Volume 102, Issue 6, 11 February 2013
- photonics and optoelectronics
- surfaces and interfaces
- structural, mechanical, optical, and thermodynamic properties of advanced materials
- magnetics and spintronics
- superconductivity and superconducting electronics
- dielectrics, ferroelectrics, and multiferroics
- nanoscale science and technology
- organic electronics and photonics
- device physics
- biophysics and bio-inspired systems
- energy conversion and storage
- interdisciplinary and general physics
- referee acknowledgment
Index of content:
This study investigates the peri-tumor signal abnormalities of a spontaneous brain tumor in a rat by using a 4 cm high-temperature superconducting (HTS) surface resonator. Fractional anisotropy (FA) values derived from diffusion tensor imaging reflect the interstitial characteristic of the peri-lesional tissues of brain tumors. Low FA indicates interstitial tumor infiltration and tissue injury, while high FA indicates better tissue integrity. Better delineation of tissue contents obtained by the HTS surface resonator at 77 K may facilitate therapeutic strategy and improve clinical outcomes.
- PHOTONICS AND OPTOELECTRONICS
102(2013); http://dx.doi.org/10.1063/1.4790834View Description Hide Description
The insulator-metal phase transition of a correlated-electron material, vanadium dioxide, is used to demonstrate electrically controlled, compact, broadband, and low voltage plasmonic switches. The devices are micron-scale in length and operate near a wavelength of 1550 nm. The switching bandwidths exceed 100 nm and 400 mV is sufficient to attain extinction ratios in excess of 20 dB. The results illustrate the promise of using phase transition materials for efficient and ultra-compact plasmonic switches and modulators.
102(2013); http://dx.doi.org/10.1063/1.4792271View Description Hide Description
We report on the electro-refractive effect in Ge/SiGe multiple quantum wells grown by low energy plasma enhanced chemical vapor deposition. The electro-refractive effect was experimentally characterized by the shift of Fabry-Perot fringes in the transmission spectra of a 64 μm long slab waveguide. A refractive index variation up to 1.3 × 10−3 was measured with an applied electric field of 88 kV/cm at 1475 nm, 50 meV below the excitonic resonance, with a VπLπ figure of merit of 0.46 V cm. The device performances are promising for the realization of Mach Zehnder modulators in the Ge-Si material platform.
102(2013); http://dx.doi.org/10.1063/1.4791581View Description Hide Description
We propose an idea of using a convergent dipole wave at the aperture, radiated from a dipole at distance of z 0, to produce a perfect focusing at z 0. We verified this idea through simulation and experimental observation. It is demonstrated that the zone plate designed based on the idea can provide a subwavelength superfocusing by effectively bending the surface waves in a Fresnel region of 100 nm to a couple of wavelengths and is suitable for a situation where a superresolution at a micro working distance is essential.
102(2013); http://dx.doi.org/10.1063/1.4792220View Description Hide Description
Frequency-modulated light field fluctuations due to moving particles in colloidal suspensions are examined using heterodyne interferometry. The power spectrum is the combined result of a time-of-flight-related frequency distribution due to light scattering and frequency shifts due to the Doppler effect. An approximation model is developed based on diffusion theory and verified experimentally. The potential for application towards comprehensive diagnosis of both particle dynamics and optical properties of the examined media is discussed.
Mobility enhancement of top contact pentacene based organic thin film transistor with bi-layer GeO/Au electrodes102(2013); http://dx.doi.org/10.1063/1.4792235View Description Hide Description
The enhancement of the charge injection and field effect mobility by inserting a thin (5 nm) germanium oxide (GeO) interlayer between the Au electrode and pentacene layer in a top contact pentacene based organic thin-film transistor (OTFTs) was reported. In comparison with the pentacene-based OTFT with only-Au electrode, the device performance has been considerably improved, which exhibits the highest field effect mobility of 0.96 cm2/Vs. The improvement was attributed to significant reduction of barrier height at Au/pentacene interfaces and smoothed surface of pentacene layer after inserting a thin GeO layer.
Harnessing second-order optical nonlinearities at interfaces in multilayer silicon-oxy-nitride waveguides102(2013); http://dx.doi.org/10.1063/1.4792272View Description Hide Description
We demonstrate multi-layer silicon-oxy-nitride (SiON) waveguides as a platform for broadband tunable phase-matching of second-order nonlinear interactions arising at material interfaces. Second-harmonic generation (SHG) is measured with a 2 ps pulsed pump of 1515–1535 nm wavelength, where 6 nW power is generated by an average pump power of 30 mW in a 0.92 mm long device. The wavelength acceptance bandwidth of the SHG is as broad as 20 nm due to the low material dispersion of SiON waveguides. The waveguide structure provides a viable method for utilizing second order nonlinearity for light generation and manipulation in silicon photonic circuits.
102(2013); http://dx.doi.org/10.1063/1.4792277View Description Hide Description
This paper describes a VO2-based smart structure with an emittance that increases with the temperature. A large tunability of the spectral emittance, which can be as high as 0.90, was achieved. The transition of the total emittance with the temperature was fully reversible according to a hysteresis cycle, with a transition temperature of 66.5 °C. The total emittance of the device was found to be 0.22 and 0.71 at 25 °C and 100 °C, respectively. This emittance performance and the structure simplicity are promising for the next generation of energy-efficient cost-effective passive thermal control systems of spacecrafts.
102(2013); http://dx.doi.org/10.1063/1.4792312View Description Hide Description
We report on the enhanced holographic performance by employing a strong volume holographic absorption grating induced by localized surface plasmon resonance effect in a bulk gold nanoparticles doped photopolymer. The contributions of plasmon-induced volume holographic absorption grating is characterized through the Kogelnik's coupled wave model and demonstrated experimentally by using two-beam interference technology. At the 0.05 vol. % concentration of the gold nanoparticles in the bulk photopolymer, 101.8% increase in the diffraction efficiency and more than four times suppression of the first side lobe in angular selectivity have been achieved.
Integrated sensor for ultra-thin layer sensing based on hybrid coupler with short-range surface plasmon polariton and dielectric waveguide102(2013); http://dx.doi.org/10.1063/1.4792319View Description Hide Description
Based on a hybrid coupler composed of short-range surface plasmon polariton (SRSPP) and dielectric waveguides, an integrated sensor for ultra-thin layer sensing has been realized. The simulation and experiment results demonstrate that the thickness variation of detection layer (polymer layer) about several nanometers could be detected. The measured thickness-detection sensitivity is as high as 0.67 dB/nm. And the sensitive region for thickness variation of polymer layer can be adjusted widely by varying the thickness of the SRSPP waveguide.
Low-threshold and quasi-single-mode random laser within a submicrometer-sized ZnO spherical particle film102(2013); http://dx.doi.org/10.1063/1.4792349View Description Hide Description
An unique random laser exhibiting quasi-single-mode and low lasing threshold is developed by a homogenized submicrometer-sized zinc oxide particle film dispersed with intentionally introduced polymer particles as point defects. Such unique random lasing is dominantly initiated at the defect sites, although multi-mode peaks with a collapsed broad emission spectrum are observed at the defect-free sites as in the conventional random lasers. Thus our proposed simple structure can possibly provide the controllability of lasing properties even in random structures.
Large photoresponse of Cu:7,7,8,8-tetracyanoquinodimethane nanowire arrays formed as aligned nanobridges102(2013); http://dx.doi.org/10.1063/1.4792470View Description Hide Description
We report large photoresponse in an array of Cu:TCNQ (TCNQ-7,7,8,8-tetracyanoquinodimethane) nanowires fabricated as nanobridge device. The device shows highest photoresponse for excitation wavelength = 405 nm. The current gain at zero bias can reach ∼104 with an illumination power density of 2 × 106 W/m2. The zero bias responsivity is ∼0.3 mA/W, which increases upto 1 A/W for an applied bias of 2.0 V. Dark and illuminated I-V data are analyzed by a model of two Schottky diodes connected back-to-back, which shows that the predominant photocurrent in the device arises from the photoconductive response of the nanowires.
102(2013); http://dx.doi.org/10.1063/1.4792508View Description Hide Description
Electrical plasmonic sources with compact sizes are a fundamental component in plasmonics. Here, we report a simple plasmonic diode having an Ag/InGaAsP quantum well Schottky structure. The polarization ratio (TM:TE) of the edge-emission photoluminescence for the quantum wells is about 2:1 and increases to about 3:1 after covered by Ag. As contrast, the electroluminescence polarization ratio exceeds 10:1 at a low current, indicating a high plasmon generation efficiency but drops gradually as current increasing; simultaneously, the peak wavelength red shifts evidently, which are attributed to the recombination zone shift and quantum confinement Stark effect.
102(2013); http://dx.doi.org/10.1063/1.4791593View Description Hide Description
Lasers are ubiquitous in materials processing, but the requirement of precise control of the focal plane in order to ensure optimal performance constitutes a time limiting step for high-throughput laser manufacturing. Here, we overcome this limitation by axially scanning the focus at high speeds using an acoustically driven liquid lens. We demonstrate this approach by processing silicon surfaces, and we find it is possible to enhance the depth-of-field by an order of magnitude without loss in lateral resolution. These results open the door to a fundamental change in the paradigm for laser processing by eliminating the need in z-focus control.
Conical air prism arrays as an embedded reflector for high efficient InGaN/GaN light emitting diodes102(2013); http://dx.doi.org/10.1063/1.4773559View Description Hide Description
The effect of the combination of triangular prisms and cones as air-void structures arrays on the enhancement of light extraction efficiency of InGaN light-emitting diodes (LEDs) is investigated. The arrays embedded at the sapphire/GaN interface act as light reflectors and refractors, and thereby improve the light output power due to the redirection of light into escape cones on both the front and back sides of the LED. Enhancement in radiometric power as high as 74% and far-field angle as low as 125° is realized with a compact arrangement of arrays compared with that of a conventional LED.
102(2013); http://dx.doi.org/10.1063/1.4793207View Description Hide Description
A strong enhancement of Eu3+ luminescence in europium-implanted GaN samples is obtained by codoping with silicon (Si) and magnesium (Mg), simultaneously. The Eu3+ intensity in the 5D0 to 7F2 transition region is found to be 30 times higher compared to europium-implanted undoped GaN. The major contribution to this overall enhancement is due a weak peak present only in europium-implanted Mg-doped GaN at 2.0031 eV (618.9 nm) which is strongly enhanced by codoping both Mg and Si. The excitation process of europium ions is proposed to take place through a donor-acceptor pair related energy transfer mechanism.
- SURFACES AND INTERFACES
102(2013); http://dx.doi.org/10.1063/1.4790579View Description Hide Description
In this letter, we report an easy and tenable way to tune the type of charge carriers in graphene, using a buried layer of AlBr3 and its derivatives on the graphene/Ir(111) interface. Upon the deposition of AlBr3 on graphene/Ir(111) and subsequent temperature-assisted intercalation of graphene/Ir(111) with atomic Br and AlBr3, pronounced hole doping of graphene is observed. The evolution of the graphene/Br-AlBr3/Ir(111) system at different stages of intercalation has been investigated by means of microbeam low-energy electron microscopy/electron diffraction, core-level photoelectron spectroscopy, and angle-resolved photoelectron spectroscopy.
102(2013); http://dx.doi.org/10.1063/1.4792694View Description Hide Description
Strain relaxation mechanisms were investigated in epitaxial AlN layers deposited on (0001)-oriented AlN substrates by metalorganic chemical vapor deposition. It was revealed that epitaxial AlN layers under tensile strain can exhibit micro-cracks and nano-pits. A correlation existed between the amount of strain and number of pits in localized areas. Pit densities as high as 1010 cm−2 were observed in areas where the tensile strain reached ∼0.4%, while unstrained areas of the film showed step flow growth. These nano-pits occurred as a strain relaxation mechanism and were not related to intrinsic defects, such as threading dislocations or inversion domains.
Experimental evidence of the atmospheric convective transport contribution to sessile droplet evaporation102(2013); http://dx.doi.org/10.1063/1.4792058View Description Hide Description
We investigate the contribution of the natural convective transport in the vapor phase on the evaporation rate of an evaporating sessile droplet. When comparing the experimental data with the quasi-steady diffusion-controlled evaporation model, an increasing deviation with substrate temperature that was attributed to the effect of the natural convection on the vapor field has been recently highlighted. To validate this analysis, we present experimental results obtained with two gravity levels: 1 g and . The contribution of the natural convection is analyzed with the Grashof number, and an empirical model is developed combining diffusive and convective transport.
Gold ion implantation induced high conductivity and enhanced electron field emission properties in ultrananocrystalline diamond films102(2013); http://dx.doi.org/10.1063/1.4792744View Description Hide Description
We report high conductivity of 185 (Ω cm)−1 and superior electron field emission (EFE) properties, viz. low turn-on field of 4.88 V/μm with high EFE current density of 6.52 mA/cm2 at an applied field of 8.0 V/μm in ultrananocrystalline diamond (UNCD) films due to gold ion implantation. Transmission electron microscopy examinations reveal the presence of Au nanoparticles in films, which result in the induction of nanographitic phases in grain boundaries, forming conduction channels for electron transport. Highly conducting Au ion implanted UNCD films overwhelms that of nitrogen doped ones and will create a remarkable impact to diamond-based electronics.
- STRUCTURAL, MECHANICAL, OPTICAL, AND THERMODYNAMIC PROPERTIES OF ADVANCED MATERIALS
102(2013); http://dx.doi.org/10.1063/1.4791573View Description Hide Description
Here, digital image correlation is demonstrated to be an accurate tool for the noncontact, non-destructive, and rapid characterization of the converse effect of piezoelectric materials. The longitudinal (d 33) and transverse (d 31) piezoelectric strain coefficients of lead zirconate titanate-5H wafers are measured simultaneously by imaging the wafer's cross section. The results are validated through laser interferometry and the large piezoresponse at switching domains is observed in strain-electric field butterfly loops. The proposed technique is simple and low cost requiring only an optical microscope and unlike indirect measurement methods requires little sample preparation and no information regarding the mechanical properties of the specimen.