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25 Jul 2011

Volume 99, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 99, 041102 (2011); http://dx.doi.org/10.1063/1.3615051 (3 pages)

M. Davanço, M. T. Rakher, D. Schuh, A. Badolato, and K. Srinivasan
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Enhancement-mode buried strained silicon channel quantum dot with tunable lateral geometry

T. M. Lu, N. C. Bishop, T. Pluym, J. Means, P. G. Kotula, J. Cederberg, L. A. Tracy, J. Dominguez, M. P. Lilly, and M. S. Carroll

Appl. Phys. Lett. 99, 043101 (2011); http://dx.doi.org/10.1063/1.3615288 (3 pages) | Cited 3 times

Online Publication Date: 25 July 2011

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We propose and demonstrate a relaxed-SiGe/strained-Si enhancement-mode gate stack for quantum dots. A mobility of 1.6 × 105 cm2/Vs at 5.8 × 1011/cm2 is measured in Hall bars that witness the same device process flow as the quantum dot. Periodic Coulomb blockade measured in a double-top-gated lateral quantum dot nanostructure terminates with open diamonds up to ±10 mV of dc voltage across the device. The devices were fabricated within a 150 mm Si foundry setting that uses implanted ohmics and chemical-vapor-deposited dielectrics. A modified implant, polycrystalline silicon formation and annealing conditions were utilized to minimize the thermal budget that potentially leads to Ge/Si interdiffusion.
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85.30.Tv Field effect devices
72.20.My Galvanomagnetic and other magnetotransport effects
73.23.Hk Coulomb blockade; single-electron tunneling
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Cy Elemental semiconductors
81.07.Ta Quantum dots

Amorphization of Cu nanoparticles: Effects on surface plasmon resonance

H. Amekura, B. Johannessen, D. J. Sprouster, and M. C. Ridgway

Appl. Phys. Lett. 99, 043102 (2011); http://dx.doi.org/10.1063/1.3615307 (3 pages) | Cited 3 times

Online Publication Date: 25 July 2011

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Crystalline copper nanoparticles (NPs) were formed in silica by multi-energy MeV ion implantations and then transformed to amorphous NPs by irradiation with 5 MeV Sn3+ ions. Optical absorption spectra of both the phases were evaluated in the ultra-violet to near-infrared regions. Compared with corresponding crystalline NPs of the same mean diameter, the amorphous NPs showed a low-energy shift of the surface plasmon resonance around 2.2 eV and less prominent absorption structure around 4 eV. These differences are explained by a strongly reduced electron mean-free-path in the amorphous NPs due to the loss of lattice periodicity.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
64.70.Nd Structural transitions in nanoscale materials
72.15.Lh Relaxation times and mean free paths
73.22.Lp Collective excitations
78.30.Er Solid metals and alloys
78.40.Kc Metals, semimetals, and alloys

Self-aligned fabrication of in-plane SiGe nanowires on rib-patterned Si (001) substrates

G. Chen, G. Springholz, W. Jantsch, and F. Schäffler

Appl. Phys. Lett. 99, 043103 (2011); http://dx.doi.org/10.1063/1.3608149 (3 pages) | Cited 2 times

Online Publication Date: 25 July 2011

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SiGe heteroepitaxy on Si (001) substrates induces three-dimensional Stranski–Krastanow growth. In this work, in-plane nanowires were produced during the growth of Si0.8Ge0.2 onto rib-patterned Si (001) templates oriented in [010] direction. Atomic force microscopy reveals initially hut-shaped SiGe islands on the upper (001) area of the ribs form extended nanowires with lengths of up to 10 μm via coalescence and self-alignment to the rib direction. Finite element simulations show that these phenomena can be attributed to the minimization of the surface and strain energy density. This method provides a route towards devices based on in-plane SiGe nanowires.
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81.16.Dn Self-assembly
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)
81.07.Gf Nanowires
68.35.Md Surface thermodynamics, surface energies
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Effects of silica particles on the electrical percolation threshold and thermomechanical properties of epoxy/silver nanocomposites

Seungwoong Nam, Hyun Woo Cho, Taeho Kim, Daeheum Kim, Bong June Sung, Soonho Lim, and Heesuk Kim

Appl. Phys. Lett. 99, 043104 (2011); http://dx.doi.org/10.1063/1.3615690 (3 pages) | Cited 4 times

Online Publication Date: 27 July 2011

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We experimentally and theoretically demonstrated that the addition of silica particles could improve both the electrical conductivity and the thermomechanical properties of epoxy/silver nanocomposites. As silica particles were added, the electrical percolation threshold concentration of silver nanoparticles decreased and the electrical resistivity of the composite decreased by about 8 orders of magnitude. The coefficient of thermal expansion also decreased with increasing volume fraction of silica particles. Molecular simulations showed that the additional silica particles made the effective intermolecular interactions between silver nanoparticles attractive, thereby enhancing the formation of an electrical percolation network.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Tm Composite materials
81.40.Gh Other heat and thermomechanical treatments
65.40.De Thermal expansion; thermomechanical effects

Al1.3Sb3Te material for phase change memory application

Cheng Peng, Zhitang Song, Feng Rao, Liangcai Wu, Min Zhu, Hongjia Song, Bo Liu, Xilin Zhou, Dongning Yao, Pingxiong Yang, and Junhao Chu

Appl. Phys. Lett. 99, 043105 (2011); http://dx.doi.org/10.1063/1.3616146 (3 pages) | Cited 8 times

Online Publication Date: 27 July 2011

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Comparing with Ge2Sb2Te5, Al1.3Sb3Te is proved to be a promising candidate for phase-change memory use because of its higher crystallization temperature (∼210 °C), larger crystallization activation energy (3.32 eV), and better data retention ability (124 °C for 10 yr). Furthermore, Al1.3Sb3Te shows fast phase change speed and crystallizes into a uniformly embedded crystal structure. As short as 10 ns width, voltage pulse can realize reversible operations for Al1.3Sb3Te based phase-change memory cell. Moreover, phase-change memory cell based on Al1.3Sb3Te material also has good endurance (∼2.5 × 104 cycles) and an enough resistance ratio of ∼102.
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61.66.Fn Inorganic compounds
84.30.Sk Pulse and digital circuits

Room temperature picowatt-resolution calorimetry

Seid Sadat, Yi Jie Chua, Woochul Lee, Yashar Ganjeh, Katsuo Kurabayashi, Edgar Meyhofer, and Pramod Reddy

Appl. Phys. Lett. 99, 043106 (2011); http://dx.doi.org/10.1063/1.3617473 (3 pages) | Cited 10 times

Online Publication Date: 28 July 2011

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Picowatt-resolution calorimetry is necessary for fundamental studies of nanoscale energy transport. Here, we report a microfabricated device capable of <4 pW resolution—an order of magnitude improvement over state-of-the-art room temperature calorimeters. This is achieved by the incorporation of two important features. First, the active area of the device is thermally isolated by thin and long beams with a total thermal conductance (G) of ∼600 nW/K. Further, a bimaterial cantilever thermometer capable of a temperature resolution (ΔTres) of ∼4 μK is integrated into the microdevice. The small thermal conductance and excellent temperature resolution enable measurements of heat currents (q = G × ΔTres) with a resolution <4 pW.
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07.20.Fw Calorimeters

Soft carrier multiplication by hot electrons in graphene

Anuj Girdhar and J. P. Leburton

Appl. Phys. Lett. 99, 043107 (2011); http://dx.doi.org/10.1063/1.3615286 (3 pages) | Cited 3 times

Online Publication Date: 28 July 2011

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By using the Boltzmann formalism, we show that carrier multiplication by impact ionization can take place at relatively low electric fields during electronic transport in graphene. Because of the absence of an energy gap, this effect is not characterized by a field threshold but is a quadratic function of the electric field, unlike in conventional semiconductors. We also show that the resulting current is an increasing function of the electronic temperature but decreases with increasing carrier concentration.
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72.80.Vp Electronic transport in graphene
81.05.ue Graphene
72.20.Ht High-field and nonlinear effects

Accelerating the L10 ordering transition of FePt(001) nanograins using composite buffer layers

Guoqing Li, Yuanping Zheng, Kenichi Hayashi, and Koki Takanashi

Appl. Phys. Lett. 99, 043108 (2011); http://dx.doi.org/10.1063/1.3619204 (3 pages)

Online Publication Date: 28 July 2011

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This paper reports fabrication of 2-nm-thick L10 FePt films at a low substrate temperature of 400 °C using composite MgO and FeAl buffer layers on (001) MgO substrates. The FeAl buffer layer is crucial in promoting the ordered L10 growth of (001) FePt by allowing additional heat uptake. The MgO buffer layer prevents interlayer diffusion of FeAl into the FePt films and induces (001) texture growth. The deposited FePt films consist of isolated nanograins about 13 nm in size. These films have (001) texture and perpendicular magnetic anisotropy with a coercivity of up to 19 kOe. They have potential applications in perpendicular magnetic recording.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.50.Ss Magnetic recording materials
75.50.Vv High coercivity materials

Minimum thermal conductance in graphene and boron nitride superlattice

Jin-Wu Jiang, Jian-Sheng Wang, and Bing-Shen Wang

Appl. Phys. Lett. 99, 043109 (2011); http://dx.doi.org/10.1063/1.3619832 (3 pages) | Cited 4 times

Online Publication Date: 29 July 2011

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The minimum thermal conductance versus supercell size (ds) is revealed in graphene and boron nitride superlattice with ds far below the phonon mean free path. The minimum value is reached at a constant ratio of ds/L ≈ 5%, where L is the thickness of the superlattice; thus, the minimum point of ds depends on L. The phenomenon is attributed to the localization property and the number of confined modes in the superlattice. With the increase of ds, the localization of the confined mode is enhanced while the number of confined modes decreases, which directly results in the minimum thermal conductance.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
63.22.Rc Phonons in graphene
65.80.Ck Thermal properties of graphene
81.05.ue Graphene
63.22.Np Layered systems

Giant electric field controlled magnetic anisotropy in epitaxial BiFeO3-CoFe2O4 thin film heterostructures on single crystal Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrate

Zhiguang Wang, Yaodong Yang, Ravindranath Viswan, Jiefang Li, and D. Viehland

Appl. Phys. Lett. 99, 043110 (2011); http://dx.doi.org/10.1063/1.3619836 (3 pages) | Cited 6 times

Online Publication Date: 29 July 2011

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We have deposited self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) thin films on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrates and studied the change in magnetic anisotropy under different strain conditions induced by an applied electric field. After electric field poling, we observed (i) giant magnetization change: magnetization of original CFO phase is three times larger than that of strained one and (ii) magnetic force microscopy line profiles that exhibited significant change in the CFO magnetic domain response in accordance to magnetization-field (M-H) loops. Together, these results demonstrate good control of the magnetic properties of CFO via an electric field induced strain.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Optical frequency signal detection through surface plasmon polaritons

Takuma Aihara, Kyohei Nakagawa, Masashi Fukuhara, Yen Ling Yu, Kenzo Yamaguchi, and Mitsuo Fukuda

Appl. Phys. Lett. 99, 043111 (2011); http://dx.doi.org/10.1063/1.3619849 (3 pages) | Cited 3 times

Online Publication Date: 29 July 2011

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We demonstrated experimentally that an optical frequency signal can be detected through surface plasmon polaritons (SPPs) using an optical heterodyne technique. We fabricated an SPP detector consisting of a Au/Si Schottky diode with seven 10-μm-long and 150-nm-wide parallel slits (a multi-slit grating). When two beams of light with slightly different wavelengths irradiated the multi-slit grating of the SPP detector, a beat signal, corresponding to the optical frequency signal, was clearly observed.
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81.05.Cy Elemental semiconductors
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
85.30.Kk Junction diodes
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Structure and optical properties of self-assembled multicomponent plasmonic nanogels

T. Cong, S. N. Wani, P. A. Paynter, and R. Sureshkumar

Appl. Phys. Lett. 99, 043112 (2011); http://dx.doi.org/10.1063/1.3615785 (3 pages) | Cited 2 times

Online Publication Date: 29 July 2011

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Multicomponent plasmonic nanogels (PNGs) capable of broadband absorption of light in the 400−700 nm wavelength range were synthesized by the self-assembly of metal nanoparticles with wormlike surfactant micelles. Small angle x-ray scattering and rheological experiments suggest that the nanoparticles bridge micelle fragments to aid the formation a stable gel phase with exceptional color uniformity. Their optical absorbance could be robustly tuned by changing the nanoparticle type (Au/Ag), size, shape, and/or concentration. The PNGs have relatively low viscosity and are thermoreversible. Potential applications to the manufacturing of coatings and interfaces for solar energy harvesting and reconfigurable optical devices can be envisioned.
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81.16.Dn Self-assembly
73.22.Lp Collective excitations
82.70.Gg Gels and sols
78.70.Ck X-ray scattering
78.40.Dw Liquids
78.30.cc Inorganic liquids

Plasmon induced transparency in a dielectric waveguide

Yingran He, Hao Zhou, Yi Jin, and Sailing He

Appl. Phys. Lett. 99, 043113 (2011); http://dx.doi.org/10.1063/1.3621860 (3 pages) | Cited 5 times

Online Publication Date: 29 July 2011

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A classical effect of electromagnetically induced transparency (EIT) is demonstrated in a dielectric slab waveguide at visible frequencies. Two nano-sized elliptical silver particles are placed inside the waveguide core layer, and their localized plasmonic resonances are utilized to obtain bright and dark states. The destructive interference between the two resonance paths leads to an EIT-like transmission spectrum of the waveguide. The contrast between the transmission peak and dip can be further enhanced by incorporating the Fabry-Perot resonance effect. The influence of Joule loss on the EIT performance is also investigated.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.79.Gn Optical waveguides and couplers
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