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4 Jun 2007

Volume 90, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 90, 233105 (2007); http://dx.doi.org/10.1063/1.2747052 (3 pages)

Youhui Gao, Daisuke Shindo, Yuping Bao, and Kannan Krishnan
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Sharp assembly of small clusters obtained by atom deposition for room temperature Coulomb blockade

N. Lidgi-Guigui, P. Seneor, F. Nguyen Van Dau, A. Friederich, A. Vaurès, and C. Deranlot

Appl. Phys. Lett. 90, 233101 (2007); http://dx.doi.org/10.1063/1.2741399 (3 pages)

Online Publication Date: 4 June 2007

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The growth of a nanocluster assembly on a processed AlOx and its electronic transport behavior are investigated. An Ar+ plasma was used in order to create defects of high trapping energy on an AlOx layer. This process promotes a shift of the cluster distribution towards smaller sizes and allows to sharpen it. In a second part, the authors show that the application of this techniqueto clusters inserted in a tunnel junction can lead to a dramatic increase in the temperature range over which Coulomb blockade can be observed.
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81.16.Dn Self-assembly
73.23.Hk Coulomb blockade; single-electron tunneling
81.15.Jj Ion and electron beam-assisted deposition; ion plating
52.77.Dq Plasma-based ion implantation and deposition
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)

Formation and photopatterning of nanoporous titania thin films

Oun-Ho Park, Joy Y. Cheng, Hyun Suk Kim, Philip M. Rice, Teya Topuria, Robert D. Miller, and Ho-Cheol Kim

Appl. Phys. Lett. 90, 233102 (2007); http://dx.doi.org/10.1063/1.2746081 (3 pages) | Cited 7 times

Online Publication Date: 4 June 2007

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Photopatternable nanoporous titania thin films were generated from mixtures of an organic diblock copolymer, poly(styrene-b-ethylene oxide) (PS-b-PEO), and an oligomeric titanate (OT) prepared from a chelated titanium isopropoxide. The PS-b-PEO templates well-defined microdomains in thin films of the mixtures, which upon thermal treatment at 450 °C, become nanopores in titania. Average pore size and porosity are controlled by the molecular weight and loading level of the PS-b-PEO, respectively. Patterns of nanoporous titania were created by selectively exposing UV light on the mixture films. The UV irradiation destroys the chelating bond and induces the cross-linking reaction of the OT. Subsequent wet development followed by thermal treatment gives patterned nanoporous films of anatase phase titania.
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81.05.Rm Porous materials; granular materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Rf Micro- and nanoscale pattern formation
68.55.A- Nucleation and growth
81.40.Gh Other heat and thermomechanical treatments
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Control of magnesium oxide nanowire morphologies by ambient temperature

Kazuki Nagashima, Takeshi Yanagida, Hidekazu Tanaka, and Tomoji Kawai

Appl. Phys. Lett. 90, 233103 (2007); http://dx.doi.org/10.1063/1.2746086 (3 pages) | Cited 21 times

Online Publication Date: 4 June 2007

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Although controlling morphologies of oxide nanowires formed using vapor-liquid-solid (VLS) mechanism is desired in developing functional oxide-nanowire applications, a comprehensive understanding of the key factors affecting oxide-nanowire VLS growth is still lacking. Here, the authors demonstrate the controllability of magnesium oxide nanowire morphologies by varying the ambient temperature and discuss the underlying mechanism. Decreasing the ambient temperature resulted in shorter, tapered, and square-rod shaped nanowires, whereas increasing the ambient temperature allowed fabricating longer and untapered nanowires. The variation of oxide-nanowire morphologies is interpreted in terms of the competition between the VLS growth and the sidewall growth due to the variation of adatom transport.
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61.46.-w Structure of nanoscale materials

In situ study of the growth of ZnO nanosheets using environmental scanning electron microscope

Jingmin Zhang, Xinzheng Zhang, Li Chen, Jun Xu, Liping You, Hengqiang Ye, and Dapeng Yu

Appl. Phys. Lett. 90, 233104 (2007); http://dx.doi.org/10.1063/1.2746947 (3 pages) | Cited 8 times

Online Publication Date: 4 June 2007

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The authors demonstrated an investigation of the real-time growth of ZnO nanosheets via in situ observation in an environmental scanning electron microscope. It was found that ZnO nanosheets were grown in a two-stage process: [2mathmath0]-oriented nanowires were grown first, and then ZnO nanosheets grew perpendicularly on the parent nanowires along the [0001] axis. The authors’ results revealed that the change of the ZnO growth direction from [2mathmath0] (a axis) to [0001] (c axis) can be achieved by control of the growth temperature.
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81.16.-c Methods of micro- and nanofabrication and processing
68.65.La Quantum wires (patterned in quantum wells)

Electron holography of core-shell Co/CoO spherical nanocrystals

Youhui Gao, Daisuke Shindo, Yuping Bao, and Kannan Krishnan

Appl. Phys. Lett. 90, 233105 (2007); http://dx.doi.org/10.1063/1.2747052 (3 pages) | Cited 2 times

Online Publication Date: 5 June 2007

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Phase profiles of core-shell Co/CoO nanocrystals are imaged using off-axis electron holography. Contributions of mean inner potential and magnetic induction to the phase shift are extracted, respectively, to quantitatively characterize the nanocrystal geometry and magnetic spin arrangement in a self-assembled nanocrystal chain. It is also found that the spin of 11 nm diameter Co core encapsulated with 5-nm-thick CoO shell remains stable even at an elevated temperature of 200 °C, indicating that the magnetically thermal stability of cobalt nanocrystals is remarkably improved due to the exchange coupling between the ferromagnetic core and antiferromagnetic shell.
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61.46.Hk Nanocrystals
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions

Development of a vitamin-protein sensor based on carbon nanotube hybrid materials

Takamichi Hirata, Shoji Amiya, Masahiro Akiya, Osamu Takei, Takafumi Sakai, and Rikizo Hatakeyama

Appl. Phys. Lett. 90, 233106 (2007); http://dx.doi.org/10.1063/1.2746077 (3 pages) | Cited 6 times

Online Publication Date: 5 June 2007

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A bionanosensor consisting of a field effect transistor chip and containing a mixture of poly(ethylene glycol)-grafted single-walled carbon nanotubes (SWCNTs) and SWCNTs modified with a protein (avidin) which binds with a specific vitamin (biotin) is developed. An increase in impedance due to biotin-avidin binding is observed when biotin is injected, while the injection of other vitamins resulted in a decrease in impedance. This bionanosensor reacts quickly ( ∼ 60 s); in addition, the impedance recovers almost to its initial value when the bionanosensor is washed with distilled water; thus, the vitamins do not bind directly with the SWCNTs.
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87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.80.-y Biophysical techniques (research methods)
87.14.E- Proteins
87.15.N- Properties of solutions of macromolecules
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Polycrystalline tetrabenzoporphyrin organic field-effect transistors with nanostructured channels

Patrick B. Shea, Charlene Chen, Jerzy Kanicki, Lisa R. Pattison, Pierre Petroff, Hiroko Yamada, and Noboru Ono

Appl. Phys. Lett. 90, 233107 (2007); http://dx.doi.org/10.1063/1.2745227 (3 pages) | Cited 15 times

Online Publication Date: 5 June 2007

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Solution-processed organic thin-film field-effect transistors (OFETs) were fabricated using a precursor form of the organic semiconductor tetrabenzoporphyrin (TBP) deposited on a thermal silicon oxide gate insulator patterned with nanometer-scale trenches. Thermal conversion of the precursor film to TBP was enhanced by ordered TBP aggregation in the prepatterned trenches, demonstrating precise control and placement of long- and short-range ordering of the organic semiconductor. OFETs with channels parallel to trench direction growth were found to have field-effect mobility approaching one order of magnitude greater than transistors fabricated with the channel oriented perpendicular to dendrimer growth.
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85.30.Tv Field effect devices

Intrinsic current gain cutoff frequency of 30 GHz with carbon nanotube transistors

A. Le Louarn, F. Kapche, J.-M. Bethoux, H. Happy, G. Dambrine, V. Derycke, P. Chenevier, N. Izard, M. F. Goffman, and J.-P. Bourgoin

Appl. Phys. Lett. 90, 233108 (2007); http://dx.doi.org/10.1063/1.2743402 (3 pages) | Cited 26 times

Online Publication Date: 5 June 2007

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High frequency capabilities of carbon nanotube field-effect transistors (CNTFETs) are investigated. Structures with a large number of single-walled carbon nanotubes were fabricated using dielecrophoresis to increase the density of nanotubes in the device channel. The authors obtained an intrinsic current gain cutoff frequency of 30 GHz establishing state-of-the-art high frequency (hf) potentialities of CNTFETs. The device also showed a maximum stable gain above 10 dB at 20 GHz. Finally, the parameters of an equivalent circuit model of multitube CNTFET at 20 GHz are determined, which open the route to the modeling of nanotubes-based hf electronics.
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85.35.Kt Nanotube devices
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Adaptive bonding technique for precise assembly of three-dimensional microstructures

Sang-Hu Park, Jun-Ho Jeong, Dae-Geun Choi, Ki-Don Kim, Ali Ozhan Altun, Eung-Sug Lee, Dong-Yol Yang, and Kwang-Sup Lee

Appl. Phys. Lett. 90, 233109 (2007); http://dx.doi.org/10.1063/1.2746085 (3 pages) | Cited 5 times

Online Publication Date: 6 June 2007

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Precise fabrication of three-dimensional (3D) self-standing microstructures on thin glass plates via two-photon induced polymerization (TPP) has been an important issue for innovative 3D nanodevices and microdevices. However, there are still issues remaining to be solved, such as building 3D microstructures on opaque materials via TPP and being able to implant them as functional parts onto practical systems. To settle these issues simply and effectively, the authors propose a contact print lithography (CPL) method using an ultraviolet-curable polymer layer. They report some of the possibilities and potential of CPL by presenting their results for transplanting 3D microstructures onto large-area substrates and also their examination of some of the effects of the process parameters on CPL.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Nanowire metal-oxide-semiconductor field effect transistor with doped epitaxial contacts for source and drain

G. M. Cohen, M. J. Rooks, J. O. Chu, S. E. Laux, P. M. Solomon, J. A. Ott, R. J. Miller, and W. Haensch

Appl. Phys. Lett. 90, 233110 (2007); http://dx.doi.org/10.1063/1.2746946 (3 pages) | Cited 26 times

Online Publication Date: 6 June 2007

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The authors report the fabrication of a p-field effect transistor (FET) and an n-FET with a silicon nanowire channel and doped silicon source and drain regions. The silicon nanowires were synthesized by the vapor-liquid-solid method. For p-FETs the source and drain regions were formed by adding boron doped silicon to the unintentionally doped nanowire body at predefined locations using in situ doped silicon epitaxy. For n-FETs the epitaxial source and drain regions were grown undoped and were later implanted with P and As. The measured Id-Vg characteristics of the devices exhibited unipolar transport, while reference FETs made with nanowires from the same batch but with Schottky (metal) contacts exhibited ambipolar characteristics.
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85.30.Tv Field effect devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Self-annihilation of electron-irradiation-induced defects in InAsxP1−x/InP multiquantum well solar cells

Aurangzeb Khan, A. Freundlich, Jihua Gou, A. Gapud, M. Imazumi, and M. Yamaguchi

Appl. Phys. Lett. 90, 233111 (2007); http://dx.doi.org/10.1063/1.2747180 (3 pages) | Cited 2 times

Online Publication Date: 6 June 2007

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Irradiation by 1 MeV electron of InAsxP1−x/InP multiquantum well (MQW) solar cells results in the appearance of a dominant electron-emitting level E1, in the upper half of the band gap. The level E1, however, exhibits an interesting behavior as it was found to completely anneal out with storage at room temperature with no change in other majority carrier levels. No any other defect has been observed in electron-irradiated n-type InAsxP1−x/InP MQW solar cell structures, which contrasts to conventional n-InP solar cell counterparts (structures without QWs). The study reveals that introduction of QWs in the intrinsic region of p-i-n structures enhances significantly the device radiation tolerance well beyond what has been thus far reported for conventional Si or III-V semiconductor-based solar cells.
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84.60.Jt Photoelectric conversion
61.80.Fe Electron and positron radiation effects
61.82.Fk Semiconductors
71.55.Eq III-V semiconductors
68.65.Fg Quantum wells
61.72.Cc Kinetics of defect formation and annealing

Fe/Fe oxide nanocomposite particles with large specific absorption rate for hyperthermia

Q. Zeng, I. Baker, J. A. Loudis, Y. Liao, P. J. Hoopes, and J. B. Weaver

Appl. Phys. Lett. 90, 233112 (2007); http://dx.doi.org/10.1063/1.2746064 (3 pages) | Cited 18 times

Online Publication Date: 7 June 2007

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Using a water-in-oil microemulsion with cetyl trimethyl ammonium bromide as the surfactant, iron was reduced to form a metallic core on which a passivating oxide shell was grown. Transmission electron microscopy, vibrating sample magnetometry, and heating measurements were used to characterize these monodispersed magnetic Fe/Fe3O4 composite nanoparticles with respect to the possible application for magnetic hyperthermia treatments of cancer. The aim is to utilize the fact that an iron core (high saturation magnetization) will give a greater heating effect than iron oxide, while the iron oxide coating will allow the nanoparticles to be observed using magnetic resonance imaging so that therapy can be effectively monitored and targeted. The largest specific absorption rate obtained was 345 W/g under an alternating magnetic field of 150 Oe at 250 kHz.
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87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.50.wp Therapeutic applications
87.19.Pp Biothermics and thermal processes in biology
87.61.-c Magnetic resonance imaging
82.70.Kj Emulsions and suspensions
82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)
81.65.Rv Passivation

Characterization of pattern transfer in the fabrication of magnetic nanostructure arrays by block copolymer lithography

T. Kubo, J. S. Parker, M. A. Hillmyer, and C. Leighton

Appl. Phys. Lett. 90, 233113 (2007); http://dx.doi.org/10.1063/1.2743900 (3 pages) | Cited 11 times

Online Publication Date: 7 June 2007

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The authors report the fabrication of large-area antidot arrays using cylinder-forming polystyrene-polyisoprene-polylactide triblock terpolymer templates. 30 nm antidots were generated after removal of the minority polymer component by aqueous degradation, oxygen reactive ion etching, and subsequent Ar ion beam milling to transfer the pattern to an underlying Ni80Fe20 film. Emphasis was placed on characterization of the pattern transfer, which was tracked using a combination of atomic force microscopy, magnetometry, and magnetotransport. It is demonstrated that variable temperature magnetometry and transport measurements are excellent probes of the progress of the ion milling into underlying magnetic layers.
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81.07.Ta Quantum dots
81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
68.65.Hb Quantum dots (patterned in quantum wells)
75.75.-c Magnetic properties of nanostructures
73.63.Kv Quantum dots

Theoretical consideration on the formation of nanotube following the Kirkendall effect

S. Prasad and A. Paul

Appl. Phys. Lett. 90, 233114 (2007); http://dx.doi.org/10.1063/1.2747184 (3 pages) | Cited 7 times

Online Publication Date: 7 June 2007

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Theoretical understanding on the formation of nanotube following the Kirkendall effect is developed. The relations for growth rate of the product phase and consumption rate of core and shell are derived considering diffusion-controlled process. The controlling factors to produce good nanotube following the Kirkendall effect are identified.
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81.16.-c Methods of micro- and nanofabrication and processing
68.35.Fx Diffusion; interface formation
61.46.Fg Nanotubes

Growth of zinc oxide nanopillars on an iridium/yttria-stabilized zirconia/silicon substrate

Günther M. Prinz, Anton Reiser, Tobias Röder, Martin Schirra, Martin Feneberg, Uwe Röder, Rolf Sauer, Klaus Thonke, Stefan Gsell, Matthias Schreck, and Bernd Stritzker

Appl. Phys. Lett. 90, 233115 (2007); http://dx.doi.org/10.1063/1.2747191 (3 pages) | Cited 7 times

Online Publication Date: 7 June 2007

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Zinc oxide nanopillars were grown by a self-catalyzed growth process on an epitaxial Ir/yttria-stabilized zirconia/Si(111) multilayer structure in an optically heated tube furnace. The pillars obtained stand upright parallel to each other with their c-axis perpendicular to the sample surface. Problems due to alloying of Zn with Si are completely avoided, and no irregularities of the pillars in the initial growth phase are found. Cathodoluminescence measurements show narrow linewidths below 700 μeV due to the excellent crystal quality. Termination of ZnO pillars with a flat metallic iridium layer is an attractive issue towards an optical cavity for laser action.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
78.55.Et II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence

Detection of nanomechanical motion by evanescent light wave coupling

I. De Vlaminck, J. Roels, D. Taillaert, D. Van Thourhout, R. Baets, L. Lagae, and G. Borghs

Appl. Phys. Lett. 90, 233116 (2007); http://dx.doi.org/10.1063/1.2746067 (3 pages) | Cited 19 times

Online Publication Date: 11 June 2007

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The authors demonstrate a technique allowing sensitive nanomechanical motion detection based on the evanescent light wave coupling between two photonic nanowires. Any relative motion between the nanowires results in a change in light coupling, providing a means of registering motion. The in-plane vibrations of a 220 nm×400 nm×10 μm nanomechanical resonator were recorded using this method. An analysis of the sensitivity reveals the potential of this integrated technique to provide fast and sensitive motion detection.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Band gap energy modifications observed in trivalent In substituted nanocrystalline SnO2

C. Drake and S. Seal

Appl. Phys. Lett. 90, 233117 (2007); http://dx.doi.org/10.1063/1.2746407 (3 pages) | Cited 11 times

Online Publication Date: 11 June 2007

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The effect of In doping concentration on the optical band gap of nano-SnO2 is investigated as a function of calcination temperature. Changes in the band gap explain the room temperature H2 gas sensing of doped nano-SnO2. The band gap was found to be lower than those reported for SnO2 (3.6 eV) from 2.55 to 3.43 eV and may be explained by the presence of nonequilibrium oxygen vacancies in the oxide lattice and band bending effects at the nanoscale.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds
73.22.-f Electronic structure of nanoscale materials and related systems
61.72.S- Impurities in crystals
61.72.J- Point defects and defect clusters
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Scanning gate microscopy of InAs nanowires

X. Zhou, S. A. Dayeh, D. Wang, and E. T. Yu

Appl. Phys. Lett. 90, 233118 (2007); http://dx.doi.org/10.1063/1.2746422 (3 pages) | Cited 5 times

Online Publication Date: 11 June 2007

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Scanning gate microscopy, in which a conductive probe tip in an atomic force microscope is employed as a local, nanoscale top gate contact, has been used to characterize local carrier and current modulation effects in a 45 nm diameter InAs semiconductor nanowire grown by metal organic chemical vapor deposition. Measurement of current flow in the nanowire as a function of tip position reveals that for both positive and negative tip bias voltages, carrier and current modulation is strongest when the probe tip is near the source and drain nanowire contacts, reaching a global maximum approximately 100–200 nm distant from the source contact and a secondary maximum a similar distance from the drain contact and decreasing at greater tip-contact distances. This effect is explained, with verification by numerical simulation, as a consequence of the capacitance between the tip and the source and drain contacts as a function of tip location. Measurement of transconductance as a function of tip position reveals that the transconductance is approximately 80%–90% greater near the source contact than at the center of the nanowire.
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68.65.La Quantum wires (patterned in quantum wells)
73.63.Nm Quantum wires
68.37.Ps Atomic force microscopy (AFM)

Sensitive detection of nanoparticles using metallic nanoslit arrays

Kuang-Li Lee, Chia-Wei Lee, and Pei-Kuen Wei

Appl. Phys. Lett. 90, 233119 (2007); http://dx.doi.org/10.1063/1.2746957 (3 pages) | Cited 5 times

Online Publication Date: 11 June 2007

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The detection sensitivity of small nanoparticles was studied using surface plasmons in a metallic nanoslit array. When 13 nm gold nanoparticles were immobilized on the array, the resonant wavelength and intensity of surface plasmons are substantially changed. Spectroscopic measurements and finite-difference time-domain calculations identified that the surface plasmons in the slit gap had a greater sensitivity than those on the outside surface. Using a nanoslit array with a gap of 50 nm, a thickness of 150 nm, and a period of 600 nm, the authors achieved a detection sensitivity of 1 nanoparticle/μm2 for a 0.2% intensity change.
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81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
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