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23 Jan 2012

Volume 100, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 100, 041101 (2012); http://dx.doi.org/10.1063/1.3675885 (4 pages)

Seung Ho Choi and Young L. Kim
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Plasmonic light trapping leads to responsivity increase in colloidal quantum dot photodetectors

F. Pelayo García de Arquer, Fiona J. Beck, María Bernechea, and Gerasimos Konstantatos

Appl. Phys. Lett. 100, 043101 (2012); http://dx.doi.org/10.1063/1.3678039 (4 pages) | Cited 4 times

Online Publication Date: 23 January 2012

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We report broadband responsivity enhancement in PbS colloidal quantum dot (CQDs) photoconductive photodetectors due to absorption increase offered by a plasmonic scattering layer of Ag metal nanoparticles. Responsivity enhancements are observed in the near infrared with a maximum 2.4-fold increase near the absorption band edge of ∼1 μm for ∼400 nm thick devices. Additionally, we study the effect of the mode structure on the efficiency of light trapping provided by random nanoparticle scattering in CQD films and provide insights for plasmonic scattering enhancement in CQD thin films.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
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Transforming graphite to nanoscale diamonds by a femtosecond laser pulse

R. Nüske, A. Jurgilaitis, H. Enquist, M. Harb, Y. Fang, U. Håkanson, and J. Larsson

Appl. Phys. Lett. 100, 043102 (2012); http://dx.doi.org/10.1063/1.3678190 (4 pages) | Cited 1 time

Online Publication Date: 23 January 2012

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Formation of cubic diamond from graphite following irradiation by a single, intense, ultra-short laser pulse has been observed. Highly oriented pyrolytic graphite (HOPG) samples were irradiated by a 100 fs pulse with a center wavelength of 800 nm. Following laser exposure, the HOPG samples were studied using Raman spectroscopy of the sample surface. In the laser-irradiated areas, nanoscale cubic diamond crystals have been formed. The exposed areas were also studied using grazing incidence x-ray powder diffraction showing a restacking of planes from hexagonal graphite to rhombohedral graphite.
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64.70.K- Solid-solid transitions
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
64.70.Nd Structural transitions in nanoscale materials
78.30.Na Fullerenes and related materials

Metal-insulator transition sustained by Cr-doping in V2O3 nanocrystals

Yoichi Ishiwata, Tatsuya Shiraishi, Naoki Ito, Satoshi Suehiro, Tetsuya Kida, Hirofumi Ishii, Yasuhisa Tezuka, Yuji Inagaki, Tatsuya Kawae, Hirotaka Oosato, Eiichiro Watanabe, Daiju Tsuya, Masashi Nantoh, and Koji Ishibashi

Appl. Phys. Lett. 100, 043103 (2012); http://dx.doi.org/10.1063/1.3679396 (3 pages) | Cited 2 times

Online Publication Date: 24 January 2012

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We have obtained monodisperse (V1−xCrx)2O3 nanocrystals with crystal sizes of 21.0 ± 4.1 nm using organic-phase synthesis. The (V1−xCrx)2O3 nanocrystals clearly show the transition from a corundum structured paramagnetic metal to a monoclinic structured antiferromagnetic insulator in contrast to non-doped V2O3 nanocrystals, in which the disappearance of the metal-insulator transition has been observed. We have found that Cr doping works effectively in narrowing the a1g band, which tends to be broadened by nanocrystallization. This result suggests that chemical doping is useful for control of material phase transitions at the nanoscale.
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81.07.Bc Nanocrystalline materials
61.72.up Other materials
64.70.dg Crystallization of specific substances
64.70.Nd Structural transitions in nanoscale materials
71.30.+h Metal-insulator transitions and other electronic transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Improved electron field emission from morphologically disordered monolayer graphene

Srikrishna Pandey, Padmnabh Rai, Shashikant Patole, Fethullah Gunes, Gi-Duk Kwon, Ji-Beom Yoo, Pavel Nikolaev, and Sivaram Arepalli

Appl. Phys. Lett. 100, 043104 (2012); http://dx.doi.org/10.1063/1.3679135 (4 pages) | Cited 3 times

Online Publication Date: 24 January 2012

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Graphene was synthesized on copper foil by thermal chemical vapor deposition technique. To investigate the field electron emission property, planar graphene (PG) and morphologically disordered graphene (MDG) were fabricated on the doped silicon substrate by transfer of as-grown graphene. Incorporation of morphological disorder in graphene creates more emission sites due to the additional defects, edges, and atomic scale ripples. This resulted in (1) a dramatic increase in the maximum current density by a factor of 500, (2) considerable increase in the enhancement factor, and (3) decrease in the turn-on field of MDG compared to PG.
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81.05.ue Graphene
79.70.+q Field emission, ionization, evaporation, and desorption
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.48.Gh Structure of graphene

Nano-hole array structure with improved surface plasmon energy matching characteristics

Mohamadreza Najiminaini, Fartash Vasefi, Bozena Kaminska, and Jeffrey J. L. Carson

Appl. Phys. Lett. 100, 043105 (2012); http://dx.doi.org/10.1063/1.3679173 (4 pages) | Cited 4 times

Online Publication Date: 24 January 2012

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We present a nano-hole array structure in an opaque gold film that contains a cavity beneath each nano-hole. The cavity contributes to surface plasmon energy matching between the top and bottom surfaces of the gold and within the nano-hole structures. Based on bulk surface plasmon resonance (SPR) sensing experiments, the SP-matched structure had 2.8-fold higher differential transmission, 2-fold higher sensitivity, and a 7-fold higher ratio of extraordinary optical transmission at resonance to the nearby minimum compared to a conventional NHA. The results suggest that the structure with cavities has potential to improve performance of bulk SPR sensing applications.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

High magnetic field annealing effect on visible photoluminescence enhancement of TiO2 nanotube arrays

Mingjie Yang, Wei Liu, Jia-Lin Sun, and Jia-Lin Zhu

Appl. Phys. Lett. 100, 043106 (2012); http://dx.doi.org/10.1063/1.3679621 (4 pages)

Online Publication Date: 25 January 2012

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TiO2 nanotube arrays with remarkable visible photoluminescence were prepared by high magnetic field annealing in air at 450 °C due to the involvement of oxygen vacancies (OVs). A field with the intensities of 0, 2, 4, 6, and 8 T were applied in the annealing processing, along the directions set at 0°, 50°, and 90° from the surface normal of the substrate. The results demonstrated that the density of oxygen vacancies in TiO2 nanotubes can be controlled by varying the intensity and direction of the magnetic field. The mechanism for the effect of the high magnetic field has been investigated. This study opens an effective way to control the oxygen vacancies in nanomaterials to improve their performance.
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75.60.Nt Magnetic annealing and temperature-hysteresis effects
78.20.Ls Magneto-optical effects
78.55.Hx Other solid inorganic materials
78.67.Ch Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing

Effective energy gap of the double-walled carbon nanotubes with field effect transistors ambipolar characteristics

Takahiro Morimoto, Akihiro Kuno, Shota Yajima, Koji Ishibashi, Koji Tsuchiya, and Hirofumi Yajima

Appl. Phys. Lett. 100, 043107 (2012); http://dx.doi.org/10.1063/1.3679639 (3 pages) | Cited 1 time

Online Publication Date: 26 January 2012

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We have investigated the transport property of the double-walled carbon nanotubes (DWCNT)-field effect transistor (FET) devices with HfO2 insulating layers at room temperature and 4.2 K. These devices show the ambipolar FET characteristics after deposition of HfO2 insulating layer. The off-regions of ambipolar behavior have clear dependence on their DWCNT diameter. The conversion factor of gate voltages and bias voltages is estimated from low temperature Coulomb Diamond measurement. Using same device structure and dimensions to all devices, these off-regions of threshold voltage are converted to effective energy gap. These energy gaps are in good agreement with theoretical predictions.
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85.35.Kt Nanotube devices

Plasmon assisted light propagation and Raman scattering hot-spot in end-to-end coupled silver nanowire pairs

Rohit Chikkaraddy, Danveer Singh, and G. V. Pavan Kumar

Appl. Phys. Lett. 100, 043108 (2012); http://dx.doi.org/10.1063/1.3679649 (3 pages) | Cited 4 times

Online Publication Date: 26 January 2012

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Herein, we report on the experimental observation of light propagation and localization capabilities of end-to-end connected silver nanowire (Ag NW) pairs. By exciting the surface plasmon polaritons at one end of Ag NW pair, we observed relatively intense light emission at the junction and weak light emission at the distal end of the pair. To probe the localization of light at nanowire junction, we captured far-field Raman image of an isolated Ag NW pair adsorbed with rhodamine 6 G and observed enhanced Raman scattering at the nanowire junction. Such nanophotonic modules with light propagation and localization capabilities can be harnessed for multiplexed on-chip plasmonics.
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73.22.Lp Collective excitations
78.30.Er Solid metals and alloys
68.43.Mn Adsorption kinetics
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Anomalous electron transport in back-gated field-effect transistors with TiTe2 semimetal thin-film channels

J. Khan, C. M. Nolen, D. Teweldebrhan, D. Wickramaratne, R. K. Lake, and A. A. Balandin

Appl. Phys. Lett. 100, 043109 (2012); http://dx.doi.org/10.1063/1.3679679 (4 pages) | Cited 9 times

Online Publication Date: 26 January 2012

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The authors report on “graphene-like” mechanical exfoliation of thin films of titanium ditelluride and investigation of their electronic properties. The exfoliated crystalline TiTe2 films were used as the channel layers in the back-gated field-effect transistors fabricated with Ti/Al/Au metal contacts on SiO2/Si substrates. The room-temperature current-voltage characteristics revealed strongly non-linear behavior with signatures of the source-drain threshold voltage similar to those observed in the charge-density-wave devices. The drain-current showed an unusual non-monotonic dependence on the gate bias characterized by the presence of multiple peaks. The obtained results can be potentially used for implementation of the non-Boolean logic gates.
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85.75.Hh Spin polarized field effect transistors
68.55.-a Thin film structure and morphology
73.61.-r Electrical properties of specific thin films

Side-dependent electron escape from graphene- and graphane-like SiC layers

Paola Gori, Olivia Pulci, Margherita Marsili, and Friedhelm Bechstedt

Appl. Phys. Lett. 100, 043110 (2012); http://dx.doi.org/10.1063/1.3679175 (4 pages) | Cited 3 times

Online Publication Date: 26 January 2012

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The structural and electronic properties of SiC-based two-dimensional (2D) crystals are studied by means of density functional theory and many-body perturbation theory. Such properties cannot simply be interpolated between graphene and silicene. The replacement of half of the C atoms by Si atoms opens a large direct electronic gap and destroys the Dirac cones. Hydrogenation further opens the gap and significantly reduces the electron affinity to 0.1 or 1.8 eV in dependence on the carbon or silicon termination of the 2D crystal surface, thus showing a unique direction dependent ionization potential. This suggests the use of 2D-SiC:H as electron or hole filter.
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73.22.Pr Electronic structure of graphene
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.61.Wp Fullerenes and related materials
61.48.Gh Structure of graphene
68.65.Pq Graphene films
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