Laboratory for Surface Modification (LSM)

Seminars Archives

September 2018 | October 2018 | November 2018

Thursday, October 04, 2018
Suspended Graphene Under Strain
Xu Du
Stony Brook University
Department of Physics and Astronomy
12:00 Noon CHEM 260

The flexibility and structural strength in 2D materials make them ideal systems for studying “straintronics”. In graphene, strain effectively induces a gauge field which affects the transport of Dirac electrons. Here I will discuss our work on transport study of graphene in nanoelectromechanical devices. Suspended graphene field effect transistors were fabricated on top of flexible substrates, allowing independent tuning of tensile strain while maintain ultra-high device quality. Through mechanical resonance measurements we show resonance frequency and non-linear dynamics may be used to accurately determine the strain in graphene. And in charge transport measurements we show that the energy dependence of the strain-induced resistivity agrees with the theoretical prediction on random strain-induced gauge field scattering of Dirac electrons. The impact of strain on coherence transport and quantum Hall effect will also be discussed.
Thursday, October 11, 2018
Electro-Fluidic Micro- and Nanotechnologies for Health and Environmental Monitoring
Mehdi Javanmard
Rutgers University
Electrical and Computer Engineering Department
12:00 Noon CHEM 260

In this talk, I will discuss my groups work on fabricating micro- and nanosensing platforms for biomolecular and biochemical detection. In the first part of my talk, I will discuss a digital microfluidic platform for detection of inflammatory proteins in blood and saliva. I will then discuss a novel scheme for barcoding microparticles nanoelectronically, for multiplexed detection of analytes. We have also developed a novel electrochemical sensor using reduced graphene oxide for detection of inflammatory markers in exhaled breath condenstate for management of chronic respiratory diseases. Finally, I will talk about my groups efforts in developing novel probes for characterization of biological organisms on-the-field, along with sensors for detection of toxic compounds in environmental samples
Thursday, October 18, 2018
Band-Offset “Bulk-Like” Mystery Solved: Lessons from Covalent and Ionic Heterojunctions
Ray Tung
Physics Department
12:00 Noon CHEM 260

The insensitivity of semiconductor heterojunction band offset (BO) on the orientation and the atomic structure of the interface, combined with the observed “transitivity” of BOs among some semiconductors, led to the suggestion that the formation mechanism of BO is “bulk-like”, namely, the BO is decided by bulk properties of semiconductors. At the same time, BO’s at heterovalent interfaces are known to be tunable and non-transitive. Because the BO is a direct result of the equilibrium charge distribution at the heterojunction interface, and the formation of the latter is governed by energy minimization, the observed bulk-like behavior for some interfaces and tunability for others must both have explanations within the concept of energy minimization. In this talk, we briefly review results previously obtained from analysis of charge distribution at covalent zinc blende interfaces and describe recent DFT results from heterojunctions between lattice-matched perovskite oxides. The BO’s for perovskite oxides, which depend very significantly on the orientation and atomic structure of unrelaxed interfaces, i.e. tunable, converge sharply upon lattice relaxation, i.e. become bulk-like, to magnitudes that agree with predictions of neutral polyhedra theory (NPT), previously developed for zinc blende interfaces. The unexpected success of the NPT for both covalent and ionic heterojunctions unmasks a link between a main assumption of this theory and energy minimization in general. The seemingly bulk-like BO behavior thus appears to reflect an independence of junction electrostatics on atomic arrangement at a relaxed interface, following this simple rule on energy minimization. The tunability of BO under other circumstances identifies bonding geometries where this rule is relaxed. Because energy minimization governs the formation of all charge distributions, NPT is expected to be valuable for other types of interfaces.

* Work done in collaboration with L. Kronik, Weizmann Institute of Science
Thursday, October 25, 2018
Multiferroicity in Hexagonal Rare Earth Ferrites
Xiaoshan Xu
University of Nebraska-Lincoln
Department of Physics
12:00 Noon CHEM 260

Multiferroic materials exhibit multiple ferroic orders simultaneously, which enables novel application in information storage and processing, as well as in sensor and actuators. Hexagonal rare earth ferrites stand out in multiferroic materials due to the coexisting spontaneous magnetic and electric dipole moment, meaning they are both ferromagnetic and ferroelectric. Importantly, both the magnetic and ferroelectric order hinges on the structural distortions in the layered structure. The ferroelectricity is induced by the structural distortion below about 1000 K with sizable electric polarization. Below about 100 K, the antiferromagnetic order, which is topologically forbidden in undistorted structure, develops in a non-collinear fashion, together with the ferromagnetism originated from the canted moments. In this talk, I will discuss our recent work on the coupling between the crystal structure and the multiferroicity in hexagonal rare earth ferrites, and the structural tuning of the multiferroic properties.

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