Surface Analysis Facility

 
The University of Delaware

  Department of
Chemistry & Biochemistry
 
 

Consulting and Services in:

INTRODUCTION. The University of Delaware's research community includes many research groups that make use of experimental surface analysis in their research. These research groups come from several departments in two colleges. In 1995 the Surface Analysis Facility was established by Tom Beebe at the University of Utah in the Chemistry Department through funding by the National Science Foundation (NSF). In September of 2001, this facility was moved to the University of Delaware, where it is managed by Beebe.

MISSION OF THE FACILITY. The Surface Analysis Facility exists primarily to support the federally funded research projects of University of Delaware faculty members, and it has been subsidized from University sources to do so. To help defray operating costs, the Facility also welcomes, and the NSF encourages, collaborative interactions with other universities and colleges, as well as local, regional and national for-profit companies. The Facility charges a fee for services in accordance with NSF guidelines and University policies (see later section NSF Guidelines for Sharing of Instrumentation).

SAMPLE HANDLING CAPABILITIES. We are able to handle and analyze conducting and insulating samples at temperatures from -170 C to 1500 C. Water- or oxygen-sensitive samples can be loaded in your inert-atmosphere glove box and transferred with ~1 ppm water and oxygen levels to the XPS system. This transfer capability is coming soon for the TOF-SIMS. Although the ideal sample size is 1 cm 1cm a few mm, sample dimensions as large as 25 mm 75 mm and no thicker than 10 mm can be analyzed. Very small sample sizes and powders can also be handled. Frozen, hydrated sample introduction and analysis is planned for the future. Please call to discuss any special sample-handling needs.

XPS. X-ray photoelectron spectroscopy is a widely used method of determining the chemical composition of a surface. X-rays impinge upon a sample and ionize atoms, releasing core-level photoelectrons. The escaping photoelectron's kinetic energy limits the depth from which it can emerge, giving XPS its high surface sensitivity and sampling depth of a few nanometers. Photoelectrons are collected and analyzed by the instrument to produce a spectrum of emission intensity versus electron binding energy. Peak areas at nominal binding energies can be used to quantify elemental composition, and small shifts in these binding energies (chemical shifts) provide powerful information about sample chemical states and short-range chemistry. XPS is suitable for the analysis of conductors and insulators such as polymers (see example below).

XPS INSTRUMENTATION. One workhorse instrument in the Surface Analysis Facility is the VG Scientific 220i-XL imaging multitechnique surface analysis system. The system is pictured on the front of this brochure and includes a monochromatic high-flux microfocused Al X-ray source for high-resolution, high-sensitivity work; a magnetic immersion lens for high collection efficiency and stable charge compensation; and a unique detector system for spectral and imaging data acquisition. An Al/Mg twin anode source is also available. Quantitative peak-area ratios for the three types of carbon in polyethylene terephthalate (PET) polymer can be seen below. Spectral resolution is on the order of 0.75 eV for the carbonyl C1s component of PET (see below, 30kcps, 2 min acquisition), and considerably higher for conductors.


 

 

 

XPS IMAGING. The instrument can also rapidly collect XP images with a lateral resolution of approximately 1 micron and sufficient spectral resolution to discern, for example, carbidic and graphitic carbon domains in a few minutes of acquisition time. All image pixels are collected in parallel with a large time advantage over serial imaging methods. The combination electrostatic-magnetic lens system provides higher spatial resolution than an electrostatic-only system. Small-spot spectral analysis down to approximately 20 microns is available.


 

AUGER ELECTRON SPECTROSCOPY AND MICROSCOPY. The multitechnique system includes a LaB6 electron gun as an excitation source for Auger. This gun can also be used for 200-nm-resolution SEM. In Auger, an incident primary electron creates an excited ion near the surface which decays by the emission of a secondary Auger electron, whose kinetic energy is measured. As in photoelectron spectroscopy, the escaping Auger electron's kinetic energy limits the depth from which it can emerge, giving AES its high surface sensitivity and few nanometer sampling depth. Auger electron spectra can be acquired from a selected area mapped out in an SEM image of the sample (e.g., from within a rectangle, along a line, or at points; at right an AFM cantilever is seen poised above a patterned surface; three analysis points are selected). Auger images or maps can also be generated for specific elements with approximately 200-nm resolution. Auger finds its greatest strengths in the analysis of inorganic materials not susceptible to electron-beam damage.

ToF-SIMS. The Facility also houses the technique of time-of-flight secondary-ion mass spectrometry, with the ION-TOF TOF-SIMS IV system. Support was derived from the NSF (DMR-9724307). ToF-SIMS is a surface sensitive technique used to probe a material's long-range chemical structure through the mass spectral analysis of desorbed molecules and molecular fragment ions. An incident primary ion produces molecular fragments from the sample surface; positive or negative secondary ions are collected from these fragments and their mass is determined by flight time to a detector. Several operational modes are now available in the facility:

  • static SIMS mode - very low incident ion doses are used to probe the molecular structure and long-range chemistry of surfaces; the low ion dose ensures that intrinsic surface chemistry, and not ion-induced chemistry, is being probed; static SIMS is highly complementary to XPS for monolayer and polymer surface analysis of organic materials, providing long-range chemical information.
  • dynamic SIMS mode - high incident ion doses are used to sputter off surface layers and probe elemental composition as a function of depth into a sample; most molecular information is scrambled; quantitation and sensitivity can be as high as parts per billion in some cases; dynamic SIMS is useful for layered samples, inorganic materials and impurity analysis.
  • imaging SIMS mode - a focused ion beam can be rastered over a surface to collect static SIMS spectra as a function of lateral position; resolution better than 100 nm can be achieved with very high mass resolution (m/Dm > 10,000). An example of such an image of a patterned surface is shown below, in which the protein fibronectin is present in the squares (CN- ion image), and a polyethylene oxide brush polymer is present between the squares (O- and CH3O+ ion images).
  • ToF-SIMS IMAGES OF PROTEIN PATTERNS.

    154 154 m2

    154 154 m2

    154 154 m2

    O- ion image

    CN- ion image

    CH3O+ ion image

  • SEM mode - a focused ion beam (sub-50-nm) can be rastered over a surface while secondary electrons are collected, as in a conventional SEM. This mode can be used to locate features of interest.

RESEARCH-TRAINING IN THE FACILITY. In addition to research support, the Facility plays an important role in education and research-training activities. Analysis of samples with understanding of the science is best accomplished when the student, postdoc or researcher is present and participates in the analysis. A yearly graduate-level course in surface analysis, taught by Professor Tom Beebe, is structured around the Facility, and includes a student-generated lab project on the instruments for research-training objectives. Other faculty are encouraged to employ the Facility in this manner for both graduate and undergraduate courses.

This facility was originally funded by the

 

Contacting the Facility

Please first call or e-mail:

Professor Thomas P. Beebe, Jr., Ph.D.

175 Brown Laboratory

302-831-1888 phone with voice mail

beebe@udel.edu

www.udel.edu/chem/beebe/beebe.html

Ms. Zhanping Zhang (TOF-SIMS)
gnahzpz@yahoo.com
302-831-2579
or Mr. Matt Wells (XPS)
mc_wells@yahoo.com
302-831-2579
U of D Surface Analysis Facility
023 Lammot DuPont Laboratory
Department of Chemistry & Biochemistry
University of Delaware
Newark, DE 19716
302-831-3051 phone
302-831-6335 fax in Chemistry office

NSF GUIDELINES FOR SHARING INSTRUMENTATION The NSF has partially funded this facility (CMS-9413498; DMR-9724307). NSF "encourages the sharing of instrumentation - both among academic institutions and, when appropriate, among the academic, industrial and public sectors." These collaborations make available new and unique instrumentation which would not otherwise be available, thereby benefiting the company, the university and the economy; they "strengthen scientific research potential of the Nation." But despite the NSF's "preference for sharing of instrumentation, it is contrary to the NSF's intent for grantees to use NSF-supported research instrumentation or facilities to provide services for a fee in direct competition with private companies that provide equivalent services." NSF guidelines are available (NSF Important Notice 91 and Attachment; www.nsf.gov/pubs/1998/iin122/iin122.txt ). We encourage our would-be collaborators to carefully review these guidelines, which can be accessed via NSF's web site at www.nsf.gov. The Department's web site is www.udel.edu/chem/. We also encourage for-profit surface analysis laboratories to contact us directly regarding their concerns about unfair competition. We would be happy to pass along information about your company to interested parties that inquire of our facility.

http://www.udel.edu/chem/beebe/surface.htm