C. M. Gilmore

Electrical, optical, and structural properties of indium-tin-oxide thin films for organic light-emitting devices

High-quality indium–tin–oxide (ITO) thin films (200–850 nm) have been grown by pulsed laser deposition (PLD) on glass substrates without a postdeposition annealing treatment. The structural, electrical, and optical properties of these films have been investigated as a function of target composition, substrate deposition temperature, background gas pressure, and film thickness. Films were deposited from various target compositions ranging from 0 to 15 wt % of SnO2 content. The optimum target composition for high conductivity was 5 wt % SnO2+95 wt % In2O3. Films were deposited at substrate temperatures ranging from room temperature to 300 °C in O2 partial pressures ranging from 1 to 100 mTorr. Films were deposited using a KrF excimer laser (248 nm, 30 ns full width at half maximum) at a fluence of 2 J/cm2. For a 150-nm-thick ITO film grown at room temperature in an oxygen pressure of 10 mTorr, the resistivity was 4×10−4 Ω cm and the average transmission in the visible range (400–700 nm) was 85%. For a 170-n...

Transparent conducting aluminum-doped zinc oxide thin films for organic light-emitting devices

Aluminum-doped zinc oxide (AZO) thin films (∼3000 A) with low electrical resistivity and high optical transparency have been grown by pulsed-laser deposition on glass substrates without a postdeposition anneal. Films were deposited at substrate temperatures ranging from room temperature to 400 °C in O2 partial pressures ranging from 0.1 to 50 mTorr. For 3000-A-thick AZO films grown at room temperature in an oxygen pressure of 5 mTorr, the electrical resistivity was 8.7×10−4 Ω cm and the average optical transmittance was 86% in the visible range (400–700 nm). For 3000-A-thick AZO films deposited at 200 °C in 5 mTorr of oxygen, the resistivity was 3.8×10−4 Ω cm and the average optical transmittance in the visible range was 91%. AZO films grown at 200 °C were used as an anode contact for organic light-emitting diodes. The external quantum efficiency measured from these devices was about 0.3% at a current density of 100 A/m2.

Effect of aluminum doping on zinc oxide thin films grown by pulsed laser deposition for organic light-emitting devices

Transparent conducting aluminum-doped zinc oxide (AZO) thin films have been deposited on glass substrates by pulsed laser deposition. The structural, electrical and optical properties of these films were investigated as a function of Al-doping amount (0–4 wt.%) in the target. Films were deposited at a substrate temperature of 200°C in 0.67 Pa of oxygen pressure. It was observed that 0.8-wt.% of Al is the optimum doping amount in the target to achieve the minimum film resistivity and the maximum film transmission. For the 300-nm thick AZO film deposited using a ZnO target with an Al content of 0.8 wt.%, the electrical resistivity was 3.7×10−4 Ω-cm and the average transmission in the visible range (400–700 nm) was 90%. The AZO films grown by PLD were used as transparent anodes to fabricate organic light-emitting diodes. The device performance was measured and an external quantum efficiency of 0.3% was measured at a current density of 100 A/m2.

The effect of annealing on the microwave properties of Ba0.5Sr0.5TiO3 thin films

Oriented, single phase thin films (∼5000 A thick) of Ba0.5Sr0.5TiO3 (BST) have been deposited onto (100) MgO and (100) LaAlO3 (LAO) substrates using pulsed laser deposition. The capacitance and dielectric Q (1/tan δ) of as-deposited and annealed films have been measured from 1 to 20 GHz as a function of electric field (0–80 kV/cm) at room temperature using interdigitated Ag electrodes deposited on top of the film. For films deposited onto MgO, it is observed that, after a postdeposition anneal (1000–1200 °C), the dielectric constant decreases and the dielectric Q increases. For films deposited onto LAO, a postdeposition anneal (⩽ 1000 °C) resulted in a significant increase in the dielectric constant and a decrease in Q. The observed dielectric properties of the BST films are attributed to the changes in film stress, which affects the extent of ionic polarization.

Effect of film thickness on the properties of indium tin oxide thin films

Transparent conducting indium tin oxide (ITO) thin films (40–870 nm) were grown by pulsed laser deposition on amorphous substrates and the structural, electrical, and optical properties of these films were investigated. Films were deposited using a KrF excimer laser (248 nm, 30 ns FWHM) at a fluence of 2 J/cm2, at substrate temperature of 300 °C and 10 mTorr of oxygen pressure. For ITO films (30–400 nm thickness) deposited at 300 °C in 10 mTorr of oxygen, a resistivity of 1.8–2.5×10−4 Ω cm was observed and the average transmission in the visible range (400–700 nm) was about 85%–90%. The Hall mobility and carrier density for ITO films (40–870 nm thickness) were observed to be in the range of 24–27 cm2/V s and 8–13×1020 cm−3, respectively. The ITO films have been used as the anode contact in organic light emitting diodes and the effect of ITO film thickness on the device performance has been studied. The optimum thickness of the ITO anode for the maximum device efficiency was observed to be about 60–100 nm....

Influence of strain on microwave dielectric properties of (Ba,Sr)TiO3 thin films

Epitaxial Ba1−xSrxTiO3 (BST) thin films have been deposited onto (100)MgO and LaAlO3 substrates using pulsed-laser deposition. Thick (>1 μm) Ag interdigitated capacitors capped with a thin protective layer of Au have been deposited on top of the BST films using electron-beam deposition. The capacitance (C) and dielectric quality factor (Q=1/tan δ) of the structure has been measured at microwave frequencies (1–20 GHz) as a function of electric field (E⩽67 kV/cm) at room temperature. In epitaxial BST films, either high dielectric tuning (4:1), which is defined as {[C(0)−C(E)]/C(0)}×100, or high dielectric Q (∼100–250) was observed but not both at the same time. Film strain was observed by x-ray diffraction and is closely related to the dielectric properties as limiting the ability to obtain both high tuning and high dielectric Q in epitaxial BST thin films. A thin BST buffer layer was used to relieve the strain in the films. In strain-relieved films, both dielectric tuning and dielectric Q were increased af...

Fatigue and microstructural properties of quenched Ti- 6Al- 4V

The mechanical properties and microstructures of Ti-6A1-4V were determined for specimens heat treated at temperatures from 843 °C to 1065 °C for 10 minutes and water quenched; these properties were compared with those of α-β annealed specimens. Specimens heat treated at 900 °C and water quenched had higher fatigue lives by a factor of four to ten relative to the other treatments; in addition, this treatment resulted in high ductility, yield strength, tensile strength, and elastic modulus. Micro-structure studies utilizing optical and transmission microscopy showed that the improved fatigue lives were a result of a strain induced transformation of retained β to martensite. The amount of retainedβ and its relative stability were shown to depend upon the heat treatment temperature. The lower the heat treatment temperature below theβ transus the smaller the amount ofβ phase present before the quench and the richer theβ phase inβ stabilizer. The greater the concentration ofβ stabilizer in theβ phase the greater the probability that theβ phase was retained. High heat treatment temperatures resulted in a greater amount ofβ that was less stable and more probable to transform to martensite during a water quench.

ROOM TEMPERATURE CREEP OF TI-6AL-4V

Recent investigations have shown both that Ti-6A1-4V does and does not exhibit room temperature creep at low stress. In the present investigation three different microstructures (α β anneal, recrystallization anneal and β anneal) of Ti-6A1-4V were examined under dead weight torsional loading. The loading sequence was forward, reverse and second forward loading. It was concluded that even at a stress level well below the yield stress the alloy exhibits creep in forward loading and increased creep strain in reverse loading and second forward loading. Furthermore the rate of creep at constant stress was different in different microstructures of the alloy; the maximum creep rate occurred with the recrystallization anneal and the minimum creep rate occurred with the β anneal. At the maximum stress in forward loading there appeared to be a change in creep mechanism.

Molecular dynamics simulations of film-substrate interface mixing in the energetic deposition of fcc metals

Abstract Embedded-atom-method molecular dynamic simulations have been performed to examine the interface mixing produced by deposition of fcc metals on fcc metal substrates. Atom arrival energies of 0.1, 10, 20, and 40 eV have been studied. The interface mixing initiated by atom impacts on the substrate surface was found to increase significantly with increasingly negative heats of solution of film atoms in the substrate lattice. As expected, both the total amount of interface mixing and the depth over which it occurred increased with increasing atom deposition energy. Comparison of the interface mixing results for two different temperature-control algorithms led to the conclusion that the interface mixing was very sensitive to short-lived localized substrate lattice excitations in the vicinity of atom impacts. This concept of interface mixing has some similarities to the concept of a thermal spike in bulk ion mixing, but does not involve any localized melting of the lattice. For a simulation of 0.1 eV Ni deposition on a Au substrate, a thermally-activated interface mixing process with a low activation energy was observed, driven by the difference between the surface energies of Ni and Au.

Relative interfacial free energies in pure nickel, dispersion hardened nickel, and a precipitation hardened nickel-base alloy

Abstract The ratio of the twin boundary free energy to grain boundary free energy, δtb/δgb, for coherent twin boundary-grain boundary intersecting systems in thin foils of nickel, TD-nickel, and Inconel 600 has been measured by transmission and diffraction electron microscopy. Final, corrected mean ratios of 0·031, 0·025 and 0·022 for δtb/δgb were obtained for nickel. TD-nickel and Inconel 600 respectively. Using experimentally measured and estimated values of δgb, the twin boundary free energy δtb, for nickel, TD-nickel and Inconel 600 was observed to be approximately 27, 27 and 19 ergs/cm2 respectively.