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14 May 2007

Volume 90, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 201101 (2007); http://dx.doi.org/10.1063/1.2739308 (3 pages)

Luca Sapienza, Angela Vasanelli, Cristiano Ciuti, Christophe Manquest, Carlo Sirtori, Raffaele Colombelli, and Ulf Gennser
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Direct observation of electromigration-induced surface atomic steps in Cu lines by in situ transmission electron microscopy

Kuan-Chia Chen, Chien-Neng Liao, Wen-Wei Wu, and Lih-Juann Chen

Appl. Phys. Lett. 90, 203101 (2007); http://dx.doi.org/10.1063/1.2740109 (3 pages) | Cited 8 times

Online Publication Date: 14 May 2007

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Surface atomic steps in unpassivated copper lines under electromigration (EM) have been directly observed in ultrahigh vacuum by in situ transmission electron microscopy (in situ TEM). The combination of {111} planes and ⟨110⟩ directions for crystalline Cu were found to be the most favored EM paths. The in situ TEM study of EM-induced evolution of Cu surface structures provides a sound basis for understanding the dependence of EM-induced atomic migration mechanism on crystal orientation of crystalline Cu. The understanding shall lead to the effective strategy of using appropriate passivation layer to suppress the electromigration.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.65.Rv Passivation

Fabrication of comblike nanostructures using self-assembled cluster arrays of molybdenum oxides

Arifumi Okada, Masamichi Yoshimura, and Kazuyuki Ueda

Appl. Phys. Lett. 90, 203102 (2007); http://dx.doi.org/10.1063/1.2739088 (3 pages) | Cited 1 time

Online Publication Date: 15 May 2007

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Self-assembled cluster arrays formed at the initial stage of Mo(110) oxidation and subsequent fabrication of comblike structures have been studied by scanning tunneling microscopy. After 180 L oxygen exposure, large protrusions are arranged as self-assembly along the [math13] or [1math3] direction. The average diameter and height of each protrusion are estimated to be approximately 0.8 and 0.15–0.2 nm, which correspond to the sizes of clusters of several atoms. The cluster arrays correspond to the MoO3 nucleation at the antiphase boundaries of the MoO2 surface. After thermal evaporation of the cluster arrays, comblike step structures consisting of narrow branches and trenches are obtained.
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81.16.Dn Self-assembly
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.43.Mn Adsorption kinetics

Drift-compensated data acquisition performed at room temperature with frequency modulation atomic force microscopy

Masayuki Abe, Yoshiaki Sugimoto, Takashi Namikawa, Kenichi Morita, Noriaki Oyabu, and Seizo Morita

Appl. Phys. Lett. 90, 203103 (2007); http://dx.doi.org/10.1063/1.2739410 (3 pages) | Cited 35 times

Online Publication Date: 15 May 2007

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The authors have performed distortionless atom imaging and force mapping experiments, under a large thermal drift condition at room temperature (RT), using frequency modulation atomic force microscopy (FM-AFM) that had been done previously only at low temperature. In the authors’ experimental scheme, three-dimensional position feedback with atom tracking detects the thermal drift velocity that is constant for a period of time at RT. The detected velocity is then used as the model for implementing the feedforward in order to compensate for the thermal drift. This technique can be expected to be used for precise positioning of the tip-sample in atom manipulation experiments using the FM-AFM at RT.
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07.79.Lh Atomic force microscopes
07.05.Hd Data acquisition: hardware and software

Study of the initial nucleation and growth of catalyst-free InAs and Ge nanowires

Hyun D. Park and S. M. Prokes

Appl. Phys. Lett. 90, 203104 (2007); http://dx.doi.org/10.1063/1.2740105 (3 pages) | Cited 8 times

Online Publication Date: 15 May 2007

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The authors have examined the nucleation conditions in the growth of catalyst-free InAs and Ge nanowires (NWs) on porous Si, as well as the growth of InAs NWs on a SiO2 substrate using 10 nm sized In nanoparticles. The NW growths were performed in a closed system. The results suggest that all the NWs grew from a solid nucleation state. For the growth using In nanoparticles, the results suggest that the growth mechanism is very different from the vapor-liquid-solid, in that the nanowire growth only begins after the nucleation particle solidifies.
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81.05.Ea III-V semiconductors
81.05.Cy Elemental semiconductors
68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires

Faceting during GaAs quantum dot self-assembly by droplet epitaxy

Ch. Heyn, A. Stemmann, A. Schramm, H. Welsch, W. Hansen, and Á. Nemcsics

Appl. Phys. Lett. 90, 203105 (2007); http://dx.doi.org/10.1063/1.2737123 (3 pages) | Cited 16 times

Online Publication Date: 16 May 2007

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Strain-free GaAs quantum dots (QDs) are grown in a self-assembled fashion by applying Ga droplet epitaxy. The QDs are studied using electron diffraction and atomic force microscopy. Two distinct regimes are observed for the QD shape. QDs whose volume exceeds approximately 3×105 Ga atoms are shaped like truncated pyramids with side facets having an angle of about 55°. Smaller QDs are pyramidlike with 25° facets.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.05.Ea III-V semiconductors
81.16.Dn Self-assembly
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Ps Atomic force microscopy (AFM)

Tailored polymer microlenses on treated glass surfaces

Mordechai Sokuler, Daniel Aronov, Gil Rosenman, and Levi A. Gheber

Appl. Phys. Lett. 90, 203106 (2007); http://dx.doi.org/10.1063/1.2739087 (3 pages) | Cited 2 times

Online Publication Date: 16 May 2007

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Integrating arrayed biosensors (biochips) or micro- and nanofluidic devices with readout systems is an important step towards their realization in lab-on-a-chip devices. To this end, we present a straightforward method of fabricating polymer microlenses in precise locations, with desired optical characteristics, using a combination of two methods: surface energy tuning using low-energy electron irradiation, to control the numerical aperture, and time-controlled nanofountain pen deposition of polymer microlenses, to control the focal length. The authors demonstrate the tuning of focal length between 8 and 20 μm with numerical apertures between 0.16 and 0.26.
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42.79.Bh Lenses, prisms and mirrors
42.70.Jk Polymers and organics
81.65.Ps Polishing, grinding, surface finishing
42.70.Ce Glasses, quartz

Derivation of length of carbon nanotube responsible for electron emission from field emission characteristics

Y. Gotoh, Y. Kawamura, T. Niiya, T. Ishibashi, D. Nicolaescu, H. Tsuji, J. Ishikawa, A. Hosono, S. Nakata, and S. Okuda

Appl. Phys. Lett. 90, 203107 (2007); http://dx.doi.org/10.1063/1.2740199 (3 pages) | Cited 3 times

Online Publication Date: 16 May 2007

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A method for deriving the length of carbon nanotube (CNT) in field emission arrays is proposed. Unlike the direct method of observation using a microscope, this method gathers information from functional measurements. Electron emission characteristics of CNT’s printed on glass substrate were measured in a diode configuration. The macroscopic part of the voltage field conversion factor β was obtained from the relationship between the slope and intercept of the Fowler-Nordheim plot, and also from modeling of the electrodes. The length of the CNT was derived comparing the two values for β. The estimated length of the CNT agrees with direct measurements.
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61.46.Fg Nanotubes
85.45.Db Field emitters and arrays, cold electron emitters
79.70.+q Field emission, ionization, evaporation, and desorption

Electrical polarizability of carbon nanotubes in liquid suspension

Matthew S. Brown, Jerry W. Shan, Chen Lin, and Frank M. Zimmermann

Appl. Phys. Lett. 90, 203108 (2007); http://dx.doi.org/10.1063/1.2740186 (3 pages) | Cited 12 times

Online Publication Date: 16 May 2007

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The alignment and polarizability of single-wall carbon nanotubes in dilute ethanol suspensions under low-frequency, alternating-current electric fields were investigated through optical polarimetry. The nematic order parameter was determined by measuring changes in the state of polarization of a laser beam transmitted through the sample. The dependence of the measured alignment on the electric field was found to be consistent with a thermal-equilibrium distribution of freely rotating, polarizable rods. The polarizability determined by fitting to this model is consistent with the classical result for a conducting ellipsoid of the dimensions of the nanotubes.
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61.46.Fg Nanotubes
82.70.Kj Emulsions and suspensions
78.67.Ch Nanotubes

In situ ion scattering and x-ray photoelectron spectroscopy studies of stability and nanoscale oxidation of single crystal (100) InAs

Chia-Lin Chang, Vaithiyalingam Shutthanandan, Subhash C. Singhal, and Shriram Ramanathan

Appl. Phys. Lett. 90, 203109 (2007); http://dx.doi.org/10.1063/1.2740200 (3 pages) | Cited 4 times

Online Publication Date: 16 May 2007

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The authors report on the synthesis of clean and smooth surfaces of single crystal InAs (100) by hydrogen molecular cleaning along with in situ studies on the stability of such surfaces against oxide formation. Nanoscale oxidation studies have been performed in detail using in situ nuclear reaction analysis and x-ray photoelectron spectroscopy. Ion channeling studies have been performed to verify atomically smooth surfaces after postcleaning. Stability and kinetic boundaries of cleaned InAs (100) surfaces against oxidation have been experimentally derived. These results are important not only in preparing clean surfaces of InAs but also in understanding fundamentals of oxide/III–V semiconductor interfaces.
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81.05.Ea III-V semiconductors
81.16.Pr Micro- and nano-oxidation
81.65.Cf Surface cleaning, etching, patterning
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Poly(ether sulfone) as a negative resist for electron beam lithography

R. M. Bryce, M. R. Freeman, and M. Aktary

Appl. Phys. Lett. 90, 203110 (2007); http://dx.doi.org/10.1063/1.2740582 (3 pages) | Cited 1 time

Online Publication Date: 17 May 2007

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The sulfone containing polymer poly(butene sulfone) has long been used as positive electron beam resist due to the high scission rate of sulfone under electron irradiation. The authors demonstrate that poly(ether sulfone) acts as a high resolution negative electron beam resist which displays good chemical and dry-etch resistance. The electron beam exposure sensitivity at 10 kV was found to be approximately 230 μC/cm2 for poly(ether sulfone), roughly 2.3 times that of poly(methyl methacrylate). As poly(ether sulfone) is a robust engineering polymer that can withstand etching this polymer is a suitable mask material and has properties of interest for direct incorporation in devices.
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85.40.Hp Lithography, masks and pattern transfer
42.82.Cr Fabrication techniques; lithography, pattern transfer

Coulomb oscillation of a proton in a Ni–Nb–Zr–H glassy alloy with multiple junctions

Mikio Fukuhara, Asahi Kawashima, Shinichi Yamaura, and Akihisa Inoue

Appl. Phys. Lett. 90, 203111 (2007); http://dx.doi.org/10.1063/1.2739080 (3 pages) | Cited 18 times

Online Publication Date: 18 May 2007

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Electric current-induced voltage oscillation at 500–560 kHz was observed in the current-voltage curves of nanoscopic size ( ∼ 0.9 nm) tunnel junctions arranged in a low-capacitance ( ∼ 1 aF), multiple-junction configuration of (Ni42Nb28Zr30)100−xHx (5.2 ⩽ x ⩽ 15.2) glassy alloys in the temperature range of 205–6 K. This behavior appeared to be derived from Coulomb oscillation resulting from the tunneling of individual protons charging and discharging the vacancy capacitance of Zr–H-◻-H–Zr atomic bond arrays among Zr-tetrahedral clusters, where ◻ is the vacancy barrier, termed the free volume, in the glassy alloys.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.40.Gk Tunneling
73.63.-b Electronic transport in nanoscale materials and structures

Structural and optical properties of the three-dimensional CdS nanocone arrays on the self-assembled Cd/CdS core-shell microspheres

Qingtao Zhou, Yiqing Chen, Weihai Kong, Yong Su, Bo Peng, Chong Jia, Xinhua Zhang, Song Yin, and Sen Li

Appl. Phys. Lett. 90, 203112 (2007); http://dx.doi.org/10.1063/1.2740471 (3 pages) | Cited 2 times

Online Publication Date: 18 May 2007

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The authors report on an approach to homoepitaxial growth of the three-dimensional CdS nanocone arrays, in which the Cd/CdS core-shell sphere is designed to serve as a template. The alternation of the wurtzite (WZ) and zinc blende (ZB) phases along the growth direction of the nanocones is observed in the as-synthesized CdS nanocones. The WZ/ZB admixtures exhibit the features of a quantum well, which causes the two peaks centered at 506 and 503 nm in the room-temperature photoluminescence spectrum.
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68.65.Fg Quantum wells
78.67.De Quantum wells
78.55.Et II-VI semiconductors
81.16.Dn Self-assembly

Spatially resolved biosensing with a molded plasmonic crystal

Viktor Malyarchuk, Matthew E. Stewart, Ralph G. Nuzzo, and John A. Rogers

Appl. Phys. Lett. 90, 203113 (2007); http://dx.doi.org/10.1063/1.2740591 (3 pages) | Cited 15 times

Online Publication Date: 18 May 2007

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The authors report the use of a type of quasi-three-dimensional plasmonic crystal for spatially resolved detection of biochemical binding events, with a spatial resolution of tens of microns and submonolayer binding sensitivity. In demonstration experiments, fibrinogen patterns nonspecifically adsorbed to the crystal surface were spatially and spectroscopically resolved using monochromatic and white light illumination. The experimental simplicity of the fabrication and use of these sensors, their compact form factors together with the high detection sensitivities and spatial resolution that can be achieved, collectively make these devices interesting as candidates for label-free array-based bioanalytical detection.
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87.80.-y Biophysical techniques (research methods)
87.14.E- Proteins
87.15.N- Properties of solutions of macromolecules
82.80.-d Chemical analysis and related physical methods of analysis
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Nanolithography of a full-coverage octadecylphosphonic acid monolayer spin coated on a Si substrate

H.-Y. Nie, N. S. McIntyre, and W. M. Lau

Appl. Phys. Lett. 90, 203114 (2007); http://dx.doi.org/10.1063/1.2741119 (3 pages)

Online Publication Date: 18 May 2007

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The authors describe a lithographic method based on a scanning probe technique to selectively remove octadecylphosphonic acid (OPA) molecules from their self-assembled monolayers (SAMs) spin coated on a Si substrate. This lithographic technique involves the use of a positively biased probe tip to scan an OPA SAM having a thickness of ∼ 2 nm and provides an opportunity for developing a scanning probe based lithography that accommodates the need for ever-decreasing size of semiconductor devices.
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81.16.Nd Micro- and nanolithography
81.16.Dn Self-assembly
68.37.-d Microscopy of surfaces, interfaces, and thin films

Nanoimprint mold fabrication and replication by room-temperature conformal chemical vapor deposition

Patrick F. Murphy, Keith J. Morton, Zengli Fu, and Stephen Y. Chou

Appl. Phys. Lett. 90, 203115 (2007); http://dx.doi.org/10.1063/1.2741122 (3 pages) | Cited 7 times

Online Publication Date: 18 May 2007

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The authors present a technique for the replication of molds for nanoimprint lithography (NIL) without solvents or etching. A thin hard amorphous silicon film is deposited onto imprinted or self-assembled polymer nanostructures by room-temperature conformal plasma-enhanced chemical vapor deposition. After attachment to another substrate and separation from the polymer original, the thin hard film forms a NIL mold that is the inverse of the polymer original. Using this technology, the authors demonstrate the replication of a 200 nm pitch grating mold and sub-50-nm features over wafer-scale areas without introducing additional line edge roughness associated with conventional replication methods.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Sz Deposition technology

Difference between bending and stretching moduli of single-walled carbon nanotubes that are modeled as an elastic tube

Christopher M. DiBiasio, Michael A. Cullinan, and Martin L. Culpepper

Appl. Phys. Lett. 90, 203116 (2007); http://dx.doi.org/10.1063/1.2741144 (3 pages) | Cited 10 times

Online Publication Date: 18 May 2007

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The authors show that an elastic tube model of a (5,5) carbon nanotube predicts stretching and bending moduli that differ by 19%. This is due to (1) differing energy storage mechanisms in each mode and (2) the inability of the tube model to capture these effects. Conventional tube models assume a common energy storage mechanism in stretching and bending. They show that energy is stored primarily through bond stretching/rotation and bond torsion/van der Waals interactions in stretching and bending, respectively. This knowledge underscores the need to use different moduli to predict stretching, bending, and combined bending and stretching when using the tube model.
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62.25.-g Mechanical properties of nanoscale systems
61.46.Fg Nanotubes
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
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