NIST reveals nanoscale thermogravimetric analysis
The thermogravimetric analysis (TGA) technique, places a microbalance on top of a vibrating quartz crystal, enabling measurements almost 1,000-times more sensitive than what can be measured with current equipment.
"We wanted to analyse the purity of small carbon nanotube samples," said Elisabeth Mansfield, a chemist at NIST. The 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," she added.
TGA is a 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. However, current equipment requires several milligrams of sample for measurement. The new quartz-crystal enabled TGA requires only micrograms of a material—a thousand times less. Thus, the technique can be used to characterise nanotechnology compounds and small surface chemistry features in thin films.
The microbalance was built atop a piezoelectric disc of quartz sandwiched between two 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 vaporise 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.
- R. Colin Johnson