PORTLAND, Ore.—Using a new twist on the traditional thermogravimetric analysis (TGA) technique, the National Institute of Standards and Technology (NIST) demonstrated a new method for taking Nanoscale measurements of the purity of carbon-nanotubes, coated-nanoparticles and surface features on thin films.
NIST demonstrated its new TGA microbalance built atop a vibrating quartz crystal, thereby enabling measurements almost 1000-times more sensitive than today.
"We wanted to analyze the purity of small carbon nanotube samples," said NIST chemist Elisabeth Mansfield about the new technique that has also been used to successfully measure the nanoscale thickness of application-specific surface coatings on gold nanoparticles. "Measuring how much material coats a particle's surface is very hard to do right now."
Traditional TGA is an industry standard way of measuring the precise mix of elements in complex compounds. Since each element in a compound breaks down and vaporizes at a different temperature, accurately measuring its weight as it is heated yields a unique plot that can be used to verify the purity of a sample. Unfortunately, today samples need to be several milligrams in size for traditional TGA. NIST's new quartz-crystal enabled TGA requires only micrograms of a material—a thousand times smaller. The smaller sample size makes the technique available to characterize nanotechnology compounds as well as small surface chemistry features in thin films.
NIST prepares quartz crystal microbalance disks with samples of carbon nanotubes for microscale thermogravimetric analysis with sample sizes as small as one microgram. Credit: Kar/NIST.
The extremely sensitive microbalance for TGA was built atop a piezoelectric disk of quartz sandwiched between to electrodes and set to vibrating at an ultrasonic frequency. The added mass of the sample causes its resonant frequency to change. After settling, the microbalance is slowly heated allowing each component in the compound to vaporize separately, producing an ultra accurate assay of the compound despite its small size. Next the researchers plan to build an integrated unit that can automate the process of performing nanoscale TGAs.