Design of a spectroscopic low-energy electron microscope

Veneklasen, Lee H.

doi:10.1016/0304-3991(91)90139-w

Cited by 72 publications

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“…From a thermodynamic perspective, faceting induced by the formation of a surface reconstruction is very similar to faceting induced by impurity adsorption. Faceting of systems under adsorption is common [6,12], and thus our observations in principle are important for many different systems.The LEEM used in these experiments is discussed elsewhere [13,14]. The silicon specimens used in this experiment were cut and polished along orientations slightly away from [111] toward [211] [2].…”

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Crossover from metastable to unstable facet growth on Si(111)

et al. 1993

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Vicinal SiC 111) surfaces misoriented towards the [211] direction facet reversibly upon cooling through the (1x1) to (7x7) reconstructive phase transition. We have used low-energy electron microscopy to examine the kinetics of this phase separation. Nucleation and growth of facets occur when the surfaces are quenched just below the phase boundary. However, at lower temperatures we find evidence for the existence of a spinodal which divides the faceting kinetics into unstable and metastable regions. The location of the spinodal is consistent with previous measurements of Si (111) step energetics.PACS numbers: 68.35.Md, 61.16.Bg, 81.60.Cp, 82.65.Dp As surfaces are becoming better characterized, the importance of surface morphology in determining surface characteristics is becoming increasingly evident [1][2][3][4][5][6]. A dramatic manifestation of the variability of surface morphology is "faceting" in which a flat surface breaks into a hill-and-valley structure, thus increasing total area. One of the most thoroughly studied of the faceting systems is vicinal SiC 111) [2,3]. Here surfaces which consist of a uniform array of steps at high temperature facet into singular (111) regions and step "bunches" at low temperature. The faceting is initiated by a change in the surface structure [from (lxl) to (7x7) periodicity], which occurs in a strongly first-order transition at about 870 °C on singular, unstepped surfaces. This faceting is reversible, and there is a well-defined temperature-orientation phase diagram [2] which determines the temperature dependence of the average spacing between steps in a step bunch. In this paper we discuss our low-energy electron microscopy (LEEM) observations of the kinetics of the faceting of these Si surfaces.The principal result of this paper is that the analogy of faceting with phase separation extends also to the kinetics. In previous work we have focused on the nucleation and growth of facets near the thermodynamic phase boundary, comparing observations with the predictions of the classical theories of nucleated facet growth by Mullins [7,8]. However, in systems which phase separate there is often a sharp transition between temperature regimes in which regions of a second phase nucleate and grow within the first, and lower temperatures where the system is unstable with respect to spontaneous decomposition everywhere into two phases [9]. The line separating these two kinetic regimes is called the spinodal The existence of a spinodal is particularly important in explaining the decomposition of metal alloys [10]. For example, microscopy studies often show marked changes in the morphology of phase separation as a function of quench conditions [11]. Here we present evidence for the existence of a spinodal for vicinal SiC 111).We emphasize at the outset that we expect our observations and arguments to apply generally. From a thermodynamic perspective, faceting induced by the formation of a surface reconstruction is very similar to faceting induced by impurity adsorption. Faceting of sy...

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“…The LEEM used in these experiments is discussed elsewhere [13,14]. The silicon specimens used in this experiment were cut and polished along orientations slightly away from [111] toward [211] [2].…”

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Crossover from metastable to unstable facet growth on Si(111)

et al. 1993

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“…Such analyzers were also combined with PEEM. Systems with 90°analyzer 26) and 180°a nalyzer 6) have been built and successfully operated. A combination of two 90°analyzers has been proposed, 27) as has a system of two opposite concentric spherical deflectors connected by a relay lens.…”

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Nanoscale Imaging and Spectroscopy with XPEEM

Heun

2005

Journal of The Surface Science Society of Japan

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The continuous miniaturization and increasing complexity of the materials used in modern technology requires to have access to chemical composition, electronic structure, magnetization, and fluctuations in these properties at sub-micron and nanometer scales. X-ray photoemission electron microscopy (XPEEM) can provide this information. The recent years have seen a strong increase in XPEEM activities worldwide. This paper reviews the present situation and future developments of XPEEM in combination with synchrotron radiation. In particular, the role of energy filtering, aberration correction, and temporal resolution is discussed. 1．IntroductionX-ray photoelectron spectroscopy (XPS) and the related technique , X-ray absorption spectroscopy (XAS), are powerful tools for the analysis of surfaces, as widely discussed in this issue. In a traditional experimental setup, the spectroscopic signal is obtained from a spot of some 100 µm to millimeters in diameter, and therefore averages over this area. On the other hand, the progress in modern nanotechnology has fueled an evergrowing demand to perform XPS and XAS from areas as small as the smallest building blocks of those nanostructures . This has triggered the development of special instruments which combine spectroscopy and microscopy and allow to perform XPS and XAS with the highest possible lateral resolution of less than 100 nm. 1)More than 10 years ago, two basic, complemetary design principles have been identified to achieve this goal:2) the scanning and the direct imaging type instruments. In the scanning type instruments the photon beam is demagnified, i.e. the X-rays are focused by an optical system (like a Fresnel zone plate or a Schwarzschild objective) on a small spot on the sample. The photoelectrons excited from this area are then collected by a detector. The lateral resolution of the instrument is given by the size of the illuminated area. A surface map can be obtained by scanning the sample relative to the beam. More details of this kind of instruments can be found in the article of T. Munakata in this issue.

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“…3 Over the last 3 decades PEEM ͑see Ref. 4͒ and LEEM have been subjects of intense instrumental efforts, [5][6][7][8][9][10][11][12] leading to additional imaging techniques with elemental 13 and magnetic sensitivity. 14,15 Nevertheless, the application of these techniques has not been widespread.…”

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The novel surface science instrument: Double reflection electron emission microscope

Grzelakowski

1999

Review of Scientific Instruments

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Articles you may be interested inDevelopment of compact field emission scanning electron microscope equipped with multiwalled carbon nanotube bundle cathode A universal UHV instrument, the double reflection electron emission microscope ͑DREEM͒, for surface imaging, diffraction, and local ͑1 m resolution͒ measurements is presented. DREEM consists of three fully electrostatic lens systems: electron gun column, immersion objective lens, and imaging column. The novel illumination system incorporates an electron microreflector in the back focal plane of the objective, where the perpendicular optical axes of the electron gun and imaging column cross. The electron microreflector consists of the tip of a ͑001͒-oriented single-crystalline W wire with a face of area 200 m 2 . The primary electrons of energy from 1 to 6 keV elastically reflect from the W tip surface and are decelerated between the objective and grounded sample to the desired impact energy from 0 eV to 5 keV. Numerous contrast mechanisms are expected for image formation with DREEM including topographic, magnetic, chemical ͑Auger, core level͒, phase shift, and work function. The instrument is capable of operating in low energy electron diffraction, mirror electron microscopy, low energy electron emission microscope, and photoelectron emission microscope modes. The first results obtained with the DREEM are presented.

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Design of a spectroscopic low-energy electron microscope

Cited by 72 publications

References 3 publications

Crossover from metastable to unstable facet growth on Si(111)

Crossover from metastable to unstable facet growth on Si(111)

Nanoscale Imaging and Spectroscopy with XPEEM

The novel surface science instrument: Double reflection electron emission microscope

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