Tag Archives: Pennsylvania State University (Penn State)

Cannibalisitic nanostructures

I think this form of ‘cannibalism’ could also be described as a form of ‘self-assembly’. That said, here is an August 31, 2018 news item on ScienceDaily announcing ‘cannibalistic’ materials,

Scientists at the [US] Department of Energy’s [DOE] Oak Ridge National Laboratory [ORNL] induced a two-dimensional material to cannibalize itself for atomic “building blocks” from which stable structures formed.

The findings, reported in Nature Communications, provide insights that may improve design of 2D materials for fast-charging energy-storage and electronic devices.

An August 31, 2018 DOE/Oak Ridge National Laboratory news release (also on EurekAlert), which originated the news item, provides more detail (Note: Links have been removed),

“Under our experimental conditions, titanium and carbon atoms can spontaneously form an atomically thin layer of 2D transition-metal carbide, which was never observed before,” said Xiahan Sang of ORNL.

He and ORNL’s Raymond Unocic led a team that performed in situ experiments using state-of-the-art scanning transmission electron microscopy (STEM), combined with theory-based simulations, to reveal the mechanism’s atomistic details.

“This study is about determining the atomic-level mechanisms and kinetics that are responsible for forming new structures of a 2D transition-metal carbide such that new synthesis methods can be realized for this class of materials,” Unocic added.

The starting material was a 2D ceramic called a MXene (pronounced “max een”). Unlike most ceramics, MXenes are good electrical conductors because they are made from alternating atomic layers of carbon or nitrogen sandwiched within transition metals like titanium.

The research was a project of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, a DOE Energy Frontier Research Center that explores fluid–solid interface reactions that have consequences for energy transport in everyday applications. Scientists conducted experiments to synthesize and characterize advanced materials and performed theory and simulation work to explain observed structural and functional properties of the materials. New knowledge from FIRST projects provides guideposts for future studies.

The high-quality material used in these experiments was synthesized by Drexel University scientists, in the form of five-ply single-crystal monolayer flakes of MXene. The flakes were taken from a parent crystal called “MAX,” which contains a transition metal denoted by “M”; an element such as aluminum or silicon, denoted by “A”; and either a carbon or nitrogen atom, denoted by “X.” The researchers used an acidic solution to etch out the monoatomic aluminum layers, exfoliate the material and delaminate it into individual monolayers of a titanium carbide MXene (Ti3C2).

The ORNL scientists suspended a large MXene flake on a heating chip with holes drilled in it so no support material, or substrate, interfered with the flake. Under vacuum, the suspended flake was exposed to heat and irradiated with an electron beam to clean the MXene surface and fully expose the layer of titanium atoms.

MXenes are typically inert because their surfaces are covered with protective functional groups—oxygen, hydrogen and fluorine atoms that remain after acid exfoliation. After protective groups are removed, the remaining material activates. Atomic-scale defects—“vacancies” created when titanium atoms are removed during etching—are exposed on the outer ply of the monolayer. “These atomic vacancies are good initiation sites,” Sang said. “It’s favorable for titanium and carbon atoms to move from defective sites to the surface.” In an area with a defect, a pore may form when atoms migrate.

“Once those functional groups are gone, now you’re left with a bare titanium layer (and underneath, alternating carbon, titanium, carbon, titanium) that’s free to reconstruct and form new structures on top of existing structures,” Sang said.

High-resolution STEM imaging proved that atoms moved from one part of the material to another to build structures. Because the material feeds on itself, the growth mechanism is cannibalistic.

“The growth mechanism is completely supported by density functional theory and reactive molecular dynamics simulations, thus opening up future possibilities to use these theory tools to determine the experimental parameters required for synthesizing specific defect structures,” said Adri van Duin of Penn State [Pennsylvania State University].

Most of the time, only one additional layer [of carbon and titanium] grew on a surface. The material changed as atoms built new layers. Ti3C2 turned into Ti4C3, for example.

“These materials are efficient at ionic transport, which lends itself well to battery and supercapacitor applications,” Unocic said. “How does ionic transport change when we add more layers to nanometer-thin MXene sheets?” This question may spur future studies.

“Because MXenes containing molybdenum, niobium, vanadium, tantalum, hafnium, chromium and other metals are available, there are opportunities to make a variety of new structures containing more than three or four metal atoms in cross-section (the current limit for MXenes produced from MAX phases),” Yury Gogotsi of Drexel University added. “Those materials may show different useful properties and create an array of 2D building blocks for advancing technology.”

At ORNL’s Center for Nanophase Materials Sciences (CNMS), Yu Xie, Weiwei Sun and Paul Kent performed first-principles theory calculations to explain why these materials grew layer by layer instead of forming alternate structures, such as squares. Xufan Li and Kai Xiao helped understand the growth mechanism, which minimizes surface energy to stabilize atomic configurations. Penn State scientists conducted large-scale dynamical reactive force field simulations showing how atoms rearranged on surfaces, confirming defect structures and their evolution as observed in experiments.

The researchers hope the new knowledge will help others grow advanced materials and generate useful nanoscale structures.

Here’s a link to and a citation for the paper,

In situ atomistic insight into the growth mechanisms of single layer 2D transition metal carbides by Xiahan Sang, Yu Xie, Dundar E. Yilmaz, Roghayyeh Lotfi, Mohamed Alhabeb, Alireza Ostadhossein, Babak Anasori, Weiwei Sun, Xufan Li, Kai Xiao, Paul R. C. Kent, Adri C. T. van Duin, Yury Gogotsi, & Raymond R. Unocic. Nature Communicationsvolume 9, Article number: 2266 (2018) DOI: https://doi.org/10.1038/s41467-018-04610-0 Published 11 June 2018

This paper is open access.

Is the medium the message? Virtual museums and the the user’s experience technology experience

A Sept. 21, 2015 Pennsylvania State University (Penn State) news release by Matt Swayne (also on EurekAlert) puts a different spin on art/science (Note: Links have been removed),

Museum curators planning to develop virtual exhibits online should choose communication and navigation technologies that match the experience they want to offer their visitors, according to a team of researchers.

“When curators think about creating a real-world exhibit, they are thinking about what the theme is and what they want their visitors to get out of the exhibit,” said S. Shyam Sundar, Distinguished Professor of Communications and co-director of the Media Effects Research Laboratory. “What this study suggests is that, just like curators need to be coherent in the content of the exhibit, they need to be conscious of the tools that they employ in their virtual museums.” [emphasis mine]

For some reason that phrase “need to be conscious of the tools that they employ” reminds of Marshall McLuhan and his dictum “the medium is the message.” Here’s more about study from the news release,

Many museum curators hope to create an authentic experience in their online museums by using technology to mimic aspects of the social, personal and physical aspects of a real-world museum experience. However, a more-is-better approach to technology may actually hinder that authentic experience, the researchers suggest.

In a study, visitors to an online virtual art museum found that technology tools used to communicate about and navigate through the exhibits were considered helpful when they were available separately, but less so when they were offered together. The researchers tested customization tools that helped the participants create their own art gallery, live-chat technology to facilitate communication with other visitors and 3-D tool navigation tools that some participants used to explore the museum.

The participants’ experiences often depended on what tools and what combinations of tools they used, according to the researchers, who released their findings in a recent issue of the International Journal of Human-Computer Interaction.

The news release goes on to provide some examples of when technologies do not mesh together for a good experience,

“When live chat and customization are offered together, for example, the combination of tools may be perceived to have increased usability, but it turns out using either customization or live chat separately was greater than either both functions together, or neither of the functions,” said Sundar. “We saw similar results not just with perceived usability, but also with sense of control and agency.”

The live chatting tool gave participants a feeling of social presence in the museum, but when live chatting was used in conjunction with the 3D navigation tool, the visitor had less of a sense of control, said Sundar, who worked with Eun Go, assistant professor of broadcasting and journalism, Western Illinois University; Hyang-Sook Kim, assistant professor of mass communication and media communication studies, Towson University and Bo Zhang, doctoral candidate in mass communications, Penn State.

Similarly, participants indicated the live chatting function lessened the realistic experience of the 3D tool, according to the researchers, who suggested that chatting may increase the user’s cognitive burden as they try to navigate through the site.

Each of these tools carries unique meaning for users, Sundar said. While customization provides an individualized experience, live-chatting signals a social experience of the site.

“Our data also suggest that expert users prefer tools that offer more agency or control to users whereas novices appreciate a variety of tools on the interface,” he added.

Users may react to these tools on other online platforms, not just during visits to online museums, Sundar said.

“We might be able to apply this research on tools you might add to news sites, for example, or it could be used to improve educational sites and long-distance learning,” he added. “You just have to be careful about how you deploy the tools because more is not always better.”

The researchers recruited 126 participants for the study. The subjects were assigned one of eight different website variations that tested their reactions to customization, live chat, 3D navigation and combinations of those tools during their visit to a virtual version of the Museum of Modern Art. The museum’s artworks were made available through the Google Art Project.

Here’s a link to and a citation for the paper,

Communicating Art, Virtually! Psychological Effects of Technological Affordances in a Virtual Museum by S. Shyam Sundar, Eun Goc, Hyang-Sook Kim, & Bo Zhang. International Journal of Human-Computer Interaction
Volume 31, Issue 6, 2015 pages 385-401 DOI: 10.1080/10447318.2015.1033912 Accepted author version posted online: 15 Apr 2015

This paper is behind a paywall.