporous SiC:H film has been developed in the present work for the 65 nm node and below. It is shown that the multilayer of CuSiN (4 nm)/SiC:H (15 nm)/SiCN:H (10–15 nm) as a capping barrier have the enough ability to prevent copper diffusion at elevated temperatures even up to 500 °C, good barrier hermeticity, and appropriate mechanical characteristics. With this kind of barrier stack, higher interfacial adhesion between the Cu film and dielectric barrier is achieved. The mechanisms involved have been analyzed based on detailed characterization studies. [ABSTRACT FROM AUTHOR]

The oscillatory magnetoresistance of the two-dimensional electron gas (2DEG) in AlxGa1-xN/GaN heterostructures has been studied by means of magnetotransport measurements at low temperatures and high magnetic fields. The split peaks of the Shubnikov–de Haas oscillations are observed at high magnetic fields, which are attributed to the spin splitting of the 2DEG. It is found that the spin splitting energy becomes smaller with an increase in magnetic field, indicating that the Zeeman spin splitting is not dominant at measured magnetic field range. Within this magnetic field range, the zero-field spin splitting, as well as Zeeman spin splitting, affects the split peaks in the oscillatory magnetoresistance of the 2DEG in AlxGa1-xN/GaN heterostructures. [ABSTRACT FROM AUTHOR]

The paper examines the effect of exposure time of Langmuir probes in an atmospheric premixed methane-air flame. The effects of probe size and material composition on current measurements were investigated, with molybdenum and tungsten probe tips ranging in diameter from 0.0508 to 0.1651 mm. Repeated prolonged exposures to the flame, with five runs of 60 s, resulted in gradual probe degradations (-6% to -62% area loss) which affected the measurements. Due to long flame exposures, two ion saturation currents were observed, resulting in significantly different ion densities ranging from 1.16 x 1016 to 2.71 x 1019 m-3. The difference between the saturation currents is caused by thermionic emissions from the probe tip. As thermionic emission is temperature dependent, the flame temperature could thus be estimated from the change in current. The flame temperatures calculated from the difference in saturation currents (1734-1887 K) were compared to those from a conventional thermocouple (1580-1908 K). Temperature measurements obtained from tungsten probes placed in rich flames yielded the highest percent error (9.66%-18.70%) due to smaller emission current densities at lower temperatures. The molybdenum probe yielded an accurate temperature value with only 1.29% error. Molybdenum also demonstrated very low probe degradation in comparison to the tungsten probe tips (area reductions of 6% vs. 58%, respectively). The results also show that very little exposure time (<5 s) is needed to obtain a valid ion density measurement and that prolonged flame exposures can yield the flame temperature but also risks damage to the Langmuir probe tip. [ABSTRACT FROM AUTHOR]

We investigate the performance of n-type GaAs plasmon emitters with surface layers grown by low-temperature molecular-beam epitaxy. The emitters have as-grown Be-doped low-temperature-grown GaAs layers on the top surface, which radiate terahertz transients with a power four times greater than reference emitters without low-temperature-grown (LTG) GaAs layers. The power generated by the structures with low-temperature-grown GaAs layers shows much weaker saturation at large excitation densities. The mechanism of the surface field screened by photoexcited holes has been discussed to explain the negative dip in the THz wave form when the emitter is coated by a LTG GaAs layer. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report that β-relaxation of amorphous NiW alloy film was effectively enhanced by adding two thin crystalline layers into the amorphous layer. Correspondingly, more bright bands, i.e., nano shear bands, were captured in the amorphous layer, which experienced more pronounced β-relaxations. Based on the potential energy landscape theory, the bright band was proposed to be the localized percolation of flow units corresponding to β-relaxation. Our findings may help connecting experimentally β-relaxation with flow units and shed light on the microstructure origin of β-relaxation. [ABSTRACT FROM AUTHOR]

We present unusual high hardness (up to 7.7 GPa) achieved in Cu/Al multilayers relative to monolithic Cu and Al films (∼2 GPa and ∼1 GPa, respectively). Nanotwins and stacking faults (SFs) were proposed to be the main contributors of hardness enhancement, especially when h < 5 nm. Using molecular dynamics simulations of deposition, we demonstrated that intermixing near Cu/Al interface was paramount in stabilizing the SFs in both Cu and Al layers. Our experimental results indicated that the high strength caused by layer intermixing was in sharp contrast to the general belief that only sharp interface structures could strengthen the multilayers. [ABSTRACT FROM AUTHOR]

This paper investigates the physical mechanisms that cause beneficial and detrimental performance effect observed to date in Hall effect thrusters with wall electrodes. It is determined that the wall electrode sheath can reduce ion losses to the wall if positioned near the anode (outside the dense region of the plasma) such that an ion-repelling sheath is able to form. The ability of the wall electrode to form an ion-repelling sheath is inversely proportional to the current drawn--if the wall electrode becomes the dominant sink for the thruster discharge current, increases in wall electrode bias result in increased local plasma potential rather than an ion-repelling sheath. A single-fluid electron flow model gives results that mimic the observed potential structures and the currentsharing fractions between the anode and wall electrodes, showing that potential gradients in the presheath and bulk plasma come at the expense of current draw to the wall electrodes. Secondary electron emission from the wall electrodes (or lack thereof) is inferred to have a larger effect if the electrodes are positioned near the exit plane than if positioned near the anode, due to the difference in energy deposition from the plasma. [ABSTRACT FROM AUTHOR]

We demonstrate a protocol, that combines quantum uncollapsing and dynamical decoupling, to protect the quantum state stored in a qubit against decoherence errors. The protocol can simultaneously suppress the two kinds of decoherence processes: the energy relaxation and the low-frequency noise induced dephasing. We present the analytical derivation and numerical simulations in detail. We also provide a preliminary experimental test in superconducting phase qubits, using the process fidelity to calibrate the performance of the protocol. Our results suggest that the protocol can be effective against errors due to both energy relaxation and the low-frequency dephasing noise, except at a reduced probability of success. [ABSTRACT FROM AUTHOR]

Characteristics of phase-locking between Gunn effect-based planar nano-oscillators are studied using an ensemble Monte Carlo (EMC) method. Directly connecting two oscillators in close proximity, e.g. with a channel distance of 200 nm, only results in incoherent oscillations. In order to achieve in-phase oscillations, additional considerations must be taken into account. Two coupling paths are shown to exist between oscillators. One coupling path results in synchronization and the other results in anti-phase locking. The coupling strength through these two paths can be adjusted by changing the connections between oscillators. When two identical oscillators are in the anti-phase locking regime, fundamental components of oscillations are cancelled. The resulting output consists of purely second harmonic oscillations with a frequency of about 0.66 THz. This type of second harmonic generation is desired for higher frequency applications since no additional filter system is required. This transient phase-locking process is further analyzed using Adler's theory. The locking range is extracted, and a criterion for the channel length difference required for realizing phased arrays is obtained. This work should aid in designing nanooscillator arrays for high power applications and developing directional transmitters for wireless communications. [ABSTRACT FROM AUTHOR]

We report a direct experimental study on the surface dynamics of reactive-sputtered compositionally graded (CG) CrNx films. Based on the dynamic scaling analysis, an intriguing transition of surface dynamics from Family-Vicsek scaling (I regime) to "oscillating" mode (II regime) and then to anomalous rapid-roughening scaling (III regime) is observed. This transition is closely related to the reactive sputtering process of CG nitride films. Especially, it is found that the oscillating behavior of surface dynamics in regime II originates from the alternate growth of crystalline and amorphous phases on the growing surface. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation is performed to analyze the deformation mechanism of graphene nanoribbons. When the load is applied along the zigzag orientation, tensile stress yields brittle fracture and compressive stress results in lattice shearing and hexagonal-to-orthorhombic phase transformation. Along the armchair direction, tensile stress produces lattice shearing and phase transformation, but compressive stress leads to a large bonding force. The phase transformation induced by lattice shearing is reversible for 17% and 30% strain in compressive loading along the zigzag direction and tensile loading along the armchair direction. The energy dissipation is less than 10% and resulting pseudo-elasticity enhances the ductility. [ABSTRACT FROM AUTHOR]

Scanning tunneling microscopy (STM) is performed to study the formation mechanism of graphene on 6H-SiC by thermal decomposition in situ and the evolution of an atomically resolved 6×6 structure in the buffer layer is revealed. The long-range order of the 6×6 structure is maintained during growth, but the short-range arrangement changes with temperature. Based on STM images acquired at different voltages, a structure consisting of triangular silicon clusters with the 6×6 structure and filled by amorphous carbon atoms is proposed. The 6×6 silicon clusters serve as the template and amorphous carbon atoms provide the carbon source for graphene growth. [ABSTRACT FROM AUTHOR]

Scanning tunneling microscopy is used to study the edge orientation of graphene fabricated by thermal decomposition of 6H-SiC. The exploration on the atomically resolved structures and the patterns in reciprocal space demonstrates that the armchair direction is always parallel to the basic vector of 6 × 6 reconstruction as well as the close-packed direction of 6H-SiC substrate. This can be used as the criterion to characterize the edge direction of graphene. With this method, it is found that armchair edges are preferred in both monolayer and bilayer regions. This special edge certainly will affect the electronic states and consequently the properties. [ABSTRACT FROM AUTHOR]

First-principle calculation based on density functional theory is performed to study the lattice vibration, heat capacity, and thermal conductivity of graphene under strain. Two degenerate optical branches in the phonon dispersion curves split near the G points due to the reduced crystal symmetry, and the frequencies of the optical phonon modes shift down thus inducing more phonon modes at a given temperature. The heat capacity is increased, but the thermal conductivity is reduced because of enhanced Umklapp scattering among more phonons. This phenomenon should be considered when determining the heat management of graphene-based devices. [ABSTRACT FROM AUTHOR]

Pulse-modulated RF atmospheric pressure glow discharges (APDGs) were investigated in recent years to reduce the thermal accumulation and extend the operation region of the stable alpha glow mode. Different pulse-modulated voltage and current waveforms were acquired in previous experiments, but no attention was paid to the interpretation. We investigated this issue and associated phenomenon via positive and negative feedback effects derived from varying the series capacitor in the inversely L-shaped matching network used in our pulse-modulated RF APGD source. The evolutions of pulse-modulated RF waveforms were found to be associated with the feedback region and the pulsed plasma absorbed RF power. In the positive feedback region, pulse-modulated RF APGDs are relatively stable. In the negative feedback region, wide spikes as well as undershoots occur in RF voltage and current waveforms and the plasma absorbed RF power. In case of a high RF power discharge with a low modulation frequency, the pulse-modulated RF APGD is extinguished and re-ignited due to the enhanced undershoot during the initial pulse phase. The pulse-modulated RF APGD can transit from positive to negative feedback region in a range of series capacitance. Experimental results are discussed by the aid of equivalent circuit, negative and positive feedback effects. [ABSTRACT FROM AUTHOR]

A study on the bound states of Fe impurities in GaN by ultraviolet photoluminescence (PL) emissions is presented. Two elusive PL lines were observed at 3.463 eV (L1) and 3.447 eV (L2), respectively. The intensities of the two lines are proportional to the Fe concentration. The temperature dependence of L1 and L2 revealed acceptor-like and strong localized characteristic, respectively. Furthermore, Raman analysis indicated that L2 is correlated to an exciton bound to a nitride-vacancy (VN) related complex, i.e., [Fe2+-VN]. By co-doping with Si, the [Fe2+-VN]-related bound state will enable the spin-coupling between isolated iron ions. [ABSTRACT FROM AUTHOR]

Amorphous silicon carbon nitrogen (SiCN) films deposited on stainless steel by radio frequency magnetron sputtering are annealed at different temperatures in hydrogen to investigate the phase transformation kinetics and the impact on film hardness. The SiCN films with polycrystalline structure are formed after annealing at 900 °C and the polycrystalline structures contain SiC, Si3N4, and C3N4 phases. The polycrystalline transformation is discussed using a thermodynamics mechanism. Our results reveal that the emergence of homogeneous particle reinforced composite SiCN structure and polycrystalline phases related to SiC, Si3N4, and C3N4 may be responsible for the hardness enhancement of the annealed SiCN films. [ABSTRACT FROM AUTHOR]

Measurements of the spatial distribution of the rf electric field intensities and phases induced in a free-electron laser (FEL) amplifier operating in the collective (Raman) regime are reported. The studies are carried out at a microwave frequency of ∼10 GHz in a FEL using a mildly relativistic electron beam of ∼160 keV energy and 1– 4 A current. The probing of the ponderomotive (space-charge) and electromagnetic waves is accomplished by means of small movable electric dipole antennas inserted into the interaction region. [ABSTRACT FROM AUTHOR]

Experiments, theory, and simulations are reported on the effects of electron prebunching in a mildly relativistic, low-current (200 kV, 1 A) free-electron laser amplifier operating in the collective (Raman) regime at a frequency of ∼10 GHz. Prebunching is established by injecting an electromagnetic wave into a bifilar helical wiggler and then transporting the bunched beam into a second magnetic wiggler region. The wave growth rate, Γ≡(1/P)(dP/dz), is deduced from measurements of the radiation intensity as a function of interaction length. Observations show that prebunching can increase the radiation growth rate Γ manyfold as compared with a system without prebunching. [ABSTRACT FROM AUTHOR]

In this letter, a nanoscale opto-mechanical actuator driven by gradient optical force is designed and demonstrated. The nanoscale actuator can achieve a maximum displacement of 67 nm with a response time of 94.5 ns. The optical force is estimated as 1.01 pN/μm/mW in C-band operating wavelengths. The device is fabricated on silicon-on-insulator wafer using standard dry etching processes. Compared with traditional microelectromechanical systems actuators driven by electrostatic force, the nanoscale opto-mechanical actuator has the advantages of high resolution of actuation, nanoscale displacement, and fast operating speed. It has potential applications in optical signal processing, chemical, and biological sensing. [ABSTRACT FROM AUTHOR]

Band offsets at the interfaces of n- and p-type InP ((100) and (111)A) and atomic-layer-deposited (ALD) Al2O3 were measured with internal photoemission and spectroscopic ellipsometry. Similarly, the band offsets at the interface of semi-insulating InP (100) and ALD HfO2 were also determined. The barrier between the top of InP valence band (VB) and the bottom of Al2O3 conduction band (CB) is found to be 3.44 eV for p-type material and 3.53 eV for n-type. The photoemission thresholds are found to be sensitive to the annealing conditions, and blue shifts are observed after annealing. The offsets from InP valence band to the HfO2 conduction band for the HfO2/InP stack are found to be 3.89 eV, and we observed an increase of 60 meV if the InP surface is passivated. [ABSTRACT FROM AUTHOR]

We fabricated (Ga,Mn)As/AlOx/Co40Fe40B20 magnetic tunnel junctions with ferromagnetic semiconductor/insulator/ferromagnetic metal (S/I/F) structure. The treatments of pre-annealing and post-plasma cleaning on the (Ga,Mn)As film were introduced before the growth of the subsequent layers. A high tunneling magnetoresistance (TMR) ratio of 101% is achieved at 2 K, and the spin polarization of (Ga,Mn)As, P = 56.8%, is deduced from Jullière's formula. The improved TMR ratio is primarily due to the improved magnetism of (Ga,Mn)As layer by low-temperature annealing and cleaned interface between (Ga,Mn)As and AlOx attained by subsequent plasma cleaning process. [ABSTRACT FROM AUTHOR]

The dislocation multiplication and movement mechanism in GaN single crystals has been studied using nanoindentation and cathodoluminescence. Dislocation loops can multiply and move from plane to plane by cross-slip, thus producing a wide plastic deformation in GaN during indentation. This mechanism is further supported by the remarkable movement of indentation induced dislocations during annealing. Furthermore, the so-called pop-in events, in which the indenter suddenly enters deeper into the material without the application of any additional force, can be better understood by considering the cross-slip mechanism. [ABSTRACT FROM AUTHOR]