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3 Apr 2006

Volume 88, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 143508 (2006); http://dx.doi.org/10.1063/1.2191448 (3 pages)

R. Chan, M. Feng, N. Holonyak, A. James, and G. Walter
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Room temperature demonstration of GaN/AlN quantum dot intraband infrared photodetector at fiber-optics communication wavelength

A. Vardi, N. Akopian, G. Bahir, L. Doyennette, M. Tchernycheva, L. Nevou, F. H. Julien, F. Guillot, and E. Monroy

Appl. Phys. Lett. 88, 143101 (2006); http://dx.doi.org/10.1063/1.2186108 (3 pages) | Cited 31 times

Online Publication Date: 3 April 2006

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We fabricated a communication wavelength photodetector based on intraband transition in GaN/AlN self-assembled quantum dot heterostructures. The quantum dot photodetector is based on in-plane transport and has a room temperature spectral peak responsivity of 8 mA/W at wavelength of 1.41 μm. We use multipass waveguide geometry to show that the polarization sensitive optical absorption spectrum of the heterostructure is nearly the same as its photocurrent spectral response. This establishes that the detector’s response is due to the presence of quantum dots in its active layer. We use photoluminescence, transmission, and intraband photocurrent spectroscopy to consistently describe the alignment between the energy levels of the quantum dots and that of the wetting layer.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

ZnGa2O4 nanotubes with sharp cathodoluminescence peak

Y. J. Li, M. Y. Lu, C. W. Wang, K. M. Li, and L. J. Chen

Appl. Phys. Lett. 88, 143102 (2006); http://dx.doi.org/10.1063/1.2191418 (3 pages) | Cited 27 times

Online Publication Date: 3 April 2006

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Single-crystal ZnGa2O4 nanotubes were grown using well-aligned ZnO nanorods as templates by a vapor transport method. Ga and O vapors were reacted with ZnO to form ZnO/ZnGa2O4 core-shell nanostructure, and single-crystal ZnGa2O4 nanotubes were obtained by the removal of ZnO cores with a dilute HCl solution. The cathodoluminescence spectra indicate that the ZnGa2O4 nanotubes emit near ultraviolet (UV) and blue lights (380 and 464 nm). The sharp near UV peak shall be beneficial for optical applications.
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81.05.Hd Other semiconductors
81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
78.67.Ch Nanotubes
61.46.Fg Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Model of spin localization in activated carbon fibers

Mateusz Kempiński, Wojciech Kempiński, Jacek Kaszyński, and Małgorzata Śliwińska-Bartkowiak

Appl. Phys. Lett. 88, 143103 (2006); http://dx.doi.org/10.1063/1.2187416 (3 pages) | Cited 6 times

Online Publication Date: 3 April 2006

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Mechanisms of spin localization in graphitic nanoparticles of activated carbon fibers (ACFs) are discussed. Electronic properties of ACFs are described by the model which is the fusion of two approaches: Langevin paramagnetism represented by Curie law in electron paramagnetic resonance measurements and granular metal model used to describe conducting properties of separated fibers according to metal-insulator transition. This approach shows the possibility of changing the electronic properties of ACFs by temperature or adsorbed molecules as a main factors.
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72.25.-b Spin polarized transport
75.50.Tt Fine-particle systems; nanocrystalline materials
75.20.Ck Nonmetals
76.30.-v Electron paramagnetic resonance and relaxation
71.30.+h Metal-insulator transitions and other electronic transitions

Luminescent enhancement in europium-doped yttria nanotubes coated with yttria

Xue Bai, Hongwei Song, Guohui Pan, Zhongxin Liu, Shaozhe Lu, Weihua Di, Xingguang Ren, Yanqiang Lei, Qilin Dai, and Libo Fan

Appl. Phys. Lett. 88, 143104 (2006); http://dx.doi.org/10.1063/1.2187518 (3 pages) | Cited 26 times

Online Publication Date: 3 April 2006

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Europium-doped yttria nanotubes were coated with yttria by a simple two-step hydrothermal method, forming the Y2O3:Eu3+/Y2O3 core-shell composite. Remarkable improvement of photoluminescence was observed in the core-shell composite under both violet and ultraviolet excitations. These characteristics were attributed to the reduced influence of surface defects on host excitation, charge transfer transitions, and f−f inner-shell transitions of the Eu3+ ions. Due to striking red luminescence under ultraviolet excitation, the core-shell structure has potential application in plasma display panel devices.
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78.67.Ch Nanotubes
78.55.Hx Other solid inorganic materials
61.46.Fg Nanotubes
78.40.Ha Other nonmetallic inorganics

Single-crystalline trumpetlike zinc phosphide nanostructures

G. Z. Shen, Y. Bando, J. Q. Hu, and D. Golberg

Appl. Phys. Lett. 88, 143105 (2006); http://dx.doi.org/10.1063/1.2192090 (3 pages) | Cited 8 times

Online Publication Date: 3 April 2006

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Single-crystalline trumpetlike Zn3P2 nanostructures composed of hollow cones supported by nanowires have been prepared via a simple thermochemical method, which utilized ZnS and GaP as the source materials. The as-synthesized nanostructures are composed of single-crystalline Zn3P2 nanowires with diameters of ∼ 50 nm and large diameter hollow cones with diameters increasing from 50 nm at the bottom to 600 nm at the top. Photoluminescence study of the trumpetlike Zn3P2 nanostructures shows a broad emission centered at ∼ 585 nm at room temperature.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Hx Other solid inorganic materials

Quantum size effects in the volume plasmon excitation of bismuth nanoparticles investigated by electron energy loss spectroscopy

Y. W. Wang, J. S. Kim, G. H. Kim, and Kwang S. Kim

Appl. Phys. Lett. 88, 143106 (2006); http://dx.doi.org/10.1063/1.2192624 (3 pages) | Cited 17 times

Online Publication Date: 3 April 2006

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Quantum size effects in volume plasmon excitation of bismuth nanoparticles with diameters ranging from 5 to 500 nm have been studied by electron energy loss spectroscopy. The Bi nanoparticles were prepared by reducing Bi3+ with sodium borohydride in the presence of poly(vinylpyrroldone). The volume plasmon energy and its peak width increase with decreasing nanoparticle diameter, due to the quantum size effect. For the particles with diameter less than 40 nm, the increase of the volume plasmon energy is proportional to the inverse square of the nanoparticle diameter, confirming the semimetal to semiconductor transition in Bi nanoparticles.
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79.20.Uv Electron energy loss spectroscopy
72.30.+q High-frequency effects; plasma effects
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Monolayers and nanoparticles on nickel silicide for molecular electronics

Eike Marx, Marco Chiesa, Malin Borg, Stefan Bengtsson, Robert J. Less, Paul R. Raithby, Christopher J. B. Ford, and Neil C. Greenham

Appl. Phys. Lett. 88, 143107 (2006); http://dx.doi.org/10.1063/1.2190458 (3 pages)

Online Publication Date: 3 April 2006

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We describe the use of nickel silicide as an electrode in molecular electronics applications. Formation of monolayers of aliphatic and aromatic hydrocarbons on nickel silicide is demonstrated, and these monolayers are used to link CdSe nanocrystals to the substrate. Using the conjugated linker molecule 1,4-ethynylphenyl-2′-nitro-1-benzene-dithiolate, scanning tunneling spectroscopy measurements at 120 K show evidence of Coulomb blockade and resonant tunneling behavior associated with the nanocrystals. These measurements demonstrate the feasibility of using nickel silicide as an electrode in molecular electronic devices.
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68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.23.Hk Coulomb blockade; single-electron tunneling
73.40.Gk Tunneling
73.63.Bd Nanocrystalline materials
73.40.Ns Metal-nonmetal contacts

Comparative study for colloidal quantum dot conduction band state calculations

Jun-Wei Luo, Shu-Shen Li, Jian-Bai Xia, and Lin-Wang Wang

Appl. Phys. Lett. 88, 143108 (2006); http://dx.doi.org/10.1063/1.2192575 (3 pages) | Cited 8 times

Online Publication Date: 4 April 2006

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By comparing the results of some well-controlled calculation methods, we analyze the relative importance of bulk band structure, multi-bulk-band coupling, and boundary conditions in determining colloidal quantum dot conduction band eigenenergies. We find that while the bulk band structure and correct boundary conditions are important, the effects of multi-bulk-band coupling are small.
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73.21.La Quantum dots

Nanoscale characterization of strained silicon by tip-enhanced Raman spectroscope in reflection mode

Y. Saito, M. Motohashi, N. Hayazawa, M. Iyoki, and S. Kawata

Appl. Phys. Lett. 88, 143109 (2006); http://dx.doi.org/10.1063/1.2191949 (3 pages) | Cited 44 times

Online Publication Date: 4 April 2006

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We observe localized strains in strained silicon by tip-enhanced near-field Raman spectroscope in reflection mode. The tip-enhanced Raman spectra show that the Raman frequency and intensity of strained silicon were different within a crosshatch pattern induced by lattice mismatch. Micro-Raman measurements, however, show only uniform features because of averaging effect due to the diffraction limit of light. Nanoscale characterization of strained silicon is essential for developing reliable next generation integrated circuits. This technique can be applicable not only to strained silicon but also to any other crystals.
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78.30.Am Elemental semiconductors and insulators
62.25.-g Mechanical properties of nanoscale systems
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Ion implantation based selective synthesis of silica nanowires on silicon wafers

Dinesh Kumar Sood, Praveen Kumar Sekhar, and Shekhar Bhansali

Appl. Phys. Lett. 88, 143110 (2006); http://dx.doi.org/10.1063/1.2192148 (3 pages) | Cited 17 times

Online Publication Date: 4 April 2006

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A new method for selective growth of silica nanowires on silicon wafers is demonstrated by using ion implantation through a mask. Pd ions are implanted into Si (100) to form nanoclusters of Pd. The nanoclusters get activated and act as catalyst silicide seeds for nanowire growth, when heated in an open tube quartz furnace, using Ar as carrier gas. Silica nanowires grow selectively only on the implanted region. The vapor-liquid-solid model of nanowire formation is shown to be valid. This method facilitates controlled localized and directed bottom-up growth of silica nanowires and may enable applications such as in on-chip optoelectronics, biosensors, microantennae, and metallic nanotubes.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
61.72.uf Ge and Si

Silver nanocrystal superlattices: Self-assembly and optical emission

T. Qiu, X. L. Wu, Y. C. Cheng, G. G. Siu, and Paul K. Chu

Appl. Phys. Lett. 88, 143111 (2006); http://dx.doi.org/10.1063/1.2192645 (3 pages) | Cited 5 times

Online Publication Date: 4 April 2006

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Unique passivated silver nanocrystal superlattices were fabricated via a conventional hydrothermal method. The method is based on a general phase transfer and separation mechanism occurring at the interfaces of the liquid, solid, and solution phases present during the synthesis. A photoluminescence (PL) band centered at 390 nm was recorded from the obtained superlattice samples. Spectral analyses suggest that the PL arises from the radiative recombination of sp-band electrons with d-band holes in the silver nanocrystals and its intensity enhancement is due to the surface plasmon and an electrostatic enhancement mechanism analogous to that in surface enhanced Raman scattering.
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81.07.Bc Nanocrystalline materials
81.05.Bx Metals, semimetals, and alloys
81.16.Dn Self-assembly
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Hx Other solid inorganic materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Fabrication of 100 nm metal lines on flexible plastic substrate using ultraviolet curing nanoimprint lithography

Heon Lee, Sunghoon Hong, Kiyeon Yang, and Kyungwoo Choi

Appl. Phys. Lett. 88, 143112 (2006); http://dx.doi.org/10.1063/1.2193653 (3 pages) | Cited 17 times

Online Publication Date: 5 April 2006

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Since polymer is flexible, lightweight, reliable and transparent and its material properties can easily be modified, it is a suitable substrate material for organic electronic devices, biomedical devices, and especially for flexible displays. To build a nano-device on a polymer substrate, nano to microsized patterning must be done. However, conventional photolithography cannot be used to fabricate patterns on flexible polymer substrate, due to the focusing and substrate handling issue associated with flexibility of polymer substrate and potential interaction between polymer and developer or other organic solvents used in photolithography. Degradation of polymer substrate during resist baking process over 120 °C can be another problem. In this study, 100 nm sized resist patterns were made on flexible polyethylene-terephthalate (PET) film using newly developed monomer based UV curing imprinting lithography. Compared to conventional imprint lithography, UV curing imprint lithography uses monomer based liquid phase resin and thus patterns can be fabricated without residual layer at room temperature and at much lower pressure (<3–5 atm) with UV illumination. No degradation of PET film was observed due to the imprint process and, as a result, 100 nm sized Ti–Au metal patterns were successfully formed on PET film using UV curing imprint lithography and lift-off process.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer

Patterned regions of porous silicon through trapped hydrogen bubbles

Fung Suong Ou, Laxmikant V. Saraf, and Donald. R. Baer

Appl. Phys. Lett. 88, 143113 (2006); http://dx.doi.org/10.1063/1.2188039 (3 pages) | Cited 6 times

Online Publication Date: 5 April 2006

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Hydrogen (H2) bubbles trapped around lithographically formed etch pits on silicon single crystal surfaces were used to guide the formation of patterned regions of porous silicon (PSi). Lithography and (electro) chemical etching were utilized to form PSi and guide this growth. It was observed that the pits were surrounded by round regions of PSi suggesting that H2 bubbles defined the areas of PSi formation. PSi porosity seemed to form primarily at the bubble edges, lowering overall etch rate near the bubble center. This is consistent with a variable rate of bubble expansion and an ability of the H2 to mask or slow the reaction in the bubble center. Contrary to our initial expectations, the surface profile suggested that the region away from the bubbles was also etched, but very uniformly.
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68.47.Fg Semiconductor surfaces
61.72.Qq Microscopic defects (voids, inclusions, etc.)
81.05.Cy Elemental semiconductors
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.65.Cf Surface cleaning, etching, patterning
42.82.Cr Fabrication techniques; lithography, pattern transfer

Electrical conductivity of a single electrospun fiber of poly(methyl methacrylate) and multiwalled carbon nanotube nanocomposite

Bibekananda Sundaray, V. Subramanian, T. S. Natarajan, and K. Krishnamurthy

Appl. Phys. Lett. 88, 143114 (2006); http://dx.doi.org/10.1063/1.2193462 (3 pages) | Cited 34 times

Online Publication Date: 5 April 2006

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Electrospinning produces polymeric fibers with diameters in the range of 10 μm–10 nm by accelerating a charged polymer jet under a high electric field. We report the preparation of conducting nanocomposite fibers of poly(methyl methacrylate) (PMMA) and multiwalled carbon nanotubes (MWCNTs) by electrospinning. The fibers obtained are long and well aligned. The carbon nanotubes are found to be oriented along the fiber axis. The room temperature dc electrical conductivity of a single fiber with MWCNT (0.05% w/w) shows about a ten orders of magnitude improvement from the pure PMMA. The conductivity increases with MWCNT concentration.
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73.63.-b Electronic transport in nanoscale materials and structures
61.46.-w Structure of nanoscale materials
81.16.-c Methods of micro- and nanofabrication and processing

Strain rate sensitivity of a nanocrystalline Cu synthesized by electric brush plating

Zhonghao Jiang, Xianli Liu, Guangyu Li, Qing Jiang, and Jianshe Lian

Appl. Phys. Lett. 88, 143115 (2006); http://dx.doi.org/10.1063/1.2193467 (3 pages) | Cited 26 times

Online Publication Date: 5 April 2006

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A method for synthesizing bulk nanocrystalline Cu by an electric brush-plating technique is reported. This brush-plated nanocrystalline Cu has a fine (26 nm) and quite uniform grain structure and predominant high-angle grain boundaries. A pronounced strain rate sensitivity of the stress with an m of 0.104 and the Coble creep and a subsequent transition to the power-law creep were observed in room temperature tensile and creep tests. The dominant grain boundary deformation due to the truly nanocrystalline structure of this nanocrystalline Cu is responsible for the observed strain rate sensitivity.
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81.15.Pq Electrodeposition, electroplating
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
61.72.Mm Grain and twin boundaries
81.40.Lm Deformation, plasticity, and creep
62.20.Hg Creep

Effect of nanofluid on the heat transport capability in an oscillating heat pipe

H. B. Ma, C. Wilson, B. Borgmeyer, K. Park, Q. Yu, S. U. S. Choi, and Murli Tirumala

Appl. Phys. Lett. 88, 143116 (2006); http://dx.doi.org/10.1063/1.2192971 (3 pages) | Cited 55 times

Online Publication Date: 5 April 2006

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By combining nanofluids with thermally excited oscillating motion in an oscillating heat pipe (OHP), we developed an ultrahigh-performance cooling device, called the nanofluid oscillating heat pipe. Experimental results show that when the OHP is charged with nanofluid, heat transport capability significantly increases. For example, at the input power of 80.0 W, diamond nanofluid can reduce the temperature difference between the evaporator and the condenser from 40.9 to 24.3 °C. This study will accelerate the development of a highly efficient cooling device for ultrahigh-heat-flux electronic systems.
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47.85.Np Fluidics
07.20.Pe Heat engines; heat pumps; heat pipes
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.27.te Turbulent convective heat transfer

Laser-induced structural modifications in nanocrystalline silicon/amorphous silicon dioxide superlattices

B. V. Kamenev, H. Grebel, and L. Tsybeskov

Appl. Phys. Lett. 88, 143117 (2006); http://dx.doi.org/10.1063/1.2193040 (3 pages) | Cited 7 times

Online Publication Date: 5 April 2006

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We calculate and experimentally detect the laser melting threshold in nanocrystalline Si/amorphous SiO2 superlattices. Using laser energy density slightly above the melting threshold, we observe two types of laser-induced structural modifications: (i) disappearance of nanocrystalline Si phase in the samples with thin ( ∼ 2 nm) SiO2 layers and (ii) amorphization of Si nanocrystals in the samples with thicker ( ≥ 5 nm) SiO2 layers. The observed Si nanocrystal amorphization increases optical absorption and intensity of visible photoluminescence in nanocrystalline Si/amorphous SiO2 superlattices.
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68.65.Cd Superlattices
42.62.-b Laser applications
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
61.46.-w Structure of nanoscale materials
61.43.Er Other amorphous solids
78.55.Hx Other solid inorganic materials

Effect of size in nanowires grown by the vapor-liquid-solid mechanism

Zhuo Chen and Chuanbao Cao

Appl. Phys. Lett. 88, 143118 (2006); http://dx.doi.org/10.1063/1.2193051 (3 pages) | Cited 14 times

Online Publication Date: 5 April 2006

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The effects of size on the growth kinetics of nanowires by the vapor-liquid-solid mechanism are presented. The dependences of the growth rate and the activation energy of crystallization on size are given quantitatively. The obtained theoretical results show that the smaller the nanowire radius, the slower the growth rate, and the activation energy of crystallization will increase with decreasing radius of the nanowire. These theoretical predictions are in agreement with the experimental cases.
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68.65.La Quantum wires (patterned in quantum wells)
61.46.-w Structure of nanoscale materials
64.70.K- Solid-solid transitions

Surface stress control using ultraviolet light irradiation of plasma-polymerized thin films

Shinichi Igarashi, Akiko N. Itakura, Masahiro Kitajima, Anye N. Chifen, Renate Förch, and Rüdiger Berger

Appl. Phys. Lett. 88, 143119 (2006); http://dx.doi.org/10.1063/1.2183807 (3 pages) | Cited 5 times

Online Publication Date: 6 April 2006

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We investigated the surface stress change of plasma-polymerized allylamine films on 2 μm thick silicon micromechanical cantilever substrates induced by ultraviolet light (UV) irradiation. Compressive surface stress was generated during the UV irradiation of the plasma-polymerized films in a dry environment, whereas tensile stress was measured in a humid environment. Fourier transform infrared spectroscopic analysis indicated two mechanisms taking place depending on the environmental conditions. These were attributed to crosslinking and oxidation reactions of the plasma polymer. UV irradiation of plasma polymerized allylamine films at defined humidity suggests a feasible method for achieving tensile and compressive surface stress patterning.
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68.60.Bs Mechanical and acoustical properties
78.66.Qn Polymers; organic compounds
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.30.Jw Organic compounds, polymers
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Coherent acoustic phonons in strain engineered InAs/GaAs quantum dot clusters

E. W. Bogaart, T. van Lippen, J. E. M. Haverkort, R. Nötzel, and J. H. Wolter

Appl. Phys. Lett. 88, 143120 (2006); http://dx.doi.org/10.1063/1.2193460 (3 pages) | Cited 3 times

Online Publication Date: 6 April 2006

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Coherent excitation of the quasilongitudinal and quasitransverse acoustic phonon mode in strain engineered InAs/GaAs quantum dot (QD) clusters grown on (311)B GaAs is monitored by means of time-resolved differential reflection spectroscopy. Carrier capture within the ordered QD clusters initiate coherent acoustic phonon excitation, which induces a transient modulation of the local strain-induced piezoelectric field within the QD clusters. The excited acoustic phonons then modulate the optical properties of the QDs through the quantum-confined Stark effect, causing distinct oscillations of the differential reflection signal.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.Hc Quantum dots

Surface-enhanced Raman scattering efficiency of truncated tetrahedral Ag nanoparticle arrays mediated by electromagnetic couplings

Monica Baia, Lucian Baia, Simion Astilean, and Juergen Popp

Appl. Phys. Lett. 88, 143121 (2006); http://dx.doi.org/10.1063/1.2193778 (3 pages) | Cited 25 times

Online Publication Date: 6 April 2006

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Surface-enhanced Raman scattering (SERS) efficiency assessment of truncated tetrahedral Ag nanoparticle arrays with different vertical dimensions prepared by nanosphere lithography provides the experimental evidence of the electromagnetic (EM) coupling sensitivity to the nanoparticle heights. It is demonstrated that the EM couplings between the localized plasmon resonance of each particle and photonic modes of the particles array are solely accountable for the SERS enhancement of the rhodamine 6G molecules adsorbed on these substrates. Similar nanoparticle height dependent SERS enhancement trend is observed for the resonant excitation of the probe molecule.
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78.30.Er Solid metals and alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Toward rapid and inexpensive identification of bulk carbon nanotubes

K. E. H. Gilbert, J. H. Lehman, A. C. Dillon, and J. L. Blackburn

Appl. Phys. Lett. 88, 143122 (2006); http://dx.doi.org/10.1063/1.2193797 (3 pages) | Cited 2 times

Online Publication Date: 6 April 2006

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The volume fraction of metallic and semiconducting carbon single-wall nanotubes (SWNTs) has been estimated for purified laser vaporization SWNTs, from an effective medium approximation and the measured spectral responsivity of a LiTaO3 pyroelectric detector covered with SWNT “bucky” paper. The detector spectral responsivity from 600 to 2000 nm is proportional to the expected absorption coefficient of the SWNTs, and variations near 700, 950, and 1750 nm correlate with characteristic interband transitions and proportions of SWNTs consistent with 20% metal and 80% semiconductor materials.
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78.67.Ch Nanotubes
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Fy Semiconductors
78.40.Ri Fullerenes and related materials
78.30.Am Elemental semiconductors and insulators

Cryogenic two-photon laser photolithography with SU-8

Kwan H. Lee, Alex M. Green, Robert A. Taylor, David N. Sharp, Andrew J. Turberfield, Frederic S. F. Brossard, David A. Williams, and G. Andrew D. Briggs

Appl. Phys. Lett. 88, 143123 (2006); http://dx.doi.org/10.1063/1.2194311 (3 pages) | Cited 2 times

Online Publication Date: 6 April 2006

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We have shown that photolithography can be used to create alignment markers on a semiconductor substrate at cryogenic temperatures. The epoxy resist SU-8 can be exposed effectively by two-photon absorption at a temperature of 4 K. By this means a spectroscopy apparatus can be used to find the positions of randomly distributed structures at low temperatures, such as InGaAs/GaAs quantum dots, and mark their positions. We present a systematic study of the optical exposure parameters for cryogenic two-photon laser photolithography with SU-8.
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85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer

Single-walled carbon nanotubes as shadow masks for nanogap fabrication

E. P. De Poortere, H. L. Stormer, L. M. Huang, S. J. Wind, S. O’Brien, M. Huang, and J. Hone

Appl. Phys. Lett. 88, 143124 (2006); http://dx.doi.org/10.1063/1.2192636 (3 pages) | Cited 11 times

Online Publication Date: 6 April 2006

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We describe a technique for fabricating nanometer-scale gaps in Pt wires on insulating substrates, using individual single-walled carbon nanotubes as shadow masks during metal deposition. More than 80% of the devices display current-voltage dependencies characteristic of direct electron tunneling. Fits to the current-voltage data yield gap widths in the 0.8–2.3 nm range for these devices, dimensions that are well suited for single-molecule transport measurements.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
73.40.Gk Tunneling
85.65.+h Molecular electronic devices

Nucleation of pentacene thin films on silicon dioxide modified with hexamethyldisilazane

Aravind S. Killampalli and J. R. Engstrom

Appl. Phys. Lett. 88, 143125 (2006); http://dx.doi.org/10.1063/1.2182012 (3 pages) | Cited 14 times

Online Publication Date: 7 April 2006

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Nucleation and growth of pentacene on silicon dioxide surfaces modified with hexamethyldisilazane, HN[Si(CH3)3]2, has been examined using supersonic molecular beam techniques and atomic force microscopy. Similar to growth on clean SiO2 surfaces, the rate of deposition at a fixed incident flux decreases with increasing kinetic energy of incident pentacene, indicative of trapping mediated adsorption. Unlike clean, unmodified SiO2 surfaces, however, growth on the modified surface exhibits characteristics of heterogeneous nucleation, where the maximum island density is independent of deposition rate. Further, islands in the submonolayer regime are two molecules high, unlike the one molecule high islands observed on clean SiO2.
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68.55.A- Nucleation and growth
68.37.Ps Atomic force microscopy (AFM)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.43.Mn Adsorption kinetics
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