This work focused on developing novel nano-sized thermal sensors based on a multifunctional core/shell and nano-channel design that can be used to measure temperature and retaining thermal history of the biological agents experienced during the testing of agent-defeat weapons.
Au-based nanostructure in thin film geometry was explored as potential nano-sized dynamic thermal sensors. The Au ultrathin films with different thicknesses varying from 1 to 5 nm were prepared by thermal vaporation on silica substrates, and the film morphology was characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Thermal shock of Au ultrathin films was performed using a tube furnace within the temperature range from 200 to 700 °C, and the duration varies from 3 to 180 seconds. The morphological change of the Au film upon thermal treatment was characterized using AFM, SEM, and x-ray diffraction (XRD), and their optical responses (localized surface plasmon absorption and surface enhanced Raman spectroscopy) were investigated by UV-vis-IR photospectrometer and Raman spectroscopy.
The effects of thickness on the temperature sensitivity were investigated, which allows the design of various nano-sized dynamic sensors for desired temperature regimes. Based on the systematic structural investigation and optical characterization, the correlation among the absorption band, FWHM, and the morphological characteristics such as particle size, shape, interparticle spacing, and fraction of open dewetting area was established. A simplified model was derived to correlate the change of the absorption band with the temperature and duration, which enable prediction of the thermal profile sensor materials experienced during a thermal event. The thermal history model was also experimentally validated.
Significant advancement was achieved in developing a core/shell nanostructure as ultrafast dynamic nano-thermometers with extreme sensitivity and fast response to rapid temperature variation. Particularly, silica/Au core shell nanostructures with well controlled surface morphologies were synthesized, and the surface plasmon resonance properties upon thermal shock were investigated in order to explore their potential as ultrafast dynamic thermometers. The correlation between different synthesis conditions and the surface plasma resonance (SPR) was identified, and reproducibility of materials synthesis was evaluated.
Thermal shock experiments were performed within the time of 100 ms up to 2 seconds using a pyroprobe, and the properties variation of the SiO2/Au core shell nanostructures were investigated as a function of temperature and duration. The thermal history model was also developed based on the dynamics of the morphology changes as controlled by the thermaldewetting, and the potential of using SPR variation upon thermal shock as effective sensing mechanisms was evaluated. A 3D contour map was developed that enables establishment of the connection among the SPR peak shift, temperature, and duration of a thermal event. This systematic investigation leads to the development of an ex-situ, ultrafast, dynamic nano-thermometer based on silica/Au core shell nanostructures with extremely fast response below sub-second and even 100 ms, and sensitivity at a temperature of 300 °C.
A key issue for the potential application of the silica/Au core shell nanostructure for real detection is the reproducibility and sensitivity in a real environment. The scientific principle for temperature sensing for the core shell structure is based on the thermal dewetting-induced morphology and the associated optical properties variation. The debris of the detonation event may affect the sensitivity and applicability as sensor elements based on optical properties vary. To test this, systematic studies were conducted to investigate the interference and impact of heterogeneous phase or impurity with the sensor elements with the focus on the reproducibility of the absorption spectra. These results indicated that the optical properties won’t be affected by the second phase or impurity as it relates to the intrinsic electrical structure and electron field/nanostructure interaction. Therefore, the core shell does show potential when used as a sensor in a detonation event.
This work was done by Jie Lian of Rensselaer Polytechnic Institute and Qingkai Yu of Texas State University for the Defense Threat Reduction Agency. DTRA-0004
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Multifunctional Core-Shell and Nanochannel Design for Nano-sized Thermosensor
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