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Highlights

Highlights

(a) High-resolution transmission electron micrograph showing the interface between PbSe and an InAs substrate. (b) Mid-infrared photoluminescence spectra from IV-VI/GaAs heterostructures overlapping with absorption of methane
(a) High-resolution transmission electron micrograph showing the interface between PbSe and an InAs substrate. (b) Mid-infrared photoluminescence spectra from IV-VI/GaAs heterostructures overlapping with absorption of methane
May 20, 2020
University of California, Santa Barbara

Interfacing with Topological Crystalline Insulators

B. Haidet, UC Santa Barbara E. Hughes, UC Santa Barbara K. Mukherjee, UC Santa Barbara
We demonstrate a route to high quality interfaces between IV-VI PbSnSe and conventional III-V semiconductors, offering means to host and manipulate electronic states that arise at this interface. We can now clarify the extent to which topological protection from backscattering persist in systems at relevant length scales for logic and interconnects using these novel materials. Heterostructures between IV-VI and III-V materials may enable mid-infrared on-chip environmental and biological sensing.
Point Defects in hexagonal BN for Quantum Information Science
Point Defects in hexagonal BN for Quantum Information Science
May 20, 2020
University of California, Santa Barbara

Point Defects in hexagonal BN for Quantum Information Science

M. E. Turiansky, UC Santa Barbara A. Alkauskas, Kaunas University of Technology L. C. Bassett, Unversity of Pennsylvania C. G. Van de Walle, UC Santa Barbara
Hexagonal boron nitride is a suitable host for single-photon emitters and single-spin centers.  Strong single-photon emission has been observed, but the source was not identified.  Based on advanced first-principles simulations, the origins have now been pinpointed: the 2 eV emission has been attributed to boron dangling bonds, and 4 eV emission to carbon-carbon dimers.
Modeling liquid-liquid phase separation to control polymer architecture.
Modeling liquid-liquid phase separation to control polymer architecture.
May 20, 2020
University of California, Santa Barbara

Microstructure modeling in nonsolvent induced phase separation (NIPS) 

Tree, BYU Dos Santos, UC Santa Barbara Wilson, UC Santa Barbara Scott, UC Santa Barbara Garcia, UC Santa Barbara Fredrickson, UC Santa Barbara
NIPS is a non-equilibrium liquid-liquid phase separation phenomenon used to make polymer membranes through solvent-nonsolvent exchange. Newly developed phase-field simulations allow investigation of coupled mass transfer, flow and thermodynamic instability during processing and the corresponding microstructures that result from variations in film composition and thickness. These simulation tools provide critical insight into the nonequilibrium processing of complex fluids to make architectured, resilient solids and soft materials.
Left: Crystal structure of FePd1−xPtxMo3N. Right: Magnetic phase diagram of FePtMo3N showing the emergence of a skyrmion state in the “A” region. FD shows the fluctuation disordered regime.
Left: Crystal structure of FePd1−xPtxMo3N. Right: Magnetic phase diagram of FePtMo3N showing the emergence of a skyrmion state in the “A” region. FD shows the fluctuation disordered regime.
May 20, 2020
University of California, Santa Barbara

Controlling skyrmion size in the alloy FePd1−xPtxMo3N

Kautzsch, UC Santa Barbara Bocarsly, UC Santa Barbara Felser, MPI-CPFS, Dresden Wilson, UC Santa Barbara Seshadri, UC Santa Barbara
After discovering a new magnetic host of skyrmion states, UC Santa Barbara IRG-1 researchers were able to show that chemically alloying the compound FePd1−xPtxMo3N allows for the size of the skyrmion defects to be controlled while still preserving their stability.  Skyrmion states are broadly sought in new materials due to their potential uses in low power memory devices and other spin-based electronics.
Image source: M. K. Mahanthappa, M. A. Hillmyer, T. M. Reineke, T. P. Lodge and J. I. Siepmann
Image source: M. K. Mahanthappa, M. A. Hillmyer, T. M. Reineke, T. P. Lodge and J. I. Siepmann
May 15, 2020
University of Minnesota - Twin Cities

Computational Design of Triblock Amphiphiles with 1-nm Domains

M. K. Mahanthappa, M. A. Hillmyer, T. M. Reineke, T. P. Lodge and J. I. Siepmann
Block polymers are a class of versatile self-assembling soft materials that can form exquisite nanostructures for applications including ion transport membranes for batteries and fuel cells, and templates for inorganic oxide catalysts. Using molecular dynamics simulations and transferable force fields, we designed a series of symmetric triblock amphiphiles (or high-χ “block oligomers”) comprising incompatible sugar-based (A) and hydrocarbon (B) blocks that can self-assemble into ordered nanostructures with full domain pitches as small as 1.2 nm.
Image source: C. Leighton and C. Daniel Frisbie
Image source: C. Leighton and C. Daniel Frisbie
May 15, 2020
University of Minnesota - Twin Cities

From Semiconductor to Metal in Two-dimensional Tellurium

C. Leighton and C. Daniel Frisbie, University of Minnesota
Atomically-thin sheets of semiconductors have been of immense interest since the Nobel-Prize-winning discovery of graphene or two-dimensional (2D) carbon. Such materials represent the ultimate limit of “scaling” to small sizes, of vital importance in the semiconductor device industry. A particularly exciting recent (2017) finding is that the elemental semiconductor tellurium can be created in 2D sheets, with highly mobile electrons.
BResearchers at Cornell have developed a new class of voltage-controllable electrochemical actuators that operate at low voltages (200 mV), and are completely compatible with silicon processing. The actuators are made of a 7-nm thin film of platinum capped on one side by titanium dioxide. When voltage is applied to the titanium, ions from the surrounding solution adsorb onto its uncapped surface causing surface stresses that bend the film. To demonstrate their potential, standard silicon fabrication was employed to make prototype sub-100-micron walking robots with these actuators. These results establish a clear pathway to mass-manufactured, complex and functional robots too small to be resolved by the naked eye.
BResearchers at Cornell have developed a new class of voltage-controllable electrochemical actuators that operate at low voltages (200 mV), and are completely compatible with silicon processing. The actuators are made of a 7-nm thin film of platinum capped on one side by titanium dioxide. When voltage is applied to the titanium, ions from the surrounding solution adsorb onto its uncapped surface causing surface stresses that bend the film. To demonstrate their potential, standard silicon fabrication was employed to make prototype sub-100-micron walking robots with these actuators. These results establish a clear pathway to mass-manufactured, complex and functional robots too small to be resolved by the naked eye.
May 15, 2020
Cornell University

Breakthrough in materials for actuators paves way to electronically integrated microscopic robots

Fifty years of Moore’s Law scaling in microelectronics have brought remarkable opportunities for the rapidly-evolving field of microscopic robotics. Electronic, magnetic, and optical systems now offer an unprecedented combination of complexity, small size, and low cost, and could readily be appropriated to form the intelligent core of microscopic robots. But one major roadblock exists: there is no micron-scale actuator system that seamlessly integrates with semiconductor processing and responds to standard electronic control signals.
Difference in internal polarization fields at the metal-polar GaN/AlN interface gives rise to a negative sheet charge, which induces a layer of mobile positive holes– no chemical impurity doping is required. The resulting holes maintain their high densities at temperatures down to 10 degrees above absolute zero.
Difference in internal polarization fields at the metal-polar GaN/AlN interface gives rise to a negative sheet charge, which induces a layer of mobile positive holes– no chemical impurity doping is required. The resulting holes maintain their high densities at temperatures down to 10 degrees above absolute zero.
May 15, 2020
Cornell University

High-conductivity 2D holes induced by polarization discontinuity in GaN/AlN

Chaudhuri R., S. J. Bader, Z. Chen, D. A. Muller, H. G. Xing, and D. Jena (all Cornell University)
When an electrically-insulating material is grown on top of another insulator, the interface between the two insulators can be populated by mobile electrons. This has been achieved in interfaces that have a polarization discontinuity, such as AlGaN/GaN and LaAlO3/SrTiO3. It would be valuable to create a layer of mobile positive charges called holes, because electronic devices rely on charge carried by both electrons and holes.
Designing the flow properties of concentrated particle suspensions
Designing the flow properties of concentrated particle suspensions
May 15, 2020
University of Chicago

Designing the flow properties of concentrated particle suspensions

Abhinendra Singh (University of Chicago), Christopher Ness (University of Edinburgh), Ryohei Seto (Wenzhou Institute, University of Chinese Academy of Sciences), Juan J de Pablo (University of Chicago), Heinrich M Jaeger (University of Chicago)
In a concentrated suspension of small solid particles in a liquid under shear, a large number of dynamically evolving particle-particle and particle-liquid interfaces controls the overall flow properties.
Wafer-scale synthesis of monolayer two-dimensional porphyrin polymers
Wafer-scale synthesis of monolayer two-dimensional porphyrin polymers
May 15, 2020
University of Chicago

Wafer-scale synthesis of monolayer two-dimensional porphyrin polymers

Yu Zhong, Baorui Cheng, Chibeom Park, Ariana Ray, Sarah Brown, Fauzia Mujid, Jae-Ung Lee, Hua Zhou, Joonki Suh, Kan-Heng Lee, Andrew J. Mannix, Kibum Kang, S.J. Sibener, David A. Muller, and Jiwoong Park
At the University of Chicago MRSEC, Park and Sibener developed a synthesis of two-dimensional (2D) polymers with wafer-scale homogeneity, one monolayer thick, using a general and scalable growth method called laminar assembly polymerization.

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