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Germanium diselenide (GeSe2) nanobelts are synthesized by atmospheric-pressure chemical vapor deposition under low temperature by using Se and Ge powders as precursor materials in a quartz tube furnace with double heating zones. The GeSe2 nanobelts thus prepared exhibit growth directionality. Unidirectional nanobelt clusters are tightly spaced and shaped as rectangular nanobelt arrays. Additionally, the thickness of the prepared GeSe2 material is less than 5 nm, and the area of a single array can attain 0.96 mm2. Our experimental results show that hydrogen directly affects the growth of GeSe2. First-principles calculations reveal the electronic properties and in-plane anisotropic optical absorption of the few-layer two-dimensional GeSe2 material. Optical absorbance measurements of GeSe2 nanobelt arrays reveal high ultraviolet absorbance of GeSe2 (200–400 nm). Photodetectors based on GeSe2 nanobelts are p-type, with high responsivity, superior detectivity, and a fast response time. These results show that GeSe2 is an excellent ultraviolet photoelectric material with potential photoelectronic applications.

The angle dependence of field-induced switching was investigated in magnetic tunnel junctions with in-plane magnetization and a pinned synthetic antiferromagnet reference layer. The 60 × 90 nm2 elliptical nanopillars had sharp single switches when the field was applied along the major axis of the ellipse, but even with small (20°) deviations, reversal occurred through an intermediate state. The results are interpreted with a model that includes the external applied field and the effective fields due to shape anisotropy and the fringe field of the synthetic antiferromagnet and used to extract the magnetization direction at various points in the magnetoresistance loop. The implications for faster spintronic probabilistic computing devices are discussed.

The concept of the Internet of Things (IoT) is a future development opportunity for mankind, which is a system that realize the interaction of various electronic devices through wireless communication. With the rise and development of this concept, the energy demand gap of self-powered equipment in IoT has emerged. The construction of an off-grid power system will make the wireless network of IoT easy to integrate and meet the higher requirements of power supply equipment in terms of size, weight, energy-consumption, and cost. Indoor photovoltaics (IPVs) can provide stable and long-term power guarantee by collecting indoor light, which are perfectly matched with IoT. Photovoltaic cells based on a-silicon, dye, organic compounds, and halide perovskite have been proved to be suitable for IPVs. Among them, perovskite indoor photovoltaics (PIPVs) have attracted much attention due to its advantages of tunable bandgap, high output voltage, flexible preparation, and low cost. In addition, the indoor stability and toxicity of PIPVs are also discussed in this Perspective.

Quantum capacitance of two-dimensional (2D) systems contains useful physical information. Here, we report a high sensitivity quantum capacitance measurement with an improved radio frequency superheterodyne bridge technique for probing the electronic characteristic of Ge/SiGe 2D hole gas (2DHG) at low temperatures and under a perpendicular magnetic field B⊥. At low fields, a rapid decrease in quantum capacitance following [Formula: see text] dependence is observed, indicating an abrupt change in chemical potential near the gate boundary at high frequencies; at high fields, a series of capacitance oscillations are observed due to the Landau quantization and Zeeman splitting of the Ge/SiGe 2DHG, where gate-dependent effective [Formula: see text] factor under B⊥ is extracted. These results represent implementation of the high-precision capacitance measurement for exploring the physical properties of Ge/SiGe 2DHG.

Miniaturization is a trend of development toward practical applications for diamond nitrogen-vacancy centers-based sensors. We demonstrate a compact diamond magnetic field sensor device using a standard microfabrication process. A single-crystal-diamond plate is embedded in a cavity formed with stacking of three silicon chips. Thermal compression bonding is implemented at silicon–silicon and diamond–silicon interfaces ensuring mechanical robustness. The specific construction volume for the essential sensor component is about 10 × 10 × 1.5 mm3. By integrating a gradient index lens pigtailed fiber to the sensor device, 532-nm laser light and emitted fluorescence share a common path for excitation and detection. An omega-shaped transmission line for applied microwave power is fabricated directly on the surface of diamond. The integrated sensor device exhibits an optimized sensitivity of 2.03 nT·Hz−1/2 and over twofold enhancement of fluorescence collection efficiency compared to bare diamond. Such a sensor is utilized to measure a magnetic field change caused by switching a household electrical appliance.

Organic photovoltaic cells are appealing as indoor illumination harvesters to drive off-grid electronics in the Internet of things. However, a desirable output power usually requires expansive and dark active layers to absorb sufficient incident photons. The deployment of such large-scale dark objects is detrimental to the elaborately designed indoor lighting environment and affects human visual perceptions. Here, we propose a free-contact strategy to adjust the chromaticity of the transmitted indoor light by applying one-dimensional photonic crystals. Combining photonic crystals with various transmittances outside the photovoltaic cells, the spectral power distribution of the transmitted light can be precisely manipulated to realize a broad and consecutive color modulation covering the region from blue to orange. For certain photonic crystals, the chromaticity of propagated light can be recovered close to the light source. This work presents a solution to relieve light-disturbing in the application of organic photovoltaic cells under indoor illuminations.

We demonstrate a compact in-fiber integrated microresonator based on a silica microsphere and microstructure fiber. Whispering-gallery-modes (WGMs) are effectively excited through evanescent field coupling between the silica microsphere and one of the input tube waveguides of negative curvature fiber. The WGM spectrum with the Q-factor of ∼2.56 × 103 and the extinction ratio of ∼15.2 dB is achieved. The transmission spectra evolution for 5 h reveals the long-term stability of WGM excitation. The experimental results indicate that the in-fiber integrated resonator has the advantages of high stability, high integration, robustness, alignment-free assembly structure, and low cost, motivating potential applications in the lab-in-fiber platform.

Semiconductor self-assembled single quantum dots (QDs) provide a promising solid-state light source for single photons and entangled photons. The structural asymmetry in QDs results in fine structure splitting (FSS) of exciton and biexciton emission lines. Here, we propose a method to study QD symmetry by measuring the difference in two different polarized lifetimes of QD excitonic emission lines under applied stress. The method can be reasonably correlated with the direct FSS measurement. Actually, due to the limitation of the resolution of the spectrometer, the zero value of FSS is difficult to measure. Instead, the lifetime measurement is an effective method to judge the symmetry condition of single QDs.

The semiconductor MoS 2 has attracted much attention owing to its sizable energy bandgap, significant spin–orbit coupling, and quantum effects such as the valley Hall effect and gate-induced superconductivity. However, in electronic devices, the energy bandgap usually gives rise to the formation of Schottky barriers at the interface to the contact metal, which may render devices intended for quantum transport inapplicable at low temperature. Therefore, the fabrication of Ohmic contacts operational at low temperature is crucial. Yet, it currently remains a substantial challenge to produce low resistive contacts with a simple process. We manifest that low temperature Ohmic contacts to mono- and few-layer MoS 2 can be achieved with Tin (Sn) as the contact metal. Sn is directly evaporated onto MoS 2, and hence, this establishes a much easier fabrication method than tunneling barriers, for example. We provide detailed device characterization, extract Schottky barrier heights, demonstrate multiterminal measurements, and propose a possible explanation: strain induced deformation of MoS 2 imposed by Sn.

The integration of quantum materials like topological insulators (TIs) with magnetic insulators (MIs) has important technological implications for spintronics and quantum computing. Here we report excellent crystallinity of c-axis oriented epitaxial TI films Bi2Se3 grown on MI films, a rare earth iron garnet (ReIG), such as thulium iron garnet (Tm3Fe5O12, TmIG) by molecular beam epitaxy (MBE) with a Se-buffered low-temperature (SBLT) growth technique. We demonstrated a streaky reflection high-energy electron diffraction pattern starting from the very first quintuple layer of Bi2Se3, indicating the high-quality interface between TmIG and Bi2Se3, a prerequisite for studying interfacial exchange coupling effects. The strong interfacial exchange interaction was manifested by observations of anomalous Hall effect in the Bi2Se3/TmIG bilayer and a shift of ferromagnetic resonance field of TmIG induced by Bi2Se3. We have reproducibly grown high-quality Bi2Se3/ReIG and interfaces using this new TI growth method, which may be applied to grow other types of van der Waals (vdW) hetero-structures., Comment: 17 pages, 4 figures

We demonstrate that a graphene-based attenuator on a half-mode substrate integrated waveguide (HMSIW) can achieve dynamically tunable attenuation. This attenuator is produced by depositing a graphene sandwich structure (GSS) on the substrate of a HMSIW. By applying a bias voltage on the GSS, the surface impedance of graphene and the attenuation of the attenuator can be tuned. A prototype was fabricated and measured to verify the analysis. The measurement results manifest that as the bias voltage increases from 0 V to 4 V, the attenuation can be increased from 3 dB to 14 dB at the frequency from 7.7 GHz to 19 GHz, while |S11| of the attenuator can always remain at a low level smaller than −20 dB.

The development of simple and sensitive sensors with the capability of simultaneously detecting magnetic field intensity and its direction in three-dimensional (3D) space is a technical imperative for magnetic field detection. In this paper, we first demonstrated the mechanism of anisotropic manipulation of ferromagnetism nanoparticles (FMNPs) in a non-continuous magnetic fluid film with the aid of varying magnetic fields. Second, based on the anisotropic distribution of the FMNPs around an optical fiber, we fabricated a vector magnetometer with a direction error of ±1.9° and an intensity sensitivity of 222.0 pm/mT, respectively. The sensing mechanism relies on the magnetism-controllable effective refractive index modification of asymmetric cladding modes in an in-line fiber-optic Mach-Zehnder interferometer. Compared to the previously reported intensity-based magnetometers, the as-fabricated magnetometer also provides an avenue to monitor the vector direction of the magnetic field in 3D space.

This paper proposes a 1D plasmonic multilayer structure as a high-contrast mid-infrared thermal emitter with three distinct resonant wavelengths. The three resonance modes, based on the localized surface plasmon, provide an omnidirectional thermal emission. The emissivity spectrum reveals high polarization and strongly angle-independent properties. The resonance-assisted emissivity can be as high as 19.5 dB relative to off-resonant sideband emissivity. Such extremely low sideband emissivity makes the proposed plasmonic thermal emitter an efficient, high-contrast emitter, which will be useful for thermophotovoltaic and thermal sensing applications.

Amorphous silicon (a-Si) was crystallized by femtosecond laser annealing (FLA) using a near-infrared (λ≈800nm) ultrafast Ti:sapphire laser system. The intense ultrashort laser pulses lead to efficient nonlinear photoenergy absorption and the generation of very dense photoexcited plasma in irradiated materials, enabling nonlinear melting on transparent silicon materials. We studied the structural characteristics of recrystallized films and found that FLA assisted by spatial scanning of laser strip spot constitutes superlateral epitaxy that can crystallize a-Si films with largest grains of ∼800nm, requiring laser fluence as low as ∼45mJ∕cm2, and low laser shots. Moreover, the optimal annealing conditions are observed with a significant laser-fluence window (∼30%).

This work reports on the interface microstructures and interface electrical and optical properties of wafer-bonded semiconductors using In/Sn and Cu/Ti as the metallic interlayers. The interface microstructures of the wafer-bonded semiconductors were characterized using transmission electron microscopy and scanning electron microscopy. The interface imperfections and their potential influences on the interface electrical performances were discussed. The interface electrical and optical characteristics of the metal-bonded wafers were also compared with those of directly fused wafers.

We present microphotoluminescence (PL) and micro-Raman measurements with varying the applied electric field in InxGa1−xN/GaN multiple quantum wells (MQWs). The InGaN A1(LO) phonon was found to show a redshift in frequency with the increase of applied electric field. And, a blueshift in PL spectra has been observed when the applied electric field was increased. Quite interestingly, the change in the refractive index was also observed, which was determined accurately from the interference pattern shown in the emission spectra. This finding correlates very well with the blueshift of PL spectra and the redshift of the InGaN A1(LO) phonon. Based on the stress change induced by the compensation between piezoelectric and external fields, our results firmly establish that strong electro-optical and photoelastic effects do exist in InxGa1−xN/GaN MQWs, which is important in the design of optoelectronic devices.

The optical properties of InxAlyGa1−x−yN quaternary alloys were investigated by photoconductivity (PC), persistent photoconductivity (PPC), photoluminescence (PL), and photoluminescence excitation (PLE) measurements. Quite interestingly, persistent photoconductivity was observed. Through the combination of our optical studies, we show that the PPC effect arises from composition fluctuations in InxAlyGa1−x−yN quaternary alloys. From the analysis of the decay kinetics, the localization depth caused by composition fluctuations was determined. A comparison between the PL, PLE, and PC measurements gives a direct access to the Stokes’ shift. The Stokes’ shift can be explained in terms of localization due to the existence of nanoscale clusters, and it is consistent with the PPC result. The results shown here provide concrete evidence to support our previously proposed model that the existence of InGaN-like clusters is responsible for the strong luminescence in InxAlyGa1−x−yN quaternary alloys.

We report firm evidence for the underlying mechanism of the enhanced luminescence in InxAlyGa1−x−yN quaternary epilayers. Photoluminescence, Raman scattering, field emission scanning electron microscopy (SEM), energy dispersive x-ray spectrometry (EDS), and cathodoluminescence (CL) measurements have been employed to study the correlation between optical and structural properties in these alloys. The phonon replica structures accompanying luminescence line, InGaN-related phonon modes in Raman spectra, SEM images, element composition analysis by EDS, and localized CL spectra provide the evidence to show that the existence of InGaN-like nanoclusters is responsible for the enhanced luminescence in InxAlyGa1−x−yN quaternary alloys. Our result therefore gives an excellent demonstration showing that because of the existence of nanoclusters a very defective alloy can exhibit a strong emission even at room temperature.

We have fabricated and characterized donor-mode nanocavities formed by a single defect cavity defined within a two-dimensional photonic crystal slab. Quantum dots emitting in the 1.1-1.3 micron range were used as luminescence sources, and a design using fractional edge dislocations was used to demonstrate well-confined dipole modes with high quality factors. By applying the fractional dislocation geometry, the measured quality factor could be increased to values as high as 2800. This compares with typical quality factors of around 1500 measured from more conventional shallow donor mode cavities with larger mode volumes.

We have characterized the modes within two-dimensional photonic crystal nanocavities with self-organized indium arsenide quantum dots as an active material. Highly localized donor mode resonances with 3 to 5 nm linewidth were observed when spatially selective optical pumping the cavities. These modes could be lithographically tuned from 1100 to 1300 nm. Other, more extended modes, were also characterized and exhibited narrower resonance linewidths ranging from 0.6 to 2 nm.

The effect of a thin interlayer of Pt on the stability of NiSi films on Si(111) substrates has been investigated. Both x-ray diffraction (XRD) data and sheet resistance measurements show a remarkable improvement in the thermal stability of NiSi due to the Pt interlayer. Detailed study on the XRD data shows PtSi and NiSi form a solid solution following a Vegard’s law. It was found in Ni/Pt/Si samples that a transition in NiSi texture from (200)NiSi‖(111)Si to (002)NiSi‖(111)Si took place before the nucleation of NiSi2, which may contribute to the enhanced stability of NiSi films.

In this letter, we report on the resistive switching originating from the rupture/rejuvenation of single-crystalline Cu filaments in a nitrogen-doped porous carbon-based memristive device Cu/CN0.15/Pt. Cu filaments are confined in conical nanopores in CN0.15 thin films. Dislocations exist in the Cu filaments, resulting in obvious crystal lattice distortions. The Cu/CN0.15/Pt device shows outstanding high temperature retention performance for both ON and OFF states, indicating that it is promising for resistance memory applications. Furthermore, continuous RESET (ON-to-OFF switching) and SET (OFF-to-ON switching) processes could be realized indicating the adaptive learning ability of Cu/CN0.15/Pt, which has potential applications in synaptic devices.

Bismuth selenide Bi$_2$Se$_3$ was grown by molecular beam epitaxy while carrier density and mobility were measured directly \emph{in situ} as a function of film thickness. Carrier density shows high interface n-doping (1.5 x 10$^{13}$ cm$^{-2}$) at the onset of film conduction, and bulk dopant density of $\sim$5 x 10$^{18}$ cm$^{-3}$, roughly independent of growth temperature profile. Mobility depends more strongly on the growth temperature and is related to the crystalline quality of the samples quantified by \emph{ex-situ} AFM measurements. These results indicate that Bi$_2$Se$_3$ as prepared by widely employed parameters is \emph{n}-doped before exposure to atmosphere, the doping is largely interfacial in origin, and dopants are not the limiting disorder in present Bi$_2$Se$_3$ films., 4 pages, 4 figures

We achieved direct visualization of the piezoelectric potentials in a single bent ZnO microwire (MW) using focused synchrotron radiation (soft x-ray) scanning photoelectron spectro-microscopy. Using radial-line scan across the bent section of ZnO MW, the characteristic core-level shifts were directly related to the spatial distribution of piezoelectric potentials perpendicular to the ZnO polar direction. Using piezoelectric modeling in ZnO, we delineated the band structure distortion and carrier concentration change from tensile to compressed sides by combining the spatial resolved cathodoluminescence characteristics in an individual microwire. This spectro-microscopic technique allows imaging and identification of the electric-mechanical couplings in piezoelectric micro-/nano-wire systems.

Split-ring resonators (SRRs) have been the subject of investigation as plasmonic sensors that operate by sensing plasmon resonance shift δλ when exposed to a medium with a refractive index change δn. However, conventional planar SRRs have their plasmon fields spread into the substrates, reducing accessible sensing volume and its sensing performance. Such a limitation can be eradicated with vertical SRRs in which the plasmon fields localized in SRR gaps are lifted off from the substrate, allowing for greatly enhanced sensitivity. Here, we demonstrate the highest sensitivity among reported SRR-based sensors in optical frequencies.

Tuning of the Fermi level is investigated in graphene channels using two in-plane gates with significantly different-sized isolating gaps. While the n-type tuning was achievable in both schemes, the wide-gap device had an enhanced minimum drain current and less prominent current modulation than the narrow-gap device. In addition, further p-type tuning was not observed in the wide-gap device at negative gate biases. These phenomena indicated that both devices had distinct field-strength dependences and Fermi level tuning effects, which may be critical for the practical design of devices.

We report interfacial characterization of 3,4,9,10-perylene-teracarboxylic dianhydride (PTCDA)-based organic spin valves (OSV) dusted with a thin layer of partially oxidized alumina at the organic semiconductor (OSC)/ferromagnet (FM) interfaces. Up to 13.5% magnetoresistance is achieved at room temperature. X-ray photoelectron spectroscopy measurements reveal interfacial electronic interaction between PTCDA and FM while the application of a thin alumina layer at the PTCDA/FM interfaces prevents the electronic hybridization and effectively preserves the spin injection into the OSC spacer. This finding demonstrates the critical effect of interfacial structure on magnetotransport behavior in OSV.

We investigate the electronic properties of p-type graphene transistors on silicon dioxide with dual-cut channels that were scraped using atomic force microscope tips. In these devices, the current is forced to squeeze into the path between the two cuts rather than flow directly through the graphene sheet. We observe that the gate voltages with minimum current shift toward zero bias as the sizes of the dual-cut regions increase. These phenomena suggest that the Fermi levels in the dual-cut regions are shifted toward the Dirac points after the mechanical scraping process.

Graphene has been regarded as a prospective transparent electrode for a GaN-based light-emitting diode (LED), but fundamental knowledge about the intrinsic properties of the graphene/GaN contact is lacking. We have studied the optical and electronic properties of graphene exfoliated on an n-type GaN surface. The graphene visibility was simulated based on Fresnel's law and confirmed with an optical microscope and micro-Raman spectra. The interfacial electronic property was studied with a scanning photoelectron microscope. We found that the Schottky barrier height of the graphene/n-GaN is decreased with decreasing graphene number of layers, yielding an improved GaN-based LED performance.

We propose an approach for reduction of the contact resistance by inducing dielectric breakdown in a Si-dielectric-metal contact stack. We observe a 36% reduction in the contact resistance as well as an improvement in the uniformity in the distribution after dielectric breakdown. The results open up interesting device applications in complementary metal oxide semiconductor technology.

Al-doped ZnO (AZO) deposited by radio frequency co-sputtering is formed on epitaxial Mg-doped GaN template at room temperature to achieve n-AZO/p-GaN heterojunction. Alignment of AZO and GaN bands is investigated using synchrotron radiation based cross-sectional scanning photoelectron microscopy and spectroscopy on the nonpolar side-facet of a vertically c-axis aligned heterostructure. It shows type-II band configuration with valence band offset of 1.63 ± 0.1 eV and conduction band offset of 1.61 ± 0.1 eV, respectively. Rectification behavior is clearly observed, with a ratio of forward-to-reverse current up to six orders of magnitude when the bias is applied across the p-n junction.

Three two-dimensional SiOx (x ≡ O/Si content ratio and x > 2) protrusion layers of ∼0.5, ∼4, and ∼6 nm high were induced on a native SiO2 layer by atomic force microscopy (AFM) probes. X-ray photoemission spectroscopy (XPS) was used to reveal the elemental quantity of the photoelectrons, Si 2p core-levels, and Si oxidation states in the three SiOx protrusion layers and native SiO2 layer. Pt-coated conductive AFM probes were also exploited to acquire the rectifying current-voltage (IV) characteristics of the three SiOx protrusion layers and the native SiO2 layer, indicating all the three SiOx protrusion layers to be good Schottky diodes.

A fiber taper-based method is proposed for formation and targeted positioning of bubbles in water. By launching a laser of 1.55-μm wavelength with an optical power of over 20 mW into the fiber taper, a microbubble was formed at the taper tip. The mechanism of growth and decay of the microbubble was discussed. With the assistance of a moveable bare fiber, a train of bubbles with controllable diameters from 10 to 600 μm was formed and transported by the moveable fiber. Alternatively, by only moving the fiber taper, the formed bubbles can be easily positioned at targeted positions.

This study achieved controlling the positions of spontaneous growth of tin whiskers. We surmounted the unpredictable growing nature of such whiskers and performed accurately quantitative analyses of the growth kinetics and yielded precise measurement of the growth rate. Furthermore, using synchrotron radiation x-ray, this study determined the stress variations in conjunction with whisker growth that fitted appropriately to the model. Accordingly, the results could address the debate held for decades and prove that forming a surface oxide layer is one of the required and necessary conditions for controlling the positions of spontaneous growth of tin whiskers.

Valence band alignments of wurtzite III-nitride semiconductorheterojunctions are investigated using cross-sectional scanning photoelectron microscopy and spectroscopy on the nonpolar side-facet of a vertically −c-axis-aligned heterostructurenanorod array. The nonpolar measurement geometry and near fully relaxed lattice structure allow for the determination of “natural” band alignments without the influence of spontaneous and piezoelectricpolarization fields. The valence band offsets of InN/GaN, GaN/AlN, and InN/AlN are measured to be 0.8 ± 0.1, 0.6 ± 0.1, and 1.4 ± 0.1 eV, respectively. These results are in good agreement with previous data for heteroepitaxial films and obey the expected transitivity rule.

We report on precise control of film crystal polarity in fully relaxed, thin InN/AlN heterojunctions grown on sapphire by plasma-assisted molecular beam epitaxy. Using these samples, we have measured asymmetric valence band offset values (0.8 {+-} 0.1 eV for the In/Al- and 1.8 {+-} 0.1 eV for the N-polar case) at polar InN/AlN heterojuncitons by synchrotron soft x-ray photoelectron spectroscopy. We confirm that the discontinuities of spontaneous polarizations at polar InN/AlN heterointerfaces lead to the large core level shift of the Al 2p peak related to the In 4d peak (1.0 eV).

A photonic crystal (PC) microdisk laser cavity was introduced and demonstrated. The microlaser utilizes lossless surface modes within the PC forbidden band for vertical confinement and whispering gallery modes for lateral confinement. Analysis showed that this type of cavity mode has a smaller mode volume and a larger confinement factor than other resonant modes in the microdisk stacks. Initial experiments demonstrated lasing of optically pumped wavelength-size microdisks with four period GaAs/AlGaAs PCs and InGaAs quantum dots as gain media.

Recent experiments indicate the universality of electron accumulation and downward surface band bending at as-grown InN surfaces with polar or nonpolar orientations. Here, we demonstrate the possibility to prepare flatband InN ( 000 1 ¯ ) surfaces. We have also measured the surface stoichiometry of InN surfaces by using core-level photoelectron spectroscopy. The flatband InN ( 000 1 ¯ ) surface is stoichiometric and free of In adlayer. It implies that the removal of In adlayer at the InN ( 000 1 ¯ ) surface leads to the absence of downward surface band bending. On the other hand, the stoichiometric InN (0001) surface still exhibits surface band bending due to the noncentrosymmetry in the wurtzite structure.

Photoconductivity of individual aluminum nitride (AlN) nanowires has been characterized using different subband gap excitation sources. It is interesting that both positive (under 1.53 and 2.33 eV excitations) and negative (under 3.06 and 3.81 eV excitations) photocurrent responses are observed from the wide band gap nitride nanowires. The negative photoconductivity, which is attributed to the presence of electron trap and recombination center in the bulk of AlN, is capable to be inversed by a strong positive photoconductive mechanism of surface while changes the ambience from the atmosphere to the vacuum. An oxygen molecular sensitization effect is proposed to be the reason resulting in the enhancement of positive photocurrent and the inversion of negative photoresponse in the vacuum. Understanding of the diverse photoconductivity and its molecular effect is of great importance in the development of energy-selective and highly sensitive nanowire photodetector of AlN in the visible and ultraviolet ranges.

Ultrathin {beta}-Si{sub 3}N{sub 4}(0001) epitaxial films formed by N{sub 2}-plasma nitridation of Si(111) substrates have been studied by photoelectron spectroscopy using synchrotron radiation. The valence band offset at the {beta}-Si{sub 3}N{sub 4}/Si interface was determined by valence-band photoelectron spectra to be 1.8 eV. Furthermore, the Si 2p core-level emissions were analyzed for nitride (Si{sup 4+}) and subnitride (Si{sup 3+} and Si{sup +}) components to characterize the interface stoichiometry. In contrast to the interfaces formed by ammonia thermal nitridation and N{sub 2}-plasma nitridation at room temperature, the interface formed by N{sub 2}-plasma nitridation at high substrate temperature is very close to subnitride free with an abrupt composition transition.

We demonstrate a man-made lighting device of organic light-emitting diode (OLED) capable of yielding a sunlight-style illumination with various daylight chromaticities, whose color temperature ranges between 2300 and 8200 K, fully covering those of the entire daylight at different times and regions. The OLED employs a device architecture capable of simultaneously generating all the emissions required to form a series of daylight chromaticities. The wide color-temperature span may be attributed to that the recombination core therein can easily be shifted along the different emissive zones simply by varying the applied voltage via the use of a thin carrier-modulating layer.

Giant electrocaloric effect was observed in lead-free material for the first time. A demonstration of large electrocaloric effect in 200 nm sol-gel thin film SrBi2Ta2O9 is described here. The ferroelectric hysteresis loops and the film permittivity were measured. The extracted data characterized the electrocaloric temperature change, up to 4.93K in 12V (i.e., 0.41 K V−1) near the Curie point. It is concluded that the giant electrocaloric effect exists in lead-free materials, and a large family of layered perovskite oxides may exhibit analogical property. The absence of lead allows eco-friendly application and enhances compatibility with integrated circuit process in future applications.

uted by them to the existence of high-density steps and defects at the cleavage surface. In this work, we provide direct evidence for the unpinned nature of cleaved a-plane GaN surfaces. Furthermore, we report on the application of XSPEM/S technique for direct imaging of GaN p-n junction. The sample structure for this study is N-polar p-GaN 1.5 m /n-GaN 1.5 m /AlN 25 nm /Si 3 N 4 /Si111, which was grown by plasma-assisted molecular beam epitaxy PA-MBE on a Si wafer. Details of the growth technique can be found elsewhere. 11 The n- and p-type doping was performed by using high-purity Si and Mg solid cells during the PA-MBE growth process. The Mg concentration as determined by secondary ion mass spectroscopy is 7

An optical wave guiding structure based on the omnidirectional reflection of one-dimensional photonic crystals is presented. The dispersion and transmission characteristics of flexible waveguides using this structure are investigated by numerical simulations using plane wave expansion method and finite-difference time-domain method, respectively. Calculated results indicate that for waveguide bends of arbitrary angles with a curved radius less than several wavelengths, a very high transmission (>97%) over wide frequency range is observed. Owing to this unique advantage of flexibility, it is expected to be applied to highly dense photonic integrated circuits after further research.

The characteristics of CoTiO3 high-k dielectric prepared by sol-gel spin coating method had been demonstrated. High electrical permittivity (k∼40.2) of CoTiO3 dielectric was extracted via the transmission electron microscopy image and capacitance-voltage curves. In addition, the valence band offset between thermal SiO2 and spin-on CoTiO3 was about 4.0 eV, which was detected by x-ray photoelectron spectroscopy. The band gaps of thermal SiO2 and spin-on CoTiO3 were 9.0 and 2.2 eV, respectively. Energy band alignment of spin-on CoTiO3 directly with SiO2 and indirectly with Si was determined in this work.

We experimentally examined the near-field and far-field optical properties of a subwavelength annular aperture (SAA) made on silver film and undertook finite difference time domain simulations. In our near-field measurements, an interference pattern with a period very close to half of the surface plasmon (SP) wavelength (λSP∕2) was found on the surface of the silver film. Moreover, we observed that the transmitted light of the 442nm incident laser was focused at several micrometers behind the silver SAA structure at a tiny spot (354nm) and with a remarkable 31μm depth of focus. This implies that the silver SAA structure can generate a nondiffraction beam and can be used to fabricate high aspect ratio subwavelength structures.

A method for studying heterojunction band lineups on the submicrometer scale is demonstrated by using synchrotron-radiation photoelectron microscopy and spectroscopy. In particular, an in situ sample cleavage technique is adopted here to reveal the cross-sectional, nonpolar a-plane face of InN∕GaN heterojunction grown on Si(111) along the polar −c axis with fully relaxed lattice structure, eliminating the polarization effects associated with the interface charge/dipole normal to the cleaved surface. The “intrinsic” valence band offset at the cleaved InN∕GaN heterojunction has been determined to be 0.78eV. Additionally, using known material parameters, the values of InN∕GaN conduction band offset and InN electron affinity are also estimated.