摘要:

The surface of boron-doped layers formed by rapid vapor-phase doping was analyzed by x-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared-attenuated total reflection (FTIR-ATR), to determine the role of the hydrogen carrier gas. Boron doping was carried out with aB2H6source gas and a hydrogen carrier gas at 800 and 900 °C. A nitrogen carrier gas was also used for comparison. Using hydrogen carrier gas, no evidence of boron segregation was observed in the XPS spectra. FTIR-ATR analysis confirmed that the hydrogen termination of the surface was maintained during doping. Using nitrogen carrier gas, layers that included segregated boron and silicon nitride were produced on the surface, which led to poor controllability of the boron concentration. When a hydrogen carrier gas is used, the hydrogen termination should promote the surface migration of adsorbed species. The hydrogen carrier gas plays an important role in terminating the silicon dangling bonds, thus preventing excessive chemisorption of boron.

ISSN:0734-2101    

DOI:10.1116/1.580969

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Adhesion of plasma-depositedSiO2on stainless steel is shown to be enhanced after Ar,N2,andNH3plasma pretreatments of the substrate. Adhesion is related to the chemical bonding at the interface. Therefore, it is studied by x-ray photoemission spectroscopy (XPS) andin situIR ellipsometry performed on very thin films (≈30 Åthick). IR ellipsometry reveals the removal of adsorbed hydrocarbons on the metallic surface by all plasma treatments. XPS measurements show the removal ofNOxspecies, related to the sample electropolishing, usingN2andNH3plasmas; in contrast, Ar has practically no effect in this case. Plasma-induced modifications are not limited to surface cleaning. Some nitrogen is incorporated in the substrate afterN2andNH3plasmas. In particular, nitrogen is found bonded to Si and to Cr afterNH3andN2treatments, respectively, we interpret the adhesion enhancement by hardening of the substrate surface region in the case ofN2plasma, while, in the case ofNH3, it may be related to the formation of silicon nitride. Cr–N–Si linkages between the substrate and the film may also contribute to adhesion improvement. We also observed changes in the early stages of the film growth. A higher sticking coefficient of dissociated species on the surface is revealed after plasma pretreatment. Narrowing of the Si2ppeak in XPS spectra observed in pretreated samples is attributed to a better orderedSiO2structure at Si sites in terms of bond angles and/or lengths. In contrast, both IR ellipsometry and XPS show no change at O sites.

ISSN:0734-2101    

DOI:10.1116/1.581013

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

X-ray photoelectron spectroscopy was employed for thein situstudy of the interactions between thermally deposited Al atoms and polyaniline films of different intrinsic oxidation states. Quantitative changes in the N 1score-level line shape, the evolution of the Al 2pcore-level spectra, and the changes in surface stoichiometry of these films throughout the Al deposition process were carefully tracked. Although the nitrogen sites appear to be more attractive to the incoming Al atoms and the emeraldine and nigraniline films undergo an apparent decrease in intrinsic oxidation state ([=N–]/[–NH–]ratio) as a result of Al deposition, there is no direct interaction between the two species, and the adsorbed oxygen from the bulk of the polymer film plays a dominant role in the interfacial interactions between the polymer and the metal.

ISSN:0734-2101    

DOI:10.1116/1.580961

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

A three chamber ultrahigh vacuum (UHV) surface analysis system combined with high pressure reaction cells has been designed. It can be used for the preparation and characterization of ordered metal oxide model catalyst surfaces and for the investigation of heterogeneous catalytic reactions there on also under high pressures. The reaction cells are completely separated from the UHV analysis chambers. They can be used for oxidation treatments and reaction studies at total pressures up to 1 bar. A new sample transfer mechanism together with sapphire sample holders and sample heating–cooling stations on the analysis chamber manipulators provides electron beam and resistive sample heating, liquid nitrogen sample cooling, and precise thermocouple temperature control. First experimental results obtained on single crystalline iron oxide dehydrogenation films grown onto Pt(111) substrates are presented. These results demonstrate the capability of the system forin situinvestigation of a sample surface using scanning tunneling microscopy, low-energy electron diffraction, Auger electron spectroscopy, photoelectron emission microscopy, and temperature programmed desorption before and after catalytic reactions at high pressures. This single crystal surface science approach provides new insight into the atomic scale surface chemistry of metal oxides under real catalysis conditions.

ISSN:0734-2101    

DOI:10.1116/1.580975

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

The interactions of low-energy (20–800 eV) nitrogen ions with Cu(100) at room temperature have been investigated by using temperature programmed desorption (TPD) mass spectrometry and high-resolution electron energy loss spectroscopy. The desorption feature observed at 760 K can be attributed to adsorption of surface atomic nitrogen on fourfold-hollow sites. When the impact energy (IE) of the nitrogen ions used for the irradiation exceeded 75 eV, our TPD results further revealed a new desorption feature at 520 K, which can be tentatively assigned to ion-implanted atomic and/or molecular nitrogen. The intensities and temperatures of the desorption maxima of the surface (chemisorption) and ion-implantation (entrapment) features were found to greatly depend on the IE and the dosage of the ions. Other effects including the creation of defect sites as a result of the ion irradiation are also investigated.

ISSN:0734-2101    

DOI:10.1116/1.580988

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

The chemical structure of two homogeneously doped polyenes, namely poly(propargylalcohol) (PPOH) and poly(N,N-dimethylpropargylamine) (Pd-PDMPA), has been investigated by means of x-ray photoelectron spectroscopy (XPS). The study of FeCl3and I2doped PPOH films gave evidence of different chemical states for the dopants into the polymeric chain. This result confirms that a charge transfer reaction between the polymer and dopant occurs, as found for analogous systems. An interaction between PPOH and the FeCl3 species, involving the metal and the pendant groups of the polymer, is observed. The analysis of HCl doped Pd-PDMPA films shows that the dopant interacts with the polymer by an acid-base reaction leading to the protonation of the N atoms. Scanning electronic microscopy images of the PPOH and Pd-PDMPA pristine films show that the final result of the polymerization process is the formation of a flat, enamel-like surface. The chain growth of Pd-PDMPA occurs by a dendrite growth. The enamel-like surface of the PPOH films is maintained upon homogeneous doping reaction, whereas a “craquelet ” effect is observed when the pristine films are exposed to iodine vapors. Homogeneous doping of Pd-PDMPA with HCl exhibits a dramatic modification of the surface with the appearance of a crystalline structure, due to the acid-base reaction also revealed by the XPS study.

ISSN:0734-2101    

DOI:10.1116/1.581006

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

The surfaces of vanadium dioxide thin films(VO2)in phase transition were studied at visible wavelength by laser scanning microscopy (LSM). Samples were laser ablatedVO2onAl2O3andSiO2/Sisubstrates at different temperatures and in different oxygen pressures. Using the differential interference method in the observation by LSM, real-time surface images for the samples in transition were successfully obtained by changing their temperature. The results showed the strong influence of deposition temperature, the oxygen pressure and the substrate type on the clarity and orientation of transition areas, which appeared as the difference of the brightness in the images.

ISSN:0734-2101    

DOI:10.1116/1.581009

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

An optical method for measuring scattered light, namely by analyzing the transmitted light, is used to characterize the optical properties of low-density foams that are candidates as targets for inertial confinement fusion. This method allows us to simultaneously measure both scattering and intrinsic absorption in the foam. Three types of foams have been examined: two have similar chemistries and are based on either ethylene glycol dimetacrylate (EGDM) or trimethylolpropane trimethacrylate (TMPT). The other one is based on resorcinol formaldehyde (RF). We observe that while the RF foams are orange in color and nearly transparent, the EGDM/TMPT based foams are white and opaque. The opacity of these foams is shown to be due to light scattering by particles having dimensions on the order of 200 nm. In contrast, the light scattering from the RF foams indicates that the structures scattering light are on the order of 20 nm. The orange color of the RF foams is shown to be due to intrinsic absorption of light by the polymer comprising the foam. The onset of absorption is seen to shift towards the blue as the foams age. Index matching to the TMPT foam using ethanol is shown to significantly reduce the scattering.

ISSN:0734-2101    

DOI:10.1116/1.581010

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

The effects of microwave electron cyclotron resonance (ECR) plasma oxidation on smooth as well as purposely roughened Si surfaces were studied using atomic force microscopy with fractal analysis and the results were compared to thermal oxidation. In addition, spectroscopic immersion ellipsometry was employed to obtain information on theSi/SiO2interface without the necessity of physically removing the oxide overlayer. The results are concordant and show that during both the ECR plasma and thermal oxidation processes, theSi/SiO2interface roughness decreases for the purposely roughened Si surfaces, but increases for initially smooth Si surfaces. Besides the initial surface roughness dependence, the change of this interface roughness depends mostly on the extent of oxidation, but also on temperature. The decreasing roughness for plasma oxidation is thought to be driven by the Kelvin equation, but enhanced by an applied external electric field. Ion bombardment, localized defects, and nucleation are eliminated as causative for roughening of initially smooth Si surfaces, and the results suggest a chemically enhanced roughening transition.

ISSN:0734-2101    

DOI:10.1116/1.581011

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

The evolution during growth of the vibrational properties in several plasma depositeda-SiO2thin films is studied. We mainly compare densea-SiO2deposited either at low pressure in an integrated distributed electron cyclotron resonance (IDECR) reactor or at higher pressure in a dual mode reactor. The latter system also allows one to vary thea-SiO2film density. Growth is studied byin situinfrared ellipsometry on stainless steel andc-Si substrates in the1000–1400 cm−1region. This region corresponds to the Si–O–Si asymmetric stretching mode which is split into transverse optical (TO) and longitudinal optical modes. Vibrational modes are revealed by inflection points in the ellipsometric angle Δ. LO modes are predominantly observed with metallic substrates, whereas onc-Si TO and LO modes are simultaneously observed. Vibrational properties of the IDECR films are found to be very close to the reference thermal silica over the whole range of thicknesses (up to more than 1000 nm), whereas the dual mode plasma deposited oxides have their vibrational modes shifted towards small frequencies and are broadened. This difference is mainly found in films with a higher H concentration which were deposited at high pressure(>9%)rather than in the IDECR film(<2%).The study of the Δ inflection point frequencies versus film thickness also shows differences in the interface formation. Contrary to the IDECR case, the vibrational properties of the dual mode plasma deposited oxides are stable only at large thicknesses. Vibrational properties are then compatible with two Lorentz oscillators: a strong one near1050 cm−1(with a strengthF=0.65and width50 cm−1) and a weaker one near1175 cm−1.In contrast, at small thicknesses, upward shifts in the LO frequency are observed. An interpretation in terms of disorder induced mode coupling at the interface between the two vibrations is proposed. We discuss the possible role of nucleation processes, due to high pressure, in correlation with the observed influence of film morphology and the nature of the substrate.

ISSN:0734-2101    

DOI:10.1116/1.581012

出版商:American Vacuum Society    

年代:1998

数据来源: AIP