Chemistry Department Seminar

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Dr. Song Xu of Keysight Technologies will be presenting a seminar titled Beyond Tapping Mode - Advanced Imaging Modes based on the Oscillation of an Atomic Force Microscope Cantilever.  

Abstract: We will start with discussing the basics of physics and mathematics of the working principle of Atomic Force Microscopes.  The seminar will cover aspects of AFM such as signal driver, the scanning mechanism, the feedback loop and the design concerns, in order to give the audience an overview of the basic principles of this technology.

Tapping mode is a widely used basic imaging mode of Atomic Force Microscopy.   In tapping mode, the cantilever is driven to oscillate up and down at near its resonance frequency by a small piezoelectric element mounted in the AFM tip holder.  An electronic servo adjusts the height of the cantilever to maintain a set cantilever oscillation amplitude as the cantilever is scanned over the sample while the Z movement is recorded as the topographic (height) image. 
 
The cantilever of an atomic force microscope is a very sensitive force sensor. Various short and long range forces allow high resolution mapping not only the physical shape, but also mechanical, magnetic and electrical property.   The forces between the tip and sample could come various physical and chemical interactions, such as electrostatic force, physical repulsive force, van de Waals force, dipole-dipole interaction, magnetic force, chemical bonding, hydrogen bonding, friction etc.  Many advanced imaging modes were developed and continuously been developed to map more physical and chemical information of materials.  In this web seminar, we will introduce many advanced imaging modes based on cantilever oscillating technology. These imaging modes include Phase Imaging, MFM (Magnetic Force Microscopy), EFM (Electrostatic Force Microscopy), KFM (Kelvin Force Microscopy), and frequency modulated Scanning Probe Force Microscopy.  We will discuss the basic physics behind these advanced AC imaging modes, the mathematics of the feedback mechanism and example applications in different research fields.
 

Faculty Host: Dr. Jason DeRouchey

 

Date:
-
Location:
CP-114A/B

Discrete CATS Seminar

Title: Representing discrete Morse functions with polyhedra



Abstract: Discrete Morse theory is a method of reducing a CW complex to a simpler complex with similar topological properties. Well-known approaches to this task are due to Banchoff, whose process involves embedding a polyhedron in Euclidean space and considering the projections of its vertices onto a straight line, and to Forman, whose process involves finding special functions from the face poset of a complex to the real numbers. In this talk, I will discuss a result by Bloch which gives a relationship between these two methods. In particular, given a discrete Morse function on a CW complex, there exists a corresponding polyhedral embedding of the barycentric subdivision of X such that the discrete Morse function and the projection of the vertices of the polyhedron onto a line give the same critical cells.



 

Date:
-
Location:
745 Patterson Office Tower
Event Series:
DISCRETE CATS SEMINAR

Arabic Tables

Speak Arabic with Native Arabic Speakers

تحدث باللغة الإنجليزية مع الناطقين بها.

 

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Date:
-
Location:
POT rm 1643

Arabic Tables

Speak Arabic with Native Arabic Speakers

تحدث باللغة الإنجليزية مع الناطقين بها.

Date:
-
Location:
POT rm 113

Condensed Matter Seminar: Weyl semimetal: topology meets 3d graphene

Recent discovery of topological insulators highlighted a new class of quantum phases, namely topological phases, characterized by exotic surface states and quantized response functions. While topological insulators are well understood, topological aspects of metals are less clear. In this talk, I’ll discuss a class of electronic topological semimetals, which are 3d analogies of graphene. They are solid state realizations of Weyl fermions, hence coined Weyl semimetals. I’ll discuss their topological properties, including surface Fermi arcs and bulk quantum Hall effects. In the presence of electronic interactions, charge density wave and superconductivity can develop in Weyl semimetals. I’ll show that these symmetry breaking states inherit the nontrivial topology from Weyl semimetals.

Date:
-
Location:
CP179
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