Browsing by Author "Su, Charmain"
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Item Chemical and biological sensing using polarity of material(SPIE, 2020-04-24) Emge, Ian; Su, Charmain; Sood, Rachit; Arnold, Bradley; Choa, Fow-Sen; Kelly, Lisa; Mandal, K. D.; Verma, Manish K.; Singh, N. B.Polarity is very important in developing materials with colossal dielectric. To meet the demands for the tunable devices and high dielectric parallel plate capacitors, several perovskites such as CaCu₃Ti₄O₁₂ (CCTO), La₂∖₃Cu₃Ti₄O₁₂ (LCTO) Pr₂∖₃Cu₃Ti₄O₁₂ (PCTO) and several other materials of this class have been studied all over the world. Detailed studies showed that results vary a lot based on processing methods, such as powder vs. multi crystals and single crystals. In spite of great progress in processing, low resistivity and process driven variables in properties remain a big hurdle for its applications as a dielectric capacitor. We observed that dielectric values are significantly changed when these materials are exposed to chemicals and biological agents. We used parallel plate capacitor design for making chemical and biological sensors from CCTO member of this group. The data indicated huge difference in the dielectric and resistivity of the exposed samples.Item Design and measurements of n for the multicomponent semiconductor(SPIE, 2020-08-20) Setera, Brett; Arnold, Bradley; Choa, Fow-Sen; Kelly, Lisa; Emge, Ian; Su, Charmain; Machuga, Krishna S.; Singh, N. B.A great deal of research has been performed on refractive index n and extinction coefficient k due to varieties of applications in optical industries. The dispersion equation is described for the photons of varying energies and their interactions with materials since there is a strong correlation of n and k with wavelength. Measurements based on reflectance can be expensive and are very difficult due to compositional variations. We present a low-cost reflectance probe fiber optics designed in-house to determine the absorption coefficients and refractive index of solids. The solutions using a modified Beer-Lamberts Law and merging the concentration and extinction coefficient terms into an absorption coefficient, α, can be given by the equation I = I0 exp (-α* d) where I is the transmitted intensity, I0 is incident intensity and d is the thickness. We have experimented with several semiconductor compounds for this study.Item Effect of Doping on the Electrical Characteristics of ZnSe(MDPI, 2020-06-27) Singh, Narsingh Bahadur; Su, Ching-Hua; Choa, Fow-Sen; Arnold, Bradley; Gill, Puneet; Su, Charmain; Emge, Ian; Sood, RachitThe effect of sulfur, iron, and chromium doping on the electrical characteristics of ZnSe single crystals was studied. The crystals, grown by the physical vapor transport method (PVT) at NASA Marshall Space Flight Center, were characterized by measuring electrical resistivity, capacitance, and dielectric constant using LCR meter. The morphology was studied by scanning electron microscopy to determine the crystallinity and micro defects. The measured resistivity and dielectric constant showed tunability as the function of frequency in the range of 100 Hz to 100,000 Hz, indicating the suitability of doped material for tuning devices. Besides, for the range from 50 mV to 1000mV, there was no difference in values for the studied frequency range, indicating no degradation or breakdown in the material. All doped ZnSe crystals with sulfur, iron, and chromium showed a similar trend as the function of frequency. Cr-ZnSe showed very high resistivity and lower dielectric constant compared to S-ZnSe and Fe-ZnSe crystals.