Engineering topics

Cullum, Brian

Publications and source records attributed to Cullum, Brian.

11 records

NASA NTRS2019

Design of Materials for IR Detectors Using High Z Elements for High Energy Radiation Environment

There is a strong need for rad hard and high operating temperature IR detectors for space environment. Heavy metal Selenides (high Z and large density) have been investigated for more than half century for high operating temperature mid wave infrared (MWIR) applications. Most of the efforts have been devoted to make detector arrays on high-resistivity Si substrates for operating wavelengths in the 1.5 to 5.0 m region using physical vapor transport grown poly crystalline materials. For most of the biological spectral and imaging applications, short wave infrared (SWIR) detectors have shown better performance. Recent growth materials have shown variation in morphology with slight change in growth conditions and hence variation in performance parameters such as bandgap, mobility and resistivity from sample to sample. We have performed growth and optical characterization of binary materials CdSe-PbSe to determine the suitability for IR detector. We have determined bandgap using several theoretical models for different morphologies observed during growth on silicon wafers.

Saraf, Sonali↗

NASA NTRS2019

Effect of Processing on Morphology of Hydroxyapatites: Bioactive Glasses and Crystalline Composites

Recent studies on multinary oxides for applications as laser hosts and high dielectric capacitors have shown that processing at high temperature provides glassy or crystalline materials based on thermal treatments and cooling rates. Since hydroxyapatites are now subject of great interests due to their bioactivity, interest in producing soft and hard materials with glassy and crystalline nature by processing parameters has become very important. Crystalline materials by using Bridgman, Czochralski and flux growth methods are costly and require huge investment. We have observed that even low temperature solidification in organic flux produced oriented fibers. This organic treated material has different characteristics than in situ oxide materials prepared by sintering and grain growth. Examples of phosphate and silicate-based systems will be presented to demonstrate soft and hard materials. Effect of TiO2 and other hardening elements will be also reported.

McAdams, Joel↗

NASA NTRS2018

Effect of Radiation on Biologically Active Glasses

Multifunctional hydroxyapatites single crystals have been studied for their applications as the laser host material since past several decades. It is only recently their potential has been evaluated for bioactive materials. In the past researches, Czochralski and flux growth methods have been utilized to achieve single crystals. We have used low temperature processing techniques for synthesis. Organic melt was used to achieve oriented fibers by the directional solidification method. This organic treated material has different characteristics than coarsened oxide materials. Our approach involved low temperature processing using nano engineered powders of the material system Na2O-K2O-CaO- MgO-SrO-SiO2. Also, borates were processed by sintering and grain growth. Effect of -ray was studied by measuring the electrical characteristics of radiated samples. Our experiments to further improve mechanical characteristics indicate that substitution of calcium with some other elements such as gallium have great potential to improve the radiation hardening and mechanical properties of bones.

Tufail, Areeba↗

NASA NTRS2018

Development of Large Bandgap Materials Using Reactive Growth in Al-SI Eutectic for Optical and RF Applications

Carbon was utilized as reactive element to modify the microstructure using forced mixing during crystallization of the Al-Si alloy by rotation and stirring. We nucleated the material on SiC substrates while the Al-Si melt was rotated with a speed of 30rpm in a graphite crucible. Several experiments were performed and parameters such as time of mixing, soaking temperature, rotation rate of the substrate and rate of cooling during the solidification was changed. We observed dendrite and cell morphologies during the solidification of rotating melt. The microstructure was characterized by optical microscopy and SEM-EDX and compositional spectroscopy. The effect of carbon impurities was studied on the solidifying microstructure. When we used the longer soak time of the melt in presence of carbon impurities we observed the destruction of dendritic morphology and the formation of cellular and colony structures. Similar approach has been used for Ga2O3, a novel large bandgap material also.

Singh, N. B.↗

NASA NTRS2018

Surface Modification at Nanoscale; Nanoparticle-Nanowire Transition

Binary, ternary and quaternary oxides and selenides have been developed and used in multiple applications including high power lasers, detectors, dielectric energy storage and variety of optical devices. These materials have been grown by Bridgman, physical vapor transport (PVT), chemical vapor transport (CVT) methods and flux methods in the form of bulk thin film, nanocrystals and nanowires. With increasing thrust of bio applications, nanoparticles it is essential to understand nucleation and nanomorphological transition during drug delivery, growth of nanoengineered bio composites in body, grain growth and final morphology. Addition of fluorides and selenides have increased significantly in synthetic tissue constituents because of some advantages in adhesion and stability. We have performed experiments on multinary oxides Sr-Ba-O-F, Se-Tl-As and Se-Pb-Sn-Se using several growth methods to demonstrate nanoparticle and nanowire transition. This study has great potential to increase surface area and also provides understanding to the mechanism of nanowire growth.

Singh, N. B.↗

NASA NTRS2018

Nanoengineered Materials for SWIR HOT Detectors

Heavy metal Selenide has been investigated for more than half century for high operating temperature (HOT) mid wave infrared (MWIR) applications. Most of the efforts have been devoted to make detector arrays on high-resistivity Si substrates for operating wavelengths in the 1.5 to 5.0 m region using physical vapor transport grown poly crystalline materials. For most of the biological spectral and imaging applications, short wave infrared (SWIR) detectors have shown better performance. Recent growth materials have shown variation in morphology with slight change in growth conditions and hence variation in performance parameters such as bandgap, mobility and resistivity from sample to sample. We have performed growth and optical characterization of pure and doped PbS and PbSe and have determined bandgap using available theoretical models for different morphologies.

Singh, N. B.↗

NASA NTRS2018

Design and Characteristics of Hydroxyapatites: Effect of Radiation

Hydroxyapatites single crystals have been investigated their applications as the laser host material. Czochralksi and flux growth methods have been utilized to achieve single crystals. Because of their bioactivities with tissues these have attracted interest for bone applications. For low temperature processing we have used several techniques. We utilized some organic melt and oriented the grains by the directional solidification method. This organic treated material has different characteristics than coarsened oxide materials. Our approach involved low temperature processing using nano-engineered powders of the material system MgO-Na2O-K2O-CaO-SrO-SiO2 and also borates were processed by sintering and grain growth. Our results indicate that substitution of calcium and strontium with some other elements such as gallium and magnesium have great potential to improve the mechanical properties of bones.

Bhavsar, Jayati↗

NASA NTRS2018

Design and Characteristics of Hydroxyapatites: Effect of Radiation

We have prepared silicate based hard materials and have processed it with organic flux. Because of the bioactivities of hydroxyapatites with tissues, this class of materials have attracted interest for bone applications. We have utilized low temperature processing techniques. Organic melt was used and the directional solidification method to cast the shaped sample. This organic treated material has different characteristics than coarsened oxide materials. Our approach involved low temperature processing using nano and micron sized powders of the material system Na2O-K2O-CaO- MgO-Ga2O3-SiO2, and titanates were processed by sintering and grain growth. Our results indicate that substitution of gallium and magnesium or titanium with some variation in processing methods have great potential to improve the glassy characteristics without decreasing the mechanical properties of bones. Effect of radiation on bone was studied by exposing with commercially available Cs137 gamma ray source. It was observed that electrical resistivity increased due to radiation exposure for this system.

Bhavsar, Jayati↗

NASA NTRS2018

Role of a Chemist in Modern Industries: Design and Development of Nanoengineered Multifunctional Materials

During the past fifteen years significant investment has been made for the applications of nanotechnology in almost every aspect of life. Almost every area of research has projected improvements including biotechnology, bioinspired electronic, optical and radiological sensors, or a promise for the emergence of some novel device technologies. For such applications major focus has been placed on research nanoparticles, nanotubes nanorods and two-dimensional structures similar to that of graphene. Some near- term applications of nano- particles and nanowires have produced very promising results for better synthesis of energy storage materials, design of biologically active composites like apatites, laser host crystals, photodetectors and sensor materials for radiation detection. To achieve desired morphologies, nanomaterials can be utilized some organic melt and orient the grains by the directional solidification method. The organic treated materials produce different characteristics than coarsened oxide materials. The focus is also understanding the morphology and performance function in human organs that occur because of aging or disease, and responses to interventions. We annealed to determine the changes in morphologies and hence effect of aging. In this presentation, we will discuss correlation between the designed composition, micromorphology and the performance parameters of nanomaterials. To understand the mechanism of formation of nanoparticles, nanoboloids, fibers experimental details and observations on the of multinary compounds will be presented. These observations on the transition of nanomorphology can highlight the mechanism of the phase transition in some oxides and selenides.

Singh, N. B.↗

NASA NTRS2016

Growth Mechanism of Nanowires: Binary and Ternary Chalcogenides

Semiconductor nanowires exhibit very exciting optical and electrical properties including high transparency and a several order of magnitude better photocurrent than thin film and bulk materials. We present here the mechanism of nanowire growth from the melt-liquid-vapor medium. We describe preliminary results of binary and ternary selenide materials in light of recent theories. Experiments were performed with lead selenide and thallium arsenic selenide systems which are multifunctional material and have been used for detectors, acousto-optical, nonlinear and radiation detection applications. We observed that small units of nanocubes and elongated nanoparticles arrange and rearrange at moderate melt undercooling to form the building block of a nanowire. Since we avoided the catalyst, we observed self-nucleation and uncontrolled growth of wires from different places. Growth of lead selenide nanowires was performed by physical vapor transport method and thallium arsenic selenide nanowire by vapor-liquid-solid (VLS) method. In some cases very long wires (>mm) are formed. To achieve this goal experiments were performed to create situation where nanowires grew on the surface of solid thallium arsenic selenide itself.

Singh, N. B.↗

NASA NTRS2016

Growth Mechanism of Nanowires: Ternary Chalcogenides

In the past two decades there has been a large rise in the investment and expectations for nanotechnology use. Almost every area of research has projected improvements in sensors, or even a promise for the emergence of some novel device technologies. For these applications major focuses of research are in the areas of nanoparticles and graphene. Although there are some near term applications with nanowires in photodetectors and other low light detectors, there are few papers on the growth mechanism and fabrication of nanowire-based devices. Semiconductor nanowires exhibit very favorable and promising optical properties, including high transparency and a several order of magnitude better photocurrent than thin film and bulk materials. We present here an overview of the mechanism of nanowire growth from the melt, and some preliminary results for the thallium arsenic selenide material system. Thallium arsenic selenide (TAS) is a multifunctional material combining excellent acousto-optical, nonlinear and radiation detection properties. We observed that small units of (TAS) nanocubes arrange and rearrange at moderate melt undercooling to form the building block of a nanowire. In some cases very long wires (less than mm) are formed. Since we avoided the catalyst, we observed self-nucleation and uncontrolled growth of wires from different places.

Singh, N. B.↗