Photoelectron microscopy

One of the more recent advances in XPS is the development of photoelectron microscopy [ ]. By either focusing the incident x-ray beam, or by using electrostatic lenses to image a small spot on the sample, spatially-resolved XPS has become feasible. The limits to the spatial resolution are currently of the order of 1 pm, but are expected to improve. This teclmique has many teclmological applications. For example, the chemical makeup of micromechanical and microelectronic devices can be monitored on the scale of the device dimensions. 

Birrell, G. B., Hedberg, K. K., and Griffith, P. H. (1987) Pitfalls of immunogold labeling analysis by light microscopy, transmission electron microscopy, and photoelectron microscopy. J. Histochem. Cytochem. 35, 843-853. 

The simple estimations show that the uncertainty principle limits the spatial resolution of photoelectron microscopy on the level 20-30 A for photoion microscopy this is below 1 A. 

The magnification attended in the experiment with the photoelectron microscope was M = 10s, and the spatial resolution was around 30 nm, which proved sufficient for the visualization of individual color centers in a LiF crystal with the concentration of such centers less than 10l7cm 3. The results obtained in Ref. 9 may be considered the first successful implementation of laser resonance photoelectron microscopy possessing both subwavelength spatial resolution and chemical selectivity (spectral resolution). It will be necessary to increase the spatial resolution of the technique by approximately an order of magnitude and substantially improve its spectral resolution by effecting resonance multistep photoionization by means of tunable ultrashort laser pulses. 

Femtosecond photoion (photoelectron) microscopy combines the merits of two types of microscopy the high spatial resolution of ion projective microscopy and the high spectral (energy) resolution of optical spectroscopy. From this point of view, photoion microscopy is an interesting example of wave-corpuscular microscopy. Indeed, there are two well-known types of microscopy wave (optical) and corpuscular (electron, ion). 

We have used both transmission electron microscopy (TEM) and Raman spectroscopy to characterize the different DWNTs samples. TEM allows direct imaging of the DWNTs and gives indications for the presence of other species along with the DWNTs. In the TEM images, we seldom encountered SWNTs or MWNTs. Besides providing information on the nature and dimensions of DWNTs, Raman spectroscopy helps to characterize the purity and quality of the DWNTs. Electron energy loss spectroscopy (EELS), carried out in a high-resolution electron microscope, and X-ray photoelectron microscopy have been employed to determine the elemental composition of the DWNTs. 

Miscellaneous Physical Chemistry. A kinetic study has been made of the electrochemical reduction of /8-carotene. The photoelectron quantum yield spectrum and photoelectron microscopy of /3-carotene have been described. Second-order rate constants for electron-transfer reactions of radical cations and anions of six carotenoids have been determined. Electronic energy transfer from O2 to carotenoids, e.g. canthaxanthin [/8,/3-carotene-4,4 -dione (192)], has been demonstrated. Several aspects of the physical chemistry of retinal and related compounds have been reported, including studies of electrochemical reduction, the properties of symmetric and asymmetric retinal bilayers, retinal as a source of 02, and the fluorescence lifetimes of retinal. Calculations have been made of photoisomerization quantum yields for 11-cis-retinal and analogues and of the conversion of even-7r-orbital into odd-TT-orbital systems related to retinylidene Schiff bases. ... 

The photoelectron microscopy results described above were necessarily acquired in vacuum. Under such conditions there is no doubt that the Na is present on the Pt surface as sodium metal. However, under reaction conditions, this cannot be the case it is to be expected that the alkali would be present as a submonolayer quantity of surface compound, and indeed this is just what is observed. Furthermore, also in accordance with expectation, the nature of the alkali promoter compound is dependent on the composition of the gas atmosphere. Figure 7 shows postreaction XPS and XANES spectra acquired from Pt/Na P" alumina EP samples after exposure to reaction conditions and without exposure to laboratory atmosphere for the Pt-catalyzed reactions NO-fpropene [Figure 7(a)] and 02-fpropene [Figure 7(b)], respectively. In the first case the promoter phase consists of a mixture of NaN02 and NaNOs, in the second case it consists of Na2C03. This is important... 

Figure 6 Photoelectron microscopy of Na electro-pumped to a Pt catalyst film (a) showing up-welling of Na from a surface source upon switching from positive to negative catalyst potential and (b) showing time dependence of Na spillover.

Olefins.—Experimental results have been explained by assuming the existence of a number of chemisorbed states from complete dissociation through bound methylene and vinyl groups to 77-complexes. The wealth of material cannot be detailed here. In summary it can be seen that for all adsorptives the adsorbate may take a number of forms and each may occur over a range of adsorption energies. The possibilities for the spillover of dissociated species are more readily visualized than for the associated types. It must be supposed that for the switch to take place the valency state of the adsorbate on the good adsorber (as found by photoelectron microscopy, for instance) should be particularly appropriate. 

An experimental study on the oxidation of alloys containing 0-9 mass% Cr and 0-1 mass% Si in carbon dioxide at 500°C has been reported by [1982Mos], Several experimental techniques were used for this investigation (X-Ray, TEM, SEM, Photoelectron microscopy), fliey studied flic silicon distribution in the alloys and compared the results with theoretical predictions by an oxidation model. An attempt to grow materials with a eutectic composition in this ternary system by directional soUdrfication was made by [1978Hao]. However, the alloys were found to have no eutectic. 

X-ray diffraction (XRD), SEM and TEM, X-ray absorption spectroscopy (XAS), X-photoelectron microscopy (XPS), Raman Spectrum are the most commonly used techniques to characterize the composition and crystal phase of electrocatalysts. Here, we give only several examples to illustrate the usage of these tools. 

Figure 12.2 Dependence of sampling depth on the angle of sample tilt in X-ray photoelectron microscopy. ...

X-rays) in X-ray photoelectron microscopy, also known as electron spectroscopy for chemical analysis (ESCA). 

Abbreviations AES, Auger emission spectrometry CRM, Certified reference material DL, Detection limit ED, Energy dispersive ESRF, European Synchrotron Radiation Facility EXAES, Extended X-ray absorption fine structure NEXAFS, Near edge X-ray absorption fine structure PCI, Phase contrast imaging RM, Reference material SR, Synchrotron radiation SRM, Standard reference material TXRF, Total reflection X-ray fluorescence XANES, X-ray absorption near edge structure XAS, X-ray absorption spectrometry XDM, X-ray diffraction microscopy XFCT, X-ray fluorescence computerized microtomography XPEEM, X-ray photoelectron microscopy XPS, X-ray photoelectron spectrometry XRD, X-ray diffraction XRF, X-ray fluorescence... 

Doh WH, Gregoratti L, Amati M et al (2013) Scanning photoelectron microscopy study of the Pt/phosphoric-acid-imbibed membrane interface under polarization. ChemElectroChem 1 180-186... 

Historically, the lack of imaging capabilities has hampered polymer characterisation by XPS. The combination of microscopy and spectroscopy has been the goal of a number of groups exploring photoelectron microscopy with X-ray or synchrotron radiation sources. The first real step towards imaging XPS (iXPS) was in 1988 (VG ESCAscope). The system allowed obtaining 2D spatial maps with a lateral resolution of < 10 /xm. The second generation of this instrument achieved a spatial resolution of approximately 2 /txm [764,769]. 

Dickie and co-workers [27] derivitised surface hydroxy groups on acrylic copolymers with ammonia then characterised them by x-ray photoelectron microscopy. 

Table 9.7 Multiple technique polymer studies - infrared spectroscopy -x-ray photoelectron microscopy...

Techniques that have been applied include time of flight static secondary ion mass spectrometry (SSIMS)/ " low energy ion scattering spectromehy, x-ray photoelectron microscopy scanning electrochemical microscopy (SECM), laser ionization mass spectrometry, surface enhanced infrared reflection spectroscopy, Fourier Transform infrared spechoscopy and nuclear magnetic resonance spectroscopy. ... 

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