M. D. Aggarwal

Synthesis and characterization of various Schiff bases for non-linear optical applications

A series of salicylidenes have been synthesized to investigate non-linear optical properties. Attempts have been made to correlate second harmonic generation properties of these Schiff base compounds with ring substitution patterns, as well as the nature of the ring substituents. The result of double substitutions to the aniline moiety is also discussed. It is reported that meta substitution in the aniline moiety gives comparable values for second harmonic generation with respect to urea.

Studies on DTGS:PVDF Composites for Pyroelectric Infrared Detectors

The search for new materials for pyroelectric infrared sensors and ultrasonic transducers has led to the design of ferroelectric composites [1–4]. Recent studies on pyroelectric-polymer composites do show their usefulness in large area, light weight, high strength and flexible infrared sensing devices [2, 3]. Among available materials, deuterated triglycine sulfate (DTGS) shows highest pyroelectric performance [5]. The current work describes the fabrication of DTGS:PVDF composites with varying DTGS particle size powders and composition embedded in poly-vinylidene fluoride (PVDF) matrix which is also an important pyroelectric polymer. In this communication we report the results of investigation of the dielectric and pyroelectric properties of new composites. Using these properties, applicable materials figures of merit are calculated for their use in infrared detecting devices, and are also compared with investigated pyroelectric composites. The results are encouraging for their use as infrared sensors.

Modified Bridgman-Stockbarger growth of a novel NLO organic crystal (2-methoxyphenyl)-methylene-propanedinitrile

Abstract The Bridgman-Stockbarger method offers a unique opportunity for positioning the solid-liquid interface in the hot zone by a suitable adjustment of the two zone temperatures. The method, however, yields inhomogeneous organic crystals in relation to the progressive degradation of the material during growth. To solve this problem, a modified Bridgman-Stockbarger method (MBS) has been developed and is used to keep the smallest possible quantity of product in the melt for a short time period. In this method, the gradient is chosen to be 5 to 10°C/cm and the ampoules downward rate is chosen to be 0.1 to 0.3 mm/h. For the given conditions, several (2-methoxyphenyl)-methylene-propanedinitrile or 2-dicyanovinylanisole (DIVA) single crystals of good optical quality and a size of 10 × 10 × 50 mm 3 have been successfully grown. Preliminary results on the characterization of these crystals are presented.

Predicted Frequency Response of Integrated Pyroelectric PNZT Infrared Detectors

Numerous studies have been carried out on the fabrication of ferroelectric lead titanate (PT) and lead zirconate titanate (PZT) thin films and their applications to pyroelectric sensors [1–3]. Not many efforts have been made to integrate the films with silicon technology. In this article, we report on the growth of lead-zirconium-titanates films doped with niobium (PNZT) by a sol-gel method on platinized Si substrates along with its characteristics for use in infrared sensor applications.

New sensory materials for structural health monitoring

As space flight materials become stronger, lighter weight, and applied with lower margins of potential failure, the problem of determining their state of health in real time is not only more important but more difficult. Current techniques of visual inspection is only possible in particular situations where access and time are available; and, even at that, internal damage such as de-bonds de-laminations in composites are impossible to discern via visual inspection alone. Other techniques such as bonded fiber optics and/or other strain gauging sensors are fragile, labor intensive to apply, and limited in their ability to discern the timing of structurally damaging events. This paper reports on work being done at the Alabama A&M University as well as other research institutions on the nature of certain triboluminescent materials and their potential applicability as real time sensors for structural damage monitoring. The properties of several triboluminescent materials will be presented along with conceptual designs of how these properties can provide valuable insight into real time structural damage mechanisms. The status and scope of ongoing work at the Alabama A&M University labs along with identification and status of work by colleagues at other research institutions will be discussed.

Electrical properties of TGS crystals grown by a new technique

The cooled sting technique used to grow triglycine sulphate (TGS) crystals is investigated. The sting procedure, which achieves supersaturation by cooling the seed crystal mounted on the sting is described and a diagram is provided. Temperature differentials of 1.5 and 1.0 C are optimum for growing (001) and (010) orientation TGS seeds. The data obtained are compared with previous data and good correlation is shown; it is inferred that TGS crystals of any orientation can be grown at a uniform rate of 1 mm/day using this technique.