Volume 100, Issue 5, 30 January 2012
- 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:
Single molecular memory operation was observed on a porphyrin derivative by scanning tunneling microscopy at room temperature. A porphyrin derivative with four disulfide groups was chemically synthesized and chemisorbed on a Au(111) surface. Coulomb blockade behaviors and switching behaviors in current-voltage (I-V) characteristics were observed on a single porphyrin derivative by scanning tunneling spectroscopy. Based on the switching behaviors, the memory operation of electrical conductance in the porphyrin derivative was demonstrated by applying a programmed pulse sequence with an on/off ratio of 2.9 at room temperature.
- PHOTONICS AND OPTOELECTRONICS
Distributed Bragg reflectors based on diluted boron-based BAlN alloys for deep ultraviolet optoelectronic applications100(2012); http://dx.doi.org/10.1063/1.3679703View Description Hide Description
Highly reflective deep UVdistributed Bragg reflectors(DBRs) based on the BAlN material system have been grown by metalorganic vapour phase epitaxy on AlN template substrates. These structures make use of the transparency of BAlN in the deep UV and the high refractive index contrast between BAlN and AlN, which has been demonstrated to exceed 0.27 at 280 nm. 18-pair BAlN/AlN DBRs showed experimental peak reflectivity of 82% at 311 nm and a stop-bandwidth of 20 nm. At 282 nm, a 24-pair BAlN/AlN DBR structure is demonstrated with experimental peak reflectivity of 60% and stop-bandwidth of 16 nm.
Comparison of scanning tunneling microscope-light emission and photoluminescence from porphyrin films using ultra-high vacuum scanning tunneling microscopy100(2012); http://dx.doi.org/10.1063/1.3680597View Description Hide Description
In order to study the interaction between molecules and photon fields, including plasmonic and external laser fields, we have carried out in situ measurements of photoluminescence(PL) from porphyrin molecules on Au substrates with and without a scanning tunneling microscope (STM) tip. Measurements were performed in a ultra-high vacuum scanning tunneling microscope chamber during irradiation by a He-Cd laser with incident power varying in the 10−3 to 10−7 W range. At an incident power of around 10−7 W, the spectra depend strongly on the presence of STM tip, which is associated with STM light emission from molecules. We estimated the ratio of quantum efficiency of scanning tunneling microscope-induced light emission (STML) from molecules to PL on the basis of the STML/PL intensity ratio observed experimentally at a laser power of 7.5 × 10−8 W, with the use of a 40 μm laser beam diameter and an effective area of 2 nm for STML. The estimated quantum efficiency for an electron in STML is roughly 1010 times larger than that for one photon of PL. This anomalous enhancement will be discussed on the basis of plasmon-enhanced light emission from molecules in a STM nano-cavity.
100(2012); http://dx.doi.org/10.1063/1.3680234View Description Hide Description
A moving array of optical traps created by interference of two counter-propagating evanescent waves has been used for delivery of particle chains up to 18 micro-particles long immersed in water. The particles were optically self-arranged into a linear chain with well-separated distances between them. We observed a significant increase in the delivery speed of the whole structure as the number of particles in the chain increased. This could provide faster sample delivery in microfluidic systems. We quantified the contributions to the speed enhancement caused by the optical and hydrodynamic interactions between the particles.
100(2012); http://dx.doi.org/10.1063/1.3681135View Description Hide Description
Transmission enhancement via transverse mode control through an aluminum hollow tapered waveguide with a sub-100 nm aperture is simulated with optical wavefront modulations via a binary optical element. Efficient delivery of an input field by exciting the fundamental propagating mode near the apex is realized, giving rise to a significant transmission enhancement through the nano-tip.
100(2012); http://dx.doi.org/10.1063/1.3681139View Description Hide Description
We investigate the temperature and pressure dependence of the light-current characteristics and electroluminescencespectra of GaAs1−xBix/GaAs light emitting diodes. The temperature dependence of the emission wavelength shows a relatively low temperature coefficient of emission peak shift of 0.19 ± 0.01 nm/K. A strong decrease in emission efficiency with increasing temperature implies that non-radiative recombination plays an important role on the performance of these devices. The pressure coefficient of the GaAs0.986Bi0.014bandgap is measured to be 11.8 ± 0.3 meV/kbar. The electroluminescence intensity from GaAsBi is found to decrease with increasing pressure accompanied by an increase in luminescence from the GaAs cladding layers suggesting the presence of carrier leakage in the devices.
100(2012); http://dx.doi.org/10.1063/1.3681171View Description Hide Description
We present the design of a fiber-optic gas refractometer that enables spectrally resolved measurements of both real and imaginary parts of the complex refractive index. The proposed concept is based on a Mach-Zehnder-type interferometer with a hollow-core photonic bandgap fiber in one of the interferometer’s arms. The fiber is used simultaneously as an optical waveguide and an analyte containing cell. We demonstrate the performance of the device by measuring the complete complex refractive index of an air-acetylene gas mixture within the optical C-band. The introduced concept leads towards versatile applications in optics as well as atomic and molecular physics.
Optical detection of melting point depression for silver nanoparticles via in situ real time spectroscopic ellipsometry100(2012); http://dx.doi.org/10.1063/1.3681367View Description Hide Description
Silvernanoparticlefilms were deposited by sputtering at room temperature and were annealed while monitoring by real time spectroscopic ellipsometry (SE). The nanoparticledielectric functions (0.75 eV–6.5 eV) obtained by SE were modeled using Lorentz and generalized oscillators for the nanoparticle plasmon polariton (NPP) and interband transitions, respectively. The nanoparticle melting point could be identified from variations in the oscillator parameters during annealing, and this identification was further confirmed after cooling through significant, irreversible changes in these parameters relative to the as-deposited film. The variation in melting point with physical thickness, and thus average nanoparticle diameter, as measured by SE enables calculation of the surface energy density.
100(2012); http://dx.doi.org/10.1063/1.3681802View Description Hide Description
We have experimentally generated a radially polarized (RP) beam with controllable state of spatial coherence by using a rotating ground-glass plate and a radial polarization converter. Furthermore, experimental and theoretical analysis of the focusing properties of a partially coherent RP beam is carried out. Our results show that we can shape the beam profile of the focused RP beam by varying its initial spatial coherence, which is useful for material thermal processing and particle trapping. The experimental results are in complete agreement with the theoretical predictions.
100(2012); http://dx.doi.org/10.1063/1.3681399View Description Hide Description
We have investigated the temperature-dependent, intraexcitonic AC Stark effect that manifests itself in a line splitting of the heavy-hole 1s exciton transition in a GaAs/AlGaAs multi quantum well when the 1s-2p intraexciton transition is driven by intense THz light. The observed wavelength-dependent splitting at Helium temperature can still be distinguished at elevated temperatures up to 200 K. Although the thermal energy exceeds the exciton binding energy by a factor of 1.7, thermal excitonionization influences the coherent nonlinear effect only indirectly via thermal line broadening. With a threefold transmission change on ultrafast timescales in a region accessible to Peltier-cooling the scheme could be promising for optical modulators.
Surface depletion mediated control of inter-sub-band absorption in GaAs/AlAs semiconductor quantum well systems100(2012); http://dx.doi.org/10.1063/1.3680232View Description Hide Description
The modification of quantum well inter-sub-band absorption properties due to surface depletion induced band bending is reported. Fourier transform infrared spectroscopy measurements of a GaAs/AlAs multiple quantum well system reveal a reduction in the characteristic absorption resonance in correlation with wet chemical etching. High resolution transmission electron microscopy confirms the presence of the quantum wells after etching, suggesting the quantum wells are positioned within the surface depletion region of the structure. This method of inter-sub-band absorption modification could be used for the formation of quantum dots from a quantum well system with the precise, deterministic control of their location.
100(2012); http://dx.doi.org/10.1063/1.3681365View Description Hide Description
We demonstrate single-beam coherent anti-Stokes Raman spectroscopy(CARS), for detecting and identifying traces of solids, including minute amounts of explosives, from a standoff distance (>50 m) using intense femtosecond pulses. Until now, single-beam CARS methods relied on pulse-shapers in order to obtain vibrational spectra. Here, we present a simple and easy-to-implement detection scheme, using a commercially available notch filter that does not require the use of a pulse-shaper.
Fabrication of flower-like silver nanostructure on the Al substrate for surface enhanced fluorescence100(2012); http://dx.doi.org/10.1063/1.3681420View Description Hide Description
Surface-enhanced fluorescence (SEF) substrates consisting of flower-like nanostructure of electromagnetically coupled silver dendrites on Alsurface were manufactured by modified galvanic displacement process between Ag ion and Al at room temperature. Substrate enhancement efficiency, which was evaluated from SEF intensities of the adsorbed Rhodamine 6 G(Rh6G), was found to increase rapidly with reaction time. The observation highlights the importance of strong coupling effects between nanobranches in SEF. The variation of SEF efficiency can be qualitatively explained with local surface plasmon resonance model of coupled silvernanostructures.
100(2012); http://dx.doi.org/10.1063/1.3681787View Description Hide Description
We propose a full quantum model based on non-equilibrium Green function method to simulate short channel, ohmic-carbon nanotubefield effect transistor as light emitter. We consider carrier annihilation using self-energy concept in non-ballistic regime, regarding current conservation. Using this model, we calculate radiative recombination rate and electroluminescence spectrum of device. Since, higher bias voltage causes higher carrier injection, we expect to observe more recombination rate by increasing drain or gate voltage. Variation of gate voltage can shift the electroluminescence peak due to slight band gap change. The device current confirms that the electrical and optical properties of device are correlated.
- SURFACES AND INTERFACES
100(2012); http://dx.doi.org/10.1063/1.3681382View Description Hide Description
Capacitively and inductively coupled plasmas were investigated in order to deposit functional plasmapolymers. Considering plasma chemical and surface processes, comparable films can be obtained with both plasma sources yielding distinctly higher deposition rates for ICP. While the gas phase processes scaled with the energy input into the plasma, the surface processes were controlled by the energy dissipated during film growth (ion bombardment).
Cation stoichiometry optimization of SrTiO3 (110) thin films with atomic precision in homogeneous molecular beam epitaxy100(2012); http://dx.doi.org/10.1063/1.3681796View Description Hide Description
We study the evolution of surface reconstructions on SrTiO3 (110) determined by cation concentration ratio and find it detectable by high energy electron diffraction (RHEED) even at high temperature up to 800 °C. The evaporation rate of Sr and Ti sources can be calibrated precisely by monitoring RHEEDpatternsin situ and in real time during the extended homogeneous oxide molecule beam epitaxygrowth of SrTiO3 (110) film. High quality film is obtained with deviation of cation stoichiometry less than 0.5%.
- STRUCTURAL, MECHANICAL, OPTICAL, AND THERMODYNAMIC PROPERTIES OF ADVANCED MATERIALS
100(2012); http://dx.doi.org/10.1063/1.3680600View Description Hide Description
In the light of recently reported pressure-volume-temperature relationships in diamond, we show that the self-diffusion coefficient of diamond as a function of temperature and pressure can be satisfactory reproduced in terms of the bulk elastic and expansivity data by means of a thermodynamical model that interconnects the parameters of point defects to the bulk properties. Our calculated self-diffusion coefficients are in good agreement with the experimental ones when the uncertainties are taken into account.
100(2012); http://dx.doi.org/10.1063/1.3673553View Description Hide Description
The polar surfaces of wurtzite-type zinc oxide (ZnO) were characterized by x-ray photoemission spectroscopy to identify the origin of the polarity dependence of the valence bandspectra. A characteristic sub-peak always appeared in the valence bandspectra of the (0001) face regardless of the surface preparation conditions. It also appeared in the valence bandspectra of the (102) face, but only when the photoelectron take-off angle was parallel to the c-axis of ZnO. Our analysis demonstrates that this take-off angle dependency originates not from the surface state, photoelectron diffraction, or the presence of surfactants but from the crystal polarity.
100(2012); http://dx.doi.org/10.1063/1.3681799View Description Hide Description
One of the most important advantages of graphene is the capability of dynamically tuning its conductivity by means of chemical doping or gate voltage. Based on this property, we propose a planar gradient index graphene-based lens transforming spherical waves of the transverse-magnetic (TM) surface plasmon polariton (SPP) wave to plane waves of the TM SPP wave with specific beam deflections. Using numerical simulations, it is confirmed that a single-atomic-layered graphene can be a platform for planar gradient-index lens, which can be applied to modulate the propagation of SPP waves.
Time-of-flight-photoelectron emission microscopy on plasmonic structures using attosecond extreme ultraviolet pulses100(2012); http://dx.doi.org/10.1063/1.3670324View Description Hide Description
We report on the imaging of plasmonic structures by time-of-flight-photoemission electron microscopy (ToF-PEEM) in combination with extreme ultraviolet (XUV) attosecond pulses from a high harmonic generation source. Characterization of lithographically fabricated Au structures using these ultrashort XUV pulses by ToF-PEEM shows a spatial resolution of ∼200 nm. Energy-filtered imaging of the secondary electrons resulting in reduced chromatic aberrations as well as microspectroscopic identification of core and valence band electronic states have been successfully proven. We also find that the fast valence band electrons are not influenced by space charge effects, which is essentially important for attosecond nanoplasmonic-field microscopy realization.
100(2012); http://dx.doi.org/10.1063/1.3681581View Description Hide Description
Magnetic-field(H)-induced shape memory effect without temperature variation is demonstrated by a combination of H-sweep and H-rotation in an orbital-spin-coupled spinel-type insulating system MnV2O4. A rotation of the direction of a magnetic field of 5 T in the low-temperature tetragonal phase gives rise to a large macroscopic strain up to 1%, which stems from a 90° rotation of tetragonal domains. The results show several possible ways of macroscopic shape control in this class of matter, and may open a possibility of high-speed actuators free from the eddy current.