Creating ‘movies’ of thin film g…

Creating ‘movies’ of thin film growth

From paint on a wall to tinted car windows, thin films make up a wide variety of materials found in ordinary life. But thin films are also used to build some of today’s most important technologies, such as computer chips and solar cells. Seeking to improve the performance of these technologies, scientists are studying the mechanisms that drive molecules to uniformly stack together in layers—a process called crystalline thin film growth. Now, a new research technique could help scientists understand this growth process better than ever before.

Researchers from the University of Vermont, Boston University, and the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have demonstrated a new experimental capability for watching thin film growth in real-time. Using the National Synchrotron Light Source II (NSLS-II)—a DOE Office of Science User Facility at Brookhaven—the researchers were able to produce a “movie” of thin film growth that depicts the process more accurately than traditional techniques can. Their research was published on June 14, 2019 in Nature Communications.

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A new quasi-2D superconductor that bridges a…

A new quasi-2D superconductor that bridges a ferroelectric and an insulator

Researchers at the Zavoisky Physical-Technical Institute and the Southern Scientific Center of RAS, in Russia, have recently fabricated quasi-2-D superconductors at the interface between a ferroelectric Ba0.8Sr0.2TiO3 film and an insulating parent compound of La2CuO4. Their study, presented in a paper published in Physical Review Letters, is the first to achieve superconductivity in a heterostructure consisting of a ferroelectric and an insulator.

The idea of forming a quasi-2-D superconducting layer at the interfacebetween two different compounds has been around for several years. One past study, for instance, tried to achieve this by creating a thin superconducting layer between two insulating oxides (LaAlO3 and SrTiO3) with a critical temperature of 300mK. Other researchers observed the thin superconducting layer in bilayers of an insulator (La2CuO4) and a metal (La1.55Sr0.45CuO4), neither of which is superconducting in isolation.

“Here we put forward the idea that thin charged layer on the interface between ferroelectric and insulator is formed in order to screen the electric field,” Viktor Kabanov and Rinat Mamin, two researchers who carried out the study, told via email. “This thin layer may be conducting or superconducting depending on the properties of the insulator. In order to get a superconducting layer, we chose La2CuO4 – an insulator that becomes a high Tc superconductor when it is doped by carriers.”

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Ice lithography: Opportunities and challenge…

Ice lithography: Opportunities and challenges in 3-D nanofabrication

Nanotechnology and nanoscience are enabled by nanofabrication. Electron-beam lithography (EBL), which makes patterns down to a few nanometers, is one of the fundamental pillars of nanofabrication. In the past decade, significant progress has been made in electron-beam-based nanofabrication, such as the emerging ice lithography (IL) technology, in which ice thin-films are used as resists and patterned by a focused electron-beam. The entire process of IL nanofabrication is sustainable and streamlined because spin coating and chemical developing steps commonly required for EBL resists are made needless.

A fresh review “Ice lithography for 3-D nanofabrication” by Prof. Min Qiu at Westlake University is published in Science Bulletin. In this review, the authors present current status and future perspectives of ice lithography (IL). Different ice resists and IL instrument design are also introduced. Special emphasis is placed on advantages of IL for 3-D nanofabrication.

The IL technology was first proposed by the Nanopore group at Harvard University in 2005. Water ice is the first identified ice resist for IL, and it is still the only one positive-tone lithography resist so far. As shown in Fig.1, water ice is easily removed within the electron-beam exposure area. Organic ice condensed from simple organic molecules, such as alkanes, demonstrates a negative-resist-like capability, which means only exposed patterns remain on the substrate after heating the sample to room temperature.

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Researchers find a way to produce free-stand…

Researchers find a way to produce free-standing films of perovskite oxides

A team of researchers from Nanjing University in China, the University of Nebraska and the University of California in the U.S. has found a way to produce free-standing films of perovskite oxide. In their paper published in the journal Nature, the group describes the process they developed and how well it worked when tested. Yorick Birkhölzer and Gertjan Koster from the University of Twente have published a News and Views piece on the work done by the team in the same journal issue.

Birkhölzer and Koster point out that many new materials are made by going to extremes—making them really big or really small. Making them small has led to many recent discoveries, they note, including a technique to make graphene. One area of research has focused on ways to produce transition-metal oxides in a thinner format. It has been slow going, however, due to their crystalline nature. Unlike some materials, transition-metal oxides do not naturally form into layers with a top layer that can be peeled off. Instead, they form in strongly bonded 3-D structures. Because of this, some in the field have worried that it might never be possible to produce them in desired forms. But now, the researchers with this new effort have found a way to produce two transition-metal oxides (perovskite oxides strontium titanate and bismuth ferrite) in a thin-film format.

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New Flatland material: Physicists obtain qua…

New Flatland material: Physicists obtain quasi-2D gold

Researchers from the MIPT Center for Photonics and 2-D Materials have synthesized a quasi-2-D gold film, revealing how materials not usually classified as two-dimensional can form atomically thin layers. Published in Advanced Materials Interfaces, the study shows that by using monolayer molybdenum disulfide as an adhesion layer, quasi-2-D gold can be deposited on an arbitrary surface. The team says the resulting ultrathin gold films, which are only several nanometers thick, conduct electricity very well and are useful for flexible and transparent electronics. The finding might contribute to a new class of optical metamaterials with the unique potential to control light.

The first 2-D material discovered, graphene is a one-atom-thick sheet of carbon atoms in a honeycomb formation. Its synthesis and the study of its exciting properties have given rise to an entirely new field of science and technology. The groundbreaking experiments regarding graphene earned MIPT graduates Andre Geim and Kostya Novoselov the 2010 Nobel Prize in physics.

Since then, more than 100 graphene cousins have been discovered. Their intriguing properties had applications in biomedicine, electronics and the aerospace industry. These materials belong to the class of layered crystals whose layers are weakly bound to one another but have strong internal integrity. For example, the graphite in a pencil is essentially many stacked-up layers of graphene bound so weakly that Geim and Novoselov famously used sticky tape to peel them off.

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Inorganic perovskite absorbers for use in th…

Inorganic perovskite absorbers for use in thin-film solar cells

Teams all over the world are working intensively on the development of perovskite solar cells. The focus is on what are known as metal-organic hybrid perovskites whose crystal structure is composed of inorganic elements such as lead and iodine as well as an organic molecule.

Completely inorganic perovskite semiconductors such as CsPbI3 have the same crystalline structure as hybrid perovskites, but contain an alkali metal such as caesium instead of an organic molecule. This makes them much more stable than hybrid perovskites, but usually requires an extra production step at very high temperature – several hundred degrees Celsius. For this reason, inorganic perovskite semiconductors have thus far been difficult to integrate into thin-film solar cells that cannot withstand high temperatures. A team headed by Dr. Thomas Unold has now succeeded in producing inorganic perovskite semiconductors at moderate temperatures so that they might also be used in thin-film cells in the future.

The physicists designed an innovative experiment in which they synthesised and analysed many combinations of material within a single sample. Using co-evaporation of caesium-iodide and lead-iodide, they produced thin layers of CsPbI3, systematically varying the amounts of these elements, while the substrate-temperature was less than 60 degrees Celsius.

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Tiny pinholes in thin film could pave the wa…

Tiny pinholes in thin film could pave the way for 3-D holographic displays

Researchers in Korea have designed an ultrathin display that can project dynamic, multi-colored, 3-D holographic images, according to a study published in Nature Communications.

The system’s critical component is a thin film of titanium filled with tiny holes that precisely correspond with each pixel in a liquid crystal display (LCD) panel. This film acts as a ‘photon sieve,’ whereby each pinhole diffracts light emerging from it widely, resulting in a high-definition 3-D image observable from a wide angle.

The entire system is very small: it comprises a 1.8-inch off-the-shelf LCD panel with a resolution of 1024 x 768. The titanium film, attached to the back of the panel, is a mere 300 nanometres thick.

“Our approach suggests that holographic displays could be projected from thin devices, like a cell phone,” says Professor YongKeun Park, a physicist at KAIST who led the research. The team demonstrated their approach by producing a hologram of a moving, tri-coloured cube.

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Researchers discover an economical way to pr…

Researchers discover an economical way to produce high-performance thin films for electronics

Researchers at Missouri S&T have found an unprecedented, economical method for creating high-performance inorganic thin films, or “epitaxial” films, used in the manufacture of semiconductors for flexible electronics, LEDs and solar cells.

The research is published today in Science in the paper titled “Spin Coating Epitaxial Films.”

“We’ve come up with a super-easy method that has never been done before to make these films from a solution using commercial spin coaters,” says Dr. Jay Switzer, the Donald L. Castleman/Foundation for Chemical Research Professor of Discovery in Chemistry at Missouri S&T. “This is an inexpensive and readily accessible route to single-crystal-like materials that should exhibit superior electronic and optical properties.

"In particular, our work with highly ordered epitaxial deposits of the perovskite material cesium lead bromide, a novel semiconductor used in highly efficient photovoltaic solar cells, stands to increase the efficiency of solar cells produced with this material,” Switzer adds.

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