Electron spectroscopic characterization of oxygen adsorption on gold surfaces: I. Substrate impurity effects on molecular oxygen adsorption in ultra high vacuum

Tentative adsorption on clean gold (110) and (111) crystals of molecular oxygen in the pressure range 10 ^?10 to 10 ^?5 Torr, at a temperature varying between 100 and 800 K is reported together with the subsequent characterization of the surfaces by High Resolution Electron Energy Loss, Auger and X-ray Photoelectron Spectroscopies. It is found that oxygen does not adsorb in these UHV conditions, except when a contaminant is present on the surface. Such an interaction with a low level silicon impurity is described.     

Fundamental processes of aluminium corrosion studied under ultra high vacuum conditions

Surface sensitive electron spectroscopy was applied to study the fundamental processes of aluminium corrosion. We used metastable induced electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS) for the investigation of the densities of states of surface and bulk, respectively. Furthermore we applied X-ray photoelectron spectroscopy (XPS) to investigate the chemical composition of the top surface layers. All measurements were performed under ultra high vacuum conditions.Al films with thicknesses of 7 nm were investigated. Both the interaction of oxygen and water with these films leads to the formation of an aluminium-oxygen layer, which is partly composed of stoichiometric Al₂O₃. Weak heat treatment at 770 K transforms the surface layer into Al₂O₃ with a thickness of about 2 nm. Further gas offer does not lead to an increase of this thickness, neither for oxygen nor for water. Additional to the oxygen offer, water exposure leads to the formation of OH species in the top aluminium-oxygen layer to a small amount. Weak heat treatment to 770 K removes this species completely. Water exposure leads to a much faster oxide formation than oxygen exposure. We try to give a model for the fundamental corrosion processes on a molecular scale.     

Auger and electron energy loss spectroscopic study of surfaces of iron-sulfur alloy,Fe7S8 and FeS2 cleaved in ultra high vacuum

The surfaces of an iron-210 at. ppm sulfur alloy, Fe₇S₈ and FeS₂ cleaved in an ultra high vacuum were studied by Auger (AES) and electron energy loss Spectroscopy (EELS). The S LVV Auger transition for the intergranular fracture plane of the alloy indicates that the sulfur is bonded to the surface as though it were adsorbed. The loss energies of the transition from valence to conduction bands for the surface are identical to those for the transgranular fracture planes. The trans- and intergranular fracture planes have very similar fine structure in the Fe MVV Auger transition profile. This indicates that the interaction between iron and sulfur is too weak to perturb the electronic structure at the fracture surface. The spectral features of the electron transitions having kinetic energies between approximately 40 and 50 eV are explained by a normal Fe MVV Auger transition and an autoionization process after excitation of Fe 3p electrons. The low spin ferrous ion in FeS₂ results in triplet peaks for the Fe MVV transition and doublet peaks for the autoionization event, but similar transitions for Fe₇S₈ exhibit singlet peak for each process.     

Molecular dynamics investigation of water adsorption on rutile surfaces

Born-Oppenheimer molecular dynamics (MD) simulations were performed in the framework of the semi-empirical molecular orbital method MSINDO to study water adsorption on rutile surfaces. Monolayer and doublelayer water coverage was considered on the rutile (1 1 0) and (1 0 0) surfaces and the adsorbate structures were determined. Vibrational density of states of hydrogen atoms were calculated by constant temperature MD simulations at 100 K. These were used to interpret the experimental vibrational spectrum by assigning all peaks to the particular types of hydrogen atoms.     

FTIR spectroscopic characterization of the adsorption and desorption of ammonia on MgO surfaces

In the present paper an attempt is made to disentangle the complex IR spectra obtained in the course of the adsorption of NH₃ on high surface area MgO. For this purpose two simplifications were introduced in comparison to previous studies: (a) Only uniformly hydroxylated MgO surfaces (degassing temperature: 200 °C) and completely dehydroxylated MgO surfaces (degassing temperature: 1000 °C) were used as adsorbent, (b) The equilibrium pressure of the adsorbate NH₃ was generally maintained below 200 Pa in all adsorption and desorption experiments. Under these conditions the position and the pressure dependence of the resulting bands may consistently be interpreted in terms of characteristic surface species. Only the completely dehydroxylated MgO surface gives rise to a heterolytic dissociation into neighbouring NH₂ and OH groups. In addition, NH₃ is physically adsorbed on less reactive sites via diverse types of hydrogen bonds. Less well defined hydroxylation states give rise to considerably more complicated spectra. In a first approximation they may be constructed by linearly combining two spectral patterns, one related to a uniformly hydroxylated and the other to a dehydroxylated surface. NH₃ pressures around and beyond 1 kPa give rise to significant changes of band positions and band shapes compared to those observed below 200 Pa. The interpretation of these effects which have previously been ignored must necessarily rely on more complicated models.     

Thick-film technology for ultra high vacuum interfaces of micro-structured traps

We adopt thick-film technology to produce ultra high vacuum compatible interfaces for electrical signals. These interfaces permit voltages of hundreds of volts and currents of several amperes and allow for very compact vacuum setups, useful in quantum optics in general, and in particular for quantum information science using miniaturized traps for ions (Kielpinski et al. in Nature 417:709, 2002) or neutral atoms (Folman et al. in Phys. Rev. Lett. 84:4749, 2000; Treutlein et?al. in Fortschr. Phys. 54:702, 2006; Hofferberth et al. in Nat. Phys. 2:710, 2006). Such printed circuits can also be useful as pure in-vacuum devices. We demonstrate a specific interface which provides 11 current feedthroughs, more than 70?dc feedthroughs and a feedthrough for radio frequencies. We achieve a pressure in the low 10^-11?mbar range and demonstrate the full functionality of the interface by trapping chains of cold ytterbium ions, which requires the presence of all of the above mentioned signals. In order to supply precise time-dependent voltages to the ion trap, a versatile multi-channel device has been developed.     

Infrared spectroscopic characterization of the properties of oxide films grown on Zr surfaces doped under ion-beam irradiation in a vapor-water medium

Infrared spectroscopy is shown to be applicable to the nondestructive check of the state of oxide films on metal substrates doped under irradiation by an ion beam. The reflection spectra of oxide films on zirconium surfaces doped under ion-beam irradiation are obtained. Oxide films were grown by means of oxidation in a vapor-water medium. The analysis of the fine structure of IR spectra has revealed that, at wavelengths of 1–10 μm, the spectra contain resonance lines corresponding to ZrH-and ZrOH-type molecular compounds, OH groups, and other components of oxide.     

Surface control of CdSe nanocrystals by UV-exposure in air and successive thermal treatment under ultra high vacuum

Colloidal CdSe nanocrystals were synthesized through a solution process. The CdSe nanocrystals coated on Si(1 0 0) wafers were UV-exposed in either an air or argon atmosphere to distinguish the effect of generated ozone from UV-radiation at 365 nm on the removal of surface capping pyridine molecules. The pyridine on the CdSe nanocrystal's surface could be effectively removed by the ozone generated during UV-exposure with an accompanying highly oxidized surface state of the CdSe nanocrystals. For the removal of surface oxides of CdSe nanocrystals, a successive thermal treatment under ultra high vacuum (UHV) was adopted. The optical energy bandgap measured by using UV-vis absorption spectroscopy showed a red shift with treatment with an increase of annealing temperature. The electronic energy structure of UHV-annealed CdSe nanocrystals film was analyzed in situ using X-ray absorption and photoelectron spectroscopy. A great resemblance was found between the values of the optical and electron energy bandgaps of effectively surface-treated CdSe nanocrystals film after UHV-annealing at 400 °C.     

两类无油超高真空系统的实验方法

对涡轮分子泵无油超高真空系统及溅射离子泵无油超高真空系统的结构及操作方法作了介绍,并对它们相关的特性进行了讨论。     

An electron spectroscopic investigation of the adsorption of NO on Ni(111)

The adsorption, decomposition, and desorption of NO on the close packed Ni(111) surface have been investigated by XPS, XPS satellites, XAES, UPS, and LEED between 125 and 1000 K. At adsorption temperatures below 300 K a single molecular species (v) is formed with about unit sticking coefficient, which is interpreted as bridge-bonded; its saturation coverage is about 85% of that of CO, i.e. 0.5 relative to surface Ni atoms. Adsorption at 300 to 400 K yields dissociative adsorption (β) followed by molecular adsorption; above 400 K only dissociated species are formed. Upon heating, a full molecular layer dissociates only after some NO desorption (at 380–400 K), while dilute layers (below half coverage) dissociate already above 300 K without NO desorption. Together with quantitative findings this shows that for dissociation of one v-NO, the space of two is required. N₂ desorption from the β-layer occurs above 740 K; the oxygen staying behind diffuses into the crystal above 800 K. Readsorption of NO onto a β-layer or onto an oxygen precoverage at 125 K leads, besides to an α₁-state similar to v-NO, to another molecular state (α₂) which is interpreted as linearly bound. The resulting total coverage is considerably higher than in a virgin layer. This shows that the blocking of dissociation in a full v-layer is probably not due to β requiring the same sites, but to kinetic hindrance; an influence of β-induced surface reconstruction cannot be excluded, however. The LEED results agree with a previous report and are well compatible with the other results.     

A high throughput approach to quantify protein adsorption on combinatorial metal/metal oxide surfaces using electron microprobe and spectroscopic ellipsometry

Although metallic biomaterials are widely used, systematic studies of protein adsorption onto such materials are generally lacking. Combinatorial binary films of Al_1−xTi_x and Al_1−xNb_x (0  x  1) and corresponding pure element films were produced on glass substrates using a unique magnetron sputtering technique. Fibrinogen and albumin adsorption amounts were measured by wavelength-dispersive spectroscopy (WDS) and spectroscopic ellipsometry (SE) equipment, both high throughput techniques with automated motion stage capabilities. X-ray diffraction revealed that the binary films have crystalline phases present near the ends of the compositional gradient with an amorphous region throughout the interior of the gradient. X-ray photoelectron spectroscopy provided the surface chemistry along the binary films and showed that Al₂O₃ preferentially formed at the surface. Protein adsorption onto these films was found to be closely correlated to the alumina surface fraction, with high alumina content at the surface leading to low amounts of adsorbed fibrinogen and albumin. Protein adsorption amounts obtained with WDS and SE were in excellent agreement for all films. This suggests that this combinatorial materials approach combined with these state-of-the-art, automated high throughput instruments provides a novel way to accurately monitor protein adsorption taking place at the surfaces of these metal/metal oxide materials.     

X-ray photoelectron spectroscopic investigation of electrochemically oxidised and reduced platinum surfaces

The growing of oxide layer with the time of anodic oxidation in 1M, 3.5M and 8.8M perchloric acid solutions has been investigated by XPS on smooth and platinised Pt surfaces. Pure metallic Pt surfaces were prepared by acidic digestion, ignition and cathodic reduction, and their electron spectra have been compared. The presence of a single species, probably PtO, can be evaluated from the XPS measurements. Calculated values of PtO film thickness for different time intervals of electrolytic oxidation are given at various concentrations of HClO₄.