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26 Dec 2011

Volume 99, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 99, 261101 (2011); http://dx.doi.org/10.1063/1.3660243 (3 pages)

T. Schwarzbäck, H. Kahle, M. Eichfelder, R. Roßbach, M. Jetter, and P. Michler
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Wavelength tunable ultraviolet laser emission via intra-cavity frequency doubling of an AlGaInP vertical external-cavity surface-emitting laser down to 328 nm

T. Schwarzbäck, H. Kahle, M. Eichfelder, R. Roßbach, M. Jetter, and P. Michler

Appl. Phys. Lett. 99, 261101 (2011); http://dx.doi.org/10.1063/1.3660243 (3 pages) | Cited 1 time

Online Publication Date: 27 December 2011

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We demonstrate an optically pumped vertical external-cavity surface-emitting laser in a compact v-shaped cavity configuration for frequency doubling to the ultraviolet (UV) spectral range at ∼330 nm. The fundamental red laser emission is realized with a metal-organic vapor-phase epitaxy grown (GaxIn1−x)0.5P0.5/[(AlxGa1−x)yIn1−y]0.5P0.5 multi-quantum-well structure. Second harmonic generation is accomplished by using a beta barium borate non-linear crystal to generate maximum UV output powers exceeding 100 mW. By using a birefringent filter, we are able to tune the fundamental laser resonance to realize a maximum tuning range of 7.5 nm of the second harmonic.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Ci Filters, zone plates, and polarizers

Effect of asymmetric Schottky barrier on GaN-based metal-semiconductor-metal ultraviolet detector

Dabing Li, Xiaojuan Sun, Hang Song, Zhiming Li, Hong Jiang, Yiren Chen, Guoqing Miao, and Bo Shen

Appl. Phys. Lett. 99, 261102 (2011); http://dx.doi.org/10.1063/1.3672030 (3 pages) | Cited 2 times

Online Publication Date: 27 December 2011

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An asymmetric Schottky barrier metal-semiconductor-metal (MSM) ultraviolet (UV) detector with Ni/GaN/Au structure was designed and the effect of the asymmetric Schottky barrier on the detector response was investigated. This detector had response at 0 V bias and increased responsivity when a positive bias was applied to the Ni/GaN contact; however, the internal gain disappeared when a negative bias was applied to this point. This contrasts with a symmetric Ni/GaN/Ni Schottky barrier MSM UV detector which had no internal gain under positive/negative bias and almost no response at 0 V bias. The improved performance of the asymmetric Schottky barrier detector was because of the lower work function of Au causing reduction of Schottky barrier and hence enhancing a hole-accumulating and trapping process, which resulted in internal gain.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Realization of tightly confined channel plasmon polaritons at low frequencies

Tao Jiang, Linfang Shen, Jin-Jei Wu, Tzong-Jer Yang, Zhichao Ruan, and Lixin Ran

Appl. Phys. Lett. 99, 261103 (2011); http://dx.doi.org/10.1063/1.3672048 (3 pages) | Cited 5 times

Online Publication Date: 27 December 2011

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Subwavelength guiding of channel plasmon polaritons (CPPs) is realized by a properly structured metallic groove at frequencies far below the plasma frequency of metal. Compared with CPPs at visible frequencies, more versatile physical mechanisms can be introduced in these CPPs by surface patterning, so that they can exhibit superior features as visible CPPs, while eliminating the potential drawbacks of the latter. Such designer CPPs are explained physically with the effective-index method and verified experimentally in the microwave regime.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces

High power, continuous wave, quantum cascade ring laser

Y. Bai, S. Tsao, N. Bandyopadhyay, S. Slivken, Q. Y. Lu, D. Caffey, M. Pushkarsky, T. Day, and M. Razeghi

Appl. Phys. Lett. 99, 261104 (2011); http://dx.doi.org/10.1063/1.3672049 (3 pages) | Cited 2 times

Online Publication Date: 28 December 2011

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We demonstrate a quantum cascade ring laser with high power room temperature continuous wave operation. A second order distributed feedback grating buried inside the waveguide provides both in-plane feedback and vertical power outcoupling. Total output power reaches 0.51 W at an emission wavelength around 4.85 μm. Single mode operation persists up to 0.4 W. The far field analysis indicates that the device operates in a high order mode. The magnetic and electric components of the ring-shaped lasing beam are in radial and azimuthal directions, respectively.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Dj Gratings

Effect of temperature and strain on the optical polarization of (In)(Al)GaN ultraviolet light emitting diodes

Tim Kolbe, Arne Knauer, Chris Chua, Zhihong Yang, Viola Kueller, Sven Einfeldt, Patrick Vogt, Noble M. Johnson, Markus Weyers, and Michael Kneissl

Appl. Phys. Lett. 99, 261105 (2011); http://dx.doi.org/10.1063/1.3672209 (4 pages) | Cited 3 times

Online Publication Date: 28 December 2011

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The temperature and strain dependence of the polarization of the in-plane electroluminescence of (0001) orientated (In)(Al)GaN multiple quantum well light emitting diodes in the ultraviolet spectral range has been investigated. For light emitting diodes with emission wavelength shorter than 300 nm the transversal-electric polarized emission intensity increases relative to the transversal-magnetic emission with increasing temperature, whereas it decreases for ultraviolet light emitting diodes with longer emission wavelength. This effect can be attributed to occupation of deeper valence bands with increasing temperature. In addition, strain also strongly influence the in-plane light polarization of near ultraviolet light emitting diodes. The transversal-magnetic polarized emission becomes more dominant with decreasing in-plane tensile strain of the InGaN/(In)(Al)GaN multiple quantum well active region.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Microfabricated continuous cubic phase plate induced Airy beams for optical manipulation with high power efficiency

Rui Cao, Yong Yang, Jingang Wang, Jing Bu, Mingwei Wang, and X.-C. Yuan

Appl. Phys. Lett. 99, 261106 (2011); http://dx.doi.org/10.1063/1.3672210 (3 pages) | Cited 1 time

Online Publication Date: 28 December 2011

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We studied and demonstrated optical trapping capabilities of an Airy beam generated with a cubic phase plate incorporated into a conventional optical tweezer system. The power efficiency and damage threshold of the cubic phase plate were found to be much higher when spatial light modulators were employed in beam generation.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.79.Hp Optical processors, correlators, and modulators

Performance of large-area few-layer graphene saturable absorber in femtosecond bulk laser

Jin-Long Xu, Xian-Lei Li, Jing-Liang He, Xiao-Peng Hao, Yong-Zhong Wu, Ying Yang, and Ke-Jian Yang

Appl. Phys. Lett. 99, 261107 (2011); http://dx.doi.org/10.1063/1.3672213 (4 pages) | Cited 7 times

Online Publication Date: 29 December 2011

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Using large-area graphene sheets of 1-10 layers prepared by the improved liquid phase exfoliation technique, the mode locking operation of a diode-pumped Yb:KGW laser was demonstrated. Near-transform-limited 428 fs pulses were yielded at 1031.1 nm with an output power of 504 mW, corresponding to the slope efficiency of 27% and peak power of 13.8 kW. The output power ratio and the slope efficiency ratio of mode locking to free running were as high as 93% and 100%, respectively. This demonstration may open a proper way to achieve low-cost and efficient femtosecond bulk laser.
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42.60.Fc Modulation, tuning, and mode locking
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.60.By Design of specific laser systems
42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

On-chip single photon emission from an integrated semiconductor quantum dot into a photonic crystal waveguide

Andre Schwagmann, Sokratis Kalliakos, Ian Farrer, Jonathan P. Griffiths, Geb A. C. Jones, David A. Ritchie, and Andrew J. Shields

Appl. Phys. Lett. 99, 261108 (2011); http://dx.doi.org/10.1063/1.3672214 (3 pages) | Cited 15 times

Online Publication Date: 29 December 2011

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We demonstrate the in-plane emission of highly polarized single photons from an InAs quantum dot embedded into a photonic crystal waveguide. The spontaneous emission rates are Purcell-enhanced by the coupling of the quantum dot to a slow-light mode of the waveguide. Photon-correlation measurements confirm the sub-Poissonian statistics of the in-plane emission. Under optical pulse excitation, single photon emission rates of up to 19 MHz into the guided mode are demonstrated, which corresponds to a device efficiency of 24%. These results herald the monolithic integration of sources in photonic quantum circuits.
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42.82.Et Waveguides, couplers, and arrays
42.50.-p Quantum optics
42.70.Qs Photonic bandgap materials
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Low-loss flake-graphene saturable absorber mirror for laser mode-locking at sub-200-fs pulse duration

B. V. Cunning, C. L. Brown, and D. Kielpinski

Appl. Phys. Lett. 99, 261109 (2011); http://dx.doi.org/10.1063/1.3672418 (3 pages) | Cited 9 times

Online Publication Date: 29 December 2011

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Saturable absorbers are a key component for mode-locking femtosecond lasers. Polymer films containing graphene flakes have recently been used in transmission as laser mode-lockers but suffer from high nonsaturable loss, limiting their application in low-gain lasers. Here, we present a saturable absorber mirror based on a film of pure graphene flakes. The device is used to mode lock an erbium-doped fiber laser, generating pulses with state-of-the-art, sub-200-fs duration. The laser characteristic indicates that the film exhibits low nonsaturable loss (13% per pass) and large absorption modulation depth (45% of low-power absorption).
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42.60.Fc Modulation, tuning, and mode locking
42.79.Bh Lenses, prisms and mirrors

Lasing in planar semiconductor diodes

Giorgio De Simoni, Lukas Mahler, Vincenzo Piazza, Alessandro Tredicucci, Christine A. Nicoll, Harvey E. Beere, David A. Ritchie, and Fabio Beltram

Appl. Phys. Lett. 99, 261110 (2011); http://dx.doi.org/10.1063/1.3672438 (4 pages)

Online Publication Date: 30 December 2011

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We present a planar laser diode based on a simple fabrication scheme compatible with virtually any geometry accessible by standard semiconductor lithography technique. We show that our lasers exhibit ∼1 GHz -3 dB-modulation-bandwidth already in this prototypical implementation. Directions for a significant speed increase are discussed.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Electrically pumped simultaneous ultraviolet and visible random laser actions from ZnO-CdO interdiffused film

Ye Tian, Xiangyang Ma, Luelue Xiang, and Deren Yang

Appl. Phys. Lett. 99, 261111 (2011); http://dx.doi.org/10.1063/1.3672831 (4 pages) | Cited 1 time

Online Publication Date: 30 December 2011

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We have demonstrated electrically pumped simultaneous ultraviolet (UV) and visible random laser (RL) actions from ZnO-CdO interdiffused film. The interdiffusion between ZnO and CdO films at 700 °C forms composition-graded CdxZn1−xO alloy within the ZnO-CdO interdiffused film, which is luminescent in both UV and visible regions. A device based on SiO2/ZnO-CdO/SiO2 double-barrier structure on silicon substrate, where SiO2 acts as the barrier, is constructed for electrical pumping of the ZnO-CdO interdiffused film. As the device is applied with sufficiently high forward bias with negative voltage connecting to the silicon substrate, the UV and visible RL actions simultaneously occur. The mechanism for such electrically pumped RL actions has been tentatively elucidated.
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78.60.Fi Electroluminescence
42.55.Zz Random lasers
42.55.Px Semiconductor lasers; laser diodes

Whispering gallery modes with different polarizations in semiconductor microrod with rectangle shape

Xiaoliang Ye, Huibing Mao, Jiqing Wang, and Ziqiang Zhu

Appl. Phys. Lett. 99, 261112 (2011); http://dx.doi.org/10.1063/1.3673329 (3 pages) | Cited 1 time

Online Publication Date: 30 December 2011

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The whispering gallery modes (WGMs) of the ZnO photoluminescence emission were investigated in this paper. The transmission electron microscopy and X-ray diffraction results confirm that the rectangle microrod has a single crystalline wurtzite structure. Except for the band-edge emission, the visible luminescence band of the ZnO microrod presents the WGMs with two different polarizations. In a large waveband, the WGMs modes with two different polarizations have same mode spacing. Because of the phase difference in reflectance for two polarizations, the WGMs for s and p polarizations are distributed interlacedly. Due to the property difference, the WGMs for two polarizations have different appearances.
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78.55.Et II-VI semiconductors
78.40.Fy Semiconductors
81.05.Dz II-VI semiconductors
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Characterization and mechanism of He plasma pretreatment of nanoscale polymer masks for improved pattern transfer fidelity

F. Weilnboeck, D. Metzler, N. Kumar, G. S. Oehrlein, R. L. Bruce, S. Engelmann, and N. Fuller

Appl. Phys. Lett. 99, 261501 (2011); http://dx.doi.org/10.1063/1.3671995 (4 pages) | Cited 1 time

Online Publication Date: 27 December 2011

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Roughening of nanoscale polymer masks during plasma etching (PE) limits feature critical dimensions in current and future lithographic technologies. Roughness formation of 193 nm photoresist (PR) is mechanistically explained by plasma-induced changes in mechanical properties introduced at the PR surface (∼2 nm) by ions and in parallel in the material bulk (∼200 nm) by ultraviolet (UV) plasma radiation. Synergistic roughening of polymer masks can be prevented by pretreating PR patterns with a high dose of He plasma UV exposure to saturate bulk material modifications. During subsequent PE, PR patterns are stabilized and exhibit improved etch resistance and reduced surface/line-edge roughness.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
68.35.bm Polymers, organics
81.16.Rf Micro- and nanoscale pattern formation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.16.Nd Micro- and nanolithography

Measurement of valence band structure in boron-zinc-oxide films by making use of ion beams

Han S. Uhm, Gi C. Kwon, and Eun H. Choi

Appl. Phys. Lett. 99, 261502 (2011); http://dx.doi.org/10.1063/1.3672052 (3 pages) | Cited 2 times

Online Publication Date: 27 December 2011

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Measurement of valence band structure in the boron-zinc oxide (BZO) films was developed using the secondary electron emission due to the Auger neutralization of ions. The energy distribution profile of the electrons emitted from boron-zinc-oxide films was measured and rescaled so that Auger self-convolution arose; thus, revealing the detailed structure of the valence band and suggesting that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film.
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71.20.Nr Semiconductor compounds
73.61.Ga II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
79.20.Fv Electron impact: Auger emission
79.20.Hx Electron impact: secondary emission
61.80.Jh Ion radiation effects

Intense terahertz emission from atomic cluster plasma produced by intense femtosecond laser pulses

Fazel Jahangiri, Masaki Hashida, Takeshi Nagashima, Shigeki Tokita, Masanori Hangyo, and Shuji Sakabe

Appl. Phys. Lett. 99, 261503 (2011); http://dx.doi.org/10.1063/1.3672814 (3 pages) | Cited 3 times

Online Publication Date: 28 December 2011

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Terahertz (THz) emission from argon cluster plasma, generated by intense femtosecond laser pulses in the energy range of 10–70 mJ, has been investigated. THz polarization, energy dependence, and angular distribution were measured to provide an initial discussion on the mechanisms of THz emission. THz pulses of much higher energy were generated from argon clusters than from argon gas, which indicates that plasma produced from atomic clusters holds considerable promise as an intense THz source.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.50.Dg Plasma sources

Comparison of the electron density measurements using Thomson scattering and emission spectroscopy for laser induced breakdown in one atmosphere of helium

E. Nedanovska, G. Nersisyan, T. J. Morgan, L. Hüwel, C. L. S. Lewis, D. Riley, and W. G. Graham

Appl. Phys. Lett. 99, 261504 (2011); http://dx.doi.org/10.1063/1.3672817 (3 pages) | Cited 1 time

Online Publication Date: 28 December 2011

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Thomson scattering from laser-induced plasma in atmospheric helium was used to obtain temporally and spatially resolved electron temperature and density profiles. Electron density measurements at 5 μs after breakdown are compared with those derived from the separation of the allowed and forbidden components of the 447.1 nm He I line. Plasma is created using 9 ns, 140 mJ pulses from Nd:YAG laser at 1064 nm. Electron densities of ∼5 × 1016 cm−3 are in good agreement with Thomson scattering measurements, benchmarking this emission line as a useful diagnostic for high density plasmas.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Vp Discharge in vacuum
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Determination of miscibility in MgO-ZnO nanocrystal alloys by x-ray absorption spectroscopy

Sukit Limpijumnong, Jaru Jutimoosik, Nirawith Palakawong, Wantana Klysubun, Jiti Nukeaw, Mao-Hua Du, and Saroj Rujirawat

Appl. Phys. Lett. 99, 261901 (2011); http://dx.doi.org/10.1063/1.3671987 (4 pages) | Cited 3 times

Online Publication Date: 27 December 2011

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The local structure of MgxZn1−xO nanocrystals is studied using synchrotron x-ray absorption near edge structures (XANES) over the full range of composition, from x = 0 to 1. Mg and Zn K-edges XANES measurements allow us to selectively study the local environments around Mg and Zn atoms in these nanocrystalline samples. Our results indicate that, for MgO-ZnO alloys, Zn is highly miscible in the rocksalt domain (i.e., up to ∼50 at. %) while the miscibility of Mg in the wurtzite domain is much less but is still substantial (i.e., up to ∼20 at. %). The simulated XANES spectra, based on first principles methods, are consistent with the observed spectra, confirming our finding. Because it is short-ranged and element-specific, the technique is useful for local structure and crystal phase determination of nanostructures, quantum dots, and mixed-phase alloys in general.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.46.Hk Nanocrystals
64.75.Bc Solubility
78.70.Dm X-ray absorption spectra
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Revealing low-temperature atomic ordering in bulk Co-Pt with the high-throughput ab-initio method

Roman V. Chepulskii and Stefano Curtarolo

Appl. Phys. Lett. 99, 261902 (2011); http://dx.doi.org/10.1063/1.3671992 (3 pages) | Cited 5 times

Online Publication Date: 27 December 2011

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The low-temperature phase diagram of bulk Co-Pt is studied with a high-throughput ab-initio method. Global, hcp-, and fcc-restricted convex hulls are constructed to evaluate stable and metastable phases. It is found that fcc-L10 is energetically degenerate with hcp-B19. Both structures are unstable with respect to phase decomposition into hcp-D019↔fcc-β2 at low temperature. Furthermore, L10 is an adaptive structure on the fcc-restricted convex hull which relates to the low energies of antiphase boundaries. Fcc-L12 is energetically degenerate with fcc-D023 for both Co3Pt and CoPt3. L12-Co3Pt and L10-CoPt belong to the fcc-restricted convex hull. They might stabilize above the Co hcp/fcc transition and remain kinetically frozen below. L12-CoPt3 is energetically well above the convex hull. Its experimental observation may result from yet unexplained finite-temperature effects.
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81.30.Bx Phase diagrams of metals, alloys, and oxides
71.15.-m Methods of electronic structure calculations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kd Metals and alloys
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.20.Be Transition metals and alloys

Microsecond linear optical response in the unusual nematic phase of achiral bimesogens

V. P. Panov, R. Balachandran, M. Nagaraj, J. K. Vij, M. G. Tamba, A. Kohlmeier, and G. H. Mehl

Appl. Phys. Lett. 99, 261903 (2011); http://dx.doi.org/10.1063/1.3671996 (3 pages) | Cited 7 times

Online Publication Date: 28 December 2011

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Some hydrocarbon linked mesogenic dimers are known to exhibit an additional nematic phase (Nx) below a conventional uniaxial nematic (Nu) phase. Although composed of non-chiral molecules, the Nx phase is found to exhibit linear (polar) switching under applied electric field. This switching has remarkably low response time of the order of a few microseconds. Two chiral domains with opposite handedness and consequently opposite responses are found in planar cells. Uniformly lying helix, electroclinic, and flexoelectric effects are given as possible causes for this intriguing phenomenon.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
77.65.-j Piezoelectricity and electromechanical effects

Ultra-coherent single photon source

H. S. Nguyen, G. Sallen, C. Voisin, Ph. Roussignol, C. Diederichs, and G. Cassabois

Appl. Phys. Lett. 99, 261904 (2011); http://dx.doi.org/10.1063/1.3672034 (3 pages) | Cited 11 times

Online Publication Date: 28 December 2011

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We present an original type of single photon source in solid state, based on the coherent laser light scattering by a single InAs quantum dot. We demonstrate that the coherence of the emitted single photons is tailored by the resonant excitation with a spectral linewidth below the radiative limit. Our ultra-coherent source opens the way for integrated quantum devices dedicated to the generation of single photons with high degrees of indistinguishability.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Facile creation of bio-inspired superhydrophobic Ce-based metallic glass surfaces

Kesong Liu, Zhou Li, Weihua Wang, and Lei Jiang

Appl. Phys. Lett. 99, 261905 (2011); http://dx.doi.org/10.1063/1.3672036 (4 pages) | Cited 7 times

Online Publication Date: 29 December 2011

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A bio-inspired synthesis strategy was conducted to fabricate superhydrophobic Ce-based bulk metallic glass (BMG) surfaces with self-cleaning properties. Micro-nanoscale hierarchical structures were first constructed on BMG surfaces and then modified with the low surface energy coating. Surface structures, surface chemical compositions, and wettability were characterized by combining scanning electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy, and contact angle measurements. Research indicated that both surface multiscale structures and the low surface free energy coating result in the final formation of superhydrophobicity.
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61.43.Dq Amorphous semiconductors, metals, and alloys
81.05.Kf Glasses (including metallic glasses)
68.35.bj Amorphous semiconductors, glasses
68.08.Bc Wetting
68.35.Md Surface thermodynamics, surface energies
79.60.Bm Clean metal, semiconductor, and insulator surfaces

High temperature thermal properties of thin tantalum nitride films

Elah Bozorg-Grayeli, Zijian Li, Mehdi Asheghi, Gil Delgado, Alexander Pokrovsky, Matthew Panzer, Daniel Wack, and Kenneth E. Goodson

Appl. Phys. Lett. 99, 261906 (2011); http://dx.doi.org/10.1063/1.3672098 (3 pages) | Cited 2 times

Online Publication Date: 29 December 2011

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Tantalum Nitride (TaN) films carry high heat fluxes in a variety of applications including diffusion barriers in magnetoresistive random access memory and buffer/absorbers in extreme ultraviolet masks. The thicknesses of these films are usually of the same order as the thermal energy carrier mean free path, which complicates the study of heat conduction. This paper presents thermal (cross-plane) and electrical (in-plane) conductivity measurements on TaN films with thicknesses of 50, 75, and 100 nm. Picosecond thermoreflectance is used to extract the thermal boundary resistance between TaN and Al and the intrinsic thermal conductivity of TaN for temperatures of 300–700 K. The data and the relative importance of boundary resistances, electron-boundary scattering, and electron-defect scattering are interpreted using the electrical and thermal transport data. These data facilitate comparison of the phonon and electron contributions to thermal conduction in TaN.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
73.61.Ng Insulators
78.20.N- Thermo-optic effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Structural variability in La0.5Sr0.5TiO3±δ thin films

Meng Gu, Craig R. Dearden, Chengyu Song, Nigel D. Browning, and Yayoi Takamura

Appl. Phys. Lett. 99, 261907 (2011); http://dx.doi.org/10.1063/1.3672217 (3 pages) | Cited 3 times

Online Publication Date: 29 December 2011

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La0.5Sr0.5TiO3±δ films were grown by pulsed laser deposition and characterized using aberration-corrected scanning transmission electron microscopy. Single-phase films with low resistivity and a near Ti3+ valence state were stabilized by a large concentration of oxygen vacancies under reducing conductions. In contrast, single-phase films transformed into “superlattices” upon exposure to an oxygen rich environment through the formation of stacking faults and cation vacancies in order to reach the stable Ti4+ valence state. The resistivity of the superlattices exceeded that of single phase films by two orders of magnitude, indicating that the observed structural order had a significant effect on the overall film properties.
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68.55.aj Insulators
81.15.Fg Pulsed laser ablation deposition
61.72.Nn Stacking faults and other planar or extended defects
61.72.jd Vacancies
68.65.Cd Superlattices
73.61.Ng Insulators

The indirect to direct band gap transition in multilayered MoS2 as predicted by screened hybrid density functional theory

Jason K. Ellis, Melissa J. Lucero, and Gustavo E. Scuseria

Appl. Phys. Lett. 99, 261908 (2011); http://dx.doi.org/10.1063/1.3672219 (3 pages) | Cited 12 times

Online Publication Date: 29 December 2011

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Molybdenite (MoS2) undergoes a transition from an indirect to direct gap semiconductor exhibiting strong photoluminescence when confined in a 2D monolayer. We investigate the effect of interlayer interactions on the band structure and density of states using the screened hybrid functional of Heyd, Scuseria, and Ernzerhof. We show that for the bulk and monolayer systems, our short-range screened hybrid functional produces band gaps in good agreement with experiment. Our functional includes only interlayer interactions of non-van der Waals origin, predicts properties consistent with recent experiments, and provides predictions for few-layered systems.
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64.70.K- Solid-solid transitions
78.55.Hx Other solid inorganic materials
71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.21.Ac Multilayers
73.20.At Surface states, band structure, electron density of states

Formation of metallic colloids in CaF2 by intense ultraviolet light

Stephan Rix, Ute Natura, Felix Loske, Martin Letz, Claudia Felser, and Michael Reichling

Appl. Phys. Lett. 99, 261909 (2011); http://dx.doi.org/10.1063/1.3673301 (3 pages)

Online Publication Date: 29 December 2011

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Highest purity CaF2 single crystals are irreversibly modified when irradiated with millions of pulses of 193 nm light at fluences of 120 mJ/cm2. Mie theory explains the observed haze by attributing the wavelength dependent extinction and the ratio between absorption and scattering to metallic colloids with radii in the range of 20 to 30 nm and a fractional volume of up to 2.8·10-7. Non-contact scanning force microscopy (NC-AFM) measurements performed on a surface produced by in-vacuo cleavage reveals that laser irradiation additionally produces a 104 times higher volume density of colloids with a radius of 1 to 2 nm.
Show PACS
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
79.20.Ds Laser-beam impact phenomena
82.70.Dd Colloids
68.35.bt Other materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
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