Volume 104, Issue 1, 06 January 2014
- 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
Index of content:
Monolayer Mo1−xWxSe2 (x = 0, 0.14, 0.75, and 1) alloys were experimentally realized from synthesized crystals. Mo1−xWxSe2 monolayers are direct bandgap semiconductors displaying high luminescence and are stable in ambient. The bandgap values can be tuned by varying the W composition. Interestingly, the bandgap values do not scale linearly with composition. Such non-linearity is attributed to localization of conduction band minimum states around Mo d orbitals, whereas the valence band maximum states are uniformly distributed among W and Mo d orbitals. Results introduce monolayer Mo1−xWxSe2 alloys with different gap values, and open a venue for broadening the materials library and applications of two-dimensional semiconductors.
- PHOTONICS AND OPTOELECTRONICS
104(2014); http://dx.doi.org/10.1063/1.4858966View Description Hide Description
We report the demonstration of single-photon emission from cubic GaN/AlN quantum dots grown by molecular beam epitaxy. We have observed spectrally clean and isolated emission peaks from these quantum dots. Clear single-photon emission was detected by analyzing one such peak at 4 K. The estimated g (2) value is 0.25, which becomes 0.05 when corrected for background and detector dark counts. We have also observed the single-photon nature of the emission up to 100 K (g (2) = 0.47). These results indicate that cubic GaN quantum dots are possible candidates for high-temperature operating UV single-photon sources with the possibility of integration into photonic nanostructures.
Ultrafast all-optical switching and error-free 10 Gbit/s wavelength conversion in hybrid InP-silicon on insulator nanocavities using surface quantum wells104(2014); http://dx.doi.org/10.1063/1.4861121View Description Hide Description
Ultrafast switching with low energies is demonstrated using InP photonic crystal nanocavities embedding InGaAs surface quantum wells heterogeneously integrated to a silicon on insulator waveguide circuitry. Thanks to the engineered enhancement of surface non radiative recombination of carriers, switching time is obtained to be as fast as 10 ps. These hybrid nanostructures are shown to be capable of achieving systems level performance by demonstrating error free wavelength conversion at 10 Gbit/s with 6 mW switching powers.
104(2014); http://dx.doi.org/10.1063/1.4861124View Description Hide Description
A pulsed ∼2-μm thulium-doped fiber laser passively modulated by distributed stimulated Brillouin scattering achieves 10.2 W average power and >100 kHz repetition rate with a very simple all-fiber configuration. The maximum pulse energy and peak power surpass 100 μJ and 6 kW, respectively. Another distinct property is that the pulse width is clamped around 17 ns at all power levels. All the average-power, pulse energy, and peak power show the highest values from passively modulated fiber lasers in all wavelength regions.
104(2014); http://dx.doi.org/10.1063/1.4861159View Description Hide Description
The InAs/InAsSb type-II superlattice materials studied to date for infrared detector applications have been residually n-type, but p-type absorber regions with minority carrier electrons can result in increased photodiode quantum efficiency, RoA, and detectivity. Therefore, Be-doped InAs/InAsSb superlattices were investigated to determine the p-type InAs/InAsSb superlattice material transport properties essential to developing high quality photodiode absorber materials. Hall measurements performed at 10 K revealed that the superlattice converted to p-type with Be-doping of 3 × 1016 cm−3 and the hole mobility reached 24 400 cm2/Vs. Photoresponse measurements at 10 K confirmed the 175 meV bandgap and material optical quality.
104(2014); http://dx.doi.org/10.1063/1.4859635View Description Hide Description
We propose and theoretically study a hybrid structure consisting of a photonic crystal waveguide (PhC-wg) and a two-wire metallic transmission line (TL), engineered for efficient transfer of mid-infrared (mid-IR) light between them. An efficiency of 32% is obtained for the coupling from the transverse magnetic (TM) photonic mode to the symmetric mode of the TL, with a predicted intensity enhancement factor of 53 at the transmission line surface. The strong coupling is explained by the small phase velocity mismatch and sufficient spatial overlapping between the modes. This hybrid structure could find applications in highly integrated mid-IR photonic-plasmonic devices for biological and gas sensing, among others.
Enhanced ultraviolet GaN photo-detector response on Si(111) via engineered oxide buffers with embedded Y2O3/Si distributed Bragg reflectors104(2014); http://dx.doi.org/10.1063/1.4861000View Description Hide Description
Based on a virtual GaN substrate approach on Si(111) by a step graded double oxide (Sc2O3/Y2O3) buffer, we report a “proof of principle” study on the enhanced photo-response of ultraviolet GaN photo-detectors due to embedded DBRs (distributed Bragg reflectors). Embedded DBRs benefit from an order of magnitude lower number of superlattice sequences in contrast to III- nitride systems due to the high refractive index contrast between high-k Y2O3 and low-k Si. The UV (ultraviolet) reflectance efficiency of the designed DBR is proven by a considerable photo-response increase in the UV range in comparison to reference GaN layers on Si(111) without DBRs.
104(2014); http://dx.doi.org/10.1063/1.4861122View Description Hide Description
Electrical laser emission frequency tuning of a three terminal THz quantum cascade laser is demonstrated. A high electron mobility transistor structure is used in a surface plasmon waveguide to modulate the electron density in a channel, controlling the effective refractive index of the waveguide. The threshold current density was modulated by 28% via applying voltage from −3 to 2 V. The observed laser emission frequency shift by electric field was 2 GHz. By using the three terminal devices, pure frequency modulation of the output light is, in principle, achievable.
104(2014); http://dx.doi.org/10.1063/1.4861422View Description Hide Description
We present the design and realization of ultra-thin chiral metasurfaces with giant broadband optical activity in the infrared wavelength. The chiral metasurfaces consisting of periodic hole arrays of complementary asymmetric split ring resonators are fabricated by femtosecond laser two-photon polymerization. Enhanced transmission with strong polarization conversion up to 97% is observed owing to the chiral surface plasmons resulting from mirror symmetry broken. The dependence of optical activity on the degree of structural asymmetry is investigated. This simple planar metasurface is expected to be useful for designing ultra-thin active devices and tailoring the polarization behavior of complex metallic nanostructures.
104(2014); http://dx.doi.org/10.1063/1.4844675View Description Hide Description
We present a method for fluid velocimetry based on a single-exposure analysis of the streak speckle pattern generated by sub-micron tracking particles illuminated with coherent light. It works in real-time and provides two dimensional velocity mappings in the direction orthogonal to the optical axis, independently of particle concentration and size. It is immune of any spurious light acting as undesired heterodyne signal and can probe velocities much higher (∼three orders of magnitude) than methods based on double-exposure analysis. The method has been tested by using rigid diffusers of different heterodyne strength and applied to map the flow of a confined fluid.
104(2014); http://dx.doi.org/10.1063/1.4861621View Description Hide Description
The transmission of electromagnetic waves through a sub-wavelength aperture is described by Bethe's theory. This imposes severe limitations on using apertures smaller than ∼1/100 of the wavelength for near-field microscopy at terahertz (THz) frequencies. Experimentally, we observe that the transmitted evanescent field within 1 μm of the aperture deviates significantly from the Bethe dependence of E ∝ a 3. Using this effect, we realized THz near-field probes incorporating 3 μm apertures and we demonstrate transmission mode THz time-domain near-field imaging with spatial resolution of 3 μm, corresponding to λ/100 (at 1 THz).
104(2014); http://dx.doi.org/10.1063/1.4860576View Description Hide Description
Placing graphene on uniaxial substrates may have interesting application potential for graphene-based photonic and optoelectronic devices. Here, we analytically derive the dispersion relation for graphene plasmons on uniaxial substrates and discuss their momentum, propagation length, and polarization as a function of frequency, propagation direction, and both ordinary and extraordinary dielectric permittivities of the substrate. We find that the plasmons exhibit an anisotropic propagation, yielding radially asymmetric field patterns when a point emitter launches plasmons in the graphene layer.
104(2014); http://dx.doi.org/10.1063/1.4861473View Description Hide Description
We demonstrate that the long-range interaction between surface-functionalized microparticles immersed a nematic liquid crystal—a “nematic colloid”—and a laser-induced “ghost colloid” can be enhanced by a low-voltage quasistatic electric field when the nematic mesophase has a negative dielectric anisotropy. The optoelastic trapping distance is shown to be enhanced by a factor up to 2.5 in presence of an electric field. Experimental data are quantitatively described with a theoretical model accounting for the spatial overlap between the orientational distortions around the microparticle and those induced by the trapping light beam itself.
104(2014); http://dx.doi.org/10.1063/1.4860982View Description Hide Description
The paper reports on the realization of multilayer (In,Ga)As/GaP quantum dot (QD) lasers grown by gas source molecular beam epitaxy. The QDs have been embedded in (Al,Ga)P/GaP waveguide structures. Laser operation at 710 nm is obtained for broad area laser devices with a threshold current density of 4.4 kA/cm2 at a heat-sink temperature of 80 K.
104(2014); http://dx.doi.org/10.1063/1.4861374View Description Hide Description
Photostructural changes in a hybrid photonic crystal fiber with chalcogenide nanofilms inside the inner surface of the cladding holes are experimentally demonstrated. The deposition of the amorphous chalcogenide glass films inside the silica capillaries of the fiber was made by infiltrating the nanocolloidal solution-based As25S75, while the photoinduced changes were performed by side illuminating the fiber near the bandgap edge of the formed glass nanofilms. The photoinduced effect of the chalcogenide glass directly red-shifts the transmission bandgap position of the fiber as high as ∼20.6 nm at around 1600 nm wavelength, while the maximum bandgap intensity change at ∼1270 nm was −3 dB.
Subwavelength light focusing with a single slit lens based on the spatial multiplexing of chirped surface gratings104(2014); http://dx.doi.org/10.1063/1.4861595View Description Hide Description
A lens consisting of a subwavelength slit engraved into a metal film and surrounded by periodic surface gratings and spatial multiplexing chirped surface gratings (SMCSGs) for focusing light is proposed. The focal length of the lens can be accurately designed and tuned by controlling the periods of the local gratings of the SMCSGs. Simulation results show that a subwavelength beam spot can be produced by the lens at a distance of several times the incident wavelength from the slit and the difference between the simulated and designed focal lengths can be reduced to below 3% of the designed focal length.
- SURFACES AND INTERFACES
104(2014); http://dx.doi.org/10.1063/1.4860960View Description Hide Description
Diffusion of indium through HfO2 after post deposition annealing in N2 or forming gas environments is observed in HfO2/In0.53Ga0.47As stacks by low energy ion scattering and X-ray photo electron spectroscopy and found to be consistent with changes in interface layer thickness observed by transmission electron microscopy. Prior to post processing, arsenic oxide is detected at the surface of atomic layer deposition-grown HfO2 and is desorbed upon annealing at 350 °C. Reduction of the interfacial layer thickness and potential densification of HfO2, resulting from indium diffusion upon annealing, is confirmed by an increase in capacitance.
The application of localized surface plasmons resonance in Ag nanoparticles assisted Si chemical etching104(2014); http://dx.doi.org/10.1063/1.4855615View Description Hide Description
Localized surface plasmons excited by Ag nanoparticles are introduced in the chemical etching process of silicon. A special crateriform structure with gradually varying radius is achieved by the surface electromagnetic field enhancement effect of localized surface plasmons resonance (LSPR). Theoretical analysis demonstrates that the formation kinetics of the crateriform structures conforms to the local electromagnetic field enhancement and forward scattering induced by LSPR. The LSPR assisted photocatalytic etching offers a potential approach for the preparation of the surface microstructures used in optoelectronic devices.
104(2014); http://dx.doi.org/10.1063/1.4861622View Description Hide Description
Atomic force microscopy (AFM), field-emission scanning electron microscopy, and energy dispersive X-Ray spectroscopy are used to study morphological and compositional variations of metal-organic interfaces in organic bistable devices. The results show that bias voltage causes rougher interfaces with new protrusions, and the switching phenomena origins from the evolution of these protrusions under external electric field. In order to exclude other possible factors, three types of bistable devices are designed and examined. In addition, metal-coated AFM probes are utilized to simulate the switching process, which yields similar results and corroborates our conclusion.
- STRUCTURAL, MECHANICAL, OPTICAL, AND THERMODYNAMIC PROPERTIES OF ADVANCED MATERIALS
104(2014); http://dx.doi.org/10.1063/1.4860951View Description Hide Description
Superelastic behavior at nano-scale has been studied along cycling in Cu-Al-Ni shape memory alloy micropillars. Arrays of square micropillars were produced by focused ion beam milling, on slides of  oriented Cu-Al-Ni single crystals. Superelastic behavior of micropillars, due to the stress-induced martensitic transformation, has been studied by nano-compression tests during thousand cycles, and its evolution has been followed along cycling. Each pillar has undergone more than thousand cycles without any detrimental evolution. Moreover, we demonstrate that after thousand cycles they exhibit a perfectly reproducible and completely recoverable superelastic behavior.
104(2014); http://dx.doi.org/10.1063/1.4860416View Description Hide Description
A polarized Raman analysis of ferroelectric (K0.5 Na 0.5)NbO3 (KNN) single crystals is presented. The Raman modes of KNN single crystals are assigned to the monoclinic symmetry. Angular-dependent intensities of A′, A″, and mixed A′ + A″ phonons have been theoretically calculated and compared with the experimental data, allowing the precise determination of the Raman tensor coefficients for (non-leaking) modes in single-domain monoclinic KNN. This study is the basis for non-destructive assessments of domain distribution by Raman spectroscopy in KNN-based lead-free ferroelectrics.