Laboratory for Surface Modification (LSM)

Seminars Archives

March 2018 | April 2018

Thursday, April 05, 2018
Electrical Control of Magnetism in 2D
Jie Shan
Applied and Engineering Physics
Cornell University
12:00 Noon CHEM 260

Controlling magnetism by electrical means is a key challenge to better information technology. Electrical control of magnetism has been explored in a variety of materials including dilute magnetic semiconductors, ferromagnetic metal thin films, magneto-electrics and multiferroics. The emergence of atomically thin materials with unique orbital and spin magnetic properties that can be readily integrated into van der Walls heterostructures to form field-effect devices, has presented a unique and promising system for electrical control of magnetism. In this talk, I will demonstrate the generation of magnetization by a current in monolayer transition metal dichalcogenides as a result of the Berry curvature effect. I will also discuss our recent results on tuning the magnetic properties of 2D magnet CrI3 by electric field or electrostatic doping. In particular, in bilayer CrI3, which consists of two Ising ferromagnetic monolayers coupled antiferromagnetically in the ground state, we have achieved reversible switching of the interlayer magnetic order between the antiferromagnetic and ferromagnetic states.
Thursday, April 12, 2018
Ions and Solvent Structure at Mineral - Aqueous Interfaces
Eric Borguet
Department of Chemistry
Temple University
12:00 Noon CHEM 260

Interfacial water structure is key to many chemical and physical processes. It can be probed by vibrational sum-frequency generation (vSFG) spectroscopy as well as ultrafast time-resolved vSFG. However, a more complete microscopic understanding requires additional techniques such as molecular dynamics simulations. Our experiments show that in the absence of surface charge (pH 2), water at silica surfaces exhibits significantly slower OH stretch vibrational relaxation (~600 fs) compared to bulk water. However, at charged silica surfaces (e.g., pH 6), bulk-like fast dynamics (~200 fs) are observed at low ionic strength. This decelerates to ~600 fs with the addition of NaCl. In parallel, vSFG results demonstrated that silica interfacial water structure is most sensitive to ions at pH=6-8, correlating with the known salt and pH dependence of silica surface reactivity. Consequently, it is unclear whether the observed slowing of the vibrational dynamics is due to the reduction in the Debye length, or because of changes in the local hydrogen bonding environment caused by the electrolyte and how this might depend on the identity of the ions. The combination of molecular dynamics simulations with spectroscopic and time-resolved vSFG experiments on aqueous Al2O3 interfaces sheds light on the ongoing debate on the role of ions in interfacial water structure and whether the observed behavior is specific to silica/water interfaces or can be generalized to other aqueous interfaces.
Thursday, April 26, 2018
Visualizing and Shaping the Nanoworld: From the Quantitative Interrogation of Site- and Species-Specific Interactions of Atoms to the Millimeter-Scale Engineering of Structures with Angstrom Precision
Udo Schwarz
Departments of Mechanical Engineering & Materials Science and Chemical & Environmental Engineering
Yale University
12:00 Noon CHEM 260

The interactions a material exhibits with the environment are largely determined by the properties of the material’s surfaces. In the first part of this talk, we describe recent efforts to characterize a surface’s structure by enabling species-specific atomic resolution imaging and quantify chemical interaction strengths in three dimensions with picometer and piconewton resolution using noncontact atomic force microscopy [1, 2] and outline how this information can be combined with local electronic information [3, 4]. Applications to explore topics such as surface chemistry [5, 6] or the atomic origins of friction [7, 8] will be presented for various model systems including oxides, metals, ionic crystals, and layered materials, as well as recent extensions towards the single-molecule characterization of surface reactions.

In the second part of the talk, we will then expand on the theme of atomic-scale manipulation by asking how surface morphologies of samples as large as multiple mm2 can be shaped at will with Angstrom precision. Here we demonstrate the imprinting of atomic step edges of a SrTiO3 single crystal used as mold into a Pt-based bulk metallic glass (BMG). Systematic studies revealed that (i) terraces on the BMG replicas possess atomic smoothness, (ii) the same mold can be used multiple times without degradation of mold or replicas, and (iii) the atomic-scale features on as-imprinted BMG surfaces have impressive long-term stability (years), thereby opening the possibility to induce surface properties by imprinting appropriate atomically defined surface morphologies.

[1] B. J. Albers et al., Nature Nanotechnology 4, 307 (2009).
[2] O. E. Dagdeviren et al, Nanotechnology 27, 065703 (2016).
[3] M. Z. Baykara et al., Physical Review B 87, 155414 (2013).
[4] H. Mönig et al., ACS Nano 7, 10233 (2013).
[5] M. Z. Baykara et al., Advanced Materials 22, 2838 (2010).
[6] M. Z. Baykara et al., Applied Physics Letters 108, 071601 (2016).
[7] D. Dietzel et al., Physical Review Letters 101, 125505 (2008).
[8] D. Dietzel et al., Physical Review Letters 111, 235502 (2013).

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