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2 Dec 2002

Volume 81, Issue 23, pp. 4315-4476

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Effect of particle size on magnetic properties of zinc chromite synthesized by sol–gel method

X. H. Chen, H. T. Zhang, C. H. Wang, X. G. Luo, and P. H. Li

Appl. Phys. Lett. 81, 4419 (2002); http://dx.doi.org/10.1063/1.1526921 (3 pages) | Cited 13 times

Online Publication Date: 25 November 2002

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Spinel zinc chromite nanocrystals with various grain sizes ranging from 6.8 to 32 nm have been synthesized using a formalin sol–gel method. Samples were characterized by x-ray diffraction, transmission electron micrograph, and superconducting quantum interference device magnetometer. An effect of particle size on magnetic properties is observed. The decrease in particle size leads to a large enhancement of magnetization. Antiferromagnetic transition disappears when the particles reach a critical size, which can be explained by the deviation from the normal spinel structure in the cation distribution induced by particle size. © 2002 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Ee Antiferromagnetics
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

“Gentle lithography” with benzene on Si(100)

Peter Kruse and Robert A. Wolkow

Appl. Phys. Lett. 81, 4422 (2002); http://dx.doi.org/10.1063/1.1526459 (3 pages) | Cited 14 times

Online Publication Date: 25 November 2002

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A scanning tunneling microscopy (STM) based nanolithographic method has been demonstrated. The previously reported tip-induced desorption of benzene from Si(100) was utilized to pattern the surface with close to atomic precision. This kind of lithography can take place under very mild conditions. Writing occurs with a STM tip bias of 2.8 V. No heating, etching, or exposure to photons is required. The method is best suited for small to medium sized molecules and can be said to be reliable for resolutions of 2 nm and above. In this letter, we have demonstrated patterning areas of the surface with ethylene and vinyl ferrocene. © 2002 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors
81.16.Ta Atom manipulation

Cu/SiO2−x nanowires with compositional modulation structure grown via thermal evaporation

Y. G. Wang, A. Z. Jin, and Z. Zhang

Appl. Phys. Lett. 81, 4425 (2002); http://dx.doi.org/10.1063/1.1526453 (3 pages) | Cited 5 times

Online Publication Date: 25 November 2002

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One-dimensional compositional modulation has been achieved in Cu/SiO2−x nanowires prepared at the substrate temperature of 1000 °C by thermal evaporation of a cuprous oxide and silicon mono-oxide mixture. The synthesized nanowires consist of the Cu spheres uniformly piled up along the longitudinal direction of the nanowires to form a modulation structure with an average period of about 140 nm. This periodicity could be adjusted by changing the CuO concentration in the source materials mixture. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials

Measurement of three-dimensional force fields with atomic resolution using dynamic force spectroscopy

H. Hölscher, S. M. Langkat, A. Schwarz, and R. Wiesendanger

Appl. Phys. Lett. 81, 4428 (2002); http://dx.doi.org/10.1063/1.1525056 (3 pages) | Cited 60 times

Online Publication Date: 25 November 2002

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Using dynamic force microscopy and spectroscopy in an ultrahigh vacuum (“noncontact atomic force microscopy”) at low temperatures, we measured three-dimensional force fields with atomic resolution. The method is based on the systematic recording of the frequency shift of a cantilever oscillating near the sample surface. The presented experimental results were obtained on a NiO(001) sample surface with an iron-coated silicon tip, but the measurement principle can be extended to any tip–sample system. © 2002 American Institute of Physics.
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68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
07.79.Lh Atomic force microscopes

Fabrication of 70 nm channel length polymer organic thin-film transistors using nanoimprint lithography

Michael D. Austin and Stephen Y. Chou

Appl. Phys. Lett. 81, 4431 (2002); http://dx.doi.org/10.1063/1.1526457 (3 pages) | Cited 107 times

Online Publication Date: 25 November 2002

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We report on the fabrication of short-channel polymer organic thin-film transistors (OTFTs) using nanoimprint lithography. Currently, there is significant interest in OTFTs due to their potential application in inexpensive, large-area electronics. However, polymer carrier mobilities are typically poor, and thus to increase the OTFT drive current per unit area, there is a need for short-channel devices. We have fabricated working devices with channel lengths from 1 μm down to 70 nm with high yields. The performance of these devices was studied as the channel length was reduced. We find that drive current density increases as expected, while the on/off current ratio remains 104. However, at short-channel lengths, OTFTs no longer saturate due to space charge limiting current effects. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Fabrication and thermal stability of arrays of Fe nanodots

Kai Liu, J. Nogués, C. Leighton, H. Masuda, K. Nishio, I. V. Roshchin, and Ivan K. Schuller

Appl. Phys. Lett. 81, 4434 (2002); http://dx.doi.org/10.1063/1.1526458 (3 pages) | Cited 60 times

Online Publication Date: 25 November 2002

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We have fabricated arrays of 60-nm-size magnetic Fe nanodots over a 1-cm2-size area using nanoporous alumina membranes as shadow masks. The size and size distribution of the nanodots correlate very well with that of the membrane pores. By placing an antiferromagnetic FeF2 layer underneath the Fe nanodots, an exchange anisotropy can be introduced into the Fe/FeF2 system. We have observed an increase in the magnetic hysteresis loop squareness in biased nanodots, suggesting that exchange bias may be used as a tunable source of anisotropy to stabilize the magnetization in such nanodots. © 2002 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.07.Bc Nanocrystalline materials

Fabrication of nanoporous gold nanowires

Chunxin Ji and Peter C. Searson

Appl. Phys. Lett. 81, 4437 (2002); http://dx.doi.org/10.1063/1.1526920 (3 pages) | Cited 53 times

Online Publication Date: 25 November 2002

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We report a method for the fabrication of nanoporous nanowires with high surface area and well-defined pore morphology. The nanoporous nanowires are formed in a two-step process involving electrochemical deposition of a single-phase, two-component AxB1−x alloy into a nanoporous template, and subsequent chemical etching of one component from the alloy after removal from the template. Here, we demonstrate the fabrication of nanoporous gold nanowires and also show that nonporous segments can be incorporated into multisegment nanowires. © 2002 American Institute of Physics.
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81.07.Vb Quantum wires
81.05.Bx Metals, semimetals, and alloys
81.05.Rm Porous materials; granular materials
81.07.Bc Nanocrystalline materials
68.65.La Quantum wires (patterned in quantum wells)
61.46.-w Structure of nanoscale materials

Optical characteristics of SiO2 photonic band-gap crystal with ferroelectric perovskite oxide

Bog G. Kim, Kunjal S. Parikh, Geoffrey Ussery, Anvar Zakhidov, Ray H. Baughman, Eli Yablonobitch, and Bruce S. Dunn

Appl. Phys. Lett. 81, 4440 (2002); http://dx.doi.org/10.1063/1.1526163 (3 pages) | Cited 9 times

Online Publication Date: 25 November 2002

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We have made SiO2 photonic band-gap crystal infiltrated with ferroelectric perovskite oxide (BaTiO3, PbTiO3, SrTiO3) by using self-assembly and sol-gel methods. Microscopic optical reflectivity has been measured to characterize pseudogap properties of small single crystallites with different orientations. We have found significant redshift of pseudogap in opal infiltrated with BaTiO3 or PbTiO3, whereas negligible shift in opal with SrTiO3 infiltration. © 2002 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Ha Other nonmetallic inorganics

Photon mapping of quantum dots using a scanning tunneling microscope

U. Håkanson, M. K.-J. Johansson, M. Holm, C. Pryor, L. Samuelson, W. Seifert, and M.-E. Pistol

Appl. Phys. Lett. 81, 4443 (2002); http://dx.doi.org/10.1063/1.1527239 (3 pages) | Cited 16 times

Online Publication Date: 25 November 2002

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Scanning tunneling microscopy (STM) and scanning tunneling luminescence (STL) have been used to investigate the geometric and optical properties of individual self-assembled InP quantum dots overgrown with a thin layer of GaInP. STL spectra and monochromatic photon maps were used to correlate the surface topography with the optical properties of single quantum dots. We find a spatial resolution of about 10 nm in the photon maps. Theoretical emission spectra were calculated by six-band k⋅p theory using a realistic shape of the dot as well as of the cap layer. The calculated emission spectrum of a single dot is in good agreement with the experimental findings. © 2002 American Institute of Physics.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
73.21.La Quantum dots
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
78.60.Hk Cathodoluminescence, ionoluminescence
78.55.Cr III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
71.15.-m Methods of electronic structure calculations

Variation of Raman feature on excitation wavelength in silicon nanowires

Shu-Lin Zhang, Wei Ding, Yan Yan, Jiang Qu, Bibo Li, Le-yu Li, Kwok To Yue, and Dapeng Yu

Appl. Phys. Lett. 81, 4446 (2002); http://dx.doi.org/10.1063/1.1527228 (3 pages) | Cited 20 times

Online Publication Date: 25 November 2002

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A variation of Raman feature on excitation wavelength in silicon nanowires was observed. Based on the quantum size confinement effect, the resonant Raman scattering phenomenon and the existence of different sizes of Si grains in the samples, a plausible mechanism to interpret the novel feature was proposed and supported by experimental facts. © 2002 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.-w Structure of nanoscale materials

Spontaneous localization in InAs/GaAs self-assembled quantum-dot molecules

Weidong Sheng and Jean-Pierre Leburton

Appl. Phys. Lett. 81, 4449 (2002); http://dx.doi.org/10.1063/1.1526167 (3 pages) | Cited 23 times

Online Publication Date: 25 November 2002

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Spontaneous localization of hole states is predicted at all separations in vertically stacked InAs/GaAs self-assembled quantum dots. Eight-band k⋅p theory shows that valence band mixing enhanced by the unique three-dimensional strain distribution, subjects holes to very different environment than electrons. As a result, low energy holes are confined to their respective dots without forming bonding or antibonding states. This localization plays the same role as a vertically applied electric field in coupled quantum systems, and substantially decreases the exciton binding energy, which may be an impediment to the formation of entangled states in quantum-dot molecules. © 2002 American Institute of Physics.
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73.21.La Quantum dots
73.20.At Surface states, band structure, electron density of states
71.15.-m Methods of electronic structure calculations
03.67.Lx Quantum computation architectures and implementations

Spontaneous growth of an InAs nanowire lattice in an InAs/GaSb superlattice

B. Z. Nosho, B. R. Bennett, L. J. Whitman, and M. Goldenberg

Appl. Phys. Lett. 81, 4452 (2002); http://dx.doi.org/10.1063/1.1526164 (3 pages) | Cited 13 times

Online Publication Date: 25 November 2002

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We describe a lattice of InAs nanowires that spontaneously organizes in three dimensions within an InAs/GaSb superlattice grown under high As4 flux. As characterized by x-ray diffraction and cross-sectional scanning tunneling microscopy, the periodic nanowires are ∼10 nm high, 120 nm wide, and many microns long along [110], with face-centered cubic-like vertical ordering within the superlattice. The unusual vertical ordering creates a lateral composition modulation with half the period of the nanowires. The structure appears to arise from the InAs misfit stress combined with specific InAs and GaSb growth kinetic effects. © 2002 American Institute of Physics.
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68.65.Cd Superlattices
81.07.Vb Quantum wires
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Nanomechanical resonant structures in nanocrystalline diamond

L. Sekaric, J. M. Parpia, H. G. Craighead, T. Feygelson, B. H. Houston, and J. E. Butler

Appl. Phys. Lett. 81, 4455 (2002); http://dx.doi.org/10.1063/1.1526941 (3 pages) | Cited 78 times

Online Publication Date: 25 November 2002

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We report the fabrication and the operation of nanomechanical resonant structures in nanocrystalline diamond. For this purpose, continuous diamond films as thin as 80 nm were grown using microwave plasma enhanced chemical vapor deposition. The lateral dimensions of the fabricated structures were as small as 50 nm and the measured mechanical resonant frequencies were up to 640 MHz. The mechanical quality factors were in the range of 2500–3000 at room temperature. The elastic properties of these films obtained via the resonant measurements indicate a Young’s modulus close to that of single-crystal diamond. © 2002 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.05.U- Carbon/carbon-based materials
62.25.-g Mechanical properties of nanoscale systems
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.)
62.20.D- Elasticity
07.10.Cm Micromechanical devices and systems

Nanowire resonant tunneling diodes

M. T. Björk, B. J. Ohlsson, C. Thelander, A. I. Persson, K. Deppert, L. R. Wallenberg, and L. Samuelson

Appl. Phys. Lett. 81, 4458 (2002); http://dx.doi.org/10.1063/1.1527995 (3 pages) | Cited 156 times

Online Publication Date: 25 November 2002

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Semiconductor heterostructures and their implementation into electronic and photonic devices have had tremendous impact on science and technology. In the development of quantum nanoelectronics, one-dimensional (1D) heterostructure devices are receiving a lot of interest. We report here functional 1D resonant tunneling diodes obtained via bottom-up assembly of designed segments of different semiconductor materials in III/V nanowires. The emitter, collector, and the central quantum dot are made from InAs and the barrier material from InP. Ideal resonant tunneling behavior, with peak-to-valley ratios of up to 50:1 and current densities of 1 nA/μm2 was observed at low temperatures. © 2002 American Institute of Physics.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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