The alignment of spectrometers and quantitative measurements in X-ray photoelectron spectroscopy

The alignment of the sample in X-ray photoelectron spectrometers is usually made to optimize the spectral intensities. There are two important classes of spectrometer: (i) those in which the analyser acceptance area is independent of the analysed electron kinetic energy; and (ii) those in which this area varies. Model experiments show how an example of a VG ESCALAB II conforms to class (i) whereas an example of an SSI X-probe is of class (ii) and shows an analyser acceptance area which depends approximately inversely on the emitted electron kinetic energy. This latter result means that the SSI X-probe spectrometer must be aligned for the electrons of the highest kinetic energy (smallest analyser acceptance area). A misalignment of 0.1 mm in the sample height can cause a 10% change in the relative intensities between 0 and 1000 eV binding energies. This dependence of the analyser acceptance area with energy is an effect likely to be common in the advanced electron optical systems of modern electron spectrometers and should be understood in order to use such spectrometers effectively. Such dependencies should be determined by analysts for their own instruments in the operating mode that is used for conducting work in which the repeatability of intensity measurements is important.     

Measurement of the transmission function of the hemispherical energy analyser of ADES 400 electron spectrometer

For determination of the transmission function of a hemispherical energy analyser of an ADES 400 photoelectron spectrometer (V. G. Sci.) a direct method is used. This method is based on the definition of the transmission coefficient of an energy analyser. The number of impinging electrons from an electron gun is measured by a Faraday cup and the current of passed electrons is determined as a peak area of the current signal from the channel multiplier which is used as the Faraday cup. The transmission function of the energy analyser of the ADES 400 photoelectron spectrometer is measured for four values of the analyser pass energy.Presented at the Seminar on Secondary Electrons in Electron Spectroscopy, Microscopy, and Microanalysis, Chlum (The Czech Republic), 21–24 September, 1993.     

Graduation of electron spectrometer intensity scale. Part 1. A theoretical approach

We consider an ordinary spectrometer equipped with a dispersing field analyser (e.g. cylindrical mirror analyser (CMA)), an electron multiplier, and analogue differentiation facilities. Transformation of the true energy distribution of secondary electrons to the spectrometer output voltage is described mathematically using a spectrometer operator. Conditions are established that allow the mathematical expression of the operator to be reduced to a graduation function G(E′) of pass energy E′. The G(E′) function is defined as the product of a probability function definite integral and a multiplier gain coefficient. The operator and/or the graduation function take account of influences of any extraneous fields on the spectrometer output voltage.     

Buchbesprechugen

In charge collecting semi-conductor detectors the absorbed radiation energy E causes a proportional signal which is fed to a multi-channel analyser after suitable amplification and filtering. Full width at half maximum, δE, (half width) is defined as the energy resolution.     

Principle and applications of a floating energy analyser

We describe a new type of energy analyser suitable for the use in plasmas having no external potential reference like ICPs and microwave discharges. It can be used to determine the ion distribution function (IDF) at a negatively biased surface and the high energy tail of the plasma electron distribution function (EDF). The EDF is measured without distortions by ion currents. This analyser was tested in a dc glow discharge and its results compared to measurements with Langmuir probes and a analyser with grounded reference. Some preliminary measurements were also performed in a rf parallel plate discharge. Dedicated to Prof. Jan Janča on the occasion of his 60th birthday, in remembrance of a fruitful and friendly European co-operation. This work was supported by the Deutsche Forschungsgemeinschaft Bonn by Sonderforschungsbereich 191 and by the Directorate-General XII Science, Research and Development of European Commission, under Grant ERBCIPACT924034.     

Determination of Calcium and Iron and Measurements of Ash Content in the Brown Coal

Applying the XRF technique and the low-energy X-ray backscattering method an attempt of calcium and iron determination, as well as measurement of the ash content in the brown coal was made. A ²³⁸Pu source, an argon filled propotional counter and a three channel pulse height analyser were used. A simple theoretical model is proposed and obtained results are discussed.     

Intensity and energy calibration in AES: The effect of analyser modulation

To a large extent, Auger electron spectra (AES) are recorded and portrayed in the differential mode using the potential-modulation method with a phase-sensitive detector. The precise intensities of the peaks and their energy positions depend on the modulation amplitude in a nonlinear manner. This dependence, in turn, is also a function of the resolution and detailed construction of the analyser. Thus, accurate quantification and accurate assignments of peak energies depend on a detailed knowledge of the effect of analyser modulation in AES. The theoretical response of spectrometers to a Gaussian line is here analysed and compared with measurements for “singlet” peaks using several different commercial spectrometers. This shows that, in certain circumstances, the traditional methods of intensity and energy measurement can be transferred with accuracies as high as 3% and 0.05 eV, respectively. A method for calibrating the effective modulation amplitude, vital for accurate quantification, is presented in the following paper.     

Zur Sekundärelektronenemission durch Argonionen und Argonatome im Energiebereich von 1 bis 20 keV

Be-, CuBe-, Cu- and Al-targets are bombarded by single A⁺ and A⁰ in the energy range from 1 to 20 keV. The secondary electrons accelerated by 20 keV are counted by a proportional counter backed by a multichannel analyser. The probability distributionP _n of emission ofn=0,1, 2, 3, ... secondary electrons can be found from the pulse height distribution. WhenP _n is known the yield for A⁺ and A⁰ can be calculated. The counting of neutrals in the energy range investigated is discussed.     

Avalanche Phenomenon of Superthermal Electrons Measured by SDD with New SPHA during ECRH

Two high performance silicon drift detectors （SDD） are installed at the equatorial port with z = 0 and z = -16.4 cm on HL-2A tokamak, respectively. These SDDs combine with the new and non-conventional software pulse height analyser （SPHA ） successfully developed more recently by us to measure the time evolution of soft x-rays spectra, the thermal and superthermal electron temperatures. The high-quality three-dimensional figure of time evolution for soft x-rays energy spectra is easily obtained by combination of a new SPHA and computer. Therefore, the measurement accuracies and the time resolutions of thermal and superthermal electron temperatures are also improved. The enhancement phenomenon of superthermal electron during electron cyclotron resonance heating （ECRH） can be explained by the combination of superthermal electron avalanche theory and experimental parameters.     

Characterisation and application of a SPLEED-based spin polarisation analyser

A commercial electron spin analyser, based on spin-polarised low-energy electron diffraction (SPLEED) from W(1 0 0), has been characterised with incident polarised electron beams from a standard GaAs polarised electron source. The dependence of the Sherman function on the scattering energy and elapse time after CO-flash of the tungsten crystal of the analyser have been measured. The influence of the stray magnetic field on the performance of the analyser has been investigated. The spin analyser has been applied in monitoring the reorientation transition of the easy magnetisation direction of Fe films on W(1 1 0) upon the exposure of CO adsorbent on the surface.     

The relationship between transmission efficiencies in the FRR and fat modes of an electron spectrometer

The electron transmission efficiency as a function of kinetic energy for an electron spectrometer operating in the fixed analyser transmission (FAT) mode has been determined by direct comparison with the known transmission efficiency in the fixed retard ratio (FRR) mode. Results obtained from the background intensity and from the relative peak heights of a number of elements compare well with each other. They suggest that transmission in the FAT mode is nearly independent of kinetic energy.     

Multiple‐element spectrometer for non‐resonant inelastic X‐ray spectroscopy of electronic excitations

A multiple‐analyser‐crystal spectrometer for non‐resonant inelastic X‐ray scattering spectroscopy installed at beamline ID16 of the European Synchrotron Radiation Facility is presented. Nine analyser crystals with bending radii R = 1 m measure spectra for five different momentum transfer values simultaneously. Using a two‐dimensional detector, the spectra given by all analysers can be treated individually. The spectrometer is based on a Rowland circle design with fixed Bragg angles of about 88°. The energy resolution can be chosen between 30–2000 meV with typical incident‐photon energies of 6–13 keV. The spectrometer is optimized for studies of valence and core electron excitations resolving both energy and momentum transfer.     

Microspectroscopy and spectromicroscopy with photoemission electron microscopy using a new kind of imaging energy filter

The use of an imaging retarding field analyser attached to the FOCUS IS-PEEM is described. This kind of energy filter is a simple, powerful tool to obtain microspectra from areas of down to about 1 μm using (V)UV and X-ray excitation sources. First results of microspectroscopy measured by excitation with a laboratory as well as a synchrotron X-ray source are presented.     

Reduction of energy-loss “ghost structures” observed in electrostatic deflection type electron analysers

Ghost lines due to electron reflections occurring on the wall plates of an electrostatic deflection type electron analyser are observed and studied as a function of electron intensity and energy, in the kinetic energy range 25–40keV. The model by Froitzheim et al. [3] is found to be in good agreement with our measurements. A new method, based on the angular separation of the ghost beam from the analysed beam, is used to reduce the ghost structure intensity by a factor of about 300.     

Angle-resolved ups measurements in a modified LEED system

A LEED chamber has been modified to include a differentially pumped discharge lamp (He or Ne) and an additional retarding grid electron energy analyser for UPS. This small analyser is located at right angles to the LEED analyser and does not interfere with normal LEED and Auger operations. The UPS signal is amplified by a channel plate multiplier and accelerated onto a phosphor-coated screen. Directional information is obtained by scanning this screen with a collimated photomultiplier detector. A phase-lock amplifier is used to differentiate the signal from the photomultipler. Alternatively the phosphor screen can be used as a collector to measure a total spectrum. The acceptance angle of the UPS analyser is 90°. In the angular resolving mode it is possible to observe emission from a (100) fcc crystal in the 〈100〉, 〈110〉 and 〈111〉 directions with a fixed incident photon angle in the range 20–40° to the normal. The acceptance angle of the detector was usually ~7° but this can be varied by changing the collimating tube on the photomultipler. The direction dependent features of the d-band spectrum of clean nickel with a (100) surface have been examined. Characteristic features were observed for each of the 〈100〉, 〈111〉 and 〈110〉 directions. These are compared with those reported for crystals with the corresponding surface orientations. The effects resulting from the chemisorption of nitric oxide on this nickel crystal have also been investigated.     

Ion Temperature Measurement in the Edge Region of SINP Tokamak by a Retarding Field Analyser

Based on the principle of retarding field analyser an ion energy analyser has been developed for the measurement of ion temperature in the edge plasma region of the SINP tokamak. This has been used to determine the dependence of the ion temperature on the safety factor q in the normal q region (q=2 to 4), plasma current, plasma electron temperature and also the Spitzer resistivity.     

酞菁铜薄膜的折射率及吸收特性

通过真空镀膜法在单晶硅制备了酞菁铜薄膜，在波长扫描和入射角可变全自动椭圆偏振光谱仪上研究了ＣｕＰｃ薄膜的椭偏光谱并分析了其电子结构。     

酞菁钴薄膜的折射率及吸收特性

通过真空镀法在单晶硅片上制备了酞菁钴薄膜，在波长扫描和入射角可变全自动椭圆偏振光谱仪上研究了ＣｏＰｃ薄膜的椭偏光谱并分析了其电子结构。     

Design and construction of multicrystal analyser detectors using Rowland circles: application to MAD26 at ALBA

A concept is given for describing multicrystal analyser detectors (MADs), as they are in use for synchrotron powder diffraction, on the basis of the Rowland circle construction. The Rowland circle is typically used to describe focusing geometries and can be adapted for the case of MADs working at a single energy as well as in a limited energy range. With this construction it is also possible to quantify and optimize the walk of the beam along non‐central crystals which is inevitable in certain detector designs. The results of this geometrical inspection are correlated with a real detector design that is implemented at the ALBA synchrotron facility in Spain. An error budget is given to estimate the influence and amount of tolerance of the manufacturing process.