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A surface potential based compact model for two-dimensional field effect transistors (2D-FETs) is proposed to incorporate the structural disorders induced transition behaviors among variable range hopping (VRH), nearest neighbor hopping (NNH), and band-like transport in most 2D materials. These functions coupled with effective transport energy and multiple trapping and releasing theory enable our developed model to predict the temperature and carrier density dependent current characteristics. Its validity is confirmed by the experimental results such as the metal insulator transition (MIT) in transition metal dichalcogenides and VRH-NNH transition in black phosphorus nanoribbon. Based on this model, the band-tail effects on the crossover gate voltage of MIT behavior are quantitatively investigated. It is found that the transition behavior is closely related to the distribution of the band-tail states. Furthermore, this model is implemented in Verilog-A for circuit-level prediction and evaluation of 2D-FETs to provide deeper insight into the relationship between material properties, device physics, and circuit performances. [ABSTRACT FROM AUTHOR]

Low-temperature photoluminescence (PL) measurements of Ga[As.xub.1-x][N.sub.x] epitaxial layers grown on GaAs have revealed an anomalous second peak in solid-source molecular beam epitaxy. The lower energy peak (gamma) is due to the accumulation of N content near the GaAs/GaAsN interface and hence this abnormal annealing behavior has occurred in layers with nonuniform N concentration at the GaAsN/GaAs interface.

The etching characteristics of atomic force microscopy (AFM) probe-grown ultrathin oxides (AFM oxides) are described. The probe revealed that AFM oxide growth is related to Si out-diffusion while the etching rate of ultrathin AFM oxides is dependent on the SiOH silanol reactive sites.

Silicon surface gratings, made with the fourth harmonic of a Q-switched Nd:YAG laser, were studied.

Research describing bismuth-layered ferroelectric thin films is presented. In particular the effects of annealing temperature on crystal structure and metal diffusion are investigated.

Results reveal that introduction of carbon into the Si(sub)1-x-(sub)yGe(sub)xC(sub)y film confers compressive or tensile strain in the film and the structural aspects of the oxidized film depends on the crbon concentration of the as-prepared film.

Indium tin oxide (ITO) films were produced from an oxidized target with In2O3 and SnO2 using the radiofrequency magnetron sputtering technique. Hydrogen was added to the gas mixture during the preparation of the ITO films. The effect of hydrogen partial pressure on the structural and optoelectronic characteristics of the ITO films was investigated. Hall effect measurements showed that the addition of hydrogen in the sputtering gas mixture caused an increase in the number of charge carriers in the ITO films. However, the carrier mobility did not increase substantially.

A study on materials which exhibit the highest levels of magnetic field-induced volumetric/uniaxial strains near room temperature presents measurements of giant magnetoelastic behavior in MnAs samples accompanying the paramagnetic-to-ferromagnetic transition. The MnAs samples were prepared from elemental precursors by powder processing. Results indicate that MnAs has significant potential for use in magnetically activated sensors and transducers.

First-principles calculations have been performed to investigate electronic band structures, vibrational characters, and related transport properties of pnictogen-substituted skutterudites filled with alkaline-earth elements (MxCo4A6B6, where M=Ca, Sr, or Ba, A=Ge or Sn, B=Se or Te, and x=0.5 or 1). Electronic transport properties related to thermoelectricity, including the Seebeck coefficient and the electrical conductivity, are computed by using the Boltzmann transport formalism within the constant-relaxation-time approximation. The results are compared against the corresponding properties of the unfilled pnictogen-substituted ternary skutterudites (CoA1.5B1.5) to identify the effects of filling to estimate the potential for thermoelectric applications. The changes in the ionic character of the interatomic bonding between the Group 14 (A) and Group 16 (B) elements, which was suspected to be a major scattering source in unfilled pnictogen-substituted ternary skutterudites, are probed by analyzing the projected density of states, the charge densities, and the Born effective charges, in an attempt to identify a potential path for improvement of the thermoelectric performance. Our computational results suggest that the analyzed performance of the filled pnictogen-substituted skutterudites should exhibit no significant improvement over that of the corresponding unfilled pnictogen-substituted ternary skutterudites, unless significant reduction in thermal conductivity is achieved by the rattling motion of the filler atoms. [ABSTRACT FROM AUTHOR]

In this work, we present a detailed investigation of FePt-substrate interfaces and their influence towards the microstructural and magnetic configurations of the resulting metallic films. Discontinuous FePt films of roughly 15 nm thickness are deposited at 750 °C on MgO, MgAl2O4, SrTiO3, and (La,Sr)(Al,Ta)O3 single-crystalline substrates. All of these films mainly show out-of-plane textured FePt islands; however, fractions of L12 and in-plane oriented crystals are observed for the films on substrates with reduced lattice mismatch. Reduced easy axis coercivities and enhanced hard axis remanence values affirm this observation. Moreover, quantitative highresolution transmission electron microscope analysis reveals that the reduced lattice mismatch results in a decreased density of dislocations, especially misfit dislocations, at the FePt-substrate interface. To further extend the research, carbon-doped FePt+32%C films are deposited on single-crystalline and sputtered MgO at 750 °C and 650 °C, respectively, to characterize the influence of a segregating media and reduced grain size. A comparison to the pure FePt sample reveals that the presence of seed layer grain boundaries leads to an increased fraction of in-plane oriented material, while the density of misfit dislocations solely depends on the degree of lattice mismatch. [ABSTRACT FROM AUTHOR]

A low-k dielectric barrier based on silicon oxycarbide for copper damascene processes has been developed in this work. The optimal process conditions that allow the deposition of silicon oxycarbide films with a dielectric constant of 3.74 and copper diffusion depth of 290 Å after thermal stress at 400 °C for 3 h has been identified. Copper diffusion depth is defined as the copper and dielectric interfacial region with three-order magnitude reduction in copper concentration. A multilayered structure consisting of black diamond/SiOC/Cu/TaN/Si is fabricated. 3-methyl silane and oxygen in varying concentration is used for the deposition of SiOC using plasma enhanced chemical vapor deposition. The composition of the films is studied by Fourier transform infrared spectroscopy. Dielectric constant and dielectric breakdown of the films are also evaluated. Secondary ion mass spectrometry is employed to investigate the copper diffusion property of the films. The electronic component of the dielectric constant has been found to be most significant in affecting the overall dielectric constant in SiOC films. [ABSTRACT FROM AUTHOR]

A study was conducted on the interdiffusion coefficient of AlGaAs/GaAs over the 750-1150-degrees centigrade temperature range. The values obtained were validated against those derived from previous studies. Results reveal that a single activation energy can account for all the data. Results also show that previous examinations involve either samples of As rich or capped anneals or samples annealed using gallium rich overpressure.

Large size monolayer Molybdenum disulphide (MoS2) was successfully grown by chemical vapor deposition method under an atmospheric pressure. The electrical transport properties of the fabricated back-gate monolayer MoS2 field effect transistors (FETs) were investigated under low temperatures; a peak field effect mobility of 59 cm2V–1s–1 was achieved. With the assist of Raman measurement under low temperature, this work identified the mobility limiting factor for the monolayer MoS2 FETs: homopolar phonon scattering under low temperature and electron-polar optical phonon scattering at room temperature. [ABSTRACT FROM AUTHOR]

We demonstrate the localized excitation and dc electrical detection of magnetostatic surface spin waves (MSSWs) in yttrium iron garnet (YIG) by a shorted coaxial probe. Thin films of NiFe and Pt are patterned at different regions onto a common bulk YIG substrate. A shorted coaxial probe is used to excite spin precession locally near various patterned regions. The dc voltages across the corresponding regions are recorded. For excitation of the Pt regions, the dc voltage spectra are dominated by the spin pumping of MSSWs from YIG, where various modes can be clearly distinguished. For the NiFe region, it is also found that spin pumping from MSSWs generated in YIG dominated the spectra, indicating that the spin pumped currents are dissipated into charge currents via the inverse Spin Hall effect (ISHE) in NiFe. For all regions, dc signals from YIG MSSWs are observed to be much stronger than the ferromagnetic resonance (FMR) uniform mode, likely due to the nature of the microwave excitation. The results indicate the potential of this probe for microwave imaging via dc detection of spin dynamics in continuous and patterned films. [ABSTRACT FROM AUTHOR]

Under zero external magnetic fields, single-layer FeCo thin films exhibit no ferromagnetic resonance (FMR) peaks, while multiple FMR peaks were obtained by growing FeCo thin films on NiFe underlayers with various thicknesses up to 50?nm. Comprehensive investigations of the dynamic magnetic properties and origin of the peaks were conducted through measurements of microwave permeability via a shorted microstrip perturbation technique. Through fitted values of saturation magnetization Ms, uniaxial anisotropy HKsta, and rotatable anisotropy HKrot extracted from the FMR experiments, it was found that two of the three resonance peaks originate from FeCo, and the third from NiFe. The two magnetic phases of FeCo grains are found to have different values of HKrot and explained by the exchange interaction between FeCo and NiFe grains. [ABSTRACT FROM AUTHOR]

In magnetic recording media, the grains or clusters reverse their magnetization over a range of reversal field, resulting in a switching field distribution. In order to achieve high areal densities, it is desirable to understand and minimize such a distribution. Clusters of grains which contain stacking faults (SF) or fcc phase have lower anisotropy, an order lower than those without them. It is believed that such low anisotropy regions reverse their magnetization at a much lower reversal field than the rest of the material with a larger anisotropy. Such clusters/grains cause recording performance deterioration, such as adjacent track erasure and dc noise. Therefore, the observation of clusters that reverse at very low reversal fields (nucleation sites, NS) could give information on the noise and the adjacent track erasure. Potentially, the observed clusters could also provide information on the SF. In this paper, we study the reversal of nucleation sites in granular perpendicular media based on a magnetic force microscope (MFM) methodology and validate the observations with high resolution cross-section transmission electron microscopy (HRTEM) measurements. Samples, wherein a high anisotropy CoPt layer was introduced to control the NS or SF in a systematic way, were evaluated by MFM, TEM, and magnetometry. The magnetic properties indicated that the thickness of the CoPt layer results in an increase of nucleation sites. TEM measurements indicated a correlation between the thickness of CoPt layer and the stacking fault density. A clear correlation was also observed between the MFM results, TEM observations, and the coercivity and nucleation field of the samples, validating the effectiveness of the proposed method in evaluating the nucleation sites which potentially arise from stacking faults. [ABSTRACT FROM AUTHOR]

Research into the thermal stability of partial domain wall-mediated bias on compensated and uncompensated antiferromagnetic interfaces is presented. It was established that pinning of partial walls to the interface was sensitive to the thermally averaged magnitudes of antiferromagnet spins near the interface.

Research into exchange biasing effects in single-crystal Fe/polycrystalline KNiF3 bilayers grown by molecular beam epitaxy is presented. Evidence was found of interlayer exchange coupling between the ferromagnetic Fe and antiferromagnetic KNiF3.

High resolution X-ray diffractometry (HR-XRD), Photoluminescence, Raman spectroscopy, and Transmission electron microscope measurements are reported for GaN deposited on a conventional Si(111) substrate and on the {111} facets etched on a Si(100) substrate. HR-XRD reciprocal space mappings showed that the GaN(0002) plane is tilted by about 0.63° ± 0.02° away from the exposed Si{111} growth surface for GaN deposited on the patterned Si(100) substrate, while no observable tilt existed between the GaN(0002) and Si(111) planes for GaN deposited on the conventional Si(111) substrate. The ratio of integrated intensities of the yellow to near band edge (NBE) luminescence (IYL/INBE) was determined to be about one order of magnitude lower in the case of GaN deposited on the patterned Si(100) substrate compared with GaN deposited on the conventional Si(111) substrate. The Raman E2(high) optical phonon mode at 565.224 ± 0.001 cm-1 with a narrow full width at half maximum of 1.526 ± 0.002 cm-1 was measured, for GaN deposited on the patterned Si(100) indicating high material quality. GaN deposition within the trench etched on the Si(100) substrate occurred via diffusion and mass-transport limited mechanism. This resulted in a differential GaN layer thickness from the top (i.e., 1.8 μm) of the trench to the bottom (i.e., 0.3 μm) of the trench. Mixed-type dislocation constituted about 80% of the total dislocations in the GaN grown on the inclined Si{111} surface etched on Si(100). [ABSTRACT FROM AUTHOR]

Through a systematic investigation of the field-dependent dynamic magnetization of a series of NiFe films with and without stripe domains in conjunction with the static magnetization process, we demonstrate that the experimental rotatable anisotropy field is not a fixed value but strongly varied with the external in-plane magnetic field, being qualitatively associated with the emergence of stripe domains. Moreover, the frequency linewidth spectra of the films with stripe domains show an abnormal behavior with three distinct regimes which are strongly correlated with both the static magnetization process and the competition between external magnetic field and dynamic anisotropy field. The results are discussed in terms of the effect of inhomogeneous magnetization associated with the formation of stripe domains and the field-dependent dynamic anisotropy that cause the broadening of frequency linewidth. [ABSTRACT FROM AUTHOR]

A low-k dielectric barrier on silicon oxycarbide for copper damascene processes is developed. The optimal process conditions that allow the deposition of silicon oxycarbide films with a dielelctric constant of 3.74 and copper diffusion depth of 290 angstrom after thermal stress at 400 degree Celsius is identified.

Diamond-like carbon and amorphous carbon films are known for their high smoothness root mean square values which can be as low as 0.1 nm. When used in field emission, physical aspects of enhancement are often disregarded for such flat film emitters. However, it is proven that these films may not be as flat as they appear to be. We present an experimental validation that shows a tube or needle-like emission mechanism for nanosized graphite clusters embedded in an amorphous carbon matrix. Films were deposited with in situ heating at 100, 400 and 700 °C and enhancement factors were seen to increase twofold as temperature was increased. By varying the anode-cathode distances, the films exhibited a distance dependency that is only observed for tubes and needle structures. This suggests that flat films can exhibit an emission mechanism akin to carbon nanotubes, thus confirming the presence of conductive channels within the films for nanoclustered amorphous carbon films. [ABSTRACT FROM AUTHOR]

The epitaxial growth of graphene on inexpensive, commercially available, free-standing polycrystalline 3 C-SiC has been achieved by solid state graphitization in ultrahigh vacuum. The structural and electronic properties of such epitaxial graphene (EG) have been explored by Raman spectroscopy, scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS). The Raman results show that the grown EG is compressively stressed. The quality of such EG is similar to that on single-crystalline hexagonal SiC substrates. The STM measurements show that the EG grown on polycrystalline SiC presents atomically smooth surfaces across large regions of the underlying SiC substrate with some nanometer-scale features, such as one-dimensional (1-D) ridges, 1-D grain boundaries, and graphene in different stacking sequences. The STS measurements reveal the electronic properties of such EG at an atomic scale. Our approach suggests a more inexpensive way to grow high quality and large scale graphene and represents a promising step toward commercialization of graphene-based electronics. [ABSTRACT FROM AUTHOR]

Spherical Ge nanocrystals well-dispersed in amorphous silicon oxide matrix have been synthesized with different sizes, and significant size-dependent Raman shift and broadening have been observed. The lattice constant of Ge nanocrystals well-bonded to silicon oxide matrix has been characterized nearly size-independent. With our proposed stress generation and relaxation mechanisms, stress effects in our samples have been analyzed to be insignificant with respect to phonon confinement effects. The phenomenological model introduced by [Richter, Wang, and Ley, Solid State Commun. 39, 625 (1981] with Gaussian weighting function and TO2 phonon dispersion function has been found to give a quite good description of the measured size-dependence of Raman shift and broadening. A 3-peak fitting method has been proposed to determine Ge nanocrystal size and film crystallinity. After physically quantizing quantum-confined one-dimensional elastic waves, we have deduced that each quantum-confined phonon possesses an instantaneous momentum of a given magnitude hk with an equal chance of being either positive or negative and momentum conservation is retained in an electron-phonon scattering process. Therefore, on the basis of the first-principle microscopic model and our experimental results, we deduced that Raman scattering in spherical nanocrystals is a concurrent two-phonon process, one phonon generation and one phonon transition. [ABSTRACT FROM AUTHOR]

In this study, the effect of Ag or Sb addition on the thermoelectric properties of PbTe including the Seebeck coefficient, the electrical resistivity, and the thermal conductivity, was studied in the temperature range from 323 to 723 K. The major carriers in the Ag-doped and the Sb-doped PbTe are holes and electrons, respectively. A degenerate semiconductor behavior in the electrical transport properties was observed in the Ag-doped, whereas the semi-metallic in the Sb-doped. It was suggested from the results of the Hall effect measurement and the Seebeck coefficient that the effective mass was significantly altered by the Sb-doping. The maximum dimensionless figure of merit, ZT, of Pb1-xAgxTe and Pb1-xSbxTe (x=0.1) alloys showed 0.27 and 0.62 at 723 K, respectively. Based on the analysis of the Seebeck coefficient of the Ag or the Sb-doped PbTe, the interaction between Ag and Sb in PbTe, as expected in the AgPbmSbTem+2 (LAST-m), may be supposed. [ABSTRACT FROM AUTHOR]

We demonstrate that the electron injection barrier (Δe) between Co and C60 can be tuned by inserting a thin Alq3 interlayer. Using ultraviolet photoemission spectroscopy, Δe of C60 on Alq3-predecorated Co (Δe=0.3 eV) was found to be reduced by 0.3 eV compared with that of C60 deposited directly on the bare Co metal surface (Δe=0.6 eV). Due to Fermi level pining at the Alq3/Co interface, this tuning effect is independent of the thickness of Alq3 interlayer from multilayer to monolayer. Based on the experimental results, band level alignment diagrams are proposed for C60/Co and C60/Alq3/Co interfaces with two different Alq3 thicknesses. Our findings could have potential applications for the reduction in the carrier injection barrier in organic spin valves. [ABSTRACT FROM AUTHOR]

The interface electronic structure of C60/CuPc and C60 heterojunctions on SiO2 and highly oriented pyrolytic graphite has been studied using ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, and synchrotron based photoelectron spectroscopy. Fermi level pinned to the negative integer charge transfer state of C60 molecules on the standing CuPc film has been observed, while nearly vacuum-level alignment is observed for C60 on the lying CuPc film. We also found small vacuum-level shifts for C60 on both standing and lying F16CuPc films, which can be attributed to the rearrangement of underlying F16CuPc molecules. With the use of orientation-controlled CuPc and F16CuPc thin films, C60 highest occupied molecular orbital energy levels relative to the substrate Fermi level can be tuned from 1.9 eV for C60 on the standing CuPc film to 1.0 eV on the standing F16CuPc film. [ABSTRACT FROM AUTHOR]

Photocurrent generation and photodetection are usually based on semiconductor crystals including Si, CdS, and PbS. This work reports the enhanced photoabsorption and photodetection of close-packed metallic Au nanoparticles (NPs) in the UV-VIS (visible)-NIR (near infrared) region. Photoabsorption in the UV-VIS regions is associated with the interband transition and surface plasmon resonance of AuNPs, while the enhanced NIR absorption is due to the collective effect of interacting AuNPs in the close-packed network. Consequently, the AuNPs exhibits photodetection behavior in the wavelength range of 300–1500 nm. It is proposed that the inter-AuNP photoejection and delocalization of electron-hole pairs changes the carrier lifetime and transit dynamics in favor of photocarrier conduction, thus significantly facilitating photocurrent generation in the metallic AuNP close-pack. Moreover, due to the power-law conduction mechanism in AuNP networks, the quantum yield of AuNPs can be tuned from 10-6 to 10-1 photoelectron/photon by increasing the bias voltage from 0 to 5 V. The AuNP quantum yield of 10-1 at 5 V is as high as that of commercial Si photodetectors at 0 V, and this demonstrates the immediate applicability of AuNPs in photodetection. In view of the compatibility of AuNPs with wet-chemistry and inkjet printing processes at low temperatures, metallic AuNPs may provide a convenient alternative to semiconductor crystals in photodetection and perhaps photovoltaic applications. [ABSTRACT FROM AUTHOR]

Molecular orientation-controlled charge transfer has been observed at the organic-organic heterojunction interfaces of copper-hexadecafluoro-phthalocyanine (F16CuPc) or copper(II) phthalocyanine (CuPc) on both standing-up and lying-down CuPc or F16CuPc thin films. In situ synchrotron-based photoemission spectroscopy reveals that the charge transfer at the standing F16CuPc/CuPc or CuPc/F16CuPc interface is much larger than that at the lying F16CuPc/CuPc or CuPc/F16CuPc interface. This can be explained by the orientation-dependent ionization potentials of well-ordered organic thin films, which place the highest-occupied molecular orbital of the standing CuPc film much closer to the lowest-unoccupied molecular orbital of the standing F16CuPc film, facilitating stronger charge transfer as compared to that at the lying OOH interfaces. Our results suggest the possibility of manipulating interfacial electronic structures of organic heterojunctions by controlling the molecular orientation, in particular for applications in ambipolar organic field transistors and organic photovoltaics. [ABSTRACT FROM AUTHOR]

This paper reports a comprehensive experimental study on the effects of hydrogen microwave plasma treatment on nonhydrogenated high sp3 content tetrahedral amorphous carbon (ta-C) film. In this study, a surface C–H dipole layer was first observed by high resolution electron energy loss spectroscopy, showing the presence of C–H bonding states. This resulted in the enhancement of electron field emission of the plasma treated films by largely lowering the turn-on field. Thermal stability tests using in situ ultraviolet photoelectron spectroscopy confirm that the C–H dipole layer not only reduces the work function of the films, it is extremely stable in both ambient and vacuum conditions and can sustain up to 600 °C annealing in vacuum. Atomic force microscopy studies also show minimal modifications to the surface morphology, leading to the conclusion that the C–H dipole layer is responsible for lowering the work function. This has improved the electron emission properties which can lead to potential applications such as electron emission displays. [ABSTRACT FROM AUTHOR]

In this study, the thermoelectric properties of AgPbmSbTem+2 (LAST-m, m=12, 16, 18, 20, 22, and 26), including the Seebeck coefficient, the electrical resistivity, and the thermal conductivity, were studied in the temperature range from 323 to 773 K. The Seebeck coefficient and the electrical resistivity exhibited the behavior of a degenerate semiconductor. The measured results of the carrier concentration supported the conclusions of the electrical transport properties. The lowest electrical resistivity and the thermal conductivity were observed, which leads to the best thermoelectric performance in LAST-18 and the dimensionless figure of merit ZT value of 0.8 at 773 K. [ABSTRACT FROM AUTHOR]

The field emission characteristics of the core-shelled nanostructures obtained by directly coating molybdenum oxide onto vertically aligned multiwalled carbon nanotubes (MWNTs) was investigated. A metal-organic chemical vapor deposition technique was used with Mo(CO)6 as the precursor and films deposited at process temperatures of 200, 400, and 700 °C. X-ray photoelectron spectroscopy, scanning electron microscopy, and x-ray diffraction were used to study and understand the material properties of the deposited coatings. Enhanced field emission performance was observed for molybdenum oxide coated MWNT samples at 400 °C with a turn-on field of 1.33 V μm-1 and a field enhancement factor β estimated to be ∼7000. The enhanced performance may be due to both the shape of the coated emitters and a decrease in the effective barrier height. [ABSTRACT FROM AUTHOR]

We present a comprehensive study relating the magnetic properties to structural properties of Mn+-implanted Si1-xGex films as a function of Ge content (x=0–0.5). Ferromagnetic ordering with three critical temperatures, TB∼10–16 K, TC1∼650–780 K, and TC2∼825–860 K, are reported in this material system. Element specific x-ray absorption fine structure results show that the majority of the Mn ions are nonsubstitutional in all samples. The transmission-electron microscopy coupled with z contrast and chemical analysis reveals the presence of Mn-rich nanosized clusters including Mn4Si7 in Si-rich samples and Mn7Ge3 phases in Ge-rich samples. A composition transition occurred at x∼0.2–0.3, where we observe a change in bond lengths and defect structures. Additionally, an enhancement in magnetizations with an increase in both TB and TC1 as well as a conversion from n-type to p-type conduction are also detected. [ABSTRACT FROM AUTHOR]

In this work, we address the spatiotemporal evolution of micro/nanoscopic pattern formation on polymer films by atomic force microscope (AFM) assisted electrohydrodynamic (EHD) nanolithography. This patterning method combines the locality and site specificity of AFM and the surface wave amplification of EHD instability for pattern creation and is capable of generating a series of structures corresponding to the zeroth- to second-order wave patterns. Detailed simulations in the framework of nonlinear three-dimensional analysis are presented to elucidate the localized EHD pattern formation. The experimental and theoretical results are quantitatively compared to address the characteristics of the AFM-assisted EHD pattern formation. The impact of key experimental parameters such as the tip bias voltage and bias duration on the formation rate, morphology, and lateral dimension of the wave patterns are discussed. The AFM assisted EHD nanolithography would open new route to the fabrication of complex polymer nanostructures. [ABSTRACT FROM AUTHOR]

We describe the spatiotemporal evolution of the nanoscale tip-surface junction during field-induced water meniscus formation in the junction. The motion of the meniscus and tip was analyzed on the basis of typical parameters concerning the nanoscale meniscus and tip-surface configuration. Being attracted by the electric field, the meniscus generates a repulsive hydrodynamic impact force counteracting the electrostatic force on the tip. The imbalance of the forces leads to an increase of the tip-surface separation distance, and the increase is related to the initial experimental parameters including tip bias voltage and tip spring constant. An explicit equation was derived for the estimation of the tip-surface junction enlargement effect. The theoretical results were confirmed by atomic force microscope (AFM) in situ observations of tip repulsion under electric fields. The induced tip-surface junction enlargement has significant implications in AFM nanolithography, e.g., it could facilitate the formation of nanostructures with high vertical dimensions/aspect ratios. [ABSTRACT FROM AUTHOR]

Thick, epitaxial NdBa2Cu3O7-δ (NdBCO) films (up to 2.1 μm) with a high density of nanoscale columnar defects parallel to the c-axis of the film were deposited on ion-beam assisted deposition-MgO templates via pulsed laser deposition. The columnar defects were composed of self-assembled BaZrO3 (BZO) nanodots. A significant enhancement in Jc for H|c is found for these films. In addition, an overall improvement in the in-field Jc at all field orientations is observed. Compared to pure NdBCO of similar thickness, the in-field Jc at H|c for 0.7 μm thick NdBCO+BZO film is improved by a factor of 2–4 in the field range of 0.1–4 T and 10–20 at 7–8 T at 77 K. In addition, a smaller α∼0.17 is found in the field regime where Jc∼H-α. Also, a higher maximum pinning force, Fpmax∼14 GN/m3, is found at 3 T and a larger Hirr over 8 T is found for the NdBCO films with columnar defects. [ABSTRACT FROM AUTHOR]

The conformation degree and molecular orientation during the growth of rubrene films on Si(111) and Au(111) have been studied by in situ x-ray absorption spectroscopy. The backbones of rubrene molecules on Au(111) are twisted at the first few layers; in contrast, no appreciable twisting is observed on Si(111) even at a thickness of approximately 1.5 nm. The planarization of the backbone in the first few layers is due to strong molecule–substrate interactions between rubrene and Si(111). The rubrene molecules on Au(111) have a backbone tilt angle of 41° and a phenyl side group tilt of 64° with respect to the substrate surface, suggesting the crystalline nature of the films. Ex situ atomic force microscopy measurements confirm that the rubrene film grown on Au(111) is crystalline and the growth direction is along its crystallographic c axis. [ABSTRACT FROM AUTHOR]

MnSb nanocrystallites and thin films have been grown on highly oriented pyrolytic graphite (HOPG) by codeposition of Mn and Sb in ultrahigh vacuum. The surface morphologies of these MnSb structures were investigated using in situ scanning tunneling microscopy (STM). With 5 nm nominal deposition, MnSb nanocrystallite chains with a typical width of 50 nm are formed along the HOPG step edges. A continuous MnSb film is formed after Mn and Sb codeposition on a HOPG precovered with an Sb wetting layer. The MnSb thin film surface exhibits mostly hexagonal-shaped MnSb(0001) plateaus of a few atomic layers in height. Atomic-resolution STM images revealed 2×2 and (23×23)R30° reconstructions on the MnSb(0001) surface and a 2×1 superstructure on MnSb(1011). X-ray photoelectron spectroscopy study showed that the Mn 2p peaks shift 2.5 eV with respect to that of elemental Mn, indicating the formation of MnSb compound. Vibrating sample magnetometry measurement showed that the MnSb film is ferromagnetic at room temperature, and is composed of mostly (0001)-oriented grains as well as some with other orientations. [ABSTRACT FROM AUTHOR]

Interdiffusion in In0.32Ga0.68As0.984N0.016/GaAs multiple quantum wells with well widths of 2 and 4 nm, respectively, was investigated both experimentally and theoretically. Maximum blueshifts of 206 and 264 meV in the photoluminescence spectra were observed. Secondary ion mass spectrometry showed that both In–Ga and N–As interdiffusions played key roles for the large blueshifts. The significant In–Ga interdiffusion occurred at 650 °C while the N diffusion occurred at a temperature above 700 °C. The theoretical results are in good agreement with the experimental observations. [ABSTRACT FROM AUTHOR]

The thermal stability of nitrogen-doped SrTiO3 (001) films in terms of electronic and optical properties has been studied by using x-ray photoemission spectroscopy, x-ray absorption spectroscopy, and spectroscopic ellipsometry techniques. The chemical states of nitrogen in nitrogen-doped SrTiO3 films include both substitutional and interstitial states. The N 2p states localized above the O 2p-derived valence band maximum are attributed to the change of optical properties. Postannealing will induce the valence band edge shift due to the thermal instability of interstitial N states, which may degrade the photocatalysis of nitrogen-doped SrTiO3 films during applications. [ABSTRACT FROM AUTHOR]

Low-temperature (10 K) photoluminescence measurements of GaAs1-xNx epitaxial layers grown on GaAs reveal an anomalous second peak in solid-source molecular beam epitaxy. Rapid thermal annealing (RTA) of a specific GaAsN sample reveals a lower energy peak (γ) which redshifts and a higher energy peak (α) which blueshifts under increasing annealing temperature. The band-anticrossing model is used to identify the origins of the two peaks and we propose a model to explain the RTA observations by the concept of increased confinement in areas of higher N concentrations by trapped N localized states. The γ peak is due to the accumulation of N content near the GaAs/GaAsN interface. Hence, this abnormal annealing behavior occurs in layers with nonuniform N concentration at the GaAsN/GaAs interface. [ABSTRACT FROM AUTHOR]

We report the study of the etching characteristics of atomic force microscopy (AFM) probe-grown ultrathin oxides (AFM oxides, up to 5 nm thick). In our method, an AFM localized depth analysis technique was employed to monitor the atomic layer-by-layer etching of AFM oxides. Insights into the growth mode and etching mechanism of AFM oxides were acquired on the basis of the etching results: it was found that AFM oxide growth is related to Si out-diffusion. For the formation of ultrathin oxides in ambient conditions, it is evident that oxidation-enhanced Si diffusion facilitates the layer-by-layer oxide growth in AFM anodic oxidation. The etching rate of ultrathin AFM oxides is dependent on the SiOH silanol reactive sites. Thermal annealing could reduce the content of silanol groups and enhance the chemical stability of AFM oxides against etching. [ABSTRACT FROM AUTHOR]

To obtain depth-resolved magnetic information from Fe films grown on fcc Co/Cu(001), we have used various signal sources for the detection of x-ray absorption spectroscopy. These include total electron yield (TEY) and partial electron yield (PEY) of inelastic electrons at various kinetic energies between 70 and 470 eV as well as PEY using photoelectrons at a fixed binding energy (constant initial state: CIS) near the Fermi level. Inelastic electron yield at electron emission angles up to 87° from the surface normal was found to be as nonsurface sensitive as TEY, however, the CIS mode shows a shorter information depth, comparable to the inelastic mean free path of photoelectrons. No difference in the dichroic signal at the Fe L3 edge was found between the CIS and TEY modes for a 2-monolayer (ML) Fe/Co film, but an 8-ML Fe/Co film showed a much higher dichroic signal in the CIS mode than that in the TEY mode. This is consistent with a homogeneous magnetic film at an Fe thickness of 2 ML and a nonhomogeneous magnetic film with a live ferromagnetic layer on the surface with nonferromagnetic underlayers at an Fe thickness of 8 ML. Thus, it is possible to extract depth-resolved magnetic information from x-ray magnetic circular dichroism by combining the surface sensitive CIS mode with other detection modes with less surface sensitivity. [ABSTRACT FROM AUTHOR]

We present a study on the redistribution of boron in (100) crystalline silicon and silicon-on-insulator (SOI) substrates after rapid thermal processing (RTP). The use of SOI back-side secondary ion mass spectrometry (SIMS) technique in obtaining an accurate diffusion profile is also investigated. Our results show that the boron diffusion profiles (using conventional frontside SIMS) do not deviate in any of the two types of substrates after RTP with a soak time of 30 sec, indicating that the insulating effect of SOI substrate does not enhance the diffusion of boron. Since the profile obtained by the back-side SIMS technique is always shallower than that of front-side SIMS, it is deduced that the back-side SIMS technique gives a better representation of the real profile. [ABSTRACT FROM AUTHOR]

In this paper, we report the systematic investigation on the melt characteristics of silicon during laser thermal processing (LTP) of amorphous silicon (a-Si) gates on ultrathin gate oxides. LTP is used to reduce the gate depletion effect in advanced semiconductor devices. The influence of implantation-induced damage and chemical inhomogeneities on the melt behavior of ion-implanted a-Si is studied using in situ time-resolved reflectance (TRR) measurements and ex situ secondary ion mass spectrometry. The results from TRR measurements indicate the presence of a buried melt for a-Si implanted with B+ at a subamorphizing dose. In contrast, such a melt behavior is not observed during LTP of undoped a-Si and a-Si implanted with As+ at an amorphizing dose. We attribute the marked difference in the melt characteristics to the competitive effects between compositional inhomogeneities and the extent of amorphization in the a-Si layer. It should be noted that the as-deposited a-Si gate is not really “amorphous” in the sense of an ion beam-induced amorphous layer. This postulation is verified by the absence of a buried melt in a-Si films implanted with Si+ prior to B+ implantation, where the dose of the Si+ implant is sufficient to cause amorphization in silicon and the amorphization depth greatly exceeds the projected range of the boron implant. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Nitrogenated tetrahedral amorphous carbon (N:ta-C) films prepared by the filtered cathodic vacuum arc technique were studied by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, spectroscopic ellipsometry, ultraviolet photoelectron spectroscopy and temperature dependent resistance measurement. As the nitrogen flow rate varies from 0 to 20 sccm, the nitrogen content in the deposited film increases from 0 to 4.6 at.%. Curve fitting of the C 1s and N 1s XPS spectra shows that the C-C sp[SUP3] fraction decreases with an increase in nitrogen content and that the nitrogen atoms are mainly bonded in sp[SUP2] C-N bonds. The pure ta-C film has a work function of 4.35 eV and the N:ta-C films have a value around 4.55 eV. With an increase in nitrogen flow rate, the intensity ratio of the D peak to the G peak, I[SUBD]/i[SUBG] increases monotonously from 0.44 to 1.25 and the G peak width decreases from 220 to 199 cm[SUP-1]. The Tauc optical band gap decreases from 2.2 to 1.8 eV. [ABSTRACT FROM AUTHOR]

In this article we report the role of excess interstitials in the end-of-range region in transient enhanced diffusion of boron during annealing of laser-processed samples. The results show that although the amorphous layer in preamorphized silicon can be completely annealed by laser irradiation, the end-of-range damages were not sufficiently annealed. The end-of-range region contains a supersaturation of interstitial defects that enhance the diffusion of boron during a post-laser processing anneal. It is found that the transient enhanced diffusion is significantly suppressed when the melt depth is extended beyond the amorphous layer such that the interstitial dose in the region adjacent to the laser-melted layer is minimized. In this way, the abruptness of laser-processed ultrashallow junctions can be maintained upon further annealing at moderately high temperatures. Cross-sectional transmission electron microscopy shows that a virtually defect-free regrown layer is obtained by overmelting beyond the amorphous layer into the substrate. [ABSTRACT FROM AUTHOR]

The oxide growth of rf sputtered polycrystalline Si[sub 1-x]Ge[sub x] films was found not sensitive to the Ge concentration in the films. The infrared results showed that the oxide grown on Si[sub 0.61]Ge[sub 0.39] film mainly contained GeO[sub 2] and the oxide contained Ge–O–Ge and Si–O–Ge bonds when grown on Si[sub 0.73]Ge[sub 0.27] film. X-ray photoelectron spectroscopy results showed the absence of Ge in the bulk of the oxides for Si[sub 1-x]Ge[sub x] films with x<0.27 and no pile-up of Ge at the SiO[sub 2]/Si[sub 1-x]Ge[sub x] interface. The electrical breakdown fields of oxides grown on Si[sub 1-x]Ge[sub x] films were lower than the oxide breakdown field of polysilicon. The D[sub it] and Q[sub f] values of the SiO[sub 2]/Si[sub 1-x]Ge[sub x] system were found to be rather high at ∼2.1–2.6×10[sup 12] eV[sup -1] cm[sup -2] and ∼1.1–2.7×10[sup 12] cm[sup -2], respectively. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]