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8 Oct 2007

Volume 91, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 153101 (2007); http://dx.doi.org/10.1063/1.2793688 (3 pages)

B. J. Lee, K. Park, and Z. M. Zhang
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Investigation of magnetic and electronic coupling between two (Ga,Mn)As layers in (Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junctions

Z. Ge, Y. Y. Zhou, Y.-J. Cho, X. Liu, J. K. Furdyna, and M. Dobrowolska

Appl. Phys. Lett. 91, 152109 (2007); http://dx.doi.org/10.1063/1.2799238 (3 pages) | Cited 11 times

Online Publication Date: 12 October 2007

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The coupling between the two magnetic layers in a series of (Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junctions with different nonmagnetic spacer thicknesses tNM were studied by magnetization and planar Hall effect (PHE) measurements. The PHE data indicate that the magnetization reversals of the two layers are strongly correlated when the tNM is less than 3 nm and are independent when tNM is larger than 15 nm. From the results, it is concluded that considerable redistribution of hole wave functions plays a major role for small tNM. The PHE results for the sample with 6 nm spacer also suggest an antiferromagnetic interlayer exchange coupling.
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75.50.Pp Magnetic semiconductors
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms

Possible efficient p-type doping of AlN using Be: An ab initio study

R. Q. Wu, L. Shen, M. Yang, Z. D. Sha, Y. Q. Cai, Y. P. Feng, Z. G. Huang, and Q. Y. Wu

Appl. Phys. Lett. 91, 152110 (2007); http://dx.doi.org/10.1063/1.2799241 (3 pages) | Cited 4 times

Online Publication Date: 12 October 2007

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Spin density functional theory based ab initio study is carried out to investigate the feasibility of fabricating p-type AlN using Be as an efficient dopant. It is found that substitutional BeAl is an acceptor with an activation energy of 0.34 eV. To overcome the low solubility of direct incorporation of Be into AlN and self-compensation from Be interstitials, we propose a hydrogen-assisted growth scheme which improves the solubility and suppresses interstitials. Oxygen is also found to be an effective codopant to activate Be in AlN. Our results suggest the possibility of improving p-type conductivity of AlN by Be doping.
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61.72.uj III-V and II-VI semiconductors
61.72.J- Point defects and defect clusters
61.72.Bb Theories and models of crystal defects

High efficiency double heterojunction polymer photovoltaic cells using highly ordered TiO2 nanotube arrays

Gopal K. Mor, Karthik Shankar, Maggie Paulose, Oomman K. Varghese, and Craig A. Grimes

Appl. Phys. Lett. 91, 152111 (2007); http://dx.doi.org/10.1063/1.2799257 (3 pages) | Cited 86 times

Online Publication Date: 12 October 2007

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Vertically oriented TiO2 nanotube arrays formed by anodization offer a highly ordered material architecture for efficient charge generation and collection in photoelectrochemical devices. A blend of regioregular poly(3-hexylthiophene) and a methanofullerene (phenyl C71-butyric acid methyl ester) was infiltrated into transparent TiO2 nanotube films. The heterojunction poly(3-hexylthiophene) (P3HT)-([6,6]-phenyl-C71-butyric acid methyl ester) and P3HT-TiO2 interfaces both result in charge separation. The resulting solid state solar cells show a short-circuit current density of 12.4 mA/cm2, 641 mV open circuit potential, and a 0.51 fill factor, yielding power conversion efficiencies of 4.1% under AM 1.5 sun.
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84.60.Jt Photoelectric conversion
85.35.Kt Nanotube devices
85.65.+h Molecular electronic devices
82.47.Jk Photoelectrochemical cells, photoelectrochromic and other hybrid electrochemical energy storage devices
82.45.Yz Nanostructured materials in electrochemistry
82.45.Wx Polymers and organic materials in electrochemistry
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Ferromagnetic CrxTi1−xN solid solution nitride thin films grown by pulsed laser deposition and their magnetoresistance

Kei Inumaru, Kunihiko Koyama, Yuji Miyaki, Kazuma Tanaka, and Shoji Yamanaka

Appl. Phys. Lett. 91, 152501 (2007); http://dx.doi.org/10.1063/1.2776853 (3 pages) | Cited 6 times

Online Publication Date: 8 October 2007

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Epitaxial nitride films of CrxTi1−xN were grown on MgO (001) by pulsed laser deposition under nitrogen radical irradiation, and their magnetic and transport properties were investigated, which was motivated by calculations on magnetism pointing out similarities of CrN to LaMnO3, the parent compound of colossal magnetoresistance oxides. The films showed ferromagnetism for 0.28 ⩽ x ⩽ 0.5 and the TC showed a maximum (140 K) at x = 0.5. When x exceeded 0.5(x = 0.58) ferromagnetism disappeared completely. At x = 0.5, the nitride film showed a large magnetoresistance (6%–7% at 5 T), which had a maximum at 130 K.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Fg Pulsed laser ablation deposition

Magnetic properties and microstructure of FePt/BN nanocomposite films with perpendicular magnetic anisotropy

Bao-He Li, Chun Feng, Xin Gao, Jiao Teng, Guang-Hua Yu, Xianran Xing, and Zhong-Yuan Liu

Appl. Phys. Lett. 91, 152502 (2007); http://dx.doi.org/10.1063/1.2798584 (3 pages) | Cited 7 times

Online Publication Date: 8 October 2007

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We have prepared L10-FePt/BN nanocomposite films by depositing the FePt/BN mutilayers on the MgO(100) substrates using magnetron sputtering followed by a postannealing process. We found the excellent perpendicular magnetic anisotropy of [FePt (2 nm)/BN (0.5 nm)]10 film after annealing at 700 °C for 1 h x-ray diffraction patterns also indicate an excellent (001) texture of the film. This film shows a perpendicular coercivity of 7.48 kOe and the ratio of the remnant magnetization Mr to the saturation one MS of as high as 0.93. We also found the good epitaxial growth of FePt grains on the MgO(100) substrate by cross-section high resolution transmitting microscopy.
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75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ss Magnetic recording materials

Estimation of Mn4+ ion content ratio in self-doped compound La1−xMnO3−δ

G. D. Tang, D. L. Hou, W. Chen, P. Hao, G. H. Liu, S. P. Liu, X. L. Zhang, and L. Q. Xu

Appl. Phys. Lett. 91, 152503 (2007); http://dx.doi.org/10.1063/1.2794777 (3 pages) | Cited 7 times

Online Publication Date: 9 October 2007

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A method based on the thermal equilibrium theory of crystal defects for estimating the Mn4+ ion content ratio (RM4) at B sites in ABO3 self-doped manganite La1−xMnO3−δ is presented. For this kind of manganite, the relationship between the Curie temperature (TC) and RM4 can be explained by the double exchange mechanism of Zener, which is similar to that in the perovskite manganite La1−xCaxMnO3.
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61.72.S- Impurities in crystals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Spin-polarized current versus stray field in a perpendicularly magnetized superconducting spin switch

A. Singh, C. Sürgers, R. Hoffmann, H. v. Löhneysen, T. V. Ashworth, N. Pilet, and H. J. Hug

Appl. Phys. Lett. 91, 152504 (2007); http://dx.doi.org/10.1063/1.2794424 (3 pages) | Cited 12 times

Online Publication Date: 10 October 2007

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In superconducting Co/Pt–Nb–Co/Pt multilayers with perpendicular magnetic anisotropy, the superconducting transition temperature Tc is considerably higher in the parallel (P) orientation of the two Co/Pt magnetizations compared to the antiparallel (AP) orientation. Low temperature magnetic-force microscopy reveals that the individual ferromagnetic layers are uniformly magnetized in both configurations and do not exhibit a magnetic stray field arising from a multidomain state. We also demonstrate that the difference ΔTc = TcP−TcAP between both Tc values is enhanced at higher transport currents due to the increasing imbalance of spin-polarized charge carriers in the superconducting Nb layer. Hence, the spin switch can be controlled by the transport current in future superconducting devices.
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74.78.Fk Multilayers, superlattices, heterostructures
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.62.Yb Other effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Magnetic field dependent behavior in perpendicular antiferromagnetically coupled multilayer films

Y. Fu, W. Pei, J. Yuan, T. Wang, T. Hasegawa, T. Washiya, H. Saito, and S. Ishio

Appl. Phys. Lett. 91, 152505 (2007); http://dx.doi.org/10.1063/1.2798496 (3 pages) | Cited 10 times

Online Publication Date: 10 October 2007

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Magnetization reversal and magnetic domain structures controlled by the magnetostatically induced stray field in perpendicular antiferromagnetically coupled [Pd/Co]7/Ru/Co/[Pd/Co]7 multilayer were investigated by magnetic force microscopy. For the sample demagnetized in plane, field-induced ferromagnetic domains at the boundary of antiferromagnetic domains provide the nucleation channel. The ferromagnetic domains in the channel are parallel aligned along the applied field out of plane firstly, and then the magnetization reversal is dominated by the propagation of the ferromagnetic channels toward the region of antiferromagnetic domains. The sample demagnetized in perpendicular direction shows antiferromagnetic coupling state. Ultraslow reversal dynamics were observed under a perpendicular critical magnetic field (Hcri) in a long time. The reversal process can be explained by the inhomogeneous local stray field and the competition between magnetostatic energy and exchange energy.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
75.50.Ee Antiferromagnetics

Giant magnetocaloric effect in antiferromagnetic ErRu2Si2 compound

Tapas Samanta, I. Das, and S. Banerjee

Appl. Phys. Lett. 91, 152506 (2007); http://dx.doi.org/10.1063/1.2798594 (3 pages) | Cited 44 times

Online Publication Date: 11 October 2007

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Giant magnetocaloric effect has been observed in ErRu2Si2, which is associated with field-induced metamagnetic transition from antiferromagnetic to ferromagnetic state. The maximum values of magnetic entropy change (−ΔSMmax) and adiabatic temperature change (ΔTadmax) for a field change of 7 T are evaluated to be 19.3 J/kg K and 15.9 K, respectively, around 5.5 K within the temperature range of 4–25 K. The value of ΔTadmax is even larger than other potential magnetic refrigerant materials reported in the same temperature range and also comparable to room temperature giant magnetocaloric materials exhibiting first-order magnetic transition from paramagnetic to ferromagnetic state.
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75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys
75.30.Sg Magnetocaloric effect, magnetic cooling
75.20.En Metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Low-field positive magnetoresistance near room temperature in three-component perovskite-type artificial superlattices

Kun Zhao, Meng He, and Hui-bin Lu

Appl. Phys. Lett. 91, 152507 (2007); http://dx.doi.org/10.1063/1.2799162 (3 pages) | Cited 6 times

Online Publication Date: 11 October 2007

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Perovskite-type superlattices consisting of La0.9Sr0.1MnO3, LaAlO3, and SrTiO3 were fabricated on (001) SrNb0.01Ti0.99O3 substrates by laser molecular beam epitaxy. The three-component superlattice exhibited desirable low-field magnetoresistance effects. At a given current bias of 10 μA, positive magnetoresistance ratio was enhanced from 2% to 15% and 22% with increasing temperatures from 15 to 300 and 325 K at 300 Oe, at which a maximum value occurred from the external magnetic field dependence of magnetoresistance. The nature of the enhanced magnetoresistance is discussed in connection to the interfacial effect.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Current-in-plane magnetoresistance of spin valve elliptical rings

W. Jung, F. J. Castaño, and C. A. Ross

Appl. Phys. Lett. 91, 152508 (2007); http://dx.doi.org/10.1063/1.2798495 (3 pages) | Cited 7 times

Online Publication Date: 12 October 2007

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The giant magnetoresistance of NiFe/Cu/Co/IrMn spin valve elliptical rings with 3.2/1.9 μm major/minor diameter and widths of 340–370 nm has been characterized in a current-in-plane geometry. Spin valve rings show asymmetric magnetoresistance curves with three different resistance levels. Minor loop magnetoresistance measurements, which correspond to the switching of only the NiFe free layer, demonstrate that individual control of the chirality of the magnetization vortex in each ferromagnetic layer is possible, enabling at least 16 distinct magnetic configurations to be formed in a spin valve ring.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Chemical composition changes across the interface of amorphous LaScO3 on Si (001)

F. Liu and G. Duscher

Appl. Phys. Lett. 91, 152901 (2007); http://dx.doi.org/10.1063/1.2798246 (3 pages)

Online Publication Date: 8 October 2007

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An amorphous, high-dielectric-constant LaScO3 film was deposited directly on Si (001) by molecular-beam deposition at ∼ 100 °C. Various transmission electron microscopy techniques were applied to study the interface at atomic resolution. We observed an ∼ 3.5-nm-thick interfacial layer that was not previously detected with other techniques. The interfacial layer contained defects and its density changes gradually. The interface was not only structurally sharp but also chemically sharp within the detection limit of the experimental methods. The chemical composition of the bulk oxide film was stoichiometric, but the interfacial layer was oxygen poor.
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68.35.Dv Composition, segregation; defects and impurities
68.35.Ct Interface structure and roughness
61.43.Er Other amorphous solids
61.66.Bi Elemental solids
61.66.Dk Alloys
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Enhanced quality factors in aperiodic reflector resonators

Jonathan Breeze, Jerzy Krupka, and Neil McN Alford

Appl. Phys. Lett. 91, 152902 (2007); http://dx.doi.org/10.1063/1.2798055 (3 pages) | Cited 3 times

Online Publication Date: 9 October 2007

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Cavity resonators that employ the high reflectivity of periodic arrays of dielectric layers exhibit enhanced quality factors compared with dielectric resonators. Their quality factor is limited by the exponential decay of the electric field penetrating the structure. We show that an aperiodic reflector array with dielectric layers thinner than a quarter-wave near the defect site and asymptotically approaching quarter-wave thickness distant from the site can exhibit very high quality factors. A spherical aperiodic reflector resonator consisting of nested alumina shells is simulated and shown to exhibit quality factors greater than 107 at 10 GHz and room temperature.
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84.40.Az Waveguides, transmission lines, striplines
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Dynamic magnetoelectric coupling in “electronic ferroelectric” LuFe2O4

Ji Yong Park, Jung Hwan Park, Young Kyu Jeong, and Hyun M. Jang

Appl. Phys. Lett. 91, 152903 (2007); http://dx.doi.org/10.1063/1.2798597 (3 pages) | Cited 26 times

Online Publication Date: 9 October 2007

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Magnetoelectric (ME) coupling characteristics of LuFe2O4 were examined by monitoring the electrical voltage induced by an oscillating magnetic field under a static bias field (H0). Interestingly, the room-temperature dynamic ME output exhibited a constant plateau behavior up to a certain static-field strength but showed a sudden drop above this critical value. In addition, two evidences of the intrinsic ME coupling were obtained by monitoring the pyroelectric response near the ferrimagnetic ordering temperature ( ∼ 250 K) and by examining the temperature-dependent magnetization near the ferroelectric transition point ( ∼ 345 K) between the two-dimensional charge-density-wave (CDW) state and the three-dimensional CDW state.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Gg Ferrimagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
77.80.B- Phase transitions and Curie point
77.70.+a Pyroelectric and electrocaloric effects
71.45.Lr Charge-density-wave systems

Effect of kerf filler on the electromechanical coupling coefficient of an ultrasonic transducer array element

Jungsoon Kim, Moojoon Kim, and Wenwu Cao

Appl. Phys. Lett. 91, 152904 (2007); http://dx.doi.org/10.1063/1.2795333 (3 pages)

Online Publication Date: 10 October 2007

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Electromechanical coupling coefficient directly reflects the electromechanical energy conversion capability of a piezoelectric device. We show theoretically that the kerf filler in the ultrasonic array transducer can degrade this coupling coefficient. A closed form expression has been derived that can quantitatively describe the electromechanical coupling coefficient of an ultrasonic transducer array element with arbitrary aspect ratio and having polymer kerf filler in between transducer elements.
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43.38.Hz Transducer arrays, acoustic interaction effects in arrays
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Improved electrical properties of metal-oxide-semiconductor capacitor with HfTiON gate dielectric by using HfSiON interlayer

J. P. Xu, F. Ji, C. X. Li, P. T. Lai, J. G. Guan, and Y. R. Liu

Appl. Phys. Lett. 91, 152905 (2007); http://dx.doi.org/10.1063/1.2798248 (3 pages) | Cited 4 times

Online Publication Date: 10 October 2007

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Metal-oxide-semiconductor (MOS) capacitor with HfTiON/HfSiON stack structure as high-k gate dielectric is fabricated, and its electrical properties are compared with those of a similar device with HfTiON only as gate dielectric. Experimental results show that the device with HfTiON/HfSiON gate dielectric exhibits better interface properties, lower gate leakage current, and enhanced high-field reliability. All these improvements should be attributed to the fact that the HfSiON buffer layer effectively blocks the diffusion of Ti atoms to the Si substrate, thus resulting in a SiO2/Si-like HfSiON/Si interface.
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84.32.Tt Capacitors

Thermal annealing effect on the interface structure of high-κ LaScO3 on silicon

F. Liu and G. Duscher

Appl. Phys. Lett. 91, 152906 (2007); http://dx.doi.org/10.1063/1.2799177 (3 pages) | Cited 1 time

Online Publication Date: 10 October 2007

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The thermal stability of LaScO3 on Si was examined by various transmission electron microscopy techniques. The film remained amorphous up to 700 °C and became polycrystalline at 800 °C. All samples showed an interfacial layer about 3.5 nm thick, except for the 1000 °C-annealed sample, which had a thicker interfacial layer containing a thin silicate layer close to the interface with the substrate. Although the chemical composition of the bulk film was stoichiometric, the interfacial layer was oxygen-rich after postannealing. The interfacial layer remained amorphous up to 1000 °C, indicating that this interfacial layer itself may be used as a gate dielectric.
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68.35.Ct Interface structure and roughness
77.55.-g Dielectric thin films
61.66.Bi Elemental solids
61.66.Dk Alloys

Structurally frustrated polar nanoregions in BaTiO3-based relaxor ferroelectric systems

Y. Liu, R. L. Withers, B. Nguyen, and K. Elliott

Appl. Phys. Lett. 91, 152907 (2007); http://dx.doi.org/10.1063/1.2790481 (3 pages) | Cited 9 times

Online Publication Date: 11 October 2007

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This letter presents direct electron diffraction evidence that structurally frustrated one-dimensional polar nanoregions arising from anticorrelated displacements of Ti and nearest neighboring O ions are responsible for the relaxation behavior observed in doped BaTiO3 relaxor ferroelectrics, rather than chemical short range ordering. The role of the dopant ions is not to directly induce polar nanoregions but rather to set up random local strain fields preventing homogeneous strain distortion, thereby suppressing transverse correlation from one ⟨001⟩ chain dipole to the next and hence the development of long range ferroelectric order.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
77.80.B- Phase transitions and Curie point

5-nm-thick TaSiC amorphous films stable up to 750 °C as a diffusion barrier for copper metallization

Ting-Yi Lin, Huai-Yu Cheng, Tsung-Shune Chin, Chin-Fu Chiu, and Jau-Shiung Fang

Appl. Phys. Lett. 91, 152908 (2007); http://dx.doi.org/10.1063/1.2799245 (3 pages) | Cited 15 times

Online Publication Date: 12 October 2007

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Ultrathin TaSiC amorphous films prepared by magnetron cosputtering using TaSi2 and C targets on Si(100), in a sandwiched scheme Si(100)/TaSiC(5 nm)/Cu, were evaluated for barrier performance in copper metallization. Optimizing carbon content maximizes thermal stability of the films as depicted by sheet-resistance, x-ray diffraction, and transmission electron microscopy examination. The stability temperatures of 700 °C (24 at. % C) and 750 °C (34 at. % C) have been systematically verified and discussed. Since Ta, Si, and C are compatible with integrated circuit (IC) processing, the TaSiC films are readily applicable for sub-65-nm IC production.
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68.55.-a Thin film structure and morphology
73.61.-r Electrical properties of specific thin films
66.30.-h Diffusion in solids

Thickness dependency of 180° stripe domains in ferroelectric ultrathin films: A first-principles-based study

Bo-Kuai Lai, Inna Ponomareva, Igor Kornev, L. Bellaiche, and Greg Salamo

Appl. Phys. Lett. 91, 152909 (2007); http://dx.doi.org/10.1063/1.2799252 (3 pages) | Cited 12 times

Online Publication Date: 12 October 2007

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A first-principles-based scheme is used to investigate the thickness dependency of domain width of 180° stripe domains in Pb(Zr,Ti)O3 ultrathin films. Our study shows that (1) more metastable states with energy closer to the 180° stripe domain ground state occur in thicker films, (2) the Kittel law is valid for 180° stripe domains when the film thickness is above 1.6 nm, and (3) below 1.2 nm, the Kittel law cannot be applied anymore due to the disappearance of domains. The thickness dependency of the domain morphology is also discussed.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.Dj Domain structure; hysteresis
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Energy pathways in nanoscale thermal radiation

B. J. Lee, K. Park, and Z. M. Zhang

Appl. Phys. Lett. 91, 153101 (2007); http://dx.doi.org/10.1063/1.2793688 (3 pages) | Cited 10 times

Online Publication Date: 8 October 2007

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We show in this letter that when nanoscale radiation between two parallel plates is considered, the Poynting vector is decoupled for each parallel wavevector component (β) due to the nature of thermal emission, as manifested by the fluctuation-dissipation theorem. The streamlines calculated by tracing the Poynting vector vividly demonstrate that the spectral radiative energy travels in infinite directions along curved lines. Depending on the β value, the energy pathway may exhibit considerable lateral shift. This letter elucidates the fundamental characteristics of nanoscale thermal radiation that is important for applications, such as near-field optical sensors and energy conversion devices.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Thermally induced capacitive effect of a nanoporous monel

Yu Qiao, Venkata K. Punyamurtula, and Aijie Han

Appl. Phys. Lett. 91, 153102 (2007); http://dx.doi.org/10.1063/1.2798245 (3 pages) | Cited 4 times

Online Publication Date: 8 October 2007

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As temperature changes, the equilibrium condition at a solid-liquid interface would be disrupted and the ion density varies, which, in turn, affects the interface potential. In the current study, this phenomenon is analyzed by using nanoporous monel electrodes. The experimental data show that, as the ion density is thermally adjusted, the capacitive effect leads to a significant thermal-to-electric energy conversion.
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84.60.Rb Thermoelectric, electrogasdynamic and other direct energy conversion
82.45.Fk Electrodes
82.45.Yz Nanostructured materials in electrochemistry

Nanopore in metal-dielectric sandwich for DNA position control

Stas Polonsky, Steve Rossnagel, and Gustavo Stolovitzky

Appl. Phys. Lett. 91, 153103 (2007); http://dx.doi.org/10.1063/1.2798247 (3 pages) | Cited 18 times

Online Publication Date: 8 October 2007

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We present the concept of a nanoelectromechanical device capable of controlling the position of DNA inside a nanopore with a single nucleotide accuracy. The device utilizes the interaction of discrete charges along the backbone of a DNA molecule with the electric field inside the nanopore. In analogy to solid state transistors in which a small voltage controls the current between two electrodes, a voltage strategically located inside the nanopore can control the translocation of a single DNA molecule between a cis and a trans reservoirs. We propose an immediate application of the device as a replacement of capillary electrophoresis in DNA sequencing.
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82.37.Rs Single molecule manipulation of proteins and other biological molecules
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
82.39.Pj Nucleic acids, DNA and RNA bases

Structural characterization and low temperature growth of ferromagnetic Bi–Cu codoped ZnO bicrystal nanowires

C. Xu, J. Chun, D. Kim, B. Chon, and T. Joo

Appl. Phys. Lett. 91, 153104 (2007); http://dx.doi.org/10.1063/1.2791005 (3 pages) | Cited 8 times

Online Publication Date: 8 October 2007

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Ferromagnetic Bi–Cu codoped ZnO nanowires were fabricated at temperatures as low as 300 °C via a vapor phase transport using the mixture of Zn, BiI3 and CuI powders. They are grown as a bicrystal, along the [01math2] direction, have a width of 40–150 nm, and a length of a few microns. The investigation of the growth mechanism proposes that the synergy of BiCu and iodine/iodide induces the formation of bicrystallinity. The photoluminescence measurement shows the cooperative effect of Bi and Cu ions. The ferromagnetism observed in this study is the result of the combined effect of structural defects, the substitution of Cu into Zn site along the c axis, and codoping of Bi.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.La Quantum wires (patterned in quantum wells)
78.67.Lt Quantum wires
75.50.Pp Magnetic semiconductors
78.55.Et II-VI semiconductors

Spin field effect transistor with a graphene channel

Y. G. Semenov, K. W. Kim, and J. M. Zavada

Appl. Phys. Lett. 91, 153105 (2007); http://dx.doi.org/10.1063/1.2798596 (3 pages) | Cited 36 times

Online Publication Date: 9 October 2007

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A spin field effect transistor (FET) is proposed by utilizing a graphene layer as the channel. Similar to the conventional spin FETs, the device involves spin injection and spin detection by ferromagnetic source and drain. Due to the negligible spin-orbit coupling in the carbon based materials, spin manipulation in the channel is achieved via electrical control of the electron exchange interaction with a ferromagnetic gate dielectric. Numerical estimates indicate the feasibility of the concept if the bias can induce a change in the exchange interaction energy of the order of meV. When nanoribbons are used for a finite channel width, those with armchair-type edges can maintain the device stability against the thermal dispersion.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors
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