Photoemission electron microscopy

X-rays are shone onto a sample to eject photoelectrons. These are collected and focused onto a phosphor screen to produce a magnified, real time, high-resolution image of the distribution of elements and/or magnetic domains over the sample surface. 

This technique generally requires UHY An X-ray beam from an anode or synchrotron source is used to excite photoelectrons from the sample. These pass through a series of electrostatic lens which focus them to form a magnified real time image of photoelectron distribution on a phosphor screen in a maimer that is analogous to optical microscopes but which is element specific. This image can either be viewed directly by eye or with a CCD camera interfaced to image analysis software. 

The tunable photon energies available at a synchrotron source can be used to significantly enhance the elemental contrast available in PEEM by choosing a photon energy that corresponds to an absorption edge of a particular element of interest, thus greatly increasing the number of photoelectrons emitted from those areas that specifically contain that element. 

By using circularly polarized X-rays from a synchrotron source the intensity of photoemission becomes dependent on the magnetisation of the sample. This can be used to provide element specific magnetic contrast for imaging magnetic domains whose behaviour can then be studied in real time. 

Topographical features of the sample produce distortions in the image and this effect can be used to provide additional topographical contrast. 

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With certain critical Pco/Poi ratios, structural oscillations can be observed [306]. Patterns of stationary and/or traveling waves can actually be seen by means of photoemission electron microscopy (see Ref. 313, and note Section XVIII-7B. Such behavior can be modeled mathematically (e.g.. Refs. 214, 314). 

S. Kelling, S. Cerasari, H.H. Rotermund, G. Ertl, and D.A. King, A photoemission electron microscopy (PEEM) study of the effect of surface acoustic waves on catalytic CO oxidation over Pt(110), Chem. Phys. Lett. 293, 325-330 (1998). 

Scanning Tunneling Microscopy (STM) Photoemission Electron Microscopy (PEEM) Ellipsometry Microscopy for Surface Imaging (EMSI)... 

Low Energy and Photoemission Electron Microscopy (LEEM, PEEM)... 

Figure 7.23 Ordering of adsorbates on a surface into islands gives rise to regions of different work function, which can be imaged because of the associated differences in photoelectron intensity. The principle forms the basis of photoemission electron microscopy (PEEM). The same principle underlies the imaging of single molecules in the field electron microscope (FEM) (see also Fig. 7.9).

NEXAFS experiments on NOM can be conducted in several modes that differ in the type of detected particle and objectives of the experiment transmission (X rays transmitted through the sample), fluorescence (fluorescent X rays due to absorption of the X-ray beam), or electron yield (photo-emitted electron) (Sparks, 2003). Alternatively, the techniques can be divided into full-field applications such as transmission X-ray microscopy (TXM) and X-ray photoemission electron microscopy (PEEM), in comparison to scanning techniques such as scanning transmission X-ray microscopy (STXM) and scanning photoemission microscopy (SPEM) that provide spatial information of elemental forms. 

PACS PCA PDB PEEM PESTM PET PrP Picture Archiving and Communication Systems Principal Component Analysis Protein Data Bank Photoemission Electron Microscopy STM Photoemission Spectroscopy Positron Emission Tomography Prion Protein... 

Several ways exist to image these regions of different work function. SEM and FEM have been discussed earlier in this chapter. As an alternative, scanning photoemission microscopy is carried out by scanning a focused UV beam (beam diameter 0.5 pm) over the surface and recording the photoemission intensity point by point. This is of course a slow procedure, but much faster imaging in real time becomes available if the electrons are collected from the entire surface in parallel, as is carried out in photoemission electron microscopy (PEEM). The lateral resolution of this technique is presently around 200 nm, but by using... 

Fig. 28. Sequence of snapshots of the spatial pattern evolution on a Pt(100) surface during oscillatory CO oxidation as recorded by photoemission electron microscopy. (From Ref. 136.)...

Dip-pen nanolithography has been employed to obtain magnetic nanopattems of y-Fe203 nanocrystals on mica and silicon substrates. The chemical and magnetic nature of the patterns have been characterized employing low-energy electron microscopy, x-ray photoemission electron microscopy, and magnetic force microscopy measurements. 2004 American Institute of Physics. 

In a recent study, photoemission electron microscopy (85) was used to reveal remarkable patterns of spaciotemporal variations, as shown in Fig. 5 (86). These patterns are similar to those observed with a homogeneous solution in which the Belousov-Zhabotinsky reaction (97) is occurring. 

M. Mundschau, M. E. Kordesch, B. Rausenberger, W. Engel, A. M. Bradshaw, and E. Zeitler, Real-time observation of the nucleation and propagation of reaction fronts on surfaces using photoemission electron microscopy. Surf. Sci., 227 (1990) 246. 

The lateral chemical and topographical resolution of the morphology was investigated with atomic-force microscopy (AFM) and X-ray photoemission electron microscopy (XPEEM). 

Abstract The controlled in-situ deposition of sexiphenyl (6P) on the (2x1) oxygen reconstruction of Cu (110) is shown to give rise to the ordered growth of large anisotropic needle-like structures on the surface. Photoemission electron microscopy (PEEM) and atomic force microscopy (AFM) results are presented for the growth of 6P (20-3) crystalline needles for a range of substrate temperatures. In addition, desorption and other interesting phenomena are discussed. 

Scholl A, Ohldag H, Nolting F, Stohr J, Padmore HA (2002) X-ray photoemission electron microscopy, a tool for the investigation of complex magnetic structures. Rev Sci Instrum 73 (3, Pt. 2) 1362-1366... 

In general, except for such idealized cases as just described, the diffusion coefficient for adsorbates will be sensitively affected by the surface structure and the coverage. Nevertheless, data derived on larger scales by macroscopic techniques (such as photoemission electron microscopy (PEEM) [42]) will be of relevance for modeling surface reactions on these scales. 

The H2 + O2 reaction on Pt(l 11), discussed in Section 6.4, had already demonstrated that a nonlinear reaction system may cause the formation of propagating concentration waves with typical length scales of >1 pm, given by the diffusion length of the adsorbates. Imaging of these features may be achieved by photoemission electron microscopy (PEEM) [14] or by optical techniques [15]. 

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