High Vacuum Annealing Research Articles

Sub-surface retention of Pb atoms in silicon after low-energy ion implantation and electron beam annealing

Low-energy Pb ion implantation into (100) Si and subsequent high-vacuum electron beam annealing was used to study the potential of sub-surface retention of Pb atoms after applying a high temperature annealing process. 7keV Pb+ ions were implanted into p-type (100) Si at room temperature with a fluence of 4×1015ionscm−2. The implantation results in a Pb depth distribution that has a calculated Pb peak concentration of 23.9at.% at a depth of 8.0nm. The Pb implanted Si substrates were annealed with a high-current 20keV electron beam at 200–700°C for 15s. The Pb loss by out-diffusion was measured with RBS. Key results are: (i) minimal Pb loss in samples annealed up to 400°C, (ii) emerging out-diffusion above 400°C, (iii) retention of Pb atoms in the near-surface region in samples annealed up to 700°C. Comparison of the RBS data with the calculated evaporation rate of Pb under similar conditions reveals two distinctive temperature ranges in which the measured Pb loss of the implanted samples disagrees with the calculated Pb loss: (1) Pb atoms diffused out of the samples at a higher rate in the temperature range up to 400°C and (2) the Pb atoms diffused out of the samples at a much slower rate above 450°C. Both phenomena are attributed to the ion implantation process.

Photocatalytic activity of high-vacuum annealed CdS–TiO 2 thin film

CdS–TiO 2 thin film heterojunctions were prepared on glass and indium tin oxide (ITO) substrates with the aim of improving photocatalytic efficiency both in UV–visible and visible light irradiation. The CdS under-layers were prepared by chemical bath deposition technique and subsequently they were annealed in the high vacuum of 5 × 10 − 5 Pa at the temperature of 400 °C. The structural and optical properties of all the CdS–TiO 2 thin films were studied with the help of X-ray diffractometer, atomic force microscope and ultraviolet–visible spectrophotometer. The photocatalytic activity of the thin films was evaluated by the decomposition of methanol by the use of fourier transform infrared spectrophotometer. It is revealed that the use of ITO substrate and high-vacuum annealing after deposition significantly enhance photocatalytic activity.

XPS Study of the Electronic Properties of the Ce/4H-SiC Interface, and the Formation of the SiO<sub>2</sub>/Ce<sub>2</sub>Si<sub>2</sub>O<sub>7</sub>/4H-SiC Interface Structure upon Oxidation

The deposition and annealing in ultra high vacuum (UHV) of 5-6 monolayers (ML) of cerium on clean reconstructed Si-face 4H-SiC (0001) is studied by x-ray photoemission spectroscopy (XPS). Band bending as a function of annealing was studied by shifts of the bulk peak contribution in the C1s and Si2p spectra relative to the clean reconstructed surface. Additional datapoints for Schottky barrier formation on 4H-SiC are thus obtained by the low work function rareearth metals, and presented in the framework of the metal-induced-gap states and electronegativity model. A Ce/CeSi2-x/4H-SiC interface alloy forms by annealing to 850-1050oC. Kinetic information from the oxidation of the Ce/CeSi2-x/4H-SiC interface alloy is also reported. In particular, a SiO2- x/Ce-Si mixed oxide/4H-SiC forms upon oxidation. The shift of the C1s SiC-bulk-peak towards higher binding energies upon oxidation indicates that the mixed Ce-Si oxide interface layer appears to passivate the near Fermi-level 4H-SiC interface states at least as well as SiO2, and are expected to modify the electrical interface characteristics.

STM and XPS characterisation of vacuum annealed nanocrystalline WO 3 films

Scanning tunnelling microscopy and X-ray Photoelectron Spectroscopy were conducted on magnetron sputtered WO 3 thin films, following a sequence of ultra high vacuum anneals from 100 °C to 900 °C. Annealing from 100 °C to 400 °C induced an upward surface band bending of about 0.3 eV, attributed to the oxygen migration from the bulk to the surface, but no changes in the surface topography. Chemical changes occurred from 600 °C to 800 °C, associated with the formation of secondary oxide species. STM imaging showed that the film surface consists of amorphous particles 35 nm in size up to 600 °C, while higher temperatures resulted in an increase in particle size. Crystallisation of the nanoparticles started to occur after annealing at 600 °C. The implications in terms of gas sensing are discussed.

Suppression of secondary phase formation in Fe implanted ZnO single crystals

Unwanted secondary phases are one of the major problems in diluted magnetic semiconductor creation. Here, the authors show possibilities to avoid such phases in Fe implanted and postannealed ZnO(0001) single crystals. While α-Fe nanoparticles are formed after such doping in as-polished crystals, high temperature (1273K) annealing in O2 or high vacuum before implantation suppresses these phases. Thus, the residual saturation magnetization in the preannealed ZnO single crystals is about 20 times lower than for the as-polished ones and assigned to indirect coupling between isolated Fe ions rather than to clusters.

Sublimation behavior of SiO2 from low- and high-index silicon surfaces

The authors have used atomic force microscopy to investigate the sublimation behavior of 100-nm-thick oxide layers from the low-index Si(001) and Si(111) surfaces, as well as the stable, high-index Si(113) and Si(5 5 12) surfaces. Similar to previous thin-film (<50nm) sublimation studies, high vacuum annealing results in the formation of circular voids that grow laterally with annealing time (1–6min, 1150–1350°C). The depth of these voids is ∼200nm, or twice the thickness of the original oxide film, which is consistent with the thermal decomposition of SiO2 to form volatile SiO. There are subtle morphological differences, however, between the voids formed on the different surface orientations. Line profiles of the bottom Si surfaces inside the voids indicate flat terraces for the (111) and (113) orientations and sloped conic sections for the (001) and (5 5 12) orientations, indicating that the latter surfaces are less stable with respect to step formation during oxide sublimation. At the centers of voids, features such as deep pits (5μm diameter, 200–700nm depth) or vertical structures (1μm diameter, up to 700nm height) are present. Deep depressions are also observed at vertical sidewalls that occur during sequential anneals or on a patterned surface. After the thick oxide is completely desorbed, an undulating surface morphology occurs on all surface orientations due to the coalescence of the void sidewalls.

Effects of thermal treatments on chemical composition and electrical properties of ultra-thin Lu oxide layers on Si

The correlation between chemical composition, layered structure evolution, and electrical properties of ultra-thin (2-5 nm) Lu oxide layers grown on chemically oxidized Si(100) and exposed to different thermal treatments was monitored by x-ray photoelectron spectroscopy, x-ray reflectivity and C-V, G-V measurements, respectively. These ultra-thin Lu 2O 3 films in contact with Si are not stable against silicate formation upon both ultra high vacuum (UHV) annealing and rapid thermal processing (RTP) in N 2 atmosphere. A procedure to convert the Lu-silicate layer back to continuous Lu 2O 3 oxide on Si using high-temperature UHV annealing was identified.

Room temperature ferromagnetism in Cr-doped In2O3 on high vacuum annealing of thin films and bulk samples

We report on the observation of room temperature ferromagnetism in Cr-doped In2O3 bulk samples and spin-coated thin films. The samples showed a clear ferromagnetism above 300K with magnetic moments of 0.008 and 0.22μB∕Cr at 300K for the bulk and thin film, respectively, only after high vacuum (HV) annealing at 600°C. The vacuum annealed Cr-doped In2O3 thin films showed a typical semiconducting behavior with a room temperature resistivity of 0.73Ωcm, while bulk samples were more conducting (23mΩcm). We present systematic investigations on the influence of HV annealing on the carrier concentrations, resistivity, and magnetic properties of the samples.

Structural and magnetic characterization of composite YCo5/α-Fe (20 wt%) powders prepared by mechanical alloying and subsequent annealing

Powder mixtures of YCo5+α-Fe (20wt%) were prepared by high energy mechanical alloying under Ar using a SPEX 8000 mill and subsequent vacuum annealing. The structural and magnetic properties were investigated by X-ray diffraction, DSC, and magnetic measurements. After 4h of milling, the alloyed powders were found to be composed of an amorphous Y–Co phase and α-Fe with a mean grain size strongly reduced. The DSC curves exhibited an irreversible broad exothermic peak with a maximum at 555°C associated with the crystallization process. Subsequent high vacuum annealing in the temperature range 550–750°C led to the formation of rhombohedral Th2Zn17-type and α-Fe(Co) phases. Samples were magnetically soft showing low remanence and room temperature coercivity in the range 470–800Oe. The latter is in agreement with the low magnetocrystalline anisotropy along the basal plane exhibited by the Y2(Co,Fe)17 phase.

Formation of anisotropic ferromagnetic response in rutile (TiO2) implanted with cobalt ions

The (100)- and (001)-monocrystalline plates of rutile (TiO2) were implanted by 40keV Co+ ions with fluences in wide range of 0.15–1.5×1017ion/cm2 to study the development of ferromagnetism in the diamagnetic TiO2. With increase of fluence the implanted rutile plates reveal sequentially paramagnetic, superparamagnetic, weak ferromagnetic and, eventually, strong anisotropic ferromagnetic response at room temperature. The thermo-magnetic analysis shows that the ferromagnetic samples exhibit two magnetic transitions with temperatures of the ferromagnetic ordering TC1∼700K and TC2∼850K, correspondingly. Heating of the samples in air strongly suppresses the ferromagnetic phases if the temperature of heating exceeds the corresponding transition temperature. Subsequent high-vacuum annealing restores only the low-temperature ferromagnetic phase. The origin of the two magnetic phases and anisotropy of the ferromagnetism in the Co-implanted rutile are discussed in the model of two cobalt-rich layers with different concentration and valence states of the implanted cobalt.

Iridium Silicide: a Promising Electrode for Metallic Source/Drain in Decananometer MOSFETs

A detailed study of the formation of iridium like silicide obtained on ultra high vacuum annealing and on rapid thermal annealing is proposed using x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and electrical characterizations. Using XPS analysis, the stochiometry of silicidation (IrSi, IrSi1.6) is identified. A very uniform IrSi layer obtained at low temperature gave a lower Schottky barrier height than a PtSi silicide. Lastly, the IrSix phase, obtained at 900{degree sign}C, proposed a very poor film quality.

Superconducting Nd1.85Ce0.15CuO4 films grown by the pulsed electron deposition technique

Nd1.85Ce0.15CuO4−δ superconducting thin films were prepared on (100) SrTiO3 substrates by pulsed electron deposition technique without reducing atmosphere. Oxygen content is finely controlled by high temperature vacuum annealing, and optimal superconductivity has been obtained. The deposition conditions of the film are discussed in details. Higher deposition temperature and lower gas pressure result in the loss of copper and the appearance of the foreign phase Ce0.5Nd0.5O1.75. High quality Nd1.85Ce0.15CuO4−δ epitaxial films are deposited at 840–870°C in the mixed gas with a ratio of O2:Ar=1:3.

Effect of amorphous Si layer on the reaction of carbon and silicon in the C/Si multilayer by high vacuum annealing

Crystalline silicon carbide can be formed on the crystalline silicon (c-Si) substrates by reaction of amorphous silicon (a-Si) and carbon (C) layers when annealed at high temperature. The a-Si layer position under or sandwiching the C layer will affect reaction temperature between the a-Si and C layers at constant annealing time. Vacuum annealing at 500–900 °C was performed to study the effect of a-Si layer on the reaction between C and Si in the three kinds of structures, i.e. C, C/a-Si and a-Si/C/a-Si deposited on c-Si substrates. There was no interdiffusion between the single-layer C and c-Si substrate when annealed up to 900 °C for 1.5 h. But some interdiffusion occurred between C and a-Si of the two-layer C/a-Si structure when annealed at 900 °C for 1.5 h. Simultaneously, transformation of a-Si to polycrystalline Si was detected. The interdiffusion between C and Si in the three-layer a-Si/C/a-Si was more pronounced than in the two-layer C/a-Si. In the a-Si/C/a-Si structure, the transformation of a-Si to polycrystalline Si was observed at 700 °C and significant interdiffusion occurred at 900 °C as well as crystalline SiC formation in the multilayer. The SiC formation temperature is lower than conventional crystalline SiC which is formed at 1200 °C in chemical vapor deposition process. The two a-Si layers sandwiching the C layer in the three-layer a-Si/C/a-Si structure lead to the formation of the nanocomposite structure of SiC, C and Si phases at 900 °C. A possible interdiffusion and reaction mechanism between C and Si in the C/Si multilayers through the grain boundaries of polycrystalline Si is proposed.

Preparation of vanadium oxide thin films with high temperature coefficient of resistance by facing targets d.c. reactive sputtering and annealing process

Vanadium oxide thin films have been deposited on glass substrates by facing targets d.c. reactive sputtering at room temperature for uncooled microbolometers. The temperature coefficient of resistance (TCR) of vanadium oxide thin films as-deposited, which is the vital bolometric parameter, is above − 4.5%/°C, but the room resistance of vanadium oxide thin films is also a little large, about 30–80 kΩ/square. Since large thin film resistance can induce a high noise of uncooled microbolometers, which is unexpected, a following vacuum annealing has been introduced to reduce the resistance of the film. The result shows a better trade-off between the TCR and resistance. The TCR is high up to − 4.4%/°C around room temperature and the sheet resistance is about 20 kΩ/square. Furthermore, chemical composition, phase identification and morphology of the film surface have been characterized using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). It is shown that high vacuum annealing induces reduction of V 2O 5 into lower oxides by XPS spectrum, as well, fine grains and a more homogeneous film surface have also been observed in the AFM images.

Influence of high vacuum annealing treatment on some properties of carbon nanotubes

Carbon nanotubes (CNTs) were synthesized using a chemical vapour deposition (CVD) method. The properties of CNTs before and after vacuum annealing treatment were studied using scanning electron microscopy (SEM), scanning tunneling microscopy/spectroscopy (STM/STS) and thermogravimetric analysis (TG). Field emission characteristics of the raw and vacuum heated (up to 650°C) carbon nanotube films (CNTFs) were measured in a diode system. Emissive properties of the CNTFs depend on an annealing process during which structural changes in the nanotube walls take place. The structural changes, related to saturation of dangling bonds, influence a rate of oxidation process and also improve the emissive field properties.

Correlation between optical properties and Si nanocrystal formation of Si-rich Si oxide films prepared by plasma-enhanced chemical vapor deposition

We have investigated the phase separation and silicon nanocrystal (Si NC) formation in correlation with the optical properties of Si suboxide (SiO x , 0 < x < 2) films by thermal annealing in high vacuum. The SiO x films were deposited by plasma-enhanced chemical vapor deposition at different nitrous oxide/silane (N 2O/SiH 4) flow ratios. The as-deposited films show increased Si concentration with decreasing N 2O/SiH 4 flow ratio, while the deposition rate and surface roughness have strong correlations with the flow ratio in the N 2O/SiH 4 reaction. After thermal annealing at temperatures above 1000 °C, Fourier transform infrared spectroscopy, Raman spectroscopy, and transmission electron microscopy manifest the progressive phase separation and continuous growth of crystalline-Si (c-Si) NCs in the SiO x films with increasing annealing temperature. We observe a transition from multiple-peak to single peak of the strong red-range photoluminescence (PL) with increasing Si concentration and annealing temperature. The appearance of the single peak in the PL is closely related to the c-Si NC formation. The PL also redshifts from ∼1.9 to 1.4 eV with increasing Si concentration and annealing temperature (i.e., increasing NC size). The good agreements of the PL evolution with NC formation and the PL peak energy with NC size distribution support the quantum confinement model.

In situ transport in alumina-based magnetic tunnel junctions during high-vacuum annealing

We have performed in situ transport measurements on CoFeB∕AlO∕Co spin-valve magnetic tunnel junctions during annealing up to 200 °C. For optimally oxidized junctions we observe a marked decrease in the parallel state junction resistance, which occurs at around 150 °C and continues throughout the anneal process until the temperature is reduced back below 150 °C. Spectroscopic measurements reveal a stronger bias dependence due to enhanced magnon-assisted tunneling, and show that features relating to weak fcc texture in the cobalt upper electrode fade after annealing at 200 °C. We attribute this to a possible amorphization of the cobalt electrode in close proximity to the barrier interface.

Mass dependent surface interface modification of Ag/Co films under controlled ion beam irradiation

Modification difference of surface and interfaces, due to Ar+ and Kr+ irradiation under identical conditions of an immiscible bilayer thin film, Ag/Co (∼25nm), deposited sequentially on Si(001) substrate by magnetron sputtering, is studied by X-ray reflectivity measurements and atomic force microscopy. Irradiations are done by150keV ion beams with fluences of 1×1014–5×1014ions/cm2. X-ray reflectivity data are collected with monochromatized Cukα1 X-ray in specular geometry and atomic force microscopic studies of the surface are made at contact mode. From the reflectivity data, fitted with a nonlinear least square fitting program, film thickness, surface and interface roughness and electron density profile (EDP) along the growth direction are found out. These observations are compared with that of high vacuum annealing of as grown samples at 75 and 500°C for 1h. It is observed that at 1×1014ions/cm2 fluence, both for argon and krypton ion irradiation, bilayer thickness as well as the thickness of the constituent films decreased, electron densities increased and the interface became sharper than that of the as grown sample. For argon it is sharper and for krypton the surface roughness is more. At 5×1014ions/cm2 fluence, for argon Ag moved into Co layer over a certain depth and for krypton the interface zone broadened and bilayer structure of the film is damaged and the surface roughness became high. Vacuum annealing at 75°C made the interface sharp but surface roughness increased by coalescence of islands. Annealing at 500°C made the interface broad and the surface became very rough. The thickness and electron density of Ag layer decreased due to vaporizing of Ag in high vacuum at 500°C. Atomic force microscopy also revealed that for lower Ar fluence the surface got smoother and for all other treatment the surface roughness increased.

Annealing and oxidation of silicon oxide films prepared by plasma-enhanced chemical vapor deposition

We have investigated phase separation, silicon nanocrystal (Si NC) formation and optical properties of Si oxide (SiOx, 0&amp;lt;x&amp;lt;2) films by high-vacuum annealing and dry oxidation. The SiOx films were deposited by plasma-enhanced chemical vapor deposition at different nitrous–oxide/silane flow ratios. The physical and optical properties of the SiOx films were studied as a result of high-vacuum annealing and thermal oxidation. X-ray photoelectron spectroscopy (XPS) reveals that the as-deposited films have a random-bonding or continuous-random-network structure with different oxidation states. After annealing at temperatures above 1000 °C, the intermediate Si continuum in XPS spectra (referring to the suboxide) split to Si peaks corresponding to SiO2 and elemental Si. This change indicates the phase separation of the SiOx into more stable SiO2 and Si clusters. Raman, high-resolution transmission electron microscopy and optical absorption confirmed the phase separation and the formation of Si NCs in the films. The size of Si NCs increases with increasing Si concentration in the films and increasing annealing temperature. Two photoluminescence (PL) bands were observed in the films after annealing. The ultraviolet (UV)-range PL with a peak fixed at 370–380 nm is independent of Si concentration and annealing temperature, which is a characteristic of defect states. Strong PL in red range shows redshifts from ∼600 to 900 nm with increasing Si concentration and annealing temperature, which supports the quantum confinement model. After oxidation of the high-temperature annealed films, the UV PL was almost quenched while the red PL shows continuous blueshifts with increasing oxidation time. The different oxidation behaviors further relate the UV PL to the defect states and the red PL to the recombination of quantum-confined excitions.

Optical properties of SiOx nanostructured films by pulsed-laser deposition at different substrate temperatures

Silicon oxide (SiOx) nanostructured films have been formed by pulsed-laser deposition of Si in oxygen at different substrate temperatures, in order to study the structures and optical properties related to quantum confinement effects. After laser ablation, the single-crystal Si(100) target is converted to a polycrystal structure and shows weak photoluminescence (PL). The as-deposited SiOx nanostructured films show large particles (i.e., droplets) on a uniform background film. The droplets with weak PL emission have the same high crystallinity as the Si(100) target. Strong PL is observed from the amorphouslike background films rather than from the crystalline droplets. As substrate temperatures increase from room temperature (23°C)to800°C, the PL band continually redshifts from 1.9to1.6eV and the optical band gap decreases from 2.9to2.1eV due to the increased Si concentration in the films. After high-vacuum annealing at 800°C, both the PL and optical absorption are enhanced. The optical band gap also decreases after annealing. Combined with the progressive PL redshifts of the SiOx films with increasing Si concentration by plasma-enhanced chemical vapor deposition, the results support the quantum confinement theory.