Marissa E. Morales-Rodriguez

We report on a standoff spectroscopic technique for detecting chemical residues on surfaces. An infrared (IR) camera was used in combination with a wavelength tunable mid-IR quantum cascade laser to acquire multispectral image arrays of a surface with explosive residue. IR spectral signatures of residue of cyclotrimethylenetrinitramine (commonly known as RDX) were extracted in the wavelength range 7.9 to 9.7 $\mu \text{m}$ from the multispectral IR images. Detection of RDX was achieved for a lower surface concentration of $5~\mu \text{g}$ cm ⁻² and a higher surface concentration of $20~\mu \text{g}$ cm ⁻² at distances of 0.15 m and 1.5 m, respectively. We performed no background subtraction and the resulting IR spectra of RDX were compared with reference Fourier Transform IR Spectroscopy data that were acquired by placing 20 $\mu \text{g}$ of RDX on a ZnS window. We found that the detection of RDX can be made with negligible interfering contribution of reflected IR photons from the substrate surface.

We describe a new approach for high sensitivity and real-time online measurements to monitor the kinetics in the processing of nuclear materials and other chemical reactions. Mid infrared (Mid-IR) quantum cascade laser (QCL) high-resolution spectroscopy was used for rapid and continuous sampling of nitrates in aqueous and organic reactive systems, using pattern recognition analysis and high sensitivity to detect and identify chemical species. In this standoff or off-set method, the collection of a sample for analysis is not required. To perform the analysis, a flow cell was used for in situ sampling of a liquid slipstream. A prototype was designed based on attenuated total reflection (ATR) coupled with the QCL beam to detect and identify chemical changes and be deployed in hostile environments, either radiological or chemical. The limit of detection (LOD) and the limit of quantification (LOQ) at 3σ for hydroxylamine nitrate ranged from 0.3 to 3 and from 3.5 to 10 g·L⁻¹, respectively, for the nitrate system at three peaks with wavelengths between 3.8 and 9.8 μm.

Advancements in additive manufacturing techniques, printed electronics, and nanomaterials have made it possible for the cost-effective fabrication of sensors and systems. Low-cost sensors for continuous and real time monitoring of physical and chemical parameters will directly impact the energyefficiency, safety, and manufacturing challenges of diverse technology sectors. In this paper, we present the design, printing, and characterization of a two-port surface acoustic wave (SAW) integrated on LiNbO3 substrate. The aerosol jet printer was used for direct-writing of interdigitated transducers for SAW devices with center frequency in the range of 40-87 MHz. The linear response of a temperature sensor based on the SAW design shows promise for direct-writing of environmental sensors on low-temperature substrates.