Biomimetic Sniffing Improves the Detection Performance of a 3D Printed Nose of a Dog and a Commercial Trace Vapor Detector

Unlike current chemical trace detection technology, dogs actively sniff to acquire an odor sample. Flow visualization experiments with an anatomically-similar 3D printed dog’s nose revealed the external aerodynamics during canine sniffing, where ventral-laterally expired air jets entrain odorant-laden air toward the nose, thereby extending the “aerodynamic reach” for inspiration of otherwise inaccessible odors. Chemical sampling and detection experiments quantified two modes of operation with the artificial nose-active sniffing and continuous inspiration-and demonstrated an increase in odorant detection by a factor of up to 18 for active sniffing. A 16-fold improvement in detection was demonstrated with a commercially-available explosives detector by applying this bio-inspired design principle and making the device “sniff” like a dog. These lessons learned from the dog may benefit the next-generation of vapor samplers for explosives, narcotics, pathogens, or even cancer, and could inform future bio-inspired designs for optimized sampling of odor plumes.United States. Department of Homeland Security. Advanced Research Projects Agency (Interagency Agreement HSHQPM-13-X-00107)United States. Air Force (Contract FA8721-05-C-0002)United States. Air Force (Contract FA8702-15-D-0001

Optimization of ultraviolet Raman spectroscopy for trace explosive checkpoint screening

Abstract Raman spectroscopy has long been considered a gold standard for optically based chemical identification, but has not been adopted in non-laboratory operational settings due to limited sensitivity and slow acquisition times. Ultraviolet (UV) Raman spectroscopy has the potential to address these challenges through the reduction of fluorescence from background materials and increased Raman scattering due to the shorter wavelength (relative to visible or near-infrared excitation) and resonant enhancement effects. However, the benefits of UV Raman must be evaluated against specific operational situations: the actual realized fluorescence reduction and Raman enhancement depend on the specific target materials, target morphology, and operational constraints. In this paper, the wavelength trade-space in UV Raman spectroscopy is evaluated for one specific application: checkpoint screening for trace explosive residues. The optimal UV wavelength is evaluated at 244, 266, and 355 nm for realistic trace explosive and explosive-related compound (ERC) residues on common checkpoint materials: we perform semi-empirical analysis that includes the UV penetration depth of common explosive and ERCs, realistic explosive and ERC residue particle sizes, and the fluorescence signal of common checkpoint materials. We find that while generally lower UV wavelength provides superior performance, the benefits may be significantly reduced depending on the specific explosive and substrate. Further, logistical requirements (size, weight, power, and cost) likely limit the adoption of optimal wavelengths. Graphical abstrac

Theoretical Bounds on Electron Energy Filtering in Disordered Nanomaterials

This manuscript presents a theoretical model for determining the electron energy filtering properties of nanocomposite materials. Individual nanoparticles can serve as energy filters for tunneling electrons due their discretized energy levels. Nanomaterials comprised of many individual nanoparticles can in principle serve the same purpose, however, particle polydispersity can lead to an additional source of energetic broadening. We describe a simple theoretical model that includes the effects of discrete energy levels and inhomogeneous broadening. We use this model to identify the material parameters needed for effective energy filtering by quantum dot solids

High-sensitivity detection of trace gases using dynamic photoacoustic spectroscopy

Lincoln Laboratory of Massachusetts Institute of Technology has developed a technique known as dynamic photoacoustic spectroscopy (DPAS) that could enable remote detection of trace gases via a field-portable laser-based system. A fielded DPAS system has the potential to enable rapid, early warning of airborne chemical threats. DPAS is a new form of photoacoustic spectroscopy that relies on a laser beam swept at the speed of sound to amplify an otherwise weak photoacoustic signal. We experimentally determine the sensitivity of this technique using trace quantities of SF[subscript 6] gas. A clutter-limited sensitivity of ~100  ppt is estimated for an integration path of 0.43 m. Additionally, detection at ranges over 5 m using two different detection modalities is demonstrated: a parabolic microphone and a laser vibrometer. Its utility in detecting ammonia emanating from solid samples in an ambient environment is also demonstrated.United States. Dept. of the Air Force (Contract FA8721-05-C-0002

Theoretical Bounds on Electron Energy Filtering in Disordered Nanomaterials

Electron energy filters have recently been proposed as a method of reducing the effects of thermal broadening in device and sensing applications, enabling substantial improvements in their room temperature performance. Nanostructured materials can act as electron energy filters by funneling thermally broadened electrons through discrete energy levels. In this study, we develop a theoretical model of the electron filtering properties of nanostructured materials that explicitly includes the effects of thermal broadening and size heterogeneity on the heterogeneity of nanostructure energy levels. We find that under certain conditions quantum dot solids can perform as effective electronic energy filters. We identify a material-specific length scale parameter, Lcrit, that specifies the maximum mean quantum dot size that can yield effective energy filtering. Moreover, we show that energy filtering materials composed of quantum dots with size near Lcrit are maximally robust to heterogeneity in quantum dot size, tolerating variations ∼10% of the mean size. The length scale Lcrit can be estimated directly from the widely tabulated density of states effective mass and shows that semiconductors with light conduction band electrons, such as III-V type materials InSb and GaAs, are the most forgiving for energy filtering applications. Taken together, these results provide a practical set of quantitative design principles for semiconductor electron filters.United States. Air Force (Contract FA8702-15-D-0001

Fate Dynamics of Environmentally Exposed Explosive Traces

The chemical and physical fates of trace amounts (<50 μg) of explosives containing 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and pentaerythritol tetranitrate (PETN) were determined for the purpose of informing the capabilities of tactical trace explosive detection systems. From these measurements, it was found that the mass decreases and the chemical composition changes on a time scale of hours, with the loss mechanism due to a combination of sublimation and photodegradation. The rates for these processes were dependent on the explosive composition, as well as on both the ambient temperature and the size distribution of the explosive particulates. From these results, a persistence model was developed and applied to model the time dependence of both the mass and areal coverage of the fingerprints, resulting in a predictive capability for determining fingerprint fate. Chemical analysis confirmed that sublimation rates for TNT were depressed by UV (330–400 nm) exposure due to photochemically driven increases in the molecular weight, whereas the opposite was observed for RDX. No changes were observed for PETN upon exposure to UV radiation, and this was attributed to its low UV absorbance

• ROTHSCHILD ET AL. Recent Trends in Optical Lithography Recent Trends in Optical Lithography

■ The fast-paced evolution of optical lithography has been a key enabler in the dramatic size reduction of semiconductor devices and circuits over the last three decades. Various methods have been devised to pattern at dimensions smaller than the wavelength used in the process. In addition, the patterning wavelength itself has been reduced and will continue to decrease in the future. As a result, it is expected that optical lithography will remain the technology of choice in lithography for at least another decade. Lincoln Laboratory has played a seminal role in the progress of optical lithography; it pioneered 193-nm lithography, which is used in advanced production, and 157-nm lithography, which is under active development. Lincoln Laboratory also initiated exploration of liquidimmersion lithography and studied the feasibility of 121-nm lithography. Many of the challenges related to practical implementation of short-wavelength optical lithography are materials-related, including engineering of new materials, improving on existing materials, and optimizing their photochemistry. This article examines the technical issues facing optical lithography and Lincoln Laboratory’s contributions toward their resolution. Optical lithography, the technology of patterning, has enabled semiconductor devices to progressively shrink since the inception of integrated circuits more than three decades ago. Throughout the 1980s and 1990s, the trend of miniaturization continued unabated and even accelerated. Current semiconductor devices are being mass produced with 130-nm dense features; by 2007 these devices will have 65-nm dense features. Optical lithography has been, and will remain for the foreseeable future, the critical technology that makes this trend possible. (To learn the fundamentals of optical lithography, see the sidebar entitled “Optical Lithograph