Showing papers on "Annealing (metallurgy) published in 2012"

Flexible metal-oxide devices made by room-temperature photochemical activation of sol–gel films

Abstract: A method for annealing metal-oxide semiconductor films with deep-ultraviolet light yields thin-film transistors with performance comparable to that of thermally annealed devices, and widens the range of substrates on which such devices can be fabricated. Solution-processable metal-oxide semiconductors are attractive materials for low-cost, flexible electronics, but the need to anneal the deposited materials at relatively high temperatures limits the range of substrates on which such devices can be fabricated. Now Yong-Hoon Kim and colleagues demonstrate that irradiating the solution-cast films with deep ultraviolet light can obviate the need for an annealing step. In this system, photochemical activation serves essentially the same purpose as annealing, and the resulting semiconducting materials have device performance levels comparable to those produced using the high-temperature techniques. Amorphous metal-oxide semiconductors have emerged as potential replacements for organic and silicon materials in thin-film electronics. The high carrier mobility in the amorphous state, and excellent large-area uniformity, have extended their applications to active-matrix electronics, including displays, sensor arrays and X-ray detectors1,2,3,4,5,6,7. Moreover, their solution processability and optical transparency have opened new horizons for low-cost printable and transparent electronics on plastic substrates8,9,10,11,12,13. But metal-oxide formation by the sol–gel route requires an annealing step at relatively high temperature2,14,15,16,17,18,19, which has prevented the incorporation of these materials with the polymer substrates used in high-performance flexible electronics. Here we report a general method for forming high-performance and operationally stable metal-oxide semiconductors at room temperature, by deep-ultraviolet photochemical activation of sol–gel films. Deep-ultraviolet irradiation induces efficient condensation and densification of oxide semiconducting films by photochemical activation at low temperature. This photochemical activation is applicable to numerous metal-oxide semiconductors, and the performance (in terms of transistor mobility and operational stability) of thin-film transistors fabricated by this route compares favourably with that of thin-film transistors based on thermally annealed materials. The field-effect mobilities of the photo-activated metal-oxide semiconductors are as high as 14 and 7 cm2 V−1 s−1 (with an Al2O3 gate insulator) on glass and polymer substrates, respectively; and seven-stage ring oscillators fabricated on polymer substrates operate with an oscillation frequency of more than 340 kHz, corresponding to a propagation delay of less than 210 nanoseconds per stage.

Graphene Annealing: How Clean Can It Be?

Abstract: Surface contamination by polymer residues has long been a critical problem in probing graphene’s intrinsic properties and in using graphene for unique applications in surface chemistry, biotechnology, and ultrahigh speed electronics. Poly(methyl methacrylate) (PMMA) is a macromolecule commonly used for graphene transfer and device processing, leaving a thin layer of residue to be empirically cleaned by annealing. Here we report on a systematic study of PMMA decomposition on graphene and of its impact on graphene’s intrinsic properties using transmission electron microscopy (TEM) in combination with Raman spectroscopy. TEM images revealed that the physisorbed PMMA proceeds in two steps of weight loss in annealing and cannot be removed entirely at a graphene susceptible temperature before breaking. Raman analysis shows a remarkable blue-shift of the 2D mode after annealing, implying an anneal-induced band structure modulation in graphene with defects. Calculations using density functional theory show that l...

Annealing effect on photovoltaic performance of CdSe quantum-dots-sensitized TiO 2 nanorod solar cells

Abstract: Large area rutile TiO2 nanorod arrays were grown on F:SnO2 (FTO) conductive glass using a hydrothermal method at low temperature. CdSe quantum dots (QDs) were deposited onto single-crystalline TiO2 nanorod arrays by a chemical bath deposition (CBD) method to make a photoelectrode. The solar cell was assembled using a CdSe-TiO2 nanostructure as the photoanode and polysulfide solution as the electrolyte. The annealing effect on optical and photovoltaic properties of CdSe quantum-dotssensitized TiO2 nanorod solar cells was studied systematically. A significant change of the morphology and a regular red shift of band gap of CdSe nanoparticles were observed after annealing treatment. At the same time, an improved photovoltaic performance was obtained for quantum-dots-sensitized solar cell using the annealed CdSe-TiO2 nanostructure electrode. The power conversion efficiency improved from 0.59% to 1.45% as a consequence of the annealing effect. This improvement can be explained by considering the changes in the morphology, the crystalline quality, and the optical properties caused by annealing treatment.

Evolution of microstructure and mechanical properties of medium Mn steels during double annealing

Abstract: A double annealing process was applied to cold rolled medium Mn steel. The evolution of both microstructure and mechanical properties during the second annealing were analysed. Austenite reverted transformation (ART) was observed during intercritical annealing. It was shown that a complex ultra-fine microstructure composed of three phases (retained austenite/martensite/ferrite) was formed and two types of morphologies were detected (lath-like and polygonal). Furthermore, a high volume fraction of retained austenite (22%), which was stabilized at room temperature, was the origin of a TRIP effect. A good balance between strength and ductility can be achieved by optimizing the heat treatment. The various results are discussed and some mechanisms are proposed to explain the observations.

Significant enhancement of blue emission and electrical conductivity of N-doped graphene

Abstract: Nitrogen (N)-doped graphene with different atomic percentages (2.3–4.7 at%) of N has been synthesized by thermal annealing of reduced graphene oxide (RGO) in ammonia gas for different times. The effects of annealing time on the structure, electrical and optical properties of N-doped graphene have been systematically investigated by using various analytical techniques. XPS, FTIR, Raman, and XRD studies show that there is a gradual structural change in N-doped graphene sheets with increasing annealing time, resulting from the increase of carbon and simultaneous decrease of oxygen and N contents. High resolution N1s spectra reveal that the pyridine-N and pyrrolic-N contents decrease with increasing annealing time, whereas the amount of quaternary-N increases. Importantly, it has been found that the annealing time caused significant changes in both the electrical and the optical properties of N-doped graphene. The electrical resistance of N-doped graphene is greatly reduced compared to that of GO and RGO, and found to further decrease with increasing annealing time, possibly due to the increase of sp2 carbon networks and decrease of oxygen content as well as defects associated with the incorporation of N. The room-temperature photoluminescence (PL) properties of graphene oxide (GO), RGO and N-doped graphene were systematically studied with regard to the annealing time. The results showed that the PL spectrum of GO exhibits a peak emission maximum at around 700 nm, while that of RGO is found to be strongly blue-shifted with two distinct emission peaks: green emission at 485–500 nm and blue emission at 420–428 nm. For N-doped graphene samples, the blue emission intensity could significantly be enhanced by controlling the annealing time, which leads to a promising blue and green light-emitting material with controllable optical properties.

NO2-sensing properties of porous WO3 gas sensor based on anodized sputtered tungsten thin film

Abstract: In this paper, a novel porous WO3 sensor was prepared by anodic oxidation of DC magnetron sputtered metallic tungsten (W) film deposited on alumina substrate. The structural and morphological properties of these films are investigated using field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). Coral-like porous crystalline WO3 film with a grain size of about 9.3 nm was obtained after annealing of the anodized W film. The porous WO3 sensor achieved its maximum response value to NO2 at a low operating temperature of 150 °C. In comparison to sputtered WO3 sensor, the porous WO3 sensor showed markedly higher responses, much better response–recovery characteristics and lower optimal operating temperature to different concentration of NO2 gas due to its high specific surface area and small grain size.

Simultaneous modification of pyrolysis and densification for low-temperature solution-processed flexible oxide thin-film transistors

Abstract: High-pressure annealing (HPA) affected the thermodynamics of the formation of a solution-processed oxide film through the simultaneous modification of thermal decomposition and compression, and enabled the use of lower annealing temperatures, which was favourable for device implementation. HPA also reduced the film thickness and decreased the porosity, resulting in enhanced device characteristics at low temperature. Surface and depth profile characterization using X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and ellipsometry suggested that the HPA process supported the effective decomposition of commercial metal-nitrate and/or -salt precursors and strong bonding between oxygen and the metal ions, ultimately reducing the amount of organic residue. The as-optimized HPA process allowed for high-performance solution-processed flexible InZnO (IZO) TFTs on a polymeric substrate at 220 °C with low sub-threshold voltage swing (as low as 0.56 V dec−1), high on–off ratio of over 106, and field-effect mobility as high as 1.78 cm2 V−1 s−1, respectively. These results demonstrate that this is a simple and efficient promising approach for improving the performance of solution-processed electronic devices at low temperatures.

Effect of large strain cold rolling and subsequent annealing on microstructure and mechanical properties of an austenitic stainless steel

Abstract: The microstructural evolution of an S304H steel during bar rolling to a strain of 4 and subsequent annealing as well as its effect on the mechanical properties were investigated. The cold working was accompanied by a strain-induced martensitic transformation, leading to the development of lamellar-type microstructure consisting of highly elongated austenite/ferrite subgrains with a mean transverse size of approximately 50 nm; the austenite volume fraction was approximately 0.35. This material exhibited a yield strength above 2000 MPa. The subsequent annealing resulted in grain coarsening following the ferrite → austenite reversion, which led to almost full austenitization at temperatures above 700 °C. The formation of the austenite/ferrite lamellar structure that mixed with separate equiaxed grains occurred after annealing at temperatures of T ≤ 700 °C. The grain coarsening was accompanied by a degradation in strength, although the yield strength of above 1000 MPa remained after 2 h of annealing at 700 °C. The discontinuous recrystallization of austenite resulted in the development of a relatively coarse-grained microstructure at T ≥ 800 °C.

Grain boundary relaxation strengthening of nanocrystalline Ni–W alloys

Abstract: The hardening effect caused by the relaxation of nonequilibrium grain boundary structure has been explored in nanocrystalline Ni–W alloys. First, the kinetics of relaxation hardening are studied, showing that higher annealing temperatures result in faster, more pronounced strengthening. Based on the temperature dependence of relaxation strengthening kinetics, triple junction diffusion is suggested as a plausible kinetic rate limiter for the removal of excess grain boundary defects in these materials. Second, the magnitude of relaxation strengthening is explored over a wide range of grain sizes spanning the Hall–Petch breakdown, with an apparent maximum hardening effect found at a grain size below 10 nm. The apparent activation volume for plastic deformation is unaffected by annealing for grain sizes down to ∼10 nm, but increases with annealing for the finest grain sizes, suggesting a change in the dominant deformation mechanism for these structures.

Influence of annealing and Al2O3 properties on the hydrogen-induced passivation of the Si/SiO2 interface

Abstract: Annealing at moderate temperatures is required to activate the silicon surface passivation by Al2O3 thin films while also the thermal stability at higher temperatures is important when Al2O3 is implemented in solar cells with screenprinted metallization. In this paper, the relationship between the microstructure of the Al2O3 film, hydrogen diffusion, and defect passivation is explored in detail for a wide range of annealing temperatures. The chemical passivation was studied using stacks of thermally-grown SiO2 and Al2O3 synthesized by atomic layer deposition. Thermal effusion measurements of hydrogen and implanted He and Ne atoms were used to elucidate the role of hydrogen during annealing. We show that the passivation properties were strongly dependent on the annealing temperature and time and were significantly influenced by the Al2O3 microstructure. The latter was tailored by variation of the deposition temperature (Tdep = 50 °C–400 °C) with hydrogen concentration [H] between 1 and 13 at.% and mass den...

Effect of Copper TSV Annealing on Via Protrusion for TSV Wafer Fabrication

Abstract: Three-dimensional (3D) integrated circuit (IC) technologies are receiving increasing attention due to their capability to enhance microchip function and performance. While current efforts are focused on the 3D process development, adequate reliability of copper (Cu) through-silicon vias (TSVs) is essential for commercial high-volume manufacturing. Annealing a silicon device with copper TSVs causes high stresses in the copper and may cause a “pumping” phenomenon in which copper is forced out of the blind TSV to form a protrusion. This is a potential threat to the back-end interconnect structure, particularly for low-κ materials, since it can lead to cracking or delamination. In this work, we studied the phenomenon of Cu protrusion and microstructural changes during thermal annealing of a TSV wafer. The extruded Cu-TSV was observed using scanning electron microscopy (SEM), 3D profilometry, and atomic force microscopy (AFM). The electron backscatter diffraction (EBSD) technique was employed to study the grain orientation of Cu-TSV and evolution of the grain size as a function of annealing temperature. The elastic modulus and yield stress of copper were characterized using nanoindentation. A model for Cu protrusion is proposed to provide insight into the failure mechanism. The results help to solve a key TSV-related manufacturing yield and reliability challenge by enabling high-throughput TSV fabrication for 3D IC integration.

Conductivity enhancement of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) films post-spincasting

Abstract: Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) thin films on indium tin oxide and glass substrates have been fabricated and subjected to a non-adiabatic annealing process. The films showed subtle changes in their structure and optical properties as well as an increase in conductivity due to the effects of rapid thermal annealing. Through a combination of Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy studies in conjunction with electrical characterization, and four-point probe measurements, material enrichment of conductive PEDOT domains at the polymer-metal interface have been demonstrated, which well explains the surface conductivity improvement of a thin film of PEDOT:PSS after annealing.

Methods and apparatus for conformal doping

Abstract: Methods and apparatus for processing a substrate are provided herein. In some embodiments, a method of doping a substrate may include forming a dopant region on a substrate by implanting one or more dopant elements into the dopant region of the substrate using a plasma doping process; forming a cap layer atop the dopant region; annealing the dopant region after forming the cap layer; and removing the cap layer after annealing the dopant region.

Independent control of bulk and interfacial morphologies of small molecular weight organic heterojunction solar cells.

Abstract: We demonstrate that solvent vapor annealing of small molecular weight organic heterojunctions can be used to independently control the interface and bulk thin-film morphologies, thereby modifying charge transport and exciton dissociation in these structures. As an example, we anneal diphenyl-functionalized squaraine (DPSQ)/C60 heterojunctions before or after the deposition of C60. Solvent vapor annealing of DPSQ before C60 deposition results in molecular order at the heterointerface. Organic photovoltaics based on this process have reduced open circuit voltages and power conversion efficiencies relative to as-cast devices. In contrast, annealing following C60 deposition locks in interface disorder found in unannealed junctions while improving order in the thin-film bulk. This results in an increase in short circuit current by >30% while maintaining the open circuit voltage of the as-cast heterojunction device. These results are analyzed in terms of recombination dynamics at excitonic heterojunctions and d...

Crystal growth behaviour in Au-ZnO nanocomposite under different annealing environments and photoswitchability

Abstract: The growth of gold nanoparticles and ZnO nanorods in atom beam co-sputtered Au-ZnO nanocomposite (NC) system by annealing at two different ambient conditions is demonstrated in this work. Annealing in a furnace at 600 °C (air environment) confirmed the formation of ZnO nanorods surrounded with Au nanoparticles. In-situ annealing inside a transmission electron microscope (TEM) led to the formation of gold nanocrystals with different polygonal shapes. TEM micrographs were obtained in real time at intermediate temperatures of 300 °C, 420 °C, and 600 °C under vacuum. The growth mechanisms of Au nanocrystals and ZnO nanorods are discussed in the framework of Au-Zn eutectic and Zn-melting temperatures in vacuum and air, respectively. Current-voltage responses of Au-ZnO NC nanorods in dark as well as under light illumination have been investigated and photoswitching in Au-ZnO NC system is reported. The photoswitching has been discussed in terms of Au-ZnO band-diagram.

Efficiency Enhanced Hybrid Solar Cells Using a Blend of Quantum Dots and Nanorods

Abstract: The cell performance of organic-inorganic hybrid photovoltaic devices based on CdSe nanocrystals and the semiconducting polymer poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) is strongly dependent on the applied polymer-to-nanocrystal loading ratio and the annealing temperature. It is shown here that higher temperatures for the thermal annealing step have a beneficial impact on the nanocrystal phase by forming extended agglomerates necessary for electron percolation to enhance the short-circuit current. However, there is a concomitant reduction of the open-circuit voltage, which arises from energy-level alterations of the organic and the inorganic component. Based on quantum dots and PCPDTBT, we present an optimized organic–inorganic hybrid system utilizing an annealing temperature of 210 °C, which provides a maximum power conversion efficiency of 2.8%. Further improvement is obtained by blending nanocrystals of two different shapes to compose a favorable n-type network. The blend of spherical quantum dots and elongated nanorods results in a well-interconnected pathway for electrons within the p-type polmer matrix, yielding maximum efficiencies of 3.6% under simulated AM 1.5 illumination.

Process for Preparing Graphene on a SiC Substrate Based on Metal Film-Assisted Annealing

Abstract: Provided is a process for preparing graphene on a SiC substrate, based on metal film-assisted annealing, comprising the following steps: subjecting a SiC substrate to a standard cleaning process; placing the cleaned SiC substrate into a quartz tube and heating the quartz tube up to a temperature of 750 to 1150° C.; introducing CCl 4 vapor into the quartz tube to react with SiC for a period of 20 to 100 minutes so as to generate a double-layered carbon film, wherein the CCl 4 vapor is carried by Ar gas; forming a metal film with a thickness of 350 to 600 nm on a Si substrate by electron beam deposition; placing the obtained double-layered carbon film sample onto the metal film; subsequently annealing them in an Ar atmosphere at a temperature of 900 to 1100° C. for 10-30 minutes so as to reconstitute the double-layered carbon film into double-layered graphene; and removing the metal film from the double-layered graphene, thereby obtaining double-layered graphene. Also provided is double-layered graphene prepared by said process.

Dopant Segregation and Space Charge Effects in Proton-Conducting BaZrO3 Perovskites

Abstract: In a humidified atmosphere, acceptor-doped BaZrO3 perovskites exhibit a high bulk proton conductivity, but the total conductivity is severely decreased by the blocking character of the grain boundaries. In our study, we compare rapidly densified Y- and Sc-doped BaZrO3 ceramics (Spark Plasma Sintering, 5 min at 1600 °C) with samples after extended annealing at high temperature (20 h at 1700 °C). Under these conditions, the dopants become mobile, resulting in a strong grain boundary conductivity enhancement, although no grain growth occurs. This increase is accompanied by a significant increase in dopant concentration in the grain boundary region, as evidenced by transmission electron microscopy. The correlation between the electrical properties of grain boundaries and their chemical composition is consistent with the interpretation in terms of the space charge model with a positive excess charge in the grain boundary core and adjacent proton depletion zones.

Synthesis and Characterization of Co 3 O 4 Thin Film

Abstract: Nanosized Co3O4 thin films were prepared on glass substrates by using sol-gel spin coating technique. The effect of annealing temperature (400°C - 700°C) on structural, morphological, electrical and optical properties of Co3O4 thin films were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Electrical conductivity and UV-visible Spectroscopy (UV-Vis). XRD measurements show that all the films are nanocrystallized in the cubic spinel structure and present a random orientation. Six prominent peaks, corresponding to the (111) phase (2θ ≈ 18.90°), (220) phase (2θ ≈ 31.29°), (311) phase (2θ ≈ 36.81°), (222) phase (2θ ≈ 38.54°), (400) phase (2θ ≈ 44.80°), (511) phase (2θ ≈ 59.37°) and (440) phase (2θ ≈ 65.27°) appear on the diffractograms. The crystallite size increases with increasing annealing temperature. These modifications influence the optical properties. The morphology of the sol gel derived Co3O4 shows nanocrystalline grains with some overgrown clusters and it varies with annealing temperature. The optical band gap has been determined from the absorption coefficient. We found that the optical band gap energy decreases from 2.58 eV to 2.07 eV with increasing annealing temperature between 400°C - 700°C. These mean that the optical quality of Co3O4 films is improved by annealing. The dc electrical conductivity of Co3O4 thin films were increased from 10–4 to 10–2 (Ω.cm)–1 with increase in annealing temperature. The electron carrier concentration (n) and mobility (μ) of Co3O4 films annealed at 400°C - 700°C were estimated to be of the order of 2.4 to 4.5 × 1019 cm–3 and 5.2 to 7.0 × 10–5 cm2.V–1.s–1 respectively. It is observed that Co3O4 thin film annealing at 700°C after deposition provide a smooth and flat texture suited for optoelectronic applications.

Selective Plasmonic Gas Sensing: H2, NO2, and CO Spectral Discrimination by a Single Au-CeO2 Nanocomposite Film

Abstract: A Au-CeO2 nanocomposite film has been investigated as a potential sensing element for high-temperature plasmonic sensing of H2, CO, and NO2 in an oxygen containing environment. The CeO2 thin film was deposited by molecular beam epitaxy (MBE), and Au was implanted into the as-grown film at an elevated temperature followed by high temperature annealing to form well-defined Au nanoclusters. The Au-CeO2 nanocomposite film was characterized by X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). For the gas sensing experiments, separate exposures to varying concentrations of H2, CO, and NO2 were performed at a temperature of 500 °C in oxygen backgrounds of 5.0, 10, and ∼21% O2. Changes in the localized surface plasmon resonance (LSPR) absorption peak were monitored during gas exposures and are believed to be the result of oxidation–reduction processes that fill or create oxygen vacancies in the CeO2. This process affects the LSPR peak position either by charge exchange with the Au nanopart...