Browse Prior Art Database

Surface Reflectance Spectroscopy System

IP.com Disclosure Number: IPCOM000088338D
Original Publication Date: 1977-May-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Rubloff, GW: AUTHOR

Abstract

This is a broad wavelength range (photon energy 0.2 - 9.0 eV) system for measurement of optical reflectance changes at a solid surface. The features of this system are:. (1) Broad photon energy range scanning surface reflectance spectroscopy system, including a vacuum ultraviolet (VUV) region as well as infrared, visible, and near ultraviolet. (2) Compatible with standard ultrahigh vacuum (UHV) systems for surface analysis.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 47% of the total text.

Page 1 of 3

Surface Reflectance Spectroscopy System

This is a broad wavelength range (photon energy 0.2 - 9.0 eV) system for measurement of optical reflectance changes at a solid surface. The features of this system are:. (1) Broad photon energy range scanning surface reflectance spectroscopy system, including a vacuum ultraviolet (VUV) region as well as infrared, visible, and near ultraviolet. (2) Compatible with standard ultrahigh vacuum (UHV) systems for surface analysis.

References [1] and [2] demonstrate that surface reflectance spectroscopy can be a useful tool for surface physics. However, these technique have previously been limited to the photon energy range below 5-6 eV; they have not included the VUV region above 6 eV, even though the fundamental excitations of adsorbed atoms and molecules on a surface, i.e., those involving adsorbate orbitals, usually are at these larger photon energies. Further, the original work noted in [1] and [2] was carried out in a tedious fashion by making individual gas exposures for each photon energy in the range measured. Finally, this early work required a rather restricted geometry in which the sample had to be just behind (1-2 cm) an ultrahigh vacuum window rather than in the center of the chamber on a conventional manipulator.

The present design is compatible with standard UHV systems in which the sample is located on a manipulator near the center of the chamber ~ 3-4'' from the viewports. By using an oscillating chopper in a doublebeam optical system with stationary optics and beam splitter, mechanical noise is drastically reduced compared to previous rotating-light-pipe techniques [1,2]. This makes it possible to scan the clean surface spectrum, expose the surface to the adsorbate gas, and then rescan the spectrum for modified surface. Stability of the system allows measurement of the relative change in optical reflectance Delta R/R, with a high relative precision, ~ 2 - 3x10/-14/ for photon energies h Omega < or = 7 eV and ~ 1 - 2x10/-3/ for 7 < or = h Omega < or = 9 eV. Since a single monolayer of adsorbed gas produces delta R/R ~ 1%, spectral measurements at submonolayer coverage are possible in the most interesting region of the spectrum (the VUV) as well as in the infrared (to 0.2 eV).

A commercial vacuum ultraviolet monochromator and associated light sources provide a monochromatic photon beam covering the range 0.2 - 9.0 eV. All optics (except the beam splitter) are Al/MgF(2)-coated. A vacuum-tight mirror box (O-ring sealed) houses the reflectance optics, as shown by the drawing. The light beam from the monochromator exit slit is reflected from a plane mirror PM1 and then refocussed by a commercially available 40 Degrees toroidal mirror TM1 (1:1 imaging). After TM1 the beam is split by a thin MgF(2) transparent plate beam splitter (BS). The reflected light from the front and rear surfaces of this beam splitter strikes another plane mirror PM2 and forms a reference beam focus RBF in the pla...