New UD spectrometer can detect surface materials, down to individual atoms

Editor’s note: An open house is planned at the University of Delaware’s Surface Analysis Facility, located in Lammot du Pont Laboratory on UD’s Newark campus Friday, Sept. 23, from noon to 2 p.m. The event will display a newly-acquired instrument called a time-of-flight secondary ion mass spectrometer, which can detect surface materials at the atomic level. People on campus and in the wider community can look at the new device and others in the laboratory.

The University of Delaware’s chemical detection capabilities gained some extra-powerful research muscle recently, with the acquisition of a time-of-flight secondary ion mass spectrometer (ToF-SIMS).

The instrument was purchased from ION-TOF USA, Inc., a leading electronics manufacturing company. The purchase was made possible through funding from the National Science Foundation, and it will enable faculty, researchers and students to rapidly analyze the surface of a sample and detect precisely what it’s made of and its reactivity. It’s the kind of information that can help advance research relevant to nanotechnology and materials design, catalysis, solar, cultural heritage, microplastics and more.

ToF-SIMS mass spectrometry uses a pulsed ion beam to remove the outermost layer of a sample. It’s not like scraping a layer of paint from a piece of furniture, though.

“Basically, you shoot high-energy clusters of ions at the surface of a material sample and look at the ions that are coming off. This is different from conventional mass spectrometry, and it allows researchers to have an extremely high-resolution look at, for example, biological samples, plastics and even solid films,” said Andrew Teplyakov, professor of chemistry and biochemistry, who led the proposal that brought the instrument to UD.

It is a critical technique needed to understand surface composition and reactivity across chemistry, material science, environmental science, chemical engineering, conservation science and physics. Before its arrival, no other instrument like it was available to researchers in the state of Delaware.

The new ToF-SIMS mass spectrometer shoots high-energy clusters of ions at the surface of a material sample and records information about the secondary ions that come off the sample. This provides extremely high-resolution chemical and molecular information that researchers can use in their work.

The instrument can analyze chemical information from the original surface in the parts-per-million range. It is like detecting a single defective tile among those covering the entire sports complex at UD. It also has the capability to reveal the distribution of elements and molecules on a surface with a lateral resolution down to 70 nanometers, about 1,000 times smaller than a human hair. This resolution is higher than any optical microscope can provide.

Additionally, ToF-SIMS provides researchers the ability to construct a 3D depth profile of materials at a depth resolution better than one nanometer. For a simple comparison, if the diameter of a marble was one nanometer, then the diameter of our planet would be about one meter.

This is essential when working with interfaces.

“My field is surface functionalization and surface chemistry,” Teplyakov said. “My research group focuses on applications for making or controlling molecules at the surface and interfaces between materials. We’re talking about applications where entire devices could be 400 times smaller than a human hair. If you’re making a sensor based on a certain material, having this extremely high-resolution surface and in-depth chemical information that’s accurate down to about one billionth of a meter is critical. This is pretty much the only selective technique that can do this.”

Among his projects, Teplyakov’s research group will use this instrument to illuminate how organic molecules bond at a solid surface. He also plans to investigate why and how solar cells degrade to develop ways to make solar technology last longer. Understanding where defects occur could be key — and the ToF-SIMS instrument can provide this information.

Jocelyn Alcántara-García, associate professor in art conservation with a joint appointment in chemistry and biochemistry, as well as at Winterthur Museum’s Scientific Research and Analysis laboratory, is excited to apply the ToF-SIMS to explore how colored historical textiles decay and why some substances applied as part of conservation methods fail, aging and degrading much like the materials they are meant to preserve. Part of studying dyed textiles requires extracting the dye or color molecules, called chromophores, through sampling. Some of these extraction techniques are aggressive and can destroy the fragile color molecules, while others are so mild that the extractions are incomplete and require larger-than-wanted samples.

Jocelyn Alcántara-García is using results from analyses of historical textiles from the late 18th – early 19th c. Norwich, United Kingdom, to develop surrogate materials for testing dye mixture trends in her work. These surrogate materials are based on findings from Norwich worsted textiles, like the ones in this pattern book (c. 1790–1793), accession number 65 x 695.3 Winterthur Museum, Garden and Library. UD’s time-of-flight instrument can advance this work by providing detailed information about how color molecules bind to textile fibers.

“TOF-SIMS will help us to learn how color molecules chemically bond to textile fibers, leading to more efficient extraction procedures from smaller samples,” said Alcántara-García.

Alcántara-García also is eager to understand how historical materials, such as dyed textiles, painted surfaces and coatings were made to drive better methods for studying and preserving material culture.

“Studying textiles at different stages of deterioration can help us see, for example, which bond is more prone to a specific type of degradation, say light sensitivity. This would be central for display and storage decisions,” she said.

The instrument will enable the work of over 25 research groups on campus.

For instance, for researchers developing microelectronics technologies, the ability to analyze a sample’s depth profile will provide atomic-scale knowledge to advance the creation of very precise and repeatable materials, information useful for design processes or equipment manufacturing. Meanwhile, extreme close-ups of biological devices, films, microfluidic channels and more could one day enable next-generation nanosystems, such as those used in biomedical device interfaces for cardiac stimulation and mapping devices, cochlear and retinal implants, or brain-machine interfaces.

It also could help researchers better understand microplastics, problematic particles found in various states of repair in the ocean and other waterways. Each microplastic particle degrades at a different rate, so having chemical information about the surface of different samples will provide important clues about what’s happening to the material at different stages and how that affects the surrounding environment.

Access to this highly sophisticated instrumentation, such as the new time-of-flight secondary ion mass spectrometer, provides unique training opportunities for students that can help set them apart in the job market.

Equipping students for a bright future

From undergraduate students to postdoctoral fellows, access to this highly sophisticated instrumentation provides unique training opportunities that can help set them apart in the job market.

“There are not many opportunities for students to gain hands-on experience on these highly-sought instruments in the country. Here at UD, we are proud to offer comprehensive operation training and practical courses to our students at various levels to enrich their skillset in analytical chemistry,” said Xu Feng, director of the Surface Analysis Facility. “As the U.S. works to bring back the manufacturing of semiconductors, it’s a huge boost to get them noticed in the job market of microelectronics and semiconductors.”

This includes students involved in two UD Research Experience for Undergraduate (REU) programs: the REU program for students with disabilities and a recently established REU program for undergraduate students from South America.

“Normally REU students come to UD for a reasonably short period of time. The expectation that you can have a result, or maybe even a paper, after a few months’ work … that’s exciting and attractive to students,” said Teplyakov.

State-of-the-art shared facility

The ToF-SIMS complements a suite of other contemporary instruments in the Surface Analysis Facility, including an atomic force-Raman microscope (AFM-Raman) to help researchers acquire topographical information about materials and an X-ray photoelectron spectrometer for securing molecular information on solid surfaces. Having these highly complementary techniques available in one laboratory allows researchers to be strategic in considering what information they want to capture.

This figure shows the type of depth profile that is possible with the time-of-flight secondary ion mass spectrometer. On the left is a graph depicting the distribution and depth of the individual elements at the interface between a two-nanometer titanium dioxide film and a silicon wafer. The image on the right is a 3D reconstruction of the uniformity of this film over the surface. This information can help researchers investigate films and surface features of just a few atomic layers thick.

“With these three instruments, we now have a first-rate surface analysis capability to support new lines of academic research and attract industrial collaborators,” said Teplyakov.

Already, the new instrument has drawn inquiries and interest from local companies interested in analyzing samples, including Chemours, Air Liquide, DuPont and others. Feng and his staff, meanwhile, are standing by to help with these inquiries and discuss possible research approaches.

“We warmly welcome researchers within and beyond the university to come in and enjoy these top-notch surface analysis techniques,” Feng said.

Article by Karen B. Roberts | Photos by Evan Krape and courtesy of Jocelyn Alcántara-García and Xu Feng | September 22, 2022