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Rayleigh surface acoustic wave (SAW) devices based on 128° YX LiNbO3 and ZnO/Si substrates with different resonant frequencies from ∼62 MHz to ∼275MHz were fabricated and characterized. Effects of SAW frequency and power on microfluidic performance (including streaming, pumping, and jetting) were investigated. SAW excitation frequency influenced the SAW attenuation length and hence the acoustic energy absorbed by the liquid. At higher frequencies (e.g., above 100 MHz), the SAW dissipated into liquid decays more rapidly with much shorter decay lengths. Increasing the radio frequency (RF) frequencies of the devices resulted in an increased power threshold for streaming, pumping, and especially jetting, which is attributed to an increased absorption rate of acoustic wave energy. ZnO SAW devices could achieve similar streaming, pumping, and jetting effects as well as frequency effect, although the SAW signals are relatively weaker. [ABSTRACT FROM AUTHOR]

The transport properties of B-doped single-walled carbon nanotubes (SWNTs) are studied from both experimental and theoretical standpoints. Experimentally, it is found that the semiconducting behavior of SWNTs is drastically changed after B-doping, and the unusual abrupt current drops are observed at low temperatures, which may imply the possibility of superconducting transition in B-doped SWNTs. Using the density-functional tight-binding calculation, it is observed that B-doping induces the presence of density of state peaks near the Fermi level which shifts toward the valence band region, showing a clear charge-transfer characteristic, which agrees well with the experimental observations. [ABSTRACT FROM AUTHOR]

Crystal growth of liquid silicon on the heterogeneous surfaces of carbon nanotubes (CNTs) is simulated. Silicon atoms are concentrated to form perfect coaxial cylindrical configurations around CNT cores. The heredity effect makes silicon imprint cylindrical shapes of CNTs during the solidification. The CNTs have a great influence on the stacking sequence of silicon atoms. Growth competition between CNT cores is clearly observed, which results in defects at the shared interface. The internal potential field around CNTs is responsible for growth competition and the heredity effect. [ABSTRACT FROM AUTHOR]

Doping efficiency and optical and electrical properties of the N-doped ZnO films grown on c-sapphire were investigated. An anomalous Raman mode at 275 cm-1 was observed in the films grown at high Zn temperature, which implied that the films have a large number of defects induced by high N concentration. The intensity ratio of the donor-acceptor pair (DAP)/donor-bound exciton (DX) increases with increasing Zn temperature; this was attributed to the increase of N concentration. The films exhibit a conversion from n-type to p-type conductivity with increasing Zn temperature, and reproducible p-type conductivity was obtained at the Zn temperature of 255 °C. This study offers a simple and effective route to enhance the N solubility in ZnO films and confirms that the anomalous Raman mode at 275 cm-1 was related to substitution of N for O site (NO) and not related to substitution of N2 for O site (N2)O. [ABSTRACT FROM AUTHOR]

The authors report negative differential resistance (NDR) characteristics observed in nanodevices constructed using three types of fullerenes (C60, C70, and C84) encapsulated metallic double-walled carbon nanotubes. The NDR behavior persists from room temperature (300 K) to lower temperatures, and a significantly high on-off peak-to-valley current ratio is observed for many of the devices examined. The fullerene species exerts a strong influence on the peak voltage of the NDR, which exhibits a linear decrease with increasing fullerene size. The observed current-voltage curves are highly reproducible during measurements, and fully reversible upon change in the bias sweep direction. In addition, the peak current of the NDR is found to increase significantly under light illumination and is recoverable in the absence of light, which indicates potential for applications such as logic optoelectronic devices. [ABSTRACT FROM AUTHOR]

The relationship between band gap and biaxial stress in wurtzite ZnO thin films has been investigated by side-inclination x-ray diffraction technique and optical absorbance spectrum as well as ab initio calculation. The experimental result shows that differing from other semiconductor thin films with hexagonal structure, such as GaN, the band gap of ZnO thin films increases with the increase in biaxial tensile stress. For explaining the difference, ab initio calculation is performed to simulate the relationship between band gap and biaxial stress of wurtzite ZnO and GaN. The calculated result indicates that the band gap of ZnO increases under biaxial tensile stress but GaN is opposite, supporting our experimental result. The band offset calculation shows that the conduction-band minimum (CBM) and the valence-band maximum (VBM) of ZnO and GaN offset to low energy under biaxial tensile stress. The VBM offset of ZnO is larger than the CBM, responsible for the increase in band gap. The VBM offset of GaN is smaller than the CBM, responsible for the decrease in band gap. The difference between ZnO and GaN is attributed to the strong p-d coupling in valence band of ZnO, but strong p-p coupling in valence band of GaN. [ABSTRACT FROM AUTHOR]

Using density functional theory (DFT) computations, we investigated pyridinelike structures in a series of single-walled CNx nanotubes and found that tube chirality and diameter play important roles in the formation of pyridinelike structures. Not pyridinelike structures but more NC defects (N atoms substituting for C atoms) should be responsible for the experimentally observed donor states of CNx nanotubes. The adsorption energies of Li at the pyridinelike defect are so large and the energy barrier for lithium penetrating the defect is so low that CNx nanotubes with pyridinelike structures have enhanced capability for lithium storage. [ABSTRACT FROM AUTHOR]

The synthesis of Cs-encapsulated single-walled carbon nanotubes (Cs@SWNTs) and double-walled carbon nanotubes (Cs@DWNTs) is realized by a plasma ion-irradiation method. Transmission electron microscopy observations confirm that chainlike and amorphous Cs fill SWNTs and DWNTs, respectively. The electronic transport properties of Cs@SWNTs and Cs@DWNTs are experimentally investigated at both room and low temperatures by fabricating them as the channels of field-effect transistor devices. Our results reveal that both Cs@SWNTs and Cs@DWNTs exhibit n-type semiconducting behavior at room temperature. The electronic properties of the Cs-encapsulated nanotubes can be controlled by adjusting the Cs filling levels during the plasma ion irritation process. At low temperatures, Coulomb blockade transport characteristics are observed for both encapsulated nanotubes, and the size of quantum dots formed in Cs@DWNTs is much smaller than that formed in Cs@SWNTs. More importantly, the n-type characteristics of Cs@SWNTs and Cs@DWNTs are found to remain stable, even in air, owing to Cs encapsulation. [ABSTRACT FROM AUTHOR]

Five kinds of nanowires and a nanochain that is embedded in a carbon nanotube have been optimized by density function theory, and the electronic transport properties through these nanowires and nanochain are studied. Our results indicate that the transmission spectra exhibit size-dependent oscillations. We observe and study the nonlinear contribution to the I-V characteristic (current-voltage) curves that is due to the quantum size effect. The I-V curve of the single chain is different from that when the chain is embedded in a carbon nanotube. The results provide valuable information on the correlation between the transport properties of nanowires and their microstructures. [ABSTRACT FROM AUTHOR]

The circular magnetization process of FeSiBCuNb amorphous and nanocrystalline wires has been followed by the impedance measurements as a function of the amplitude and the frequency of driving current. The domain structure and consequently, the magnetization process have been tailored by suitable thermal processing. The different circular coercivity mechanisms are deduced by analyzing the magnetic losses. We find that the coercivity is due to domain-wall pinning for wire with axial domain, while the coercivity is from domain nucleation for one with transverse domain structure. In addition, the influence of axially applied field H is different for wires with different domain structure. The application of tensile stress to a wire with positive magnetostriction can be taken as an axial induced anisotropy, which makes the circular permeability decrease and the coercivity increase. Finally, the influence of driving current frequency on the circular magnetization process has been also studied for the wire with transverse domain structure. The results indicate that the frequency effect is from the eddy-current damping. [ABSTRACT FROM AUTHOR]

Two pieces of Fe[SUB73.5] Cu[SUB1] Nb[SUB3] Si[SUB13.5] B[SUB9] amorphous wires were submitted to thermal treatment without (S1) or under (S2) applied tensile stress, so inducing nanocrystalline structure characterized by two different types of magnetic anisotropy. Sample S1 exhibits longitudinal domain structure with small anisotropy constant, while a transverse domain structure with large transverse anisotropy is induced by stress annealing for sample S2. The specific magnetoimpedance response of each nanocrystalline wire has been studied as a function of the applied torsion, &Xgr;. Both samples show the giant magnetoimpedance (GMI) effect, with GMI ratios of 190% and 145% at &Xgr; = 0 for wires S1 and S2, respectively. Applied torsion modifies the form as well as the amplitude of magnetoimpedance, which is discussed in terms of the competition between the magnetoelastic anisotropy induced by the processing and the helical anisotropy induced by the torsion. The torsion impedance has been modeled for the case of sample S1 under large enough helical anisotropy. The observed giant torsion-impedance effect of 320% and 235% for samples S1 and S2, respectively, is proposed to be employed in magnetoelastic torsion sensors. The use of the GMI effect is further emphasized to be a powerful tool to explore the magnetic structure and the magnetic anisotropy. [ABSTRACT FROM AUTHOR]

The magnetoimpedance (MI) effect has been investigateded in Fe[sub 63.5]Cr[sub 10]Si[sub 13.5]B[sub 9]Cu[sub 1]Nb[sub 3] alloy wire exhibiting an ultrasoft magnetic character after suitable thermal treatment at 525 °C. It has been measured as a function of the sample length and of the distance to the ends of the wire (MI profile). The observed dependence on both parameters is correlated with the local particularities of the magnetization process: complex domain structures emerging near the ends to decrease the magnetostatic energy modify the local magnetic susceptibility and consequently the MI response. The present study points out the importance of geometrical dimensions of samples and measuring conditions when reporting numerical values in MI studies. This wire, showing large magnetoimpedance together with optimized soft magnetic behavior and improved corrosion properties seems to be indicated as a sensing element in GMI based sensors. [ABSTRACT FROM AUTHOR]

Presents a study which analyzed the temperature behavior and memory effect in standard spin valves with synthetic antiferromagnetic subsystems. Development of spin-valve structures; Details on the memory effect phenomenon.

Proton emissions from vacuum-gapped cascaded-ultrathin-foil targets irradiated with low-contrast intense picosecond laser pulses were measured. The maximum energy of the proton beam and the laser-to-proton energy conversion efficiency were both increased in comparison with those from the single-layer reference targets. A transition from plateau to exponential profile in proton energy spectral shape was found for the target with a front-foil thickness of above 500 nm. The measured annular x-ray emissions from both target front and rear sides indicate that the proton enhancement could be attributed to the modified preplasma distribution. A simple model and hydrodynamic simulations further show that the optimal acceleration occurs when the front shutter foil is right swelled onto the front surface of the rear source foil by the prepulses at the arrival of the main laser pulse. This cascaded thin-foil target design can be popularized in improving laser-driven proton beams for wide applications. [ABSTRACT FROM AUTHOR]

To improve the coercivity of the Nd-Fe-B sintered magnets, the Cu29.8Al70.2 (at.%) powders with low melting point were introduced into the Nd-Fe-B magnets. The magnetic properties, microstructure, thermal stability and corrosion behavior of the sintered magnets with different amount of Cu29.8Al70.2 (0,0.25,0.50,0.75,1.0 wt.%) were investigated. When the amount of doped Cu29.8Al70.2 was less than 0.75 wt.%, the coercivity was improved, especially that of the magnets with 0.25 wt.% Cu29.8Al70.2, markedly increased to 13.97 kOe from 12.67 kOe (without CuAl). The improvement of magnetic properties could be attributed to enhanced wettability between Nd2Fe14B phase and Nd-rich phase and decreased exchange coupling between grains, which depended on the optimization of grain boundary microstructure and their distribution by codoping Cu and Al. With the addition of 0-1.0 wt.% Cu29.8Al70.2 powders, the reversible temperature coefficients of remanence and coercivity of the magnets could be also improved. The corrosion resistances was also found to be improved through small addition of Cu29.8Al70.2 powder in 3.5 wt.% NaCl solution by electrochemical and immersion tests, which could be due to the enhancement of the Nd-rich intergranular phase by addition Cu29.8Al70.2. [ABSTRACT FROM AUTHOR]

We report on a plasma optical shutter to reduce the intensity level of a nanosecond-duration pedestal of amplified spontaneous emission (ASE) using an ultrathin foil. The foil is ionized by the ASE prepulse and forms an expanding underdense preplasma, which enables the main laser pulse transmission, leading to an enhancement in temporal contrast. When such a plasma shutter is placed in front of a main target of interest, the preplasma profiles observed are similar to that produced from a single-layer reference target irradiated by a high-contrast laser, and can be finely tuned by varying the shutter thickness. Proton beams with significantly reduced divergence and higher flux density were measured experimentally using the double-foil design. The reduction in beam divergence is a characteristic signature of higher contrast laser production as a combined consequence of less target deformation and flatter sheath-acceleration field, as supported by the two-dimensional (2D) hydrodynamic and particle-in-cell simulations. The plasma shutter holds the promise to enhance the laser contrast and manipulate the preplasma conditions for application in high-field-physics experiments. [ABSTRACT FROM AUTHOR]

The transport eddy-current loss of a nearly nonmagnetostrictive CoFeSiB amorphous wire under a large longitudinal bias field can be several times greater than the value commonly expected by the classical model. Related to the overlarge circular susceptibility under the same condition, this is attributed to the formation of disklike soft-magnetic microstructures around hard magnetic inclusions randomly embedded in a soft magnetic matrix. [ABSTRACT FROM AUTHOR]

By incorporating magnetic particles into elevated temperature-curing adhesives, or hot-meltable thermoplastics, induction fields can be used to heat bondlines and join composite adherends. In this article we investigate the fundamental heating behaviors of such magnetic particles in order to aid in the design and selection of improved magnetic materials. Magnetic inductive heating tests were performed on two types of magnetic materials: Co[SUB2]Ba[SUB2]Fe[SUB12]O[SUB2] semihard ferrites and NiFe[SUB2]O[SUB4] soft ferrites. The Curie temperatures of these ferrites were also varied through Zn substitution. All of the samples clearly demonstrated Curie temperature-controlled final heating behavior. The magnitude of heat generation has been related to dc magnetic hysteresis measurements, with reasonable agreement. Deviations are theorized to be due to domain wall resonance effects. [ABSTRACT FROM AUTHOR]

dc, ac field cool, and their various combinations were applied to standard top and bottom spin valves. While dc field cool from the above blocking temperatures helps to align the antiferromagnetic (AFM) spins, therefore introducing exchange bias, ac field cool statistically randomizes the AFM spins, thus effectively erasing it. The various combinations of these two processes help to separate the contribution to the total exchange bias from different AFM grain sizes. It is found that, compared to the smaller grains, the local exchange bias for larger AFM grains is smaller, but with better temperature stability. More detailed analysis of the temperature dependence of the exchange bias reveals that it is influenced not only by the exchange coupling between FM and AFM layers, but also the interaction among different AFM grains. Such interactions include the direct antiferromagnetic interactions among AFM grains, and the indirect ferromagnetic interaction through the adjacent FM layer. The net interaction is the result of the competition of both, which can be either antiferromagnetic or ferromagnetic. [ABSTRACT FROM AUTHOR]

Memory effect has been observed in both standard top and bottom spin valves. The change of the magnetization state in the pinned FM layer, below the blocking temperature, reverses the direction of the exchange bias and destroys the magnetoresistance properties. This reversed exchange bias is much weaker, causing severe consequences in SV applications. This behavior can be explained in terms of blocking temperature distribution in the AFM layer perhaps due to the structural randomness. By varying cooling procedures, the exchange coupling in regions with different blocking temperatures can be separated. It is found that the maximum exchange bias is very close to the sum of the exchange biases in different regions. The domain wall energy in the FM layer has to be taken into account in order to explain the behavior of the reversed bias. The insertion of a synthetic antiferromagnetic subsystem (Co/Ru/Co) stabilizes the magnetization state in the pinned layer because of the additional interlayer coupling through the Ru layer. This suppresses the memory effect. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Soft magnetic crystalline alloys have been fabricated in a tube form by electrodepositing magnetic FeNi and FeNi–Al[sub 2]O[sub 3] onto W fibers with a diameter of 25 μm. Fine Al[sub 2]O[sub 3] particles have also been incorporated into the magnetic matrix to improve mechanical properties. As-prepared materials are not magnetically soft. With heat treatment, the magnetic properties of these composites are similar to commercial bulk soft FeNi alloys. A giant magnetoimpedance value as large as 190% has been found in as-prepared FeNi-W with a magnetic layer thickness of 20 μm. This value is comparable to GMI observed in amorphous magnetic wires. Experiments also show that GMI values decrease when the Al[sub 2]O[sub 3] content increases in a range from 0 to 7.0 at. %. This behavior is due to the increase in electrical resistivity and magnetic permeability of the samples that modifies the skin effect. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The nucleation field in a synthetic antiferromagnet has been studied as a function of the stabilization strength. The results can be used to predict the magnetic stability in a GMR read-back head, that utilizes a synthetic antiferromagnet instead of a single pinned layer. Experimental studies showed substantially improved magnetic stability at higher temperature in synthetic antiferromagnet spin valves. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

(LWFA) with a charge of 620 pC and a maximum energy up to 0.6 GeV by irradiating 80 TW laser pulses at a 3 mm Helium gas jet. The charge of injected electrons is much larger than the normal scaling laws of LWFA in bubble regime. We also got a quasi-monoenergetic electron beam with energy peaked at 249 MeV and a charge of 68 pC with the similar laser conditions but lower plasma density. As confirmed by 2D particle-in-cell simulations, the boosted bunch charge is due to the continuous injection caused by the self-steepening and self-compression of a laser pulse. During the nonlinear evolution of the laser pulse, the bubble structure broadens and stretches, leading to a longer dephasing length and larger beam charge. [ABSTRACT FROM AUTHOR]

We demonstrate a novel plasma device for magnetic reconnection, driven by Gekko XII lasers irradiating a double-turn Helmholtz capacitor-coil target. Optical probing revealed an accumulated plasma plume near the magnetic reconnection outflow. The background electron density and magnetic field were measured to be approximately 1018cm-3 and 60 T by using Nomarski interferometry and the Faraday effect, respectively. In contrast with experiments on magnetic reconnection constructed by the Biermann battery effect, which produced high beta values, our beta value was much lower than one, which greatly extends the parameter regime of laser-driven magnetic reconnection and reveals its potential in astrophysical plasma applications. [ABSTRACT FROM AUTHOR]

A simple scheme to produce strong magnetic fields due to cold electron flow in an open-ended coil heated by high power laser pulses is proposed. It differs from previous generation of magnetic fields driven by fast electron current in a capacitor-coil target [S. Fujioka et al., Sci. Rep. 3, 1170 (2013)]. The fields in our experiments are measured by B-dot detectors and protonradiography, respectively. A 205 T strong magnetic field at the center of the coil target is generated in the free space at I?² of 6.85 × 1014 W cm-2 µm², where I is the laser intensity, and ? is the laser wavelength. The magnetic field strength is proportional to I?². Compared with the capacitor-coil target, the generation mechanism of the magnetic field is straightforward and the coil is easy to be fabricated. [ABSTRACT FROM AUTHOR]

By adjusting the focus geometry of a spatially structured laser pulse, single, double, and treble quasi-monoenergetic electron beams were generated, respectively, in laser-wakefield acceleration. Single electron beam was produced as focusing the laser pulse to a single spot. While focusing the laser pulse to two spots that are approximately equal in energy and size and intense enough to form their own filaments, two electron beams were produced. Moreover, with a proper distance between those two focal spots, three electron beams emerged with a certain probability owing to the superposition of the diffractions of those two spots. The energy spectra of the multiple electron beams are quasi-monoenergetic, which are different from that of the large energy spread beams produced due to the longitudinal multiple-injection in the single bubble. [ABSTRACT FROM AUTHOR]

We report an efficient Mo Kα x-ray source produced by interaction of femtosecond Ti: sapphire laser pulses with a solid Molybdenum target working at 1 kHz repetition rate. The generated Mo Kα x-ray intensity reaches to 4.7 x 1010 photons sr-1 s-1, corresponding to an average power of 0.8 mW into 2π solid angle. The spatial resolution of this x-ray source is measured to be 26 lp/mm. With the high flux and high spatial resolution characteristics, high resolving in-line x-ray radiography was realized on test objects and large size biological samples within merely half a minute. This experiment shows the possibility of laser plasma hard x-ray source as a new low cost and high resolution system for radiography and its ability of ultrafast x-ray pump-probe study of matter. [ABSTRACT FROM AUTHOR]

Ga-doped ZnO (GZO)/graphene multilayer film was fabricated on the polyethylene terephthalate substrate at room temperature. The obtained GZO/graphene multilayer showed a transparence of 75% at 550nm and a sheet resistance of 721Ω/sq. Our findings indicate that the graphene intermediate layer plays a critical role in improving the conductivities of GZO. Under a tensile strain, the sheet resistance of the GZO electrode without graphene exhibited a sharp increase owing to the plenty of cracks formed in the GZO layer. In contrast, the GZO/graphene multilayer displayed a relatively stable and low resistance during the tensile deformation due to the excellent mechanical and electrical stabilities of the graphene. [ABSTRACT FROM AUTHOR]

The intergranular exchange coupling effects are investigated via thermal activation of magnetization reversal in the magnetic relaxation process, combined with Henkel plots and the measurement of susceptibilities in three types of Pr9Fe85.5B5.5 ribbons. Exchange interaction between hard-hard grains is proposed in optimal melt-spun ribbons, as well as in over melt-spun ribbons even bearing a weak exchange coupling between soft-hard grains. In under melt-spun ribbons, the decoupled effect is proposed between hard-hard grains. These investigations may contribute to a clear understanding about the complicated nature of the intergranular exchange coupling in nanocomposite magnets. [ABSTRACT FROM AUTHOR]

The photoinduced insulator-metal phase transition and relaxation characteristics have been investigated in bare SrTiO3 single crystals. The photoinduced relaxation time constant after the irradiation shows an increase with increasing temperatures. The SrTiO3 single crystal has a cutoff wavelength and an absorption edge of spectrum at about 385 nm, which agrees well with the band gap. The photocurrent responsivity is 1.36 × 10-5 A/W at 300 nm wavelength. The relative change in resistance is more than above six orders at room temperature, possessing potential applications in ultraviolet sensitive and detecting devices. [ABSTRACT FROM AUTHOR]

Room temperature ferromagnetism (RTFM) was observed in Li-N codoped ZnO thin films [ZnO:(Li, N)] fabricated by plasma-assisted molecular beam epitaxy, and p-type ZnO:(Li, N) shows the strongest RTFM. Positron annihilation spectroscopy and low temperature photoluminescence measurements indicate that the RTFM in ZnO:(Li, N) is attributed to the defect complex related to VZn, such as VZn and Lii-NO-VZn complex, well supported by first-principles calculations. The incorporation of NO can stabilize and enhance the RTFM of ZnO:(Li, N) by combining with Lii to form Lii-NO complex, which restrains the compensation of Lii for VZn and makes the ZnO:(Li, N) conduct in p-type. [ABSTRACT FROM AUTHOR]

Similar to the water wave on a pond caused by dropping a pebble, the formation of ripples is shown in a single layer graphene (SLG) when it is stroked by a C60 molecule, no matter whether the graphene is plane or corrugated. The controllable ripple in SLG is investigated by molecular dynamics simulations. Noticeable diffraction and interference of the ripples are observed. This study indicates that the ripple propagation in graphene can be used to detect defects. [ABSTRACT FROM AUTHOR]

Lithium and nitrogen dual-doped ZnO films [ZnO:(Li, N)] with Li concentrations of 0%-11.2% were grown on sapphire by plasma-assisted molecular beam epitaxy, and a stable p-type ZnO:(Li, N) film was obtained by doping 6.1% of Li. The p-type conductivity of ZnO:(Li, N) is attributed to the formation of the Lii-NO complex, which depresses the compensation of Lii donor for LiZn acceptor and the generation of (N2)O donors. It is demonstrated that the Lii-NO complex can form an impurity band above the valance band maximum, resulting in a decrease in the ionization energy of the acceptor and an improvement in the conductivity and stability of the p-type ZnO:(Li, N). [ABSTRACT FROM AUTHOR]

We have investigated the possibility of using single-walled carbon nanotubes (SWNTs) as the infrared energy conversion material based on the configuration of SWNT/Si heterojunction. The performance of solar cells based on SWNTs has been examined under illumination by the light with different wavelengths. Our experimental results confirm that SWNTs play a critical role in transforming the infrared light (1550 nm) into the electrical energy. The encapsulation of C60 fullerene inside SWNTs is found to significantly enhance the performance of solar cells through adjusting the Fermi level of SWNTs. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are performed to examine the heterogeneous solidification of silicon on foreign graphite sheets (GSs). It clearly indicates that silicon atoms are concentrated to form hierarchical nanostructures composed of equidistant nanolayers. Graphite plate induces strong ordered liquid silicon layers near the surfaces of GSs. This study suggests ordered liquid layers should be the early form of the solid crystal, which determine the subsequent nucleation. The confined nanospace between two GSs favors the solidification and results in the decrease in the distance between layers. GSs make silicon atoms solidify into an hcp crystal rather than fcc structure. [ABSTRACT FROM AUTHOR]

The transport properties of single-stranded DNA (ssDNA) wrapped single-walled carbon nanotubes (SWNTs) are studied from low to room temperature. Atomic force microscopy reveals a regularly patterned geometry of ssDNA molecules on the surface of SWNTs. Our measurements indicate that the semiconducting behavior of SWNTs is drastically changed after ssDNA modification, showing a clear charge-transfer process at room temperature. At low temperatures single-electron tunneling features are observed up to 80 K, demonstrating clearly that quantum dots in series are created in the SWNTs due to the ssDNA wrapping. [ABSTRACT FROM AUTHOR]

Molecular dynamics studies are carried out to examine the spiral nucleation mode of silicon solidified on the surface of carbon nanocones (CNCs). The silicon atoms are concentrated to form magic multilayered nanocones composed of coaxial and equidistant conical shells. Heterogeneous nucleation that occurred on CNCs follows a spiral nucleating mechanism. The structures of so-formed silicon cones show strict structural matching and strong structural relevance with CNCs. The uniform internal potential field around the CNCs is responsible for the formation of the coaxial conical shells. [ABSTRACT FROM AUTHOR]

We discuss the advantages of “chaotic cavity transducer focusing” to enhance the localization of microdamage in conjunction with nonlinear elastic wave spectroscopy methods. Chaotic cavity transducer focusing is defined as the hardware-software combination of a piezoelectric ceramic glued on a cavity of chaotic shape on the one hand with the reciprocal time reversal (or inverse filter) technique on the other hand. Additional optimization through the use of sweeps and inverse filtering techniques are discussed as well. The technique is applied to image a crack in a steel sample. [ABSTRACT FROM AUTHOR]

A study of the free energy of the perovskite manganites was performed by fitting experimental results for the temperature dependence of the crystal cell volume using a detailed semiclassical model of the free energy. The fitted results coincide with the experimental results for the samples La1-xCaxMnO3 (x=0.2, 0.25, 0.3, and 0.5). The free energy includes the energy corresponding to thermal vibration of the crystal lattice, the ionic cohesive energy, and additional energies produced by electrical carriers from the double exchange mechanism and the thermal activation of small polarons. [ABSTRACT FROM AUTHOR]

The growth of silicon atoms at the heterogeneous surface of carbon nanotubes (CNTs) is studied by means of molecular dynamics simulations. The results indicate that silicon atoms are concentrated to form an “annual ring” structure around CNTs. The structures of CNTs have strong correlation with the stacking sequence of silicon atoms. Heredity effect can be clearly observed during the heterogeneous nucleation. The uniform internal potential field around CNTs results in the formation of annual ring structures. [ABSTRACT FROM AUTHOR]

Valence-band offset (VBO) of n-ZnO/p-NiO heterojunction has been investigated by x-ray photoelectron spectroscopy. Core levels of Zn 2p and Ni 2p were used to align the VBO of n-ZnO/p-NiO heterojunction. It was found that n-ZnO/p-NiO heterojunction has a type-II band alignment and its VBO is determined to be 2.60±0.20 eV, and conduction-band offset is deduced to be 2.93±0.20 eV. The experimental VBO value is in good agreement with the calculated value based on the electron affinity of ZnO and NiO. [ABSTRACT FROM AUTHOR]

The valence-band offset of ZnO/MgO (111) heterojunction has been directly measured by x-ray photoelectron spectroscopy. Excluding the strain effect, the valence-band offset is determined to be 0.87±0.20 eV, and the conduction-band offset ΔEC is deduced to be -3.59±0.20 eV, indicating that ZnO/MgO heterojunction has a type-I band alignment. The conduction-band and valence-band offset of MgO/ZnO is used to interpret the origination of p-type conduction in undoped MgxZn1-xO alloy and deeper acceptor level in undoped and N-doped p-type MgxZn1-xO alloy than in ZnO. [ABSTRACT FROM AUTHOR]

The transport properties of field-effect transistors based on C60 fullerene peapods have been investigated and our findings indicate that the transport characteristics of single-walled carbon nanotubes (SWNTs) are highly sensitive to the encapsulated fullerenes due to the charge-transfer effect. Under light illumination, the photoinduced electron transfer characteristics are found in C60 peapods, which is different from those observed for empty SWNTs. The response characteristic of peapod devices to light is reflected in a shift of threshold voltage toward negative values, indicating an electron-doping process. After removing light the photoresponse is fully recoverable, indicating complete restoration of transferred electrons. [ABSTRACT FROM AUTHOR]

Our Raman measurement indicates that the intensity of the peaks (510 and 645 cm-1) related to nitrogen concentration is enhanced in MgZnO compared with that in ZnO. Using first-principles band structure methods, we calculated the formation energy and transition energy level for nitrogen acceptor in ZnO and random MgxZn1-xO (with x=0.25) alloy. Our calculations show that the incorporation of nitrogen can be enhanced as Mg is alloyed into ZnO, which agrees with our experiments. The acceptor energy level deeper in the alloy ascribes to the downward shift of the valence-band maximum edge in the presence of magnesium. [ABSTRACT FROM AUTHOR]

Undoped MgxZn1-xO thin films with Mg content of 0≤x≤0.20 were grown on c-sapphire substrate by plasma-assisted molecular beam epitaxy. The MgxZn1-xO shows n-type conduction in Mg content of x≤0.05, and the carrier concentration decreases slowly from 1018 to 1017 cm-3 with increasing Mg content. However, as x>=0.10, the MgxZn1-xO begins to show p-type conduction, and the carrier concentration goes down sharply to 1015 cm-3 firstly and then increases slowly with increasing Mg content from 1015 to 1016 cm-3. The mechanism of transformation from n to p type and change of the carrier concentrations with Mg content were investigated by photoluminescence and absorption measurements as well as first-principle calculation [ABSTRACT FROM AUTHOR]

Biaxial stress of ZnO film deposited on quartz was measured by side-inclination x-ray diffraction technique, indicating that the film is subjected to a tensile stress. One part of the stress is induced by thermal mismatch between the ZnO and the quartz and increases with annealing temperature, while another part results from lattice mismatch and is about 1.03 GPa. The optical band gap of the ZnO film shows a blueshift with increasing biaxial tensile stress, opposed to the change of the band gap with biaxial tensile stress for GaN. The mechanism of the stress-dependent band gap is suggested in the present work. [ABSTRACT FROM AUTHOR]