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7 Aug 2000

Volume 77, Issue 6, pp. 767-915

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Porous-silicon vapor sensor based on laser interferometry

Jun Gao, Ting Gao, and Michael J. Sailor

Appl. Phys. Lett. 77, 901 (2000); http://dx.doi.org/10.1063/1.1306640 (3 pages) | Cited 44 times

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Certain porous-silicon (PS) films exhibit well-resolved Fabry–Pérot fringes in their optical reflection spectra due to thin-film interference. The fringes shift to higher wavelengths when the PS is exposed to vapors from organic solvents, as a result of an increase in the average refractive index of the PS layer. If a small diode laser is used as the light source, the shift of the Fabry–Pérot fringes upon analyte adsorption results in a change in the reflected light intensity, which correlates with the concentration of the analyte (ethanol) in an air stream. Based on this principle, a PS vapor sensor has been demonstrated with a detection limit of 500 ppb and a dynamic range of nearly five orders of magnitude. © 2000 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
81.05.Cy Elemental semiconductors
81.05.Rm Porous materials; granular materials
78.66.Db Elemental semiconductors and insulators
61.43.Gt Powders, porous materials
68.55.-a Thin film structure and morphology
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.25.Hz Interference
07.60.Ly Interferometers

High-efficiency organic electrophosphorescent devices with tris(2-phenylpyridine)iridium doped into electron-transporting materials

Chihaya Adachi, Marc A. Baldo, Stephen R. Forrest, and Mark E. Thompson

Appl. Phys. Lett. 77, 904 (2000); http://dx.doi.org/10.1063/1.1306639 (3 pages) | Cited 422 times

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We demonstrate high-efficiency organic light-emitting devices employing the green electrophosphorescent molecule, fac tris(2-phenylpyridine)iridium [Ir(ppy)3], doped into various electron-transport layer (ETL) hosts. Using 3-phenyl-4-(1′-naphthyl)-5-phenyl-1,2,4-triazole as the host, a maximum external quantum efficiency (ηext) of 15.4±0.2% and a luminous power efficiency of 40±2 Im/W are achieved. We show that very high internal quantum efficiencies (approaching 100%) are achieved for organic phosphors with low photoluminescence efficiencies due to fundamental differences in the relationship between electroluminescence from triplet and singlet excitons. Based on the performance characteristics of single and double heterostructures, we conclude that exciton formation in Ir(ppy)3 occurs within close proximity to the hole-transportlayer/ETL:Ir(ppy)3 interface. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
71.35.-y Excitons and related phenomena

Amorphous silicon air-gap resonators on large-area substrates

M. Boucinha, P. Brogueira, V. Chu, and J. P. Conde

Appl. Phys. Lett. 77, 907 (2000); http://dx.doi.org/10.1063/1.1306912 (3 pages) | Cited 16 times

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Air-gap resonators composed of bridges of hydrogenated amorphous silicon and aluminum bilayers on glass and polyethylene terephthalate substrates are realized using surface micromachining techniques. The resonance frequency of structures on plastic substrates was found to vary inversely with the square of the length of the bridge span. On glass substrates, this dependence is seen for lengths >100 μm, while for lengths <100 μm, a decrease in the frequency is attributed to compressive stress. Resonance frequencies of ∼ 500 kHz to ∼ 2 MHz were measured in bridges with lengths from 160 μm down to ∼ 80 μm. © 2000 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
81.20.Wk Machining, milling
81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
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