Volume 105, Issue 1, 01 January 2009
- lasers, optics, and optoelectronics
- plasmas and electrical discharges
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic structure and transport
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS
105(2009); http://dx.doi.org/10.1063/1.3054363View Description Hide Description
Heat assisted magnetic recording (HAMR) technique requires an optical head that can efficiently generate a subwavelength optical spot. The results of finite difference time domain simulation shows that two subwavelength rectangular holes adjacent to a metallic slit aperture make an optical spot from the slit smaller and its peak intensity higher. A subwavelength spot of (full width at half maximum) in the recording medium is obtainable when a pair of rectangular holes is flanked adjacent to the slit aperture with a much smaller distance than the optical wavelength. This configuration provides a high transmittance of the slit aperture and a high expectation for a high controllability of both a thickness of the slit and a distance between the slit and the rectangular hole by the use of the planar process. By using a plasmonwaveguide to guide light into the metallic slit aperture, a thin and efficient optical head for HAMR is achieved.
105(2009); http://dx.doi.org/10.1063/1.3054918View Description Hide Description
:Ag-antimony glass nanocomposites are synthesized in a new reducing glass (dielectric) matrix by a single-step melt-quench technique involving selective thermochemical reduction. The UV-vis-near-infrared absorption spectra show typical surface plasmon resonance (SPR) band of nanoparticles (NPs) in addition to the distinctive absorption peaks of ion. X-ray diffraction and selected area electron diffraction results indicate formation of NPs along the (200) plane direction. The transmission electron microscopic image reveals the formation of spherical, fractal, and rod-shaped NPs having maximum size . The rod-shaped NPs have aspect ratio . The field emission scanning electron microscopic image shows development of three dimensional cornlike microstructures. Photoluminescent upconversion under excitation at 798 nm exhibit two prominent emission bands of ions centered at 536 (green) and 645 (red) nm due to and transitions, respectively. Both the bands undergo a maximum of three- and eightfold intensity enhancement, respectively, at concentration of . Local field enhancement induced by SPR is found to be responsible for enhancement while energy transfer from and optical reabsorption due to SPR for quenching.
105(2009); http://dx.doi.org/10.1063/1.3055264View Description Hide Description
In this work, we have grownmultiple quantum well(MQWs)epitaxial structure on vicinal sapphire substrates by low pressure metal-organic chemical vapor deposition and investigated the relationship between carrier localization degree and vicinal angles of sapphire substrates. The optical analysis confirmed that the MQWsgrown on 0.2°-off sapphire substrate exhibited the smallest carrier localization degree and more ordered MQW structure. In addition, mechanisms for carrier localization in MQWsgrown on vicinal substrate were discussed based on the results obtained from the power and temperature dependent photoluminescence measurements. The Raman spectrum showing the in-plane compressive stress of the GaNepitaxial structures grown on vicinal sapphire substrates revealed the relation between the dislocation density and the carrier localization degree in MQWs. From transmission electron microscopy images, the threading dislocation density (TDD) of MQWsgrown on 0.2° vicinal sapphire substrate at the bottom of -GaN layer was about and reduced to at the top of -GaN layer. We also obtained the TDD of in the MQW region and only in the -GaN region. Based on the results mentioned above, 0.2°-off substrate can offer MQW blue light-emitting diode structures with benefits, such as high crystal quality, low defects, and small carrier localization degree.
Analytic modal solution to transmission and collimation of light by one-dimensional nanostructured subwavelength metallic slits105(2009); http://dx.doi.org/10.1063/1.3043885View Description Hide Description
Light transmitting through a subwavelength slit on an ordinary metal plate is diffracted to all directions but if the exit plane of the slit is patterned with periodical nanostructures, the diffracted light may be compressed into a collimated beam within a small angle. In this paper, we develop a rigorous theoretical method for solving the surface wave induced beam collimation in nanostructured subwavelength metallic slits. The method combines the analytical modal expansion method, the supercell technique, the transfer-matrix method, and the conventional Kirchhoff’s diffraction theory. It allows for quantitative investigation of coupling of the incident light into the guided wave of the slit and coupling of the guided wave out of the nanostructured exit plane. We have used the method to examine light transmission through the nanostructured metallic slit and the corresponding diffraction and beam collimation behaviors. We have extensively analyzed the angular transmission spectrum as a function of the nanostructure period and the incident light wavelength and revealed the condition at which good beam collimation can take place. The result shows that the beam collimation is caused by the excitation of the surface waves supported on the periodical nanostructured pattern and subsequent coupling into the radiation light. Several scattering channels can coexist for coupling the surface waves into the observed diffractionwaves and they can act constructively to create one or more collimation beams with excellent directionality and high brightness. The diffraction field patterns in the large area confirm the angular spectrum analysis.
Investigation of Förster-type energy transfer in organic light-emitting devices with 4-(dicyanomethylene)-2--butyl-6-(1,1,7,7-tetramethy ljulolidin-4-yl-vinyl)--pyran doped cohost emitting layer105(2009); http://dx.doi.org/10.1063/1.3039412View Description Hide Description
Organic light-emitting devices(OLEDs) with cohosted emitter, which is composed of 9,10-di(2-naphthyl)anthracene (ADN) and tris(8-hydroxy-quinolinato) aluminum and doped with 4-(dicyanomethylene)-2--butyl-6-(1,1,7,7-tetramethy ljulolidin-4-yl-vinyl)--pyran (DCJTB), were fabricated and studied. The efficiency of OLEDs with a cohost emitter was higher than that with a single host emitter. For the cohost emitter with weight ratio of 75:25, the 3.4 cd/A efficiency of the resulted OLEDs was obtained. It is found that the absorption spectra of DCJTB and the emission spectra of changed with the composition of the emitter. This phenomenon is attributed to the polarization effect. On the basis of the Förster’s theory, the resulted overlap integral exhibits the highest value for this cohost emitter. The experimental results reveal that the cascade energy transfer plays an important role in the luminance efficiency enhancement of the cohost emitter in OLEDs.
Fast detector of the ellipticity of infrared and terahertz radiation based on HgTe quantum well structures105(2009); http://dx.doi.org/10.1063/1.3056393View Description Hide Description
We report a fast, room temperature detection scheme for the polarization ellipticity of laser radiation, with a bandwidth that stretches from the infrared to the terahertz range. The device consists of two elements, one in front of the other, that detect the polarization ellipticity and the azimuthal angle of the ellipse. The elements, respectively, utilize the circular photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic effect in a bulk piezoelectric semiconductor. For the former we characterized both a HgTe quantum well and bulk Te, and for the latter, bulk GaAs. In contrast with optical methods we propose is an easy to handle all-electric approach, which is demonstrated by applying a large number of different lasers from low power, continuous wave systems to high power, pulsed sources.
105(2009); http://dx.doi.org/10.1063/1.3037240View Description Hide Description
We present a metal organic chemical vapor deposition(MOCVD)growth study of unconventional alloys of InGaP (with In fraction of 0.2–0.4) grown on fully relaxed GaAsP virtual substrates for the application of high performance visible light emitting diodes (LEDs) and lasers in the green to red range of the visible spectrum. Several defects which are harmful to optical performance were identified, characterized, and removed. These include CuPt–B order (which lowers band gap),phase separation or short range order (which contributes to leakage currents and reduces luminescence) and undulation of the virtual substrate surface (which prevents high quality epitaxial growth). Each of these defects is understood through a two-step growth model which describes the formation and subsequent randomization of defects during growth. Through control of MOCVD parameters including growth temperature, V/III ratio, growth rate, and surfactant we demonstrate growth of extremely high quality InGaP heterostructures which hold promise for fabrication of light emitting devices.
105(2009); http://dx.doi.org/10.1063/1.3054561View Description Hide Description
Silicon nanocrystals (Si-ncs) have been produced by implantation of in excess into followed by both annealing and passivation using argon or nitrogen. Nitrogen increases the photoluminescence(PL) emission and shifts the spectra toward the blue. The measured Si-nc diameter is 4.3 and 3.8 nm after annealing performed under Ar and , respectively. A significant quantity of nitrogen atoms has been detected in all samples by resonantnuclear reaction analysis (RNRA). The nitrogen concentration is significantly higher when the annealing and passivation are performed in a nitrogen environment, in agreement with a larger Si–N vibration signal on the Raman spectra. The depth profiles of nitrogen are very similar to those of Si-nc, suggesting that the molecules may diffuse in the during the annealing and then are trapped in proximity to the Si-nc. In addition to , the implantation of to concentrations of 3 and produced a decrease in the PL intensity (accentuated at the higher concentration) and an increase in the Raman signal associated to Si–N vibrations. These results suggest that a relatively low nitrogen atomic fraction enhances the PL emission, since a large nitrogen concentration impedes the formation of Si-nc thus significantly decreasing the PL intensity.
Dynamic measurements of ultraviolet-enhanced silica contamination by photoluminescence-based diagnostic105(2009); http://dx.doi.org/10.1063/1.3056390View Description Hide Description
The ultraviolet-enhanced (UV-enhanced) contamination of optical components leads to an untimely aging of sealed laser systems, photolithography, and synchrotron installations. The laser-induced deposition of organic films on silica substrates and coatings significantly reduces their transmission and degrades their optical functions. In this paper, measurements of organic contaminantfilms growth under 213 nm laser irradiation performed on silica Corning 7980 grade ArF are reported. We present an in situcontaminant layer growth diagnostic based on silicaphotoluminescence measurements. The purpose was to determine the photodeposition kinetics as a function of controlled environmental conditions and fluence and to find out the experimental conditions in which the growth of contamination films was significantly reduced. We then demonstrated that with a low partial pressure of oxygen, the growth of carbonaceous films is drastically reduced during UV laser irradiation whereas with water and nitrogen it was not the case. We also proposed a physical modeling of the UV-enhanced silica contamination processes.
Simultaneous measurement of substrate temperature and thin-film thickness on wafer using optical-fiber-type low-coherence interferometry105(2009); http://dx.doi.org/10.1063/1.3058592View Description Hide Description
This paper proposes a technique for simultaneously monitoring the thickness of a thin film and the temperature of a Si substrate. This technique uses low-coherence interferometry and has the potential to be used for online monitoring of semiconductor manufacturing processes. In low-coherence interferometry, when the optical path length of a layer is shorter than the coherence length of the light source, the two interference at the top and bottom interfaces of the layer overlap each other. In this case the detected peak position of the interference is shifted from the actual interface, resulting in an error in the temperature measurement, since the temperature is derived from the optical path length of the layer. To improve the accuracy of the temperature measurement, the effect of the overlapping interference was compensated by measuring the thickness. The thickness of the Si substrate was and the thickness of the film was varied between 0 and . The thickness, which is shorter than the coherence length of the light source, was measured from the ratio of interference intensities of two superluminescent diodes (wavelengths: 1.55 and 1.31 μm). The measured ratio corresponded well with the theoretical one for film thicknesses between 0 and , and the error was less than 25 nm. The Si temperature was measured from the optical path length. In order to compensate for the overlapping interference, the shift in the peak position of the interference at the interface was estimated from the measurement results of the thickness. This improved the accuracy of the temperature measurement from 5.3 to .
105(2009); http://dx.doi.org/10.1063/1.3062150View Description Hide Description
Visually appealing simulations of the ultrafast response of an integrated-optics spectrometer reveal how interference occurs inside of the device and before the light arrives to the external measurement instrument. The device was especially designed for having no more than one pulse at a time in the common path of the spectrometer. Simulations are in excellent agreement with recent experiments involving arrayed waveguidegrating pulse shapers.
105(2009); http://dx.doi.org/10.1063/1.3053049View Description Hide Description
This article presents a direct comparison of calculated optical characteristics of polar, nonpolar, and semipolar III-nitride quantum wells. We show that the advantage of using wider quantum wells offered by nonpolar/semipolar technology is severely limited by narrower valence subband separation, thermal hole redistribution, and resulting optical gain degradation in wider wells. However, we emphasize the importance of using wider quantum wells to prevent electron leakage. We also show that gain characteristics of laser structuresgrown in nonpolar/semipolar orientations are less vulnerable to detrimental effect of nonradiative recombination.
Time-resolved spectroscopy on GaN nanocolumns grown by plasma assisted molecular beam epitaxy on Si substrates105(2009); http://dx.doi.org/10.1063/1.3062742View Description Hide Description
A detailed study of excitons in unstrained GaN nanocolumns grown by plasma assisted molecular beam epitaxy on silicon substrates is presented. The time-integrated and time-resolved photoluminescence spectra do not depend significantly on the (111) or (001) Si surface used. However, an unusually high relative intensity of the two-electron satellite peak of the dominant donor-bound exciton line is systematically observed. We correlate this observation with the nanocolumn morphology determined by scanning electron microscopy, and therefore propose an interpretation based on the alteration of wave functions of excitonic complexes and of donor states by the proximity of the semiconductor surface. This explanation is supported by a model that qualitatively accounts for both relative intensities and time decays of the photoluminescence lines.
105(2009); http://dx.doi.org/10.1063/1.3056227View Description Hide Description
Quantum simulations of spin systems could enable the solution of problems that otherwise require infeasible classical resources. Such a simulation may be implemented using a well-controlled system of effective spins, such as a two-dimensional lattice of locally interacting ions. We propose here a layered planar rf trap design that can be used to create arbitrary two-dimensional lattices of ions. The design also leads naturally to ease of microfabrication. As a first experimental demonstration, we confine ions in a millimeter-scale lattice trap and verify numerical models of the trap by measuring the motional frequencies. We also confine 440 nm diameter charged microspheres and observe ion-ion repulsion between ions in neighboring lattice sites. Our design, when scaled to smaller ion-ion distances, is appropriate for quantum simulation schemes, e.g., that of Porras and Cirac [Phys. Rev. Lett.92, 207901 (2004)]. We note, however, that in practical realizations of the trap, an increase in the secular frequency with decreasing ion spacing may make a coupling rate that is large relative to the decoherence rate in such a trap difficult to achieve.
105(2009); http://dx.doi.org/10.1063/1.3058692View Description Hide Description
We present a systematic theoretical study on optical properties of short-period InAs/GaSb type-II superlattices(SLs) which can serve for midinfrared (MIR) detection. Using the standard Kronig–Penney model we calculate the miniband structure of such SLs. The obtained band-gap energies are in line with those realized experimentally. On the basis of the energy-balance equation derived from the Boltzmann equation we develop a simple approach to calculate the optical absorption coefficient for the corresponding SL systems. Our results agree with recent experimental findings. Moreover, the dependence of MIR absorption in InAs/GaSb type-II SLs on temperature and well width are examined. This study is pertinent to the application of InAs/GaSb type-II SLs as MIR photodetectors working in the ambient condition.
105(2009); http://dx.doi.org/10.1063/1.3062522View Description Hide Description
Optical refrigeration has been demonstrated by several groups of researchers, but the cooling elements have not been thermally linked to realistic heat loads in ways that achieve the desired temperatures. The ideal thermal link will have minimal surface area, provide complete optical isolation for the load, and possess high thermal conductivity. We have designed thermal links that minimize the absorption of fluoresced photons by the heat load using multiple mirrors and geometric shapes including a hemisphere, a kinked waveguide, and a tapered waveguide. While total link performance is dependent on additional factors, we have observed net transmission of photons with the tapered link as low as 0.04%. Our optical tests have been performed with a surrogate source that operates at 625 nm and mimics the angular distribution of light emitted from the cooling element of the Los Alamos solid state optical refrigerator. We have confirmed the optical performance of our various link geometries with computer simulations using CODE V optical modeling software. In addition we have used the thermal modeling tool in COMSOLMULTIPHYSICS to investigate other heating factors that affect the thermal performance of the optical refrigerator. Assuming an ideal cooling element and a nonabsorptive dielectric trapping mirror, the three dominant heating factors are (1) absorption of fluoresced photons transmitted through the thermal link, (2) blackbody radiation from the surrounding environment, and (3) conductive heat transfer through mechanical supports. Modeling results show that a load can be chilled to 107 K with a 100 W pump laser. We have used the simulated steady-state cooling temperatures of the heat load to compare link designs and system configurations.
Electronic and optical properties of InGaN quantum dot based light emitters for solid state lighting105(2009); http://dx.doi.org/10.1063/1.3065274View Description Hide Description
In this paper, we have made a systematic study of the electronic and optical properties of InGaN based quantum dot light emitters. The valence force field model and method have been applied to study the band structures in InGaN or InN quantum dot devices. Piezoelectric and spontaneous polarizationeffects are included. A comparison with InGaNquantum wells shows that InGaNquantum dots can provide better electron-hole overlap and reduce radiative lifetime. We also find that variation in dot sizes can lead to emission spectrum that can cover the whole visible light range. For high carrier density injection conditions, a self-consistent method for solving quantum dot devices is applied for better estimation of device performance. Consequences of variations in dot sizes, shapes, and composition have been studied in this paper. The results suggest that InGaNquantum dots would have superior performance in white light emitters.
105(2009); http://dx.doi.org/10.1063/1.3065520View Description Hide Description
Nanostructured films consisting of single Si nanoparticles (NPs) and ions layers separated by nanometer-scale layers of controlled thickness have been prepared in order to tune the energy transfer between Si NPs and ions. The amorphous Si NPs with an effective diameter of are formed during growth and are able to sensitize the ions efficiently with no postannealing treatments. The characteristic distance for energy transfer from Si NPs to ions in is found to be in the 1 nm range. It is shown that in the nanostructured films, it is possible to achieve an optimized configuration in which almost all the ions have the potential to be excited by the Si NPs. This result stresses the importance of controlling the dopant distribution at the nanoscale to achieve improved device performance.
- PLASMAS AND ELECTRICAL DISCHARGES
Quenching of He-induced intensity enhancement effect in H and D emission produced by Nd-doped yttrium aluminum garnet laser irradiation on solid targets in low pressure helium gas105(2009); http://dx.doi.org/10.1063/1.3058670View Description Hide Description
An experimental study was performed on the -induced quenching of He-induced intensity enhancement effect in reduced-pressure plasma emission produced by Nd-YAG irradiation on solid zircaloy and porous fossil samples. The spatial distributions and temporal variations in the emission intensities show pronounced intensity quenching effects on the He I 667.9 nm, H I 656.2 nm, and D I 656.1 nm emission lines in both samples when a tiny amount (5% by volume) of nitrogen was added to helium gas, while leaving the spatial and temporal intensity profiles of the heavier Zr and Ca atoms virtually unaffected. In both cases of different ambient gases, the spatial and temporal variations in the He, H, and D emission intensities exhibit distinct features and changes, which are clearly distinguishable from those observed on the Zr and Ca emission lines, which were mainly produced by the shock-wave induced thermal excitation process. The analysis of these data unambiguously revealed the presence of an additional and distinct “He-assisted” excitation mechanism in the He plasma, which was further suggested to be related to the He metastable excited state. The quenching effect was therefore explained as a consequence of energy depletion of the He metastable excited state triggered by the Penning ionization process induced by the presence of nitrogen. This also explains the relatively insensitive response of the Zr and Ca emission intensity profiles to nitrogen addition despite the increased plasma electron density resulting from the ionization process.
Experimental study of femtosecond laser-stimulated electrical discharges in small gaps and surface modifications105(2009); http://dx.doi.org/10.1063/1.3055361View Description Hide Description
Femtosecond laser-stimulated discharges in nanoscale and microscale gaps between etched nanoprobe tip cathodes and goldfilmanodes with applied dc potential were experimentally studied to define parameter ranges for their controlled formation and resulting surface modifications. For appropriate values of gap length, applied potential, and laser irradiance, breakdown discharges could be reliably stimulated by femtosecond laser pulses and the mean breakdown field was approximately an order of magnitude smaller than for breakdown without laser stimulation. For 500 nm gaps, discharges were observed for applied potentials as small as 20 V and controllable goldfilmsurface melting was detected for applied potential of 27.5 V. Minor cathode tip ablation could be observed for femtosecond laser pulses that reliably stimulated discharges, suggesting that cathode material played an important role in stimulation of breakdown discharges in nanoscale gaps. Surface melting produced features as small as 60 nm on goldfilm when discharge current was limited by series resistor.