The detection of infrared radiation (IR) with pure and doped Polyvinylidene difluoride (PVDF) films has been well documented using the mechanism of pyroelectricity. Alternatively, the electrical properties of films made from Polyvinyl Alcohol (PVA) have received considerable attention in recent years. The investigation of surface resistivities of both such films, to this point, has received far less consideration in comparison to pyroelectric effects. In this research, we report temperature dependent surface resistivity measurements of commercial, and of multiwall carbon nanotubes (MWCNT), or Ag-nanoparticle doped PVA films. Without any variation in the temperature range from 22°C to 40°C with controlled humidity, we found that the surface resistivity decreases initially, reaches a minimum, but rises steadily as the temperature continues to increase. This research was conducted with the combined instrumentation of the Keithley Model 6517 Electrometer and Keithley Model 8009 resistivity test fixture using both commercial and in-house produced organic thin films. With the objective to quantify the suitability of PVDF and PVA films as IR detector materials, when using the surface resistivity phenomenon, instead of or in addition to the pyroelectricity, surface resistivity measurements are reported when considering bolometry. We find the surface resistivity of PVDF films to be in the range, which extends beyond the upper limit of our Keithley electrometer, but our measurements on PVA films were readily implemented.
In this work, we have determined the dielectric and conductance properties of multi-wall carbon nano-tubes (MWCNT) in polyvinylidene fluoride (PVDF) nanocomposite thin films as a function of temperature and frequency. Samples, ranging from 15 - 280 microns in thickness, were measured in the temperature range from 21 to 90°C and in frequencies from 50Hz to 110MHz. The samples were prepared by the solution casting technique. Measures indicate that at constant temperatures, the real dielectric constant decreases at lower frequencies, stays steady at low frequencies but rise at higher frequencies over towards the strong resonance. The dielectric loss, a particular concern as it is inversely related to the conductance, decreases also at lower frequencies but rise at higher frequencies with a steeper slope in each case. Additionally, we have measured the pyroelectric coefficient in the same temperature range, compared the pyroelectric coefficient results with previous measures made on silver nanoparticle in PVDF thin films and provided preliminary evidence of the causative microscopic response mechanism. Our MWCNT:PVDF thin films yield higher figures of merit than that indicated by pure PVDF thin films and results indicate a usage of MWCNT:PVDF thin films in infrared uncooled sensors and vidicon technology.
This research is focused on the fabrication of thin films followed by Surface Enhanced Raman Spectroscopy (SERS) testing of these films for various applications. One technique involves the mixture of nanoparticles with twophoton material to be used as an indicator dye. Another method involved embedding silver nanoparticles in a ceramic nano-membrane. The substrates were characterized by both Atom Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). We applied the nanostructured substrate to measure the SERS spectra of 10-6 Mol/L Rhodomine 6G(Rh6G), e-coli bacteria and RDX explosive. Our results showed that silver coated ceramic membranes can serve as appropriate substrates to enhance Raman signals. In addition, we demonstrated that the in-house-made colloidal silver can work for enhancement of the Raman spectra for bacteria. We measured the Raman spectra of Rh6G molecules on a substrate absorbed by a nanofluid of silver. We observed several strong Raman bands – 613cm-1,768 cm-1,1308cm-1 1356 cm-1,1510cm-1, which correspond to Rh6G vibrational modes υ53,υ65,υ115,υ117,υ146 respectively, using a ceramic membrane coated by silver. The Raman spectra of Rh6G absorbed by silver nanofluid showed strong enhancement of Raman bands 1175cm-1 and 1529cm-1, 1590 cm-1. Those correspond to vibrational frequency modes – υ103,υ151,152. We also measured the Raman spectra of e-coli bacteria, both absorbed by silver nanofluid, and on nanostructured substrate. In addition, the Fourier Transfer Infrared Spectra (FTIR) of the bacteria was measured.
Pyroelectric infrared Lithium tantalite [(LiTaO3), LT] ceramic particles and silver nanoparticles have
been incorporated into a polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE) 70/30 mol%]
copolymer matrix to form composite films. The films were prepared using solvent casting method.
Electrical properties such as the dielectric constant, dielectric loss, and pyroelectric coefficient have been
measured as a function of temperature. In addition, materials' figures-of-merit have also been calculated
to assess their use in infrared detectors. The results show that the fabricated silver nanoparticles
incorporated lithium tantalite: polyvinylidene
fluoride-trifluoroethylene composite films may have a good
potential for uncooled infrared sensor applications.
Pyroelectric infrared radiation detectors are one of kind thermal sensors, operating at ambient temperature,
unlike semiconductor detectors, which require cooling. They also have a uniform spectral response in a
wide range of wavelengths, including the main band of infrared transmission of the earth's atmosphere.
Recently, 0-3 composites consisting of ferroelectric ceramic particles dispersed in a ferroelectric polymer
have stimulated interest due to their good mechanical flexibility and strength, and excellent piezoelectric
and pyroelectric properties. Lithium tantalite [(LiTaO3), LT] ceramic particles have been incorporated into
a polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE) 70/30 mol%] copolymer matrix to form
composite films. The films were prepared using solvent casting method with the LT powder
homogeneously dispersed in the P(VDF-TrFE) copolymer matrix with various volume fractions. Electrical
properties such as the dielectric constant, dielectric loss, and pyroelectric coefficient have been measured as
a function of temperature as well as frequency. In addition, materials' figures-of-merit have also been
calculated to assess their use in infrared detectors. The results show that the fabricated lithium tantalite:
polyvinylidene fluoride-trifluoroethylene composite films have a good potential for uncooled infrared
sensor applications operating at moderate temperatures.
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