Effect Of Vacuum Annealing Research Articles

Effects of vacuum annealing on the optical and electrical properties of p-type copper-oxide thin-film transistors

We have investigated the effects of vacuum annealing on the optical and electrical properties of the p-type copper-oxide thin-film transistors (TFTs). The vacuum annealing of the copper-oxide thin-film was performed using the RF magnetron sputter at various temperatures. From the x-ray diffraction and UV-vis spectroscopy, it is demonstrated that the high-temperature vacuum annealing reduces the copper-oxide phase from CuO to Cu2O, and increases the optical transmittance in the visible part of the spectrum. The fabricated copper-oxide TFT does not exhibit the switching behavior under low-temperature vacuum annealing conditions. However, as the annealing temperature increases, the drain current begins to be modulated by a gate voltage, and the TFT exhibits a high current on–off ratio over 104 as the vacuum annealing temperature increases over 450 °C. These results show that the vacuum annealing process can be an effective method of simultaneously improving the optical and electrical performances in p-type copper-oxide TFTs.

Impact of post-growth thermal annealing and environmental exposure on the unintentional doping of CVD graphene films

The effect of vacuum annealing followed by exposure to oxygen and water vapor on the unintentional doping of CVD-grown graphene was investigated. CVD graphene samples were cycled between room temperature and 500 °C in vacuum while in situ Raman measurements were recorded. During the heating and cooling cycle, a hysteresis in the Raman response due to the desorption of p-dopants was observed. Upon exposure to O2 gas or air, a blue shift in the Raman response with respect to the as grown film was observed which was due to increased adsorption of p-dopants on the sample. Experiments showed that a combination of water vapor and oxygen is more effective in p-doping the samples than just oxygen and that the doping effects are reversible in both cases. Electrical measurements performed on back-gated field effect graphene devices indicate that shifts in the Dirac point correlate well to the shifts in the Raman peak positions as well as changes found in XPS and Kelvin Probe measurements, verifying the changes in doping of the graphene.

Effect of Vacuum Annealing on the Characteristics of Plasma Sprayed Al2O3-13wt.%TiO2 Coatings

Adhesion strength is one of the critical properties for plasma-sprayed coating. In this study, the plasma-sprayed Al2O3-13wt.%TiO2/NiCrAl coatings were annealed at 300-900 °C for 6 h in vacuum. The tensile bond strength and porosity of the coatings were investigated. The microstructure and the fracture were studied using optical microscopy, scanning electron spectroscopy, and x-ray diffraction. It was found that the tensile bond strength of coatings increased with the increase of annealing temperature until 500 °C, reaching the maximum value of 41.2 MPa, and then decreased as the annealing temperature continues to increase. All coatings presented a brittle fracture and the fracture occurred inside the ceramic coatings except for the coating annealed at 500 °C, which had a brittle-ductile mixed fracture and the fracture occurred at the interface of bond coating and the substrate.

Effect of vacuum annealing on the structural, optical, and electrical properties of spray‐deposited Ga‐doped ZnO thin films

AbstractGallium‐doped zinc oxide (GZO) transparent conducting thin films were prepared by a cost‐effective spray‐pyrolysis method on glass substrates at 400 °C for various concentration of gallium (0–5 at.%) in the spray solution. Electrical, optical, and structural properties of as‐deposited and annealed GZO films were investigated using Hall measurement, optical transmission, X‐ray diffraction, and atomic force microscopy. As‐prepared and vacuum annealed GZO films at 400 °C are preferentially orientated along the (002) crystallographic direction and annealing has enhanced the crystallinity of the films. A vacuum‐annealed GZO film (3 at.%) acquired the lowest resistivity of 6.5 × 10−3 Ω cm with Hall mobility and carrier concentration of 18 cm2/V s and 5.4 × 1019 cm−3, respectively. The transmittance of GZO film for 1 at.% is ∼84% in the visible region (400–800 nm) and it is markedly increased to ∼92% with the transmission edge shift towards the shorter‐wavelength side on annealing. However, neither doping nor vacuum annealing of ZnO films modify the near band edge (3.26 eV) of the film appreciably. Ga doping is found to compensate the radiative oxygen vacancy levels and thus quench the green luminescence at 2.8 eV.

Effect of vacuum-annealing on the d0 ferromagnetism of undoped In2O3 films

Vacuum-annealing was carried out on the pure indium oxide films deposited on Si (100) substrates by radiofrequency magnetron sputtering. Oxygen-deficiency states and room temperature d0 ferromagnetism were both detected in the as-grown and vacuum-annealed films. With more oxygen vacancies appeared through vacuum-annealing, the saturation magnetization increased rapidly from 0.5 to 5.5emu/cm3. The connection between the highly oxygen-deficiency states and the strong magnetic moment suggests that oxygen vacancies play a crucial role in mediating the ferromagnetism in In2O3 films. We think that this d0 ferromagnetism mainly stems from V0+ and oxygen vacancy clusters in the interfaces or grain boundaries.

Defects in Oxygen-Depleted Titanate Nanostructures

The identification of defects and their controlled generation in titanate nanostructures is a key to their successful application in photoelectronic devices. We comprehensively explored the effect of vacuum annealing on morphology and composition of Na(2)Ti(3)O(7) nanowires and protonated H(2)Ti(3)O(7) nanoscrolls using a combination of scanning electron microscopy, Auger and Fourier-transform infrared (FT-IR) spectroscopy, as well as ab initio density functional theory (DFT) calculations. The observation that H(2)Ti(3)O(7) nanoscrolls are more susceptible to electronic reduction and annealing-induced n-type doping than Na(2)Ti(3)O(7) nanowires is attributed to the position of the conduction band minimum. It is close to the vacuum level and, thus, favors the Fermi level-induced compensation of donor states by cation vacancies. In agreement with theoretical predictions that suggest similar formation energies for oxygen and sodium vacancies, we experimentally observed the annealing induced depletion of sodium from the surface of the nanowires.

Effects of Vacuum Annealing on the Charge–Discharge Characteristics of Eutectic Al–Si/Al Thin Film as Anode Material for Li-Ion Batteries

In this study, radio frequency magnetron sputtering was used to prepare eutectic Al­Si/Al bi-layered films as anode materials and the effect of vacuum annealing in the charge­discharge capacity characteristics at different temperatures were discussed. For the purpose of 400nm Al­Si film can possess the lowest crystallization temperature, the eutectic composition was adopted. The pre-sputtered 40nm Al thin film not only reduced the resistivity of the composite anode film, but also diffused to prevent peeling between the Al­Si films and Cu foils after vacuum annealing. While the annealing temperatures were elevated (RT ³ 400°C), indexes of crystalline (IOC) and resistivities of specimens were changed. The properties of materials containing ASEC-400 (at RT) and ASEC-200 (at 55°C) had outstanding charge­discharge characteristics. The morphology transformation at the surface and cross section resulted from annealing at different temperatures and cycling testing were examined by Focus Ion Beam (FIB). Besides, the relationship between cycling performances and electrochemical characteristics of Al­Si/Al film anodes were also investigated by Cyclic Voltammetry and Electrochemical AC Impedance Spectroscopy (EIS). [doi:10.2320/matertrans.M2012086]

A liquid crystalline copper phthalocyanine derivative for high performance organic thin film transistors

Bottom-gate, bottom-contact organic thin film transistors (OTFTs) were fabricated using solvent soluble copper 1,4,8,11,15,18,22,25-octakis(hexyl)phthalocyanine as the active semiconductor layer. The compound was deposited as 70 nm thick spin-coated films onto gold source–drain electrodes supported on octadecyltrichlorosilane treated 250 nm thick SiO2 gate insulators. The performance of the OTFTs was optimised by investigating the effects of vacuum annealing of the films at temperatures between 50 °C and 200 °C, a range that included the thermotropic mesophase of the bulk material. These effects were monitored by ultraviolet-visible absorption spectroscopy, atomic force microscopy and XRD measurements. Device performance was shown to be dependent upon the annealing temperature due to structural changes of the film. Devices heat treated at 100 °C under vacuum (≥10−7 mbar) were found to exhibit the highest field-effect mobility, 0.7 cm2 V−1 s−1, with an on–off current modulation ratio of ∼107, a reduced threshold voltage of 2.0 V and a sub-threshold swing of 1.11 V per decade.

Magneto-optical Kerr-effect enhancement in glass/Cu/SnO<sub>2</sub>/Co/SnO<sub>2</sub> thin films

We incorporate Co thin layers into the quadrilayer structure of glass/Cu/SnO2/Co/SnO2 and investigate the effect of transparent semiconductor SnO2 as cap and spacer layers on the magnitude of a magneto-optical Kerr signal. The theoretical calculations based on a 4 × 4 matrix method are exploited to find the best possible multilayer structure. Accordingly, we fabricate several samples and acquire large Kerr signals in both polar and longitudinal geometries. Furthermore, the effect of vacuum annealing on the magnetic response of the samples is investigated. It is revealed that annealing at high temperatures may reduce the Kerr response because of uncontrolled heat-induced interdiffusion of adjacent layers.

Effect of Vacuum Annealing on the Optoelectric and Morphological Properties of F16CuPc Thin Films

The effect of vacuum annealing temperature on optical and electrical properties of vacuum evaporated F16CuPc thin films have been studied spectrophotometer and Kiethely electrometer respectively. The band gap energy both fundamental and excitonic remains unchanged when the annealing temperature increased. The optical constants of thin films are obtained by means of thin film spectrophotometry. From the electrical study, the activation energies of the films, in the intrinsic region and impurity region have been determined from the Arrhenious plots of lnσ versus 1000/T. Optical data have been obtained from both absorption and reflectivity spectra over the wavelength range 200‐800 nm. The absorption coefficient α and extinction coefficient k are estimated from the spectrum. The mechanism of optical absorption follows the rule of direct transition. Using α and k, the refractive index and the dielectric constants are determined. The SEM investigations are F16CuPc thin films are expected to find application in the fabrication of optoelectronic devices such as organic transistors and LED devices.

The effect of vacuum annealing on the remediation abilities of iron and iron−nickel nanoparticles

Zero-valent iron nanoparticles are effective remediators of uranium from solution. It is postulated that the improved core crystallinity and the migration of impurity phases to the nanoparticle surfaces induced by annealing may improve their corrosion resistance and reactive lifespan. The ability of annealed and non-annealed Fe and FeNi nanoparticles to remediate a U-contaminated effluent from AWE, Aldermaston was investigated. Nanoparticles (of diameter typically between 0 and 100 nm) were introduced to the effluent and allowed to react for 7 days during which the liquid and nanoparticulate solids were periodically sampled. In all the systems, the maximum U-uptake occurred within 1 h of introduction, with variable efficiency. The Fe nanoparticles removed 98% of the total U from solution, resulting in a final U-concentration of <4 μg/L. A rapid release of Fe into solution was recorded early in the reaction period: attributed to limited partial dissolution of the nanoparticles. Annealing the Fe nanoparticles did not affect their efficiency but the dissolution of Fe was significantly reduced and X-ray Photoelectron Spectroscopy indicated slower progressive oxidation. The performance of the FeNi nanoparticles was significantly improved by annealing, with U-uptake increasing from 50 to 94%. Although the dissolution of Ni was completely inhibited by annealing, the Fe dissolution increased compared to that observed for the non-annealed FeNi nanoparticles, in contrast to behaviour exhibited by Fe-annealed nanoparticles. In all the systems, U was reduced to U(IV) and retained on the surfaces of the nanoparticulate solids for up to 48 h; the U-stability was not affected by annealing the Fe or the FeNi nanoparticles before use.

Effect of vacuum annealing and hydrogenation on ZnSe/Mn multilayer diluted magnetic semiconductor thin films

Multilayer thin films of ZnSe/Mn diluted magnetic semiconductor have been physically deposited onto a glass substrate using thermal evaporation technique and vacuum annealed at 333 K for 1 h at base pressure of 10−5 Torr. These thin films have been hydrogenated at different pressures (15–45 psi) for half an hour at room temperature. Hydrogenation process has been performed for as- grown as well as annealed thin films and named as-grown hydrogenated and annealed hydrogenated DMS thin films respectively. Structural characteristics of as-grown and vacuum annealed thin films have been performed by X-ray diffractometer. Current–voltage measurement has been studied for both as- grown hydrogenated and annealed hydrogenated DMS thin films by Keithly electrometer. X-ray diffraction pattern has been revealed nanocrystalline single phase of cubic zinc blende structure of film. Due to the annealing the conductivity has been found to be increased indicating the mixing of multilayer whereas the conductivity for as-grown hydrogenated and annealed hydrogenated ZnSe/Mn DMS thin films was found to be reduced indicating the electronic passivation effect of hydrogenation. Raman spectra of as-grown and annealed hydrogenated samples have been taken to see the presence of hydrogen in these samples. Surface topography of as-grown and annealed multilayer thin films has been confirmed by optical microscopy. Surface topography of annealed hydrogenated samples clearly shows the effect of hydrogenation at the surface.

Diameter dependence of oxidative stability in multiwalled carbon nanotubes: Role of defects and effect of vacuum annealing

While the oxidative stability of single walled carbon nanotubes has been studied extensively, very little is known about the diameter dependence of oxidative stability in multiwalled carbon nanotubes (MWNTs) and the effect of vacuum annealing on such stability. We have investigated six sets of samples with different diameters in the range of 5–100 nm systematically by thermogravimetric analysis (TGA) before and after vacuum annealing. High resolution transmission electron microscopy studies provide evidence for structural defects in the nanotube walls. Further, it reveals that with increasing diameter, interlayer d-spacing between concentric tubes decreases. Experimental TGA profile is found to constitute multiple components of oxidation as revealed from reverse Sigmoidal fitting. Analysis of the TGA profile shows that the oxidation temperature follows an exponential recovery function with increasing diameter, while width of the differentiated TGA spectra decreases. It is shown that oxidative stability of lower diameter MWNTs are primarily controlled by lattice strain, while that of large diameter MWNTs is decided by the defects in the nanotube wall. High vacuum annealing studies in the temperature range 300–1000 °C show major improvement in the structure and oxidative stability for MWNTs annealed at 500 °C. Results are compared with those of the single walled nanotubes. The observed diameter dependence is explained on the basis of strain in the nanotube lattice and defects in the nanotube walls.

Effects of Vacuum Annealing on Microstructure and Magnetostriction of TbDy-Fe GMFs

In this study, TbDy-Fe giant magnetostrictive thin films were firstly prepared by ion beam sputtering deposition (IBSD) method on water-cooled substrates, and then the films were annealed at different temperatures under vacuum condition. An Inductively Coupled Plasma Spectrometry, Scanning Electron Microscope (SEM), Scanning Probe Microscope (SPM), and Transmission Electron Microscope (TEM) were used to investigate the surface morphology and microstructure for TbDy-Fe GMFs. Besides, DWS type Ultra-precision Displacement Meter was used for measuring magnetostriction coefficient of the films by cantilever method. The results showed that TbDy-Fe GMFs of compact amorphous microstructure, smooth surface morphology, and high interfacial adhesion had been deposited under the fixed fabrication procedure. Moreover, as annealing temperature increased, microstructure of the films had been changed as following order: amorphous → amorphous + microcrystalline → nano-polycrystalline (crystallization temperature was about 400 ). It was noted that magnetostriction of TbDy-Fe GMFs could be drastically improved, particularly for low magnetic field magnetostriction sensitivity when annealed at about 400 (the value of λ was about 500ppm at 200KA•m-1).

H 2/Ar and vacuum annealing effect of ZnO thin films deposited by RF magnetron sputtering system

The properties of ZnO films were investigated as functions of annealing temperatures in H 2/Ar and vacuum. The resistivities and mobilities of ZnO films decreased with increase of annealing temperatures in vacuum and H 2/Ar ambients. However, the carrier densities of ZnO films increased with increase of annealing temperatures in vacuum and H 2/Ar ambients. The resistivities of ZnO 2 films annealed at 300 °C were ∼2186 Ω cm and ∼798 Ω cm in H 2/Ar and vacuum ambients, respectively. The resistivities of ZnO films annealed in vacuum and H 2/Ar ambients at 600 °C were similar with ∼0.040 Ω cm and ∼0.035 Ω cm, respectively. The hydrogen donor was more dominant than the oxygen vacancy or Zn interstitial donor in ZnO films annealed in ambient H 2/Ar at low temperatures. The average optical transmission was >82% and an orientation of the deposition was [0 0 2] for all ZnO films annealed in vacuum and H 2/Ar ambients.

The effect of vacuum annealing on graphene

AbstractThe effect of vacuum annealing on the properties of graphene is investigated by using Raman spectroscopy and electrical measurement. Heavy hole doping on graphene with concentration as high as 1.5 × 1013 cm−2 is observed after vacuum annealing and exposed to an air ambient. This doping is due to the H2O and O2 adsorption on graphene, and graphene is believed to be more active to molecular adsorption after annealing. Such observation calls for special attention in the process of fabricating graphene‐based electronic devices and gas sensors. On the other hand, because the quality of graphene remains high after the doping process, this would be an efficient and controllable method to introduce heavy doping in graphene, which would greatly help on its application in future electronic devices. Copyright © 2009 John Wiley &amp; Sons, Ltd.

The effects of vacuum annealing on the structure and surface chemistry of iron:nickel alloy nanoparticles

In order to increase the longevity of contaminant retention on the particle surface, a method is sought to improve the corrosion resistance of bimetallic iron nickel nanoparticles (INNP) used for the remediation of contaminated water, and thereby extend their industrial lifetime. A multi-disciplinary approach was used to investigate changes induced by vacuum annealing (<5 × 10−8 mbar) at 500 °C on the bulk and surface chemistry of INNP. The particle size was determined to increase significantly as a result of annealing and the thickness of the surface oxide increased by 50%. BET analysis recorded a decrease in INP surface area from 44.88 to 8.08 m2 g−1, consistent with observations from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which indicated the diffusion bonding of previously discrete particles at points of contact. X-ray diffraction (XRD) confirmed that recrystallisation of the metallic cores had occurred, converting a significant fraction of initially amorphous iron nickel alloy into crystalline FeNi alloy. X-ray photoelectron spectroscopy (XPS) indicated a reduction in the proportion of surface iron oxide and a change in its stoichiometry related to annealing-induced disproportionation. This was also evidenced by an increased proportion of Fe(0) and Ni(0) to Fe- and Ni-oxides, respectively. The data also indicated the concurrent development of boron oxide at the metal surfaces, which accounts for the overall increase measured in surface oxide thickness. The improved core crystallinity and the presence of passivating impurity phases at the INNP surfaces may act to improve the corrosion resistance and reactive lifespan of the vacuum annealed INNP for environmental applications.

The effects of vacuum annealing on the structure and surface chemistry of iron nanoparticles

In order to increase the longevity of contaminant retention, a method is sought to improve the corrosion resistance of iron nanoparticles (INP) used for remediation of contaminated water and thereby extend their industrial lifetime. A multi-disciplinary approach was used to investigate changes induced by vacuum annealing (<5 × 10−8 mbar) at 500 °C on the bulk and surface chemistry of INP. The particle size did not change significantly as a result of annealing but the surface oxide thickness decreased from an average of 3–4 nm to 2 nm. BET analysis recorded a decrease in INP surface area from 19.0 to 4.8 m2 g−1, consistent with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations which indicated the diffusion bonding of previously discrete particles at points of contact. X-ray diffraction (XRD) confirmed that recrystallisation of the metallic cores had occurred, converting a significant fraction of poorly crystalline iron to bcc α-Fe and Fe2B phases. X-ray photoelectron spectroscopy (XPS) indicated a change in the surface oxide stoichiometry from magnetite (Fe3O4) towards wustite (FeO) and the migration of boron and carbon to the particle surfaces. The improved core crystallinity and the presence of passivating impurity phases at the INP surfaces may act to improve the corrosion resistance and reactive lifespan of the vacuum annealed INP for environmental applications.

Electrical properties of magnesium-intercalated InSe

Indium monoselenide single crystals have been intercalated with magnesium from the vapor phase, and their electron concentration, electron Hall mobility, anisotropic electrical conductivity, and thermoelectric power have been measured as functions of temperature. The effects of vacuum annealing and Mg intercalation on the electrical properties of InSe are analyzed. Magnesium intercalation has the strongest effect on the conductivity anisotropy in the crystals.

Structural Properties of Post Annealed ITO Thin Films at Different Temperatures

Indium tin oxide (ITO) thin films were deposited on glass substrates by RF sputtering using an ITO ceramic target (In2O3-SnO2, 90-10 wt. %). After deposition, samples were annealed at different temperatures in vacuum furnace. The post vacuum annealing effects on the structural, optical and electrical properties of ITO films were investigated. Polycrystalline ITO films have been analyzed in wide optical spectrum, X-ray diffraction and four point probe methods. The results show that increasing the annealing temperature improves the crystallinity of the films. The resistivity of the deposited films is about 19×10 -4 Ωcm and falls down to 7.3×10 -5 Ωcm as the annealing temperature is increased to 500 °C in vacuum.