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20 May 2013

Volume 102, Issue 20 (partial)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 203301 (2013); http://dx.doi.org/10.1063/1.4804595 (4 pages)

Michael Salinas and Marcus Halik
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Enhanced photon-generated carrier extraction from Si nanostructure under additional infrared light irradiation

Wei Yu, Yanmei Xu, Huimin Li, Jin Wang, Guangsheng Fu, and Wanbing Lu

Appl. Phys. Lett. 102, 201101 (2013); http://dx.doi.org/10.1063/1.4807281 (4 pages)

Online Publication Date: 20 May 2013

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Recombination and trapping effect in quantum dots are large barriers to efficient photon-generated carrier extraction. In this paper, Infrared (IR)-assisted carrier extraction in a Si/SiO2 multiple quantum well is demonstrated. Operated at reverse bias, enhanced photoresponse from 300 to 700 nm is observed. External quantum efficiency nearly 200% is obtained when both visible light and IR are added. The enhancement is attributed to potential modulation by photo-illumination. A theoretical model including three processes is presented to explain this conclusion. The secondary light source IR could excite trapped carriers from the defects at the Si/SiO2 interface, improving extraction efficiency.
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82.50.Hp Processes caused by visible and UV light
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Dopant migration effects in terahertz quantum cascade lasers

C. Deutsch, H. Detz, M. Krall, M. Brandstetter, T. Zederbauer, A. M. Andrews, W. Schrenk, G. Strasser, and K. Unterrainer

Appl. Phys. Lett. 102, 201102 (2013); http://dx.doi.org/10.1063/1.4805040 (4 pages)

Online Publication Date: 20 May 2013

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We demonstrate that dopant migration and the resulting impurity scattering can strongly influence the performance of GaAs/Al0.15Ga0.85As terahertz quantum cascade lasers. A nominally symmetric structure allows us to compare the negative and positive bias behavior of the very same device. Dopants, migrated towards the upper laser level during sample growth, degrade the lasing performance due to enhanced impurity scattering rates. The consequences are a higher threshold current (+30%) and reduced optical output power (–29%) in the affected operating direction. This polarity dependent performance is reversed in an asymmetrically doped sample, which imitates the migration of dopants against the growth direction.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.U- Doping and impurity implantation

Single InAs quantum dot coupled to different “environments” in one wafer for quantum photonics

Ying Yu, Xiang-Jun Shang, Mi-Feng Li, Guo-Wei Zha, Jian-Xing Xu, Li-Juan Wang, Guo-Wei Wang, Hai-Qiao Ni, Xiuming Dou, Baoquan Sun, and Zhi-Chuan Niu

Appl. Phys. Lett. 102, 201103 (2013); http://dx.doi.org/10.1063/1.4807502 (4 pages)

Online Publication Date: 20 May 2013

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Self assembled small InAs quantum dots (SQDs) were formed in various densities and environments using gradient InAs deposition on a non-rotating GaAs substrate. Two SQD environments (SQD I and SQD II) were characterized. SQD I featured SQDs surrounded by large QDs, and SQD II featured individual SQDs in the wetting layer (WL). Micro-photoluminescence of single QDs embedded in a cavity under various excitation powers and electric fields gave insight into carrier transport processes. Potential fluctuations of the WL in SQD II, induced by charge redistribution, show promise for charge-tunable QD devices; SQD I shows higher luminescence intensity as a single-photon source.
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78.67.Hc Quantum dots
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.63.Kv Quantum dots
78.55.Cr III-V semiconductors

Generation of high-flux attosecond extreme ultraviolet continuum with a 10 TW laser

Y. Wu, E. Cunningham, H. Zang, J. Li, M. Chini, X. Wang, Y. Wang, K. Zhao, and Z. Chang

Appl. Phys. Lett. 102, 201104 (2013); http://dx.doi.org/10.1063/1.4807395 (4 pages)

Online Publication Date: 21 May 2013

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We report a laser system that delivers 15 fs pulses with 200 mJ energy at a 10 Hz repetition rate. The broadband spectrum extending from 700 nm to 900 nm was obtained by seeding a two-stage Ti:sapphire chirped-pulse power amplifier with sub-mJ white-light pulses from a gas-filled hollow-core fiber. With this laser, an extreme ultraviolet (XUV) super-continuum supporting 230 as isolated attosecond pulses at 35 eV was generated using the generalized double optical gating technique. The XUV pulse energy was ∼100 nJ at the exit of the argon gas target.
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42.65.-k Nonlinear optics
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Wd Fiber lasers
42.60.-v Laser optical systems: design and operation
42.60.By Design of specific laser systems

Excitation power dependence of the Purcell effect in photonic crystal microcavity lasers with quantum wires

J. Canet-Ferrer, I. Prieto, G. Muñoz-Matutano, L. J. Martínez, L. E. Muñoz-Camuniez, J. M. Llorens, D. Fuster, B. Alén, Y. González, L. González, P. A. Postigo, and J. P. Martínez-Pastor

Appl. Phys. Lett. 102, 201105 (2013); http://dx.doi.org/10.1063/1.4807439 (4 pages)

Online Publication Date: 21 May 2013

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The Purcell effect dependence on the excitation power is studied in photonic crystal microcavity lasers embedding InAs/InP quantum wires. In the case of non-lasing modes, the Purcell effect has low dependence on the optical pumping, attributable to an exciton dynamics combining free and localized excitons. In the case of lasing modes, the influence of the stimulated emission makes ambiguous the determination of the Purcell factor. We have found that this ambiguity can be avoided by measuring the dependence of the decay time on the excitation power. These results provide insights in the determination of the Purcell factor in microcavity lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Parasitic nonlinearities in photon pair generation via integrated spontaneous four-wave mixing: Critical problem or distraction?

L. G. Helt, M. J. Steel, and J. E. Sipe

Appl. Phys. Lett. 102, 201106 (2013); http://dx.doi.org/10.1063/1.4807503 (5 pages)

Online Publication Date: 21 May 2013

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We consider integrated photon pair sources based on spontaneous four-wave mixing and derive expressions for the pump powers at which various nonlinear processes become relevant for a variety of source materials and structures. These expressions serve as rules of thumb in identifying reasonable parameter regimes for the design of such sources. We demonstrate that if pump powers are kept low enough to suppress cross-phase modulation, multi-pair events as well as many other nonlinear effects are often also constrained to negligible levels.
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42.50.-p Quantum optics
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Stimulated Raman scattering cascade spanning the wavelength range of 523 to 1750 nm using a graded-index multimode optical fiber

Hamed Pourbeyram, Govind P. Agrawal, and Arash Mafi

Appl. Phys. Lett. 102, 201107 (2013); http://dx.doi.org/10.1063/1.4807620 (4 pages)

Online Publication Date: 21 May 2013

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We report on the generation of a Raman cascade spanning the wavelength range of 523 to 1750 nm wavelength range in a standard telecommunication graded-index multimode optical fiber. Despite the highly multimode nature of the pump, the Raman peaks are generated in specific modes of the fiber, confirming substantial beam cleanup during the stimulated Raman scattering process.
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42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.81.Ht Gradient-index (GRIN) fiber devices

Two-photon nanolithography of positive photoresist thin film with ultrafast laser direct writing

Hong-Zhong Cao, Mei-Ling Zheng, Xian-Zi Dong, Feng Jin, Zhen-Sheng Zhao, and Xuan-Ming Duan

Appl. Phys. Lett. 102, 201108 (2013); http://dx.doi.org/10.1063/1.4807678 (4 pages)

Online Publication Date: 21 May 2013

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The authors investigate two-photon nanolithography of a positive photoresist thin film and the influence factor of spatial resolution. A spatial resolution of 85 nm, about one-ninth of the laser wavelength at 780 nm, has been realized by using commercial positive AZ P4620 photoresist. Theoretical analysis based on the exposure kinetics of photoactive compound of diazonaphthoquinone is consistent with experimental results. The trench's cross-section shape and spatial resolution are influenced by the standing wave interference caused by the incident and reflected light. This study would provide a protocol for fabricating micro/nanodevices by femtosecond laser direct writing of positive photoresists.
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81.16.Nd Micro- and nanolithography
68.55.aj Insulators
42.62.-b Laser applications

Realization of an extraordinary transmission window for a seamless Ag film based on metal-insulator-metal structures

Ding Zhao, Hanmo Gong, Yuanqing Yang, Qiang Li, and Min Qiu

Appl. Phys. Lett. 102, 201109 (2013); http://dx.doi.org/10.1063/1.4807734 (4 pages)

Online Publication Date: 22 May 2013

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A polarization-sensitive, wide-angle operating antireflection coating based on a metal-insulator-metal structure is investigated. In both visible and near-infrared regions, it dramatically reduces the reflection and enhances the transmission through a seamless Ag film near a specifically designed frequency due to the surface plasmon resonance. By achieving above 70% transmission through a 20 nm-thickness Ag film theoretically, this antireflection coating is able to open an extraordinary transmission window for a metallic layer without any slits or holes.
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42.79.Wc Optical coatings
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.40.Rw Metal-insulator-metal structures
78.30.Er Solid metals and alloys
78.40.Kc Metals, semimetals, and alloys
42.70.-a Optical materials

Stimulated Raman scattering in the evanescent field of liquid immersed tapered nanofibers

Liye Shan, Gilles Pauliat, Guillaume Vienne, Limin Tong, and Sylvie Lebrun

Appl. Phys. Lett. 102, 201110 (2013); http://dx.doi.org/10.1063/1.4807170 (4 pages)

Online Publication Date: 22 May 2013

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We present the first experimental demonstrations of stimulated Raman scattering in a liquid probed by the evanescent field of a tapered silica nanofiber. Raman scattering by a pure liquid, ethanol, or mixture of liquids, toluene diluted in ethanol, is investigated. Given the large choice of available materials for the medium surrounding the nanofiber, these demonstrations pave the way to the exploration of a new class of experiments and devices.
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42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.81.Cn Fiber testing and measurement of fiber parameters

2.7 μm InAs quantum well lasers on InP-based InAlAs metamorphic buffer layers

Y. Y. Cao, Y. G. Zhang, Y. Gu, X. Y. Chen, L. Zhou, and Hsby Li

Appl. Phys. Lett. 102, 201111 (2013); http://dx.doi.org/10.1063/1.4807671 (3 pages)

Online Publication Date: 22 May 2013

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This work reports 2.7 μm InAs/In0.6Ga0.4As quantum well lasers on InP-based metamorphic InxAl1−xAs graded buffers. X-ray diffraction measurement shows favorable strain compensation effect in the quantum wells. Type-I photoluminescence emission is observed around 2.7 μm at 77 K and red-shifts to 3 μm at 300 K. The continuous-wave lasing wavelength of the laser reaches 2.7 μm at 77 K, which is the longest wavelength from the interband lasing of InP-based antimony-free structures. The threshold current density is as low as 145 A/cm2 and the continuous-wave output power at injection current of 400 mA is over 5 mW.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Conical second harmonic generation in one-dimension nonlinear photonic crystal

Ning An, Yuanlin Zheng, Huaijin Ren, Xuewei Deng, and Xianfeng Chen

Appl. Phys. Lett. 102, 201112 (2013); http://dx.doi.org/10.1063/1.4807673 (4 pages)

Online Publication Date: 22 May 2013

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We observed conical second-harmonic generation in a one-dimension anomalous-dispersion-like medium, which manifests itself as scattering-assisted nonlinear interaction via quasi-phase-matching sum frequency process. The parameters for the ring-shaped second harmonic beam are analyzed experimentally and theoretically, which disclose the structure information of the nonlinear photonic crystal and imply potential applications as characterization methods. Furthermore, by varying the angles of incident beam, the conical beam can be significantly enhanced owing to collinear nonlinear coupling between the input beam and the scattering light.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.55.Tv Photonic crystal lasers and coherent effects

Scaling and saturation of high-power terahertz radiation generation in two-color laser filamentation

T. I. Oh, Y. S. You, N. Jhajj, E. W. Rosenthal, H. M. Milchberg, and K. Y. Kim

Appl. Phys. Lett. 102, 201113 (2013); http://dx.doi.org/10.1063/1.4807790 (3 pages)

Online Publication Date: 23 May 2013

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Broadband terahertz generation via two-color femtosecond laser filamentation is studied with laser input energies up to 60 mJ. In the small f-number focusing regime, the output THz energy strongly saturates, which is attributed to ionization-induced laser defocusing in filamentation. This saturation effect can be minimized by elongating the plasma filament with weak focusing. A conversion efficiency of >10−4 is achieved in elongated filamentation.
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42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
84.40.-x Radiowave and microwave (including millimeter wave) technology

Atomically sharp 318 nm Gd:AlGaN ultraviolet light emitting diodes on Si with low threshold voltage

Thomas F. Kent, Santino D. Carnevale, and Roberto C. Myers

Appl. Phys. Lett. 102, 201114 (2013); http://dx.doi.org/10.1063/1.4807385 (4 pages)

Online Publication Date: 23 May 2013

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Self-assembled AlxGa1–xN polarization-induced nanowire light emitting diodes (PINLEDs) with Gd-doped AlN active regions are prepared by plasma-assisted molecular beam epitaxy on Si substrates. Atomically sharp electroluminescence (EL) from Gd intra-f-shell electronic transitions at 313 nm and 318 nm is observed under forward biases above 5 V. The intensity of the Gd 4f EL scales linearly with current density and increases at lower temperature. The low field excitation of Gd 4f EL in PINLEDs is contrasted with high field excitation in metal/Gd:AlN/polarization-induced n-AlGaN devices; PINLED devices offer over a three fold enhancement in 4f EL intensity at a given device bias.
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85.60.Jb Light-emitting devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Optical response of oriented and highly anisotropic subwavelength metallic nanostructure arrays

K. J. Alvine, B. E. Bernacki, W. D. Bennett, D. J. Edwards, A. Mendoza, and J. D. Suter

Appl. Phys. Lett. 102, 201115 (2013); http://dx.doi.org/10.1063/1.4807031 (5 pages)

Online Publication Date: 23 May 2013

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Here we describe the optical response of highly anisotropic subwavelength coatings with Au structures based on the open-ring-resonator and fabricated via nanoimprint lithography and metal sputtering. This approach allows fabrication of dense arrays of oriented nanostructures over large areas with a resonance in the visible wavelength range. Nanostructures are wire-like, with a nanoscale L-shaped cross section approximately 70 nm in width. The coatings exhibit a resonant transmission response that is highly angle and polarization dependent. Experimental results are presented along with complementary numerical modeling results predicting the resonance shift with corresponding changes in fabrication parameters.
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81.16.Nd Micro- and nanolithography
61.46.-w Structure of nanoscale materials
78.40.Kc Metals, semimetals, and alloys
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Evanescent-wave comb spectroscopy of liquids with strongly dispersive optical fiber cavities

S. Avino, A. Giorgini, M. Salza, M. Fabian, G. Gagliardi, and P. De Natale

Appl. Phys. Lett. 102, 201116 (2013); http://dx.doi.org/10.1063/1.4807680 (5 pages)

Online Publication Date: 23 May 2013

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We demonstrate evanescent-wave fiber cavity-enhanced spectroscopy in the liquid phase using a near-infrared frequency comb. Exploiting strong fiber-dispersion effects, we show that liquid absorption spectra can be recorded without any external dispersive element. The fiber cavity is used both as sensor and spectrometer. The resonance modes are frequency locked to the comb teeth while the cavity photon lifetime is measured over 155 nm, from 1515 nm to 1670 nm, where absorption bands of liquid polyamines are detected as a proof of concept. Our fiber spectrometer lends itself to in situ, real-time chemical analysis in environmental monitoring, biomedical assays, and micro-opto-fluidic systems.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
42.81.Dp Propagation, scattering, and losses; solitons
42.81.Pa Sensors, gyros
78.30.cb Organic liquids
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Young-Lippmann equation revisited for nano-suspensions

Daniel Orejon, Khellil Sefiane, and Martin E. R. Shanahan

Appl. Phys. Lett. 102, 201601 (2013); http://dx.doi.org/10.1063/1.4807120 (3 pages)

Online Publication Date: 20 May 2013

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We present the results of an experimental study investigating electrowetting effects in nano-suspension drops. Wetting of sessile drops of titanium oxide (TiO2) nano-particles dispersed in deionised water was studied under a DC voltage potential. The presence of nano-particles is found to further enhance spreading of drops when a DC potential is applied. Results are explained based on the change in interfacial energy induced by nano-particle adsorption at the solid-liquid interface. An amendment of the Young-Lippmann equation accounting for the presence of nano-particles is proposed. The electrowetting expression proposed is validated against the experimental data for substrates with various dielectric thicknesses.
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82.70.Kj Emulsions and suspensions
68.08.Bc Wetting
68.43.Mn Adsorption kinetics
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Fabrication and scanning tunneling microscopy characterization of suspended monolayer graphene on periodic Si nanopillars

Xin Zhao, Xiaofang Zhai, Aidi Zhao, Bing Wang, and J. G. Hou

Appl. Phys. Lett. 102, 201602 (2013); http://dx.doi.org/10.1063/1.4807139 (4 pages)

Online Publication Date: 20 May 2013

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We present the fabrication and scanning tunneling microscopy (STM) characterization of suspended monolayer graphene (SMG) on periodic Si nanostructure. Monolayer graphene (MG) was grown on Cu foils by chemical vapor deposition (CVD) and transferred onto a Si substrate with etched array of periodic nanopillars, obtaining partly suspended MG. Low-temperature STM characterization was performed on the suspension area of the MG with atomic resolution images obtained. The scanning tunneling spectroscopy of SMG shows a nonlinear behavior near the Fermi level (EF), which is attributed to the Dirac cone reshaped by electron-electron interaction.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.70.Kj Emulsions and suspensions
81.16.-c Methods of micro- and nanofabrication and processing

Investigation of the release of Si from SiO2 during the formation of manganese/ruthenium barrier layers

A. P. McCoy, P. Casey, J. Bogan, C. Byrne, and G. Hughes

Appl. Phys. Lett. 102, 201603 (2013); http://dx.doi.org/10.1063/1.4807428 (4 pages)

Online Publication Date: 20 May 2013

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The thermodynamic and structural stability of ruthenium-manganese diffusion barriers on SiO2 is assessed. A ∼2 nm film composed of partially oxidized manganese (MnOx where x < 1) was deposited on a 3 nm thick Ru film and the Mn-MnOx/Ru/SiO2 structure was subsequently thermally annealed. X-ray photoelectron spectroscopy and secondary ion mass spectroscopy studies suggest the release and upward diffusion of Si from the dielectric substrate as a result of manganese-silicate formation at the Ru/SiO2 interface. The migration of Si up through the Ru film results in further manganese-silicate formation upon its interaction with the Mn-MnOx deposited layer.
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66.30.Ny Chemical interdiffusion; diffusion barriers
79.60.Jv Interfaces; heterostructures; nanostructures
81.40.Gh Other heat and thermomechanical treatments
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
65.40.G- Other thermodynamical quantities

Interfacial chemistry and valence band offset between GaN and Al2O3 studied by X-ray photoelectron spectroscopy

T. L. Duan, J. S. Pan, and D. S. Ang

Appl. Phys. Lett. 102, 201604 (2013); http://dx.doi.org/10.1063/1.4807736 (4 pages)

Online Publication Date: 21 May 2013

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The interface region between Ga-face n-type GaN and Al2O3 dielectric (achieved via atomic-layer deposition or ALD) is investigated by X-ray photoelectron spectroscopy (XPS). An increase in the Ga-O to Ga-N bond intensity ratio following Al2O3 deposition implies that the growth of an interfacial gallium sub-oxide (GaOx) layer occurred during the ALD process. This finding may be ascribed to GaN oxidation, which may still happen following the reduction of a thin native GaOx by trimethylaluminum (TMA) in the initial TMA-only cycles. The valence band offset between GaN and Al2O3, obtained using both core-level and valence band spectra, is found to vary with the thickness of the deposited Al2O3. This observation may be explained by an upward energy band bending at the GaN surface (due to the spontaneous polarization induced negative bound charge on the Ga-face GaN) and the intrinsic limitation of the XPS method for band offset determination.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
65.40.gp Surface energy
71.20.-b Electron density of states and band structure of crystalline solids
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.30.-b Specific chemical reactions; reaction mechanisms

Gold-titania interface toughening and thermal conductance enhancement using an organophosphonate nanolayer

Philippe K. Chow, Y. Cardona Quintero, Peter O'Brien, P. Hubert Mutin, Michael Lane, R. Ramprasad, and Ganpati Ramanath

Appl. Phys. Lett. 102, 201605 (2013); http://dx.doi.org/10.1063/1.4807436 (4 pages)

Online Publication Date: 21 May 2013

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We demonstrate that a mercaptan-terminated organophosphonate nanolayer at gold-titania interfaces can give rise to two- to three-fold enhancement in the interfacial fracture toughness and thermal conductance. Electron spectroscopy reveals that interfacial delamination occurs at the metal-molecule interface near the gold-sulfur bonds, consistent with density functional theory calculations of bond energies. Qualitative correlation between interfacial fracture toughness and bond energies suggest that organophosphonate nanolayers are resilient to humidity-induced degradation. These results, and the versatility of organophosphonates as surface functionalization agents for technologically relevant materials, unlock uncharted avenues for molecular engineering of interfaces in materials and devices for a variety of applications.
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73.40.Ns Metal-nonmetal contacts
79.60.Jv Interfaces; heterostructures; nanostructures
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
62.20.mm Fracture
61.50.Lt Crystal binding; cohesive energy

Large surface-enhanced Raman scattering from self-assembled gold nanosphere monolayers

Jake Fontana, John Livenere, Francisco J. Bezares, Joshua D. Caldwell, Ronald Rendell, and Banahalli R. Ratna

Appl. Phys. Lett. 102, 201606 (2013); http://dx.doi.org/10.1063/1.4807659 (5 pages)

Online Publication Date: 21 May 2013

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We demonstrate an average surface-enhanced Raman scattering enhancement on the order of 108 from benzenethiol molecules using self-assembled, macroscopic, and tunable gold nanosphere monolayers on non-templated substrates. The self-assembly of the nanosphere monolayers uses a simple and efficient technique that allows for the creation of a high-density, chemically functionalized gold nanosphere monolayers with enhancement factors comparable to those produced using top-down fabrication techniques. These films may provide an approach for the future development of portable chemical/biological sensors.
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78.66.Bz Metals and metallic alloys
81.16.Dn Self-assembly
68.55.at Other materials
78.30.Er Solid metals and alloys

First principles study of As 2p core-level shifts at GaAs/Al2O3 interfaces

Giacomo Miceli and Alfredo Pasquarello

Appl. Phys. Lett. 102, 201607 (2013); http://dx.doi.org/10.1063/1.4807730 (4 pages)

Online Publication Date: 23 May 2013

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Arsenic 2p core-level shifts at GaAs/Al2O3 interfaces are determined with respect to bulk GaAs through density functional calculations. Atomistic interface models are constructed in which As atoms are found in various chemical environments. Both Ga-terminated and As-terminated GaAs substrates are considered, but only the former are found to be consistent with experimental data. The shifts of several oxidation states of As are calculated and a good agreement with experiment is found for the As+3 and As+5 states. Interfacial As-As dimer atoms and AsGa antisites are investigated as candidates for the experimental photoemission line assigned to As-As bonds. The calculated shifts favor an assignment to AsGa antisites.
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73.20.At Surface states, band structure, electron density of states
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Quenching of plasmons modes in air-exposed graphene-Ru contacts for plasmonic devices

Antonio Politano and Gennaro Chiarello

Appl. Phys. Lett. 102, 201608 (2013); http://dx.doi.org/10.1063/1.4804189 (4 pages)

Online Publication Date: 23 May 2013

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High-resolution electron energy loss spectroscopy has been used to investigate the effects of air exposure on the plasmon modes of a graphene-Ru contact. We found that graphene plasmons are quenched after the exposure of the sample to ambient air humidity. This finding represents a severe hurdle for THz plasmonic graphene-based devices, in which graphene-metal contacts are inevitable components.
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73.22.Pr Electronic structure of graphene
79.20.Uv Electron energy loss spectroscopy
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.40.Gh Other heat and thermomechanical treatments

Surface plasma pretreatment for enhanced diamond nucleation on AlN

P. Pobedinskas, G. Degutis, W. Dexters, W. Janssen, S. D. Janssens, B. Conings, B. Ruttens, J. D'Haen, H.-G. Boyen, A. Hardy, M. K. Van Bael, and K. Haenen

Appl. Phys. Lett. 102, 201609 (2013); http://dx.doi.org/10.1063/1.4807591 (4 pages)

Online Publication Date: 23 May 2013

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The surface of polycrystalline aluminum nitride (AlN) thin films is exposed to different gas discharge plasmas (N2, O2, and CF4) followed by a water-based colloidal seeding of ultra-dispersed nanodiamond particles. Fluorination of the AlN surface enhances the seeding density, whereas the oxidized surface does not yield any nucleation sites. In the former case, the seeding density improves by almost three orders of magnitude as compared to the untreated and N2 pretreated samples, and allows to grow pinhole-free nanocrystalline diamond film on AlN. Finally, we demonstrate a route towards selective diamond growth on AlN thin films by employing CF4 plasma pretreatment together with photolithography.
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81.65.Mq Oxidation
68.55.ag Semiconductors
52.77.-j Plasma applications
68.47.Fg Semiconductor surfaces
81.05.Ea III-V semiconductors
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