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3 Nov 2003

Volume 83, Issue 18, pp. 3647-3835

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Appl. Phys. Lett. 83, 3737 (2003); http://dx.doi.org/10.1063/1.1623315 (3 pages)

Ian Appelbaum, D. J. Monsma, K. J. Russell, V. Narayanamurti, and C. M. Marcus
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Anode material based on Zr-doped ZnO thin films for organic light-emitting diodes

H. Kim, J. S. Horwitz, W. H. Kim, S. B. Qadri, and Z. H. Kafafi

Appl. Phys. Lett. 83, 3809 (2003); http://dx.doi.org/10.1063/1.1623933 (3 pages) | Cited 31 times

Online Publication Date: 28 October 2003

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Zr-doped ZnO (ZZO) thin films have been investigated as an anode material, a potential alternative to indium tin oxide (ITO), for organic light emitting diode (OLED) devices. ZZO films have been deposited on glass substrates by pulsed laser deposition. The electrical and optical properties of these films were studied as a function of substrate temperature and oxygen pressure during deposition. For a 200-nm-thick ZZO film grown at 250 °C in 1 mTorr of oxygen, a resistivity of 5.6×10−4 Ω cm was measured and an average optical transmittance of 84% was measured in the visible range (400–700 nm). The ZZO films, grown at different oxygen pressures, were used as an anode contact for OLED devices. External electroluminescence quantum efficiencies (0.8%–0.9%) comparable to those (0.9%–1.0%) measured for control devices fabricated on commercial ITO anodes were obtained at high current densities (1000 A/m2). These results demonstrate that ZZO is a good anode material. In addition, it is an attractive alternative to ITO due to its low price and lack of toxicity. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
85.60.Jb Light-emitting devices
73.61.-r Electrical properties of specific thin films
73.50.-h Electronic transport phenomena in thin films
78.66.-w Optical properties of specific thin films
81.15.Fg Pulsed laser ablation deposition
78.60.Fi Electroluminescence
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Investigation of transport properties in polymer/fullerene blends using time-of-flight photocurrent measurements

S. A. Choulis, J. Nelson, Y. Kim, D. Poplavskyy, T. Kreouzis, J. R. Durrant, and D. D. C. Bradley

Appl. Phys. Lett. 83, 3812 (2003); http://dx.doi.org/10.1063/1.1624636 (3 pages) | Cited 69 times

Online Publication Date: 28 October 2003

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The electron and hole transport properties of blends of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1-4-phenylene vinylene], (MDMO-PPV) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) are investigated at room temperature using time-of-flight photocurrent measurements as a function of blend composition and laser excitation intensity. The experimental results are consistent with the notion of a mobility edge for holes in this material that delineates long-lived trapping and mobile carrier states. Electron transport in PCBM appears to be less dispersive than that of holes in MDMO-PPV in the blend, with electron mobilities in the former exceeding hole mobilities in the latter by up to two orders of magnitude. Photocurrent generation in corresponding solar cell devices may therefore be limited by the low hole mobility of MDMO-PPV. © 2003 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
72.80.Rj Fullerenes and related materials
72.80.Le Polymers; organic compounds (including organic semiconductors)

Shell-type micromechanical actuator and resonator

Maxim Zalalutdinov, Keith L. Aubin, Robert B. Reichenbach, Alan T. Zehnder, Brian Houston, Jeevak M. Parpia, and Harold G. Craighead

Appl. Phys. Lett. 83, 3815 (2003); http://dx.doi.org/10.1063/1.1622792 (3 pages) | Cited 14 times

Online Publication Date: 28 October 2003

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Dome-shaped radio-frequency micromechanical resonators were fabricated by utilizing the buckling of a prestressed thin polysilicon film. The enhanced rigidity of the dome structure leads to a significant increase of its resonant frequency compared to a flat plate resonator. The shell-type geometry of the structure also provides an imbedded actuation mechanism. Significant out-of plane deflections are actuated by mechanical stress introduced within the plane of the shell. We demonstrate that thermomechanical stress generated by a focused laser beam, or microfabricated resistive heater, provides an effective and fast mechanism to operate the dome as an acoustic resonator in the radio-frequency range. All-optical operation of the shell resonator and an integrated approach are discussed. © 2003 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.05.Cy Elemental semiconductors
43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators
42.79.Jq Acousto-optical devices
43.38.Zp Acoustooptic and photoacoustic transducers

Efficient, deep-blue organic electrophosphorescence by guest charge trapping

R. J. Holmes, B. W. D’Andrade, S. R. Forrest, X. Ren, J. Li, and M. E. Thompson

Appl. Phys. Lett. 83, 3818 (2003); http://dx.doi.org/10.1063/1.1624639 (3 pages) | Cited 326 times

Online Publication Date: 28 October 2003

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We demonstrate efficient, deep-blue organic electrophosphorescence using a charge-trapping phosphorescent guest, iridium(III) bis(4′,6′-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6) doped in the wide-energy-gap hosts, diphenyldi(o-tolyl)silane (UGH1) and p-bis(triphenylsilyly)benzene (UGH2), where exciton formation occurs directly on the guest molecules. Charge trapping on the guest is confirmed by the dependence of the drive voltage and electroluminescence spectrum on guest concentration. Ultraviolet photoemission spectroscopy measurements establish the relative highest occupied molecular orbital positions of FIr6 in UGH1 and UGH2. Peak quantum and power efficiencies of (8.8±0.9)% and (11.0±1.1) lm/W in UGH1 and (11.6±1.2)% and (13.9±1.4) lm/W in UGH2 are obtained, while the emission in both cases is from FIr6 and is characterized by Commission Internationale de l’Eclairage coordinates of (x = 0.16, y = 0.26) in UGH2. © 2003 American Institute of Physics.
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78.60.Fi Electroluminescence
79.60.Fr Polymers; organic compounds
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Short-channel effects in contact-passivated nanotube chemical sensors

Keith Bradley, Jean-Christophe P. Gabriel, Alexander Star, and George Grüner

Appl. Phys. Lett. 83, 3821 (2003); http://dx.doi.org/10.1063/1.1619222 (3 pages) | Cited 42 times

Online Publication Date: 28 October 2003

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We report a design for carbon nanotube field-effect transistors which tests the nanotube depletion length. In this design, the metal contacts and adjacent nanotubes were coated with impermeable silicon oxide, while the central region of nanotubes was exposed. We tested the devices by measuring sensitivity to NH3 and poly(ethylene imine). NH3 caused similar responses in passivated devices and in normal, nonpassivated devices. Thus, the device design passivates the metal-nanotube contacts while preserving chemical sensor characteristics. Poly(ethylene imine) produced negative threshold shifts of tens of volts, despite being in contact with only the center region of devices. Based on the observed device characteristics, we conclude that the length scale of the covered nanotubes in our structure is comparable to the decay length of the depletion charge in nanotube transistors. © 2003 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.35.Kt Nanotube devices
85.30.Tv Field effect devices
81.65.Rv Passivation
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