Showing papers on "Annealing (metallurgy) published in 1999"

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

Abstract: 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...

Structural, optical, and surface acoustic wave properties of epitaxial ZnO films grown on (0112) sapphire by metalorganic chemical vapor deposition

Abstract: High-quality ZnO films are receiving increased interest for use in low-loss high-frequency surface acoustic wave (SAW) devices, acousto-optic and optical modulators, as buffer layers for III-nitride growth, and as the active material in ultraviolet solid state lasers. In this work, high quality epitaxial ZnO films were grown on R-plane sapphire substrates by metalorganic chemical vapor deposition. The structural, piezoelectric, and optical properties of the ZnO films on R sapphire have been investigated. The epitaxial relationship between ZnO and R-Al2O3 was found to be (1120) ZnO∥(0112) Al2O3, and [0001] ZnO∥[0111] Al2O3. The interface between as-grown ZnO and R sapphire was atomically sharp and semicoherent, as evaluated by transmission electron microscopy. On annealing the films at temperatures above 850 °C, a solid state reaction occurred between ZnO and Al2O3, resulting in the formation of ZnAl2O4 (spinel) at the interface. A 15–20 nm spinel layer formed when the ZnO film was annealed at 850 °C fo...

Electrical properties of hafnium silicate gate dielectrics deposited directly on silicon

Abstract: Hafnium silicate (HfSixOy) gate dielectric films with ∼6 at. % Hf exhibit significantly improved leakage properties over SiO2 in the ultrathin regime while remaining thermally stable in direct contact with Si. Capacitance–voltage measurements show an equivalent oxide thickness (tox) of less than 18 A for a 50 A HfSixOy film deposited directly on a Si substrate, with no significant dispersion of the capacitance for frequencies ranging from 10 kHz to 1 MHz. Current–voltage measurements show for the same film a leakage current of 1.2×10−6 A/cm2 at 1 V bias. Hysteresis in these films is measured to be less than 20 mV, the breakdown field is measured to be EBD∼10 MV/cm, and the midgap interface state density is Dit∼1011 cm−2 eV−1. Cross-sectional transmission electron microscopy shows no signs of reaction or crystallization in HfSixOy films on Si after being annealed at 800 °C for 30 min.

Variability of apatite fission-track annealing kinetics; II, Crystallographic orientation effects

Abstract: A method is presented that permits the length of any horizontal, confined fission-track inclined at a specified angle to the crystallographic c axis in apatite to be converted to an equivalent track length parallel to the crystallographic c axis. The model is based on the results of annealing experiments for six selected apatites (five calcian fluorapatites and Durango apatite) representing a subset of the 15 total apatite specimens studied. An iterative process of calculation is required to project fission-track lengths onto the c axis and computer source code implementing the solution to this problem is presented. This method of projecting apatite fission-track lengths onto the crystallographic c axis is shown to remove effectively fission-track length variation within single fission-track populations due to anisotropic track-length reduction for all 15 apatites studied. In addition, a model is developed that offers predictions that closely reproduce published experimental data concerning the relationship between fission-track density (etched fission tracks per unit area of apatite surface) and the arithmetic mean fission-track length. Finally, it is shown that natural fission-track populations exhibit fission-track length anisotropy similar to that of fission-track populations created and annealed in the laboratory. This observation implies that the same process by which apatite fission tracks anneal in the laboratory is responsible for annealing of apatite fission tracks in the geological environment.

Stress reduction and bond stability during thermal annealing of tetrahedral amorphous carbon

Abstract: A comprehensive study of the stress release and structural changes caused by postdeposition thermal annealing of tetrahedral amorphous carbon (ta-C) on Si has been carried out. Complete stress relief occurs at 600–700 °C and is accompanied by minimal structural modifications, as indicated by electron energy loss spectroscopy, Raman spectroscopy, and optical gap measurements. Further annealing in vacuum converts sp3 sites to sp2 with a drastic change occurring after 1100 °C. The field emitting behavior is substantially retained up to the complete stress relief, confirming that ta-C is a robust emitting material.

Optical and Structural Properties of Epitaxial MgxZn1-xO Alloys

Abstract: The optical and structural properties of high-quality single-crystal epitaxial MgZnO films deposited by pulsed-laser deposition were studied. In films with up to ∼36 at. % Mg incorporation, we have observed intense ultraviolet band edge photoluminescence at room temperature and 77 K. The highly efficient photoluminescence is indicative of the excitonic nature of the material. Transmission spectroscopy was used to show that the excitonic structure of the alloys was clearly visible at room temperature. High-resolution transmission electron microscopy, x-ray diffraction, and Rutherford backscattering spectroscopy/ion channeling were used to verify the epitaxial single-crystal quality of the films and characterize the defect content. Post-deposition annealing in oxygen was found to reduce the number of defects and to improve the optical properties of the films. These results indicate that MgZnO alloys have potential applications in a variety of optoelectronic devices.

Indium tin oxide thin films for organic light-emitting devices

Abstract: 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 A) is superior to that (∼40 A) 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.

Dye-Sensitized TiO2 Solar Cells: Structural and Photoelectrochemical Characterization of Nanocrystalline Electrodes Formed from the Hydrolysis of TiCl4

Abstract: The structure and photoelectrochemical properties of TiO2 films deposited onto SnO2 conducting glass from the ambient hydrolysis of TiCl4 and annealed at temperatures ranging from 100 to 500 °C were studied by Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), intensity-modulated photovoltage spectroscopy (IMVS), and intensity-modulated photocurrent spectroscopy (IMPS) measurements. Analysis of the XRD and Raman spectra shows that TiCl4-produced TiO2 films have the rutile structure, regardless of annealing temperature. The TEM reveals that the rutile TiO2 films consist of rod-shaped particles that grow with increasing annealing temperature. The AM-1.5 short-circuit photocurrent Jsc and open-circuit photovoltage Voc of Ru[LL‘(NCS)2]-sensitized (L = 2,2‘-bypyridyl-4,4‘-dicarboxylic acid, L‘ = 2,2‘-bipyridyl-4,4-ditetrabutylammoniumcarboxylate) 4.5 μm thick rutile films increase significantly with annealing temperature, from 1.1 mA/cm2 and 602 mV at 100 °C to 8.7 mA/cm2 and ...

Characterization of treated indium-tin-oxide surfaces used in electroluminescent devices

Abstract: The influence of oxidative and reductive treatments of indium–tin–oxide (ITO) on the performance of electroluminescent devices is presented. The improvement in device performance is correlated with the surface chemical composition and work function. The work function is shown to be largely determined by the surface oxygen concentration. Oxygen-glow discharge or ultraviolet–ozone treatments increase the surface oxygen concentration and work function in a strongly correlated manner. High temperature, vacuum annealing reduces both the surface oxygen and work function. With oxidation the occupied, density of states (DOS) at the Fermi level is also greatly reduced. This process is reversible by vacuum annealing and it appears that the oxygen concentration, work function, and DOS can be cycled by repeated oxygen treatments and annealing. These observations are interpreted in terms of the well-known, bulk properties of ITO.

Production and annealing of electron irradiation damage in ZnO

Abstract: High-energy (>1.6 MeV) electrons create acceptors and donors in single-crystal ZnO. Greater damage is observed for irradiation in the [0001] direction (Zn face) than in the [0001] direction (O face). The major annealing stage occurs at about 300–325 °C, and is much sharper for defects produced by Zn-face irradiation, than for those resulting from O-face irradiation. The defects appear to have a chain character, rather than being simple, near-neighbor vacancy/interstitial Frenkel pairs. These experiments suggest that ZnO is significantly more “radiation hard” than Si, GaAs, or GaN, and should be useful for applications in high-irradiation environments, such as electronics in space satellites.

A study of low temperature crystallization of amorphous thin film indium–tin–oxide

Abstract: Deposition of tin-doped–indium-oxide (ITO) on unheated substrates via low energy processes such as electron-beam deposition can result in the formation of amorphous films The amorphous-to-crystalline transformation was studied in this system using in situ resistivity, time resolved reflectivity, glancing incidence angle x-ray diffraction, and transmission electron microscopy The resistivity of 180 nm thick In2O3(99 wt %SnO2) was monitored during isothermal anneals at 125, 135, 145, and 165 °C The dependence of the resistance on the volume fraction of crystalline phase was established using glancing incidence angle x-ray diffraction and a general two phase resistivity model for this system was developed These studies show that, upon annealing, as-deposited amorphous ITO undergoes both a structural relaxation and crystallization Structural relaxation of the amorphous material includes local ordering that increases the ionized vacancy concentration which, in turn, increases the carrier density in the

Microstructure and Electrical Properties of Lead Zirconate Titanate (Pb(Zr52/Ti48)O3) Thick Films Deposited by Aerosol Deposition Method

Abstract: Lead zirconate titanate (PZT) films with a thickness of more than 10 µm were prepared by the aerosol deposition method and their microstructure and chemical composition were investigated by transmission electron microscopy (TEM) and energy dispersive X-ray spectra (EDX) analysis. A damage layer was observed at the interface between PZT and the Si substrate during the deposition. The microstructure of the as-deposited film at room temperature consisted of randomly oriented small crystallites with sizes of less than 40 nm and large crystallites of 100 nm to 300 nm size, which were observed in the primary powder. The Pb/Ti/Zr ratio along the film stacking direction and around the grain boundaries was almost the same as that observed inside the crystallites and the primary powder with a morphotropic phase boundary composition of (Pb(Zr0.52Ti0.48)O3). The marked improvement of the electrical properties observed in the deposited films after annealing was mainly due to the crystal growth of small crystallites.

Enhancement of thermal stability of NiSi films on (100)Si and (111)Si by Pt addition

Abstract: The effect of a small amount of Pt (5 at. %) on the thermal stability of NiSi film on (100) and (111) Si substrates has been investigated both by in situ annealing inside an x-ray photoelectron spectroscopy system and by ex situ rapid thermal annealing. The addition of platinum increases the disilicide nucleation temperature to 900 °C leading to a better stability of NiSi at high temperatures. In the presence of Pt, NiSi films on both (111)Si and (100)Si substrates develop a texture with the relationship (100)NiSi∥(111)Si and (010)NiSi∥(100)Si. The increase in thermal stability has been explained in terms of the nucleation concept.

A solid-state process for formation of boron nitride nanotubes

Abstract: The formation of boron nitride (BN) nanotubes via a solid-state process is demonstrated. The nanotubes are produced by first ball-milling hexagonal BN powder to generate highly disordered or amorphous nanostructures, followed by annealing at temperatures up to 1300 °C. The annealing leads to the nucleation and growth of hexagonal BN nanotubes of both cylindrical and bamboo-like morphology. Unlike previous mechanisms for nanotube formation, the reordering and solid-state growth process of our nanotubes does not involve deposition from the vapor phase nor chemical reactions.

Microstructure and mechanical properties of Mo–Mo3Si–Mo5SiB2 silicides

Abstract: Molybdenum boron silicides consisting of 20–50 vol.% of α-Mo and different ratios of the intermetallic phases Mo5SiB2 (‘T2’) and Mo3Si were prepared by arc-melting followed by dropcasting into Cu chill molds. For α-Mo volume fractions of ≈50% sound castings were obtained. For lower α-Mo volume fractions such as 25% macroscopic cracks were often observed. Preliminary oxidation tests verified the expected increase in the oxidation resistance as the B-concentration increases and the α-Mo volume fraction decreases. Also, the formation of glass films was observed. Depending on composition and heat treatment, the room temperature flexure strengths varied usually between 300 and 600 MPa. To some extent, these variations could be rationalized by differences in the microstructures. Annealing for 1 day at 1873 K in vacuum caused distinct microstructural coarsening. Annealing was sometimes accompanied by microcracking in the Mo3Si and the T2 phases. Cooling curves suggest that the liquidus temperature of the T2 phase is above 2400 K. Depending on the composition, final freezing of Mo–Si–B alloys was found to occur at temperatures as low as 2200 K. Care is therefore required during thermomechanical processing to avoid the formation of liquid phases.

Leakage current of hadron irradiated silicon detectors - material dependence

Abstract: The leakage current increase of silicon detectors irradiated with fast neutrons was measured in the fluence range from 10 11 to 10 15 cm −2 for a wide range of different starting material. The oxygen concentration in the investigated silicon varied from 9×10 17 cm −3 to below 2×10 14 cm −3 and the carbon concentration from 2×10 16 cm −3 to below 5×10 15 cm −3 . Furthermore the resistivity differed from 100 Ω cm to 20 kΩ cm for the used n-type and from 400 Ω cm to 2 kΩ cm for the p-type silicon. It is found that up to the highest fluence the current-related damage parameter alpha is almost independent of the initial resistivity and impurity concentration. After irradiation a universal annealing behavior for all material is observed which unmistakably indicates that the microscopic defects underlying the generation of leakage current are of intrinsic origin. Furthermore it is shown that the parameterization of the annealing behavior at an elevated temperature (here 60°C) provides an excellent tool for comparing the so-called hardness factors of different irradiation sources. As an example the hardness factors for the 24 GeV/ c CERN proton synchrotron and the TRIGA research reactor in Ljubljana were determined to be 0.51 and 0.90, respectively.

Structural properties, internal stress and thermal stability of nc-TiN/a-Si3N4, nc-TiN/TiSix and nc-(Ti1−yAlySix)N superhard nanocomposite coatings reaching the hardness of diamond

Abstract: The average crystallite size, d, in the range of about 3–8 nm determined from XRD by means of the Scherrer formula and integral width of the Bragg peaks compares well with that determined from the Warren–Averbach analysis. TiN films show (200) texture which changes to random orientation of the crystallites when the silicon content reaches about 10 at.%. The biaxial stress of ≤0.4 GPa for ≤10 μm thick films is fairly low. The random stress determined from the Warren–Averbach analysis increases with decreasing crystallite size from about 1 GPa for d ≥10 nm to almost 10 GPa for d≈3 nm. A strong increase is observed for the stability of the nanostructure and of the hardness upon annealing: the recrystallization temperature increases from about 850°C for d≥5 nm to ≥1150°C for d≤3 nm. This is explained by thermodynamical stabilization of the grain boundaries due to segregation. Superhardness remains constant up to recrystallization. For superhardness of about 100 GPa, the elastic modulus of 70–500 GPa and the universal hardness of about 17–22 GPa (loads between 30 and 100 mN) compare well with the hardness of a single-phase nanocrystalline diamond. Besides this extremely high hardness, the coatings also have a very high toughness and elastic recovery of 80–90%.

Low dielectric constant films prepared by plasma-enhanced chemical vapor deposition from tetramethylsilane

Abstract: Dielectric films have been prepared by radio-frequency plasma-enhanced chemical vapor deposition from mixtures of tetramethylsilane with oxygen. The films have been characterized as-deposited and after annealing at 400 °C to determine the thermal stability of their properties. Rutherford backscattering and forward recoil elastic scattering have been used for determination of the composition of the films. Optical properties were characterized by Fourier transform infrared spectroscopy and measurements of the index of refraction and optical gap. The electrical properties were measured in a Si/insulator/metal configuration. It has been found that the index of refraction decreases and the optical gap and dielectric constant increase with increasing oxygen concentration in the gas feed. While the materials did not show a mass or composition loss after annealing, the annealing resulted in a reduction of the dielectric constant of the films. Dielectric constants as low as 3.1 have been obtained after annealing the film deposited from pure tetramethylsilane.

Thermal crystallization of amorphous Si/SiO2 superlattices

Abstract: Annealing of amorphous Si/SiO2 superlattices produces Si nanocrystals. The crystallization has been studied by transmission electron microscopy and x-ray analysis. For a Si layer thinner than 7 nm, nearly perfect nanocrystals are found. For thicker layers, growth faults and dislocations exist. Decreasing the a-Si layer thickness increases the inhomogeneous strain by one order of magnitude. The origin of the strain in the crystallized structure is discussed. The crystallization temperature increases rapidly with decreasing a-Si layer thickness. An empirical model that takes into account the Si layer thickness, the Si/SiO2 interface range, and a material specific constant has been developed.

Oxygenation and air-annealing effects on the electronic properties of Cu(In,Ga)Se2 films and devices

Abstract: Post-deposition air-annealing effects of Cu(In,Ga)Se2 based thin films and heterojunction solar cell devices are studied by photoelectron spectroscopy and admittance spectroscopy. Ultraviolet photoelectron spectroscopy reveals type inversion at the surface of the as-prepared films, which is eliminated after exposure of several minutes to air due to the passivation of surface Se deficiencies. X-ray photoelectron spectroscopy demonstrates that air annealing at 200 °C leads to a decreased Cu concentration at the film surface. Admittance spectroscopy of complete ZnO/CdS/Cu(In,Ga)Se2 heterojunction solar cells shows that the Cu(In,Ga)Se2 surface type inversion is restored by the chemical bath used for CdS deposition. Air annealing of the finished devices at 200 °C reduces the type inversion again due to defect passivation. Our results also show that oxygenation leads to a charge redistribution and to a significant compensation of the effective acceptor density in the bulk of the absorber. This is consistent wi...

Structure and Properties of Novel Asymmetric Biphenyl Type Polyimides. Homo- and Copolymers and Blends

Abstract: Asymmetric biphenyl type polyimides (PI) were prepared by thermal imidization of polyamic acids (PAA) derived from 2,3,3‘,4‘-biphenyltetracarboxylic dianhydride (a-BPDA) and p-phenylenediamine (PDA) or 4,4‘-oxydianiline (ODA). The dynamic mechanical properties of these PIs were compared with those of the isomeric PIs derived from symmetric 3,4,3‘,4‘-biphenyltetracarboxylic dianhydride (s-BPDA). a-BPDA/PDA polyimide has a considerably bent chain structure compared to semirigid s-BPDA/PDA. Nevertheless, the a-BPDA/PDA film annealed at 350 °C showed a higher Tg than the s-BPDA/PDA film prepared under the same conditions. When these PIs were annealed at 400 °C, a-BPDA/PDA exhibited an abrupt E‘ decrease at the Tg (=410 °C) as well as the counterpart annealed at 350 °C, whereas s-BPDA/PDA showed no distinct Tg in the E‘ curve. Similar annealing effects were also observed for the ODA systems. The unexpectedly higher Tg's of a-BPDA-based PIs could be explained in terms of the more restricted conformational chang...