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Contact: Brendan Lynch, KU News Service, 785-864-8855, [email protected], @BrendanMLynch

Ultrafast lasers map electrons ‘going ballistic’ in graphene, with implications for next-gen electronic devices

LAWRENCE — Research appearing in ACS Nano, a premier journal on nanoscience and nanotechnology, reveals the ballistic movement of electrons in graphene in real time.

The observations, made at the University of Kansas’ Ultrafast Laser Lab, could lead to breakthroughs in governing electrons in semiconductors, fundamental components in most information and energy technology.

“Generally, electron movement is interrupted by collisions with other particles in solids,” said lead author Ryan Scott, a doctoral student in KU’s Department of Physics & Astronomy. “This is similar to someone running in a ballroom full of dancers. These collisions are rather frequent — about 10 to 100 billion times per second. They slow down the electrons, cause energy loss and generate unwanted heat. Without collisions, an electron would move uninterrupted within a solid, similar to cars on a freeway or ballistic missiles through air. We refer to this as ‘ballistic transport.’”

Scott performed the lab experiments under the mentorship of Hui Zhao, professor of physics & astronomy at KU. They were joined in the work by former KU doctoral student Pavel Valencia-Acuna, now a postdoctoral researcher at the Northwest Pacific National Laboratory.

Zhao said electronic devices utilizing ballistic transport could potentially be faster, more powerful and more energy efficient.

“Current electronic devices, such as computers and phones, utilize silicon-based field-effect transistors,” Zhao said. “In such devices, electrons can only drift with a speed on the order of centimeters per second due to the frequent collisions they encounter. The ballistic transport of electrons in graphene can be utilized in devices with fast speed and low energy consumption.”

The KU researchers observed the ballistic movement in graphene, a promising material for next-generation electronic devices. First discovered in 2004 and awarded the Nobel Prize in Physics in 2010, graphene is made of a single layer of carbon atoms forming a hexagonal lattice structure — somewhat like a soccer net.

“Electrons in graphene move as if their ‘effective’ mass is zero, making them more likely to avoid collisions and move ballistically,” Scott said. “Previous electrical experiments, by studying electrical currents produced by voltages under various conditions, have revealed signs of ballistic transport. However, these techniques aren’t fast enough to trace the electrons as they move.”

According to the researchers, electrons in graphene (or any other semiconductor) are like students sitting in a full classroom, where students can’t freely move around because the desks are full. The laser light can free electrons to momentarily vacate a desk, or ‘hole’ as physicists call them.

“Light can provide energy to an electron to liberate it so that it can move freely,” Zhao said. “This is similar to allowing a student to stand up and walk away from their seat. However, unlike a charge-neutral student, an electron is negatively charged. Once the electron has left its ‘seat,’ the seat becomes positively charged and quickly drags the electron back, resulting in no more mobile electrons — like the student sitting back down.”

Because of this effect, the super-light electrons in graphene can only stay mobile for about one-trillionth of a second before falling back to its seat. This short time presents a severe challenge to observing the movement of the electrons. To address this problem, the KU researchers designed and fabricated a four-layer artificial structure with two graphene layers separated by two other single-layer materials, molybdenum disulphide and molybdenum diselenide.

“With this strategy, we were able to guide the electrons to one graphene layer while keeping their ‘seats’ in the other graphene layer,” Scott said. “Separating them with two layers of molecules, with a total thickness of just 1.5 nanometers, forces the electrons to stay mobile for about 50-trillionths of a second, long enough for the researchers, equipped with lasers as fast as 0.1 trillionth of a second, to study how they move.”

The researchers use a tightly focused laser spot to liberate some electrons in their sample. They trace these electrons by mapping out the “reflectance” of the sample, or the percentage of light they reflect.

“We see most objects because they reflect light to our eyes,” Scott said. “Brighter objects have larger reflectance. On the other hand, dark objects absorb light, which is why dark clothes become hot in the summer. When a mobile electron moves to a certain location of the sample, it makes that location slightly brighter by changing how electrons in that location interact with light. The effect is very small — even with everything optimized, one electron only changes the reflectance by 0.1 part per million.”

To detect such a small change, the researchers liberated 20,000 electrons at once, using a probe laser to reflect off the sample and measure this reflectance, repeating the process 80 million times for each data point. They found the electrons on average move ballistically for about 20-trillionths of a second with a speed of 22 kilometers per second before running into something that terminates their ballistic motion.

The research was funded by a grant from the Department of Energy under the program of Physical Behavior of Materials.

Zhao said currently his lab is working to refine their material design to guide electrons more efficiently to the desired graphene layer, and trying to find ways to make them move longer distances ballistically.

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Survey finds chain store pharmacy employees dissatisfied with working conditions

LAWRENCE — A newly published survey from University of Kansas researchers reveals that chain store pharmacists and pharmacy technicians were dissatisfied with certain job conditions even before the COVID-19 pandemic increased their stress, and it sheds light on some of the strike actions they’ve undertaken this year. Researchers surveyed 129 pharmacists and 111 pharmacy technicians, asking them 92 questions about their work, including perceptions of their workplace autonomy, competence, relationships, pay satisfaction and benefit satisfaction.

Advantages of scheduling retail employees with higher performers revealed in new study

LAWRENCE — New research from the University of Kansas School of Business examines how sales employees’ social contexts — particularly their being co-scheduled with higher performers — relate to changes in performance over time. Results show co-scheduling with higher performers has an immediate negative effect but is positively associated with performance over time.

Full stories below.

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Contact: Rick Hellman, KU News Service, 785-864-8852, [email protected], @RickHellman

Survey finds chain store pharmacy employees dissatisfied with working conditions

LAWRENCE — A newly published survey reveals that chain store pharmacists and pharmacy technicians were dissatisfied with certain job conditions even before the COVID-19 pandemic increased their stress, and it sheds light on some of the strike actions they’ve undertaken this year.

The paper, “Pharmacy Work: Intrinsic Motivation and Extrinsic Rewards Across Role and Setting,” was just published in the Journal of the American Pharmacists Association. The co-authors are Angela Gist-Mackey and Cameron Piercy, both associate professors in the University of Kansas Department of Communication Studies, and Jessica Bates, clinical associate professor in the KU School of Pharmacy.

They surveyed 129 pharmacists and 111 pharmacy technicians, asking them 92 questions about their work, including perceptions of their workplace autonomy, competence, relationships, pay satisfaction and benefit satisfaction. The pharmacies in which they worked were categorized into one of three settings: chain store, independent or health care system.

The survey was conducted in 2020, just before COVID-19 pandemic lockdowns were declared across the country and around the world.

“Even before the pandemic, there were stressors in the community-retail sector: just feeling a little undervalued, staff hours constantly being cut, pharmacist overlap hours being cut and additional tasks being added to your workday,” Bates said. “Then with a pandemic and the introduction of a lot more vaccinations into your normal workflow, it really adds to the stress. Plus, people were leaving the health care workforce in general just because of the pandemic, and many had fears of what the illness might do to them personally.”

Bates said that not only have “lots more vaccinations been given, but the volume of regular prescriptions is continuing to increase as the population ages.”

For Gist-Mackey, “the more compelling finding” is the perception of pay and benefits by chain store workers.

“We asked our participants about their income, and that did not vary across context. But what was really interesting was that chain employees were largely dissatisfied with their compensation and pay, even though they’re being equitably compensated,” Gist-Mackey said. “So there is something happening in chain store workplace contexts. … I would argue it’s likely they feel they’re just not being compensated enough to deal with the kinds of things chain pharmacy employees are having to deal with at work. It doesn’t seem worth it.”

These findings of relative satisfaction — with both pay and other conditions — were consistent within pharmacy setting, applying to both pharmacists and lower-paid pharmacy technicians.

“We expected, and hypothesized, that pharmacy technicians and the pharmacists would differ a lot,” Piercy said. “But what we found is the setting is the big driving force here. It’s not the role that you’re in.”

The KU researchers said they initially received some pushback from journal editors, concerned they had exaggerated the influence of the chain store setting in their study. But while in the review process, a series of strikes this fall by CVS and Walgreens pharmacists seemed to soften their objections, Gist-Mackey said.

“It helped us persuade the editorial team that we’re not exaggerating those findings around context, that where you’re working does matter, and that it is negatively affecting people’s work lives, so much so that they were willing to walk out to make a stand for better conditions,” Gist-Mackey said. “We’ll see if anything changes.”

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Refollow @KUNews for KU News Service stories, discoveries and experts.

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Contact: Jon Niccum, KU News Service, 785-864-7633, [email protected]

Advantages of scheduling retail employees with higher performers revealed in new study

LAWRENCE — One barely has to wade into a Reddit thread in which workers whine about their employer before encountering something related to shifts. This often focuses on with whom a worker is scheduled and how that makes things better or worse.

“Shift work is prevalent in most businesses, and yet it doesn’t really fit into any of our big pillars of HR research,” said Patrick Downes, associate professor of management & entrepreneurship at the University of Kansas School of Business.

That void in the literature led to his new article, “A Relational View of Shiftwork: Co-scheduling With Higher Performers.” It examines how sales employees’ social contexts — particularly their being co-scheduled with higher performers — relate to changes in performance over time. Results show co-scheduling with higher performers has an immediate negative effect but is positively associated with performance over time.

It’s published in Human Resource Management.

Co-written with KU doctoral candidate Ella Lee, the article finds that management often views shift work only from an operations perspective.

“They think, ‘If I’m going to have 1,000 customers, then I need 10 employees to service those 1,000 customers across a certain period of time. Therefore, we just need 10 bodies scheduled on Thursday,’” Downes said.

“Our point is that when you put those 10 people in there, now you’ve created all these social interactions — actually 45 possible pairs of social interactions. So how does that affect the business?”

The study determined that if a sales employee works one week with a higher performer, then the employee’s performance will initially be slightly worse. But in the following month, the employee’s performance goes up about 2% per week.

“So if you work a full month with someone better than you, then the next month you’re going to be almost 8% higher in terms of your sales,” Downes said.

Conversely, if the same employee works with a lower performer, the results do not decline.

“One of the reasons is you don’t learn from lower performers quite in the same way as higher performers. If someone is not as good, it’s not like you can learn something from them that can be put into practice,” he said.

This study applies primarily to sales-related jobs. More interdependent shift work where employees have to rely on each other – line cooks in a restaurant, for example – does not offer the same competitive component.

“Because if you’re really good, it’s not going to hurt me if we have to team up to serve this customer,” Downes said.

His theory was tested using archival records of a large U.S. consumer retail organization. Records included monthly sales metrics and shifts worked in a single year by 7,893 retail sales representatives.

“It’s a big dataset involving several hundred stores,” he said. “We looked at every shift that every employee co-worked with somebody else. Then we went back and looked at, ‘OK, this person was a better performer than you in the past, and you spent four hours with them on this day. So how did that predict your performance a month later?’”

Downes is currently in his third year at KU. He teaches topics in HR, and his research focuses on how employees’ social contexts affect their motivation. Human Resource Management awarded Downes and Lee the 2023 Best Article Award for their study.

If the professor suddenly found himself in charge of an HR department, how would he implement these findings?

“I think particularly at scale, one of the things happening now in organizations is a big push to use data to make people-related decisions. And this is a space where the big companies and medium-sized companies can do this,” Downes said.

“If you have a few hundred shift workers, it’s worth investing in some analytical models to decide who should be working with who, and when and where.”

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KU News Service

1450 Jayhawk Blvd.

Lawrence KS 66045

Phone: 785-864-3256

Fax: 785-864-3339

[email protected]

http://www.news.ku.edu

Erinn Barcomb-Peterson, director of news and media relations, [email protected]

Today’s News is a free service from the Office of Public Affairs