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18 Aug 2008

Volume 93, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 93, 073101 (2008); http://dx.doi.org/10.1063/1.2970055 (3 pages)

A. J. Du, Y. Chen, G. Q. Lu, and Sean C. Smith
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Half metallicty in finite-length zigzag single walled carbon nanotube: A first-principle prediction

A. J. Du, Y. Chen, G. Q. Lu, and Sean C. Smith

Appl. Phys. Lett. 93, 073101 (2008); http://dx.doi.org/10.1063/1.2970055 (3 pages) | Cited 13 times

Online Publication Date: 18 August 2008

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We predict here from first-principle calculations that finite-length (n,0) single walled carbon nanotubes (SWCNTs) with H-termination at the open ends displaying antiferromagnetic coupling when n is greater than 6. An opposite local gating effect of the spin states, i.e., half metallicity, is found under the influence of an external electric field along the direction of tube axis. Remarkably, boron doping of unpassivated SWCNTs at both zigzag edges is found to favor a ferromagnetic ground state, with the B-doped tubes displaying half-metallic behavior even in the absence of an electric field. Aside of the intrinsic interest of these results, an important avenue for development of CNT-based spintronic is suggested.
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61.46.Fg Nanotubes
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.up Other materials

Conducting polymer formed by low energy gold ion implantation

M. C. Salvadori, M. Cattani, F. S. Teixeira, and I. G. Brown

Appl. Phys. Lett. 93, 073102 (2008); http://dx.doi.org/10.1063/1.2973161 (3 pages) | Cited 12 times

Online Publication Date: 18 August 2008

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A buried conducting layer of metal/polymer nanocomposite was formed by very low energy gold ion implantation into polymethylmethacrylate. The conducting layer is ∼ 3 nm deep and of width ∼ 1 nm. In situ resistivity measurements were performed as the implantation proceeded, and the conductivity thus obtained as a function of buried gold concentration. The measured conductivity obeys the behavior well established for composites in the percolation regime. The critical concentration, below which the polymer remains an insulator, is attained at a dose ∼ 1.0×1016 atoms/cm2 of implanted gold ions.
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61.72.U- Doping and impurity implantation
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Controlled surface distribution and luminescence of YVO4:Eu3+ nanophosphor layers

A. F. Khan, D. Haranath, Ravishanker Yadav, Sukhvir Singh, S. Chawla, and V. Dutta

Appl. Phys. Lett. 93, 073103 (2008); http://dx.doi.org/10.1063/1.2973163 (3 pages) | Cited 9 times

Online Publication Date: 19 August 2008

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A method of dispersing YVO4:Eu quantum dots (QDs) as uniform two-dimensional (2D) layers with a high degree of homogeneity is presented. Annealing at 773 K resulted in coalescence of QDs to form nanoclusters with size of ∼ 25 nm with an improved photoluminescence and ∼ 80% transmittance at 800 nm. An efficient 5D0-7F2 transition and lifetimes of ∼ 1038 μs for the characteristic Eu3+ emission were observed. The absorption and emission peaks showed a slight blueshift, due to quantum-size effect, as compared to that for the bulk counterpart. Our method of 2D layer deposition is useful to enhance spectral response of the solar cells.
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78.67.Hc Quantum dots
78.55.Hx Other solid inorganic materials
68.65.Hb Quantum dots (patterned in quantum wells)
81.40.Gh Other heat and thermomechanical treatments

Local thermomechanical characterization of phase transitions using band excitation atomic force acoustic microscopy with heated probe

S. Jesse, M. P. Nikiforov, L. T. Germinario, and S. V. Kalinin

Appl. Phys. Lett. 93, 073104 (2008); http://dx.doi.org/10.1063/1.2965470 (3 pages) | Cited 13 times

Online Publication Date: 19 August 2008

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An approach for thermomechanical characterization of phase transitions in polymeric materials (polyethyleneterephthalate) by band excitation acoustic force microscopy is developed. This methodology allows the independent measurement of resonance frequency, Q factor, and oscillation amplitude of a tip-surface contact as a function of tip temperature, from which the thermal evolution of tip-surface spring constant and mechanical dissipation can be extracted. We demonstrate a heating protocol which keeps the contact area and contact force constant, thus allowing for reproducible measurements and quantitative extraction of material properties including temperature dependence of indentation-based elastic and loss moduli.
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82.35.Lr Physical properties of polymers
64.70.km Polymers
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Gh Other heat and thermomechanical treatments
62.20.de Elastic moduli
61.41.+e Polymers, elastomers, and plastics

Type-II behavior in wurtzite InP/InAs/InP core-multishell nanowires

B. Pal, K. Goto, M. Ikezawa, Y. Masumoto, P. Mohan, J. Motohisa, and T. Fukui

Appl. Phys. Lett. 93, 073105 (2008); http://dx.doi.org/10.1063/1.2966343 (3 pages) | Cited 16 times

Online Publication Date: 20 August 2008

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We study optical transitions from a periodic array of InP/InAs/InP core-multishell nanowires (CMNs) having a wurtzite crystal structure by using photoluminescence (PL) and PL excitation (PLE) spectroscopy. Observing a large Stokes shift between PL and PLE spectra, a blueshift of the PL peak with a cube-root dependence on the excitation power and a slow and nonexponential decay of PL with an effective decay time of 16 ns suggest a type-II band alignment. Band-offset calculation based on the “model-solid theory” of Van de Walle [ Phys. Rev. B 39, 1871 (1989) ] supports type-II band lineup if the InAs layer in the wurtzite CMNs is assumed to sustain compressive strain in all directions.
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78.55.Cr III-V semiconductors
61.66.Fn Inorganic compounds
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
81.40.Lm Deformation, plasticity, and creep
78.66.Fd III-V semiconductors
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Time-resolved characterization of InAsP/InP quantum dots emitting in the C-band telecommunication window

R. Hostein, A. Michon, G. Beaudoin, N. Gogneau, G. Patriache, J.-Y. Marzin, I. Robert-Philip, I. Sagnes, and A. Beveratos

Appl. Phys. Lett. 93, 073106 (2008); http://dx.doi.org/10.1063/1.2965112 (3 pages) | Cited 8 times

Online Publication Date: 20 August 2008

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The dynamic response of InAsP quantum dots, grown on InP(001) substrates by low-pressure metalorganic vapor phase epitaxy emitting around 1.55 μm, is investigated by means of time-resolved microphotoluminescence as a function of temperature. Exciton lifetime steadily increases from 1 ns at low temperature to reach 4 ns at 300 K while the integrated photoluminescence intensity decreases only by a factor of ⅔. These characteristics give evidence that such InAsP/InP quantum dots provide a strong carrier confinement even at room temperature and that their dynamic response is not affected by thermally activated nonradiative recombination up to room temperature.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.47.jd Time resolved luminescence
71.35.-y Excitons and related phenomena
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Electrical charging of a single quantum dot by a spin polarized electron

M. Ghali, T. Kümmell, J. Wenisch, K. Brunner, and G. Bacher

Appl. Phys. Lett. 93, 073107 (2008); http://dx.doi.org/10.1063/1.2973397 (3 pages) | Cited 5 times

Online Publication Date: 20 August 2008

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Voltage controlled electrical charging of a single InAs quantum dot by a spin polarized electron from a ZnMnSe spin aligner is presented, and the spin information is read out optically. We demonstrate that the characteristic single quantum dot photoluminescence polarization pattern of the negative trion and the neutral exciton lines directly reflects the spin state of the electrically injected electron.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.21.La Quantum dots
72.25.-b Spin polarized transport
73.61.Ey III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Nanofabrication and the realization of Feynman’s two-slit experiment

Stefano Frabboni, Gian Carlo Gazzadi, and Giulio Pozzi

Appl. Phys. Lett. 93, 073108 (2008); http://dx.doi.org/10.1063/1.2962987 (3 pages) | Cited 8 times

Online Publication Date: 20 August 2008

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Two nanosized slits are opened by focused ion beam milling in a membrane to observe, with a transmission electron microscope, electron interference fringes. Then, on the same sample, one of the slits is closed by focused ion beam induced deposition and the corresponding transmitted intensity is recorded. The comparison between the two measurements provides an impressive experimental evidence of the probability amplitude of quantum mechanics following step by step the original idea proposed by Feynman [The Feynman Lectures on Physics (Addison-Wesley, Reading, MA, 1966), Vol. 3, Chap. 1] .
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81.16.-c Methods of micro- and nanofabrication and processing
68.37.Og High-resolution transmission electron microscopy (HRTEM)

Near-to-far-field spectral evolution in a plasmonic crystal: Experimental verification of the equipartition of diffraction orders

D. J. Park, K. G. Lee, H. W. Kihm, Y. M. Byun, D. S. Kim, C. Ropers, C. Lienau, J. H. Kang, and Q-Han Park

Appl. Phys. Lett. 93, 073109 (2008); http://dx.doi.org/10.1063/1.2951587 (3 pages) | Cited 4 times

Online Publication Date: 20 August 2008

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We report on drastic changes in the near-field spectrum as it evolves into the far field in periodically corrugated metallic nanoslit arrays. The far-field spectral minimum is located exactly at the near-field spectral maximum, where a quasimonochromatic standing wave pattern is observed in the near field. These results are in excellent agreement with the equipartition of diffraction orders recently proposed [ K. G. Lee and Q-Han Park, Phys. Rev. Lett. 95, 103902 (2005) ].
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78.68.+m Optical properties of surfaces
78.66.Bz Metals and metallic alloys
73.22.Lp Collective excitations

Single-particle placement via self-limiting electrostatic gating

Hong-Wen Huang, Pradeep Bhadrachalam, Vishva Ray, and Seong Jin Koh

Appl. Phys. Lett. 93, 073110 (2008); http://dx.doi.org/10.1063/1.2972042 (3 pages) | Cited 4 times

Online Publication Date: 22 August 2008

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This letter reports single-particle placement in which exactly one nanoparticle is electrostatically guided and placed onto a target location. Using an ∼ 20 nm Au nanoparticle colloid as a model system, we demonstrate that self-limiting interactions between a charged nanoparticle and a charged substrate surface are extremely effective in positioning a single Au nanoparticle on each target location. Detailed theoretical calculations revealed that the self-limiting capability in the nanoparticle positioning is due to an increase in the free energy barrier after the first nanoparticle lands on a target position, effectively blocking the approach of other nanoparticles.
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81.07.Bc Nanocrystalline materials
82.70.Dd Colloids
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

Enhanced photoluminescence and photonic bandgap modification from composite photonic crystals of macroporous silicon and nanocrystalline PbS thin films

N. Gutman, A. Armon, A. Sa’ar, A. Osherov, and Y. Golan

Appl. Phys. Lett. 93, 073111 (2008); http://dx.doi.org/10.1063/1.2969054 (3 pages) | Cited 3 times

Online Publication Date: 22 August 2008

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We report on the fabrication of composite photonic crystals (PCs) of macroporous silicon and PbS thin films and about their passive and active optical properties. We have measured a redshift in the composite PC photonic stopbands relative to those of the PC substrate. In addition, we have measured a high extraction efficiency of the photoluminescence from the embedded PbS films due to band-edge singularities and slow-light modes of a defect-free two-dimensional composite PC. The peak extraction efficiency has been found to be six times larger than that of planar unpatterned PbS films.
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42.70.Qs Photonic bandgap materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.66.-w Optical properties of specific thin films
42.70.Km Infrared transmitting materials

Morphology of step structures on CeO2(111)

Stefan Torbrügge, Marion Cranney, and Michael Reichling

Appl. Phys. Lett. 93, 073112 (2008); http://dx.doi.org/10.1063/1.2969790 (3 pages) | Cited 17 times

Online Publication Date: 22 August 2008

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The morphology of step structures on the CeO2(111) surface is studied by dynamic scanning force microscopy (SFM) operated in the noncontact mode. The surface exhibits hexagonal islands and pits of O–Ce–O triple layer height with steps mostly enclosing an angle of 120°. Atomically resolved images reveal that the (111) surface almost exclusively exhibits alternating steps having (110) and (001) facets. Kink sites and missing oxygen atoms at step edges are identified to be the dominating defective sites at step edges. It is demonstrated that low coordinated oxygen atoms at step edges can be removed by the scanning SFM tip.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.-b Solid-gas/vacuum interfaces: types of surfaces
68.37.Ps Atomic force microscopy (AFM)

Nuclear spin pumping under resonant optical excitation in a quantum dot

M. N. Makhonin, A. I. Tartakovskii, A. Ebbens, M. S. Skolnick, A. Russell, V. I. Fal’ko, and M. Hopkinson

Appl. Phys. Lett. 93, 073113 (2008); http://dx.doi.org/10.1063/1.2958221 (3 pages) | Cited 6 times

Online Publication Date: 22 August 2008

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We demonstrate nuclear spin pumping in a single InGaAs/GaAs dot embedded in a p-i-n diode in the regime of resonant optical excitation of spin-polarized electron-hole pairs in the lowest energy states of the dot. A nuclear spin pumping mechanism is proposed relevant to the regime of high electric field where carriers escape from the dot by tunneling. The degree of nuclear spin polarization is shown to increase strongly with the applied electric field, controlling the carrier tunneling from the dot, since at low electric fields the dot is blocked for re-excitation due to the slow hole escape.
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73.63.Kv Quantum dots
72.25.Dc Spin polarized transport in semiconductors
72.25.Pn Current-driven spin pumping
73.21.La Quantum dots
73.40.Gk Tunneling
78.67.Hc Quantum dots

Strain induced change of bandgap and effective mass in silicon nanowires

Daryoush Shiri, Yifan Kong, Andrei Buin, and M. P. Anantram

Appl. Phys. Lett. 93, 073114 (2008); http://dx.doi.org/10.1063/1.2973208 (3 pages) | Cited 29 times

Online Publication Date: 22 August 2008

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This work computationally investigates the electromechanical properties of hydrogen passivated silicon nanowires under uniaxial tensile strain. It has been observed that bandgap changes can be as large as 60 and 100 meV per 1% axial strain for [100] and [110] nanowires, respectively. This rate of change in the bandgap is independent of nanowire size and depends only on the growth direction. More importantly, the nature of the bandgap can reversibly change from indirect to direct as a function of strain. It is also observed that for larger diameter nanowires, the indirect-to-direct transition occurs at smaller compressive strain.
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71.20.Mq Elemental semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Defect-induced negative differential resistance in single-walled carbon nanotubes

G. Buchs, P. Ruffieux, P. Gröning, and O. Gröning

Appl. Phys. Lett. 93, 073115 (2008); http://dx.doi.org/10.1063/1.2975177 (3 pages) | Cited 6 times

Online Publication Date: 22 August 2008

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The authors report on the observation of a negative differential resistance (NDR) behavior in tunneling spectra recorded on hydrogen and nitrogen plasma-induced atomic defects on semiconducting single-walled carbon nanotubes (SWNTs). The NDR is observed only in the positive bias range of the spectra. This bias asymmetry and the spectral shape in the NDR region can be explained on the basis of a bias-dependent tunneling barrier height model. Within this model the NDR behavior can be directly related to defect-induced sharp electronic states in the SWNT band gap created at the defect sites.
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73.63.Fg Nanotubes
73.40.Gk Tunneling
73.22.-f Electronic structure of nanoscale materials and related systems
73.20.At Surface states, band structure, electron density of states
71.20.Tx Fullerenes and related materials; intercalation compounds
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