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31 May 2004

Volume 84, Issue 22, pp. 4361-4576

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 4409 (2004); http://dx.doi.org/10.1063/1.1757648 (3 pages)

Azita Soleymani, Piroz Zamankhan, and William Polashenski
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Photocurrent in ZnO nanowires grown from Au electrodes

Kihyun Keem, Hyunsuk Kim, Gyu-Tae Kim, Jong Soo Lee, Byungdon Min, Kyoungah Cho, Man-Young Sung, and Sangsig Kim

Appl. Phys. Lett. 84, 4376 (2004); http://dx.doi.org/10.1063/1.1756205 (3 pages) | Cited 133 times

Online Publication Date: 12 May 2004

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ZnO nanowires were grown between two Au electrodes on an Al2O3-deposited Si wafer. Photoresponse, photoresponse spectrum, and current–voltage (I–V) studies were performed for the investigation into photoconduction mechanism in these nanowires. The photoresponse of the nanowires under the continuous illumination of light with above- or below-gap energies was slow, which indicates that photocurrent in the nanowires is surface-related rather than bulk-related. The photoresponse spectrum represents the above- and below-gap absorption bands for the photocurrents. The I–V characteristics under the illumination of the above-gap light are ohmic, but the characteristics under the illumination of the below-gap light are Schottky. This observation indicates that the above-gap light lowers the potential barrier built in the contact between the ZnO nanowires and electrodes, but that the below-gap light does not lower the potential barrier. © 2004 American Institute of Physics.
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73.63.Nm Quantum wires
73.50.Pz Photoconduction and photovoltaic effects

Minimization of germanium penetration, nanocrystal formation, charge storage, and retention in a trilayer memory structure with silicon nitride/hafnium dioxide stack as the tunnel dielectric

T. H. Ng, W. K. Chim, W. K. Choi, V. Ho, L. W. Teo, A. Y. Du, and C. H. Tung

Appl. Phys. Lett. 84, 4385 (2004); http://dx.doi.org/10.1063/1.1757022 (3 pages) | Cited 17 times

Online Publication Date: 12 May 2004

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Trilayer structures, consisting of a rapid thermal oxide (RTO) layer (2.5 or 5 nm thick) grown on silicon, a sputtered Ge middle layer (3–20 nm thick), and a 50-nm-thick sputtered silicon oxide capping layer, exhibit significant penetration of Ge atoms into the silicon substrate for devices with the smaller (2.5 nm) RTO thickness, resulting in negligible nanocrystal formation and hence no charge storage or memory effect. The Ge penetration is minimized by replacing the RTO layer with a high dielectric constant (high-κ) silicon nitride/hafnium dioxide stack (grown by metalorganic chemical vapor deposition) having a larger physical thickness but smaller equivalent oxide thickness of 1.9 nm. Results show that the high-κ trilayer structure exhibits better charge storage capability (in terms of a lower program voltage) and better charge retention performance as compared to the RTO trilayer structure. © 2004 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.07.Bc Nanocrystalline materials
81.16.Pr Micro- and nano-oxidation
77.22.Ch Permittivity (dielectric function)
68.65.Ac Multilayers

Omnidirectional resonance in a metal–dielectric–metal geometry

Hocheol Shin, Mehmet Fatih Yanik, Shanhui Fan, Rashid Zia, and Mark L. Brongersma

Appl. Phys. Lett. 84, 4421 (2004); http://dx.doi.org/10.1063/1.1758306 (3 pages) | Cited 34 times

Online Publication Date: 12 May 2004

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We show that a planar metallic microcavity structure can exhibit an omnidirectional resonance, i.e., a resonance for which the resonance wavelength is independent of the incidence angle of light. The structure consists of a metal–dielectric–metal configuration. The omnidirectional resonance occurs when the reflection phase shift cancels the propagation shift. We numerically demonstrate such an omnidirectional resonance in an Ag–SiO2–Ag structure with realistic material parameters. Such omnidirectionally resonant structures are important for all-angle efficiency enhancement in light emitting diodes and photodetectors. © 2004 American Institute of Physics.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.40.Rw Metal-insulator-metal structures

Atomic-scale observation of interfacial roughness and As–P exchange in InGaAs/InP multiple quantum wells

I. Yamakawa, R. Oga, Y. Fujiwara, Y. Takeda, and A. Nakamura

Appl. Phys. Lett. 84, 4436 (2004); http://dx.doi.org/10.1063/1.1758784 (3 pages) | Cited 8 times

Online Publication Date: 12 May 2004

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Cross-sectional scanning tunneling microscopy (XSTM) has been used to study interfacial properties of InP-on-InGaAs interfaces in InGaAs/InP multiple quantum wells grown by metalorganic vapor phase epitaxy with a growth interruption. XSTM has enabled us to separately identify step-like roughness and distributions of As atoms incorporated in the InP layer near the interface. The As composition profile along the growth direction analyzed from distributions of As atoms in XSTM images shows an exponential variation with distance from the InP-on-InGaAs interface. It is found that the growth interruption of 30 s reduces considerably the roughness amplitude to 0.45 nm from 1.1 nm and increases the coherent length from 22 to 27 nm. © 2004 American Institute of Physics.
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68.65.Fg Quantum wells
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.Ct Interface structure and roughness
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Ultrasensitive nanoelectromechanical mass detection

K. L. Ekinci, X. M. H. Huang, and M. L. Roukes

Appl. Phys. Lett. 84, 4469 (2004); http://dx.doi.org/10.1063/1.1755417 (3 pages) | Cited 115 times

Online Publication Date: 14 May 2004

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We describe the application of nanoelectromechanical systems (NEMS) to ultrasensitive mass detection. In these experiments, a modulated flux of atoms was adsorbed upon the surface of a 32.8 MHz NEMS resonator within an ultrahigh-vacuum environment. The mass-induced resonance frequency shifts by these adsorbates were then measured to ascertain a mass sensitivity of 2.53×10−18 g. In these initial measurements, this sensitivity is limited by the noise in the NEMS displacement transducer; the ultimate limits of the technique are set by fundamental phase noise processes. Our results and analysis indicate that mass sensing of individual molecules will be realizable with optimized NEMS devices. © 2004 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
06.30.Dr Mass and density

Radial superlattices and single nanoreactors

Ch. Deneke, N.-Y. Jin-Phillipp, I. Loa, and O. G. Schmidt

Appl. Phys. Lett. 84, 4475 (2004); http://dx.doi.org/10.1063/1.1755835 (3 pages) | Cited 40 times

Online Publication Date: 14 May 2004

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We investigate the wall structure and thermal stability of individual freestanding rolled-up nanotubes (RUNTs) using micro-Raman spectroscopy, transmission electron microscopy, and selected area electron diffraction. Our studies reveal that the walls of the InAs/GaAs RUNTs consist of a radial superlattice comprising alternating crystalline and noncrystalline layers. Furthermore, we locally heated individual RUNTs with a laser beam, and Raman spectroscopy was used in situ to monitor any structural changes. At about 300 °C the heated part of a RUNT starts to oxidize and eventually transforms into crystalline β-Ga2O3. This result shows that RUNTs can serve as nanoreactors that locally synthesize material at intentional places on a substrate surface. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
61.05.jm Convergent-beam electron diffraction, selected-area electron diffraction, nanodiffraction
68.37.Lp Transmission electron microscopy (TEM)

Nanomachining carbon nanotubes with ion beams

M. S. Raghuveer, P. G. Ganesan, J. D’Arcy-Gall, G. Ramanath, M. Marshall, and I. Petrov

Appl. Phys. Lett. 84, 4484 (2004); http://dx.doi.org/10.1063/1.1756191 (3 pages) | Cited 32 times

Online Publication Date: 14 May 2004

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We demonstrate the use of 10 and 30 keV focused beams of Ga+ ions to thin, slice, weld, and alter the structure and composition of multiwalled carbon nanotubes at precise locations along the nanotube axis. This strategy of harnessing ion-beam-induced defect generation and doping could be attractive for modulating chemical and electrical properties along the nanotube length, and fabricate nanotube heterostructures and networks for device applications. © 2004 American Institute of Physics.
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61.82.Rx Nanocrystalline materials
61.46.-w Structure of nanoscale materials
61.80.Jh Ion radiation effects
81.65.-b Surface treatments
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
81.05.ub Fullerenes and related materials
61.72.up Other materials

Composition of Ge(Si) islands in the growth of Ge on Si(111)

Fulvio Ratto, Federico Rosei, Andrea Locatelli, Salia Cherifi, Stefano Fontana, Stefan Heun, Pierre-David Szkutnik, Anna Sgarlata, Maurizio De Crescenzi, and Nunzio Motta

Appl. Phys. Lett. 84, 4526 (2004); http://dx.doi.org/10.1063/1.1758304 (3 pages) | Cited 24 times

Online Publication Date: 14 May 2004

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X-ray photoemission electron microscopy (XPEEM) is used to investigate the chemical composition of Ge/Si individual islands obtained by depositing Ge on Si(111) substrates in the temperature range 460–560 °C. We are able to correlate specific island shapes with a definite chemical contrast in XPEEM images, at each given temperature. In particular, strained triangular islands exhibit a Si surface content of 5%–20%, whereas it grows up to 30%–40% for “atoll-like” structures. The island’s stage of evolution is shown to be correlated with its surface composition. Finally, by plotting intensity contour maps, we find that island centers are rich in Si. © 2004 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.47.Fg Semiconductor surfaces
68.55.A- Nucleation and growth
68.35.B- Structure of clean surfaces (and surface reconstruction)
79.60.-i Photoemission and photoelectron spectra
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Nanowire transistors with ferroelectric gate dielectrics: Enhanced performance and memory effects

Bo Lei, Chao Li, Daihua Zhang, Q. F. Zhou, K. K. Shung, and Chongwu Zhou

Appl. Phys. Lett. 84, 4553 (2004); http://dx.doi.org/10.1063/1.1759069 (3 pages) | Cited 31 times

Online Publication Date: 14 May 2004

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Integration of ferroelectric materials into nanoscale field-effect transistors offers enormous promise for superior transistor performance and also intriguing memory effects. In this study, we have incorporated lead zirconate titanate (PZT) into In2O3 nanowire transistors to replace the commonly used SiO2 as the gate dielectric. These transistors exhibited substantially enhanced performance as a result of the high dielectric constant of PZT, as revealed by a 30-fold increase in the transconductance and a 10-fold reduction in the subthreshold swing when compared to similar SiO2-gated devices. Furthermore, memory effects were observed with our devices, as characterized by a counter-clockwise loop in current-versus-gate-bias curves that can be attributed to the switchable remnant polarization of PZT. Our method can be easily generalized to other nanomaterials systems and may prove to be a viable way to obtain nanoscale memories. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices

One-dimensional nanostructures grown inside carbon nanotubes upon vapor deposition: A growth kinetic approach

Qiu-Xiang Liu, Cheng-Xin Wang, Yu-Hua Yang, and Guo-Wei Yang

Appl. Phys. Lett. 84, 4568 (2004); http://dx.doi.org/10.1063/1.1759769 (3 pages) | Cited 8 times

Online Publication Date: 14 May 2004

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Aiming at controlling the growth of one-dimensional nanostructures inside carbon nanotubes, a growth kinetic approach was performed, with respect to the effect of nanosize induced additional pressure on growing kinetics, to theoretically elucidate the growth of one-dimensional nanostructures inside carbon nanotubes upon vapor deposition. Our analysis showed that the growth rate of one-dimensional nanostructures would go much higher once nuclei formed inside carbon nanotubes, due to the effect of surface tension induced by the nanosize curvature of carbon nanotubes. The results based on the proposed model are in good agreement with experimental data for nanowires grown inside carbon nanotubes upon vapor deposition. © 2004 American Institute of Physics.
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81.07.De Nanotubes
81.05.U- Carbon/carbon-based materials
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