Search for a wetting layer in thin film growth of para-hexaphenyl on KCl(001)

The non-existence of a strongly bound wetting layer for the system para-hexaphenyl (6P)-KCl(001) was verified by thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS). The 6P films were grown by physical vapour deposition under ultrahigh vacuum conditions at 400 K. TDS showed just a single desorption peak even down to a coverage of 0.1 nm mean film thickness. The heat of evaporation for 6P was determined to 2.3 eV. From the change of the XPS K2p substrate signal as a function of the mean film thickness one can conclude that a strong de-wetting exists at the very beginning of the 6P layer growth at 400 K. Additional investigations with atomic force microscopy reveal that at this initial stage the film grows in a form of needle like islands with a high aspect ratio and subsequently terraced mounds of 6P are formed. No dissociation of 6P on KCl was observed.     

Temperature stability of ultra-thin mixed BaSr-oxide layers and their transformation

In the context of investigations of physical, chemical and electrical properties of ultra-thin layers of epitaxial and monocrystalline Sr(0.3)Ba(0.7)O on Si(100), we also investigated their thermal stability with x-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), and low energy electron diffraction (LEED). At temperatures above 400?°C, transformation into silicate layers sets in. The stoichiometry after complete transformation was determined to be close to (Ba(0.8)Sr(0.2))(2)SiO(4) except for layers of only a few monolayers, where the silicate is not stoichiometric. There are strong indications that this silicate is stable until it desorbs at temperatures above 750?°C. Crystallinity, as seen with LEED, is lost during this transformation. Although transformation into silicate is coupled with metal desorption and compactification of the layers, they seem to remain closed. In addition, traces of Ba silicide at the Si interface were detected after layer desorption. This silicide cannot be desorbed thermally. The silicate layer has a bandgap of 5.9 ± 0.2 eV already for 3 ML thickness. Upon exposure to air, carbon and oxygen containing species, but no hydroxide, are formed irreversibly.     

Characterization of carbon surface chemistry by combined temperature programmed desorption with in situ X-ray photoelectron spectrometry and temperature programmed desorption with mass spectrometry analysis

The analysis of the surface chemistry of carbon materials is of prime importance in numerous applications, but it is still a challenge to identify and quantify the surface functional groups which are present on a given carbon. Temperature programmed desorption with mass spectrometry analysis (TPD-MS) and X-ray photoelectron spectroscopy with an in situ heating device (TPD-XPS) were combined in order to improve the characterization of carbon surface chemistry. TPD-MS analysis allowed the quantitative analysis of the released gases as a function of temperature, while the use of a TPD device inside the XPS setup enabled the determination of the functional groups that remain on the surface at the same temperatures. TPD-MS results were then used to add constraints on the deconvolution of the O1s envelope of the XPS spectra. Furthermore, a better knowledge of the evolution of oxygen functional groups with temperature during a thermal treatment could be obtained. Hence, we show here that the combination of these two methods allows to increase the reliability of the analysis of the surface chemistry of carbon materials.     

Thermal stability of Cr-doped diamond-like carbon films synthesized by cathodic arc evaporation

Cr-doped diamond-like carbon (DLC) films were synthesized using a cathodic arc evaporation (CAE) process. The thermal oxidation behavior of Cr-doped DLC films was investigated using thermal gravimetric analysis (TGA) and differential thermal analysis (DTA). The phase identification and microstructural examinations were conducted by X-ray diffraction, scanning electron spectroscopy (SEM), transmission electron spectroscopy (TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) in order to understand the characteristics of Cr-doped DLC films. The as-deposited Cr-doped DLC film exhibits a lamellar structure observed by TEM. A significant weight loss of film results from the thermal oxidation of carbon occurred at 290 to 342 °C. At the temperature higher than 342 °C, slight weight gain of specimen was observed due to the thermal oxidation of the underlying CrC_xN_y and CrN interlayer. By heat-treated specimens from 200 to 400 °C, Raman spectra reveal the increase of I_D/I_G value conforming to the graphitiation process of the Cr-doped DLC films. Finally, surface reactions of the annealed films using XPS analysis were discussed.     

Co-adsorption of CO and oxygen on W(110) surfaces

Influence of oxygen adsorption on CO chemisorption behavior over W(110) surfaces was studied using valence band spectra and thermal desorption spectroscopy (TDS). In the absence of O, CO formed a tilted and a vertical structure at 120 K on W(110). In the presence of O coadsorbate, in contrast, formation of the tilted structure of CO was suppressed. CO desorption from oxygen-covered W(110) surfaces showed indication of a strong interaction between adsorbates at ∼900 K, which was absent without O.     

Influence of synthetic parameters on the enhanced photocatalytic properties of ZnO nanoparticles for the degradation of organic dyes: a green approach

Herein, we report a green synthetic strategy using aqueous leaves extract of Actinodaphne madraspatna Bedd (AMB) for the synthesis of ZnO NPs. The physical shape, size, thermal stability, surface area, surface composition and chemical state, morphological and optical properties of the synthesized ZnO NPs are well characterized through UV–Visible diffuse reflectance spectroscopy (DRS UV), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, thermal gravimetric analysis–differential thermal analysis (TGA–DTA), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) and X-ray photon spectroscopy (XPS). FT-IR spectrum of ZnO NPs showed a characteristic peak at 416.62 cm^?1. Optical studies of prepared ZnO NPs showed the bandgap values are reduced in the range of 3.05 to 2.96 eV. The XRD and TEM data revealed the synthesized ZnO NPs exist in wurtzite crystal structure with crystallite sizes of 18 nm to 68 nm range. The variation in bandgap, surface area and crystallite structure of ZnO NPs would be achieved by changing the experimental parameters. FESEM showed spherical-shaped structure. XPS result confirmed the atomic states of Zn and O. The green synthesized ZnO NPs were examined for the photocatalytic degradation of methylene blue (MB) and acid violet 17 (AV17) dyes under UV light and the rate constants ‘k’ was calculated. It is found that the green synthesized ZnO NPs with reduced bandgap showed enhanced photocatalytic activity with higher rate constant.

     

Desorption kinetics of oxygen in plasma treated SWNTs by in situ thermoelectric power measurements

The functionalization and defect formation of SWNTs caused by isotropic plasma treatments were studied using oxygen desorption/adsorption kinetics by measuring the time dependence of the in situ thermoelectric power (TEP). It is shown that the plasma treatments result in the formation of low binding energy sites for oxygen adsorption. Raman and x-ray photoelectron spectroscopy (XPS) data are in good agreement with the results.     

Rapid evaluation of long-term thermal degradation of carbon fibre epoxy composites

Two commercially available carbon fibre reinforced composites (8552/IM7 and M18-1/G939) were exposed to heat above maximum operational temperature at various durations. Mass loss and mechanical properties were measured over time. A chemical analysis was also performed on these composites. The two primary components of each matrix, the epoxy resin and the thermoplastic, were observed to degrade at different rates under various thermal loading conditions. The epoxy resins degrade predominantly as measured by IR spectroscopy and thermal desorption/gas chromatography mass spectrometry. By using mass loss, strength, and IR spectroscopic data, a correlation was made between strength characteristics of each composite and the relative amount of the two primary matrix components. The developed relationship can be used to estimate rapidly the mechanical properties from the intensity ratio of IR bands characteristic of the two components.     

CO在SrO表面吸附的热脱附

在真空条件下,利用程序升温热脱附方法测量CO吸附在SrO表面的脱附谱.实验结果表明,SrO吸附C^18O后,在升温过程中可通过氧的同位素交换生成C^16O而脱附,同时伴随少量C^18O的直接脱附,其波峰温度分别为430 K和420 K,属于二级脱附过程.     

Adsorption and desorption of CO on Ni decorated stepped Rh(553)

Vicinal surfaces are important in surface science, as they show interesting electronic structures and reactivities due to the steps. In this paper the adsorption and desorption of carbon monoxide on the stepped Rh(553) surface decorated with Ni is reported. With 0.1 to 0.3 monolayer Ni on Rh(553) one and two atoms broad Ni wires along the Rh steps are formed. The adsorption and desorption of carbon monoxide on these surfaces is investigated using thermal desorption spectroscopy (TDS) and reflection absorption infra red spectroscopy (RAIRS). TDS shows a marked change from just one broad TDS peak on pure Rh(553) to 4 distinct peaks with increasing Ni decoration. RAIRS shows that already at 0.1 monolayer Ni the CO adsorption states on bridge sites on the Rh step atoms are completely quenched. In addition it is shown that with Ni films up to 3 monolayer the on top adsorption sites for CO on Ni are preferred over the bridge and hollow adsorption sites in contrast to what is known from the Ni(111) surface.     

Adsorption and desorption of CO on Ni decorated stepped Rh(553)

Vicinal surfaces are important in surface science, as they show interesting electronic structures and reactivities due to the steps. In this paper the adsorption and desorption of carbon monoxide on the stepped Rh(553) surface decorated with Ni is reported. With 0.1 to 0.3 monolayer Ni on Rh(553) one and two atoms broad Ni wires along the Rh steps are formed. The adsorption and desorption of carbon monoxide on these surfaces is investigated using thermal desorption spectroscopy (TDS) and reflection absorption infra red spectroscopy (RAIRS). TDS shows a marked change from just one broad TDS peak on pure Rh(553) to 4 distinct peaks with increasing Ni decoration. RAIRS shows that already at 0.1 monolayer Ni the CO adsorption states on bridge sites on the Rh step atoms are completely quenched. In addition it is shown that with Ni films up to 3 monolayer the on top adsorption sites for CO on Ni are preferred over the bridge and hollow adsorption sites in contrast to what is known from the Ni(111) surface.     

Condensation and early stages of gold growth on an Mo (110) surface

The condensation and early stages of gold growth on an Mo (110) surface was studied at various temperatures using the complementary techniques of Auger electron spectroscopy, low energy electron diffraction and thermal desorption spectrometry. The following growth mechanisms were found: a van der Merwe growth mode with no long-range order in the gold layers at 293 K and a Stranski-Krastanov mode favoured by a constrained (111) first layer formation at 933 K.     

Flash-lamp-crystallized polycrystalline silicon films with high hydrogen concentration formed from Cat-CVD a-Si films

We investigate residual forms of hydrogen (H) atoms such as bonding configuration in poly-crystalline silicon (poly-Si) films formed by the flash-lamp-induced crystallization of catalytic chemical vapor deposited (Cat-CVD) a-Si films. Raman spectroscopy reveals that at least part of H atoms in flash-lamp-crystallized (FLC) poly-Si films form Si-H₂ bonds as well as Si-H bonds with Si atoms even using Si-H-rich Cat-CVD a-Si films, which indicates the rearrangement of H atoms during crystallization. The peak desorption temperature during thermal desorption spectroscopy (TDS) is as high as 900 °C, similar to the reported value for bulk poly-Si.     

Structural characteristics of phosphorus-doped C60 thin film prepared by radio frequency-plasma assisted thermal evaporation technique

Phosphorus doped C60 (P:C60) thin films were prepared by a radio frequency plasma assisted thermal evaporation technique using C60 powder as a carbon source and a mixture of argon and phosphine (PH3) gas as a dopant precursor. The effects of the plasma power on the structural characteristics of the as-prepared films were then studied using Raman spectroscopy, Auger electron spectroscopy (AES) and X-ray photo-electrons spectroscopy (XPS). XPS and Auger analysis indicated that the films were mainly composed of C and P and that the concentration of P was proportional to the plasma power. The Raman results implied that the doped films contained a more disordered carbon structure than the un-doped samples. The P:C60 films were then used as a coating layer for the Si anodes of lithium ion secondary batteries. The cyclic voltammetry (CV) analysis of the P:C60 coated Si electrodes demonstrated that the P:C60 coating layer might be used to improve the transport of Li-ions at the electrode/electrolyte interface.     

等离子体增强化学气相淀积a-SiCOF薄膜的稳定性研究

以正硅酸乙酯（TEOS）／C4F8／Ar为气源，采用等离子体增强化学气相淀积（PECVD）方法制备了低价电常数a-SiCOF介质薄膜，并借助X射线光电子能谱（XPS）和傅立叶变换红外光谱（FTIR）对薄膜的化学键结构、热稳定性和抗吸水性进行了研究。     

金属氧化物对膨胀阻燃涂层耐火及成炭性能的影响

金属氧化物(MO)可显著影响膨胀阻燃体系的热解成炭过程, 进而改善膨胀阻燃涂层的耐火性能。将Fe₂O₃、ZnO、TiO₂分别添加到双环笼状磷酸酯膨胀阻燃环氧涂层中, 研究了MO对涂层耐火及成炭性能的影响规律。燃烧背温测试结果表明, MO可产生显著的协效耐火作用, 三种MO对耐火性能的增效能力为Fe₂O₃>ZnO>TiO₂。热失重(TGA), 激光拉曼光谱(LRS)和X射线光电子能谱(XPS)分析表明, MO促进了残炭的耐高温氧化性能及类石墨化程度的提高, 增加了涂层的高温残炭量, 三种MO提升涂层成炭性能的能力为Fe₂O₃>ZnO>TiO₂。     

Alkali-metal Na Adsorption and Promoted Oxidation on Si(100)2×1 Surface

The alkali-metal Na adsorption on Si(100)2×1 surface and its promoted oxidation and Si oxidegrowth have been investigated by means of thermal desorption,work function,Auger electronspectroscopy and photoemission electron spectroscopy.The experimental data showed that therewas a new state,interface electron state,near the Fermi level after the deposition of Na atoms.It wasfound that the presence of Na always caused an increase of the oxygen initial uptake whereas thepromotion of Si oxide growth was observed only at the coverage of Na greater than 0.5 ML.A newmechanism of Na-promoted Si oxide growth is suggested in this paper.     

Low-temperature ozone exposure technique to modulate the stoichiometry of WOx nanorods and optimize the electrochromic performance

A low-temperature ozone exposure technique was employed for the post-treatment of WO(x) nanorod thin films fabricated from hot-wire chemical vapor deposition (HWCVD) and ultrasonic spray deposition (USD) techniques. The resulting films were characterized with x-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, UV-vis-NIR spectroscopy and x-ray photoelectron spectroscopy (XPS). The stoichiometry and surface crystallinity of the WO(x) thin films were subsequently modulated upon ozone exposure and thermal annealing without particle growth. The electrochromic performance was studied in a LiClO(4)-propylene carbonate electrolyte, and the results suggest that the low-temperature ozone exposure technique is superior to the traditional high-temperature thermal annealing (employed to more fully oxidize the WO(x)). The optical modulation at 670?nm was improved from 35% for the as-deposited film to 57% for the film after ozone exposure at 150?°C. The coloration efficiency was improved and the switching speed to the darkened state was significantly accelerated from 18.0?s for the as-deposited film to 11.8?s for the film after the ozone exposure. The process opens an avenue for low-temperature and cost-effective manufacturing of electrochromic films, especially on flexible polymer substrates.     

Changes in electrical and optical properties of polycrystalline Ga-doped ZnO thin films due to thermal desorption of zinc

Influences of thermal desorption of Zn atoms on electrical and optical properties of Ga-doped ZnO (GZO) films deposited by ion plating with direct current arc discharge have been studied. The amount of Zn desorption was controlled by thermal desorption spectroscopy. The resistivity of the GZO films was not affected by the thermal desorption of Zn up to the heating temperature of 300 °C, however, the carrier concentration and the Hall mobility showed remarkable changes. The carrier concentrations decreased with increasing the Zn desorption, and the Hall mobility increased. The decrease in carrier concentration showed strong correlation with the desorption of Zn atoms from the GZO films. The transparency in near infrared wavelength region increased without change of resistivity due to the decrease in carrier concentration.     

Influences of MonoSilanolIsobutyl-POSS on thermal stability of polymethylsilxoane

Incorporation of polyhedral oligomeric silsesquioxane (POSS) molecules into polymer matrix resulted in increased used and decomposition temperatures. Polymethylsiloxane (PMS)/MonoSilanolIsobutyl-POSS hybrid copolymers containing various proportions of MonoSilanolIsobutyl-POSS were prepared. The structures and thermal properties of the obtained products were characterized with Gel Permeation Chromatography (GPC), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), differential thermogravimetric analysis (DTG) and X-ray photoelectron spectroscopy (XPS). The GPC and FTIR spectra suggested successful bonding of MonoSilanolIsobutyl-POSS and PMS. TGA, DTG and XPS analysis revealed that MonoSilanoIsobutyl-POSS reinforced PMS are thermally more stable than the original PMS, primarily by the elimination of SiOH effects, the nanoreinforcement effect of POSS, the retardation of polymer chain motion and the formation of SiO₂ protective layer.