The Optics Laboratory
Group of Hans Hallen, Physics Department, North Carolina State University
More info is in the papers.
Resonance Raman: Tuning Through the Absorption
Scanning the excitation laser over a phonon-allowed (symmetry forbidden) absorption in a liquid gives surprises: the Raman signal strength follows the isolated molecule absorption. Find out why.
Raman Lidar: A Powerful Atmospheric Tool.
Raman lidar allows remote measurement of many gas species, temperature, and true extinction. Here are examples and how it works.
Aerosols: Pollution, Climate Drivers, or just Dust?
View them, far away with lidar, up close with NSOM, study their scattering, or find out the proper way to measure the index of refraction of these often complex entities.
UV Plasmonics: With a Nano-Bowtie or Custom Particle
We have pushed the nanoplasmonics field for Raman into the deep UV using a resonant bowtie antenna, and understood the effects of real particle non-idealities on plasmonics.
UCNP plasmonics: A Great Combination
UCNP are great sensor particles, with no blinking or bleaching but good quantum efficiency. The problem is exciting them, but that is helped with plasmonics -- see how.
Split Tip: Nanoscale electro-optic measurements.
Nanoscale electrical measurements usually involve both a conducting AFM tip and the substrate. We get the substrate out of the picture to simplify analysis by making two electrodes on one tip. It happens to be perfect for injecting light right between those two electrodes for electro-optic measurements.
Nano-Plasmon Sensor: On A Tip
Plasmon sensors are an old topic on a flat surface. Here we put them on a tapered fiber, and show how they will work -- not obvious since the incident light angle usually matters a lot.
Nano-Bio Probe: Nuclear Manipulation
We solved the problem of cytoplasm sticking and found out that you can pick up a nucleus. Add a metal layer and bias to be able to drop it off also.
Self-Alignment: At the Whole Wafer Level
Self alignment of millimeter-sized objects was shown years ago. Doing it with a whole wafer is a much bigger challenge with many facets.
A Covalent Nanoglue: Stronger than the substrate.
We describe a real nanoglue -- one that can bond two wafers together -- the first we know of. It works great for flat wafers, but call upon nylon-like chemistry to make it work for typical ones.
How to oxidize a SAM: Without getting rid of the whole layer.
Chemical oxidation doesn't work very well, with only ~20% yield so that the surface isn't really hydrophilic. Start with a vinyl group, oxidize its double bond with ozone, but don't overdue it, and you will have a wetting SAM layer.
Multi-Media Ellipsometry: Full info on thin layers.
Standard ellipsometry fails to yield both the thickness and index of refraction of very thin layers (the errors diverge). Multi angles helps some, but multiple media works better. Our contribution is a data analysis scheme that uses standard data acquisition.
Hard Disc Spinner: Sample mounting.
It is great to have a spinner that you don't care about very much, when you need to coat in a >80% relative humidity environment or in a enclosed environment in which acids are produced, both of which we do. A hard disc spins at about the right rate, the problem is keeping the sample on.
Smart 'SAM' Seed: For dumb via holes.
When multiple wafers are stacked, and it is a good idea if you need to optimize substrate materials, electrical connections need to be made through wafers. One approach is to make 'smart' holes that are slightly tapered so that a seed layer for electrodeposition of copper can be done. We do the opposite: use the 'washboard-sided' holes that come with the standard fast etch, and use metal deposition on a SAM layer so that a line of sight all points on the inner surface isn't needed.
Near-Field Scanning Optical Microscopy: An Introduction
We have been leaders in the development of all aspects of NSOM for over twenty years. See what we and other groups have done with this tutorial style introduction.
Near-Field Raman Spectroscopy: Resolution, Selection Rules, Etc.
Raman spectroscopy through a near-field aperture differs from conventional Raman in more ways than better spatial resolution. The selection rules differ, the Rayleigh tail background is lower, the surface signal is enhanced, and we obtain a simultaneous topographic image. See also the first nano-Raman Images and cartoons of what Raman spectroscopy is (for the un-initiated).
Gradient-Field Raman: A New Spectroscopy
When a near-field aperture is used for Raman spectroscopy, strong gradients of the electric field strength cannot be ignored. The origin of the spectra must be re-derived, and interesting properties (including a truly near-field plasmonic effect) elucidated.
Vacancies in Gold and Oxygen in YBCO, Stability and Probe Induced Electromigration
Electrons can drive vacancies into a gold film and move them around throughout a grain -- if they have enough energy to make a localized (d-electron) excitation. Enough vacancies can be added to make a grain unstable. Oxygen can move in the high temperature superconductor YBCO. It can move naturally in time by diffusion, causing aging -- we image that with nano-scale resolution and correlate to the topography, or it can be pushed by an electric current -- electromigration. The changes in oxygen content alter the superconducting properties, so these considerations are important in reliability and lifetime estimates. We supply a current with our probe, and quantify the effects. Surprisingly, the two effects in such different metals have the same physical origin.
Nano-Scale Mapping of Carrier Lifetime: Quantitation, Resolution
We developed an all-optical, nanoscale-resolution imaging method for semiconductor characterization. Carrier lifetime can be quantitatively measured over several orders of magnitude. See how we do it and consider how it is possible (it is) to get resolution better than the average distance the carriers move in the measurement time.
Wireless Communications: The Physics of Channel Fading
Did you ever experience a radio station that chopped in and out as your car moved? The same thing happens with wireless phones. This is a new approach to combat these rapid signal power variations in digital wireless, based on physical models and communications algorithms. It's now used in 4G and will be in 5G. This work is in collaboration with Alexandra Duel-Hallen's group in Electrical and Computer Engineering.
Code Bits: in C, C++, octave, python
Here is a sampling of various utilities we use. Some are command line C or C++, some in higher level languages. Also has some hints for the command line and various other environments.
Designs: Parts to make.
Get designs for vacuum system parts, optics mounts, fixtures, and even a scanning probe microscope.
Electronics: From preamplifiers to the scanning probe electronics.
We do quite a bit of electronics, especially at the critical front end near the experiment. Here are a few designs and layouts. Some other useful tidbits too. Look below in py452 for electronics tutorials and exercises.
How To's: From the lab.
Various procedures we use, from SAM fabrication to writing papers.
the old py452 website: Has some useful instrumentation, experimental and paper writing info.
I taught the senior lab for too long, but it did get a nice web page built up. Here it is.
notes from the Physical Optics class PY 516: Currently just the lecture notes in pdf.
Funding Provided by: Army Research Office, National Science Foundation, National Institutes of Health, Office of Naval Research, Air Force Research Lab, Army Research Lab, DARPA, Environmental Protection Agency, Teledyne Lighting and Display Products, and NCSU.
More info is in the papers.
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