Research

What molecular properties give rise to a strong piezoelectric response?

  • By Burcu Ozden
  • 22 November 2017

In this study Geoffrey R. Hutchison and his colleagues tried to answer the question of " What molecular properties give rise to a strong piezoelectric response?"  To do so, they systematically probe the interplay among peptide chemical structure, folding propensity, and piezoelectric properties, uncovering in the process new insights into the origin of peptide electromechanical response. They have designed variety of peptides and peptoids and test the effect of molecular properties on piezoelectric response via serious measurements including ircular dichroism (CD), Polarization-modulated infrared reflection−absorption spectroscopy (PM-IRRAS), tomic force microscopy (AFM), piezo-force microscopy (PFM), and X-ray photoelectron spectroscopy (XPS) measurements. They showed backbone rigidity is an important determinant in peptide electromechanical responsiveness. 

New Era in Thermal Scanning Probe Lithography

  • By Burcu Ozden
  • 15 November 2017

Tevis Jacobs and his collaborators from IBM and SwissLitho were achieved sub-10 nanometer feature size in Silicon using thermal scanning probe lithography. In this work, they  the t-SPL parameters that influence high-resolution patterning on the transfer stack and demonstrate that sub-15 nm half-pitch resolution patterning and transfer by t-SPL are feasible. They found that the resolution in t-SPL is limited by the extent of the plastic zone in thermo-mechanical indentation on the pattern transfer stack because, at temperatures approaching the resist’s decomposition temperature, the line shape widens, reducing the achievable resolution. They achieved reliable transfer of patterned dense lines down to 14 nm half-pitch and in the best case 11 nm half-pitch. Furthermore, evidently they showed that an enhanced resolution below 10 nm half-pitch might be possible on a mechanically different transfer stack.

The Ability to Electrically Tune the Dimensionality of mesoscopic LAO/STO Channels

  • By Burcu Ozden
  • 27 October 2017

In this work, authors used conductive atomic force microscope (c-AFM) lithography in which the conduction is controlled by surface protons that are distributed on the LAO surface. They have created two conducting channel with varying witdhs as 10 and 200nm on a  LAO/STO heterostructures grown by pulsed-laser deposition. They designed the the devices in a way that two conducting channels connected in series with two leads and voltage probes. By using silver epoxy on the bottom of the STO substrate they created contacts for a back gate voltage. They investigated changes in the magnetotransport properties on the channels with different widths by varying back gate voltage and applied magnetic field. They measured the conductance for both narrow and wide channels and demonstarted the hysteresis of both channels with back gating. Saturation of the conductance at higher gate voltages was also shown. They were able to demonstrate dimensional crossover from 2d to 1D behavior with their magnetoconductance measurements.



Quantum materials: Where many paths meet

  • By Leena Aggarwal
  • 27 October 2017

In Nature, there exist materials with exotic properties that cannot be understood in the framework of classical theories. Such properties, however, are beautifully described by more sophisticated theoretical tools involving quantum mechanics.  Such materials are now known as the “quantum materials”. The range of exotic properties exhibited by the quantum materials is extremely broad and includes superconductivity, superfluidity, ferromagnetism, quantum hall effect, spin-liquidity, topological insulation, to name a few.

Superconductors, discovered by Kammerlingh Onnes, 1911, were first to emerge as quantum materials. In normal metals, the resistance arises due to inelastic scattering between the charge carriers (electrons) and defects in the periodic crystal lattice. The defects or scattering centres can be any distortion to the periodicity of the lattice like those due to presence of impurity or the thermal vibration of the lattice points. In superconductors, surprisingly, the resistance becomes zero despite the presence of a large number of impurities and at high temperatures where the lattice points can undergo vigorous thermal vibration. The question that how the charge carriers remained insensitive to such strong scattering centres could not be answered within any classical picture. A microscopic understanding of superconductivity was first provided by Bardeen, Cooper and Schrieffer (BCS) in 1951, only after substantial development of quantum mechanics and quantum field theories – the theories where quantum mechanics is combined with Einstein’s theory of relativity.

New Technique for Measuring the Layer-Resolved Charge Density

  • By Burcu Ozden
  • 25 October 2017

Recently Benjamin M. Hunt and his colleagues developed a new technique for measuring the layer-resolved charge density, from which they can map layer polarization of the valley or spin quantum numbers in bilayer graphine and other two dimensional materials. In this study, they demonstrated direct measurement of valley and orbital levels in bilayer graphite. They have detected that the four valley and orbital components have different weights on the two layers of the bilayer. By using Hunt’s technique one can probe layer, valley, and spin polarization quantitatively in other atomic layered materials, including twisted bilayer graphene and both homobilayer and heterobilayer of transition metal dichalcogenide

 

The new era of Polariton condensates

  • By Leena Aggarwal
  • 17 October 2017

In a recently published paper in Physics Today, David Snoke, a professor of physics and astronomy at the University of Pittsburgh and Jonathan Keeling who is a reader in theoretical condensed-matter physics at the University of St. Andrews in Scotland, have shown the superfluidity of light where photon treats as a gas of interacting bosonic atoms. They have demonstrated that how to engineer a Bose–Einstein condensation from light.

 

Trapping of Polariton in Microcavities

  • By Leena Aggarwal
  • 9 October 2017

Bose-Einstein Condensation (BEC) is a process which occurs at low temperature when an ensemble of bosons cools down and enters a single quantum state. In most of the experiments, this condensation process includes the atomic gases. But in solid-state systems, which has a long history of generating new types of particles and quasiparticles, BEC can occur in quasiparticles e.g. fermion-like excitations of Bose- condensed Cooper pairs in a superconductor.

One class of such quasiparticles is polaritons, which form from electronic excitations coupled to photons in a microcavity. Polaritons are not fundamentally different in character from elementary particles; they are just highly renormalized to have different properties. In particular, polaritons can be viewed as photons having an effective mass and much stronger interactions than photons in a vacuum.

“A carefully engineered coupling between light and matter could pave the way to a room-temperature Bose–Einstein condensate.”

 

Giannis Mpourmpakis and His Colleagues Revealed the Mystery Behind Formation of Metal Nano-particles at Specific Sizes

  • By Burcu Ozden
  • 30 August 2017

Nature Communications, co-authored by Giannis Mpourmpakis, and PhD candidate Michael Taylor, offers a possible way to unravel these mysteries, with the help of computer simulations. “In applying our new theory, we aim to accelerate discovery and application,” said Mpourmpakis. From molecular carriers for targeted drug delivery to systems for energy generation and storage to solar cells, this research could help.

Computational Study of Ni-Catalyzed C−H Functionalization: Factors That Control the Competition of Oxidative Addition and Radical Pathways

  • By Aude Marjolin
  • 2 August 2017

To guide the development of a more diverse set of Ni-catalyzed C−H bond functionalizations, a thorough understanding of the mechanisms, reactivity, and selectivity of these reactions is required. Peng Liu and his student Humair Omer have undertaken a computational study of the functionalization of the C−H bonds in molecules that contain the N,N-bidentate directing group with Ni catalyst and various coupling  partners, e.g. phenyl iodide (Ph−I), which has been published in the July 26, 2017 issue of the Journal of the American Chemical Society.

Uncovering the Connection Between Negative Stiffness and Magnetic Domain Walls

  • By Aude Marjolin
  • 19 July 2017

Nature doesn't like having interfaces—this is why bubbles like to be round, and the surface of a pond settles to flat as long as it's not disturbed. These trends minimize the total amount of interface (or surface) that is present. As an exception to this behavior, certain materials are known to have a property, called negative stiffness, where the interface prefers to become distorted, or wavy, even without any external stimulation. Interfaces with negative stiffness have been considered in crystals before, but the characteristic has now also been found in modern magnetism.

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