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1 Aug 2008

Volume 104, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 104, 031101 (2008); http://dx.doi.org/10.1063/1.2959429 (11 pages)

B. S. Kang, H. T. Wang, F. Ren, and S. J. Pearton
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Investigation on copper phthalocyanine/multiwalled carbon nanotube interface

L. Lozzi, S. Santucci, F. Bussolotti, and S. La Rosa

J. Appl. Phys. 104, 033701 (2008); http://dx.doi.org/10.1063/1.2961325 (5 pages) | Cited 1 time

Online Publication Date: 1 August 2008

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The electronic and structural properties of copper phthalocyanine deposited onto multiwalled carbon nanotubes were studied as a function of the deposition thickness. The valence band and core level spectra were investigated using photoemission spectroscopy. A shift of the organic highest occupied molecular level toward the Fermi level was observed for very thin film, together with a small shift of the nitrogen and copper core level peak positions. Scanning electron microscope images showed the formation of small particles around the nanotubes, forming a thin overlayer decorating the nanotube walls. An x-ray diffraction analysis reported that these particles present both the α and β crystalline phases.
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73.22.-f Electronic structure of nanoscale materials and related systems
61.46.Fg Nanotubes
79.60.Jv Interfaces; heterostructures; nanostructures
68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

The search for mechanically stable PbTe based thermoelectric materials

Yaniv Gelbstein, Zinovi Dashevsky, and Moshe P. Dariel

J. Appl. Phys. 104, 033702 (2008); http://dx.doi.org/10.1063/1.2963359 (4 pages) | Cited 7 times

Online Publication Date: 1 August 2008

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The search for alternative energy sources is nowadays at the forefront of applied research. In this context, thermoelectricity for direct energy conversion from thermal to electrical energy plays an important role, in particular, for the exploitation of waste heat [ G. J. Snyder and E. S. Toberer, Nat. Mater. 7, 105 (2008) ; M. S. Dresselhaus et al., Adv. Mater. (Weinheim, Ger.) 19, 1043 (2007) ]. Materials for such applications should exhibit thermoelectric potential as well as mechanical stability. PbTe based alloys have been considered for many years as state of the art thermoelectric materials for mid-temperature power generation (500–900 K), with efficiency values that are still being improved by both alloying [ P. F. P. Poudeu et al., Chem., Int. Ed. 45, 1 (2006) ; J. R. Sootsman et al., Chem. Mater. 18, 4993 (2006) ; P. F. P. Poudeu et al., Chem. Soc. 126, 14347 (2006) ; J. Androulakis et al., Adv. Mater. (Weinheim, Ger.) 18, 1170 (2006) ; K. F. Hsu et al., Science 303, 818 (2004) ] and doping [ Y. Gelbstein et al., Physica B (Amsterdam) 363, 196 (2005) ; Y. Gelbstein et al., Physica B (Amsterdam) 396, 16 (2007) ] optimizations. However, the mechanical properties of PbTe based materials are highly dependent on the conductivity type (n or p) and carrier concentrations [ Y. Gelbstein et al., Scr. Mater. 58, 251 (2008) ]. This paper puts forward the mechanical durability of thermoelectric materials and, in particular, of PbTe as a dominant factor that is nondetachable from the transport properties, which should be considered in the search for high quality thermoelectric materials. Here we discuss the microhardness enhancement of p-type PbTe alloys with hole concentrations higher than 5×1018 cm−3. This anomaly is obtained while all the other investigated n-type (up to 1020 cm−3) and p-type (up to 1018 cm−3) compositions maintained a constant microhardness value of ∼ 30 HV. The origin of this microhardness enhancement is not yet understood on a fundamental level, however two possible mechanisms are discussed. One deals with the elastic interaction between dislocations and impurities with higher covalent radius than the sublattice vacancy. The other is correlated with the existence of a second valence band of heavy holes in PbTe, which begins to fill up at the same concentration where a hardness enhancement was observed. These mechanisms correlating between mechanical end electronic properties of PbTe based alloys can serve as guidelines for the search for potential candidates, obtaining both thermoelectric potential and mechanical stability for thermoelectric applications.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Intervalley splittings of Si quantum wells

S.-H. Park, Y. Y. Lee, and Doyeol Ahn

J. Appl. Phys. 104, 033703 (2008); http://dx.doi.org/10.1063/1.2963693 (4 pages) | Cited 2 times

Online Publication Date: 1 August 2008

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Intervalley splittings of Si quantum wells are studied using a multivalley effective mass theory and a finite element method. It is found that the contributions to the valley splitting mainly come from the quantum well interfaces and the external field. Especially the derivatives of the confinement potential which appears in the valley coupling Hamiltonian cause the periodic oscillation of the splitting with the well width. Theoretical predictions are in reasonably good agreement with the recent experimental observation of valley splitting in a SiO2/Si/SiO2 quantum well, which proves the validity of our approach.
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73.21.Fg Quantum wells
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Electrical transport properties of n-type (110)-oriented bismuth thin films grown at 110 K on glass substrates

Keng Shuo Wu and Ming Yau Chern

J. Appl. Phys. 104, 033704 (2008); http://dx.doi.org/10.1063/1.2957055 (4 pages) | Cited 1 time

Online Publication Date: 1 August 2008

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The structure and properties of the Bi thin films, grown by pulsed laser deposition at 110 K on glass substrates in vacuum, were found to be very different from those grown at higher temperatures. The preferred orientation of the films changed from (111), when grown at room temperature, to (110), as characterized by x-ray diffraction. The films became very smooth with a typical surface roughness of only 0.5 nm, determined by both x-ray reflectivity and atomic force microscopy. Furthermore, the conduction type changed from p to n type, indicated by the negative Hall coefficients of the films measured from 10 to 300 K. Oscillating thickness dependence of the resistivity was observed at 10 K, which is attributed to the quantum size effect. Moreover, the temperature and thickness dependences of the electrical properties show the trend that when the films are thinner, they become more metalliclike rather than semiconductive.
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73.61.At Metal and metallic alloys
68.55.-a Thin film structure and morphology
68.35.bd Metals and alloys
81.15.Fg Pulsed laser ablation deposition
72.15.Gd Galvanomagnetic and other magnetotransport effects

Microwave properties of graphite nanoplatelet/epoxy composites

Sang-Eui Lee, Oyoung Choi, and H. Thomas Hahn

J. Appl. Phys. 104, 033705 (2008); http://dx.doi.org/10.1063/1.2965195 (7 pages) | Cited 12 times

Online Publication Date: 1 August 2008

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The complex permittivity spectra and conductivity of graphite nanoplatelet (GNP)/epoxy composites were measured to assess the application potential of these materials as conductive coatings and/or microwave absorbers with high structural integrity. The frequency used ranged from 0.05 to 18.0 GHz. The measured static conductivity was in fairly good agreement with the prediction from the Neelakanta equations. For the complex permittivity, however, the measured values were much higher than those predicted. A better prediction required the use of the order function as a semiempirical parameter to account for the particle loading effect. The surface treatment using nitric acid was found to increase both the conductivity and permittivity of the GNP/epoxy composites although the effect was small, which led to the decrease in the matching thickness of microwave absorbers.
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77.22.Ch Permittivity (dielectric function)
73.63.-b Electronic transport in nanoscale materials and structures
81.65.-b Surface treatments
72.80.Tm Composite materials

Carrier generation and transport in bulk heterojunction films processed with 1,8-octanedithiol as a processing additive

In-Wook Hwang, Shinuk Cho, Jin Young Kim, Kwanghee Lee, Nelson E. Coates, Daniel Moses, and Alan J. Heeger

J. Appl. Phys. 104, 033706 (2008); http://dx.doi.org/10.1063/1.2951957 (9 pages) | Cited 27 times

Online Publication Date: 4 August 2008

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Improved performance of polymer-based solar cells based on poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzo-thiadiazole)] PCPDTBT has been obtained by using 1,8-octanedithiol (ODT) as a processing additive in the polymer solution used to spin cast the bulk heterojunction films. Although ultrafast spectroscopy studies indicate that the carrier losses are reduced in the films processed with ODT [similar to the reduced carrier losses after thermal annealing of bulk heterojunction (BHJ) materials made from P3HT:PCBM], the magnitude of the reduction is not sufficient to explain the observed factor of 2 increase in the power conversion efficiency. From the analysis of carrier transport in field effect transistors, we find increased electron mobility in the PCPDTBT:PC70BM composites when fabricated with ODT, which is indicative of enhanced connectivity of PC70BM networks. The improved electron mobility appears to be the primary origin of the improved power conversion efficiency in BHJ films.
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84.60.Jt Photoelectric conversion
73.61.Ph Polymers; organic compounds
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Dn Low-field transport and mobility; piezoresistance
78.47.-p Spectroscopy of solid state dynamics
78.66.Qn Polymers; organic compounds

Effect of Ti substitution on multiferroic properties of BiMn2O5

D. K. Shukla, S. Mollah, Ravi Kumar, P. Thakur, K. H. Chae, W. K. Choi, and A. Banerjee

J. Appl. Phys. 104, 033707 (2008); http://dx.doi.org/10.1063/1.2964072 (10 pages) | Cited 15 times

Online Publication Date: 5 August 2008

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We present here the magnetic, dielectric, and electronic structural properties of Ti doped BiMn2O5 multiferroic materials. The x-ray diffraction (XRD) studies of BiMn2−xTixO5 (0 ≤ x ≤ 0.5) indicate no structural change up to x = 0.5, though the lattice parameters (a and c) increase with increasing value of x. Dielectric constant and magnetization data show the evolution of new dielectric anomalies at ∼ 120 K and weak magnetic feature at ∼ 86 K with the Ti substitution compared to that of undoped one. However, Ti replacement vanishes the ferroelectric transition of BiMn2O5 at ∼ 35 K and gradually suppresses the antiferromagnetic ordering at ∼ 39 K. Polarization of Bi 6s2 lone pair electrons is attributed to the reason behind new dielectric anomalies, whereas new weak magnetic feature at ∼ 86 K is attributed to strong spin-phonon coupling. X-ray absorption spectroscopy (XAS) studies on O K, Mn K, L3,2, and Ti L3,2 edges of BiMn2−xTixO5 samples along with the reference compounds have been performed and compared to bestow the exact chemical states of functioning ions. The Ti L-edge spectra clearly indicate the substitution of Ti4+ ions in all samples. XRD as well as XAS data and increase in net magnetic moment coherently indicate the replacement of Mn4+ by Ti4+.
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75.80.+q Magnetomechanical effects, magnetostriction
71.20.Ps Other inorganic compounds
77.22.Ch Permittivity (dielectric function)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.80.B- Phase transitions and Curie point
75.50.Ee Antiferromagnetics

Direct measurement of hot-spot temperature in flip-chip solder joints under current stressing using infrared microscopy

Hsiang-Yao Hsiao, S. W. Liang, Min-Feng Ku, Chih Chen, and Da-Jeng Yao

J. Appl. Phys. 104, 033708 (2008); http://dx.doi.org/10.1063/1.2949279 (6 pages) | Cited 11 times

Online Publication Date: 6 August 2008

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Several simulation studies reported that a hot spot exists in flip-chip solder bumps under accelerated electromigration. Yet, there are no experimental data to verify it. In this paper, the temperature distribution during electromigration in flip-chip SnAg3.5 solder bumps is directly inspected using infrared microscopy. Two clear hot spots are observed in the bump. One is located at the region with peak current density and the other one is at the bump edge under the current-feeding metallization on the chip side. Under a current stress of 1.06×104 A/cm2, the temperature in the two hot spots are 161.7 and 167.8 °C, respectively, which surpass the average bump temperature of 150.5 °C. In addition, the effect of under-bump-metallization (UBM) thickness on the hot spots is also examined. It indicates that the hot-spot temperature in the solder bump increases for the solder joints with a thinner UBM. Electromigration test indicates that these hot spots have significant influence on the initial failure location.
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66.30.Qa Electromigration

Investigations of dopants introduction in hafnia: Electronic properties, diffusion, and their role on the gate leakage current

Valérie Cuny and Nicolas Richard

J. Appl. Phys. 104, 033709 (2008); http://dx.doi.org/10.1063/1.2965193 (5 pages) | Cited 2 times

Online Publication Date: 6 August 2008

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To understand the role of dopants in the electronic properties of monoclinic hafnium dioxide, we have performed first-principles simulations using density functional theory. The structure, ionization energies, electron affinities, formation energies, and activation energies for fluorine and nitrogen atoms in different charge states are obtained. Compared to nitrogen incorporation, we observe that fluorine introduction improves more efficiently the dioxide performances, removing the band gap state induced by oxygen vacancy. Our results suggest that fluorine is the best passivant of oxygen vacancies and that its incorporation can be used to decrease the gate leakage current through hafnia-based devices.
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61.72.up Other materials
61.72.jd Vacancies
71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Why the long-term charge offset drift in Si single-electron tunneling transistors is much smaller (better) than in metal-based ones: Two-level fluctuator stability

Neil M. Zimmerman, William H. Huber, Brian Simonds, Emmanouel Hourdakis, Akira Fujiwara, Yukinori Ono, Yasuo Takahashi, Hiroshi Inokawa, Miha Furlan, and Mark W. Keller

J. Appl. Phys. 104, 033710 (2008); http://dx.doi.org/10.1063/1.2949700 (12 pages) | Cited 6 times

Online Publication Date: 7 August 2008

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A common observation in metal-based (specifically, those with AlOx tunnel junctions) single-electron tunneling (SET) devices is a time-dependent instability known as the long-term charge offset drift. This drift is not seen in Si-based devices. Our aim is to understand the difference between these, and ultimately to overcome the drift in the metal-based devices. A comprehensive set of measurements shows that (1) brief measurements over short periods of time can mask the underlying drift, (2) we have not found any reproducible technique to eliminate the drift, and (3) two-level fluctuators (TLFs) in the metal-based devices are not stable. In contrast, in the Si-based devices the charge offset drifts by less than 0.01e over many days, and the TLFs are stable. We also show charge noise measurements in a SET device over four decades of temperature. We present a model for the charge offset drift based on the observation of nonequilibrium heat evolution in glassy materials, and obtain a numerical estimate in good agreement with our charge offset drift observations. We conclude that, while the Si devices are not perfect and defect-free, the defects are stable and noninteracting; in contrast, the interacting, unstable glasslike defects in the metal-based devices are what lead to the charge offset drift. We end by suggesting some particular directions for the improvement in fabrication, and in particular, fabrication with crystalline metal-oxide barriers, that may lead to charge offset drift-free behavior.
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85.35.Gv Single electron devices
85.30.De Semiconductor-device characterization, design, and modeling

Dissociation of H-related defect complex in InP using high energy light ions

D. Kabiraj, A. Roy, J. C. Pivin, and Subhasis Ghosh

J. Appl. Phys. 104, 033711 (2008); http://dx.doi.org/10.1063/1.2963690 (5 pages) | Cited 1 time

Online Publication Date: 7 August 2008

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High energy light ion irradiation has been used to anneal H-related defect complexes and to modify the electronic properties of semi-insulating InP (SI-InP). Raman and infrared spectroscopic measurements have been used to investigate the annihilation of native defects in SI-InP irradiated with 85 MeV C. Irradiation resulted in a decrease in sample resistivity by four orders of magnitudes and a change in the type of conductivity. The Raman spectroscopic results indicate an improvement in the InP sample due to irradiation up to an optimum fluence. The role of high electronic energy loss in defect annealing, which includes modification of the electrical properties and crystal structure of irradiated SI-InP, is discussed.
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81.05.Ea III-V semiconductors
61.82.Fk Semiconductors
61.80.Jh Ion radiation effects
61.72.Cc Kinetics of defect formation and annealing
72.80.Ey III-V and II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors

Stability and electronic properties of native defects and substitutional impurities in GaN nanotubes

M. L. Colussi, R. J. Baierle, and R. H. Miwa

J. Appl. Phys. 104, 033712 (2008); http://dx.doi.org/10.1063/1.2963698 (8 pages) | Cited 9 times

Online Publication Date: 12 August 2008

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Spin-polarized density functional theory is used to investigate the stability and electronic properties of vacancies, antisites, and substitutional Si and C in zigzag and armchair GaN nanotubes. Antisites and vacancies present lower formation energies as compared with their counterparts in the bulk GaN system, introducing localized electronic levels within the nanotube band gap. For vacancy systems in the neutral charge state the defective levels present a spin splitting giving rise to a net magnetic moment of 1 μB. Substitutional Si and C in the Ga site have the lowest formation energy and exhibit donor properties, suggesting the formation of defect-induced n-type GaN nanotubes. Our calculated formation energies for charged defects indicate that the neutral charge states are present for all the studied defects, thus suggesting a different picture for those defects in nanotube systems when compared with their counterparts in the bulk phase.
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73.22.-f Electronic structure of nanoscale materials and related systems
72.25.-b Spin polarized transport
61.72.jd Vacancies
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.55.Eq III-V semiconductors
61.72.J- Point defects and defect clusters

Preparation and characterization of epitaxial Fe2−xTixO3 films with various Ti concentrations (0.5<x<1.0)

Y. Takada, M. Nakanishi, T. Fujii, J. Takada, and Y. Muraoka

J. Appl. Phys. 104, 033713 (2008); http://dx.doi.org/10.1063/1.2966298 (5 pages) | Cited 8 times

Online Publication Date: 13 August 2008

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An ilmenite-hematite solid solution (Fe2–xTixO3) is one of the candidates for practical magnetic semiconductors with a high Curie temperature. We have prepared well-crystallized epitaxial Fe2–xTixO3 films with a wide range of Ti concentrations—x = 0.50, 0.60, 0.65, 0.76, 0.87, and 0.94—on α-Al2O3(001) substrates. The films are prepared by a reactive helicon plasma sputtering technique to evaporate Fe and TiO targets simultaneously under optimized oxygen pressure conditions. The structural characterizations of the films reveal that all films have a single phase of the ordered structure with Rmath symmetry, where Ti-rich and Fe-rich layers are stacked alternately along the c axis. All films have large ferrimagnetic moments at low temperature, and room temperature magnetization is clearly observed at x<0.7. The inverse temperature dependence of the resistivities of the films indicates their semiconducting behavior. The film resistivities decrease with decreasing Ti concentration.
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68.55.ag Semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Cd Deposition by sputtering
75.30.Cr Saturation moments and magnetic susceptibilities

Improving light harvesting in polymer photodetector devices through nanoindented metal mask films

A. G. Macedo, F. Zanetti, A. Mikowski, J. C. Hummelen, C. M. Lepienski, M. G. E. da Luz, and L. S. Roman

J. Appl. Phys. 104, 033714 (2008); http://dx.doi.org/10.1063/1.2968250 (6 pages) | Cited 4 times

Online Publication Date: 13 August 2008

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To enhance light harvesting in organic photovoltaic devices, we propose the incorporation of a metal (aluminum) mask film in the system’s usual layout. We fabricate devices in a sandwich geometry, where the mask (nanoindented with a periodic array of holes of sizes d and spacing s) is added between the transparent electrode and the active layer formed by a blend of the semiconducting polymer P3HT and substituted fullerene. Its function is to promote trapping of the incident light into the device’s cavity (the region corresponding to the active layer). For d, we set a value that allows light diffraction through the holes in the relevant absorption range of the polymer. To optimize the mask structure, we consider a very simple model to determine the s leading to trapped fields that are relatively intense and homogeneous within the device. From measurements of the action spectra, we show that, indeed, such architecture can considerably improve the resulting photocurrent efficiencies—one order of magnitude in the best situation studied.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Highly sensitive and broadband carbon nanotube radio-frequency single-electron transistor

S. E. S. Andresen, F. Wu, R. Danneau, D. Gunnarsson, and P. J. Hakonen

J. Appl. Phys. 104, 033715 (2008); http://dx.doi.org/10.1063/1.2968123 (4 pages) | Cited 3 times

Online Publication Date: 14 August 2008

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We have investigated radio-frequency single-electron transistor operation of single-walled carbon nanotube quantum dots in the strong tunneling regime. At a temperature of 4.2 K and with a carrier frequency of 754.2 MHz, we reach a charge sensitivity of 2.3×10−6e/math over a bandwidth of 85 MHz. Our results indicate a gain-bandwidth product of 3.7×1013 Hz(3/2)/e, which is by one order of magnitude better than those for typical radio-frequency single-electron transistors.
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85.35.Gv Single electron devices

Variable range hopping in A2MnReO6 (A = Ca, Sr, Ba)

B. Fisher, J. Genossar, K. B. Chashka, A. Knizhnik, L. Patlagan, and G. M. Reisner

J. Appl. Phys. 104, 033716 (2008); http://dx.doi.org/10.1063/1.2967820 (8 pages) | Cited 1 time

Online Publication Date: 15 August 2008

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We report on transport measurements on polycrystalline samples of A2MnReO6 (A = Ca, Sr, Ba), CMRO, SMRO, and BMRO, in the Ohmic and non-Ohmic regimes. The resistivity follows, over wide ranges of temperatures, the relation derived for variable range hopping of carriers localized in a parabolic gap, ρ = ρo exp(To/T)1/2. The values of To are unusually high for the Efros Shklovskii Coulomb gap interpretation. The thermopower is large and positive for SMRO and BMRO and even larger and negative for CMRO. The magnitude of the thermopower and its temperature dependence indicate that it may be unrelated to the hopping conductivity. The theoretical relations for hopping in the intermediate electric field regime provide reasonable approximations for the measured nonlinear conductivity of most samples (and for one sample also for the high-field regime). However, localization lengths derived from the non-Ohmic regime are much larger than those estimated from To. Clues to settle these inconsistencies are suggested.
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72.20.Ee Mobility edges; hopping transport
72.20.Pa Thermoelectric and thermomagnetic effects
72.20.Fr Low-field transport and mobility; piezoresistance

Vacuum sublimed α,ω-dihexylsexithiophene thin films: Correlating electronic structure and molecular orientation

S. Duhm, I. Salzmann, N. Koch, H. Fukagawa, T. Kataoka, S. Hosoumi, K. Nebashi, S. Kera, and N. Ueno

J. Appl. Phys. 104, 033717 (2008); http://dx.doi.org/10.1063/1.2968254 (7 pages) | Cited 11 times

Online Publication Date: 15 August 2008

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In order to correlate the molecular orientation of organic thin films with charge injection barriers at organic/metal interfaces, the electronic structure and molecular orientation of vacuum sublimed thin films of α,ω-dihexylsexithiophene (DH6T) on the substrates Ag(111), highly oriented pyrolytic graphite (HOPG), and tetratetracontane (TTC) precovered Ag(111) were investigated. Results from metastable atom electron spectroscopy, ultraviolet photoelectron spectroscopy, and x-ray diffraction were used to derive growth models (including molecular orientation and conformation) of DH6T on the different substrates. On Ag(111), DH6T exhibits a transition from lying molecules in the monolayer/bilayer range to almost standing upright molecules in multilayers. This is accompanied by a shift of the molecular energy levels to a lower binding energy by 0.65 eV with respect to the vacuum level. The unit cell of standing DH6T on lying DH6T on Ag(111) is estimated to be similar to the DH6T bulk phase. On HOPG, DH6T grows in the bulk phase with lying orientation, starting already from the monolayer coverage. DH6T on TTC precovered Ag(111) grows in an almost lying orientation and a conformation that allows a strong overlap of the hexyl chains of DH6T with the alkyl chains of TTC. In all cases, the electronic structure and, particulary, the ionization energy of DH6T is dependent on the orientation of DH6T, i.e., lying DH6T has higher ionization energy than standing DH6T.
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68.55.am Polymers and organics
73.40.Ns Metal-nonmetal contacts
79.60.Jv Interfaces; heterostructures; nanostructures
71.20.Rv Polymers and organic compounds
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