Imaging doped silicon test structures using low energy electron microscopy.

Development of in situ characterization of two-dimensional materials grown on insulator substrates with spectroscopic photoemission and low energy electron microscopy

Recent advances in imaging of properties and growth of low dimensional structures for photonics and electronics by XPEEM

Low Energy Electron Microscopy (LEEM), and its close cousin Photo Electron Emission Microscopy (PEEM) have evolved from curiosities in the hands of physicists, to powerful tools for dynamic materials analysis. Invented in 1962, and first successfully realized in 1985, there are about 30 combined LEEM/PEEM instruments in the world today, in addition to about an equal number of PEEM-only instruments. Most of these instruments follow a design that is now almost 20 years old. The most advanced instruments are located at synchrotron radiation facilities, but they are relatively few in number, and not readily available to the general user. In the meantime, the field of electron microscopy is undergoing revolutionary advances fueled by dual breakthroughs in electron energy filtering and aberration correction. Similarly, the field of quantum optics is developing ever more powerful light sources in the Vacuum Ultra Violet (VUV) and soft X-ray ranges that do not depend on massive investments in national infrastructure (i.e. synchrotrons), but deliver their photons in a standard laboratory. These advances from two very different fields will combine to set the stage for the development of LEEM and PEEM over the next decade. Aberration correction will improve LEEM resolution from 5–10 nm today, to 1.5–2 nm in the near future, enough to resolve individual unit cells in the famous Si(111)-(7×7) surface, or -probably more important- sufficient to resolve the structure of nanoscale features such as magnetic domain walls. In PEEM the spatial resolution will improve from ∼ 20 nm today to 4–5 nm, while at the same time improving transmission by a factor ∼10. Energy filtering, today mostly used by synchrotron-based instruments, will be ubiquitous, powerful, simple, and relatively inexpensive.

A new aberration-corrected, energy-filtered LEEM/PEEM instrument. I. Principles and design

Low-Energy Electron Microscopy

The Photoelectron Emission Microscope (PEEM) and Low Energy Electron Microscope (LEEM) are parallel-imaging electron microscopes with highly surface-sensitive image contrast mechanisms. In PEEM, the electron yield at the illumination wavelength determines image contrast, in LEEM, the intensity of low energy (< 100 eV) electrons back-diffracted from the surface, as well as interference effects, are responsible for image contrast. Mirror Electron Microscopy is also possible with the LEEM apparatus. In MEM, no electron penetration into the solid occurs, and an image of surface electronic potentials is obtained.While the emission microscope techniques named above are not high resolution methods, the unique contrast mechanisms, the ability to use thick single crystal samples, their compatibility with uhv surface science methods and new material-growth methods, coupled with real-time imaging capability, make them very useful.These microscopes do not depend on scanning probes, and some are compatible with pressures up to 10-3 Torr and specimen temperatures above 1300K.

Defocus in cathode lens instruments

Surface studies by low-energy electron microscopy (LEEM) and conventional UV photoemission electron microscopy (PEEM)

A Contrast Transfer Function approach for image calculations in standard and aberration-corrected LEEM and PEEM

A brief history of PEEM

This article reviews laterally resolved x-ray photoemission spectroscopy (XPS) with a direct imaging photoemission electron microscope (PEEM). Applications of photoelectron spectroscopy with a sophisticated PEEM, a spectroscopic photoemission and low energy electron microscope (SPELEEM), are also given. The results of SPELEEM measurements from self-organized InAs nanocrystals are compared to conventional photoelectron spectral analyses. This comparison demonstrates that photoelectron spectroscopy with the SPELEEM is a reliable way to obtain information on the electronic structure of a sample from a sub-100 nm-sized area.KeywordsGaAs SubstrateCore LevelLateral ResolutionElectron Energy Loss SpectroscopyCore Level SpectrumThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Spectroscopic photoemission and low energy electron microscope (SPELEEM) improved its performance after installation at BL17SU/SPring-8, where a multipolarization-mode undulator is employed to produce circularly and linearly polarized soft x rays. This undulator enables us to study the domain structures of ferromagnetic and antiferromagnetic materials by x-ray magnetic circular dichroism and x-ray magnetic linear dichroism. SPELEEM is used to study light elements (C, N, and O), 3d transition-metal elements and 4f rare earth elements, utilizing a wide range of photon energies. The two cylindrical mirrors adopted in front of SPELEEM ensure an illumination area of 14 x 14 microm(2) on the samples. The lateral resolution of a secondary electron photoemission electron microscope image is estimated to be better than 85 nm, whereas the energy resolution of the instrument is better than 0.4 eV.

Catalysis is a hot topic in research with the focus on finding catalysts that show better activity or selectivity on processes on technological or industrial interest. The use of model systems of applicable materials has proven to be a successful approach in the last decades to obtain information on the fundamental properties of these materials, leading eventually to a better understanding how real catalysts work. This knowledge is extremely important in the sense that it allows an optimization of the catalyst composition, thus leading to a rational design of new materials. For these fundamental studies, a variety of probing techniques such as X-ray photo-electron spectroscopy, scanning tunnel microscopy, and temperature programmed desorption have been applied. In this article, we discuss how low energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) can contribute to the fundamental understanding of relevant surface processes taking place on model catalysts. Also, the capability of these techniques on addressing open questions in catalysis is discussed.

The application of PhotoEmission Electron Microscopy (PEEM) and Low Energy Electron Microscopy (LEEM) techniques to the study of the electronic and chemical structures of ferroelectric materials is reviewed. Electron optics in both techniques gives spatial resolution of a few tens of nanometres. PEEM images photoelectrons, whereas LEEM images reflected and elastically backscattered electrons. Both PEEM and LEEM can be used in direct and reciprocal space imaging. Together, they provide access to surface charge, work function, topography, chemical mapping, surface crystallinity, and band structure. Examples of applications for the study of ferroelectric thin films and single crystals are presented.

Medipix 2 detector applied to low energy electron microscopy