Center News

New Surface Tool in Clark Materials Facility

CCMR Staff :: Mar 2, 2007
New Surface Tool in Clark Materials Facility

ITHACA, NY (CCMR Staff) -- CCMR has a new tool for X-ray photoelectron spectroscopy (XPS) also known as Electron Spectroscopy for Chemical Analysis (ESCA). This instrument was donated to CCMR by Eastman Kodak Company, Rochester, NY.

The system is a Surface Science Instruments (SSI) model SSX-100 which utilizes monochromated Aluminum K-alpha x-rays (1486.6 eV) to strike a sample surface. Electrons bound with lower binding energy than the x-ray energy can be ejected from the atom (XPS or Auger process). The difference between the incident x-ray energy and photoelectron binding energy determines the photoelectron kinetic energy. A hemispherical analyzer scans for photoemitted electrons with binding energies between -50V to 1100V. Elements have unique XPS signatures which can be used to accurately determine atomic composition. Typical detection limits are ~0.1 to 1 atomic percentage depending on photoemission efficiency. In addition, bonding of atoms can shift the binding energies of valence electrons, and these bonded chemical states (oxides, nitrides, fluorides, silicides, etc.) can be detected by high-resolution XPS.

XPS is a very surface-sensitive technique since photoelectrons can only escape from the top few monolayers of a surface. Electron escape depth is dependent on the energy of the photoelectron as well as the sample material. Typical analysis depths are ~1 to 4 nm for metals and ~2-10 nm for polymers. X-ray analysis spot size is typically 1000 micron diameter and as small as 150 micron diameter.

The system has a turbo-pumped load-lock chamber and a main chamber with cryopump and ion pump. System operating pressure is ~2×10-9 Torr with base pressures in the 10-10 Torr range.

Samples must be vacuum compatible (cannot outgas above 10-8 Torr) and must be <100mm diameter and <50mm in height to fit into the XPS system. Most metals, ceramics, polymers and alloys can be analyzed readily.

The system is equipped with a 0-5keV Argon ion source for sample cleaning and depth profiling as well as automated in-situ sample motion, rotation and tilting.

The system is part of the Materials Facility in Clark Hall. Samples can be dropped off to Dr. Jonathan Shu (Clark D22, 255-9833, jbs24@cornell.edu) and data will be sent when analysis is completed.

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