AFRL Donates Advanced Surfaces Analysis System To Howard University

  • Published
  • By Peter S. Meltzer, Jr.
  • AFRL Materials and Manufacturing Directorate
WRIGHT-PATTERSON AFB, Ohio --  The Air Force Research Laboratory Materials and Manufacturing Directorate has donated an advanced materials analysis system capable of analyzing the surface and in-depth composition of materials with precision accuracy to Howard University's Nanoscale Science and Engineering Facility.

The system provides Secondary Ion Mass Spectrometry capability that will enable students, faculty, and other researchers at the Howard facility to identify and quantify various types of materials, including dopants (materials added to crystals to change physical properties), impurities, and contaminants. The system was transferred under an Educational Partnership Agreement between ML and Howard University.

Advanced SIMS technology greatly enhances Howard University's capability to analyze material surfaces, increases the institution's research and development potential, and expands educational opportunities in science, mathematics, and engineering. The transfer facilitates joint research between ML and the university, and also strengthens AFRL's commitment to higher education and historically black colleges and universities.
SIMS is a highly sophisticated analytical technique that combines focused primary ion beam bombardment with mass spectrometry of sputtered (ejected) secondary ions to achieve high sensitivity and high elemental selectivity. The technology has several applications vital to materials and manufacturing research, such as identifying and quantifying metal aircraft corrosion samples, and in dielectrics, coatings and thin films.

SIMS technology provides the capability for high sensitivity, three-dimensional, elemental analysis of molecular structure. There are three basic types of SIMS. The first is Static SIMS, used for surface analysis. In this instance, low-energy primary ions are used to dislodge secondary ions from the surface layers. The secondary ions are then analyzed by mass spectrometry to produce a spectrum, which can be used to identify organic and inorganic species.

The second type of SIMS, called Imaging SIMS, is used for spatial analysis, and involves scanning the primary ion beam over the surface to build up an image that reveals the distribution of species.

The third type of SIMS is Dynamic SIMS and is used for depth analysis. Surface layers are progressively etched away by concentrating the primary ion beam into a small, concise area. This allows an analysis of the subsurface region, whereby depth profiles are built up by correlating the etch time with intensity for different species. Depth profiling secures information on composition variation below the initial surface. This type of information is very useful in analyzing layered structures, such as those produced in the semiconductor industry.

Dynamic SIMS relies on the removal of atoms from the surface of a material and is therefore a destructive technique; nevertheless, it is ideally suited for depth profiling applications. A depth profile of a sample may be obtained simply by recording sequential SIMS spectra as the surface is gradually eroded away by the incident ion beam probe. A plot of the intensity of a given mass signal, as a function of time, is a direct reflection of the variation of its abundance/concentration with depth below the surface.

Some of the key applications of SIMS include education and research; chemical analysis of surfaces and mapping distribution of species; contamination analysis of thin films and surfaces; monitoring the continuity of surface coatings; failure analysis of thin film devices; and development of bioactive surfaces. These application areas are important to the Air Force, industry, and education.

The SIMS technology donated to Howard University is a surface analysis and materials characterization instrument, which combines Dynamic SIMS with Auger Electron Spectroscopy and depth profiling capability. The instrument is used for the surface and in-depth compositional analysis of impurities (SIMS) and major elements (Auger) in solid samples and is an ultra-high vacuum instrument.