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Notes: Ga0.5In0.5P layers have been grown by organometallic vapor-phase epitaxy using various values of input V/III ratio for two phosphorus precursors, phosphine, the conventional precursor, and tertiarybutylphosphine (TBP), a newly developed, less-hazardous precursor. For growth on nominally (001) GaAs substrates misoriented by 3° (and in some cases by 0° or 6°) to produce [110] steps on the surface at a growth temperature of 620 °C, the Cu–Pt-type ordering is found to be strongly affected by the input flow rate of the phosphorus precursor (V/III ratio). For decreasing input partial pressures below 3 Torr for PH3 and 0.75 Torr for TBP the low-temperature photoluminescence (PL) peak energy increases indicating a lower degree of order. This is confirmed by transmission electron diffraction results. The decrease in the degree of order corresponds to a decrease in the concentration of [1¯10]-oriented P dimers on the surface, as indicated by surface photoabsorption spectroscopy results. These data indicate that the reduction in ordering is caused by the loss of the (2×4) reconstructed surface during growth. The difference in the behavior for PH3 and TBP is interpreted as due to the lower pyrolysis efficiency of PH3. The surface structure measured using high-resolution atomic force microscopy indicates that the [110] steps produced by the intentional misorientation of the substrate are bunched to produce supersteps approximately 30–40 A(ring) in height for the lowest V/III ratios. The step height decreases markedly as the input phosphorus partial pressure increases from 0.4 to 0.75 Torr for TBP and from 1 to 3 Torr for PH3. This corresponds to a change from mainly monolayer to predominantly bilayer steps in the vicinal regions between bunched supersteps. Stabilization of the bilayer steps is interpreted as due to formation of the (2×2) reconstruction on the (111)B step edges. The degree of order is an inverted U-shaped function of the flow rate of the phosphorus precursor. Thus, use of very high input V/III ratios is also found to reduce the degree of order in the Ga0.5In0.5P layers. These high input phosphorus flow rates are found to result in a monotonic increase in the density of [1¯10]-oriented P dimers on the surface. This decrease in order is believed to be related to a change in the structure of kinks on the [110] steps at high V/III ratios. © 1996 American Institute of Physics.

Notes: A natural monolayer {111} superlattice (the CuPt ordered structure) is formed spontaneously during organometallic vapor phase epitaxial (OMVPE) growth of Ga0.52In0.48P. The extent of this ordering process is found to be a strong function of the input partial pressure of the phosphorus precursor during growth due to the effect of this parameter on the surface reconstruction and step structure. Thus, heterostructures can be produced by simply changing the flow rate of the P precursor during growth. It is found, by examination of transmission electron microscope (TEM) and atomic force microscope (AFM) images, and the photoluminescence (PL) and PL excitation (PLE) spectra, that order/disorder (O/D) (really less ordered on more ordered) heterostructures formed by decreasing the partial pressure of the P precursor during the OMVPE growth cycle at a temperature of 620 °C are graded over several thousands of Å when PH3 is the precursor. The ordered structure from the lower layer persists into the upper layer. Similarly, D/O structures produced by increasing the PH3 flow rate yield PL spectra also indicative of a graded composition at the heterostructure. The grading is not reduced by a 1 h interruption in the growth cycle at the interface. Similar heterostructures produced at 670 °C using tertiarybutylphosphine (TBP) as the P precursor show a totally different behavior. Abrupt D/O and O/D heterostructures can be produced by abruptly changing the TBP flow rate during the growth cycle. PL and PLE studies show distinct peaks closely corresponding to those observed for the corresponding single layers. TEM dark field images also indicate that the interfaces in both for D/O and O/D heterostructures are abrupt. The cause of the difference in behavior for TBP and PH3 is not clear. It may be related to the difference in temperature. © 1997 American Institute of Physics.

Notes: Surface photoabsorption (SPA) measurements were used to clarify the Cu–Pt ordering mechanism in Ga0.5In0.5P layers grown by organometallic vapor phase epitaxy. The Cu–Pt ordering is strongly affected by the growth temperature and the input partial pressure of the phosphorus precursor, i.e., the V/III ratio. SPA was used to measure the concentration of [1¯10]-oriented phosphorus dimers on the surface, which are characteristics of the (2×4) reconstruction, as a function of the growth temperature and V/III ratio. The degree of order decreases markedly with increasing growth temperature above 620 °C at a constant V/III ratio of 40 [tertiarybutylphosphine (TBP) partial pressure of 50 Pa]. This corresponds directly to a decrease of the P-dimer concentration on the surface. Below 620 °C, the degree of order decreases as the growth temperature decreases, even though the concentration of P dimers increases. This is most likely due to the slow migration of adatoms on the surface during growth. The degree of order is found to decrease monotonically with decreasing V/III ratio in the range from 160 to 8 at 670 °C. This corresponds directly to the decrease of the P-dimer concentration on the surface. The direct correlation of the [1¯10]-oriented phosphorus dimer concentration and the degree of order with changes in both temperature (≥620 °C) and V/III ratio suggests that the (2×4) surface reconstruction is necessary to form the Cu–Pt structure, in agreement with published theoretical studies. The physical structure of the surface of these Ga0.5In0.5P layers was also characterized, using atomic force microscopy. For growth at 670 °C and a V/III ratio of 160, the structure of the layers growth on exactly (001) oriented GaAs substrates consists of islands surrounded mainly by bilayer (approximately 6 A(ring)) steps. As the V/III ratio is reduced, the step height transforms to one monolayer. Exclusively monolayer steps are formed at a V/III ratio of 8. This is interpreted in terms of the stabilization of the bilayers by formation of the (2×2) reconstruction on the (111)B step face at high V/III ratios. © 1996 American Institute of Physics.

Notes: We report the results of a spectroscopic investigation of the quadratic electro-optic nonlinearity in poly(2,5-thienylene vinylene). Electroabsorption spectra closely resemble the second energy derivative of the unperturbed π-π* absorption and show oscillations associated with the strong vibronic features present therein. The dispersion of both the real and imaginary parts of χ(3) (−ω;0,0,ω) has been determined and we find that Re{χ(3)} has a peak value of 7.5×10−9 esu at 1.83 eV and Im{χ(3)} has a peak value of 6.2×10−9 esu at 1.78 eV. This nonlinearity is responsible for a photorefractive effect under resonant photoexcitation.

Notes: The surface structure of Ga0.52In0.48P was studied by surface photoabsorption. An absorption peak due to P dimers on Ga0.52In0.48P was observed at ∼400 nm, shorter than for InP (430 nm). From comparison with results for GaAs and InP, the data are interpreted to indicate that at a tertiarybutylphosphine (TBP) pressure of 50 Pa for temperatures below 670 °C, the P-stabilized surface has P dimers aligned along the [1¯10] direction, i.e., it has a (2×4)-like structure. Above 670 °C, the 400 nm peak due to the P-dimer structure disappears because of P desorption from the surface at this TBP partial pressure. Epitaxial Ga0.52In0.48P layers grown using TBP, trimethylgallium and ethyldimethylindium are nearly disordered at 670 °C and highly ordered at 620 °C. These data suggest a correlation between surface structure and ordering. © 1995 American Institute of Physics.

Notes: Substrate orientation strongly affects Cu–Pt ordering in Ga0.5In0.5P layers grown by organometallic vapor phase epitaxy. In situ surface photoabsorption (SPA) measurements were used to measure the concentration of [1¯10]-oriented P dimers, characteristic of the (2×4) reconstructed surface, as a function of substrate misorientation from (001). For substrates misoriented toward either [110] [or (111)A] or [1¯10] [or (111)B], the P-dimer concentration is found to decrease systematically as the misorientation angle increases from 0° to 15.8° at 620 °C with tertiarybutylphosphine (TBP) partial pressures of 10, 50, and 200 Pa. The P-dimer concentrations on substrates misoriented toward [110] are higher than for those misoriented toward [1¯10]. The Ga0.5In0.5P layers were found to form the Cu–Pt structure during growth. The degree of order, determined from 20 K photoluminescence measurements, shows a strong correlation with the concentration of [1¯10]-oriented P dimers. The data also clearly show the effect of step structure on Cu–Pt ordering. They indicate that [110] steps formed by misorientation toward [1¯10] enhance ordering while [1¯10] steps formed by misorientation toward [110] retard ordering. © 1996 American Institute of Physics.

Notes: High-quality indium tin oxide (ITO) thin films (150–200 nm) were grown on glass substrates by pulsed laser deposition (PLD) without postdeposition annealing. The electrical, optical, and structural properties of these films were investigated as a function of substrate temperature, oxygen pressure, and film thickness. PLD provides very uniform ITO films with high transparency (≥85% in 400–700 nm spectrum) and low electrical resistivity (2–4×10−4 Ω cm). The Hall mobility and carrier density for a 170-nm-thick film deposited at 300 °C are 29 cm2/V s and 1.45×1021 cm−3, respectively. Atomic force microscopy measurements of the ITO films indicated that their root-mean-square surface roughness (∼5 Å) is superior to that (∼40 Å) of commercially available ITO films deposited by sputtering. ITO films grown at room temperature by PLD were used to study the electroluminescence (EL) performance of organic light-emitting devices. The EL performance was comparable to that measured with commercial ITO anodes. © 1999 American Institute of Physics.

Notes: Cu–Pt ordering is widely observed in Ga0.5In0.5P layers grown by organometallic vapor phase epitaxy. The degree of order is a strong function of the input partial pressure of the phosphorus precursor, i.e., the V/III ratio, during growth. By observing the surface structure using in situ surface photoabsorption (SPA) measurements, the concentration of [1¯10]-oriented P dimers, characteristic of the (2×4) reconstructed surface, has been measured as a function of the growth conditions. For growth at 670 °C, the P-dimer concentration is found to increase systematically as the input tertiarybutylphosphine pressure is increased from 10 to 200 Pa. This corresponds directly to a monotonic increase in the degree of order, measured using transmission electron microscopy and low-temperature photoluminescence. These data strongly suggest that the (2×4) surface reconstruction is necessary for formation of the Cu–Pt structure. The step structure at the surface was also observed for these layers using atomic force microscopy. For high V/III ratios the structure of the layers grown on exactly (001) oriented GaAs substrates consists of islands surrounded mainly by bilayer (5.7 A(ring)) steps. As the V/III ratio is reduced, the step height transforms to 2.8 A(ring) (one monolayer). © 1996 American Institute of Physics.

Notes: Organic electroluminescent devices with saturated red emission were developed using 6,13-diphenylpentacene (DPP) doped into tris(8-hydroxyquinolinato) aluminum III (Alq3). DPP exhibits a narrow emission spectrum giving rise to a saturated red peak, centered around 625 nm, with excellent chromaticity coordinates (x=0.63 and y=0.34) in accordance with the Commission Internationale de l'Eclairage. An absolute photoluminescence (PL) quantum yield (φPL) of ∼30% was measured for a composite film of 0.55 mol % of DPP doped into Alq3. An electroluminescence (EL) quantum efficiency of 1.3% at 100 A/m2, close to the estimated theoretical limit (1.5%), was measured for an unoptimized device structure that consists of an active emissive layer sandwiched between hole- and electron-transport layers. In addition, the EL quantum efficiency is constant or stable over a wide range of current densities (1–1000 A/m2) or luminance values (1–1000 cd/m2). © 2001 American Institute of Physics.

Notes: In order to measure the viscoelastic properties of tissue conditioners, a series of stress relaxation tests was carried out using poly ethyl methacrylate polymer powders and liquids composed of butyl phthalyl butyl glycolate/ethyl alcohol mixtures, respectively. The analysis method using the Maxwell model analogy is discussed. The results may be summarized as follows.(i) In this study it was feasible to make the stress relaxation curves for 30min analogous to the Maxwell model, using a model with a maximum of 5 elements.(ii) The elastic modulus E1, the coefficient of viscosity ν, and relaxation time tj, for each element, and the instantaneous modulus Eo, tended to increase with time. These values in the element of the longest relaxation time were most marked in the increase among those in all the elements. Furthermore, in every element the rate of increase of ν was greater than that of E1.The method described is considered to be one of the most useful techniques available for the study of the viscoelastic properties of tissue conditioners.