322,971 research outputs found
Dielectric properties of the Si(111)2×1 surface: Optical constants and the energy-loss spectrum
No full textWe present a method of computation of the optical constants of the surface layer of a solid, starting from a differential reflectivity spectrum. The differential reflectivity was obtained by comparing the overall reflectivity of the same sample in the case of a clean and oxidized surface. The method assumes sharp interfaces at the vacuum surface and at the surface bulk side. The physical properties of the bulk and of the surface layer are described by an energy-dependent dielectric constant. This method is applied to the Si(111)2×1 surface. The surface optical constants are derived in the (0.3-4.0)-eV range. With the use of the same model and the calculated optical constants, the electron-energy-loss spectrum of the Si(111)2×1 surface has been calculated. The agreement with the experiment is good. This is assumed as a proof of the reliability of the optical constants. In addition the comparison of the calculated energy-loss spectrum and the experiment allows the explanation of the apparent disagreement between optical and energy-loss experimental data in the near-infrared range. We demonstrate the different nature between the energy-loss peak and the optical one, the first due to the excitation of the two surface interface modes of the Si(111)2×1 surface layer and the second to an interband transition
Imaging of single‐stranded DNA with the scanning tunneling microscope
No full textUncoated single-strand DNA mixed with BAC (benzyldimethylalkylammonium chloride) were deposited on gold substrates and imaged in air with the use of a high-resolution scanning tunneling microscope (STM). Constant-current and gap-modulated STM images showed both double- and single-stranded DNA. Along the single DNA backbone we have, tentatively, assigned small structures to phosphate and sugar group components; bumps aside single filaments, that correspond, presumbaly, to the bases DNA, have sometimes been observed
THE EFFECT OF SURFACE-STATES AND BAND BENDING CHANGE ON REFLECTIVITY OF CLEAVED GAAS(110) AND GAP(110
No full textSi(111) and Si(100) surfaces observed in air by scanning tunneling microscopy
No full textSi(111) and Si(100) surfaces have been observed by an air-operating scanning tunneling microscope (STM). On the cleaved Si(111) surface STM topographic images show predominantly [211BAR]-oriented monatomic steps. The distribution of the width of the terraces is centered around 4 nm. Si(100) surfaces have been hydrogen-terminated by a treatment with fluoridic acid (HF). The surface appears in the topographic STM images to be quite stable and smooth with presumably no oxide
Fault Diagnosis in VLSI IC's by Simultaneous use of Scanning Electron and Tunneling Microscopy
No full textActivated chemisorption of oxygen on Si(111)-2x1
No full textResults on the chemisorption of molecular oxygen on Si(111)-2x1 at different temperatures are reported. They show that oxygen is initially physisorbed in a precursor state, From which it can be thermally activated into the chemisorbed slate. An activation energy of 20 meV is found. The dependence of the sticking coefficient upon coverage deviates from the classical Langmuir theory. A model of chemisorption fitting the experimental observations is presented. In the frame of this model, the heights of the barriers for chemisorption and desorption are obtained
Confocal, wide band spectral reflection microscope, and relevant spectral imaging method
No full textThis invention concerns a wideband spectral reflectance confocal microscope comprising a laser source (LS), a beam expander (BE) inserted immediately after the laser source (LS), a beam splitter (BS) in an adequately transparent material through the whole spectral interval emitted by the laser source (LS), a system (OB1) to focus the laser beam on the sample (S) presenting a working distance greater than 5mm and a numerical aperture greater than 0.25, a collection system (M, OB2, PH) and an analysis system (AS) of the laser beam reflected by the sample and transmitted by the beam splitter (BS), said analysis system (AS) comprising a chromatic dispersion subsystem capable of forming the spectrum to be analysed, the microscope being characterized in that: said laser source (LS) is a source that emits simultaneously at several wavelengths in the visible and infrared regions; said focusing system (OB1 ) is free of chromatic aberration; said beam splitter (BS) is positioned at 45° in respect of the laser beam direction; said collection system (M, OB2, PH) is free of chromatic aberration; so that at each analysed point of the sample (S) corresponds unambiguously a frequency response spectrum collected by the collection system (M, OB2, PH). The invention concerns as well a spectral imaging method of a sample (S) by means of a wideband spectral reflectance confocal microscope, besides the utilisation of the microscope of this invention for the same imaging
The effect of artificial aging and sizing on discoloration of paper studied by UV-VIs-NIR spectroscopy in comparison to ancien paper
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