A variety of instruments/benches are utilized within the lab to provide both baseline and in-situ characterization of the optical, electrical and microstructural properties of tailored nanofilms for the development of novel chemical sensing solutions. A common theme in the lab is to achieve both parallel deposition and sensor testing methodologies, with nanomaterial optimization achieved through both the design of smart sensing microstructures and design of experiments techniques.
Sensor Test Stations
Low Temperature (25-100C) Optical Reflectance/Transmission
Optical reflectance/transmission of a white light source from or through tailored samples is monitored with a MTI-I Fotonics 1000 fiber optical probe as a function of both temperature and gas composition. The sample is held in a 20cc stainless steel chamber with the surrounding gas composition computer controlled using an Environics S-4000 gas mixing system to achieve ppb to % level concentrations of the target gas of interest. Humidity levels can be varied from 10 to 95% RH. Seconds level response times are achievable with this test station.
Fluorescence Based Sensing
A Varian Eclipse spectrofluorometer is the base for this testing station. A bifurcated fiber optic probe for both excitation and fluorescence collection is coupled to a 20cc stainless steel chamber where the sample is mounted. Gas compositions are controlled by an Environics S-4000 gas mixing system which is coupled to a glass bubbler for hydrocarbon vapor entrainment at 100ppb to % level concentrations. A modified micro-array plate assembly based micro-chamber can be used for testing a series of films with semi-parallel testing protocols.
High Temperature (100-1000C) Optical Transmission
Collimated light from a CW Xe flash lamp is passed through samples mounted in a quartz cell housed in a 10″ long furnace. The transmitted light is collected and coupled to an imaging monochromator with a CCD detector. Either singular or multiple films can be monitored as a function of operation temperature and gas phase composition. Hydrogen, CO, NO2 and various sulfur containing gases are mixed with air or inert carrier gases at concentrations ranging from ppb to % levels. Seconds level response times are achievable with this test station.
Kelvin Probe and Reflectance
The Kelvin probe and reflectance test station simultaneously monitors both changes in the contact potential difference (CPD) and optical reflectance of tailored sensing materials. We utilize a McAllister Technical Services Kelvin probe and a MTI-I Fotonics 1000 optical probe to monitor the CPD and the reflectance, respectively, as a function of changes in the gaseous environment. A minichamber with a 3cc internal volume is housed within the Kelvin probe mounting chamber to ensure a minimal dead volume enclosure around the sample. We have been able to measure changes in the CPD of our palladium alloy thin films upon exposure to only 100ppb of hydrogen in an air carrier gas. The Kelvin method has extremely high surface sensitivity (<0.1 meV, typically corresponding to 0.001 of an adsorbate layer) and is completely non-damaging, even to the most sensitive adsorbates, making it a unique asset to the sensor lab for development of electrically active sensing materials. The Kelvin probe is complimented with the simultaneous optical reflectance measurement which enables an understanding of the dynamics between bulk and surface limiting reactions. A computer controlled Environics S-4000 gas-mixing system is used to achieve ppb to % level concentrations of the target gas of interest.
Equipment
Dual target confocal physical vapor deposition system
Veeco Explorer AFM
Veeco Aurora near field scanning optical microscope
Coherent Ar ion CW laser
Nicolet 760 Magna FTIR spectrometer
Varian GC-MS
Varian Eclipse spectrofluorometer
Varian Cary 50 Uv-visible absorption spectrometer
An extensive array of metrology equipment within the College of Nanoscale Science and Engineering is further utilized for a complete analysis of our materials.
