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13 Mar 2000

Volume 76, Issue 11, pp. 1353-1479

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Quantum dots in photonic dots

M. V. Artemyev and U. Woggon

Appl. Phys. Lett. 76, 1353 (2000); http://dx.doi.org/10.1063/1.126029 (3 pages) | Cited 50 times

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A micrometer-sized spherical microcavity, the photonic dot, is made from semiconductor nanocrystals, the quantum dots. The coupling of electronic and photonic states is demonstrated for a single photonic dot by the observation of whispering gallery modes in the spectrum of spontaneous emission of the embedded CdSe quantum dots. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
42.70.Qs Photonic bandgap materials

Spin-exchange optical pumping using a frequency-narrowed high power diode laser

I. A. Nelson, B. Chann, and T. G. Walker

Appl. Phys. Lett. 76, 1356 (2000); http://dx.doi.org/10.1063/1.126030 (3 pages) | Cited 16 times

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We describe a method for frequency narrowing commercial high power diode lasers from 2 to 0.1 nm bandwidth with modest loss of power (<2 dB). The resulting laser light is well suited for spin-exchange optical pumping, and we demonstrate that the polarization produced by a 2.5 W narrowband laser exceeds that of a 15 W array by 40% in our optical pumping system. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

High-power wavelength-tunable circular-grating surface-emitting distributed Bragg deflector lasers

R. S. Penner, R. Bedford, H. Luo, S. Mendes, and M. Fallahi

Appl. Phys. Lett. 76, 1359 (2000); http://dx.doi.org/10.1063/1.126031 (3 pages)

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We present a promising approach to achieve wavelength tuning in high-power circular-grating surface-emitting lasers. A transparent electrode of indium tin oxide (ITO) was used to inject carriers into the second-order grating section of the device. Powers in excess of 225 mW and slope efficiencies of better than 0.40 mW/mA are reported. A continuous tuning range of 0.5 nm was achieved, while an overall wavelength shift of 1 nm was obtained for an ITO injection current of 30 mA. © 2000 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.79.Dj Gratings
42.60.Fc Modulation, tuning, and mode locking

Modulation of the second-order susceptibility in GaAs/AlAs superlattices

D. C. Hutchings

Appl. Phys. Lett. 76, 1362 (2000); http://dx.doi.org/10.1063/1.126032 (3 pages) | Cited 6 times

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The modulation of the bulk-like second-order susceptibility with quantum well disordering is calculated for a GaAs/AlAs superlattice. The calculation is based on the A⋅p form of the susceptibility, which is the more appropriate form for semiconductors, and includes the influence of the Γ15c upper conduction band set which ensures the necessary absence of inversion symmetry. The undisordered structure has the degeneracy broken between the χxyz(2) and χzxy(2) tensor elements which is restored upon disordering. The shift of the half-band gap resonance gives a maximum modulation depth Δχxyz(2) ≈ 60 pm V−1 in the transparency window for this structure. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.65.An Optical susceptibility, hyperpolarizability
73.20.At Surface states, band structure, electron density of states

Low-voltage GaN:Er green electroluminescent devices

J. Heikenfeld, D. S. Lee, M. Garter, R. Birkhahn, and A. J. Steckl

Appl. Phys. Lett. 76, 1365 (2000); http://dx.doi.org/10.1063/1.126033 (3 pages) | Cited 16 times

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Green light emission has been measured from Er-doped GaN electroluminescent devices (ELDs) at an applied bias as low as 5 V. The GaN–Er ELDs were grown by solid source molecular beam epitaxy on Si (111) substrates. We have achieved this low-voltage operation (ten-fold reduction in optical turn-on voltage) by using heavily doped (∼0.01 Ω cm) Si substrates and by decreasing the GaN–Er layer thickness to several hundred nanometers. A simple device model is presented for the indium tin oxide/GaN–Er/Si/Al ELD. This work demonstrates the voltage excitation efficiency of Er3+ luminescent centers and the compatibility of GaN rare earth-doped ELDs with low-voltage drive circuitry. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
85.60.Jb Light-emitting devices

Importance of intermolecular interactions in the nonlinear optical properties of poled polymers

I. Liakatas, C. Cai, M. Bösch, M. Jäger, Ch. Bosshard, P. Günter, C. Zhang, and L. R. Dalton

Appl. Phys. Lett. 76, 1368 (2000); http://dx.doi.org/10.1063/1.126034 (3 pages) | Cited 21 times

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A series of phenylbithiophene stilbenes and phenyltetraenes were synthesized and their first-order molecular hyperpolarizabilities determined. Optical nonlinearities up to μβo = 9300×10−69 C m5/V were measured at 1907 nm. We show that intermolecular interactions have a large influence on the optical nonlinearity of the molecules in solution and in guest-host polymers with polymethylmethacrylate and polyquinoline as the host. We propose the use of a bulky donor group and a side chain perpendicular to the molecule’s conjugate bridge to reduce aggregation. Electro-optic coefficients as high as r33 = 30 pm/V at 1.55 μm in polymethylmethacrylate with 25 wt % chromophore loading were measured. © 2000 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
78.20.Jq Electro-optical effects
42.70.Jk Polymers and organics

Ultrafast saturable absorption at 1.55 μm in heavy-ion-irradiated quantum-well vertical cavity

J. Mangeney, J. L. Oudar, J. C. Harmand, C. Mériadec, G. Patriarche, G. Aubin, N. Stelmakh, and J. M. Lourtioz

Appl. Phys. Lett. 76, 1371 (2000); http://dx.doi.org/10.1063/1.126035 (3 pages) | Cited 18 times

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Measurements of absorption saturation in heavy-ion-irradiated InGaAs/InAlAs multiplequantum-well reflection-mode vertical-cavity devices have been performed with short pulses at 1.55 μm and repetition rates up to 10 GHz. The relaxation time was essentially independent of the pulse repetition rate and optical excitation fluence, with a lower value of 2.4 ps for an ion dose of 1012 cm−2. Efficient optical switching was obtained, with a saturation energy smaller than 12 pJ, a contrast ratio up to 3.5:1, and a switching amplitude up to 20% of the incident signal. A relaxation model accounting for capture and recombination on defect levels indicates an upper limit of 2 ps of the defect level recombination time. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
61.80.Jh Ion radiation effects
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.65.Pc Optical bistability, multistability, and switching, including local field effects
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Self-frequency doubling in Yb3+ doped periodically poled LiNbO3:MgO bulk crystal

J. Capmany, E. Montoya, V. Bermúdez, D. Callejo, E. Diéguez, and L. E. Bausá

Appl. Phys. Lett. 76, 1374 (2000); http://dx.doi.org/10.1063/1.126036 (3 pages) | Cited 17 times

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Continuous-wave laser action from an Yb3+ doped periodically poled LiNbO3:MgO bulk crystal at 1.06 μm is reported. In addition, efficient and stable self-frequency-doubled laser action at 531 nm was obtained by quasiphase matching. Up to 10.5 mW of green output power is obtained from a total laser output power of 58 mW. The experiments were carried out by end pumping with a Ti:sapphire laser, as a surrogate source for a diode laser, at 980 nm. Laser operation was stable at room temperature. The results are compared with those corresponding to single-domain Yb-doped crystals. © 2000 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.60.Pk Continuous operation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Thermal amplification of photoinduced optical anisotropy of p-cyanoazobenzene polymer films monitored by temperature scanning ellipsometry

Masatoshi Kidowaki, Takenori Fujiwara, Shin’ya Morino, Kunihiro Ichimura, and Joachim Stumpe

Appl. Phys. Lett. 76, 1377 (2000); http://dx.doi.org/10.1063/1.126037 (3 pages) | Cited 23 times

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The in situ observation of thermal alteration of photoinduced optical anisotropy of ultrathin films of polymethacrylates having p-cyanoazobenzene side chains exhibiting amorphous, crystalline, and liquid-crystalline phases was performed by means of temperature scanning ellipsometry. Whereas photogenerated optical anisotropy of amorphous polymer films disappeared above glass transition temperature, the photoinduced anisotropy of films of liquid crystalline and crystalline polymer films was significantly amplified by heat treatment. In case of crystalline polymers, amplified optical anisotropy was maintained even at 300 °C. © 2000 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
42.65.-k Nonlinear optics
42.65.An Optical susceptibility, hyperpolarizability
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
42.70.Mp Nonlinear optical crystals
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Time-resolved four-wave mixing in InAs/InGaAs quantum-dot amplifiers under electrical injection

P. Borri, W. Langbein, J. M. Hvam, F. Heinrichsdorff, M.-H. Mao, and D. Bimberg

Appl. Phys. Lett. 76, 1380 (2000); http://dx.doi.org/10.1063/1.126038 (3 pages) | Cited 26 times

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Time-resolved four-wave mixing in an InAs/InGaAs/GaAs electrically pumped quantum-dot amplifier is measured at room temperature for different applied bias currents going from optical absorption to gain of the device. The four-wave mixing signal from 140 fs pulses shows a transition from a delayed photon-echo response in the absorption regime to a prompt free polarization decay in the gain regime. This corresponds to a pronounced reduction of the dephasing time from 250 fs at zero bias to less than 50 fs at the maximum applied current. The four-wave mixing response at transparency of the device shows a composite structure with both photon echo and free-polarization decay. This is a signature of the digital occupation number in quantum dots, resulting at transparency in a signal from dots occupied with either zero or two excitons corresponding to absorption or gain of the dot ground state. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.55.Px Semiconductor lasers; laser diodes
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
73.61.Ey III-V semiconductors
42.60.By Design of specific laser systems
78.47.-p Spectroscopy of solid state dynamics
71.35.-y Excitons and related phenomena

Ultrafast hot-carrier dynamics in semiconductor saturable absorber mirrors

M. Joschko, P. Langlois, E. R. Thoen, E. M. Koontz, E. P. Ippen, and L. A. Kolodziejski

Appl. Phys. Lett. 76, 1383 (2000); http://dx.doi.org/10.1063/1.126039 (3 pages) | Cited 7 times

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Femtosecond pump-probe experiments have been used to study the ultrafast nonlinear dynamics of InGaAs/InP semiconductor saturable absorber mirrors. The relative contributions of absorption bleaching and induced absorption are investigated by varying the excitation fluence over more than four orders of magnitude, well beyond complete absorption saturation. Enhanced free carrier absorption due to highly excited carriers with an extended relaxation time of 2.8 ps dominates the differential reflectivity at ultrahigh fluences and has been studied via a two-color pump-probe measurement. © 2000 American Institute of Physics.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
72.20.Ht High-field and nonlinear effects
72.80.Ey III-V and II-VI semiconductors
42.79.Bh Lenses, prisms and mirrors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics

Laser direct writing of phosphor screens for high-definition displays

J. M. Fitz-Gerald, A. Piqué, D. B. Chrisey, P. D. Rack, M. Zeleznik, R. C. Y. Auyeung, and S. Lakeou

Appl. Phys. Lett. 76, 1386 (2000); http://dx.doi.org/10.1063/1.126040 (3 pages) | Cited 21 times

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A laser-based forward transfer direct writing technique was used to deposit phosphor powder screens for high-resolution display applications. With this technique, called matrix-assisted pulsed-laser evaporation direct write, dense oxide phosphor powders of Y2O3:Eu (red) and Zn2SiO4:Mn (green) were deposited on alumina and polymer substrates. All processing was performed in air at room temperature. Cathodoluminescent measurements showed that the luminous efficiency of the phosphor powders was not degraded by the deposition process. A 6×6 red and green matrix with pixel sizes of 100 μm (250 lines per inch) with a 100 μm spot size is demonstrated; however, with smaller spot sizes this technique is easily scalable to pixel sizes <10 μm (>2500 lines per inch). © 2000 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
81.15.Fg Pulsed laser ablation deposition
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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Structures and optical properties of silicon nanocrystallites prepared by pulsed-laser ablation in inert background gas

Nobuyasu Suzuki, Toshiharu Makino, Yuka Yamada, Takehito Yoshida, and Seinosuke Onari

Appl. Phys. Lett. 76, 1389 (2000); http://dx.doi.org/10.1063/1.126041 (3 pages) | Cited 19 times

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Silicon (Si) nanocrystallites have been synthesized using pulsed-laser ablation in inert background gases, for studying the structures and optical properties as one of the quantum confinement effects. We extracted a process condition where well-dispersed Si nanocrystallites devoid of droplets and debris are prepared, by varying excitation laser conditions. Furthermore, we investigate the influence of the inert background gas pressures on transition from amorphous-like thin films to nanocrystallites. It was clarified that there is a processing window of the inert background gas pressure in which the quantum confinement effects for carriers and phonons become apparent. © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.05.Cy Elemental semiconductors
68.55.-a Thin film structure and morphology
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
81.15.Fg Pulsed laser ablation deposition
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.40.Fy Semiconductors

Scanning tunneling microscopy study of Si(111) surface morphology after removal of SiO2 by synchrotron radiation illumination

Y. Gao, H. Mekaru, T. Miyamae, and T. Urisu

Appl. Phys. Lett. 76, 1392 (2000); http://dx.doi.org/10.1063/1.126042 (3 pages) | Cited 7 times

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The surface morphology of Si(111) was investigated using scanning tunneling microscopy after desorption of surface SiO2 by synchrotron radiation (SR) illumination. The surface shows large regions of atomically flat Si(111)-7×7 structure, and is characterized by the formation of single bilayer steps nicely registered to the underlying crystal structure. This is in sharp contrast to Si(111) surfaces after thermal desorption of SiO2 at temperatures 880 °C and above, where the surface steps are much more irregular. The registration of the surface steps to the underlying crystal structure indicates that the Si(111) surface reaches thermodynamic equilibrium under SR irradiation at temperatures much lower than that necessary for thermal desorption. © 2000 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Indium nanowires in thick (InGaN) layers as determined by x-ray analysis

A. Krost, J. Bläsing, H. Protzmann, M. Lünenbürger, and M. Heuken

Appl. Phys. Lett. 76, 1395 (2000); http://dx.doi.org/10.1063/1.126043 (3 pages) | Cited 10 times

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300-nm-thick InGaN layers with In concentrations up to 21% were grown by low-pressure metalorganic chemical-vapor deposition. Besides the InGaN and GaN Bragg peaks, the symmetric (0002) x-ray spectra of strain-relaxed samples show an additional signal which could be identified stemming from metallic tetragonal indium. The indium is incorporated in InGaN with its pseudohexagonal (101) plane parallel to the InGaN(0001) plane in a sixfold configuration. From the widths and intensities of the asymmetric In(211) and the symmetric In(h0h) diffraction peaks, the lateral and perpendicular crystallite sizes of the In inclusions are estimated to be ∼30 and ∼300 nm, respectively, i.e., the In is incorporated in a wire-like manner in the growth direction. In InGaN-based devices such indium wires could act as highly conducting channels detrimental for electronic and optoelectronic applications. © 2000 American Institute of Physics.
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68.55.Nq Composition and phase identification
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Qq Microscopic defects (voids, inclusions, etc.)
81.05.Ea III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization

Saturation of THz-radiation power from femtosecond-laser-irradiated InAs in a high magnetic field

Hideyuki Ohtake, Shingo Ono, Masahiro Sakai, Zhenlin Liu, Takeyo Tsukamoto, and Nobuhiko Sarukura

Appl. Phys. Lett. 76, 1398 (2000); http://dx.doi.org/10.1063/1.126044 (3 pages) | Cited 18 times

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THz-radiation power from femtosecond-pulse-irradiated InAs is found to be saturated at the magnetic field around 3 T. Additionally, we find that this saturation magnetic field strongly depends on geometrical layout. Interesting magnetic-field dependence of the center frequency for THz radiation is also observed. © 2000 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
78.70.Gq Microwave and radio-frequency interactions
72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Ey III-V and II-VI semiconductors
84.40.-x Radiowave and microwave (including millimeter wave) technology

Formation dynamics of silicon nanoparticles after laser ablation studied using plasma emission caused by second-laser decomposition

Tetsuya Makimura, Taiji Mizuta, and Kouichi Murakami

Appl. Phys. Lett. 76, 1401 (2000); http://dx.doi.org/10.1063/1.126045 (3 pages) | Cited 18 times

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We have investigated the dynamic formation of silicon nanoparticles after pulsed-laser ablation of a silicon target into argon gas, in order to fabricate the nanoparticles that exhibit visible photoluminescence with higher efficiency. The nanoparticles growing in argon gas were detected by measuring plasma emission resulting from decomposition of the nanoparticles by a second pulsed-laser beam. It was directly observed that the nanoparticles grow on the time scale of 1 ms. © 2000 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
61.46.-w Structure of nanoscale materials
81.15.Fg Pulsed laser ablation deposition

Mechanism of diffusional transport during ion nitriding of aluminum

T. Telbizova, S. Parascandola, U. Kreissig, R. Günzel, and W. Möller

Appl. Phys. Lett. 76, 1404 (2000); http://dx.doi.org/10.1063/1.126070 (3 pages) | Cited 14 times

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The mechanism of diffusional transport during low-energy ion nitriding of aluminum has been investigated using marker and isotope sequence techniques in connection with ion-beam analysis. For an ion energy of 1 keV and a temperature of 400 °C, it is shown that the nitride grows at the surface with aluminum being supplied by diffusion from the underlying bulk. © 2000 American Institute of Physics.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
61.72.up Other materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys

Electro-optic modulation in crystal-ion-sliced z-cut LiNbO3 thin films

Tarek A. Ramadan, M. Levy, and R. M. Osgood

Appl. Phys. Lett. 76, 1407 (2000); http://dx.doi.org/10.1063/1.126046 (3 pages) | Cited 28 times

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Electro-optic modulation is demonstrated in 10-μm-thick single-crystal LiNbO3 films obtained by crystal ion slicing. This technique uses ion implantation of single-crystal bulk samples followed by selective etching. The measured electro-optic response of these films is comparable, within experimental error, to that of single-crystal bulk LiNbO3 and is superior to previously reported values for epitaxial polycrystalline thin films. The product of half-wave voltage and modulator length, VπL, is 8 V cm. Post lift-off annealing is shown to be of key importance in improving the modulator extinction ratio. © 2000 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
61.82.Ms Insulators
61.72.up Other materials
42.79.Wc Optical coatings
61.72.Cc Kinetics of defect formation and annealing
81.65.Cf Surface cleaning, etching, patterning
61.80.Jh Ion radiation effects

A relation between surface oxide and oxygen-defect complexes in solid-phase epitaxial Si regrown from ion-beam-amorphized Si layers

Mihail P. Petkov, Claudine M. Chen, Harry A. Atwater, Stefano Rassiga, and Kelvin G. Lynn

Appl. Phys. Lett. 76, 1410 (2000); http://dx.doi.org/10.1063/1.126047 (3 pages) | Cited 3 times

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We present a direct evidence that ion implantation through thin (⩽5 nm) surface oxide layers is a source of O impurities, which form O-defect complexes during thermal treatment. The impurity-defect complexes are identified by correlating the results from positron annihilation spectroscopy, secondary-ion mass spectroscopy, and Monte Carlo simulations. The O atoms are introduced in the bulk by multiple recoil implantation by the primary ions. The signatures of large VmOn formations are observed at 800 °C, which implies the existence of smaller species at lower temperatures. © 2000 American Institute of Physics.
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61.72.uf Ge and Si
61.82.Fk Semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.Yx Interaction between different crystal defects; gettering effect
61.80.Jh Ion radiation effects
78.70.Bj Positron annihilation
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.40.Gh Other heat and thermomechanical treatments

Depth analysis of buried iron disilicide formation by Fe ion implantation into Si

M. Walterfang, S. Kruijer, W. Keune, M. Dobler, and H. Reuther

Appl. Phys. Lett. 76, 1413 (2000); http://dx.doi.org/10.1063/1.126048 (3 pages) | Cited 1 time

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The depth distribution of the iron disilicide phases (α-FeSi2 and β-FeSi2) was investigated nondestructively by depth-selective conversion-electron Mössbauer spectroscopy after Fe+ implantation (200 keV, 3×1017 cm−2) and after subsequent rapid thermal annealing (RTA) at 900 °C for 30 s. The depth profiles of the two phases were found to be correlated with the Fe concentration profiles as determined by Auger electron sputter depth profiling. For the as-implanted state a broad distribution of a phase mixture of α- and β-FeSi2 is observed. Subsequent RTA induces a layered structure including a buried β-FeSi2 layer with a high phase content of 90% near 220 nm. © 2000 American Institute of Physics.
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61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.Dv Composition, segregation; defects and impurities
76.80.+y Mössbauer effect; other γ-ray spectroscopy
61.72.Cc Kinetics of defect formation and annealing

Observation of in-plane optical anisotropy of spin-cast rigid-rod electroluminescent polymer films

Carrie W. Y. Law, K. S. Wong, Z. Yang, L. E. Horsburgh, and A. P. Monkman

Appl. Phys. Lett. 76, 1416 (2000); http://dx.doi.org/10.1063/1.126049 (3 pages) | Cited 13 times

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Transmittance difference spectroscopy has been applied to study the optical properties of spin-cast rigid-rod polymer films. Significant in-plane optical anisotropy is observed for both the real and the imaginary parts of the transmittance of the poly(2,5-pyridine diyl) films. This in-plane optical anisotropy is a result of the partial alignment of the polymer chains, oriented radially outward from the center of the film, during the spin casting process. This observation has important implications for emissive polymer devices, particularly for devices sensitive to polarization direction and those using waveguide confinement where relatively long propagation distance within the films are required. © 2000 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence
42.70.Jk Polymers and organics
85.60.Jb Light-emitting devices

Evolution of sp2 bonding with deposition temperature in tetrahedral amorphous carbon studied by Raman spectroscopy

M. Chhowalla, A. C. Ferrari, J. Robertson, and G. A. J. Amaratunga

Appl. Phys. Lett. 76, 1419 (2000); http://dx.doi.org/10.1063/1.126050 (3 pages) | Cited 94 times

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Two transitions in the bonding are found in tetrahedral amorphous carbon (ta-C) films as a function of deposition temperature. The total sp3 fraction shows a sharp decrease at a transition temperature of order 250 °C. In contrast, visible Raman finds that the sp2 sites show a gradual ordering into the graphitic clusters through the sharp bonding transition. The optical gap and resistivity show a similar, gradual transition. This indicates that the sp2 cluster size determines the optical gap, even when the sp2 content does not change. The Raman I(D)/I(G) peak ratio is found to vary inversely with the square of the gap. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.43.Er Other amorphous solids
78.35.+c Brillouin and Rayleigh scattering; other light scattering
68.60.Bs Mechanical and acoustical properties
71.23.-k Electronic structure of disordered solids
73.22.-f Electronic structure of nanoscale materials and related systems
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.05.ub Fullerenes and related materials

Direct evidence for interaction of magnesium with tris(8-hydroxy-quinoline) aluminum

P. He, Frederick C. K. Au, Y. M. Wang, L. F. Cheng, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 76, 1422 (2000); http://dx.doi.org/10.1063/1.126051 (3 pages) | Cited 29 times

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The interaction between magnesium (Mg) and tris(8-hydroxy-quinoline) aluminum (Alq3) has been studied using high-resolution electron energy-loss spectroscopy (HREELS). It was found that deposition of magnesium on the Alq3 film gave rise to clear changes in the HREELS spectra. The changes are attributed to the weakly bounded Mg atoms on the Alq3 layer. Interestingly, for a given amount of magnesium (Mg to Al atoms ratio=3) on Alq3 film, remarkable changes were observed in the HREELS spectra when the sample was heated. A loss peak at 81 meV, which was assigned to Mg–O stretch mode, appeared upon annealing and increased in intensity as the annealing temperature increased up to about 360 K. This suggested that the diffusion of Mg atoms into the Alq3 layer and the reaction between Mg and Alq3 molecule occurred at the temperature range investigated. The present work has provided direct evidence for the strong interaction between magnesium and Alq3. © 2000 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
79.20.Kz Other electron-impact emission phenomena

Strain-dependent electrical resistance of tin-doped indium oxide on polymer substrates

Darran R. Cairns, Richard P. Witte, Daniel K. Sparacin, Suzanne M. Sachsman, David C. Paine, Gregory P. Crawford, and R. R. Newton

Appl. Phys. Lett. 76, 1425 (2000); http://dx.doi.org/10.1063/1.126052 (3 pages) | Cited 148 times

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The increase in sheet resistance of indium–tin–oxide (ITO) films on polyethylene terephthalate with increasing tensile strain is reported. The increase in resistance is related to the number of cracks in the conducting layer which depends upon applied strain and film thickness. We propose a simple model that describes the finite but increasing resistance in the cracked ITO layer in terms of a small volume of conducting material within each crack. © 2000 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
68.55.-a Thin film structure and morphology
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