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20 Aug 2007

Volume 91, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 91, 083504 (2007); http://dx.doi.org/10.1063/1.2772752 (3 pages)

Jeong-M. Choi, Jae Hoon Kim, and Seongil Im
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Integrated dual grating method for extended range interferometric displacement detection in probe microscopy

B. Van Gorp, A. G. Onaran, and F. L. Degertekin

Appl. Phys. Lett. 91, 083101 (2007); http://dx.doi.org/10.1063/1.2772114 (3 pages) | Cited 6 times

Online Publication Date: 20 August 2007

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The authors introduce a method that uses quadrature phase-shifted dual gratings to increase the range of optical interferometric displacement detection in phase-sensitive grating based microsensors. The concept is experimentally demonstrated on a surface micromachined probe microscopy structure suspended over a quartz substrate and two reflective gratings. Quadrature phase shift is obtained via a micromachined step in the quartz substrate below one of the gratings. Measurement of the intensity of the reflected diffraction orders from each grating while the mechanical structure is moved using an integrated actuator shows that interferometric sensitivity is maintained well beyond the quarter wavelength limit of similar sensors.
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42.87.Bg Phase shifting interferometry
07.60.Ly Interferometers
07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Low temperature aging effects on the formation of Sn nanoclusters in SiO2/Si films and interfaces

Felipe Kremer, João M. J. Lopes, Fernando C. Zawislak, and Paulo F. P. Fichtner

Appl. Phys. Lett. 91, 083102 (2007); http://dx.doi.org/10.1063/1.2772236 (3 pages) | Cited 5 times

Online Publication Date: 21 August 2007

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The formation of Sn nanocrystals (NCs) in ion implanted SiO2/Si films is investigated using Rutherford backscattering spectrometry and transmission electron microscopy. Low temperature and long time aging treatments followed by high temperature thermal annealings lead to the formation of a dense bidimensional NC array located at the SiO2/Si interface. This behavior is discussed considering the formation of small Sn clusters with a significantly improved thermal stability. The present experimental results are in good agreement with recent theoretical predictions that small Sn clusters can have their melting temperature enhanced in more than 1000 °C.
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61.46.Hk Nanocrystals
81.07.Bc Nanocrystalline materials
61.72.up Other materials
68.60.Dv Thermal stability; thermal effects

Epitaxial growth by pulsed laser deposition of Er-doped Sc2O3 films on sesquioxides monitored in situ by reflection high energy electron diffraction

Teoman Gün, Yury Kuzminykh, Klaus Petermann, Hanno Scheife, and Günter Huber

Appl. Phys. Lett. 91, 083103 (2007); http://dx.doi.org/10.1063/1.2773750 (3 pages) | Cited 2 times

Online Publication Date: 21 August 2007

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In this letter, the authors report on the epitaxial growth by pulsed laser deposition of Sc2O3 and Er(5%):Sc2O3 films on {100} and {111} oriented Sc2O3. They observed layer-by-layer growth in the orientation defined by the substrate. This was indicated by reflection high energy electron diffraction as intensity oscillations of the specularly reflected electron beam. A monolayer-smooth film surface was observed by atomic force microscopy. Such a growth behavior was also achieved during initial growth of Sc2O3 on {100} oriented Y2O3. Additional x-ray diffraction analysis shows good agreement with the growth behavior mentioned above.
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81.15.Fg Pulsed laser ablation deposition
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
68.55.-a Thin film structure and morphology

High quality SrTiO3 tunnel barrier obtained by pulsed laser deposition

T. Fix, V. Da Costa, C. Ulhaq-Bouillet, S. Colis, A. Dinia, K. Bouzehouane, and A. Barthélémy

Appl. Phys. Lett. 91, 083104 (2007); http://dx.doi.org/10.1063/1.2773752 (3 pages) | Cited 7 times

Online Publication Date: 21 August 2007

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The quality of a SrTiO3 tunnel barrier deposited by pulsed laser deposition on SrTiO3 (001)‖Sr2FeMoO6 is investigated. Epitaxy and two-dimensional growth are obtained and the root-mean-square roughness is 0.3 nm. The distribution of the local current measured by conductive atomic force microscopy indicates that hot spots are almost absent. The standard deviation of the barrier thickness distribution is lower than 0.05 nm. Current-voltage characteristics of patterned magnetic tunnel junctions provide evidence of the high quality of the barrier. The electrical properties of the SrTiO3 barrier are at least as good as the ones obtained by sputtering or e-beam evaporation.
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81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth

Ultrafine nanoporous gold by low-temperature dealloying and kinetics of nanopore formation

L. H. Qian and M. W. Chen

Appl. Phys. Lett. 91, 083105 (2007); http://dx.doi.org/10.1063/1.2773757 (3 pages) | Cited 56 times

Online Publication Date: 21 August 2007

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A low-temperature dealloying technique was developed to tailor the characteristic length scale of nanoporous gold for advanced functional applications. By systematically investigating the kinetics of nanopore formation during free corrosion, the authors experimentally demonstrated that the dealloying process is controlled by the diffusion of gold atoms at alloy/electrolyte interfaces, which strongly relies on the reaction temperatures. Low dealloying temperatures significantly reduce the interfacial diffusivity of gold atoms and result in an ultrafine nanoporous structure that has been proved to be useful with improved chemical and physical properties.
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61.43.Gt Powders, porous materials
61.46.-w Structure of nanoscale materials
81.16.-c Methods of micro- and nanofabrication and processing
81.65.-b Surface treatments
66.30.-h Diffusion in solids

Facet structure of GaAs nanowires grown by molecular beam epitaxy

S. O. Mariager, C. B. Sørensen, M. Aagesen, J. Nygård, R. Feidenhans’l, and P. R. Willmott

Appl. Phys. Lett. 91, 083106 (2007); http://dx.doi.org/10.1063/1.2769401 (3 pages) | Cited 16 times

Online Publication Date: 22 August 2007

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The shape and facets of GaAs nanowires grown by molecular beam epitaxy have been identified by the use of the diffuse scattering around the Bragg reflection from the parts of the nanowires having different crystal structures. The zinc blende parts of the nanowires are shown to have {111} facets in the form of truncated octahedrons, whereas the facets of the wurtzite structure are {10math0}. A minor part of the nanowires have a new structure consisting of a superlattice of regular and twinned structures only six bilayer thick.
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68.65.La Quantum wires (patterned in quantum wells)
61.46.-w Structure of nanoscale materials
61.66.Fn Inorganic compounds
61.72.Mm Grain and twin boundaries
81.07.Vb Quantum wires
81.05.Ea III-V semiconductors

InAs-coverage dependence of self-assembled quantum dot size, composition, and density

A. Zolotaryov, A. Schramm, Ch. Heyn, and W. Hansen

Appl. Phys. Lett. 91, 083107 (2007); http://dx.doi.org/10.1063/1.2772758 (3 pages) | Cited 5 times

Online Publication Date: 22 August 2007

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The authors report about the x-ray investigation of InAs/GaAs(001) quantum dot systems grown with varying amount of deposited InAs. It is shown that the intermixing induced composition of investigated quantum dots remains constant within the whole probed InAs deposition region. It is found that the increase of deposited InAs entirely leads to a proportional increase of surface density of dots and does not significantly influence the dot size. The dot average chemical composition was quantitatively estimated by comparison to finite-element based calculations.
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68.65.Hb Quantum dots (patterned in quantum wells)
66.30.Ny Chemical interdiffusion; diffusion barriers
82.80.-d Chemical analysis and related physical methods of analysis

Self-assembly mechanism of platelike silver mesocrystal

Jixiang Fang, Bingjun Ding, and Xiaoping Song

Appl. Phys. Lett. 91, 083108 (2007); http://dx.doi.org/10.1063/1.2772773 (3 pages) | Cited 14 times

Online Publication Date: 22 August 2007

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In this letter, two-dimensional monocrystalline silver mesocrystals with about 5–20 μm in size and 70 nm in thickness were, for the first time, large-scale synthesized within a facile and organic-free replacement reaction system. The growth process and mechanism of silver mesoscopic plates are discussed in detail. An oriented nucleation and self-assembly coarsening process were suggested to describe the formation of monocrystalline silver mesocrystals. The kinetically dominated route reported here can be extended to other metals to synthesize the mesoscopic morphology.
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81.16.Dn Self-assembly
82.70.Dd Colloids

Asymmetric strain in nanoscale patterned strained-Si/strained-Ge/strained-Si heterostructures on insulator

Pouya Hashemi, Leonardo Gomez, Judy L. Hoyt, Michael D. Robertson, and Michael Canonico

Appl. Phys. Lett. 91, 083109 (2007); http://dx.doi.org/10.1063/1.2772775 (3 pages) | Cited 4 times

Online Publication Date: 22 August 2007

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The engineering of asymmetric strain is demonstrated in nanoscale patterned strained-Si/strained-Ge/strained-Si heterostructure on insulator with body thickness of 15 nm. Starting material has layers with symmetric in-plane strain, including biaxial strained Si ( ∼ 1.8%, tension) and biaxial strained Ge ( ∼ 1.8%, compression). Micro-Raman spectroscopy is utilized to characterize the stress in heterostructures patterned into 10-μm-long bars with widths ranging from 300 to 30 nm. Raman measurements are consistent with the transformation from biaxial to uniaxial compressive strain in the Ge for 30-nm-wide bars, as predicated by simulations. Measurements also demonstrate enhanced asymmetric relaxation in the tensile strained Si cap as its thickness is increased.
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68.35.Gy Mechanical properties; surface strains
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.30.-j Infrared and Raman spectra

Effect of carrier density on the surface morphology and optical properties of nanoporous GaN prepared by UV assisted electrochemical etching

A. P. Vajpeyi, S. J. Chua, S. Tripathy, and E. A. Fitzgerald

Appl. Phys. Lett. 91, 083110 (2007); http://dx.doi.org/10.1063/1.2772753 (3 pages) | Cited 4 times

Online Publication Date: 23 August 2007

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Nanoporous GaN samples were prepared by UV-assisted electrochemical etching of Si-doped GaN using the HF-based electrolyte. The Si doping density in the as-grown GaN samples was varied from 1×1016 to 1×1019 cm−3. The surface morphology and optical quality of these nanoporous GaN films are controlled by the doping density in the as-grown films. The scanning electron microscopy results reveal that the average pore size can be tuned from 100 to 45 nm by increasing the carrier density in the as-grown GaN films from 1×1016 to 1×1019 cm−3. Photoluminescence (PL) measurements indicate that the nanoporous GaN films exhibit a higher PL intensity with redshifted band-edge PL peak compared to the as-grown GaN films. The nanoporous GaN prepared from highly doped sample gives highest PL intensity and stress relaxation due to the presence of smallest size nanopores. The redshift of the E2(high) phonon mode in the Raman spectra of nanoporous GaN prepared from heavily Si-doped samples shows a significant relaxation of the compressive stress.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Formation of self-assembled quantum dots on AlInAs and GaInAs matrices using a GaSb sublayer

Roland Enzmann, Susanne Dachs, Ralf Meyer, Jonathan Finley, and Markus-Christian Amann

Appl. Phys. Lett. 91, 083111 (2007); http://dx.doi.org/10.1063/1.2773754 (3 pages) | Cited 1 time

Online Publication Date: 23 August 2007

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In this letter, the authors present the formation of InAs quantum dots on GaInAs and AlInAs lattice matched on InP (001) substrates via molecular beam epitaxy by inserting a two monolayer GaSb sublayer below the InAs quantum dot material. They show that the formation of quantum dots is favored on indium-free and antimony-rich surfaces while quantum dashes are preferentially formed on indium-rich and antimony-free surfaces. Using a thin layer of GaSb between the InAs quantum dot material and the AlInAs or GaInAs matrix, single quantum dots were formed even with low quantum dot densities ( ≈ 1/μm2). These quantum dots give rise to photoluminescence between 1100 and 1500 nm depending on the matrix material.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
81.16.Dn Self-assembly

In-flight dry etching of plasma-synthesized silicon nanocrystals

X. D. Pi, R. W. Liptak, S. A. Campbell, and U. Kortshagen

Appl. Phys. Lett. 91, 083112 (2007); http://dx.doi.org/10.1063/1.2773931 (3 pages) | Cited 11 times

Online Publication Date: 23 August 2007

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CF4-based plasma has been employed to in-flight etch silicon nanocrystals (Si-NCs) after they are synthesized by SiH4-based plasma. The authors find that the photoluminescence (PL) of Si-NCs blueshifts when they are etched, indicating the etching-induced size reduction of Si-NCs. It is demonstrated that the power of CF4-based plasma can be tuned to control the size reduction of Si-NCs. The room-temperature atmospheric oxidation of both etched Si-NCs and unetched ones slows down significantly ∼ 100 h after production. The PL intensity of etched Si-NCs is smaller than that of unetched ones after oxidation.
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81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
81.16.-c Methods of micro- and nanofabrication and processing
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
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Generation of nanoparticle colloids by picosecond and femtosecond laser ablations in liquid flow

Stephan Barcikowski, Ana Menéndez-Manjón, Boris Chichkov, Marijus Brikas, and Gediminas Račiukaitis

Appl. Phys. Lett. 91, 083113 (2007); http://dx.doi.org/10.1063/1.2773937 (3 pages) | Cited 30 times

Online Publication Date: 23 August 2007

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Fabrication of silver nanoparticle colloids using ultrashort pulse laser ablation in water is studied. Ablation in liquid flow improves the reproducibility and increases the nanoparticle productivity by 380% compared to stationary liquid. Femtosecond laser ablation in water is 20% more efficient than picosecond laser ablation, but due to higher picosecond laser power (higher repetition rate), the nanoparticle productivity at the same pulse fluence is three times higher for picosecond laser ablation. With picosecond laser pulses, the maximum productivity of 8.6 μg/s is achieved at a pulse energy of 110 μJ and repetition rate of 50 kHz.
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81.16.Mk Laser-assisted deposition
81.15.Fg Pulsed laser ablation deposition
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
82.70.Dd Colloids

Enhanced luminescence of organic/metal nanostructure for grating coupler active long-range surface plasmonic device

Nan-Fu Chiu, Chii-Wann Lin, Jiun-Haw Lee, Chieh-Hsiung Kuan, Kuang-Chong Wu, and Chih-Kung Lee

Appl. Phys. Lett. 91, 083114 (2007); http://dx.doi.org/10.1063/1.2773961 (3 pages) | Cited 13 times

Online Publication Date: 23 August 2007

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This letter is intended to demonstrate the effect of coupled active long-range surface plasmon polaritons (SPPs) on the plasmonics response of a lamellar grating nanostructure with organic material on the surface. The phenomenon of nano-optics gives rise to a selective spectral response and a local field enhancement. The authors’ fabricated device consists of coupled organic/metal nanostructure with specific width and symmetric dielectric structure. The interaction between organic/metal interface SPPs can allow specific directional emission rather than isotropic emission. The authors present recent experimental results and discuss potential applications of such an active plasmonic biosensor with enhanced resonance energy emission due to interactions on the organic/metal nanograting.
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42.82.Et Waveguides, couplers, and arrays
42.79.Dj Gratings
42.79.Gn Optical waveguides and couplers

Multiplexing surface plasmon polaritons on nanowires

A. Imre, V. K. Vlasko-Vlasov, J. Pearson, J. M. Hiller, and U. Welp

Appl. Phys. Lett. 91, 083115 (2007); http://dx.doi.org/10.1063/1.2773992 (3 pages) | Cited 11 times

Online Publication Date: 24 August 2007

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The authors demonstrate a plasmonic device that generates and steers tightly focused plasmon beams between neighboring subwavelength metal-strip waveguides. By introducing a controlled phase shift into the plasmon condenser, they shifted the focused plasmon spot by microns with nanometer accuracy and realized the multiplexer functionality.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Anomalous strain dependent effective masses in (111) Si nanowires

G. W. Peng and Y. P. Feng

Appl. Phys. Lett. 91, 083116 (2007); http://dx.doi.org/10.1063/1.2775045 (3 pages) | Cited 3 times

Online Publication Date: 24 August 2007

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First-principles methods are employed to investigate the effect of strain on the carrier effective masses in (111) Si nanowires (SiNWs). It is found that the electron effective masses of SiNWs depend strongly on the applied axial strain. Within a certain range of strain, the electron effective masses are significantly enhanced. Most remarkably, the electron effective masses are anomalous and become infinity at a critical point of strain. This effect is associated with how strain changes the band structure with a single minimum to that with double minima or vice versa. The hole effective masses, on the other hand, decrease with the increase of the tensile strain, as a result of the strain-induced band energy shift in the vicinity of the valence band maximum. It is also shown that the band gaps of SiNWs with diameters ≥ 1.16 nm increase with the increase of the tensile strain. The tunability of the effective masses and band gaps with strain would be useful in tailoring the transport properties of SiNWs.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
71.20.Mq Elemental semiconductors
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
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