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3 May 2004

Volume 84, Issue 18, pp. 3435-3703

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Appl. Phys. Lett. 84, 3648 (2004); http://dx.doi.org/10.1063/1.1737470 (3 pages)

Jingbo Li and Lin-Wang Wang
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Synthesis of uniform GaN quantum dot arrays via electron nanolithography of D2GaN3

P. A. Crozier, J. Tolle, J. Kouvetakis, and Cole Ritter

Appl. Phys. Lett. 84, 3441 (2004); http://dx.doi.org/10.1063/1.1736314 (3 pages) | Cited 34 times

Online Publication Date: 20 April 2004

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We demonstrate the deposition of periodic arrays of uniformly sized GaN quantum dots onto a SiOx substrate. The dots are deposited using a nanolithography technique based on a combination of electron-beam-induced chemical vapor deposition and single-source molecular hydride chemistries. Under appropriate deposition conditions, we can deposit uniform dots of height 5 nm and full widths at half-maxima of 4 nm. The dot size is controlled by the spatial distribution of secondary electrons leaving the substrate surface. The smallest, most uniform void-free dots are created via nanolithography of molecules adsorbed on the substrate surface. © 2004 American Institute of Physics.
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81.07.Ta Quantum dots
81.16.Nd Micro- and nanolithography

Luminescence from processible quantum dot-polymer light emitters 1100–1600 nm: Tailoring spectral width and shape

L. Bakueva, G. Konstantatos, L. Levina, S. Musikhin, and E. H. Sargent

Appl. Phys. Lett. 84, 3459 (2004); http://dx.doi.org/10.1063/1.1737072 (3 pages) | Cited 18 times

Online Publication Date: 20 April 2004

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Electroluminescent devices combining two families of PbS colloidal quantum dots to achieve spectrally tailored two-color emission are reported. Depending on device structure selected—the use of two separated layers versus a mixture of nanocrystals—the structures demonstrated light emission either in two infrared frequency peaks corresponding to the spectral region 1.1–1.6 μm or in a wide band spanning this same spectral region. Separated-layer devices exhibit wide tunability in the relative intensity of the two peaks by varying excitation conditions. Replacing oleate with octodecylamine ligands increases the internal electroluminescence efficiency to 3.1%. © 2004 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.07.Bc Nanocrystalline materials
81.07.Ta Quantum dots
85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.30.Jw Organic compounds, polymers
78.55.Kz Solid organic materials
78.67.Hc Quantum dots

Electronic structure of ZnO nanorods studied by angle-dependent x-ray absorption spectroscopy and scanning photoelectron microscopy

J. W. Chiou, J. C. Jan, H. M. Tsai, C. W. Bao, W. F. Pong, M.-H. Tsai, I.-H. Hong, R. Klauser, J. F. Lee, J. J. Wu, and S. C. Liu

Appl. Phys. Lett. 84, 3462 (2004); http://dx.doi.org/10.1063/1.1737075 (3 pages) | Cited 29 times

Online Publication Date: 20 April 2004

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Angle-dependent x-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy measurements were performed to differentiate local electronic structures at the tips and sidewalls of highly aligned ZnO nanorods. The overall intensity of the O K-edge XANES spectra is greatly enhanced for small photon incident angles. In contrast, the overall intensity of the Zn K-edge XANES is much less sensitive to the photon incident angle. Both valence-band photoemission and O K-edge XANES spectra show substantial enhancement of O 2p derived states near the valence band maximum and conduction band minimum, respectively. The spatially resolved Zn 3d core level spectra from tip and sidewall regions show the lack of chemical shift. All the results consistently suggest that the tip surfaces of the highly aligned ZnO nanorods are terminated by O ions and the nanorods are oriented in the [000math] direction. © 2004 American Institute of Physics.
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71.20.Nr Semiconductor compounds
76.60.Cq Chemical and Knight shifts
61.46.-w Structure of nanoscale materials

Self-assembled hexagonal Au particle networks on silicon from Au nanoparticle solution

P. Y. Su, J. C. Hu, S. L. Cheng, L. J. Chen, and J. M. Liang

Appl. Phys. Lett. 84, 3480 (2004); http://dx.doi.org/10.1063/1.1737797 (3 pages) | Cited 16 times

Online Publication Date: 20 April 2004

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Self-assembled hexagonal Au particle networks, 2–12 μm in cell size, on silicon have been achieved by a simple method. Honeycomb structure of Au nanoparticles on silicon was drop cast from the Au nanoparticle solution under appropriate concentration, evaporation rate, substrate temperature, and humidity. Hexagonal networks with discrete Au particles were generated in samples annealed in N2 ambient. Two-step annealing, i.e., annealing at 400 °C followed by annealing at 1000 °C for 1 h each was found to be effective to improve the regularity of the Au particle network. As the cell size can be adjusted by the tuning of the deposition conditions, the scheme promises to be an effective patterning method without complex lithography. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing
82.70.Dd Colloids
68.47.Fg Semiconductor surfaces

Blueshift of yellow luminescence band in self-ion-implanted n-GaN nanowire

S. Dhara, A. Datta, C. T. Wu, Z. H. Lan, K. H. Chen, Y. L. Wang, Y. F. Chen, C. W. Hsu, L. C. Chen, H. M. Lin, and C. C. Chen

Appl. Phys. Lett. 84, 3486 (2004); http://dx.doi.org/10.1063/1.1738172 (3 pages) | Cited 18 times

Online Publication Date: 20 April 2004

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Optical photoluminescence studies are performed in self-ion (Ga+)-implanted nominally doped n-GaN nanowires. A 50 keV Ga+ focused ion beam in the fluence range of 1×1014–2×1016 ions cm−2 is used for the irradiation process. A blueshift is observed for the yellow luminescence (YL) band with increasing fluence. Donor–acceptor pair model with emission involving shallow donor introduced by point-defect clusters related to nitrogen vacancies and probable deep acceptor created by gallium interstitial clusters is responsible for the shift. High-temperature annealing in nitrogen ambient restores the peak position of YL band by removing nitrogen vacancies. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.65.La Quantum wires (patterned in quantum wells)
61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
61.72.Cc Kinetics of defect formation and annealing
71.55.Eq III-V semiconductors
61.72.J- Point defects and defect clusters

Direct printing of nanoparticles and spin-on-glasses by offset liquid embossing

Eric J. Wilhelm and Joseph M. Jacobson

Appl. Phys. Lett. 84, 3507 (2004); http://dx.doi.org/10.1063/1.1738942 (3 pages) | Cited 4 times

Online Publication Date: 20 April 2004

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We describe offset liquid embossing (OLE), a method for additively printing nanoparticles and spin-on-glasses. OLE utilizes the transfer of patterned material from a polydimethylsiloxane surface of tuned wettability to a rigid or flexible substrate. Multiple layers can be aligned and printed without the need for planarization. The printing is fast (10 s transfer to substrate) and can be done at ambient conditions. Bridge-like structures were printed in spin-on-glass without etching. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.65.-b Surface treatments
68.08.Bc Wetting
81.07.Bc Nanocrystalline materials

Formation mechanism of wide stacking faults in nanocrystalline Al

X. Z. Liao, S. G. Srinivasan, Y. H. Zhao, M. I. Baskes, Y. T. Zhu, F. Zhou, E. J. Lavernia, and H. F. Xu

Appl. Phys. Lett. 84, 3564 (2004); http://dx.doi.org/10.1063/1.1734689 (3 pages) | Cited 16 times

Online Publication Date: 20 April 2004

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A full dislocation often dissociates into two partial dislocations enclosing a stacking fault (SF) ribbon. The SF width significantly affects the mechanical behavior of metals. Al has very high stacking fault energy and, consequently, very narrow SF width in its coarse-grained state. We have found that some SFs in nanocrystalline Al are surprisingly 1.4–6.8 nm wide, which is 1.5–11 times higher than the reported experimental value in single crystal Al. Our analytical model shows that such wide SFs are formed due to the small grain size and possibly also to the interaction of SF ribbons with high density of dislocations. © 2004 American Institute of Physics.
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61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

ZnO nanoneedles with tip surface perturbations: Excellent field emitters

Y. B. Li, Y. Bando, and D. Golberg

Appl. Phys. Lett. 84, 3603 (2004); http://dx.doi.org/10.1063/1.1738174 (3 pages) | Cited 115 times

Online Publication Date: 20 April 2004

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ZnO nanoneedles were prepared on a silicon wafer through a chemical vapor deposition. The diameters of the needle tips were in a range of 20–50 nm. High-resolution transmission electron microscopy revealed that the nanoneedles were single crystals growing along the [001] direction and exhibiting multiple tip surface perturbations, just 1–3 nm in dimension. Field-emission measurements on the prepared nanostructures showed fairly low turn-on and threshold fields of 2.5 and 4.0 V/μm, respectively. The nanosize perturbations on the nanoneedle tips are assumed to cause such excellent field-emission performance. © 2004 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.70.+q Field emission, ionization, evaporation, and desorption
81.05.Dz II-VI semiconductors

Heteroepitaxal fabrication and structural characterizations of ultrafine GaN/ZnO coaxial nanorod heterostructures

Sung Jin An, Won Il Park, Gyu-Chul Yi, Yong-Jin Kim, Hee-Bok Kang, and Miyoung Kim

Appl. Phys. Lett. 84, 3612 (2004); http://dx.doi.org/10.1063/1.1738180 (3 pages) | Cited 34 times

Online Publication Date: 20 April 2004

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We report on heteroepitaxial fabrication and structural characterizations of ultrafine GaN/ZnO coaxial nanorod heterostructures. The coaxial nanorod heterostructures were fabricated by epitaxial growth of a GaN layer on ultrafine ZnO nanorods. Epitaxial growth and precise control of GaN overlayer thickness were obtained by low pressure metalorganic vapor-phase epitaxy. ZnO nanorods grown on Si and sapphire substrates using catalyst-free metalorganic chemical vapor deposition exhibited diameters as small as 7 nm. Furthermore, structural properties of the coaxial nanorod heterostructures were investigated using both synchrotron-radiation x-ray diffraction and high resolution transmission electron microscopy. © 2004 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.05.Ea III-V semiconductors
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Field-emission properties of quasi-one-dimensional NbOx crystals

Marko Žumer, Vincenc Nemanič, Bojan Zajec, Maja Remškar, Aleš Mrzel, and Dragan Mihailovič

Appl. Phys. Lett. 84, 3615 (2004); http://dx.doi.org/10.1063/1.1738511 (3 pages) | Cited 5 times

Online Publication Date: 20 April 2004

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The field-emission (FE) properties of quasi-one-dimensional NbOx crystals are reported for the single needle geometry. Relatively stable FE currents in excess of 1 μA were measured after a careful conditioning in vacuum of 10−7 mbar. In all our experiments, the FE current originating from a few sites prevailed over the entire current range. This can be confirmed at least in the current range where the emission pattern could be observed on a high-resolution luminescent screen. © 2004 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.44.Br Quasicrystals

Experimental test of the correction terms for Coulomb blockade thermometry

Surita Devi, Tobias Bergsten, and Per Delsing

Appl. Phys. Lett. 84, 3633 (2004); http://dx.doi.org/10.1063/1.1738519 (3 pages)

Online Publication Date: 20 April 2004

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We have experimentally investigated the higher-order correction terms for Coulomb blockade thermometry using two-dimensional arrays of small tunnel junctions and compared our results to the theory for one-dimensional arrays. We find that the correction term for the conductance dip is two times smaller, whereas the correction term for the half-width has a slightly higher value than the theoretical prediction. © 2004 American Institute of Physics.
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07.20.Dt Thermometers
73.23.Hk Coulomb blockade; single-electron tunneling
03.67.Pp Quantum error correction and other methods for protection against decoherence

Light-modulated scanning tunneling spectroscopy for nanoscale imaging of surface photovoltage

Osamu Takeuchi, Shoji Yoshida, and Hidemi Shigekawa

Appl. Phys. Lett. 84, 3645 (2004); http://dx.doi.org/10.1063/1.1737063 (3 pages) | Cited 4 times

Online Publication Date: 20 April 2004

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Light-modulated scanning tunneling spectroscopy (LM–STS) is proposed as a useful method for investigating spatially resolved surface photovoltage (SR–SPV). LM–STS provides the dependences of SR–SPV on bias voltage under constant tip-sample distance simultaneously with the entire dark/illuminated I–V curves. With this method, it is shown that SPV of a metallic Si(111) surface can be bias-dependent and SPV at zero bias voltage for Si(001) can be tip-sample-distance-dependent under conditions of small tip-sample distance and high illumination intensity. The importance of the experimental condition for interpreting experimentally obtained SR–SPV was suggested. © 2004 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
42.30.-d Imaging and optical processing
68.47.Fg Semiconductor surfaces
07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

First principle study of core/shell structure quantum dots

Jingbo Li and Lin-Wang Wang

Appl. Phys. Lett. 84, 3648 (2004); http://dx.doi.org/10.1063/1.1737470 (3 pages) | Cited 32 times

Online Publication Date: 20 April 2004

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The electronic states of core/shell CdSe/CdS and CdSe/CdTe heterostructure quantum dots are studied by large-scale first-principles calculations. According to their natural band-offset alignments CdSe/CdS is a type-I heterostructure and CdSe/CdTe is a type-II heterostructure. We found that, the electron state changes very little, but the hole wave function in CdSe/CdS quantum dots has been localized within the core, while the hole wave function in CdSe/CdTe quantum dots is localized within the shell. The hole state in CdSe/CdTe quantum dots has drastically different characteristics as in CdSe and CdSe/CdS quantum dots. The band alignment, strain effect, and quantum confinement are all important to determine the electronic structures of these systems. © 2004 American Institute of Physics.
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71.20.Nr Semiconductor compounds
71.15.-m Methods of electronic structure calculations
73.21.La Quantum dots

Fabrication and ethanol sensing characteristics of ZnO nanowire gas sensors

Q. Wan, Q. H. Li, Y. J. Chen, T. H. Wang, X. L. He, J. P. Li, and C. L. Lin

Appl. Phys. Lett. 84, 3654 (2004); http://dx.doi.org/10.1063/1.1738932 (3 pages) | Cited 192 times

Online Publication Date: 20 April 2004

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Based on the achievement of synthesis of ZnO nanowires in mass production, ZnO nanowires gas sensors were fabricated with microelectromechanical system technology and ethanol-sensing characteristics were investigated. The sensor exhibited high sensitivity and fast response to ethanol gas at a work temperature of 300 °C. Our results demonstrate the potential application of ZnO nanowires for fabricating highly sensitive gas sensors. © 2004 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires
82.80.-d Chemical analysis and related physical methods of analysis
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Metal-coated Si springs: Nanoelectromechanical actuators

J. P. Singh, D.-L. Liu, D.-X. Ye, R. C. Picu, T.-M. Lu, and G.-C. Wang

Appl. Phys. Lett. 84, 3657 (2004); http://dx.doi.org/10.1063/1.1738935 (3 pages) | Cited 32 times

Online Publication Date: 20 April 2004

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We demonstrated a nanoscale electromechanical actuator operation using an isolated nanoscale spring. The four-turn Si nanosprings were grown using the oblique angle deposition technique with substrate rotation, and were rendered conductive by coating with a 10-nm-thick Co layer using chemical vapor deposition. The electromechanical actuation of a nanospring was performed by passing through a dc current using a conductive atomic force microscope (AFM) tip. The electromagnetic force leads to spring compression, which is measured with the same AFM tip. The spring constant was determined from these measurements and was consistent with that obtained from a finite element analysis. © 2004 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
68.65.La Quantum wires (patterned in quantum wells)
68.37.Ps Atomic force microscopy (AFM)
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Electron energy-loss spectroscopy analysis of the electronic structure of nitrided Hf silicate films

Nobuyuki Ikarashi, Makoto Miyamura, Koji Masuzaki, and Toru Tatsumi

Appl. Phys. Lett. 84, 3672 (2004); http://dx.doi.org/10.1063/1.1738948 (3 pages) | Cited 16 times

Online Publication Date: 20 April 2004

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We have shown, using electron energy-loss spectroscopy, that incorporating N into a Hf silicate film reduces the band gap. We also experimentally clarified that the Hf atoms in the film are coordinated by N atoms, and we used ab initio electronic structure calculations to show that the Hf–N coordination can be a cause of the decrease in the band gap. Therefore, when a Hf silicate film is used as a gate dielectric in a metal-oxide-semiconductor field-effect transistor, N incorporation can affect the gate leakage current because the decrease in the band gap lowers the band offsets of the dielectric on Si. © 2004 American Institute of Physics.
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71.20.Ps Other inorganic compounds
61.80.Jh Ion radiation effects
61.82.Ms Insulators
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
71.15.-m Methods of electronic structure calculations
85.30.Tv Field effect devices
79.20.Uv Electron energy loss spectroscopy
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