Dennis L. Polla

Gigantic enhancement in response and reset time of ZnO UV nanosensor by utilizing Schottky contact and surface functionalization

UV response of ZnO nanowire nanosensor has been studied under ambient condition. By utilizing Schottky contact instead of Ohmic contact in device fabrication, the UV sensitivity of the nanosensor has been improved by four orders of magnitude, and the reset time has been drastically reduced from approximately 417 to approximately 0.8 s. By further surface functionalization with function polymers, the reset time has been reduced to approximately 20 ms even without correcting the electronic response of the measurement system. These results demonstrate an effective approach for building high response and fast reset UV detectors.

Multispectral EO/IR Sensor Model for Evaluating UV, Visible, SWIR, MWIR and LWIR System Performance

Next Generation EO/IR Sensors using Nanostructures are being developed for a variety of Defense Applications. In addition, large area IRFPAs are being developed on low cost substrates. In this paper, we will discuss the capabilities of a EO/IR Sensor Model to provide a robust means for comparing performance of infrared FPAs and Sensors that can operate in the visible and infrared spectral bands that coincide with the atmospheric windows - UV, Visible-NIR (0.4-1.8μ), SWIR (2.0-2.5μ), MWIR (3-5μ), and LWIR (8-14μ). The model will be able to predict sensor performance and also functions as an assessment tool for single-color and for multi-color imaging. The detector model can also characterize ZnO, Si, SiGe, InGaAs, InSb, HgCdTe and Nanostructure based Sensors. The model can predict performance by also placing the specific FPA into an optical system, evaluates system performance (NEI, NETD, MRTD, and SNR). This model has been used as a tool for predicting performance of state-of-the-art detector arrays and nanostructure arrays under development. Results of the analysis can be presented for various targets for each of the focal plane technologies for a variety of missions.

EO/IR sensors development using zinc oxide and carbon nanostructures

EO/IR Sensors have been developed for a variety of Military Systems Applications. These include UV, Visible, SWIR, MWIR and LWIR Sensors. The conventional SWIR Sensors using InGaAs Focal Plane Array (FPA) can operate in 0.4 - 1.8 micron region. Similarly, MWIR Sensors use InSb and HgCdTe based FPAs that are sensitive in 3-5 and 8-14 micron region. DOD investments in the last 10 years have provided the necessary building blocks for the IR Sensors that are being deployed in the field. In this paper, we discuss recent developments and work under way to develop Next Generation nanostructure based EO/IR detectors that can potentially cover UV, Visible and IR regions of interest. The critical technologies being developed include ZnO nanostructures with wide band gap for UV detection and Carbon Nanostructures that have shown the feasibility for IR detection. Experimental results on ZnO based nanostructures demonstrate enhanced UV sensitivity and path forward for larger arrays. Similarly, recent works on carbon nanostructures have shown the feasibility of IR detection. Combining the two technologies in a sensor can provide multispectral capability.

Ultra-high transmittance through nanostructure-coated glass for solar cell applications

Ultra-high, broadband transmittance through coated glass windows is demonstrated over a wide range of incident angles. Near perfect 100% transmittance through a glass substrate has been achieved over select spectral bands, and the average transmittance increased to over 97% for photons incident between 0° and 75° with wavelengths between 400 nm and 1600 nm. The measured improvements in transmittance result from coating the windows with a new class of materials consisting of porous SiO2 nanorods.

ZnO nanostructures for optoelectronic applications

In this Paper we present growth and characterization of ZnO nanowires on wideband gap substrates, such as SiC and GaN. Experimental results on the ZnO nanowires grown on p-SiC and p-GaN are presented with growth morphology, structure analysis, and dimensionality control. We also present experimental results on individual nanowires such as I-V measurements and UV sensitivity measurements with use of polymer coating on ZnO nanowires. The ZnO nanowires can be used for a variety of nanoscale optical and electronics applications.

Design, fabrication, and characterization of thin film PZT membranes for high flux electronics cooling applications

An extensive numerical and experimental study of deep reactive ion etched (DRIE) thin film Pb(Zr,Ti)O3 (PZT) membranes used to enhance heat transfer between an immersed integrated circuit and a dielectric fluid is presented. Modal and harmonic analysis of the vibrating PZT membranes was performed using finite element techniques for a frequency range from 0 to 5 MHz. Experimental and numerical results showed that as the size of the PZT membranes increased, their fundamental resonance frequency decreased and they exhibited an increase in the number of resonance points in a given frequency range. Square and rectangular PZT membranes showed similar resonant characteristics, while elliptic membranes displayed more resonant points than circular devices. For a specified frequency range and equivalent surface areas, square membranes had more resonant points than circular membranes. When the thin film PZT membranes are immersed in a dielectric fluid, substantial vortices and turbulences, along with distinct particle flow paths, were observed.

RF MEMS integration present & future trends

RF MEMS technologies are rapidly being integrated into RF subsystems for a variety of applications of interest to the Department of Defense. New technologies such as RF high-Q MEMS resonators and micromechanical arrays are being developed that will enable filters and other high-performance passive components for fully integrated microsystems. Large off-chip filters will be replaced by arrays of MEMS resonators to enable monolithic chip-scale spectrum analyzers and channelizers. RF MEMS switches are being continually improved for low-loss, high-isolation switching with enhanced reliability critical to the performance of both military and commercial systems.

Growth and characterization of ZnO nanowires for various sensor applications

In this Paper we present growth and characterization of ZnO nanowires on a variety of substrates, such as Silicon and SiC. Experimental results on the ZnO nanowires grown on Si and SiC are presented with growth morphology, structure analysis, and dimensionality control. The ZnO nanowires can be used for a variety of nanoscale optical and electronics sensors.

A review of growth and characterization of ZnO nanostructures for various optical applications

The ZnO nanostructures can be implemented in optoelectronic applications, piezoelectric pressure sensors, Spintronic devices, transducers and biomedical applications [1-8]. Use of these nanostructures, will also allow building of nanoscale nanosensors, nanocantilevers, field-effect transistors and nanoresonators for a variety of military, homeland security and, commercial applications. In this paper we review growth and characterization of ZnO nanowires on a variety of substrates. Experimental results on the ZnO nanowires grown on GaN and SiC are presented with growth morphology, structure analysis, and dimensionality control. We also discuss Raman and micro-Raman spectroscopy for characterization of ZnO nanostructures.

Nanostructured Detector Technology for Optical Sensing Applications

Optical sensing technology is critical for defense and commercial applications including optical communication. Advances in optoelectronics materials in the UV, Visible and Infrared, using nanostructures, and use of novel materials such as CNT and Graphene have opened doors for new approaches to apply device design methodology that are expected to offer enhanced performance and low cost optical sensors in a wide range of applications.