Particle research using AFM at Virginia Tech's Nano Earth LAB, Weinan Leng, Virginia Tech sustainable Nano Technology LAB manager & Research scientist in civil and environmental engineering

At Virginia Tech, one of the members of ceint the virginia tech center for sustainable Nanotechnology(VTSUN), is for students and postdocs who are researching environmental nanoscience and technological from different perspectives and is equipped with a range of state-of-the art nanometrolodgy tools including Atomomic Forcing Microscpe, Tem and Sem.

How do you use Atomic Force Microscopes in your research?

In most of cases, I utilize AFM for topographic measurements, such as particle size, surface roughness.

What features of Atomic Force Microscope are most useful and why?

The most useful feature of AFM is to measure incredible small particles with a high degree of accuracy.

Can you show an example of silver nano particle imaging and explain why these images were taken and what they tell us?

Figure 1. AFM images of uncoated and coated AgNPs measured after 1 and 14-days dissolution. The left panel is the AFM image for the original AgNPs without coating and dissolution; on the right side (labeled a-h) are the AFM images for uncoated and coated AgNPs after 1 and 14 days. (Liu, C., Leng, W., Vikesland, P. J., Controlled Evaluation of the Impacts of Surface Coating on Silver Nanoparticle Dissolution Rates, ES&T, 2018, 52(5),2726-2734.)

This is an example of how to utilize a highly sensitive AFM to examine engineered nanomaterial dissolution, which is one of NSF projects that has been done in the group of Prof. Peter Vikesland at Virginia Tech. The AFM images in Figure 1illustrate how surface coatings affect silver nanoparticle dissolution rates. In this research, arrays of surface adhered silver nanoparticles were produced via nanosphere lithography, and AFM provides a convenient technique to measure changes in particle height which is related to the kinetics of AgNP dissolution.

Can you show an example of gold nano particle imaging and explain why the images were taken and what they tell us?

In Figure 2, on the next page, AFM images of 5nm gold nano particle (Au NP) standard (A) and 1 nm gold hydrogel sample (B).

This is one of the most attractive applications of AFM which provides a quick survey for very small particles (less than 5 nm) in a low concentration that are not created as an artifact of the electron beam in an electron microscope. The standard image shows how accuracy of height measurements which can reflect particle size.

How do you think the imaging of NanoParticles can help us with the environmental issues we are facing?

Following the example in question 3, once a well-controlled nano structure was designed and modelled for the engineered nano materials, which can be avoidthe severe limitations of many alternative methodologies, such as the aggregation using realistic nanoparticle solution.

Findings based on AFM imaging will aid efforts to engineer environmentally benign nanomaterials and to predict their environmental impacts.

What do you like best about working in the NanoEarth group at VaTech?

I love being an instrument specialist, and being asked for my participation in a lot of cool projects of NanoEarth users. Every technical service, data report and critical observation you give will have your fingerprint on it in a good way. It gives me great job satisfaction that significantly outweighs the
stress, the time and the hard work.