Facilities & Equipment
Single Molecule Conductivity | Nanoscale Dynamics| Non-linear Spectroscopy and Dynamics|Ultrafast Infrared Sources | Sensors | FLOSS |Plasmonics | Nanomaterials
Single Molecule Conductivity in Organic and Biomimetic Molecules:
(Esteban Sanchez and Sepideh Afsari)
The conductance of single molecules depends not only on how conductive the molecule is but also on how the molecule connects to the electrodes. Our group has designed a conjugated thiol linker which can improve the conductance of the molecule-electrode junction. We continue to explore this topic by using the STM (scanning tunneling microscopy) break-junction method to study the conductance of single conjugated molecules with conjugated thiol linkers.
Conjugated Thiol Linker for Enhanced Conductivity of Gold-Molecule Contacts (Yufan He)
PNA is an artificial analog of DNA. PNA has neutral backbone may allow more compact SAM growth than for DNA. Metal ions can be introduced into PNA duplexes by replacing the natural bases with metal complexing ligands. We study the self-assembly and charge transfer of PNA using Scanning Probe Microscopy (SPM), Cyclic Voltammetry.
Nanoscale Dynamics at Liquid/Solid Interfaces:
(Esteban Sanchez, and Sepideh Afsari)
We use surface charge to control adsorbate-substrate interactions and to tune dynamics at solid-liquid interfaces. We use Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM) to study the resulting phenomena:
- Molecular redox dynamics at electrode-electrolyte interfaces.
- Molecular diffusion and self-assembly.
- Dynamics of surface reconstruction, lifting of reconstruction, nanoscale island decay/growth.
- Atomic and Molecular resolution STM/AFM at Liquid/Solid Interfaces (Yufan He, Tao Ye)
- Potential driven phase transitions in Self-assembled Monolayers (SAM) (Kyoungja Seo)
- Read/Write/Erase nanolithography (Kyoungja Seo)
Nonlinear Optical Studies of Interfaces:
(Shalaka Dewan, Aashish Tuladhar, Devika Sil, and James Choi)
Second order non-linear optical techniques, e.g. Sum Frequency Generation (SFG) and Second Harmonic Generation (SHG), provide both ultrafast time resolution and interface selectivity. Current projects focus on vibrational SFG spectroscopy to reveal the structure of water at mineral surfaces and SHG spectroscopy to probe the overtone region of the O-H strech of interfacial water.
(Shalaka Dewan and Aashish Tuladhar)
Time resolved SFG studies can provide details about the H-bonding environment of buried interfaces by measuring the vibrational relaxation times of O-H stretch. Current projects focus on the role of ions
and acid-base equilibria at mineral/water interfaces.
- SHG Spectroscopy & Dynamics of Si, Ge, and SixGe1-x Interfaces (Dora Bodlaki, Vasiliy Fomenko, Julie Fiore, Catherine Faler)
Novel Ultra-Broadband IR Laser Sources:
(Aashish Tuladhar and James Choi)
We are developing ultrabroadband IR laser sources providing pulses with bandwidths >1000 cm-1 in the ~1000 - 3000 nm wavelength range.
- Transform-limited Picosecond Infrared OPA (Dora Bodlaki)
(Devika Sil, Colin Murphy and Safiya Sylla)
Detection of bio species (cells, proteins, antibodies, ...) by surface immobilization on piezoelectric sensor devices.
- Hydrogen and Humidity Sensors
(Uduak Odoeyo and Devika Sil)
In collaboration with ASRD, we are developing surface acoustic wave sensors for NASA applications.
Fluorescence Detection of Surface Functionality:
FLOSS (Fluorescence Labeling of Surface Species) exploits the sensitivity of fluorescence and the specificity of covalent bond formation to identify and quantify low concentrations of surface functionalities. FLOSS can distinguish between COOH, OH and aldehyde groups and detect down to 1011 functional groups/cm2 on surfaces. This sensitivity is well beyond the detection limits of FTIR and XPS.
FLOSS has been applied to understand SAM photoreactivity and is being extended to other materials.
- Growth, Stability and Photoreactivity of Self Assembled Monlolayers (Tao, Ye, Eric Mc Arthur)
The localized surface plasmon resonance in metal nanoparticles is a sensitive probe of changes in the dielectric environment. We are using the LSPR of Au NPs as a probe to optically detect explosive gases like hydrogen or by measuring changes in transmission, before and after exposure to the gases of interest.
Conventional synthesis of nanoparticles, involve the use of precursors, reducing agents and surfactants.
-Properties of Carbon Nanotubes and other Carbon Materials:
Understanding the interaction between molecules and carbon nanotubes is key to a number of applications. We use NIR, Raman, FTIR, thermogravimetric analysis, TEM, AFM and TPD under vacuum conditions to probe molecular interactions with, and chemical functionality on, carbon materials. Environmental applications include development of solar energy harvesting devices as well as new and better sorbents for pollution control.