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Journal articles on the topic 'LEED (low energy electron diffraction)'

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Published: 4 June 2021

Last updated: 6 February 2022

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1

Qian, W., and J. C. H. Spence. "Theory of transmission low-energy electron diffraction." Proceedings, annual meeting, Electron Microscopy Society of America 51 (August 1, 1993): 696–97. http://dx.doi.org/10.1017/s0424820100149313.

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Interpretation of the images from a point source electron microscope requires a detailed analysis of transmission low energy electron diffraction. Here we present a general approach for solutions to the mixed Bragg-Laue case in transmission LEED (100-1000eV), based on the dynamical diffraction theory of Bethe. However, the validity of the dynamical diffraction theory to low energy electrons can be justified by its connection to the band theory for low energy crystal electrons.Assume that the incident beam forms a plane wave and the crystal is a thin slab. According to Bethe, the total electron wavefield within crystal can be written as a linear combination of Bloch waves (equation 1). The Bloch wave excitation coefficients b(j) can be determined by matching the boundary conditions, the wave amplitudes Cg(j) and the wave vectors k(j) for each Bloch wave can be obtained by solving the time independent Schrodinger equations (equation 2).

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2

Bauer, E., A. Pavlovska, and I. S. T. Tsong. "In Situ Nitride Growth Studies by Low Energy Electron Microscopy (LEEM) and Low Energy Electron Diffraction (LEED)." Microscopy and Microanalysis 3, S2 (August 1997): 611–12. http://dx.doi.org/10.1017/s1431927600009946.

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Nitride films play an increasing role in modern electronics, for example silicon nitride as insulating layer in Si-based devices or GaN in blue light emitting diodes and lasers. For this reason they have been the subject of many ex situ electron microscopic studies. A much deeper understanding of the growth of these important materials can be obtained by in situ studies. Although these could be done by SEM, LEEM combined with LEED is much better suited because of its excellent surface sensitivity and diffraction contrast. We have in the past studied the high temperture nitridation of Si(l11) by ammonia (NH3)and the growth of GaN and A1N films on Si(l11) and 6H-SiC(0001) by depositing Ga and Al in the presence of NH3 and will report some of the results of this work for comparison with more recent work using atomic nitrogen instead of NH3.

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3

Ichinokawa, Takeo. "Scanning Low-Energy Electron Diffraction Microscopy Combined with Scanning Tunnling Microscopy." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 1 (August 12, 1990): 302–3. http://dx.doi.org/10.1017/s0424820100180264.

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A ultra-high vacuum scanning electron microscope (UHV-SEM) with a field emission gun (FEG) has been operated in an energy range of from 100 eV to 3 keV. A new technique of scanning low energy electron diffraction (LEED) microscopy has been added to the other techniques: scanning Auger microscopy (SAM), secondary electron microscopy, electron energy loss microscopy and the others available for the UHV-SEM. In addition to scanning LEED microscopy, a scanning tunneling microscope (STM) has been installed in the UHV-SEM-.The combination of STM with SEM covers a wide magnification range from 105 to 107 and is very effective for observation of surface structures with a high resolution of about 1 Å.A UHV-FEG-SEM is equipped in a chamber in which the vacuum is better than 2×10-10 Torr. A movable cylindrical mirror analyzer (CMA), a two dimensional detector of diffracted LEED beams, an ion gun and a deposition source are installed in this chamber. The concept of the scanning LEED microscope is comprised of two steps: (1) the formation of a selected area LEED pattern and (2) the generation of raster images with information contained in the diffraction pattern. In the present experiment, the LEED detector assembly shown in Fig.l has been used; it consists of two hemisherical grids, a two-stage channel-plate amplifier and a position-sensitive detector. The selection of one (or more) diffracted beam is performed electronically by a window using the two-dimensional analogue comparators. The intensity of a particular beam selected by the window modulates the brightness of the scanning image and a dark field image sensitive to the surface structure is formed. The experimental spatial resolutions of 150 Å and 500 Å have been attained at the primary electron energy 1 keV and 250 eV, respectively.

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4

MORITZ, W., J. LANDSKRON, and T. GRÜNBERG. "ANALYSIS OF THERMAL VIBRATIONS AND INCOMMENSURATE LAYERS BY LOW ENERGY ELECTRON DIFFRACTION." Surface Review and Letters 04, no. 03 (June 1997): 469–78. http://dx.doi.org/10.1142/s0218625x97000456.

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The multiple scattering theory of LEED is briefly reviewed, and recent developments concerning the analysis of thermal vibrations with LEED and the analysis of lattice modulations in incommensurate layers are discussed. Usually only isotropic thermal vibrations have been considered in LEED structure analyses. This restriction can be overcome by an extension of the theory to anisotropic and anharmonic vibrations, allowing not only a higher precision in the determination of structure parameters but also the study of dynamical processes with LEED. In the case of incommensurate layers the satellite reflections arise from multiple diffraction as well as from modulations in the adsorbate or substrate lattice. It is shown that an approximation can be introduced in the multiple scattering formalism to calculate the satellite intensities. The method can be applied to incommensurate layers as well as to higher order commensurate layers.

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5

Seubert, A., D. K. Saldin, J. Bernhardt, U. Starke, and K. Heinz. "Avoidance of ghost atoms in holographic low-energy electron diffraction (LEED)." Journal of Physics: Condensed Matter 12, no. 26 (June 13, 2000): 5527–40. http://dx.doi.org/10.1088/0953-8984/12/26/301.

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6

Goritzka, Jan C., Benjamin Herd, Philipp P. T. Krause, Jens Falta, J. Ingo Flege, and Herbert Over. "Insights into the gas phase oxidation of Ru(0001) on the mesoscopic scale using molecular oxygen." Physical Chemistry Chemical Physics 17, no. 21 (2015): 13895–903. http://dx.doi.org/10.1039/c4cp06010e.

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We present an extensive mesoscale study of the initial gas phase oxidation of Ru(0001), employing in situ low-energy electron microscopy (LEEM), micro low-energy electron diffraction (μ-LEED) and scanning tunneling microscopy (STM).

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7

Chamberlin, S. E., C. J. Hirschmugl, H. C. Poon, and D. K. Saldin. "Geometric structure of (011)(21) surface by low energy electron diffraction (LEED)." Surface Science 603, no. 23 (December 2009): 3367–73. http://dx.doi.org/10.1016/j.susc.2009.09.029.

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8

Rous, P. "The tensor LEED approximation and surface crystallography by low-energy electron diffraction." Progress in Surface Science 39, no. 1 (1992): 3–63. http://dx.doi.org/10.1016/0079-6816(92)90005-3.

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9

Venables, J. A., C. J. Harland, P. A. Bennett, and T. E. A. Zerrouk. "Electron diffraction in UHV SEM, REM, and TEM." Proceedings, annual meeting, Electron Microscopy Society of America 52 (1994): 594–95. http://dx.doi.org/10.1017/s0424820100170700.

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Electron diffraction techniques are widely used in Surface Science, with the main aim of determining atomic positions in surface reconstructions and the location of adsorbed atoms. These techniques require an Ultra-high vacuum (UHV) environment. The use of a focussed beam in UHV electron microscopes in principle allows such techniques to be applied on a microscopic scale. Most obviously this has been achieved in the Low Energy Electron Microscope (LEEM), where the corresponding diffraction technique, LEED, can now be used to investigate local areas with different surface structures, and to follow both temperature and time evolution of these local structures. Some other geometries can be used to achieve similar goals. If the incident energy is raised, the incidence angle has to be moved from normal towards glancing, so that the 'perpendicular' energy is kept within the LEED range of 10-100 eV. Several reflection (REM) and scanning (SEM) instruments have been built with energies between 5 and lOOkeV. In general, the addition of RHEED to an UHV-SEM with Auger Electron Spectroscopy (AES) forms a very useful tool in Surface Science.

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10

VAN HOVE, M. A. "COMPLEX SURFACE STRUCTURES FROM LEED." Surface Review and Letters 03, no. 02 (April 1996): 1271–84. http://dx.doi.org/10.1142/s0218625x9600228x.

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The complexity of surface structures solved routinely with low-energy electron diffraction (LEED) has increased dramatically in recent years. This paper describes the evolution of the complexity that has become achievable, provides illustrations of complicated structures solved recently, and discusses the outlook for the future.

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11

YU, Z. X., S. Y. TONG, SHIHONG XU, SIMON MA, and HUASHENG WU. "STRUCTURE DETERMINATION OF THE 1 × 1GaN(0001) SURFACE BY QUANTITATIVE LOW ENERGY ELECTRON DIFFRACTION." Surface Review and Letters 10, no. 06 (December 2003): 831–36. http://dx.doi.org/10.1142/s0218625x03005657.

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A quantitative structural determination of the Ga-polar 1×1 (0001) surface of GaN is performed by quantitative low energy electron diffraction (LEED). The global best-fit structure is obtained by a new frozen LEED approach connected to a simulated annealing algorithm. The global minimization frozen (GMF) LEED search finds that the ordered structure consists of 1 ML of Ga adatoms at atop sites above Ga-terminated bilayers. The Ga adatoms are bonded with a Ga–Ga bond length of 2.51 Å. The spacings within surface bilayers show a weak oscillatory trend, with the outmost bilayer thickness expanding to 0.72 Å and the next bilayer thickness contracting to 0.64 Å, compared to the bulk thickness of 0.65 Å. The interlayer spacing between the first and second bilayers is 1.89 Å, while the next interlayer spacing is 1.94 Å, compared to the bulk value of 1.95 Å. These results are compared with data from other theoretical and experimental studies.

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12

Ismail, Ismail, Rongying Jin, David Mandrus, and Earl Ward Plummer. "Surface Structural Analysis of the Layered Perovskite Ca1.9Sr0.1RuO4 by Low Energy Electron Diffraction I-V." Aceh International Journal of Science and Technology 7, no. 1 (April 21, 2018): 56–62. http://dx.doi.org/10.13170/aijst.7.1.8497.

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Abstract – The atomic structure at surface of the layered perovskite Ca1.9Sr0.1RuO4 has been studied by Low Energy Electron Diffraction (LEED) I-V. The perovskite Ca1.9Sr0.1RuO4 of single crystal was cleaved in ultra high vacuum chamber (the pressure in the chamber was about 1x10-10 Torr). The experiments were conducted at room temperature (T=300 K). The sharp LEED pattern was observed which indicates that the surface of Ca1.9Sr0.1RuO4 is flat and it is a well ordered crystal. LEED I-V data, nine equivalent beams of the layered perovskite Ca1.9Sr0.1RuO4 were recorded at room temperature. LEED I-V calculation was performed to fit experimental data to obtain the surface atomic structure. The LEED I-V analysis reveals that in the surface of the layered perovskite Ca1.9Sr0.1RuO4 the RuO6 octahedra are rotated (in-plane rotation) alternating clockwise and counterclockwise. The in-plane rotation at the surface is 11 degree which is smaller than that in the bulk (13 degree). The Ru – O(1) bond-length at the surface is found to be 1.936 Å which is about the same as in the bulk (1.939 Å). The Ru – O(2) bond length at the surface is 1.863 Å which is much shorter than that in the bulk (2.040 Å). The volume of octahedral Ru-O6 at the surface is reduced by 9% with respect to the bulk. This finding shows that the atomic structure at surface of the layered perovskite Ca1.9Sr0.1RuO4is significantly different than that in the bulk. These lattice distortions strongly influence its electronic properties. Key words: Transition Metal Oxide; Perovskite; Surface Atomic Structure; LEED I-V

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13

McRae, EC, and RA Malic. "Applications of Low-energy Electron Diffraction to Ordering at Crystal and Quasicrystal Surfaces." Australian Journal of Physics 43, no. 5 (1990): 499. http://dx.doi.org/10.1071/ph900499.

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The value of the low-energy electron diffraction (LEED) technique for the evaluation of surface ordering depends on the ability to measure the intensity profiles of diffraction beams with respect to the associated surface component of the electron momentum transfer. Beam profiles, if measured with sufficient accuracy, may be interpreted to characterise the extent of surface order (e.g. distribution of step spacings) and to differentiate between different modes of disordering (e.g. surface melting versus roughening). The ability to measure LEED intensity profiles has been enhanced by use of low-current well-defined primary electron beams in conjunction with position-sensitive detection (PSD) of the diffracted electrons. The following are examples of applications ofLEED-PSD. Compositional Ordering at Ordering Alloy CU3Au (100) and (110) Surfaces: The ordering of the (100) surface is .believed to conform to a conventional picture in which the already-ordered bulk acts as a template, but the profiles measured in the course of ordering of the (110) surface are of the shapes expected if the ordering occurred first at the surface. Disordering of Ce(111) Surface 150 K below the Bulk Melting Temperature: The intensities and profiles are inconsistent with surface .melting or roughening, but a model based on molecular dynamics simulations is not ruled out. Order and Disordering at Decagonal Quasicrystal AI65 CUI 5 C02 0 Surfaces: At room temperature the quasi crystalline order is well developed at both the 'ten-fold' surface (perpendicular to the ten-fold surface (perpendicular to the ten-fold periodic axis) and a 'two-fold' one (parallel to the ten-fold axis) as evidenced by narrow beam profiles. The ten-fold surface undergoes a disordering transition at 700 K, but the temperature dependence of the profiles is unlike that expected for the roughening transition anticipated theoretically.

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14

Gajdardziska-Josifovska, M., J. K. Weiss, and J. M. Cowley. "Energy-filtered convergent beam RHEED rocking curves from cleaved (100) surface of MgO." Proceedings, annual meeting, Electron Microscopy Society of America 49 (August 1991): 626–27. http://dx.doi.org/10.1017/s0424820100087446.

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Reflection high energy electron diffraction (RHEED) has been used extensively to observe changes in surface reconstructions by analyzing the geometry of the RHEED pattern and to monitor growth of layers in MBE systems by measuring the changes of the intensity of the specular spot with time. RHEED is also capable of yielding the structure of the surface by using dynamical diffraction theory to analyze experimental reflection rocking curves. These rocking curves trace the change in the intensity of the RHEED spots as a function of the angle of incident illumination. They are equivalent to the intensity vs. voltage curves (I-V) obtained in low energy electron diffraction (LEED) which have been used to determine most of the known surface structures. The LEED I-V curves are energy filtered and the theoretical calculations consider only the elastically-scattered electrons. The RHEED theory is also developed only for elastic scattering, but the experimental measurements so far have not been energy filtered.

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15

Spence, J. C. H., H. C. Poon, and D. K. Saldin. "Convergent-Beam Low Energy Electron Diffraction (CBLEED) and the Measurement of Surface Dipole Layers." Microscopy and Microanalysis 10, no. 1 (January 22, 2004): 128–33. http://dx.doi.org/10.1017/s1431927604040346.

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We propose the formation of LEED patterns using a highly convergent beam forming a probe of nanometer dimensions. A reflection rocking curve may then be recorded in many diffraction orders simultaneously. Multiple scattering calculations show that the intensity variations within these rocking curves is as sensitive to the parameters describing the surface dipole layer as conventional I/V scans. However the data may be collected from areas sufficiently small to avoid defects and surface steps, radiation damage controlled by use of low voltages, and the information depth selected by choice of the (constant) voltage. We briefly discuss also the application of this method to oxides and the formation of atomic-resolution scanning images in an idealized instrument in which coherent diffracted LEED orders overlap.

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16

Tong, S. Y., and Huasheng Wu. "Direct inversion of low-energy electron diffraction (LEED) IV spectra: the surface Patterson function*." Journal of Physics: Condensed Matter 14, no. 6 (January 31, 2002): 1231–36. http://dx.doi.org/10.1088/0953-8984/14/6/310.

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17

Wichtendahl, R., R. Fink, H. Kuhlenbeck, D. Preikszas, H. Rose, R. Spehr, P. Hartel, et al. "SMART: An Aberration-Corrected XPEEM/LEEM with Energy Filter." Surface Review and Letters 05, no. 06 (December 1998): 1249–56. http://dx.doi.org/10.1142/s0218625x98001584.

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A new UHV spectroscopic X-ray photoelectron emission and low energy electron microscope is presently under construction for the installation at the PM-6 soft X-ray undulator beamline at BESSY II. Using a combination of a sophisticated magnetic beam splitter and an electrostatic tetrode mirror, the spherical and chromatic aberrations of the objective lens are corrected and thus the lateral resolution and sensitivity of the instrument improved. In addition a corrected imaging energy filter (a so-called omega filter) allows high spectral resolution (ΔE=0.1 eV ) in the photoemission modes and back-ground suppression in LEEM and small-spot LEED modes. The theoretical prediction for the lateral resolution is 5 Å; a realistic goal is about 2 nm. Thus, a variety of electron spectroscopies (XAS, XPS, UPS, XAES) and electron diffraction (LEED, LEEM) or reflection techniques (MEM) will be available with spatial resolution unreached so far.

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18

Tromp, Ruud M. "Low-Energy Electron Microscopy." MRS Bulletin 19, no. 6 (June 1994): 44–46. http://dx.doi.org/10.1557/s0883769400036757.

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For surface science, the 1980s were the decade in which the microscopes arrived. The scanning tunneling microscope (STM) was invented in 1982. Ultrahigh vacuum transmission electron microscopy (UHVTEM) played a key role in resolving the structure of the elusive Si(111)-7 × 7 surface. Scanning electron microscopy (SEM) as well as reflection electron microscopy (REM) were applied to the study of growth and islanding. And low-energy electron microscopy (LEEM), invented some 20 years earlier, made its appearance with the work of Telieps and Bauer.LEEM and TEM have many things in common. Unlike STM and SEM, they are direct imaging techniques, using magnifying lenses. Both use an aperture to select a particular diffracted beam, which determines the nature of the contrast. If the direct beam is selected (no parallel momentum transfer), a bright field image is formed, and contrast arises primarily from differences in the scattering factor. A dark field image is formed with any other beam in the diffraction pattern, allowing contrast due to differences in symmetry. In LEEM, phase contrast is the third important mechanism by which surface and interface features such as atomic steps and dislocations may be imaged. One major difference between TEM and LEEM is the electron energy: 100 keV and above in TEM, 100 eV and below in LEEM. In LEEM, the imaging electrons are reflected from the sample surface, unlike TEM where the electrons zip right through the sample, encountering top surface, bulk, and bottom surface. STM and TEM are capable of ~2 Å resolution, while LEEM and SEM can observe surface features (including atomic steps) with -100 Å resolution.

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19

Horstmann, Jan Gerrit, Gero Storeck, Bareld Wit, Theo Diekmann, Dennis Epp, Kai Rossnagel, Sascha Schäfer, Simon Vogelgesang, and Claus Ropers. "Structural phase transitions and phase ordering at surfaces probed by ultrafast LEED." EPJ Web of Conferences 205 (2019): 08005. http://dx.doi.org/10.1051/epjconf/201920508005.

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We demonstrate the capability of ultrafast low-energy electron diffraction to resolve phase-ordering kinetics and structural phase transitions on their intrinsic time scales with ultimate surface sensitivity.

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20

PENDRY, J. B. "THE CASE FOR ORDER-N METHODS IN LEED THEORY." Surface Review and Letters 04, no. 05 (October 1997): 901–5. http://dx.doi.org/10.1142/s0218625x97001000.

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Low energy electron diffraction experiments have superb sensitivity to surface structure, but rely on sophisticated theory for their interpretation. Advances in computer power, and developments in the theory itself, enable us to handle surface structures of moderate complexity. For future advances we must look to a completely new approach and the case is made for order-N methods which follow the time evolution of a point source of electrons to generate all beams for all angles of incidence and all energies in one shot.

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21

Starke, U., J. Schardt, W. Weiß, G. Rangelov, Th Fauster, and K. Heinz. "Structure of Epitaxial CoSi2 Films on Si(111) Studied with Low-Energy Electron Diffraction (LEED)." Surface Review and Letters 05, no. 01 (February 1998): 139–44. http://dx.doi.org/10.1142/s0218625x9800027x.

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Expitaxial films of CoSi 2 on Si(111) were investigated by low-energy electron diffraction. Films of approximately 12 Å thickness were prepared by simultaneous deposition of Co and Si and subsequent annealing. The films were found to crystallize in CaF 2 structure in (111) orientation. Two (1×1) phases of different stoichiometry exist. The surface phase that contains more Co is found to be a CoSi 2(111) bulklike structure terminated by a Si–Co–Si trilayer. The Si-rich phase is terminated by an additional nonrotated silicon bilayer with the lower silicon atoms bound to cobalt in the first CoSi 2 layer. Consequently, these cobalt atoms have an eightfold coordination. Due to the lattice mismatch the silicide films are expanded by 0.5% in the lateral direction and contracted by 1.4% in the vertical direction.

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22

LIU, Y., J. WANG, M. H. XIE, and H. S. WU. "INCOMMENSURATE METALLIC SURFACTANT LAYER ON TOP OF InN FILM." Surface Review and Letters 13, no. 06 (December 2006): 815–18. http://dx.doi.org/10.1142/s0218625x06008967.

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The surface structure of InN film heteroepitaxially grown on a GaN buffer layer by MBE is followed by low energy electron diffraction (LEED). The metallic surfactant layers on top of the InN surfaces show an incommensurate structure rather than being disordered. The metal in the incommensurate structure induces additional diffraction spots in the LEED. Based on the Auger experiments, not only In atoms but also Ga are present on the surface of the InN films.

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23

Rochford, L. A., A. J. Ramadan, S. Holliday, T. S. Jones, and C. B. Nielsen. "The effect of fluorination on the surface structure of truxenones." RSC Advances 6, no. 71 (2016): 67315–18. http://dx.doi.org/10.1039/c6ra14158g.

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The surface structure of partially fluorinated truxenone (F₃-truxenone) molecules on Cu (111) has been probed using a combination of scanning tunneling microscopy (STM) and low energy electron diffraction (LEED).

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24

HENZLER, M. "CAPABILITIES OF LEED FOR DEFECT ANALYSIS." Surface Review and Letters 04, no. 03 (June 1997): 489–500. http://dx.doi.org/10.1142/s0218625x9700047x.

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A diffraction pattern using low or high energy electron diffraction may be employed via the (integral) intensity of the spots to derive the atomic positions within a unit of a periodic arrangement. Spot profile analysis (SPA) provides information on periodic and nonperiodic arrangements of units as superstructure domains, terraces or facets, strained regions and so on. The first point will be the instrumentation suited for that type of analysis (SPA-LEED, SPA-RHEED and ELS-LEED, the latter using high resolution electron energy loss spectroscopy simultaneously with SPA). It will be discussed how a simple, reliable and quantitative analysis is possible within the kinematic approximation. All deviations from simple structures via defects like strain, roughness, facets or dislocations produce characteristic modifications of the spot profile, so that a specific and quantitative evaluation is possible. Finally, examples of defect analysis of heteroepitaxial films with a thickness of one to many monolayers show that many defects are necessary and therefore unavoidable for misfit accommodation. Depending on growth conditions, many other defects may appear additionally; they, however, may be reduced or avoided by appropriate growth parameters. Examples are taken from films of metals, semiconductors and insulators on quite different substrates.

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Tromp, R. M., M. Mankos, M. C. Reuter, A. W. Ellis, and M. Copel. "A New Low Energy Electron Microscope." Surface Review and Letters 05, no. 06 (December 1998): 1189–97. http://dx.doi.org/10.1142/s0218625x98001523.

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Low energy electron microscopy (LEEM) has developed into one of the premier techniques for in situ studies of surface dynamical processes, such as epitaxial growth, phase transitions, chemisorption and strain relaxation phenomena. Over the last three years we have designed and constructed a new LEEM instrument, aimed at improved resolution, improved diffraction capabilities and greater ease of operation compared to present instruments.

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26

Wong, P. C., and K. A. R. Mitchell. "Studies on surfaces of Zr(0001) that contain oxygen and show (2 × 2)-type low-energy electron diffraction patterns." Canadian Journal of Physics 65, no. 5 (May 1, 1987): 464–67. http://dx.doi.org/10.1139/p87-062.

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Oxygen chemisorption on the Zr(0001) surface has been studied in the low-exposure regime with Auger electron spectroscopy and measurements of the width of a half-order low-energy electron diffraction (LEED) beam. The new observations and conclusions are as follows. (i) The diffusion of O atoms to the bulk effectively starts at around 236 °C. (ii) Oxygen adsorbs in a disordered state at room temperature and orders sufficiently to show a (2 × 2)-type LEED pattern on heating to 220 °C. (iii) With increasing O exposure, 1/4, 1/2, and 3/4 of the available adsorption sites can be systematically filled, while showing the apparent (2 × 2)-LEED pattern, prior to the establishment of an ordered (1 × 1)-O surface. (iv) The process in (iii) can be reversed by starting with the (1 × 1)-O surface and heating above 236 °C.

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27

Touge, Mutsumi, Satoru Anan, Shogo Wada, Akihisa Kubota, Yoshitaka Nakanishi, and Junji Watanabe. "Atomic-Scale Planarization of Single Crystal Diamond Substrates by Ultraviolet Rays Assisted Machining." Key Engineering Materials 447-448 (September 2010): 66–70. http://dx.doi.org/10.4028/www.scientific.net/kem.447-448.66.

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The ultra-precision polishing assisted by the ultraviolet rays irradiation was performed to achieve the atomic-scale planarization of the single crystal diamond substrates. This polishing method is a novel and simple polishing method characterizing by a quartz disk and an ultraviolet irradiation device. The principle three crystal planes of the diamond substrate were polished by this method. The polished surfaces were evaluated by an optical interferometric profilers (Wyko), an atom force microscope (AFM) and LEED (low-energy electron diffraction). The surface roughness of the polished diamond substrates was evaluated as 0.2 ~ 0.4 nmRa in (100), (110) and (111) crystal planes. The LEED (low-energy electron diffraction) patterns indicated the almost perfect crystallographic structure without the residual processed strain beneath the polished surface. In this paper, the optimum polishing condition to achieve the atomic-scale planarization of the diamond substrates has been investigated by the evaluation of LEED patterns, Wyko and AFM images. The mechanismof the ultraviolet rays assisted polishing is discussed in detail.

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28

TURTON, S., M. KADODWALA, and ROBERT G. JONES. "POSSIBLE "HOT" MOLECULE DESORPTION BY ELECTRON STIMULATED DECOMPOSITION OF DIHALOETHANES ON Cu(111)." Surface Review and Letters 01, no. 04 (December 1994): 535–38. http://dx.doi.org/10.1142/s0218625x94000606.

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The desorption of ethene from physisorbed 1, 2-dichloroethane (DCE) and 1-bromo-2-chloroethane (BCE) on Cu(111) has been observed on irradiating the surface with electrons. The techniques used were low energy electron diffraction (LEED), Auger electron spectroscopy (AES), ultraviolet photoelectron spectroscopy (UPS), and mass spectrometric detection of the desorbed species. At 110 K physisorbed DCE and BCE underwent electron capture from low energy (<1 eV ) electrons in the secondary electron yield of the surface followed by decomposition and desorption of ethene alone. The decomposition was found to be first order in the surface coverage of the physisorbed DCE/BCE. No other molecular species desorbed from the surface, a stoichiometric amount of chemisorbed halogen was deposited and no carbon was detectable at the end of the desorption. The formation of the negative ions of these molecules by electron capture of low energy electrons in the secondary electron emission from the surface and the possible dynamics by which the negative ions undergo decomposition leaving the ethene product with sufficient energy to desorb, are discussed.

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29

Poon, H. C., X. F. Hu, S. E. Chamberlin, D. K. Saldin, and C. J. Hirschmugl. "Structure of the hydrogen stabilized MgO(111)-(1×1) surface from low energy electron diffraction (LEED)." Surface Science 600, no. 12 (June 2006): 2505–9. http://dx.doi.org/10.1016/j.susc.2006.04.010.

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30

Moula, Md Golam, Shushi Suzuki, Wang-Jae Chun, Shigeki Otani, S. Ted Oyama, and Kiyotaka Asakura. "Surface structures of Ni2P (0001)—scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) characterizations." Surface and Interface Analysis 38, no. 12-13 (2006): 1611–14. http://dx.doi.org/10.1002/sia.2404.

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31

Cantero, Esteban D., Lara M. Solis, Yongfeng Tong, Javier D. Fuhr, María Luz Martiarena, Oscar Grizzi, and Esteban A. Sánchez. "Growth of germanium on Au(111): formation of germanene or intermixing of Au and Ge atoms?" Physical Chemistry Chemical Physics 19, no. 28 (2017): 18580–86. http://dx.doi.org/10.1039/c7cp02949g.

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We studied the growth of Ge layers on Au(111) under ultra-high vacuum conditions from the submonolayer regime up to a few layers with Scanning Tunneling Microscopy (STM), Direct Recoiling Spectroscopy (DRS) and Low Energy Electron Diffraction (LEED).

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32

DHESI, S. S., S. D. BARRETT, A. W. ROBINSON, and F. M. LEIBSLE. "COMBINED USE OF QUANTITATIVE LEED AND STM ON Cu(100)-c(2×2)N SURFACES." Surface Review and Letters 01, no. 04 (December 1994): 625–29. http://dx.doi.org/10.1142/s0218625x94000813.

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Quantitative low-energy electron diffraction (LEED) has been used in conjunction with Scanning Tunneling Microscopy (STM) to demonstrate that these two techniques are complementary and that quantitative LEED can be used in surface analysis without the need for computationally intensive theoretical calculations. We present LEED intensity-voltage (I-V) curves from Cu (100)-c(2×2) N surfaces and make qualitative comparisons with quantitative LEED data that exists in the literature. The implications of these comparisons are discussed with respect to other studies of this system.

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33

VAN HOVE, M. A. "ANOTHER UNUSUAL ADSORPTION SITE FOR ALKALI ADSORPTION ON A METAL, FOUND BY AUTOMATED TENSOR LEED ON A NOTEBOOK COMPUTER: ${\rm{Rh}}\left( {111} \right) - \left( {\sqrt 3 \times \sqrt 3 } \right)R30^ \circ -{\rm{Na}}$." Surface Review and Letters 01, no. 01 (June 1994): 9–13. http://dx.doi.org/10.1142/s0218625x94000035.

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The surface structure of [Formula: see text] has been analyzed with dynamical low-energy electron diffraction (LEED) at 30 K: a simple Na overlayer is found adsorbed in the unusual hcp-hollow site. LEED theory and computer power have progressed to the point where such a detailed surface structure determination, which includes fitting many structural parameters, is routinely possible even with a portable computer, in this instance a 486/25 MHz notebook computer, using automated tensor LEED.

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SEUBERT, A., and K. HEINZ. "ITERATIVE IMAGE RECOVERY IN HOLOGRAPHIC LEED." Surface Review and Letters 09, no. 03n04 (June 2002): 1413–23. http://dx.doi.org/10.1142/s0218625x02003949.

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We report that the quality of atomic images reconstructed directly within the framework of holographic low energy electron diffraction can suffer from considerable atomic displacements. These are due to serious disturbances of the holographic object wave which exist when the object owns the same translational symmetry as the arrangement of beam splitters, for example when the latter induce a substrate reconstruction. We propose and test an iterative procedure for reducing these disturbances by a hybrid combination of the holographic reconstruction and some data fitting procedure. A reliable atomic image results after only a few iteration steps.

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35

Zeng, H. C., and K. A. R. Mitchell. "Further observations with low-energy electron diffraction for the Cu(100)-(2 × 2)-S surface structure: spot-profile and multiple-scattering analyses." Canadian Journal of Physics 65, no. 5 (May 1, 1987): 500–504. http://dx.doi.org/10.1139/p87-068.

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This study involves analyses by low-energy electron diffraction (LEED) for surface structures formed by S adsorbed on the (100) surface of copper. A LEED spot-profile investigation for a surface that shows a (2 × 2) diffraction pattern, supplemented by the effects of antiphase scattering, indicates that the domain boundaries do not correspond to microregions with local c(2 × 2) structure but rather that the beam elongations observed are consistent with local regions of the c(4 × 2) type in the approach to ¼ monolayer coverage. Diffracted-beam intensity-versus-energy curves calculated for the (2 × 2), c(2 × 2), and (2 × 1) translational symmetries, for fixed adsorption sites and S–Cu interlayer spacings, show that the intensity curves of corresponding beams can remain closely independent of actual symmetry and coverage even as the polar angle of incidence θ departs from the normal (although differences between the curves do tend to increase with θ). This observation can help simplify calculations of LEED intensities from adsorption systems with large unit meshes when the adsorbed species are in a constant environment; also, it provides an economical route for checking values of θ estimated from positions of diffraction spots on conventional LEED screens. When the latter is tested on the off-normal intensity data used in our previous analysis of the Cu(100)-(2 × 2)-S surface structure (Surf. Sci. 177, 329 (1986)), θ is indicated to be modified by 1° from the previously estimated value, but this does not significantly affect the determined S–Cu nearest neighbour bond length.

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36

Shin, J., S. V. Kalinin, H. N. Lee, H. M. Christen, R. G. Moore, E. W. Plummer, and A. P. Baddorf. "Surface stability of epitaxial SrRuO3 thin films in vacuum." Journal of Materials Research 19, no. 12 (December 1, 2004): 3447–50. http://dx.doi.org/10.1557/jmr.2004.0480.

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Surface stability of nearly defect-free epitaxial SrRuO3 thin films grown by pulsed laser deposition was studied using low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and electron spectroscopies. Even after exposure to atmosphere, surfaces exhibited distinct LEED patterns providing evidence of unusual chemical stability. Surface order disappeared after heating to 200 °C in vacuum. To investigate, SrRuO3 thin films were annealed up to 800 °C in high vacuum and examined for chemical state and topography. Formation of unit-cell deep pits and the Ru-rich particles begins at low temperatures. Hydrocarbon contamination on the surface contributes to this process.

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37

IWAMI, M., N. HATTORI, T. FUJIMOTO, M. HIRAI, M. KUSAKA, T. MORII, H. WATABE, and M. WATANABE. "STUDIES OF $4{\rm H}\mbox{--}{\rm SiC}(0001){\rm Si}(\sqrt3\times\sqrt3)$ AND (0001)C(3×3) SURFACES AND THEIR METALLIZATION PROCESS BY NI USING STM, AES AND LEED." Surface Review and Letters 07, no. 05n06 (October 2000): 679–82. http://dx.doi.org/10.1142/s0218625x00000555.

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Several methods have been tried to prepare clean surfaces of 4H–SiC(0001)Si and C, whose surface atomic, or electronic, structures have been studied by LEED (low energy electron diffraction) STM (scanning tunneling microscopy) and AES (Auger electron spectroscopy). Some sequential chemical treatments, for example, agitation in an organic solvent and dipping in HF solution, followed by the heating of a SiC wafer in UHV (ultrahigh vacuum, below 10-7 Pa) at 950°C, gave either a [Formula: see text] or 3×3 superstructure, observed by LEED (low energy electron diffraction), for the SiC(0001) Si or C surface, respectively. An elongated NH4F treatment followed by a heat treatment in UHV at ~950°C gave a rather flat region to be investigated by STM, where a [Formula: see text] superstructure for the SiC(0001) Si surface has been observed. In the case of metal (Ni) atom deposition on SiC(0001) [Formula: see text] and (0001)C(3×3) surfaces, AES and LEED analysis have clarified that deposited metal atoms form islands up to ~5 Å. However, Ni atoms dispersed uniformly at the very beginning of the deposition, which means that the Ni overlayer piles up in layer followed by island growth mode.

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38

KRUPSKI, A., and S. MRÓZ. "LEED INVESTIGATION OF THE Pb AND Sb ULTRATHIN LAYERS DEPOSITED ON THE Ni(111) FACE AT T=150–900 K." Surface Review and Letters 10, no. 06 (December 2003): 843–48. http://dx.doi.org/10.1142/s0218625x03005773.

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The atomic structure of ultrathin lead and antimony layers deposited on the Ni (111) face in ultrahigh vacuum at a substrate temperature ranging from 150 to 900 K was investigated with the use of low-energy electron diffraction (LEED). LEED patterns corresponding to p(1×1), p(3×3), p(4×4), [Formula: see text] structures and p(1×1), p(2×2), [Formula: see text], [Formula: see text] structures for the adsorption of Pb and Sb, respectively, on the Ni (111) face were observed. Experimental LEED intensity-versus-energy [I(V)] spectra have been collected for the clean Ni (111) and for the [Formula: see text], [Formula: see text], [Formula: see text] structures. The I(V) curves obtained for the clean Ni (111) structure are in good agreement with experimental spectra from the literature.

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39

ATREI, A., U. BARDI, E. ZANAZZI, G. ROVIDA, M. SAMBI, and G. GRANOZZI. "STRUCTURE OF A SINGLE ATOMIC LAYER OF NICKEL DEPOSITED ON THE Pt(111) SURFACE DETERMINED BY LOW ENERGY ELECTRON DIFFRACTION." Surface Review and Letters 06, no. 02 (April 1999): 213–17. http://dx.doi.org/10.1142/s0218625x9900024x.

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The structure of ultrathin films of Ni deposited at room temperature on the Pt (111) surface has been determined by low energy electron diffraction (LEED) intensity analysis. The first monolayer of Ni grows pseudomorphically on Pt (111) despite the 11% mismatch between the lattice parameters of nickel and platinum. The results of the analysis also show that the Ni atoms occupy face-centered-cubic sites on the substrate surface. These results in part confirm previous data obtained by X-ray photoelectron diffraction, but also provide more reliable data on the site assignment.

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40

Lalmi, B., C. Girardeaux, Alain Portavoce, Bernard Aufray, and Jean Bernardini. "Reactive Diffusion of Thin Si Deposits into Ni (111)." Defect and Diffusion Forum 323-325 (April 2012): 421–26. http://dx.doi.org/10.4028/www.scientific.net/ddf.323-325.421.

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Low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and scanning tunnelling microscopy (STM) were used to study the reactive diffusion of one monolayer of silicon deposited at room temperature onto a Ni (111) substrate. We have done isochronal and isothermal kinetics by AES, and we observed in both cases a kinetics blockage on a plateau corresponding to around one third of a silicon monolayer. STM images and LEED patterns both recorded at room temperature just after annealing, reveal formation of an ordered hexagonal superstructure corresponding probably to a two-dimensional surface silicide.

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41

Rous, P. J., and J. B. Pendry. "Tensor LEED I: A technique for high speed surface structure determination by low energy electron diffraction. TLEED1." Computer Physics Communications 54, no. 1 (April 1989): 137–56. http://dx.doi.org/10.1016/0010-4655(89)90039-8.

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42

Rous, P. J., and J. B. Pendry. "Tensor LEED II: A technique for high speed surface structure determination by low energy electron diffraction. TLEED2." Computer Physics Communications 54, no. 1 (April 1989): 157–66. http://dx.doi.org/10.1016/0010-4655(89)90040-4.

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43

El-Jawad, Mohammad, Bruno Gilles, and Frederic Maillard. "Oxygen-Induced Formation of Nanopyramids on W(111)." Advanced Materials Research 324 (August 2011): 109–12. http://dx.doi.org/10.4028/www.scientific.net/amr.324.109.

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In this study, we investigated the role of oxygen in the faceting of the W(111) surface at temperatures close to T = 2000°C. For that purpose, we characterized the W(111) surface before and after the annealing step by low energy electron diffraction (LEED), reflection high energy electron diffraction (RHEED), scanning tunneling microscopy (STM), and Auger electron spectroscopy (AES). It is found that W(111) undergoes a massive reconstruction to form three sided pyramids of nanometer dimensions with mainly {211} planes as facet sides. Interestingly, the facetted W(111) surface is deprived from oxygen. We then show how the facetted W(111) surface can be used as a template to deposit platinum by molecular beam epitaxy.

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44

Bauer, Ernst, Michael Mundschau, Waclaw Swiech, and Wolfgang Telieps. "Surface Morphology Studies by Low-Energy Electron Microscopy (LEEM)." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 1 (August 12, 1990): 294–95. http://dx.doi.org/10.1017/s0424820100180227.

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The morphology of a surface determines to a large extent its physical and chemical properties. In order to understand these properties it is frequently sufficient to image the surface with a resolution in the 10 nm range, provided that the relevant surface features show sufficient contrast, as is the case in LEEM. The talk discusses the morphology information which can be obtained with LEEM and illustrates it with various examples.Point defects, e.g. emergence points of screw dislocations, or point-like defects such as small impurity clusters cannot be resolved in LEEM but nevertheless imaged by decorating them (screw dislocations) or by their influence on surface processes (pinning centers in sublimation). Line defects, e.g. sublimation steps, growth steps or glide lines, may be imaged directly down to atomic height by geometric phase contrast or indirectly by decoration. If a step separates regions with different structures (e.g. domain orientations), then ordinary diffraction contrast will reveal the shape and location of the step. Planar defects can also be imaged by diffraction contrast but three-dimensional defects such as large sublimation hillocks frequently cause also topographic contrast.

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45

MUN, B. S., M. WATANABE, M. ROSSI, V. STAMENKOVIC, N. M. MARKOVIC, and P. N. ROSS. "THE STUDY OF SURFACE SEGREGATION, STRUCTURE, AND VALENCE BAND DENSITY OF STATES OF Pt3Ni(100), (110), AND (111) CRYSTALS." Surface Review and Letters 13, no. 05 (October 2006): 697–702. http://dx.doi.org/10.1142/s0218625x06008682.

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The surface segregation, structure, and valence band density of states of Pt 3 Ni (100), (110), and (111) single crystals are characterized with low energy ion scattering (LEIS), low energy electron diffraction (LEED), and ultraviolet photoemission spectroscopy (UPS). The results of LEIS clearly reveal the complete surface segregation of Pt to the top layer on all crystal alloys. LEED indicates the (5 × 1) surface reconstruction on the Pt 3 Ni (100), while (110) and (111) surfaces show (2 × 1) and (1 × 1) patterns, respectively, identical to Pt single crystals. The valence bands density of states on Pt 3 Ni alloys are compared to those of Pt single crystals via UPS measurements.

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46

Balzuweit, Karla, Thais MIlagres, Von Braun Nascimento, Vagner de Carvalho, Edmar Soares, and Luiz Ladeira. "LEED and TEM analysis of Bismuth Telluride." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C194. http://dx.doi.org/10.1107/s2053273314098052.

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Bismuth Telluride has recently been identified as a 3D-topological insulator [1] as well as Graphene [2]. Topological insulators are a quite recent discovered quantum mechanics characteristic of materials where essentially the surface band structure is completely different from the bulk. Bismuth Telluride, for example has its semi-metallic behavior changed into a conducting one. However it has been well known, as an excellent thermoelectric material [3]; with relatively high thermoelectric coefficients at room temperature. Bismuth Telluride is a relatively easy material to obtain and different compositions are being studied both as bulk material and as thin films. Crystals of Bi2Te3 were Bridgman grown in a sealed quartz ampoule in a directional resistance oven at a temperature of 600oC. Conventional X-ray Laue diffraction showed patterns compatible with a single crystal along the sample except for the starting point, which was discarded. Transmission and Scanning Electron Microscopy and Low Energy Electron Diffraction (LEED) were performed. The grown crystals were cleaved and small parts were crushed on a mortar with ethanol and deposited onto a holey carbon grid. Also thin slices were cut in an ultramicrotome (Leica UC6) with a diamond knife and deposited onto a holey carbon coated grid. TEM measurements showed the presence of grains on both samples with a very small deviation from the observed crystallographic axis (0001). However LEED measurements showed only a single crystalline pattern. Electron backscatter diffraction (EBSD) studies showed large granular areas with a extremely small angular variation between the grains. It is still unclear if those differences are real or due to sample preparation artifacts and effort is being put into analyzing exactly the same piece with all the different techniques.

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KONDO, Kenji, Syuji SAKAGUCHI, Takashi MATSUO, Nozomu KAWAI, Shozo HONGO, and Toshio URANO. "Low Energy Electron Diffraction (LEED) Pattern Observation and Intensity-Energy Curve (I-V curve) Evaluation of Fe/Si(111) Surfaces." Shinku 48, no. 3 (2005): 226–28. http://dx.doi.org/10.3131/jvsj.48.226.

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48

JONA, F. "STEPPED SURFACES: A CHALLENGE FOR QUANTITATIVE LEED ANALYSIS." Surface Review and Letters 06, no. 05 (October 1999): 621–26. http://dx.doi.org/10.1142/s0218625x99000585.

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Determination of the atomic structure of stepped surfaces by quantitative low-energy electron diffraction (LEED) analysis is very difficult when the spacings between layers parallel to the surface become significantly smaller than about 0.9 Å. For most of the computer programs widely used in LEED crystallography the problem is caused by numerical instabilities and lack of convergence. However, the CHANGE computer program has had remarkable success on surfaces with interlayer spacings as small as 0.5 Å. Advantages and disadvantages of this program are briefly discussed. CHANGE is now available to run conveniently on desk-top personal computers.

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Schmidt, Th, S. Heun, J. Slezak, J. Diaz, K. C. Prince, G. Lilienkamp, and E. Bauer. "SPELEEM: Combining LEEM and Spectroscopic Imaging." Surface Review and Letters 05, no. 06 (December 1998): 1287–96. http://dx.doi.org/10.1142/s0218625x98001626.

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At present the only surface electron microscope which allows true characteristic XPEEM (photoemission electron microscopy using synchrotron radiation) and structural characterization is the spectroscopic LEEM developed at the Technical University Clausthal in the early nineties. This instrument has in the past been used mainly for LEEM studies of various surface and thin film phenomena, because it had very limited access to synchrotron radiation. Now the microscope is connected quasipermanently to the undulator beamline 6.2 at the storage ring ELETTRA, operating successfully since the end of 1996 under the name SPELEEM (Spectroscopic PhotoEmission and Low Energy Electron Microscope). The high brightness of the ELETTRA light source, together with an optimized instrument, results in a spatial resolution better than 25 nm and an energy resolution better than 0.5 eV in the XPEEM mode. The instrument can be used alternately for XPEEM, LEEM, LEED (low energy electron diffraction), MEM (mirror electron microscopy) and other imaging modes, depending upon the particular problem studied. The combination of these imaging modes allows a comprehensive characterization of the specimen. This is of particular importance when the chemical identification of structurar features is necessary for the understanding of a surface or thin film process. In addition, PED (photoelectron diffraction) and VPEAD (valence photoelectron angular distribution) of small selected areas give local atomic configuration and band structure information, respectively.

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50

CHEN, WENHUA, HUASHENG WU, WING KIN HO, B. C. DENG, GENG XU, and S. Y. TONG. "THE ATOMIC STRUCTURE OF Si(111)-$(\sqrt{3}\times\sqrt{3})$R30°-Ga DETERMINED BY AUTOMATED TENSOR LEED." Surface Review and Letters 07, no. 03 (June 2000): 267–70. http://dx.doi.org/10.1142/s0218625x0000035x.

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The atomic structure of the Si (111)-[Formula: see text]R30°-Ga surface has been studied by comparing measured low-energy electron diffraction (LEED) intensity (IV) curves with calculated IV spectra using the method of automated tensor LEED. The experimental LEED IV curves used in this work contain many beams and a wide energy range. The results show that the Ga atoms occupy T4 sites, at 2.62 Å above the second-atomic-layer Si atoms. The Ga–Si vertical spacing is 1.44 Å and the bond length between the Ga atom and the first-layer Si atom is 2.52 Å. Large bucklings are found in the first and second Si bilayers below the adatom layer.

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