Ar Ambient Research Articles

Temperature Dependent Structural Evolution of Graphene Layers on 4H-SiC(0001)

In this study we examined the structural evolution of graphene grown on 8° off-axis 4H-SiC(0001) substrates at temperatures from 1600°C to 1700°C in Ar ambient. Morphological transformation of SiC substrate after annealing was examined by Tapping Mode Atomic Force Microscopy. Moreover, by etching-out graphene layers from graphitized SiC substrates in selective trenches we determined the number of graphene layers. Numbers of graphene layers were then independently confirmed by Transmission Electron Microscopy imaging.

High-corrosion-resistant Al2O3 passivation-film formation by selective oxidation on austenitic stainless steel containing Al

We have developed Al2O3 passivation film having very high anticorrosion resistance on the surface of austenitic stainless steel containing 3 wt % aluminum. Al2O3 passivation film is formed by selective oxidation of aluminum in the austenitic stainless steel in the Ar and H2 ambient including a small amount of H2O at predetermined temperatures. Al2O3 film is obtained at temperatures higher than 750 °C in the Ar and H2 ambient, where the partial pressure ratio of H2 and H2O is set higher than 2×103. Al2O3 films have been confirmed to exhibit very high anticorrosion resistance for various halogen gases and various plasma ambients (Cl2, H2, and O2) with ion-bombardment energies less than 100 eV at temperatures less than 150 °C. In the case of fluorine-gas plasma, the Al2O3 film surface has been converted to AlF3 with a depth of 15 nm, where AlF3 film is thermodynamically stable, as well as Al2O3, resulting in an excellent passivation film exhibiting very high anticorrosion capability. Moreover, the Al2O3 film surface has been confirmed to exhibit no catalytic activity for various specialty gases at temperatures less than 150 °C.

Role of Anions in the AuCl3-Doping of Carbon Nanotubes

The doping/dedoping mechanism of carbon nanotubes (CNTs) with AuCl(3) has been investigated with regard to the roles of cations and anions. Contrary to the general belief that CNTs are p-doped through the reduction of cationic Au(3+) to Au(0), we observed that chlorine anions play a more important role than Au cations in doping. To estimate the effects of Cl and Au on CNTs, the CNT film was dedoped as a function of the annealing temperature (100-700 °C) under an Ar ambient and was confirmed by the sheet resistance change and the presence of a G-band in the Raman spectra. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the doping level of the CNT film was strongly related to the amount of adsorbed chlorine atoms. Annealing at temperatures up to 200 °C did not change the amount of adsorbed Cl atoms on the CNTs, and the CNT film was stable under ambient conditions. Alternatively, Cl atoms started to dissociate from CNTs at 300 °C, and the stability of the film was degraded. Furthermore, the change in the amount of Cl atoms in CNTs was inversely proportional to the change in the sheet resistance. Our observations of the Cl adsorption, either directly or mediated by an Au precursor on the CNT surface, are congruent with the previous theoretical prediction.

Transformation from [formula omitted]-FeSi to [formula omitted]- FeSi2 in RF-sputtered FeSix films

FeSix films were deposited on Si (100) substrates using RF sputtering at room temperature and at 300 °C. After deposition, FeSix films were annealed at 400–900 °C in Ar ambient. XRD measurements revealed that the FeSix films deposited at R. T. for 30 min were completely transformed to β-phase due to annealing at 900 °C for 1 h. On the contrary, the FeSix films deposited at 300 °C for 30 min contained both ε-FeSi and β- FeSi2 after annealing at 900 °C for 1 h. The FeSix films deposited at 300 °C for 3 min were completely transformed to β-phase due to annealing at 800 °C for 1 h. For the FeSix films deposited at 300 °C for 30 min, ε-FeSi transformed to β- FeSi2 in RF-sputtered films due to long time annealing of 10 h. It can be concluded that high-temperature and long-time annealing is necessary for the ε-FeSi bonds in the FeSix films to decompose and for the Fe atoms to be diffused into Si substrates leaving only β-phase FeSi2 in the films.

Dielectric properties and interfacial microstructures of HfO2films deposited in different ambient by sputtering

Dielectric properties and interfacial microstructures of HfO2 films deposited by radiofrequency(RT) magnetron sputtering in different ambient have been investigated.It is demonstrated that the dielectric properties of HfO2 film deposited at room temperature in pure Ar ambient(effective dielectric constant is about 17.7;flat band voltage is 0.36 V and leakage current density is about 4.15 × 10?3 A cm?2 at 1 V gate voltage) are better than that of films deposited in Ar+N2 or Ar+O2 mixed ambient.Investigated by using high-resolution electron microscope and X-ray photoelectron spectroscopy,the unstoichiometric HfSixOy mixed with HfSix interfacial layers are found to exist between stoichiometric amorphous HfO2 films and Si(100) substrates.These unstoichiometric interfacial layers with low-k are responsible for the decrease of effective dielectric constant of HfO2 films and the clock-wise hysteresis of capacitance-voltage curves of MOS capacitor structures.

Ferromagnetism induced by donor-related defects in Co-doped ZnO thin films

Co-monodoped ZnO (ZnCoO), Co–Ga codoped ZnO (Zn(Co,Ga)O), and Co–Na codoped ZnO (Zn(Co,Na)O) thin films were prepared on sapphire substrates by pulsed laser deposition. Their structural, optical, electrical, and magnetic properties were studied to clarify the origin of ferromagnetism (FM) in the ZnCoO system. Both the ZnCoO and Zn(Co,Ga)O films showed an n-type conductivity with a similar room-temperature ferromagnetism (RTFM), although the electron concentration of the Zn(Co,Ga)O film (∼10 21 cm −3) was evidently higher than that of the ZnCoO film. The increasing donor density did not affect the FM greatly. The Zn(Co,Na)O film showed a p-type conductivity, but it did not show RTFM. To explore the mechanism of FM, the samples were annealed after growth. The ZnCoO and Zn(Co,Ga)O films annealed in the Ar ambient displayed similar FM features to the as-grown ones, but all of them lost their original RTFM when annealed in the O 2 ambient. The Zn(Co,Na)O film annealed in Ar exhibited a high resistivity, while a better p-type behavior than the as-grown one was observed for the Zn(Co,Na)O film annealed in O 2, however, both of them showed paramagnetism. No clusters, precipitates, or secondary phases were found from the X-ray diffraction pattern and the photoelectron K-edge X-ray absorption near-edge structure measurements. Together with the X-ray spectroscopy and photoluminescence results, it was found that the oxygen vacancy (V o), a donor-related defect, played a vital role in determining the RTFM in the ZnCoO system.

Effects of annealing atmosphere on ZnO− ions-implanted silica glass: synthesis of Zn and ZnO nanoparticles

The effects of annealing atmosphere (argon or oxygen) on Zn nanoparticles (NPs), embedded in silica glass, synthesized by implanting 50 keV ZnO− ions to a fluence of 7 × 1016 cm−2 have been studied. Optical absorption (OA) measurements carried out on the as-implanted samples have been found to result in a surface plasmon resonance (SPR) band centred at ∼255 nm due to the presence of Zn NPs in the silica glass. An increase in SPR peak intensity with a corresponding reduction of its full width at half maximum have been seen in the OA spectrum taken from the as-implanted sample following annealing in Ar ambient at 700 °C for 2 h, indicating a growth in the size of Zn NPs. However, annealing the as-implanted sample in O2 gas at 700 °C for 2 h has been found to result in a steep absorption edge at ∼364 nm in the OA spectrum which indicates the formation of ZnO NPs. These ZnO NPs show quantum confinement effects due to their small sizes. No observable photoluminescence (PL) emission has been seen from Zn NPs, whereas an excitonic band at ∼368 nm and three deep-level PL emission bands at ∼453 nm, ∼521 nm and ∼650 nm, respectively, have been seen from ZnO NPs. It was argued that the deep-level PLs were due to the singly ionized oxygen vacancies located at ZnO NPs' surfaces. These observations suggest that ZnO NPs were formed due to oxidation of Zn NPs via interaction with the indiffusing O2 molecules during annealing in O2 ambient, but not with the interaction of the implanted oxygen in silica glass.

Understanding the mechanism of nano-aluminum particle formation by wire explosion process using optical emission technique

Nano-aluminum particles are produced by a wire explosion process in different inert gas ambience. It is observed that generated particles have different sizes and it follows log–normal probability distribution. The particle size produced by the wire explosion process varies depending on the thermal conductivity of the medium and the operating pressure of the gas. To understand the mechanism of nano-particle formation, the optical-emission spectroscopic technique is used for measuring characteristics of plasma generated during the wire explosion process. Strong emission lines were observed from the species formed during the wire explosion process. Plasma temperatures are estimated based on local thermal equilibrium principle and using Al emission lines. Plasma temperature of more than 8000 K is observed in an Ar ambient. The optical emission study clearly indicates that the intensity of plasma increases with an increase in the ambient pressure. Further, it is observed that an increase in the pressure of the gas, the plasma temperature also increases. The study shows that the plasma temperature in the He gas is lesser than in the Ar gas. The plasma temperature due to the discharge plays a significant role on nano-particle formation. In addition, it is observed that irrespective of polarity, emission characteristics are almost the same.

Growth of p-type ZnO thin film on n-type silicon substrate and its application as hybrid homojunction

A report on the preparation of p-type ZnO thin films, codoped with Al and N, on n-type Si (100) substrate by RF sputtering technique is presented. The as-grown films were found to be n-type and the conduction was converted to p-type on annealing in Ar ambient. ZnO homojunction was fabricated by growing a three-dimensional ZnO hybrid structure of p-type ZnO films, n-type ZnO nanowire and n-type Al-doped ZnO films in order. The current–voltage characteristics clearly showed a diode like rectifying behavior. Room temperature photoluminescence spectra showed dominant peak at 3.20 eV with a broad deep level emission. The electroluminescence spectrum of heterojunction structure exhibited deep level emission at 2.37 eV and ultraviolet emission at 3.20 eV when the injected current attained 100 mA.

Effects of substrate temperature and RF power on the formation of aligned nanorods in ZnO thin films

We report on the effects of substrate temperature and RF power on the formation of aligned nanorod-like morphology in ZnO thin films. ZnO thin films were sputter-deposited in mixed Ar and N2 gas ambient at various substrate temperatures and RF powers. We find that the substrate temperature plays more important role than RF power in the formation of ZnO nanorod-like morphology. At low substrate temperatures (below 300°C), ZnO nanorod-like morphology does not form regardless of RF powers. High RF power helps to promote the formation of aligned ZnO nanorod-like morphology. However, lower RF powers usually lead to ZnO films with better crystallinity at the same substrate temperatures in mixed Ar and N2 gas ambient and therefore better photoelectrochemical response.

Uniformity of Epitaxial Graphene on On-Axis and Off-Axis SiC Probed by Raman Spectroscopy and Nanoscale Current Mapping

Epitaxial graphene was grown on the surface of on-axis and off-axis SiC (0001) by solid state graphitization at high temperatures (2000 °C) in Ar ambient. The effect of the miscut angle on the lateral uniformity of the few layers of graphene (FLG) was investigated by combined application of micro-Raman spectroscopy and Torsion Resonance Conductive Atomic Force Microscopy, the latter method enabling a quantification of the FLG coverage on SiC with submicrometer lateral resolution. While the on-axis samples result in uniform coverage by thin (~ 3 monolayers) FLG, the coverage for off-axis samples is much less uniform, following closely the step bunching morphology of the SiC surface.

Phase and Optical Characterizations of Annealed SnO Thin Films and Their p-Type TFT Application

Amorphous SnO thin films were prepared on quartz and 190 nm substrates by electron beam evaporation. X-ray diffraction results reveal that amorphous SnO transforms into polycrystalline (tetragonal litharge structure) after rapid thermal annealing in Ar ambient at and starts decomposing into (orthorhombic structure) with the expulsion of Sn atoms at . The optical properties were characterized via spectroscopic ellipsometry. The polycrystalline SnO thin films have a higher refractive index and a narrower bandgap than the amorphous ones, which is due to the polarizability enhancement in the crystallization process. Moreover, the relationship between and of the amorphous and polycrystalline SnO thin films can be explained by the “Moss rule” law, and a decreasing trend in was verified with the transformation from SnO to . Bottom-gate-type thin film transistors (TFTs) employing polycrystalline SnO channels on the substrates exhibit p-type field-effect transistor characteristics. The optimum field-effect mobilities and are 0.46 and , respectively, which are the same order of magnitude as those reported for epitaxial SnO TFTs.

Photoluminescence of face-centered-cubic structure silicon nanoparticles deposited by pulsed laser ablation

Face-centered-cubic (fcc) structure silicon nanoparticles (Si-nps) are synthesized by using nanosecond pulse excimer laser ablation of Si target in Ar ambient. The nonequilibrium environment caused by the plume confined in argon ambient gas is responsible for the formation of fcc Si-nps. Photoluminescence (PL), transmission electron microscopy, and X-ray photoelectron spectroscopy are used to characterize these Si-nps. Broad PL spectrum is obtained with a double-peak at 403 and 503 nm by an exciting laser of 325 nm. After exposure to air for 60 days, air oxidation over time causes a clear blue-shift in green PL peak from 503 to 484 nm and no shift in violet PL peak of 403 nm. The present results indicate that the peak of 503 nm and blue-shift from 503 to 484 nm are attributed to the band-to-band recombination of quantum confinement model, while the violet PL peak of 403 nm is due to the recombination of electron transition from interface states of suboxides.

Effect of thermal annealing on Ni/Au contact to a-InGaZnO films deposited by dc sputtering

We deposited Ni (15 nm)/Au (30 nm) layers on a-InGaZnO in order to produce low-resistance ohmic contacts by using a dc sputtering method. The samples were annealed at various temperatures for 5 min in Ar ambient. The electrical and the structural properties of the Ni/Au contact to a-InGaZnO were investigated. According to the current–voltage measurements, both the as-deposited and low-temperature annealed samples showed an ohmic behavior. The specific contact resistance of the as-deposited sample was 4.1 × 10 − 5 Ω cm 2, which was the lowest value. Further increasing the temperature above 400 °C led to an increase in the specific contact resistance. This is due to the chemical intermixing and formation of the oxide in the contact interface caused by the post-growth thermal annealing.

Comparison of structural and photoluminescence properties of zinc oxide nanostructures influenced by gas ratio and substrate bias during radio frequency sputtering

Zinc oxide (ZnO) nanostructured films were prepared on quartz glasses by radio frequency magnetron sputtering deposition of ZnO films at different argon to oxygen (Ar∕O2) gas ratios and post-treated in a reducing ambient at a low temperature. The effects of Ar∕O2 gas ratio and substrate bias on the photoluminescence and structural properties were investigated. It was found that the formed ZnO nanostructures significantly depended on the O2 fraction. The crystallinities of the ZnO nanostructures were improved, and the green emission was enhanced with the decrease of the O2 fraction in the Ar∕O2 mixtures. A green emission peak centered at 510nm was obtained after the post-treatment. In addition, the applied substrate bias contributed to remarkably improving the crystallinity of the ZnO films. The strongest green emission was obtained from the ZnO nanostructures prepared from the ZnO film deposited in a pure Ar ambient with the substrate bias applied.

Characterization and properties of Zn–O–Se ternary system thin films deposited by radio-frequency (rf)-magnetron sputtering

Zn–O–Se alloy films were grown on quartz substrate by radio-frequency (rf)-magnetron sputtering ZnSe single crystal target, with high pure Ar and O 2 as working gas. X-ray diffraction and transmission electron microscopy characterizations indicate that the films are amorphous state. Energy disperse spectroscopy and X-ray photoelectron spectroscopy measurements verify the amorphous Zn–O–Se alloy was Se doped ZnO 2 (Zn 1− x Se x O 2), in which both Zn and Se atoms are bound with O atom. Absorption spectra exhibit that the optical band gap of Zn 1− x Se x O 2 films are 4–5 eV. After annealing at 673 K in Ar ambient for 15 min, Zn 1− x Se x O 2 film was decomposed to ZnO and SeO 2, and SeO 2 sublimed while annealed. The band gap energy decreased to the 3.2 eV, which is similar to the value of ZnO film directly deposited on quartz substrate. Room-temperature photoluminescence spectrum of the film after annealed shows NBE emission at 3.26 eV.

High-temperature Process Endurance of Oxide/Electrode Stacking Structure for Resistance Random Access Memory

AbstractThe systematic investigation on the thermal stability of the CoO layer was carried out for various electrode materials. When Pt with higher oxygen potential (Gibbs free energy change of the oxidation reaction) compared to Co is used as electrodes, the resistance of the Pt/CoO/Pt devise was severely decreased by the post deposition annealing (PDA) process and the resistance switching into the high resistance state was observed in the first voltage sweep. This indicants that the reducing Ar ambient induces the quite local reduction of CoO. The reduction of the CoO layer is also expected even with the Co electrode, which is reasonably attributed to the oxygen concentration gradient at the Co/CoO interface in the Co/CoO/Pt device. With the Ti electrode having a much lower oxygen potential than Co, the reduction of CoO by Ti is also indicated electrically in the Pt/CoO/Ti device. On the other hands, W electrodes which is thought to have the solid-solution oxygen can stabilize the CoO layer during PDA although W is more affinitive with oxygen compared with Co. It can be pointed out the oxygen delivery at the electrode/oxide layer interface is a critical factor in designing the thermally stable stacking structure for resistance random access memory.

Stopping power of a buffer gas for laser plasma debris mitigation

The stopping power of a buffer gas against laser-plasma debris is quantitatively assessed by means of visualization techniques. For ablation of planar tin targets in an Ar ambient, an expanding wavefront was visualized, whose translation energy was rapidly reduced within a few millimeters above the target surface. The fastest debris component was along the normal to the target with an initial kinetic energy of 1.1 keV. The buffer gas efficiency changed in a line-of-sight-dependent way, thermalizing more efficiently the on-axis components. The maximum stopping power of the gas buffer was determined as high as 0.4 keV/mm. Due to the reduction in stopping power, nonlinearly with the debris kinetic energy, a gas buffer thickness of 10 mm is required at the studied atmospheric pressure in order to mitigate high energy debris below a fiducial threshold of 0.1 keV.

Non-crystalline Zr–Si diffusion barrier for Cu/Si contact system under different sputtering power

Non-crystalline Zr–Si diffusion barrier in Cu/Si contact systems has been investigated. Zr–Si diffusion barriers were deposited on the silicon substrates by radio frequency reactive magnetron sputtering under different sputtering power. The Cu/Zr–Si/Si structures were manufactured and the diffusion barrier properties were investigated by heat-treating the structure in Ar ambient at temperatures ranging from 500 to 650 °C for an hour. X-ray diffraction (XRD), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM) technique were applied to characterize the diffusion barrier performance for Zr–Si in Cu/Zr–Si/Si structures. It is indicated from the comparison analysis results that the Zr–Si film showed a better diffusion barrier performance with the larger sputtering power.

Thermopower and optical studies on undoped and manganese doped indium tin oxide films

Thermopower measurements in the range of 300–650K along with room temperature optical absorption and electrical resistivity studies have been performed on indium tin oxide (ITO) and manganese doped indium tin oxide (Mn:ITO) thin films grown by reactive DC sputtering. The thermopower of the films measured in Ar ambient displayed irreversible changes attributable to oxygen loss. Thermopower, carrier concentration and resistivity of the films have been found to depend on oxygen vacancies and Mn concentration. The observations have been substantiated with optical absorption and room temperature electrical resistivity results. It has also been observed that band gap tuning in these films is possible by the introduction of Mn as well as oxygen vacancies.