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Single crystalline GaN nanowires, with 100 nm typical diameters, were grown by chemical vapor deposition method, using Pt catalyst, and characterized by cathodoluminescence and electron beam induced current (EBIC) measurements at 5 K. The near band edge emission was found to be asymmetric and broad, with full width half maximum of around 150 meV, peaking at 3.55 eV, well above the GaN bulk band gap. This blueshift was ascribed to band filling effect resulting from unintentional n-type doping in the range 1019–1020 cm−3. Despite of this heavy doping, EBIC experiments showed that minority carriers can diffuse over 0.2 μm.

The efficient passive mode-locking of a Ti:sapphire laser with a monolayer graphene saturable absorber is demonstrated for the first time. High-quality and large-area (1 in.) monolayer graphene, synthesized by chemical vapor deposition, exhibits ultrafast recovery times and excellent nonlinear absorption behavior for bulk solid-state laser mode-locking near 800 nm. The continuous-wave mode-locked Ti:sapphire laser generates 63-fs pulses with output powers up to 480 mW under stable operation at 99.4 MHz.

We demonstrate that a filtration method is efficient for the fabrication of thick single-walled nanotube films and is capable of shielding terahertz waves. Shielding effectiveness can be engineered by controlling the film thickness and we achieved 38 dB for a 950-nm-thick film. In addition, we found that the films exhibit a dispersion of dielectric constant obeying the Drude free-electron model, whereas the plasma frequency decreases with increasing film thickness. Based on the nanotube films with a thickness greater than the skin depth, we fabricated grid polarizers by laser-machining process, which enable us to achieve a large polarization extinction ratio.

We demonstrate ultrafast all-optical control of terahertz (THz) radiation through nanoresonators, slot antennas with a hundred micron length but submicron width in thin gold layers, fabricated on vanadium dioxide (VO2) thin films. Our THz nanoresonators show almost perfect transmission at resonance. By virtue of phase transition of VO2 from insulating to metallic state, induced in subpicosecond time scale by moderate optical pump, ultrafast control of THz transmission is enabled. This is compared to bare VO2 films where no switching dynamics are observed under similar conditions.

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Transmission of terahertz (THz) electromagnetic waves through a series of nanoresonator arrays punctured in a thin metallic film is investigated. Over 30% of normalized transmitted amplitude is observed with only 0.18% of aperture-coverage, implying an electric field enhancement of 170. Increasing the coverage to 0.6% results in a 90% normalized amplitude, with a broader line width. Inspired by log-periodic antenna, we put ten nanoresonators with four different lengths per unit cell, succeeding in an ultrabroadband THz filter with one decade width between 0.2 and 2.0 THz.

We report on electron beam induced current (EBIC) from individual carbon nanotubes (CNTs) which are in contact with metal electrodes. The EBIC signals originate from the diffusion of excess carriers induced by the electron beam bombardment. The EBIC image enables us to locate the individual CNTs efficiently. From the polarity of the EBIC signals we can identify the electrical contacts to the metal electrodes. More importantly, we demonstrate that the EBIC can be used to characterize the local electrical properties of CNT-based devices, such as asymmetry in metal contacts and the presence of defects. EBIC is also observed regardless of the presence of insulating surfaces, indicating that the EBIC is a result of the direct interaction between the CNTs and the electron beams.

We report huge field accumulations in rectangular aperture arrays on thin metal film by using shape resonance in THz frequency region. A huge far-field transmission enhancement is observed in samples of various widths ranging from 10 mum to 1.8 mum which correspond to only an order of lambda/100. Theoretical calculations based on vector diffraction theory indicates 230 times near-field enhancement in case of the 1.8 mum wide rectangular aperture. Transmission measurement through the single rectangular aperture shows that the shape resonance, not the periodicity, is mainly responsible for the transmission enhancement and the corresponding field enhancement.

We have grown defect-rich ZnO nanowires on a large scale by the vapour phase reaction method without using any metal catalyst and vacuum system. The defects, including zinc vacancies, oxygen interstitials and oxygen antisites, are related to the excess of oxygen in ZnO nanowires and are controllable. The nanowires having high excess of oxygen exhibit a brown-colour photoluminescence, due to the dominant emission band composed by violet, blue and green emissions. Those having more balanced Zn and O show a dominant green emission, giving rise to a green colour under UV light illumination. By O2-annealing treatment the violet luminescence after the band-edge emission UV peak can be enhanced for as-grown nanowires. However, the green emission shows different changing trends under O2-annealing treatment, associated with the excess of oxygen in the nanowires.

We have studied the temporal and spectral evolution of the photoluminescence (PL) in a highly luminescent poly(2,5bis (dimethyloctylsilyl)-1,4-phenylenevinylene) in the temperature range between 12 and 300 K using the ps time-resolved PL system. The PL spectra are narrower compared with an absorption spectrum and show a red-shift as time progresses after photoexcitation, implying that excitons are generated in a distribution of conjugation lengths and migrate towards longer conjugated segments.

Transmitting and reflecting ultrafast saturable absorbers based on single-walled carbon nanotubes are developed that are applicable for stable mode locking of bulk solid-state lasers operating near 1μm. For fabrication of these saturable absorbers, relatively simple spin coating and spray methods are employed. Parameters important for stable mode locking, such as transient nonlinear absorption, saturation fluence, and recovery time, are investigated by nonlinear transmission and time-resolved pump-probe measurements near 1μm. Typical modulation depths and recovery times amount to ∼0.21%–0.25% and

The hexagonal resonator characteristics of an individual ZnO-nanonail’s head were investigated via spatially resolved cathodoluminescence (CL) at room temperature. The positions of most of distinct CL peaks in visible range were well matched to those of whispering gallery modes (WGMs) of a hexagonal dielectric cavity when we took birefringence and dispersion of refractive indices into account. The broad and weak peaks for TE polarization in long wavelength range were consistent with refractive-index values below the threshold for total internal inflection. CL peaks that were not matched to WGMs were identified as either triangular quasi-WGM or Fabry–Perot resonance modes.

We report photoconductivity (PC) in individual germanium nanowire field effect transistors (GeFETs). PC measurements with a global illumination reveal that GeFETs can be used as a polarization-sensitive nanoscale light detector in the visible range. It is also found that the PC shows sensitive optical response especially in the low intensity regime. We observe a high internal gain in PC in conjunction with strong saturation behavior, which is attributed to the filling of surface trapping states. This mechanism for high internal gain is consistent with spatially resolved scanning photocurrent measurements, whose results confirm that optical absorption is in the linear regime.

The growth of ZnO nanorods on Au-coated ITO substrates using a low temperature wet chemical process is presented. Electron microscopy and x-ray diffraction observations reveal that the crystalline ZnO nanorods are preferentially oriented along the c axis. Room temperature photoluminescence (PL) measurements reveal a strong band edge emission at 382 nm, a signature of good crystallinity, with a weak and broad orange-red emission, which is typically attributed to the oxygen interstitials, in the range between 520 and 720 nm. Other than the second order feature of the band edge emission at 760 nm, no red or near-infrared bands are observed. The effect of precursor concentration on the morphological, structural and PL properties are studied, and the results are discussed.

We have performed femtosecond and picosecond nondegenerate two-beam and three-beam (ω1, ω1;ω2) four-wave mixing experiments by using two partially synchronized, independently tunable lasers with a simple sample-and-hold switch. When the jitter is compensated for externally, heavy- and light-hole beating is observed with these two mutually incoherent lasers, and the synchronous phases of oscillations with the detuning show that these beats are true quantum beats. We also see the strong completely off-resonant signals, and the below-bandgap signals are stronger than the signals at the continuum for equivalent detunings. This off-resonance signal has a Lorentzian dependence on detuning in both the femtosecond and the picosecond experiments. When ω2 is completely above or below the excitonic resonance, the spectrum of the diffracted beam is determined mostly by the laser spectrum, which can be explained by semiconductor Bloch equations.

A low-energy femtosecond laser micromachining system, which is effectively applied to fabricate micro-structured carbon nanotube field emitter arrays with different tip sizes and shapes, is presented. Superior emission characteristics are obtained with the patterned structures.