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Kinetic models are essential for describing how molecules interact in a variety of biochemical processes. The estimation of a model's kinetic parameters by experiment enables researchers to understand how pathogens, such as viruses, interact with other entities like antibodies and trial drugs. In this work, we report a simple proof-of-principle experiment that uses quantum sensing techniques to give a more precise estimation of kinetic parameters than is possible with a classical approach. The interaction we study is that of bovine serum albumin (BSA) binding to gold via an electrostatic mechanism. BSA is an important protein in biochemical research as it can be conjugated with other proteins and peptides to create sensors with a wide range of specificity. We use single photons generated via parametric down-conversion to probe the BSA–gold interaction in a plasmonic resonance sensor. We find that sub-shot-noise-level fluctuations in the sensor signal allow us to achieve an improvement in the precision of up to 31.8% for the values of the kinetic parameters. This enhancement can, in principle, be further increased in the setup. Our work highlights the potential use of quantum states of light for sensing in biochemical research. [ABSTRACT FROM AUTHOR]

We investigated adsorption of N2 on stoichiometric and O-rich IrO2(110) surfaces using temperature programmed desorption (TPD) experiments and density functional theory (DFT) calculations. TPD shows that N2 desorbs predominantly from the stoichiometric-IrO2(110) surface in a well-defined peak at 270 K for N2 coverages below about 0.5 ML and that a shoulder centered near 235 K develops in the N2 TPD traces as the coverage approaches saturation, indicating that adsorbed N2 molecules destabilize at high N2 coverages. Experiments of N2 adsorption onto O-rich IrO2(110) surfaces provide evidence that N2 adsorbs exclusively on the coordinatively unsaturated Ir atoms (Ircus) of the surface and that pre-adsorbed O-atoms ("on-top" oxygen) stabilize adsorbed N2 molecules, causing the main N2 TPD peak to shift toward higher temperature with increasing oxygen coverages. Consistent with prior results, our DFT calculations predict that an N2 molecule preferentially adsorbs into an upright configuration on an Ircus atom of the IrO2(110) surface and achieves a binding energy of about 100 kJ/mol. The computed binding energy agrees well with our experimental estimate of ∼90 kJ/mol for low N2 coverages on stoichiometric IrO2(110). The DFT calculations also quantitatively reproduce the observed stabilization of N2 by co-adsorption on-top O-atoms and predict the destabilization of N2 on IrO2(110) as the N2 adlayer becomes crowded at high coverages. [ABSTRACT FROM AUTHOR]

The structural changes in Ru-coated Y films during hydrogenation were studied in this work. In situ XRD data were used to show that the Y to YH2 transition requires significant hydrogen loading of the Y lattice. By comparing the XRD data with the in situ spectroscopic ellipsometry data, an effective medium model for the transition was obtained. This model describes the Y to YH2 transition well. The YH2 to YH3 transition is also described by an effective medium model, however, with reduced accuracy around the midpoint of the transition. By comparing the YH2 and YH3 crystal sizes, we show that these deviations may be due to a surface plasmon resonance. The improved understanding of the ellipsometry measurements is important for optical hydrogen sensing applications. [ABSTRACT FROM AUTHOR]

Interlayer dipolar coupling is an important aspect in magnetic switching devices from the application point of view. Here, we identify various sources affecting the interlayer dipolar coupling in CoFeB-based perpendicular magnetic tunnel junctions (pMTJs). By changing the MgO tunnel barrier layer thickness, we show that it plays a crucial role in controlling the dipolar coupling between the CoFeB reference and free layers and affects the magnetic properties of pMTJ. Moreover, changes in thickness of the bottom electrode layer affect the interlayer coupling strength and change the magnetic anisotropy of the free layer from perpendicular to in-plane direction. Furthermore, it is observed that the smaller the cell size of such MTJs, the more dominating the coupling strength which is formed by stray fields. These are some of the crucial parameters which need to be investigated during the device fabrication process for optimum device performance. [ABSTRACT FROM AUTHOR]

An experimental study of oxide reduction at the surface of ruthenium layers on top of multilayer mirrors and thin Ru/Si films is presented. Oxidation and reduction processes were observed under conditions close to those relevant for extreme ultraviolet lithography. The oxidized ruthenium surface was exposed to a low-temperature hydrogen plasma, similar to the plasma induced by extreme ultraviolet radiation. The experiments show that hydrogen ions are the main reducing agent. Furthermore, the addition of hydrogen radicals increases the reduction rate beyond that expected from simple flux calculations. We show that low-temperature hydrogen plasmas can be effective for reducing oxidized top surfaces. Our proof-of-concept experiments show that an in situ, EUV-generated plasma cleaning technology is feasible. [ABSTRACT FROM AUTHOR]

In order to investigate the mechanism behind bistable resistance switching in NiO thin films, we have done detailed x-ray photon spectroscopy (XPS) and x-ray diffraction Analysis (XRD) on NiO and Ti doped NiO samples fabricated under various conditions. We discovered that a high initial resistivity was required for samples to undergo bistable resistance switching, and the presence of metallic Ni content in these samples was determined by XPS. XRD data also showed that NiO grown with a relative (200) orientation was preferred over those grown with relative (111) orientation. [ABSTRACT FROM AUTHOR]

A two-step treatment by argon (Ar) and hydrogen plasma beam scanning was developed to modify the surface bonds of a hydrogenated amorphous carbon (a-C:H) film on indium tin oxide glass. The modified a-C:H film is an excellent layer for liquid crystal alignment, on which the pretilt angle of a nematic liquid crystal (ZLI-2293) can be adjusted by the two-step scanning treatment. The chemical bonding characteristics of the as-scanned a-C:H films were measured using micro-Raman and x-ray photoemission spectroscopies. The antiparallel cells were filled with the nematic liquid crystal on the as-scanned a-C:H film to measure the pretilt angle. Experimental results indicate that the carbon dangling bonds are generated through a bond-breaking process during the Ar plasma beam scanning step (first step). The hydrogen plasma beam scanning step (second step) can passivate some of the carbon dangling bonds that are generated in the first step. The pretilt angle decreases as the hydrogen plasma beam scanning time increases. The decrease of pretilt angle is due to the formation of C–H bonds that passivate the a-C:H film and limit the formation of C–O bonds in air. [ABSTRACT FROM AUTHOR]

Buckled SiGe films on viscous oxide with different Ge content are studied by wafer bonding and smart-cut process. Compressively strained SiGe layers on the viscous oxide were relaxed to form the buckled state after thermal treatment. Two-dimensional buckling on blanket films is observed. A higher Ge concentration results in a smaller buckling amplitude and a smaller buckling period. Both buckling amplitude and period increase as oxidation time is increased. A small SiGe film (mesa) area can inhibit buckling. Semiempirical analysis gives the critical area size, below which no buckling is observed in the equilibrium states. The critical area size decreases with increasing Ge concentration and decreasing thickness of SiGe films. [ABSTRACT FROM AUTHOR]

A plasma beam scanning treatment has been developed to modify the surface of the hydrogenated amorphous carbon (a-C:H) film on the indium tin oxide glass. The plasma beam scanning treatment makes the a-C:H film an excellent layer for liquid-crystal alignment. The qualities of a-C:H films were characterized by using atomic force microscope, micro-Raman spectroscopy, and field-emission scanning electron microscope. The ultrathin a-C:H films were deposited at 50% CH4/(H2+CH4) gas ratio, 100 W radio-frequency power, and a gas pressure of 10 mtorr for 15 min by capacitive-coupled plasma chemical-vapor deposition method. The twist nematic cells were filled with liquid crystal (ZLI-2293) on the a-C:H film treated with different nitrogen plasma beam scanning time. The grooving mechanism is considered not responsible for the liquid-crystal (LC) alignment. Raman spectra suggest that a bond-breaking process of aromatic rings occurs in the a-C:H film. The O1s, C1s, and N1s core-level spectra support that the nitrogen plasma beam scanning treatment induces a bond-breaking process of aromatic rings to create available carbon dangling bonds for the formation of C–O bonds. The newly formed C–O bonds are “directional,” which favor the LC alignment on the a-C:H film. [ABSTRACT FROM AUTHOR]

The structural and optical properties of self-assembled InAs quantum dots (QDs) with various InGaAs structures were investigated by transmission electron microscopy (TEM) and photoluminescence (PL). The emission peak position of InAs QDs covered by a 6 nm In[sub 0.15]Ga[sub 0.85]As layer was 1.26 μm with PL linewidth of 31 meV, which is narrower than that of QDs in a GaAs matrix. By inserting a 1 nm In[sub 0.15]Ga[sub 0.85]As layer below the InAs QD layer with a 6 nm In[sub 0.15]Ga[sub 0.85]As overgrowth layer, the emission peak position was redshifted with larger energy-level spacing between the ground states and the first excited states compared to that of QDs with an In[sub 0.15]Ga[sub 0.85]As overgrowth layer only. By covering the InAs QDs on a 1 nm In[sub 0.15]Ga[sub 0.85]As layer with an 8 nm In[sub x]Ga[sub 1-x]As layer having graded In composition, the emission peak position was 1.32 μm with relatively larger energy-level spacing and narrower PL linewidth compared to QDs covered by an In[sub 0.15]Ga[sub 0.85]As layer. The longer emission wavelength with relatively larger energy-level spacing was largely related to the change in the QD shape and size, especially the aspect ratio (height/width), which was confirmed by cross-sectional TEM images. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We examined the crystal structure of the new thermoelectric material LaOBiS2-xSex, whose thermoelectric performance is enhanced by Se substitution, by using powder synchrotron X-ray diffraction and Rietveld refinement. The emergence of metallic conductivity and enhancement of the thermoelectric power factor of LaOBiS2-xSex can be explained with the higher in-plane chemical pressure caused by the increase of Se concentration at the in-plane Ch1 site (Ch = S, Se). High-temperature X-ray diffraction measurements for optimally substituted LaOBiSSe revealed anomalously large atomic displacement parameters (Uiso) for Bi and Ch atoms in the BiCh2 conduction layers. The anisotropic analysis of the atomic displacement parameters (U11 and U33) for the in-plane Bi and Ch1 sites suggested that Bi atoms exhibit large atomic displacement along the c-axis direction above 300 K, which could be the origin of the low thermal conductivity in LaOBiSSe. The large Bi vibration along the c-axis direction could be related to in-plane rattling, which is a new strategy for attaining low thermal conductivity and phonon-glass-electron-crystal states. [ABSTRACT FROM AUTHOR]

We herein explore the possibility of obtaining tunable tilted magnetic anisotropy in ordered-CoPt (5nm)/NiFe(tNiFe) bilayers through modifying their exchange spring behavior by inserting Pt and Ru-spacers. The tuning process of tilt angle magnetization of NiFe-layer was systematically investigated by varying the Pt or Ru thickness (tPt or tRu) from 0 to 8nm at different thicknesses of NiFe (tNiFe=1.5, 4.0, and 6.0nm). Polar magneto-optic Kerr effect (p-MOKE) studies reveal that the bilayers grown in absence of spacers exhibit almost a rectangular hysteresis loop. With the insertion of Pt-spacer, the loop becomes more and more tilted as tPt increases; whereas, in the case of Ru-spacer, the nature of the loops is not simply changing in one direction. The estimated SQR⊥ (=θr/θs) values from the p-MOKE loops are found to monotonically decrease with increasing tPt when tPt ⩽ 4nm. In contrast, in the case of Ru-spacer, an oscillatory behavior for the SQR⊥ values is apparent when tRu ⩽ 4nm. As a result, an oscillatory tilted angle of NiFe spin configuration was obtained in the case of Ru-spacer; while a decoupling effect was prominent for the Pt-spacer. The results of present study reveal that the insertion of Pt and Ru-spacers as an appropriate means for realizing tunable tilted magnetic anisotropy in the CoPt/NiFe exchange springs. [ABSTRACT FROM AUTHOR]

We have studied the effect of photoelectrons on defect formation in graphene during extreme ultraviolet (EUV) irradiation. Assuming the major role of these low energy electrons, we have mimicked the process by using low energy primary electrons. Graphene is irradiated by an electron beam with energy lower than 80 eV. After e-beam irradiation, it is found that the D peak, I(D), appears in the Raman spectrum, indicating defect formation in graphene. The evolution of I(D)/I(G) follows the amorphization trajectory with increasing irradiation dose, indicating that graphene goes through a transformation from microcrystalline to nanocrystalline and then further to amorphous carbon. Further, irradiation of graphene with increased water partial pressure does not significantly change the Raman spectra, which suggests that, in the extremely low energy range, e-beam induced chemical reactions between residual water and graphene are not the dominant mechanism driving defect formation in graphene. Single layer graphene, partially suspended over holes was irradiated with EUV radiation. By comparing with the Raman results from e-beam irradiation, it is concluded that the photoelectrons, especially those from the valence band, contribute to defect formation in graphene during irradiation. [ABSTRACT FROM AUTHOR]

Employing numerical diagonalization, we study the optical properties of an electron in a monolayer-graphene magnetic dot bound to an off-center negatively charged Coulomb impurity based on the massless Dirac-Weyl model. Numerical results show that, since the electron-hole symmetry is broken by the Coulomb potential, the optical absorption spectra of the magnetic dot in the presence of a Coulomb impurity are different between the electron states and the hole states. Effects of both the magnetic field and the dot size on the absorption coefficient are presented as functions of the incident photon energies. [ABSTRACT FROM AUTHOR]

Films of L11-type CoPt/NiFe exchange springs were grown with different NiFe (Permalloy) layer thickness (tNiFe=0-10 nm). X-ray diffraction analysis reveals that the characteristic peak position of NiFe(111) is not affected by the CoPt-layer-confirming the absence of any inter-diffusion between the CoPt and NiFe layers. Magnetic studies indicate that the magnetization orientation of NiFe layer can be tuned through varying tNiFe and the perpendicular magnetic anisotropy of L11-type CoPt/NiFe films cannot sustain for tNiFe larger than 3.0 nm due to the existence of exchange interaction at the interface of L11-CoPt and NiFe layers. Magnetic force microscopy analysis on the as-grown samples shows the changes in morphology from maze-like domains with good contrast to hazy domains when tNiFe≥3.0 nm. The three-dimensional micro-magnetic simulation results demonstrate that the magnetization orientation in NiFe layer is not uniform, which continuously increases from the interface to the top of NiFe layer. Furthermore, the tilt angle of the topmost NiFe layers can be changed over a very wide range from a small number to about 75° by varying tNiFe from 1 to 10 nm. It is worth noting that there is an abrupt change in the magnetization direction at the interface, for all the tNiFe investigated. The results of present study demonstrate that the tunable tilted exchange springs can be realized with L11-type CoPt/NiFe bilayers for future applications in three-axis magnetic sensors or advanced spintronic devices demanding inclined magnetic anisotropy. [ABSTRACT FROM AUTHOR]

Ion channeling technique using MeV C2+ ions and high resolution X-ray diffraction were used to study the crystal quality of an InAs/AlSb-based quantum wells. We found that the InAs quality has a strong dependence on the type of the interface used. With the addition of the InSb-like interface, the crystal quality of the InAs channel was greatly improved. The InAs lattice was fully strained and aligned with the lattice of the buffer layer without any lattice relaxation. On the other hand, if the interface was of the AlAs type, the lattice of the InAs quantum well was relaxed and the crystal quality was poor. This explains why a superior InAs quantum well with high electron mobility and good surface morphology can be achieved with the use of the InSb interface. [ABSTRACT FROM AUTHOR]

Using the Dirac-Weyl model, we study the low-lying spectra of a massless Dirac electron bound to a positively charged Coulomb impurity in a graphene magnetic dot, for which the inhomogeneous magnetic field is created by different magnetic fields inside and outside the dot with a field ratio α. Numerical results show that the zero energy states, in the presence of the impurity, are converted into hole-like states. Additionally, for positive and negative α values, the states are, in general, located inside and outside the dot, respectively, causing the spectra to exhibit different features. [ABSTRACT FROM AUTHOR]

Microstructural evolution of ultrananocrystalline diamond (UNCD) films as a function of substrate temperature (TS) and/or by introducing H2 in Ar/CH4 plasma is investigated. Variation of the sp2 and sp3 carbon content is analyzed using UV-Raman and near-edge X-ray absorption fine structure spectra. Morphological and microstructural studies confirm that films deposited using Ar/CH4 plasma at low TS consist of a random distribution of spherically shaped ultra-nano diamond grains with distinct sp2-bonded grain boundaries, which are attributed to the adherence of CH radicals to the nano-sized diamond clusters. By increasing TS, adhering efficiency of CH radicals to the diamond lattice drops and trans-polyacetylene (t-PA) encapsulating the nano-sized diamond grains break, whereas the addition of 1.5% H2 in Ar/CH4 plasma at low TS induces atomic hydrogen that preferentially etches out the t-PA attached to ultra-nano diamond grains. Both cases make the sp3-diamond phase less passivated. This leads to C2 radicals attaching to the diamond lattice promoting elongated clustered grains along with a complicated defect structure. Such a grain growth model is highly correlated to explain the technologically important functional property, namely, plasma illumination (PI) of UNCD films. Superior PI properties, viz. low threshold field of 0.21 V/μm with a high PI current density of 4.10 mA/cm2 (at an applied field of 0.25 V/μm) and high γ-coefficient (0.2604) are observed for the UNCD films possessing ultra-nano grains with a large fraction of grain boundary phases. The grain boundary component consists of a large amount of sp2-carbon phases that possibly form interconnected paths for facilitating the transport of electrons and the electron field emission process that markedly enhance PI properties. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) biomimetic systems hold great promise for the study of biological systems in vitro as well as for the development and testing of pharmaceuticals. Here, we test the hypothesis that an intact segment of lumbar rat spinal cord will form functional neuromuscular junctions (NMJs) with engineered, 3D muscle tissue, mimicking the partial development of the peripheral nervous system (PNS). Muscle tissues are grown on a 3D-printed polyethylene glycol (PEG) skeleton where deflection of the backbone due to muscle contraction causes the displacement of the pillar-like "feet." We show that spinal cord explants extend a robust and complex arbor of motor neurons and glia in vitro. We then engineered a "spinobot" by innervating the muscle tissue with an intact segment of lumbar spinal cord that houses the hindlimb locomotor central pattern generator (CPG). Within 7 days of the spinal cord being introduced to the muscle tissue, functional neuromuscular junctions (NMJs) are formed, resulting in the development of an early PNS in vitro. The newly innervated muscles exhibit spontaneous contractions as measured by the displacement of pillars on the PEG skeleton. Upon chemical excitation, the spinal cord-muscle system initiated muscular twitches with a consistent frequency pattern. These sequences of contraction/relaxation suggest the action of a spinal CPG. Chemical inhibition with a blocker of neuronal glutamate receptors effectively blocked contractions. Overall, these data demonstrate that a rat spinal cord is capable of forming functional neuromuscular junctions ex vivo with an engineered muscle tissue at an ontogenetically similar timescale. [ABSTRACT FROM AUTHOR]

The local structure of copper nanoparticles grown in organic solution by reducing Cu(II) hexafluoroacetylacetonate [Cu(hfac)2] was studied as-grown by the Cu K-edge x-ray absorption near-edge structure (XANES). Comparison of the experimental XANES spectra with reference materials indicated small copper clusters are formed by ligand-exchange with oleylamine and subsequent reducing by diphenylsilane. The multiple-scattering (MS) calculation for various model clusters consisting of 13-135 atoms suggests that small (13-19 atom) Cu clusters are stabilized without a large deformation. [ABSTRACT FROM AUTHOR]

Dynamic experiments with Al-W granular/porous composites revealed qualitatively different behavior with respect to shear localization depending on bonding between Al particles. Two-dimensional numerical modeling was used to explore the mesomechanics of the large strain dynamic deformation in Al-W granular/porous composites and explain the experimentally observed differences in shear localization between composites with various mesostructures. Specifically, the bonding between the Al particles, the porosity, the roles of the relative particle sizes of Al and W, the arrangements of the W particles, and the material properties of Al were investigated using numerical calculations. It was demonstrated in simulations that the bonding between the soft Al particles facilitated shear localization as seen in the experiments. Numerical calculations and experiments revealed that the mechanism of the shear localization in granular composites is mainly due to the local high strain flow of soft Al around the rigid W particles causing localized damage accumulation and subsequent growth of the meso/macro shear bands/cracks. The rigid W particles were the major geometrical factor determining the initiation and propagation of kinked shear bands in the matrix of soft Al particles, leaving some areas free of extensive plastic deformation as observed in experiments and numerical calculations. [ABSTRACT FROM AUTHOR]

The perpendicular magnetic anisotropy of a series of top MgO/CoFeB/Ta layers is studied. Similar to the bottom Ta/CoFeB/MgO structure, the critical thickness of CoFeB is limited in a range of 1.1-1.7 nm. However, the cap layer shows much sensitive effect. Not only the type of material is crucial, but the thickness of the cap layer also affects the magnetic anisotropy. The perpendicular anisotropy of a 1.2 nm-thick CoFeB can only exist with the capping Ta thickness less than 2 nm. The magnetic characterizations, including the magnetic remanence and coercivity, also show strong dependence on the Ta thickness. The diffusion of Ta into CoFeB layer is considered to play an important role, which could explain changes in perpendicular anisotropy and related magnetic responses. In addition, the asymmetric role of Ta layer in the top structure and bottom structures is also discussed. [ABSTRACT FROM AUTHOR]

The bond dissociation energy (D0) of the water dimer is determined by using state-to-state vibrational predissociation measurements following excitation of the bound OH stretch fundamental of the donor unit of the dimer. Velocity map imaging and resonance-enhanced multiphoton ionization (REMPI) are used to determine pair-correlated product velocity and translational energy distributions. H2O fragments are detected in the ground vibrational (000) and the first excited bending (010) states by 2 + 1 REMPI via the C 1B1 (000) ← X 1A1 (000 and 010) transitions. The fragments' velocity and center-of-mass translational energy distributions are determined from images of selected rovibrational levels of H2O. An accurate value for D0 is obtained by fitting both the structure in the images and the maximum velocity of the fragments. This value, D0 = 1105 ± 10 cm-1 (13.2 ± 0.12 kJ/mol), is in excellent agreement with the recent theoretical value of D0 = 1103 ± 4 cm-1 (13.2 ± 0.05 kJ/mol) suggested as a benchmark by Shank et al. [J. Chem. Phys. 130, 144314 (2009)]. [ABSTRACT FROM AUTHOR]

Molecule-substrate interaction channels of metal-phthalocyanines (MPcs, including NiPc, CuPc, ZnPc, FePc, and CoPc) on graphene on Ni(111) were investigated by employing high-resolution electron energy loss spectroscopy (HREELS). Except the expected IR-active modes, some Raman-active modes were also observed in all of MPcs, which are considered in this study. From the origination of the Raman-active features, it was deduced that MPcs are coupled with the substrate mainly through their central metal atom. The Raman-active modes appear as symmetric peaks in the HREELS in the case of MPcs with Ni, Cu, and Zn, whereas they are asymmetric and appear as a Fano line shape in the case of MPcs with Fe and Co. This spectroscopic difference indicates that the molecule-substrate coupling is completely different in the two cases mentioned above. The molecule-substrate interaction strength is considerably weak and comparable with the π-π interaction between molecules in the case of MPcs with Ni, Cu, and Zn, whereas it is much stronger in the case of MPcs with Fe and Co. From the HREELS observations, it can be suggested that the whole molecule can be effectively decoupled from the underneath Ni(111) by inserting a single layer of graphene between them in the case of MPcs with Ni, Cu, and Zn, whereas only benzene rings can be completely decoupled in the case of MPcs with Fe and Co. [ABSTRACT FROM AUTHOR]

The magneto-optical response of type-II tensily strained GaAs self-assembled quantum dots in GaSb was investigated in magnetic fields up to 14 T. By depositing different GaAs amount, the dot sizes and the corresponding emission energies were varied. We analyzed the carrier wave function extent of different dots using the diamagnetic shift results. It was found that, with the increase in the energy (the reduction in the dot size), the diamagnetic coefficient first rises quickly and then saturates at around 21 μeV/T2. Based on a simple calculation model, this unusual tendency is attributed to the electrons gradually spilling out of the quantum dot to the wetting layer as the dots get smaller. This delocalization effect is enhanced in this material system due to the tensile strain relaxation within the dots, which raises the conduction band edge over that in the wetting layer. [ABSTRACT FROM AUTHOR]

We have investigated the InGaAs/GaAsSb/InAlGaAs/InAlAs type-II 'W' quantum wells (QWs) grown on InP substrates by molecular beam epitaxy. The photoluminescence (PL) emission wavelength longer than 2.56 μm at room temperature (RT) is demonstrated for the first time in this material system. The PL emission peaks of our designed samples can cover a wide range from 2 to 2.5 μm at cryogenic temperature. The samples show good optical quality that the reduction in integrated PL intensity is only around one order of magnitude from 35 K to RT. We found that the integrated PL intensity decreased as the emission wavelength increased, which is due to the reduction in the electron-hole wave function overlap. This is consistent with the calculated result. In the power dependent PL measurements, the emission peak of 'W' type QWs show blue shifts with the excitation power (Pex) but does not follow the Pex1/3 rule as predicted by type-II band bending model. The localized states filling effect gives reasonable explanations for the observed phenomena. [ABSTRACT FROM AUTHOR]

The growth of zinc phthalocyanine (ZnPc) on Ag(100) surface from monolayer to multilayer was investigated by low-energy electron diffraction, x-ray diffraction, and high-resolution electron energy loss spectroscopy (HREELS). At monolayer coverage, ZnPc molecules form an ordered film with molecular planes parallel to the substrate. The same structure is maintained as the film thickness increases. HREELS analysis shows that intermolecular π-π interaction dominates during the film growth from monolayer to multilayer. The π-d interaction between the adsorbates and the substrate is only applicable in the first adlayer. Stronger intermolecular-layer interaction is observed at higher coverages. [ABSTRACT FROM AUTHOR]

We performed polarization Raman spectroscopy on single wurtzite GaN nanorod bundles grown by plasma-assisted molecular beam epitaxy. The obtained Raman spectra were compared with those of GaN epilayer. The spectral difference between the GaN nanorod bundles and epilayer reveals the relaxation of Raman selection rules in these GaN nanorod bundles. The deviation of polarization-dependent Raman spectroscopy from the prediction of Raman selection rules is attributed to both the orientation of the crystal axis with respect to the polarization vectors of incident and scattered light and the structural defects in the merging boundary of GaN nanorods. The presence of high defect density induced by local strain at the merging boundary was further confirmed by transmission electron microscopy. The averaged defect interspacing was estimated to be around 3 nm based on the spatial correlation model. [ABSTRACT FROM AUTHOR]

Real-time deformation of individual multiwalled boron nitride nanotubes (BNNTs) was investigated using an atomic force microscopy (AFM) stage installed inside the chamber of a transmission electron microscopy (TEM) system. These in situ AFM-TEM experiments were conducted in following two deformation regimes: a small-angle (∼65°) and a large-angle (∼120°) cyclic bending process. BNNTs survived from the low-angle test and their modulus was determined as ∼0.5 TPa. Fracture failure of individual BNNTs was discovered in the large-angle cyclic bending. The brittle failure mechanism was initiated from the outermost walls and propagated toward the tubular axis with discrete drops of applied forces. [ABSTRACT FROM AUTHOR]

Polycrystalline multiferroic La0.8Bi0.2Fe1-xMnxO3 (0.0≤x≤0.4) samples were synthesized by the conventional solid state reaction method. Reitveld refinement of the x-ray diffraction patterns confirms the single phase character of all the compositions with orthorhombic structure having space group Pnma (No. 62). Dielectric properties of the samples at temperatures 200–475 K and frequencies 500 kHz–1 MHz authenticate the stabilization of ferroelectric phase with Mn substitution. Dielectric responses of these multiferroics have been analyzed carefully, in the light of “universal dielectric response” model. While cooling from room temperature to 20 K, systematic shifts in magnetization hysteresis loops indicate the presence of exchange bias (EB) phenomenon in the system. Magnetic behavior of these samples has been briefly discussed on the basis of “EB” model for granular systems. Temperature and magnetic field dependent magnetization data demonstrate enhanced magnetization due to the Mn substitution. Magnetocapacitance measurement reveals the magnetoelectric coupling for wide range of temperature (180–280 K) and decrease in dielectric loss at high magnetic field (3 T). [ABSTRACT FROM AUTHOR]

The electronic properties of a nanographene ribbon can be significantly tuned by a spatially modulated electric field. The modulated electric potential results in the changes of the electronic properties, i.e., modified energy dispersions, creation of extra band-edge states, alteration of the energy gap, and induction of semiconductor-metal transition. The number of the free carrier increases with the increment of the field strength. Through further classification of the carbon atoms, the features of the wave functions are clearly presented, and the carrier distribution is drastically modulated under the influence of the electric field. The periodic length and the phase shift of the modulated electric field induce a change in the y-axis symmetry of the ribbon and have a significant influence on the energy of the partial flat bands, the energy gap and the carrier distribution. The characteristics of the band structure are directly revealed in the density of states (DOS). The number, heights, positions, and spacings of the peaks in DOS are significantly changed. At the Fermi level, DOS is considerably enhanced; that is, more free carriers are created. The predicted results can be verified by optical and transport experiments. [ABSTRACT FROM AUTHOR]

Via immunomagnetic reduction assay, biomolecules can be quantitatively detected with aid of biofunctionalized magnetic nanoparticles, which are used as labeling markers for specific biomolecules. To achieve ultra-high sensitivity in detecting biomolecules, superconducting quantum interference device (SQUID) is a promising candidate to act as a sensor to the magnetic signal related to the concentration of detected biomolecules. In the past, we developed a single channel SQUID-based magnetosusceptometry. In order to increase the detection through-put, multichannel SQUID-based magnetosusceptometry is developed. In this work, the design and working principle of four-channel SQUID-based magnetosusceptometry are introduced. Using utilizing scanning technology, four samples can be simultaneously logged into the SQUID-based magnetosusceptometry. Notably, only single SQUID magnetometer is used in the magnetosusceptometry. The precision and sensitivity in detecting biomolecules using the four-channel SQUID-based magnetosusceptometry are investigated. [ABSTRACT FROM AUTHOR]

Deposition sequence and substrate work function in controlling the interface energy level alignment in organic photovoltaic (OPV) devices with copper phthalocyanine (CuPc) as the donor and fullerene (C60) as the acceptor were studied using ultraviolet photoelectron spectroscopy. We found that the energy offset at the highest occupied molecular orbital of donor (HOMOD) and the lowest unoccupied orbital of acceptor (LUMOA), which limits the maximum open-circuit voltage of heterojunction OPV, can be changed from 0.64 (C60 on CuPc) to 0.86 eV (CuPc on C60) by reversing the deposition sequence. Furthermore, by controlling the substrate work function from 2.81 to 5.07 eV, the LUMOA-HOMOD offset can be effectively tuned from 0.86 to 1.27 eV. The results suggest that electrodes in OPV devices can have significant influences on the electronic structures and energy levels of the donor/acceptor interface, and thus provide a viable means for performance enhancement. [ABSTRACT FROM AUTHOR]

We present systematic experimental studies of the temperature dependence of continuous wave and time-resolved photoluminescence spectroscopy in self-assembled InAs/GaAs nanostructures as the shape of quantum structures evolved from dot to ring. The carrier dynamics show strong dependence on the geometrical shape of the nanostructures under investigation. An increase in photoluminescence decay time of the excited and ground states is observed as the shape of nanostructures changed from dot, volcano, to ring. It is attributed to the carrier thermalization between the dark and ground states. The photoluminescence excitation spectra of the quantum rings reveal resonances related to the dark states. A rate equation model is proposed to interpret the observed carrier dynamics. [ABSTRACT FROM AUTHOR]

Arrays of highly ordered ZnO nanowires have been synthesized on polycrystalline Al-doped ZnO (AZO) buffer layers prepared on p-Si substrates (7–13 Ω cm) with assistance of a thermal deposition method. The diameter and interspacing of the nanowires have been controlled by the growth conditions and properties of AZO films. The optimized array of ZnO nanowires shows low turn-on and threshold fields (∼1.1 and ∼3.0 V/μm, respectively) and displays exceptional time stability of electron field emission. The time-fluctuation instability was found to be less than 0.6% at a current density of 10 mA/cm2, as measured for 500 min. The low turn-on and threshold fields as well as the stable electron emission current suggest that the arrays of ZnO nanowires could be considered in some electron field emission applications. [ABSTRACT FROM AUTHOR]

We present an optical technique, point radiance spectroscopy, to directly recover chromophore concentrations and the reduced optical scattering coefficient spectrum from continuous wave interstitial point radiance measurements at a single-source-detector separation in turbid, tissuelike media. The method employs a spectral algorithm to fit the relative radiance data, using the P3 approximation, at only two detection angles (0° and 90°). The spectral fitting algorithm is applied to simulated data of relative point fluence and relative point radiance data with added 1% noise and shows that even under realistic experimental conditions, only point radiance information is able to provide quantitative information regarding chromophore concentrations and scattering power at distances greater than two to three mean free paths from the source. Furthermore, experimental measurements in tissue-simulating phantoms demonstrate that dye concentrations and scattering parameters can be recovered to within ¿10%. The developed point radiance technique bridges a technological gap between local surface reflectance and spatially resolved interstitial fluence methods in optical assessment of random media such as biological tissue. [ABSTRACT FROM AUTHOR]

Domain structure and magnetization reversal process of exchange-coupled ferromagnet/antiferromagnet bilayers Co(x)/Ir¿Mn(10 nm) were studied as a function of both thickness of the Co layer and annealing temperature. The exchange bias field of the thinnest film and the coercive field of the thicker films show monotonic increase at annealing temperature above 250 °C. In every case the bilayers are remagnetized by domain nucleation and domain wall motion. Domain size decreases rapidly for high annealing temperatures, while x-ray diffraction study indicated that the crystallographic texture did not change significantly. The observed features are discussed taking into account the magnetic structure at the interface and its evolution during annealing. [ABSTRACT FROM AUTHOR]

Characteristics of In(Ga)As quantum ring infrared photodetectors (QRIPs) were investigated under normal incidence configuration. Compared with quantum dot infrared photodetectors (QDIPs), QRIPs showed wider photocurrent spectra, more stable responsivity with temperature change, and lower dark current activation energy. The wide detection band comes from the transitions from the quantum ring (QR) ground states to different excited states. The shallow confinement states generate higher dark current and enhance the carrier flow between the QRs within the same QR layer. This carrier flow averages out the repulsive potential and makes QRIPs behave similarly to the quantum well infrared photodetectors instead of QDIPs. With an Al0.27Ga0.73As current blocking layer, the performance of QRIPs was greatly enhanced. [ABSTRACT FROM AUTHOR]

A method for degradation of environmentally hazardous dyes using silicon nanowires (SiNWs) has been developed. Environmentally unfriendly methyl red was degraded with assistance of H-terminated SiNWs under ultrasonic agitation. The hydrogenated surfaces of SiNWs are shown to be responsible for the surface reaction and decay of methyl red. The rate of degradation increases with the amount of SiNWs and agitation power. SiNWs after their application can be recycled and reactivated for further uses by a simple heating in hydrogen plasmas. [ABSTRACT FROM AUTHOR]

This investigation elucidates one- and biphotonic reorientational nonlinearities in dye-doped nematic liquid crystals (DDNLCs) and dye-doped cholesteric liquid crystals (DDCLCs) using the Z-scan technique. Three cases—DDNLCs stimulated by one green beam polarized linearly parallel and perpendicular to the LC director and DDCLCs stimulated by one circularly polarized green beam—are considered without and with simultaneous stimulation by one linearly polarized red beam. Green-beam-induced dye reorientation through trans-cis isomerization and red-beam-induced suppression of dye reorientation by cis-trans back isomerization are responsible for the one- and biphotonic nonlinearities, respectively. The nonlinear refractive indices obtained herein are two orders of magnitude larger than those obtained elsewhere [Fuh et al., Opt. Exp. 13, 10634 (2005)]. The induced biphotonic nonlinearities can be modulated by controlling the intensity of the red beam in different ways due to the difference among the capabilities of the red beam to suppress the reorientation of the dyes and LCs in the three cases. [ABSTRACT FROM AUTHOR]

Three types of organic-based connection units were examined for use in stacked or tandem organic light-emitting devices, which include (i) Mg-doped tris(8-hydrooxyquinoline) aluminum(III) (Alq3)/4,4′,4″-tris{N,-(3-methylphenyl)-N-phenylamino}-triphenylamine (m-MTDATA), (ii) Alq3/tetrafluorotetracyanoquinodimethane (F4-TCNQ)-doped m-MTDATA, and (iii) Mg-doped Alq3/F4-TCNQ-doped m-MTDATA. Device (iii) shows the highest current efficiency and the differences in device performance can be correlated with the electronic structure of the connection unit and its interface with the neighboring active layers. The working mechanisms of the connection-unit works are discussed in terms of band bending and charge carrier density. The electronic structures of the interface between layers in a connection unit are of particular importance to the device performance. Dopings of Mg in Alq3 and F4-TCNQ in m-MTDATA led to bipolar heterojunction. Removal of either the n-type or the p-type dopants suppresses the band bending and the formation of space charge regions. The charge density accumulated at this interface estimated from Poisson’s equation is 1018/cm3, which is respectively 12 and 6 orders of magnitude higher than that in the Mg:Alq3/m-MTDATA and Alq3/F4-TCNQ:m-MTDATA connection units. Based on these results, the critical roles of dopants in an efficient connecting unit for stacked organic light-emitting diodes are elucidated. [ABSTRACT FROM AUTHOR]

Multiple fluorocarbon (CFx) and silicon nitride (Si3N4) bilayers were applied as encapsulation cap on glass-based organic light-emitting diodes (OLEDs). When CFx/Si3N4 bilayers were deposited onto the OLED structure, the devices showed performance worse than one without any encapsulation. The adverse effects were attributed to the damage caused by reaction species during the thin-film deposition processes. To solve this problem, a CuPc interlayer was found to provide effective protection to the OLED structure. With a structure of CuPc/(CFx/Si3N4)×5, the encapsulated device showed an operation lifetime over 8000 h (higher than 80% of that achieved with a conventional metal encapsulation). [ABSTRACT FROM AUTHOR]

Selective excitation photoluminescence spectroscopy was employed to study InAs/GaAs self-assembled quantum dots (QDs). Under different excitation energies, different groups of QDs are selected and then emit light. The excited carriers relax to the ground state through different mechanisms when excited at different energies. Three distinct regions with different mechanisms in carrier excitation and relaxation are identified in the emission spectra. These three regions can be categorized from high energy to low energy, as continuum absorption, electronic state excitation, and multiphonon resonance. The special joint density of state tail of the QD that extends from the wetting layer band edge facilitates carrier relaxation and is posited to explain these spectral results. [ABSTRACT FROM AUTHOR]

In this study, the viscous flow behavior and thermomechanical properties of Mg65Cu25-xBxGd10 (x=0 and 3 at. %) bulk metallic glasses (BMGs) in the supercooled liquid region have been investigated by using differential scanning calorimetry and thermomechanical analyzer. It has been found that the fragility of the supercooled liquid is reduced by the boron addition, thus, degrading the deformability. This conclusion is supported by the many other extracted parameters. Thus, even with much higher hardness, the B-additive Mg based BMG will be more difficult to be formed, which appears to be a negative factor in applying in the microforming or nanoimprinting industry. [ABSTRACT FROM AUTHOR]

We present a phenomenological model for the lifetime prediction of GaAs based heterojunction bipolar transistors (HBTs). Both thermal activation process and recombination enhanced defect generation process were considered phenomenologically. At high stress temperatures, the lifetime of the transistor is determined by the thermal activation process and is independent of the stress current. But at low stress temperatures, the device’s lifetime is controlled by the recombination enhanced defect generation process and is dependent on the stress current. The model has been used to fit experimental data, and very reasonable agreement was obtained. The model is valid for all stress temperatures and stress currents. It provides a good guideline for projecting HBTs lifetimes using accelerated stress test. [ABSTRACT FROM AUTHOR]

A grazing incidence x-ray reflectivity technique is used to determine the electron density profile as a function of depth in CoFe-Ru-CoFe and CoFe-Ru nano-oxide layer (NOL)–CoFe trilayers. Four trilayers with ruthenium thicknesses of 8, 8.5, and 9 Å and one with Ru 8.5 Å NOL, prepared by a dc planetary sputtering system, were investigated. For all samples, the electron density profile (EDP) shows a central peak that is related to the Ru layer. Natural oxidation in all of the samples introduces a graded EDP of the top CoFe layers, which decreases gradually to zero. The large surface resistivity of Ru 8.5 Å NOL as compared to Ru 8.5 Å is related to the remarkable difference between their EDPs. EDP changes have also been investigated in Ru NOL trilayers after annealing at 280 °C. The Ru phase in the EDP was observed to confirm the thermal stability of the spacer layer after annealing. [ABSTRACT FROM AUTHOR]

The electrical-insulation degradation of BaTiO3 is now of growing interest as the BaTiO3-based dielectric layers of multilayer ceramic capacitors are getting thinner to submicron thicknesses. The degradation is understood to be due to the electrotransport of oxygen vacancies and may be monitored by the colors emanating from the cathode and/or anode. In the case of single crystal BaTiO3, a brown color emanates from the anode and a blue color from the cathode. We will experimentally review the generation of the colors in BaTiO3 in electric fields, and discuss their origins and kinetics of color front migration. From the latter the oxygen vacancy mobility against temperature in the range of 150–500 °C is subsequently determined and compared with all the literature data that have normally been estimated by other means at elevated temperatures. [ABSTRACT FROM AUTHOR]

Secondary-ion mass spectroscopy, energy dispersion spectrometry, and Raman spectroscopy reveal that SiGe dots grown by ultrahigh-vacuum chemical vapor deposition at 600 °C exhibit significant intermixing with an average Ge composition of ∼50%. Raman spectroscopy shows the top SiGe quantum dots of the 20-layer sample to be more relaxed than those of the 5-layer samples. As a result, the electroluminescence from the top SiGe quantum dots of the 20-layer sample has the higher peak energy at ∼0.84 eV as compared to ∼0.82 eV for the 5-layer sample. The external tensile mechanical strain can compensate the built-in compressive strain of SiGe quantum dots and increase electroluminescence energy. [ABSTRACT FROM AUTHOR]