Russell Chung

Rational materials design of sorbent coatings for explosives : applications with chemical sensors

A series of chemoselective polymers had been designed and synthesized to enhance the sorption properties of polymer coated chemical sensors for polynitroaromatic analytes. To evaluate the effectiveness of the chemoselective coatings, a polynitroaromatic vapor test bed was utilized to challenge polymer coated surface acoustic wave (SAW) devices with different explosive vapors. Dinitrotoluene detection limits were determined to be in the <100 parts per trillion ranges. ATR-FTIR studies were used to determine the nature of the polymer-polynitroaromatic analyte interactions, and confirm the presence of hydrogen-bonding between polymer pendant groups and the nitro functional groups of polynitroaromatic explosive materials.

Direct writing of electronic and sensor materials using a laser transfer technique

We present a laser-based direct write technique termed matrix-assisted pulsed-laserevaporation direct write (MAPLE DW). This technique utilizes a laser transparentfused silica disc coated on one side with a composite matrix consisting of the materialto be deposited mixed with a laser absorbing polymer. Absorption of laser radiationresults in the decomposition of the polymer, which aids in transferring the solute to anacceptor substrate placed parallel to the matrix surface. Using MAPLE DW, complexpatterns consisting of metal powders, ceramic powders, and polymer composites weretransferred onto the surfaces of various types of substrates with <10 micron resolutionat room temperature and at atmospheric pressure without the use of masks.Current trends for developing advanced electronic andsensor systems place great emphasis in achieving per-formance levels generally associated with integratedcircuits. This requires further miniaturization, while en-hancing the functionality and reliability of existing sys-tems. New strategies are needed in order to eliminate thelong lead times required for the fabrication of prototypesand evaluation of new materials and designs. The use ofrapid prototyping techniques such as direct write, whichdo not need photolithographic processing, provide a so-lution to the above requirements. Direct write technolo-gies do not compete with photolithography for size andscale but rather add a complementary tool for specificapplications requiring rapid turnaround and/or patterniteration, conformal patterning, or modeling difficult cir-cuits. Examples of direct write technologies for fabricat-ing or modifying metallic interconnects and/or otherelectronic passive elements include ink jet printing,

The design of functionalized silicone polymers for chemical sensor detection of nitroaromatic compounds

Abstract The solubility properties of a series of nitroaromatic compounds have been determined and utilized with known linear solvation energy relationships to calculate their sorption properties in a series of chemoselective polymers. These measurements and results were used to design a series of novel chemoselective polymers to target polynitroaromatic compounds. The polymers have been evaluated as thin sorbent coatings on surface acoustic wave (SAW) devices for their vapor sorption and selectivity properties. The most promising materials tested, include siloxane polymers functionalized with acidic pendant groups that are complimentary in their solubility properties for nitroaromatic compounds. The most sensitive of the new polymers exhibit SAW sensor detection limits for nitrobenzene (NB) and 2,4-dinitrotoluene in the low parts per billion (ppb) and low parts per trillion (ppt) concentration range, respectively. Polymers with favorable physicochemical properties exhibit low water vapor sorption, and rapid signal kinetics for NB, reaching 90% of signal response in 4 s. Studies with an in situ infrared spectroscopy technique are used to determine the mechanism of interaction between nitroaromatic compounds and the chemoselective polymer.

The “NRL-SAWRHINO”: a nose for toxic gases

Abstract At the Naval Research Laboratory (NRL), surface acoustic wave (SAW) chemical sensor systems have been in development since 1981. The primary focus has been the detection and identification of chemical agents and other toxic gases or vapors. In the recently developed “NRL-SAWRHINO” system (Rhino, Gr. Nose), a self-contained unit has been developed capable of autonomous field operation. An automated dual gas sampling system is included, for immediate and periodic detection capability. The latter, utilizes a trap-and-purge miniature gas chromatographic column, which serves to collect, concentrate, and separate vapor or gas mixtures prior to SAW analysis. The SAWRHINO includes all the necessary electronic and microprocessor control, SAW sensor temperature control, onboard neural net pattern recognition capability, and visual/audible alarm features for field deployment. The SAWRHINO has been trained to detect and identify a range of nerve and blister agents, and related simulants, and to discriminate against a wide range of interferent vapors and gases.

Performance optimization of surface acoustic wave chemical sensors

Acoustic wave devices coated with a thin layer of chemoselective material provide highly sensitive chemical sensors for the detection and monitoring of vapors and gases. In this work, a variety of coating materials and coating deposition techniques have been evaluated on surface acoustic wave (SAW) devices. A novel thin film deposition technique, matrix assisted pulsed laser evaporation (MAPLE), is utilized to coat high quality polymer films on SAW devices, and conventional pulsed laser deposition is used to deposit a passivation layer of diamond-like-carbon on a SAW device surface to prevent water adsorption. In addition, chemoselective coatings are formed by covalent attachment of functionalized species to the silica surface of SAW devices. The self-assembled monolayer or near monolayer structures are designed to populate the SAW device surface with the desirable hexafluoroisopropanol moeity. The rapid kinetic signals achievable with the various coated SAW sensors during vapor tests are examined as a function of the coating material and the quality of the thin films. In parallel to the thin film deposition, growth, and vapor testing, the electrical characteristics of the SAW sensor have been characterized. The quality factor and residual phase noise of polymer coated SAW devices are examined, and a prediction of the theoretical limit of the phase noise performance of the loop oscillator is made.

Evaluation of SAW chemical sensors for air filter lifetime and performance monitoring

Abstract A miniature surface acoustic wave (SAW) chemical sensor has been utilized to monitor the progression and breakthrough of the nerve agent simulant dimethylmethylphosphonate (DMMP) through a porous carbon filter-bed. The SAW sensor was successfully operated in carbon filter-beds under high air flow rates and a variety of humidity conditions with no active temperature control applied to the filter bed or SAW sensor. The SAW sensor successfully monitored the progression of DMMP through the filter-bed, from low to high vapor concentrations. The inclusion of the SAW sensor in the middle or at the end of the filter-bed did not degrade the performance of the filter-bed.

Laser Direct Writing of circuit elements and sensors

A novel approach for maskless deposition of numerous materials has been developed at the Naval Research Laboratory. This technique evolved from the combination of laser induced forward transfer and Matrix Assisted Pulsed Laser Evaporation (MAPLE), and utilizes a computer controlled laser micromachining system. The resulting process is called MAPLE-DW for MAPLE Direct Write. MAPLE-DW can be used for the rapid fabrication of circuits and their components without the use of masks. Using MAPLE-DW, a wide variety of materials have been transferred over different types of substrates such as glass, alumina, plastics, and various types of circuit boards. Materials such as metals, dielectrics, ferrites, polymers and composites have been successfully deposited without any loss in functionality. Using a computer controlled stage, the above mentioned materials were deposited at room temperature over various substrates independent of their stage, the above mentioned materials were deposited at room temperature over various substrates independent of their surface morphology, with sub-10micrometers resolution. In addition, multilayer structures comprising of different types of materials were demonstrated by this technique. These multilayer structures from the basis of prototype thin film electronics devices such as resistors, capacitors, cross-over lines, inductors, etc. An overview of the result obtained using MAPLE-DW as well as examples of several devices made using this technique is presented.

Sorbent coatings for detection of explosives vapor: applications with chemical sensors

A series of chemoselective polymers have been designed and synthesized in order to enhance the nitroaromatic sorption properties of coated acoustic wave devices. Acoustic wave devices coated with a thin layer of chemiselective polymer can provide highly sensitive transducers for the detection of vapors or gases. The sensitivity and selectivity of the sensor depends on several factors including the chemoselective coating used, the physical properties of the vapor(s) of interest, the selected transducer, and the operating conditions. To evalute the effectiveness of the chemoselective coatings a polynitroaromatic vapor test bed was utilized to challenge polymer coated SAW devices. Detection limits with the coated SAW sensors, as tested under laboratory conditions, are determined to be in the lower parts per trillion range. FTIR studies were undertaken to determine the nature of the polymer-polynitroaromatic interactions.

Recent developments in sorbent coatings and chemical detectors at the Naval Research Laboratory for explosives and chemical agents

New chemiselective polymers have been developed to enhance the nitroaromatic sorption properties of coated acoustic wave (AW) devices. The sensitivity and selectivity of polymer-based sensors depends on several factors including the chemiselective coating used, the physical properties of the vapor(s) of interest, the selected transducer, and the operating conditions. Detection limits with the coated SAW sensors, tested under laboratory conditions, are determined to be < 100 parts per trillion for 2,4-dinitrotoluene. A new SAW based chemical vapor detector the NRL p-CAD has been developed with dramatically improved signal kinetics offering T95 response times of less than 0.1 second for a wide range of organic compounds including the nerve agent simulant and agent precursor material dimethylmethylphosphonate. In addition, the NRL p-CAD system offers a rapid 2s baseline reset virtually eliminating baseline drift issues associated with changes in temperature and relative humidity. The p-CAD system has been successfully tested in both ground and unmanned aerial vehicle testing.

Matrix-assisted laser transfer of electronic materials for direct-write applications

A novel laser-based direct-write technique, called Matrix Assisted Pulsed Laser Evaporation Direct Write (MAPLE-DW), has been developed for the rapid prototyping of electronic devices. MAPLE-DW is a maskless deposition process operating under ambient conditions which allows for the rapid fabrication of complex patterns of electronic materials. The technique utilizes a laser transparent substrate with one side coated with a matrix of the materials of interest mixed with an organic vehicle. The laser is focused through the transparent substrate onto the matrix coating which aids in transferring the materials of interest to an acceptor substrate placed parallel to the matrix surface. With MAPLE-DW, diverse materials including metals, dielectrics, ferroelectrics, ferrites and polymers have been transferred onto various acceptor substrates. The capability for laser-modifying the surface of the acceptor substance and laser-post-processing the transferred material has been demonstrated as well. This simple yet powerful technique has been used to fabricate passive thin film electronic components such as resistors, capacitors and metal lines with good functional properties. An overview of these key results along with a discussion of their materials and properties characterization will be presented.