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7 Nov 2011

Volume 99, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 193101 (2011); http://dx.doi.org/10.1063/1.3657777 (3 pages)

Sungwook Chung, Jonathan R. Felts, Debin Wang, William P. King, and James J. De Yoreo
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Photo-induced spin filtering in a double quantum dot

J. Wätzel, A. S. Moskalenko, and J. Berakdar

Appl. Phys. Lett. 99, 192101 (2011); http://dx.doi.org/10.1063/1.3660227 (3 pages) | Cited 2 times

Online Publication Date: 7 November 2011

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We investigate the spin-dependent electron dynamics in a double quantum dot driven by sub-picosecond asymmetric electromagnetic pulses. We show analytically that applying the appropriate pulses, specified here, allows a spin separation on a femtosecond time scale in the sense that states with a desired spin projection are localized mainly on one of the dots. It is shown how to maintain in time this photo-induced spin-dependent filtering.
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81.07.Ta Quantum dots
73.63.Kv Quantum dots
72.25.-b Spin polarized transport

Abnormal electronic transport and negative differential resistance of graphene nanoribbons with defects

Yipeng An and Zhongqin Yang

Appl. Phys. Lett. 99, 192102 (2011); http://dx.doi.org/10.1063/1.3660228 (3 pages) | Cited 6 times

Online Publication Date: 8 November 2011

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Electronic transport properties of zigzag graphene nanoribbons (GNRs) with two kinds of triangular defects are explored by using an ab-initio method. At a certain bias, the current of the GNR with an upward-triangle defect can be surprisingly larger than that of the perfect GNR due to the defect-induced symmetry breaking and more conductive channels. Dissimilarly, if the orientation of the triangle is changed rightward, the current is depressed much and shows negative differential resistance behavior. Our findings indicate that defect designs can be an efficient way to tune the electronic transport of GNR nanodevices.
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73.22.Pr Electronic structure of graphene
71.55.Ht Other nonmetals
72.80.Vp Electronic transport in graphene
72.20.Ht High-field and nonlinear effects
71.15.-m Methods of electronic structure calculations
71.20.Tx Fullerenes and related materials; intercalation compounds

Electrodynamics and quantum capacity of LixFePO4 battery material

L. Craco and S. Leoni

Appl. Phys. Lett. 99, 192103 (2011); http://dx.doi.org/10.1063/1.3660247 (3 pages) | Cited 5 times

Online Publication Date: 9 November 2011

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We report on optical conductivity and dielectric properties of pure and electron-doped FePO4, an attractive material for the next generation of lithium-ion batteries. Using the local-density-approximation plus dynamical mean-field theory for the real multi-orbital case we show the importance of incoherence-induced high energy continuum in LixFePO4. Our results for the dielectric function allow us to elucidate relevant features seen in experimental potential-capacity profiles and serve as a theoretical basis for postulating that potential-capacity and electrodynamic responses are microscopically entangled in nature. Our microscopic description of quantum capacity is expected to be applicable to battery materials in general.
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82.47.Aa Lithium-ion batteries
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Dye-sensitized solar cells with modified TiO2 surface chemical states: The role of Ti3+

Yang Yu, Kunjie Wu, and Deliang Wang

Appl. Phys. Lett. 99, 192104 (2011); http://dx.doi.org/10.1063/1.3660711 (3 pages) | Cited 6 times

Online Publication Date: 9 November 2011

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Dye-sensitized solar cells (DSSCs) with TiO2 electrodes, which were modified to have different surface chemical states, were fabricated. The DSSCs had an ultra-flat TiO2 electrode, on which only a mono-layer dye was attached. The cell I-V measurement showed that Ti3+ ion had a dramatic effect on cell performance. The efficiency of a DSSC was shown to have a strong correlation with the concentration of the Ti3+ surface state, it decreased almost linearly with increased Ti3+ concentration. The oxygen vacancy-Ti3+ defect served as electron recombination center and decreased both the open-circuit voltage and the fill factor.
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88.40.jj Silicon solar cells

Measurement of backscattered 100 keV electrons on a solid substrate

David A. Czaplewski and Leonidas E. Ocola

Appl. Phys. Lett. 99, 192105 (2011); http://dx.doi.org/10.1063/1.3660712 (3 pages)

Online Publication Date: 9 November 2011

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We have measured the intensity of backscattered 100 keV electrons on a silicon substrate as a function of distance up to 50 μm from the source. The intensity of backscattered electrons was determined by measuring the thickness changes in pre-exposed, isolated 100 nm crosses in a negative resist using atomic force microscopy. The electron backscattered range was measured to be 31.08 ± 0.30 μm and showed deviation from Gaussian behavior for radii larger than 30 μm. This method produces an accurate measurement of the backscattered range because it is process independent and covers a large data range.
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79.20.Kz Other electron-impact emission phenomena

Surface effect on resistive switching behaviors of ZnO

Jr-Jian Ke, Zi-Jheng Liu, Chen-Fang Kang, Su-Jien Lin, and Jr-Hau He

Appl. Phys. Lett. 99, 192106 (2011); http://dx.doi.org/10.1063/1.3659296 (3 pages) | Cited 11 times

Online Publication Date: 9 November 2011

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The interaction between chemisorbed oxygen adatoms (O2(ad)−) and oxygen vacancies associated with the formation/rupture of conductive filaments dominates the switching yield of ZnO, which is also confirmed by the fact that the reduction of SET/RESET voltage with the temperature. The pronounced surface effect-induced conductivity lowering due to O2(ad)− chemisorption leads to increased resistance of high resistance state (HRS). The current decay of the HRS with increased temperatures/times is owing to the severe O2(ad)− chemisorption as Joule heating is continuously applied. The statistical analysis for over 400 cells provides essential evidence for evaluating the surface effect on resistive switching.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
61.72.jd Vacancies
68.43.Mn Adsorption kinetics

Probing the metal-insulator transition of NdNiO3 by electrostatic doping

Junwoo Son, Bharat Jalan, Adam P. Kajdos, Leon Balents, S. James Allen, and Susanne Stemmer

Appl. Phys. Lett. 99, 192107 (2011); http://dx.doi.org/10.1063/1.3659310 (3 pages) | Cited 3 times

Online Publication Date: 9 November 2011

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Modulation of the charge carrier density in a Mott material by remote doping from a highly doped conventional band insulator is proposed to test theoretical predictions of band filling control of the Mott metal-insulator transition without introducing lattice distortions or disorder, as is the case for chemical doping. The approach is experimentally tested using ultrathin (2.5 nm) NdNiO3 films that are epitaxially grown on La-doped SrTiO3 films. We show that remote doping systematically changes the charge carrier density in the NdNiO3 film and causes a moderate shift in the metal-insulator transition temperature. These results are discussed in the context of theoretical models of this class of materials exhibiting a metal-insulator transition.
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71.30.+h Metal-insulator transitions and other electronic transitions
73.61.Ng Insulators
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.up Other materials
68.55.aj Insulators

Microwave driven arbitrary coupling between trapped charge resonances in a silicon single electron transistor

Morteza Erfani, David G. Hasko, Alessandro Rossi, Wan Sik Cho, and Jung-Bum Choi

Appl. Phys. Lett. 99, 192108 (2011); http://dx.doi.org/10.1063/1.3659896 (3 pages)

Online Publication Date: 9 November 2011

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We report controllable coupling between coherent excitations in a silicon transistor, which is useful for double-qubit gate operation. Coupling interactions may be directed by adjusting the gate voltage in a semiconductor device or by an additional flux in a superconducting device. Here, we demonstrate an alternative approach to coupling by exploiting the nonlinear behavior of the silicon transistor. Microwave spectroscopy on a DC-biased transistor has previously been found to indicate the presence of coherent oscillating electrons. We couple two such resonances by using triple-frequency spectroscopy, where the third frequency corresponds to the frequency difference between the two on-resonance frequencies.
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85.35.Gv Single electron devices

Clarification of enhanced ferromagnetism in Be-codoped InMnP fabricated using Mn/InP:Be bilayers grown by molecular beam epitaxy

Yoon Shon, Sejoon Lee, Im Taek Yoon, H. C. Jeon, D. J. Lee, T. W. Kang, J. D. Song, Chong S. Yoon, D. Y. Kim, and C. S. Park

Appl. Phys. Lett. 99, 192109 (2011); http://dx.doi.org/10.1063/1.3660274 (3 pages) | Cited 1 time

Online Publication Date: 10 November 2011

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The p-type InMnP:Be epilayers were prepared by the sequential growth of Mn/InP:Be bilayers using molecular-beam-epitaxy and the subsequent in-situ annealing at 200–300 °C. In triple-axis x-ray diffraction patterns, the samples revealed a shoulder peak indicative of intrinsic InMnP. The ferromagnetic transition in InMnP:Be was observed to occur at the elevated temperature of ∼140 K, and the ferromagnetic spin-domains clearly appeared in magnetic force microscopy images. The improved ferromagnetic properties are attributed to the increased p–d hybridation due to high p-type conductivity of InMnP:Be (p ∼ 1020 cm−3). The results suggest that enhanced ferromagnetism can be effectively obtained from Be-codoped InMnP.
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75.70.Ak Magnetic properties of monolayers and thin films
68.37.Rt Magnetic force microscopy (MFM)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials

Excellent resistive switching in nitrogen-doped Ge2Sb2Te5 devices for field-programmable gate array configurations

Seonghyun Kim, Jubong Park, Seungjae Jung, Wootae Lee, Jiyong Woo, Chunhum Cho, Manzar Siddik, Jungho Shin, Sangsu Park, Byoung Hun Lee, and Hyunsang Hwang

Appl. Phys. Lett. 99, 192110 (2011); http://dx.doi.org/10.1063/1.3659692 (3 pages) | Cited 2 times

Online Publication Date: 11 November 2011

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The nitrogen-doped Ge2Sb2Te5 (GST) programmable metallization cell is investigated to address the low switching voltage and need for a high resistance ratio, which are critical issues for the filed-programmable gate array (FPGA) configuration. Nitrogen doping of GST yields Ge–N covalent bonds, as confirmed by x-ray photoelectron spectroscopy and Raman spectroscopy; this increases the resistivity of GST. Consequently, an excellent resistance ratio (∼107) with appropriate operating voltage and stable retention properties more than for 104 s at 85 °C are achieved. The results indicate that the film is a suitable alternative candidate for the logic switch in static-random-access-memory-based FPGA technology.
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84.30.Sk Pulse and digital circuits
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.40.Ls Metallization, contacts, interconnects; device isolation
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