GPKOW

Researchers grew a twisted multilayer crystal structure for the first time and measured the structure's key properties. The twisted structure could help researchers develop next-generation materials for solar cells, quantum computers, lasers and other devices. Researchers with the Department of Energy's SLAC National Accelerator Laboratory, Stanford University and the DOE's Lawrence Berkeley National Laboratory (LBNL) grew a twisted multilayer crystal structure for the first time and measured the structure's key properties. The twisted structure could help researchers develop next-generation materials for solar cells, quantum computers, lasers and other devices. "This structure is something that we have not seen before -- it was a huge surprise to me," said Yi Cui, a professor at Stanford and SLAC and paper co-author. "A new quantum electronic property could appear within this three-layer twisted structure in future experiments." Adding layers, with a twist The crystals the team designed extended the concept of epitaxy, a phenomenon that occurs when one type of crystal material grows on top of another material in an ordered way -- kind of like growing a neat lawn on top of soil, but at the atomic level. Understanding epitaxial growth has been critical to the development of many industries for more than 50 years, particularly the semiconductor industry. Indeed, epitaxy is part of many of the electronic devices that we use today, from cell phones to computers to solar panels, allowing electricity to flow, and not flow, through them. To date, epitaxy research has focused on growing one layer of material onto another, and the two materials have the same crystal orientation at the interface. This approach has been successful for decades in many applications, such as transistors, light-emitting diodes, lasers and quantum devices. But to find new materials that perform even better for more demanding needs, like quantum computing, researchers are searching for other epitaxial designs -- ones that might be more complex, yet better performing, hence the "twisted epitaxy" concept demonstrated in this study. In their experiment, detailed this month in Science, researchers added a layer of gold between two sheets of a traditional semiconducting material, molybdenum disulfide (MoS2). Because the top and bottom sheets were oriented differently, the gold atoms could not align with both simultaneously, which allowed the Au structure to twist, said Yi Cui, Professor Cui's graduate student in materials science and engineering at Stanford and co-author of the paper. "With only a bottom MoS2 layer, the gold is happy to align with it, so no twist happens," said Cui, the graduate student. "But with two twisted MoS2 sheets, the gold isn't sure to align with the top or bottom layer. We managed to help the gold solve its confusion and discovered a relationship between the orientation of Au and the twist angle of bilayer MoS2." Zapping gold nanodiscs To study the gold layer in detail, the researcher team from the Stanford Institute for Materials and Energy Sciences (SIMES) and LBNL heated a sample of the whole structure to 500 degrees Celsius. Then they sent a stream of electrons through the sample using a technique called transmission electron microscopy (TEM), which revealed the morphology, orientation and strain of the gold nanodiscs after annealing at the different temperatures. Measuring these properties of the gold nanodiscs was a necessary first step toward understanding how the new structure could be designed for real world applications in the future. "Without this study, we would not know if twisting an epitaxial layer of metal on top of a semiconductor was even possible," said Cui, the graduate student. "Measuring the complete three-layer structure with electron microscopy confirmed that it was not only possible, but also that the new structure could be controlled in exciting ways." Next, researchers want to further study the optical properties of the gold nanodiscs using TEM and learn if their design alters physical properties like band structure of Au. They also want to extend this concept to try to build three-layer structures with other semiconductor materials and other metals. "We're beginning to explore whether only this combination of materials allows this or if it happens more broadly," said Bob Sinclair, the Charles M. Pigott Professor in Stanford's school of Materials Science and Engineering and paper co-author. "This discovery is opening a whole new series of experiments that we can try. We could be on our way to finding brand new material properties that we could exploit."

A research team has achieved a groundbreaking advancement in nanomaterials by successfully developing a highly efficient electrocatalyst which can enhance the generation of hydrogen significantly through electrochemical water splitting. This major breakthrough has great application potential for the clean energy industry. An international team led by City University of Hong Kong (CityU) has announced a groundbreaking step forward that has added significantly to the technical know-how required to clean up the planet. The discovery, published in the journal Nature, centres on developing a highly efficient electrocatalyst that can enhance hydrogen generation through electrocatalytic water splitting. Titled "Phase-dependent growth of Pt on MoS2 for highly efficient H2 evolution," the paper was published on 13 September in London. Cleaner energy sources are desperately needed, but the challenges in weaning the world off fossil fuels and onto more sustainable energies are enormous. "Hydrogen generated by electrocatalytic water splitting is regarded as one of the most promising clean energies for replacing fossil fuels in the near future, reducing environmental pollution and the greenhouse effect," said Professor Zhang Hua, Herman Hu Chair Professor of Nanomaterials at CityU, who is spearheading the research. Professor Zhang's collaborators include Professor Anthony R. J. Kucernak from the Department of Chemistry at Imperial College London and researchers from universities and research institutes in Hong Kong, mainland China, Singapore and the UK. The critical development in the CityU-led research is establishing novel catalysts by using the transition-metal dichalcogenide (TMD) nanosheets as supports, enabling superior efficiency and high stability during the electrocatalytic hydrogen evolution reaction (HER), a vital step in electrocatalytic water-splitting, also known as the water electrolysis technique, for hydrogen production. The team has been exploring how to enhance the performance of the HER process by engineering the crystal phase of nanomaterials for several years. Although TMD nanosheets with unconventional crystal phases possess great potential to be used as catalyst supports, fabricating such sheets pure enough for HER is far from straightforward. But in this research, Professor Zhang's team has developed a new method to prepare unconventional-phase TMD nanosheets with high phase-purity and quality. Furthermore, they have investigated the crystal phase-dependent growth of noble metals on the TMD nanosheet supports. Technically speaking, they found that the 2H-phase template facilitates the epitaxial growth of Pt nanoparticles, whereas the 1T′-phase template supports single-atomically dispersed Pt atoms (s-Pt). The synthesised s-Pt/1T′-MoS2 serves as a highly efficient catalyst for HER and can work for 500 hours in the water electrolyser, demonstrating that 1T′-TMD nanosheets could be effective supports for catalysts. "We will develop more efficient catalysts based on this finding and explore their applications in various catalytic reactions," said Dr Shi Zhenyu, a postdoctoral researcher in CityU's Department of Chemistry and the first author of the paper. These findings expand the scope of phase engineering in nanomaterials, paving the way for the design and synthesis of highly efficient catalysts, contributing to cleaner energies and more sustainable development.

The electrochemical sensor, made of a graphitic nano-onion/molybdenum disulfide nanosheet composite, detects human papillomavirus (HPV)-16 and HPV-18, with high specificity SEOUL, South Korea, Sept. 8, 2023 /PRNewswire/ -- Molybdenum disulfide (MoS2) has recently garnered attention among materials science researchers owing to its ability to form two-dimensional nanosheets like graphene. The nanosheets are created by the stacking of S–Mo–S layers interacting via Van der Waals interactions. Additionally, the unique structural, optical, thermal, and electrochemical properties of MoS2 have opened up multiple research avenues across several fields, including the development of biomolecule sensing and chemical detection platforms, optoelectronics, supercapacitors, and batteries. Continue Reading Chung-Ang University researchers have developed a novel electrochemical nano-onion/molybdenum disulfide nanosheet composite-based DNA biosensor that efficiently and specifically detects human papillomavirus (HPV)-16 and HPV-18, enabling early diagnosis of cervical cancer. Traditionally, carbon nanostructures have been employed as an immobilization platform for DNA. In order to substitute carbon with MoS2 as an effective electrochemical DNA sensor, the electrical conductivity of MoS2 needs to be improved considerably. Against this backdrop, Associate Professor Eunah Kang and Mr. Youngjun Kim from the School of Chemical Engineering and Material Science at Chung-Ang University, Korea have recently come up with an elegant solution. The duo has developed an electrochemical DNA biosensor using a graphitic nano-onion/molybdenum disulfide (MoS2) nanosheet composite, which effectively detects human papillomavirus (HPV)-16 and HPV-18, and can serve as an early diagnosis of cervical cancer. "Nano-onions possess graphitic sp2 structures and are derived from crystalline sp3 nanodiamonds via thermal annealing or laser irradiation," explains Dr. Kang. Their breakthrough was published in Volume 21 of the Journal of Nanobiotechnology on 10 June 2023. The researcher duo prepared the novel electrode surface for probing DNA chemisorption by enabling chemical conjugation between two functional groups: acyl bonds on the surfaces of functionalized nano-onions and amine groups present on the modified MoS2 nanosheets. Cyclic voltammetry experiments revealed that a 1:1 composite electrode had an improved rectangular shape compared to that of an MoS2 nanosheet electrode. "This indicated the amorphous nature of the nano-onions with curved carbon layers that facilitated an enhancement in electronic conductivity compared to MoS2 nanosheet alone," highlights Dr. Kang. Additionally, the duo measured the sensitivity of their novel electrochemical DNA biosensor device towards HPV-16 and HPV-18 by employing differential pulse voltammetry (DPV) technique in the presence of methylene blue (MB) as a redox indicator. Dr. Kang elaborates: "The DPV current peak was lowered after probe DNA chemisorption and target DNA hybridization. Since the hybridized DNA was double-stranded, it induced less effective MB electrostatic intercalation, resulting in a lower oxidation peak." The duo found that, compared to the MoS2 nanosheet electrode, the nano-onion/MoS2 nanosheet composite electrode attained higher current peaks, indicating a greater change in the differential peak. This was attributed to an enhanced conductive electron transfer owing to the nano-onion. Notably, the target DNAs produced from HPV-16 and HPV-18 Siha and Hela cancer cell lines were detected by the proposed sensor effectively and with high specificity. Consequently, MoS2 nanosheets with improved electrical conductivity facilitated by complexation with nano-onions provides a suitable platform for developing effective and efficient electrochemical biosensors for the early diagnosis of a wide variety of ailments, including cervical cancer. Furthermore, combining nano-onions or nanodiamonds with different organic biomaterials can facilitate chemical functionality, electron transfer conductivity, light absorption, and more. These, in turn, can lead to innovative disease sensing, targeted drug delivery systems, and biomedical imaging and diagnostics. Reference Title of original paper: A graphitic nano-onion/molybdenum disulfide nanosheet composite as a platform for HPV-associated cancer-detecting DNA biosensors Journal: Journal of Nanobiotechnology DOI: About Chung-Ang University Website: Media contact: Se-Jin Oh [email protected] 02-820-6614 SOURCE Chung-Ang University