RTNN User Spotlight: Meet Kelly White

About Kelly: My name is Kelly White and I’m a third-year Ph.D. student from the department of chemistry at UNC Chapel Hill under advisement from professor Jim Cahoon. My work focuses on designing silicon nanowire geometric diodes for high frequency rectification. Through a combination of simulation and experiment, I seek to understand the ratcheting mechanism that makes these diodes work and establish design principles that dictate their performance. My goal is to eventually create silicon nanowire geometric diode rectenna devices that function as THz detectors. In my free time, I love playing tennis and squash, hiking with my dog, metalsmithing, and cooking.

SEM image of a surface gated silicon nanowire geometric diode device. The image is made possible by using four different CHANL instruments over nine different sessions.

What RTNN facilities or instruments are you using in your research, and how do they help you? CHANL facilities make it possible for me to do single-nanowire device fabrication and imaging. I use the SEM, DRIE, and e-beam evaporators to create devices using e-beam lithography and evaporation, and the ALD to modify nanowire surfaces and create surface gated devices. With these instruments, I am able to fabricate intricate devices on an incredibly small scale and measure the electronic properties of single silicon nanowire geometric diodes.

What about your research makes you excited about its impact? I am excited by the unique advantages of geometric diodes. Unlike traditional diodes, they are capable of rectifying high frequencies into the THz regime. If we can realize this THz rectification, silicon nanowire geometric diodes could be used for ultrafast communication and long wavelength energy harvesting, and eventually play an important role in the internet of things.

What is your favorite thing about using RTNN facilities? The RTNN staff go above and beyond when it comes to training, keeping instruments in good condition, and troubleshooting problems. I am always grateful for their willingness to drop everything and help when needed.

Free programs and events available for local companies via RTNN and First Flight Venture Center

Lunch is on us! RTNN to host free Lunch and Learn for local companies

Representatives from local companies are invited to join us on Tuesday July 12, 2022 from 11:30am-1:00pm EST at First Flight Venture Center in Research Triangle Park (Durham, NC) for an RTNN “Lunch and Learn” Event. Director Jacob Jones will present on analytical/nanofabrication facilities and expertise available across NC State University, Duke University, and UNC Chapel-Hill and RTNN’s network and affiliates and how they can be of use to research and development at companies. Lunch will be provided. Please limit company representatives to no more than 2 people.

Please RSVP by July 6, 2022 via this form:

Click Here to RSVP via Google Form

If you have any issues or questions, please contact Phillip Strader (phillip_strader@ncsu.edu)

First Flight Venture Center offering scholarships to Propeller Pre-Accelerator Program

First Flight Venture Center is offering scholarships to its Propeller Program: a 6-week entrepreneurial design thinking program which helps founders and entrepreneurs determine whether there is sufficient value to pursue a product or service idea. The program helps entrepreneurs identify potential markets, develop a path to market strategy, and learn how to communicate the value of the idea to early stakeholders and adopters. This program is an excellent opportunity for local/small companies, or anyone with a science and technology business idea seeking guidance on determine its viability and a path to success.

For more info on this program and to apply, visit FFVC’s Propeller webpage: https://www.ffvcnc.org/propeller

Free facility access available through RTNN Kickstarter program

The RTNN offers free facility access via the RTNN Kickstarter program – anyone can apply for up to $1,000 in facility access value in RTNN facilities. Applications are accepted on a rolling basis with 2 “priority” deadlines once per year. Read more and apply on the RTNN Kickstarter webpage: https://rtnn.ncsu.edu/opportunities/kickstarter/

2021 RTNN Collaborative Research Award Winners Announced!

Congratulations to the winners of our 2021 RTNN Collaborative Research Award! This award seeks to identify outstanding research projects, papers, and/or presentations that leverage the resources, equipment, and/or expertise available through the RTNN. Awarded research projects are expected to demonstrate a high-level of research progress and achievement that was made possible only by the use of two or more university sites or collaborators within the RTNN. Dr. Jill Dempsey, Dr. Michael Mortelliti, and Annie Wang share this award for their innovative use of fabrication and analytical techniques available in RTNN to better understand materials used in photo-electrosynthesis cells (DSPECs).

Problem this work addressed: The performance of dye-sensitized photoelectrosynthesis cells (DSPECs) is significantly improved when a core/shell SnO2/TiOx photoanode is utilized, as opposed to simple TiO2 nanocrystalline films. This performance enhancement has been attributed to slower charge recombination dynamics due to electron tunneling from a core-localized electron to the oxidized dye. A fixed rectangular barrier tunneling model has been proposed, in which the SnO2 conduction band is ca. 300–500 mV more positive than that of TiO2. However, this model is based on several poor assumptions and further, this model is challenged by observations in the dye-sensitized solar cell community noting that treatment of TiO2 electrodes with a chemical bath of TiCl4 (to form a TiOx coating on the core material) also enhances device efficiency. If applying a fixed rectangular barrier model based on data from bulk single crystals, as is employed for SnO2/TiOx core/shell photoanodes, no barrier to electron transfer would be expected between an electron localized in the core TiO2 and the oxidized dye.

Key Findings: In this work, the researchers obtained a unified understanding of the mechanisms by which SnO2/TiOx and TiO2/TiOx core/shell materials facilitate improved device efficiency in DSPECs and DSSCs. Specifically, they report their use of atomic layer deposition (CHANL) to fabricate an array of TiO2/TiOx and SnO2/TiOx core/shell electrode materials with different shell thicknesses and different annealing temperatures. They comprehensively characterized the electronic structure of these materials using diffuse reflectance (CHANL), X-ray photoelectron spectroscopy (CHANL), and Raman spectroscopies in conjunction with high-resolution transmission electron microscopy (AIF), powder X-ray diffraction (CHANL), and reductive electrochemistry. They then quantified charge recombination dynamics of the dye-sensitized materials using transient absorption spectroscopy. From these data, a physical model was constructed for charge recombination in core/shell materials consistent with all these data.


Impact: By correlating how the electronic structure of the shell material is responsible for impeding charge recombination, this work answers a decade-long question about the mechanism by which anode shells and coatings improve DSPEC and DSSC device performance. This work shows how shell crystallinity and trap state density is critical in the recombination mechanism, emphasizing that there is a critical annealing temperature at which a balance is realized between slow recombination and fast diffusion to the back contact for optimum device performance. This understanding thus provides an explicit blueprint for shell fabrication to improve performance DSSCs and DSPECs.

This research made use of the instrumentation in both CHANL (UNC) and the AIF (NCSU). Further, research was also supported by a grant to high school student Annie N. Wang through the North Carolina Research Triangle Nanotechnology Network, Kickstarter Program.


This work is published in the following paper:

Interfacial Electron Transfer through Ultrathin ALD TiOx Layers: A Comparative Study of TiO2/TiOx and SnO2/TiOx Core/Shell Nanocrystals

Michael J. Mortelliti, Annie N. Wang, and Jillian L. Dempsey
The Journal of Physical Chemistry C 2021 125 (23), 12937-12959

DOI: 10.1021/acs.jpcc.1c02428

New Papers Published on Responsible Innovation of Nanotechnology in Food and Agriculture

RTNN collaborators Maude Cuchiara and Khara Grieger, among others, have published two new papers in NanoImpact addressing topics on responsible innovation for nano-agrifoods, as well as insights on barriers to responsible innovation from a study of US experts, stakeholders, and developers:

Responsible innovation of nano-agrifoods: Insights and views from U.S. stakeholders

  • Stakeholder views of responsible innovation and nano-agrifoods were investigated

  • Views were dominated by environmental, health, and safety contexts.

  • A subset of views emphasized a broader set of responsible innovation considerations.

  • Challenges included lack of safety studies, regulation, and public understanding and acceptance.

  • Future work should broaden considerations for responsible nano-agrifood innovation.

Barriers to responsible innovation of nanotechnology applications in food and agriculture: A study of US experts and developers


  • This study reports the first typology of barriers to responsible innovation as perceived by researchers and product developers working in nano-agrifood sectors.

  • Identified 5 key barriers: Lack of Data, Need for Ensuring Marketability & Use, Lack of Product Oversight, Need for Increased Collaboration, and Lack of Adequate Training & Workforce.

  • Elucidates tensions between theoretical values inscribed within responsible innovationand the practical R&D within nano-agrifood sectors.

  • Identifies opportunities to improve practices and process of responsible innovation across these innovation phases as they pertain to nano-agrifood sectors.


Congratulations to our 2021 Image Contest Winners

SEM image of a mosquito stylet

A big thank you to everyone who submitted an image in the 2021 Image Competition. We are excited to announce the winners. Please vote for these amazing images in the NNCI Image Contest, There’s Plenty of Beauty at the Bottom. Voting ends October 15th!

Most Stunning

SEM image of pollen

Lungs of Nature
Hanna Varga, Duke University

The image depicts particles from a dust sample collected on the California coast. This pair of pollen grains reminded the researcher of lungs.

Most Whimsical

SEM image

Dinos Take the City
James Loveless, NC State University

This sample is Gallium nitride grown on sapphire at very high temperatures. Remarkably, this surface was intended to be flat! At these extreme conditions, the crystal growth is often three-dimensional, and we discovered a city-like landscape of thin crystalline microstructures. I thought the dust particles looked like monsters akin to Godzilla, so I added a helicopter to help protect the city.

Most Unique Capability

Our Cups Floweth Over
Greg Allion and Sravanthi Vallabhuneni, NC State University

Thick photo resist sculpted by utilizing light diffraction and image reversal. The visual beauty speaks for itself. Structures like these can be used to make super hydrophobic surfaces.