Versatile apparatus for attosecond metrology and spectroscopy

We present the AS-2 Attosecond Beamline at the Joint Laboratory for Attosecond Physics of the Max-Planck-Institut fu?r Quantenoptik and Ludwig-Maximilians-Universita?t for time resolved pump/probe experiments with attosecond resolution. High harmonic generation and subsequent filtering of the generated extreme ultraviolet (XUV) continuum by means of metal filters and XUV multilayer mirrors serve for the generation of isolated attosecond laser pulses. After high harmonic generation, the remaining fundamental laser pulse is spatially separated from the attosecond XUV pulse, to what is to our knowledge for the first time, by means of a perforated mirror in a Mach-Zehnder interferometer. Active stabilization of this interferometer guarantees the necessary temporal resolution for tracking attosecond dynamics in real time. As a proof-of-principle, photoelectron streaking experiments are performed and experimental techniques for their realization are summarized. Finally we highlight the potential of the presented beamline system for future experiments in comparison with previously demonstrated attosecond beamlines.     

Time-resolved photoelectron spectroscopy of liquids

We present a novel setup for the investigation of ultrafast dynamic processes in a liquid jet using time-resolved photoelectron spectroscopy. A magnetic-bottle type spectrometer with a high collection efficiency allows the very sensitive detection of photoelectrons emitted from a 10 μm thick liquid jet. This translates into good signal/noise ratio and rapid data acquisition making femtosecond time-resolved experiments feasible. We describe the experimental setup, a detailed spectrometer characterization based on the spectroscopy of nitric oxide in the gas phase, and results from femtosecond time-resolved experiments on sodium iodide solutions. The latter experiments reveal the formation and evolution of the solvated electron and we characterize two distinct spectral components corresponding to initially thermalized and unthermalized solvated electrons. The absence of dark states in photoionization, the direct measurement of electron binding energies, and the ability to resolve dynamic processes on the femtosecond time scale make time-resolved photoelectron spectroscopy from the liquid jet a very promising method for the characterization of photochemical processes in liquids.     

The application of photoelectron spectroscopy to the study of e. p. films on lubricated surfaces

Photoelectron spectroscopy (ESCA) has been used to examine films formed on the surfaces of steel specimens by oil solutions of e.p. additives in immersion and rubbing tests. The additives used were elemental sulphur, dibenzyl disulphide, a commercial zinc dialkyldithiophosphate and pure zinc di-n-butyldithiophosphate. In the case of the two sulphur additives immersion specimens had films containing sulphate and free sulphur, whereas rubbed surfaces had patchy coatings of sulphide with lesser amounts of sulphate. The thiophosphate additives gave broadly similar films in rubbing and immersion tests. These contained the zinc, phosphorus and part of the sulphur in the original additive in films, possibly polymeric, of somewhat variable composition. Argon ion etching was used to explore the composition of a film from a thiophosphate additive. It showed that there were no large compositional variations through the thickness of the film and that it was of a discontinuous patchy nature.     

An instrument for the investigation of actinides with spin resolved photoelectron spectroscopy and bremsstrahlung isochromat spectroscopy

A new system for spin resolved photoelectron spectroscopy and bremsstrahlung isochromat spectroscopy has been built and commissioned at Lawrence Livermore National Laboratory for the investigation of the electronic structure of the actinides. Actinide materials are very toxic and radioactive and therefore cannot be brought to most general user facilities for spectroscopic studies. The technical details of the new system and preliminary data obtained therein will be presented and discussed.     

Development of a new photoelectron spectroscopy instrument combining an electrospray ion source and photoelectron imaging

A new apparatus has been constructed that combines electrospray ionization with a quadrupole mass filter, hexapole ion trap, and velocity-map imaging. The purpose is to record photoelectron images of isolated chromophore anions. To demonstrate the capability of our instrument we have recorded the photodetachment spectra of isolated deprotonated phenol and indole anions. To our knowledge, this is the first time that the photodetachment energy of the deprotonated indole anion has been recorded.     

Slicing of soft flexible solids with industrial applications

Thin slices of soft flexible solids have negligible bending resistance and hence store negligible elastic strain energy; furthermore such offcuts are rarely permanently deformed after slicing. Cutting forces thus depend only on work of separation (toughness work) and friction. These simplifying assumptions are not as restrictive as it might seem, and the mechanics are found to apply to a wide variety of foodstuffs and biological materials. The fracture toughness of such materials may be determined from cutting experiments: the use of scissors instrumented for load and displacement is a popular method where toughness is obtained from the work areas beneath load–displacement plots. Surprisingly, there is no analysis for the variation of forces with scissor blade opening and this paper provides the theory. Comparison is made with experimental results in cutting with scissors. The analysis is generalised to cutting with blades of variable curvature and applied to a commercial food cutting device having a rotating spiral plan form blade. The strong influence of the ‘slice/push ratio’ (blade tangential speed to blade edge normal speed) on the cutting forces is revealed. Small cutting forces are important in food cutting machinery as damage to slices is minimised. How high slice/push ratios may be achieved by choice of blade profile is discussed.     

Resonant torsional apparatus for contactless measurements of electrical conductivity and magnetic susceptibility of solids

We have constructed a torsional resonance apparatus for contact-free measurements of the electrical conductivity of solids. Owing to its use of modulation spectroscopy, the technique achieves considerable enhancement of sensitivity compared to previous contactless methods. Conductivities in the range 10(-5) mho/cm to 10(-6) mho/cm can now be measured by the contactless technique. Measurements of magnetic susceptibility as low as 10(-12) can be made. This sensitivity allows for investigation of magnetic impurities as dilute as 1 part in 10(7). In samples which display both phenomena of electrical conductivity and magnetic susceptibility, the two effects can be sorted out via analysis of frequency and/or temperature dependence. The present apparatus has potential for considerable improvement.     

Time-of-flight photoelectron spectroscopy of gases using synchrotron radiation

A gas-phase time-of-flight (TOF) photoelectron spectrometer has been developed for use with synchrotron radiation. The excellent time structure of the synchrotron radiation at the Stanford Positron Electron Accelerator Ring (SPEAR) has been used as the time base for the TOF measurements. The TOF analyzer employs two multichannel plates (MCPs) in tandem as a fast electron multiplier with a matched 50-Omega anode to form an electron detector with a timing resolution of 相似文献   

Scanning photoelectron microscope for nanoscale three-dimensional spatial-resolved electron spectroscopy for chemical analysis

In order to achieve nondestructive observation of the three-dimensional spatially resolved electronic structure of solids, we have developed a scanning photoelectron microscope system with the capability of depth profiling in electron spectroscopy for chemical analysis (ESCA). We call this system 3D nano-ESCA. For focusing the x-ray, a Fresnel zone plate with a diameter of 200 μm and an outermost zone width of 35 nm is used. In order to obtain the angular dependence of the photoelectron spectra for the depth-profile analysis without rotating the sample, we adopted a modified VG Scienta R3000 analyzer with an acceptance angle of 60° as a high-resolution angle-resolved electron spectrometer. The system has been installed at the University-of-Tokyo Materials Science Outstation beamline, BL07LSU, at SPring-8. From the results of the line-scan profiles of the poly-Si/high-k gate patterns, we achieved a total spatial resolution better than 70 nm. The capability of our system for pinpoint depth-profile analysis and high-resolution chemical state analysis is demonstrated.     

Instrument combining x-ray photoelectron spectroscopy and secondary ion mass spectrometry for surface studies

X-ray Photoelectron Spectroscopy (XPS) or (ESCA) and Secondary Ion Mass Spectrometry (SIMS) have been combined in the same ultrahigh vacuum system to facilitate a new approach to studying clean and reacted surfaces. The design philosophy is to connect two satellite vacuum systems via a set of magnetically driven sample transfer devices. The advantages and capabilities of this approach are discussed with respect to its flexibility and its ability to couple to other surface techniques. XPS and static SIMS spectra of an oxidized polycrystalline indium film are presented to exemplify the type of information which can be gleaned from a multitechnique investigation of surfaces. The additional ability to prepare sample surfaces in our system by ion implantation is demonstrated by a positive-ion SIMS analysis of a gold-implanted aluminum foil.     

Sialolith characterization by scanning electron microscopy and X-ray photoelectron spectroscopy

The objective of this study has been to characterize sialolith, a calcium phosphate deposit that develops in the human oral cavity, by high-resolution field emission scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The morphological and chemical data obtained helped in the determination of their formation mechanism in salivary glands. Sialoliths in the submandibular salivary glands may arise secondary to sialodenitis, but not via a luminal organic nidus. We believe this is the first study that characterizes a sialolith by XPS.     

The transfer of polytetrafluoroethylene studied by x-ray photoelectron spectroscopy

A polytetrafluoroethylene (PTFE) sphere of radius 4.8 mm was rubbed against nickel and S-Monel at speeds from 0.94 to 94 mm s^?1 and at loads from 0.19 to 3.9 N. The transfer film of PTFE on the metal was examined with X-ray photoelectron spectroscopy. In all cases the film was found to be indistinguishable from bulk PTFE. A trace of metal fluoride was observed whether the rubbing took place on oxidized or atomically clean metal. The film was of the order of a molecule thick for the entire range of loads and did not increase with repeated passes over the same rubbed area. An erratic increase in thickness at rubbing speeds above 10 mm s^?1 was taken as evidence of random transfer of bulk material.     

Preparation of mica surfaces for enhanced resolution and cleanliness in the surface forces apparatus

We describe a simple technique for preparing arbitrarily thin mica substrates of unparalleled purity for use in the surface forces apparatus (SFA). Relatively thick mica samples (4–8 μm) are prepared in the conventional way, coated with a sputter deposited layer of silver, and attached (silver side down) to cylindrical lenses with a thick coat of thermosetting epoxy. These surfaces are then placed in a glovebox with the cell of the SFA where they are cleaved once again with a piece of tape, and then mounted and sealed in the SFA for immediate use. With this technique, the surfaces are never exposed to laboratory air, they are insensitive to asperities in the glue/silica support, and may be made arbitrarily thin by removing more mica until the desired thickness is achieved. We find that adhesion between two surfaces cleaved in this manner (∼300 mJ/m²) is significantly larger than for mica prepared in the conventional way (∼200 mJ/m²), and consistent with the adhesion measured in direct cleavage experiments. This suggests a cause for discrepancies in the measured adhesion which have appeared in the literature. This revised version was published online in July 2006 with corrections to the Cover Date.     

The tribo-chemistry of graphite fluoride studied using X-ray photoelectron spectroscopy

A preliminary investigation involving the application of X-ray photo-electron spectroscopy (XPS) for the study of the degradation, under sliding conditions, of thin graphite fluoride films on steel has been carried out. The results described here show that the technique can provide invaluable information in establishing the mode of failure of the lubricating film.     

Improving metastable impact electron spectroscopy and ultraviolet photoelectron spectroscopy signals by means of a modified time-of-flight separation

The separation of ultraviolet photoelectron spectroscopy (UPS) and metastable impact electron spectroscopy (MIES) is usually performed by a time-of-flight (ToF) separation using pre-set ToF for both types of signal. In this work, we present a new, improved ex situ signal separation method for the separation of MIES and UPS for every single measurement. Signal separation issues due to changes of system parameters can be overcome by changing the ToF separation and therefore allowing for the application of a wider range of measuring conditions. The method also enables to identify and achieve separation of the two signals without any time consuming calibration and the use of any special material for the calibration. Furthermore, changes made to the discharge source are described that enable to operate an existing MIES/UPS source over a broader range of conditions. This allows for tuning of the yield of UV photons and metastable rare gas atoms leading to an improved signal to noise ratio. First results of this improved setup are well in agreement with spectra reported in literature and show increased resolution and higher signal intensities for both MIE and UP spectra compared to the previous, non-optimized setup.     

Determination of oxygen in acid-treated high-purity niobium by X-ray photoelectron spectroscopy

High-purity niobium was immersed in nitric acid and hydrofluoric acid for two minutes and the resulting product was characterized. Scanning electron microscopy was employed to characterize the morphology of the acid treated product. Inert gas fusion was used for determination of oxygen in the high-purity niobium. X-ray photoelectron spectroscopy was employed to characterize the surface ratio of oxygen to niobium. The oxygen concentration was 30 ppm in the acid-treated material and 70 ppm in the untreated material. X-ray photoelectron spectroscopy was employed to characterize the reduction of oxygen at the surface. The ratio of oxygen to niobium decreased from 9.75 to 2.60 without treatment compared to acid treatment for two minutes. The concentrations of adsorbed water and niobium oxide decreased following etching. The acid-treated high-purity niobium was characterized by argon ion bombardment; adsorbed water molecules and niobium oxides were not present but non-lattice oxygen was observed.     

A plasticity theory for porous solids

A plasticity theory is developed for a solid weakened by numerous cracks or voids. The treatment is completely isotropic and would be suitable whenever the voids are nearly spherical or where the direction of cracks is completely random. Using simple models an explicit representation for a second-order yield surface parameterized by the void fraction is presented. The resulting constitutive law is shown to be of the hypoelastic type and simple examples are treated. An approximate expression for a deformation theory is also discussed.     

X射线光电子能谱仪应用——特殊样品测量及复杂图谱解析

x射线光电子能谱(XPS)是材料表面元素定性和半定量分析的重要手段之一。在XPS测量实验中,使用绝缘方法来安置导电不均匀样品到导电的样品台上进行常规XPS测量,方便地得到满意的图谱数据;在数据处理中,针对扫描谱图中的峰位、峰强度、峰宽和峰形等情况,利用XPS图谱分析软件的拟合分析功能,对多价态混合的复杂样品(例如:Ce和Fe的多价态样品)的XPS图谱进行处理,采用单一价态的实验数据为模版对混合图谱进行拟合处理,比较容易地获得常规方法不易得到的不同价态的定性及半定量结果。本文对以上方法分别作举例说明。     

Anisotropic oxidation of MoS2 crystallites studied by angle-resolved X-ray photoelectron spectroscopy

The oxidation behavior of the solid lubricant MoS₂ was studied using X-ray photoelectron spectroscopy. MoS₂-containing slip ring brushes were used to take advantage of anisotropic orientation of the plate-shaped MoS₂ crystallites occurring during fabrication of the brushes. Because oxidation occurs preferentially at the edges of the crystallites, greater oxidation fractions are measured when the edges are oriented toward the photoelectron energy analyzer. These results indicate a novel method for separately probing the chemistry on the edge and (lubricious) basal surfaces of MoS₂.