A Multi-Probe STM Quest for Quantum Transport at 2D Materials Boundaries
Date:
-
Location:
CP179
Event Series:
Condensed Matter Seminar
Our condensed matter seminars are held on Tuesdays at 3:30pm in Chemistry-Physics Building, Room 179, unless otherwise noted below. A number of the department colloquium may also be of interest.
Generating femtosecond second-harmonic pulses from ultrathin Archimedean nanospirals
The explosive growth in the development of plasmonic devices for sensors, switches, catalysis
and optical data links is driving the evolution of increasingly sophisticated nanostructures for
these applications. Arrays of ultrathin Archimedean nanospirals exhibit linear and nonlinear
optical properties associated with near-field plasmon resonances within the nanostructures. The
enhanced electric fields at these resonances enable efficient second-harmonic generation (SHG)
because individual nanospirals have no symmetry axis. We observe efficient SHG from arrays
of lithographically fabricated, sub-wavelength-dimension nanospirals, initiated by transform-
limited 15 fs pulses at a wavelength of 800 nm. The nanospiral arrays respond selectively to
incident linear and circular polarization states and exhibit conversion among polarization states.
I will conclude by suggesting some ways in which the asymmetry and two-dimensional chirality
of the nanospirals may lead to interesting applications in metamaterial devices.
Date:
-
Location:
CP179
Event Series:
Nanoscale probing of electromechanical responses by scanning probe microscopy: from piezoresponse to electrochemical strain
Electromechanical responses (the mechanical displacement induced by an applied electric field, and vice versa) are ubiquitous in nature. One of the most typical examples is converse piezoelectric response in ferroelectric and multiferroic materials. Another example is electrochemical strain induced by ionic motion, e.g., in Li-ion batteries and solid oxide fuel cells. Here, the recent scanning probe microscopy studies of those electromechanical responses in a variety of material systems are presented. First, the piezoresponse force microscopy (PFM) study on the origin of polarization fatigue in epitaxial ferroelectric Pb(Zr,Ti)O3 capacitors will be shown [1]. In this study, PFM allows to visualize ferroelectric domain nucleation and growth during the fatigue process at the nanoscale time and length scales. It reveals that the evolution of domain wall pinning process is the primary origin of polarization fatigue, which has been a long-standing important problem in ferroelectrics. Second, the electrochemical strain microscopy (ESM) study on the nonlinear electromechanical responses in Ag-ion based ionic conductive glasses will be presented. ESM has recently emerged as a powerful tool to probe ionic transports and electrochemical phenomena at the nanoscale in many material systems [2]. In this study, interesting anti-
correlation between the first and second harmonic ESM responses are observed, and its possible origins are discussed.
[1] S. M. Yang et al., Adv. Funct. Mater. 22, 2310 (2012).
[2] N. Balke et al., Nat. Nanotechnol. 5, 749 (2010).
Date:
-
Location:
CP179
Event Series:
Crystal growth and exotic magnetic transitions in rare earth orthoferrites RFeO3"
If time allows the speaker will also discuss
Exchange bias in Co/Ca2Ru0.98Fe0.02O4 heterostructure
Date:
-
Location:
CP179
Event Series:
