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30 Jul 2001

Volume 79, Issue 5, pp. 557-700

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Hole injection barriers at polymer anode/small molecule interfaces

A. J. Mäkinen, I. G. Hill, R. Shashidhar, N. Nikolov, and Z. H. Kafafi

Appl. Phys. Lett. 79, 557 (2001); http://dx.doi.org/10.1063/1.1386400 (3 pages) | Cited 53 times

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A photoemission study of the interface between spin-cast films of a conducting polymer blend consisting of poly(3,4-ethylenedioxythiophene) (PEDOT), poly(4-styrenesulfonate) (PSS) and glycerol as an additive, and vacuum-evaporated hole transport layers (HTL) of 4,4′-bis(carbazol-9-yl)biphenyl, N,N′-diphenyl-N,N′-bis(1-naphthyl)-1-1′biphenyl-4,4′-diamine and N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′- biphenyl-4,4′-diamine reveals a hole injection barrier between 0.5 and 0.9 eV at the glycerol-modified PEDOT-PSS/HTL interface. The measured energy barriers imply a reasonable charge injection, which is very encouraging for further development of the novel anode structures based on a conducting polymer/small molecule interface to be utilized in electro-optic applications such as organic light-emitting devices. © 2001 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ph Polymers; organic compounds
79.60.Fr Polymers; organic compounds
73.20.At Surface states, band structure, electron density of states

White light emission from blends of blue-emitting organic molecules: A general route to the white organic light-emitting diode?

J. Thompson, R. I. R. Blyth, M. Mazzeo, M. Anni, G. Gigli, and R. Cingolani

Appl. Phys. Lett. 79, 560 (2001); http://dx.doi.org/10.1063/1.1388875 (3 pages) | Cited 91 times

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We show that all possible binary combinations of molecules from four different families of organics—a diamine derivative, N,N′-bis(3methylphenyl)-N,N′-diphenylbenzidine, an oxidiazole derivative, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, a substituted thiophene dioxide, 2,5-bis(trimethylsilyl thiophene)-1,1-dioxide, and poly(9-vinylcarbazole)—produce white or near-white emission. We suggest that this is due to exciplex formation, and that this is likely to be a general phenomenon for blends of blue-emitting aromatic organics. This implies that films of spin-coated blends of blue-emitting organics represent a general, simple, and cheap route to white-emitting organic light-emitting diodes. © 2001 American Institute of Physics.
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78.55.Kz Solid organic materials
85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds

Efficient polymer light emitting diodes with metal fluoride/Al cathodes

Xiaohui Yang, Yueqi Mo, Wei Yang, Gang Yu, and Yong Cao

Appl. Phys. Lett. 79, 563 (2001); http://dx.doi.org/10.1063/1.1389323 (3 pages) | Cited 54 times

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We reported efficient polymer light emitting diodes with alkali and alkaline earth metal fluoride Al cathodes. The quantum efficiencies of these devices are more than two orders of magnitude higher than those in devices without fluoride layer, comparable to the best data reported with similar electroluminescent polymers. The mechanism of the metal fluoride/Al bilayer cathodes was also discussed based on photovoltaic, ac impedance, and photoluminescence efficiency measurement. © 2001 American Institute of Physics.
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42.70.Jk Polymers and organics
85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials

Broad-band fluorescence upconversion for femtosecond spectroscopy

R. Schanz, S. A. Kovalenko, V. Kharlanov, and N. P. Ernsting

Appl. Phys. Lett. 79, 566 (2001); http://dx.doi.org/10.1063/1.1387257 (3 pages) | Cited 20 times

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With near-infrared gating and improved light collection geometry, the entire fluorescence band can be upconverted in a broad range of 10 000 cm−1 without readjusting optical elements, thus allowing measurements with a single pump-gate scan. Monitoring of the pump-induced white light continuum provides for the time correction of the up-converted fluorescence spectra. The overall time resolution is then limited by the pump-gate cross correlation. The technique is illustrated with the femtosecond evolution of fluorescence from two molecular probes in solution. © 2001 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
33.50.Dq Fluorescence and phosphorescence spectra
07.60.Rd Visible and ultraviolet spectrometers

Cavity-enhanced and quasiphase-matched multi-order reflection-second-harmonic generation from GaAs/AlAs and GaAs/AlGaAs multilayers

Xiaodong Mu, Yujie J. Ding, Haeyeon Yang, and Gregory J. Salamo

Appl. Phys. Lett. 79, 569 (2001); http://dx.doi.org/10.1063/1.1383565 (3 pages) | Cited 2 times

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We have observed quasiphase-matched second-harmonic generation in the reflection geometry from GaAs/AlAs multilayers. By using GaAs/AlGaAs multilayers and Fresnel reflection as a cavity, we have also achieved cavity-enhanced nonphase-matched second-harmonic generation from GaAs/AlAs multilayers. The linewidth for the first order reflection-second-harmonic generation is limited only by wave-vector mismatch. In addition, we have demonstrated two-order-of-magnitude enhancement on the conversion efficiency by using the cavity. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
81.05.Ea III-V semiconductors

Quantum cascade lasers with a heterogeneous cascade: Two-wavelength operation

Claire Gmachl, Deborah L. Sivco, James N. Baillargeon, Albert L. Hutchinson, Federico Capasso, and Alfred Y. Cho

Appl. Phys. Lett. 79, 572 (2001); http://dx.doi.org/10.1063/1.1383806 (3 pages) | Cited 27 times

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A quantum cascade (QC) laser with a heterogeneous cascade containing two substacks previously optimized to emit at 5.2 μm and 8.0 μm wavelengths, respectively, is presented. The low-temperature performance of the two-wavelength laser is comparable to the respective homogeneous stack lasers, indicating no penalty from the heterogeneity of the cascade. Each substack is apportioned the optimum fraction of the applied bias. This demonstrates the general applicability of this scheme. In addition, an etch-stop layer inserted between the two substacks allowed fabrication of a “tap” into the cascade. The latter was used to selectively manipulate the laser threshold of one substack, turning the 8.0 μm laser on and off while the adjacent 5.2 μm QC laser was operating undisturbed. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Resonantly coupled surface plasmon polaritons in the grooves of very deep highly blazed zero-order metallic gratings at microwave frequencies

H. E. Went and J. R. Sambles

Appl. Phys. Lett. 79, 575 (2001); http://dx.doi.org/10.1063/1.1388878 (3 pages) | Cited 8 times

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Sharp features are observed in the wavelength-dependent reflectivity of very deep highly blazed zero-order metallic gratings at microwave frequencies. These features are attributed to the resonant excitation of self-coupled surface plasmon polaritons in the cavities of such samples. The slat structures may, in a simplistic model, be treated as a class of Fabry–Pérot cavity resonator. © 2001 American Institute of Physics.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
42.79.Dj Gratings
78.70.Gq Microwave and radio-frequency interactions

Improving the performance of polymer light-emitting diodes using polymer solid solutions

Jie Liu, Yijian Shi, and Yang Yang

Appl. Phys. Lett. 79, 578 (2001); http://dx.doi.org/10.1063/1.1389324 (3 pages) | Cited 51 times

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Optical and electronic properties of conjugated polymers can be modified significantly by arranging the polymer chains differently. For example, it is well known that polymer solutions of lower concentrations have different photoluminescence spectra from solutions of higher concentrations. In this manuscript, we demonstrated that such effects can also be achieved in solid states, i.e., in polymer solid solutions consisting of a narrower band-gap material—poly(2-methoxy-5(2′-ethyl-hexyloxy)-1,4-phenylene vinylene (MEH-PPV) with a wider band-gap polymer–poly(9,9-dioctylfluorene). At very low MEH-PPV concentrations, emission spectra of these solid solutions are similar to the photoluminescence spectrum of a diluted MEH-PPV solution in an ordinary organic solvent, suggesting the absence of a significant amount of interchain species. In addition, the electroluminescence efficiency is significant enhanced. Furthermore, the full width at half maximum (FWHM) is dramatically reduced at lower MEH-PPV concentrations, as a result of suppressed interchain interactions. This approach is particularly important for the application to display technology, in which well-defined narrow FWHM emission spectra of red, green, and blue colors are required. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics

Terahertz field characterization using Fabry–Perot-like cantilevers

D. Dragoman and M. Dragoman

Appl. Phys. Lett. 79, 581 (2001); http://dx.doi.org/10.1063/1.1390319 (3 pages) | Cited 2 times

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We show that a Fabry–Perot-like tunneling cantilever consisting of two parallel thin metallic cantilevers joined at their free ends is able to sense the power of an incoming terahertz (THz) field. An array of such microstructures, with linearly varying distances between the two parallel cantilevers, can measure simultaneously the power and frequency of the THz field in the bandwidth 1.2–58 THz. © 2001 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
06.30.Ft Time and frequency
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Optical limiting behavior of a glass–ceramic containing sodium niobate crystallites

G. S. Maciel, N. Rakov, Cid B. de Araújo, A. A. Lipovskii, and D. K. Tagantsev

Appl. Phys. Lett. 79, 584 (2001); http://dx.doi.org/10.1063/1.1390324 (3 pages) | Cited 23 times

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The nonlinear absorption properties of a glass–ceramic containing ferroelectric sodium niobate (NaNbO3) crystallites were investigated. Two- and three-photon absorption coefficients were determined using nanosecond pulsed lasers. The optical power-limiting performance for light beams at 1064 and 532 nm was dependent on the volume fraction of NaNbO3 crystallites formed during the heat-treatment process. © 2001 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Ce Glasses, quartz
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Traveling wave electro-optic phase modulators based on intrinsically polar self-assembled chromophoric superlattices

Y.-G. Zhao, A. Wu, H.-L. Lu, S. Chang, W.-K. Lu, S. T. Ho, M. E. van der Boom, and T. J. Marks

Appl. Phys. Lett. 79, 587 (2001); http://dx.doi.org/10.1063/1.1389514 (3 pages) | Cited 14 times

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Traveling-wave electro-optic modulators based on chromophoric self-assembled superlattices (SASs) possessing intrinsically polar microstructures have been designed and fabricated. Although the thickness of the SAS layer is only ∼ 150 nm, a π-phase shift is clearly observed. From the measured Vπ value, the effective electro-optic coefficient of the SAS film is determined to be ∼ 21.8 pm/V at an input wavelength of 1064 nm. © 2001 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators

Laser emission under resonant pump in the emitting level of concentrated Nd:YAG ceramics

V. Lupei, A. Lupei, N. Pavel, T. Taira, I. Shoji, and A. Ikesue

Appl. Phys. Lett. 79, 590 (2001); http://dx.doi.org/10.1063/1.1389319 (3 pages) | Cited 45 times

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The possibility of using the thermally activated optical absorption bands for a resonant pump in the emitting level of highly doped Nd laser materials is discussed. This potential is demonstrated by the continuous wave 1064 nm laser emission under 885 nm pump in concentrated (up to 6.8 at. %) Nd:YAG ceramics. © 2001 American Institute of Physics.
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42.70.Hj Laser materials
42.55.Rz Doped-insulator lasers and other solid state lasers
78.30.Hv Other nonmetallic inorganics
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