Effect of the Source toSubstrate Distance on Structural, Optoelectronic, and Thermoelectric Properties of Zinc Sulfide Thin Films

Zinc sulfide ZnS thin films with variable structural, optical, electrical, and thermoelectric properties were obtained by changing the source to substrate SSD distance in the physical vaporthermal coating PVTC system. The films crystallized into a zinc blede cubic structure with 111 preferred orientation

Tuning structural and physical properties via A-site doping in perovskite-type transition metal oxides

Advisors: Omar Chmaissem.Committee members: Dennis Brown; Bogdan Dabrowski; Yasuo Ito.Includes illustrations.Includes bibliographical references.This thesis investigates the structure-property relationship of two important classes of transition metal oxides (the perovskite-type A-site substituted titanates (Sr[sub 1-x-y]Ca[sub x]Nd[sub y])TiO[sub 3] and manganites (Sr[sub 1-x]Ba[sub x])MnO[sub 3]). A thorough evaluation is provided of their potential for prospective technological applications in heat recycling and information technology by examining the thermoelectric and multiferroic prop- erties, respectively. In the titanate compounds, we doped on the A-site with small rare earth ions in order to generate mixed valent transition metals to increase band filling while the Ca doping maintained fixed levels of distortions. In the case of the manganites, A-site Sr ions were substituted with large Ba ions for the purpose of increasing the materials strain and to promote ferroelectricity. Crystal structure was investigated using high-resolution neutron powder diffraction as a function of temperature and Nd/Ba doping. In the titanates, two series were synthesized and designed to have a nominally constant tolerance factor at room temperature. We determine the room temperature structures as tetragonal I4/mcm and orthorhombic Pbnm for the Sr-rich and Ca-rich series, respectively. Three low temperature orthorhombic structures, Pbnm, Ibmm and Pbcm were also observed for the Sr-rich series; whereas, the symmetry of the Ca-rich series remained unchanged throughout the full measured temperature range. Thermoelectricity in ternary (Sr[sub 1-x-y]Ca[sub x]Nd[sub y])TiO[sub 3] perovskites was investigated. The double substitution at the A-site maintained a fixed crystal distortion while Nd3+ doping modified the electronic properties of the materials via increased band filling. Unique compositions of cations allowed for increased A-site atomic mass disorder and the lattice thermal conductivity was significantly suppressed to values as low as ~ 1.5 W/K.m in some samples, approaching amorphous Silicon limit. Charge doping via balanced formation of Ti^3+ at the B-site has transformed materials into n-type semi-conductors. I examined the range of applicability of various conduction models, viz., variable range hopping, semiconductor-type conductivity across band gap, and small polaron hopping for the best description of the temperature variation of measured resistivity. We succeeded in achieving a relatively high figure of merit ZT=0.07 at ~ 400 K in the Sr-rich Sr[sub 0.76]Ca[sub 0.16]Nd[sub 0.08]TiO[sub 3] composition which is comparable to that of the best n-type TE SrTi[sub 0.80]Nb[sub 0.20]O[sub 3] oxide material reported to date. With an enhanced Seebeck coefficient at elevated temperatures and reduced thermal conductivity, we predict that Sr[sub 0.76]Ca[sub 0.16]Nd[sub 0.08]TiO[sub 3] and similar compositions have the potential to become some of the best materials in their class of thermoelectric oxides. We also report the structure-property phase diagram of unique single-ion type-1 multiferroic pseudocubic Sr1-xBaxMnO3 perovskites. Employing a specially designed multi-step reduction-oxidation synthesis technique, we have synthesized previously unknown Sr[sub 1-x]Ba[sub x]MnO[sub 3] compositions in their polycrystalline form with a significantly extended Ba solubility limit that is only rivaled by a very limited number of crystals and thin films grown under non-equilibrium conditions. Understanding the multiferroic interplay with structure in Sr[sub 1-x]Ba[sub x]MnO[sub 3] is of great importance as it opens the door wide to the development of newer materials from the parent (AA')(BB')O3 system with enhanced properties. To this end, using a combination of time-of-flight neutron and synchrotron x-ray scattering techniques, we determined the exact structures and quantified the Mn and oxygen polar distortions above and below the ferroelectric Curie temperature TC and the Neel temperature TN. In its ferroelectric state, the system crystalizes in the noncentrosymmetric tetragonal P4mm space group which gives rise to a large electric dipole moment PS, in the z-direction, of 18.4 and 29.5 microC/cm2 for x = 0.43 and 0.45, respectively. The two independently driven ferroelectric and magnetic order parameters are single-handedly accommodated by the Mn sublattice leading to a novel strain-assisted multiferroic behavior in agreement with many theoretical predictions. Our neutron diffraction results demonstrate the large and tunable suppression of the ferroelectric order at the onset of AFM ordering and confirm the coexistence and strong coupling of the two ferroic orders below T[sub N]. The refined magnetic moments confirm the strong covalent bonding between Mn and the oxygen anions which is necessary for stabilizing the ferroelectric phase.Ph.D. (Doctor of Philosophy

Experimental and computational study of annealed nickel sulfide quantum dots for catalytic and antibacterial activity

This research investigates the hydrothermal synthesis and annealing duration effects on nickel sulfide (NiS2) quantum dots (QDs) for catalytic decolorization of methylene blue (MB) dye and antimicrobial efficacy. QD size increased with longer annealing, reducing catalytic activity. UV–vis, XRD, TEM, and FTIR analyses probed optical, structural, morphological, and vibrational features. XRD confirmed NiS2's anorthic structure, with crystallite size growing from 6.53 to 7.81 ​nm during extended annealing. UV–Vis exhibited a bathochromic shift, reflecting reduced band gap energy (Eg) in NiS2. TEM revealed NiS2 QD formation, with agglomerated QD average size increasing from 7.13 to 9.65 ​nm with prolonged annealing. Pure NiS2 showed significant MB decolorization (89.85%) in acidic conditions. Annealed NiS2 QDs demonstrated notable antibacterial activity, yielding a 6.15 ​mm inhibition zone against Escherichia coli (E. coli) compared to Ciprofloxacin. First-principles computations supported a robust interaction between MB and NiS2, evidenced by obtained adsorption energies. This study highlights the nuanced relationship between annealing duration, structural changes, and functional properties in NiS2 QDs, emphasizing their potential applications in catalysis and antibacterial interventions

Effect of the Source-to-Substrate Distance on Structural, Optoelectronic, and Thermoelectric Properties of Zinc Sulfide Thin Films

Zinc sulfide (ZnS) thin films with variable structural, optical, electrical, and thermoelectric properties were obtained by changing the source-to-substrate (SSD) distance in the physical-vapor-thermal-coating (PVTC) system. The films crystallized into a zinc-blende cubic structure with (111) preferred orientation. The films had a wide 3.54 eV optical band gap. High-quality homogenous thin films were obtained at 60 mm SSD. The sheet resistance and resistivity of the films decreased from 1011 to 1010 Ω/Sq. and from 106 to 105 Ω-cm, when SSD was increased from 20 mm to 60 mm, respectively. The phase and band gap were also verified by first principles that were in agreement with the experimental results. Thermoelectric characteristics were studied by using the semi-classical Boltzmann transport theory. The high quality, wide band gap, and reduced electrical resistance make ZnS a suitable candidate for the window layer in solar cells

Simultaneous HPLC Determination of Clindamycin Phosphate, Tretinoin, and Preservatives in Gel Dosage Form Using a Novel Stability-Indicating Method

The most well-known, effective medicines for acne therapy are clindamycin phosphate and tretinoin. For the first time, we have developed and validated a reversed-phase HPLC stability-indicating technique for the detection of clindamycin phosphate (CLP), tretinoin (TRN), and two preservatives, methylparaben (MP) and imidazolidinyl urea (IU), simultaneously in this work. Most of the chromatographic conditions in the present study were optimized to achieve better separation. The best separation results were obtained using gradient elution on a C-18 (250 × 4.6 mm), 5 µm column, with a mobile phase consisting of solution A (1 mL/L ortho-phosphoric acid in water) and solution B (methanol), at a flow rate of 1.0 mL/min, with UV detection at wavelengths of 200 nm and 353 nm. Standard parameters such as system suitability, precision, accuracy, specificity, robustness, linearity, range, detection limit, quantification limit, and reagent stability were used to validate the developed technique. According to the standards of the International Council for Harmonization, all of the experimental parameters were found to be within allowable bounds (ICH). The simultaneous concentrations of clindamycin phosphate, tretinoin, methylparaben, and imidazolidinyl urea in pharmaceutical formulations were successfully determined using the suggested approach. The proposed RP-HPLC method detected no interfering peaks in the chromatogram. We may conclude from the data that the new RP-HPLC method can be utilized in pharmaceutical laboratories to simultaneously assess clindamycin phosphate, tretinoin, and two preservatives, methylparaben and imidazolidinyl urea, for both qualitative and quantitative analyses

Simultaneous HPLC Determination of Clindamycin Phosphate, Tretinoin, and Preservatives in Gel Dosage Form Using a Novel Stability-Indicating Method

The most well-known, effective medicines for acne therapy are clindamycin phosphate and tretinoin. For the first time, we have developed and validated a reversed-phase HPLC stability-indicating technique for the detection of clindamycin phosphate (CLP), tretinoin (TRN), and two preservatives, methylparaben (MP) and imidazolidinyl urea (IU), simultaneously in this work. Most of the chromatographic conditions in the present study were optimized to achieve better separation. The best separation results were obtained using gradient elution on a C-18 (250 × 4.6 mm), 5 µm column, with a mobile phase consisting of solution A (1 mL/L ortho-phosphoric acid in water) and solution B (methanol), at a flow rate of 1.0 mL/min, with UV detection at wavelengths of 200 nm and 353 nm. Standard parameters such as system suitability, precision, accuracy, specificity, robustness, linearity, range, detection limit, quantification limit, and reagent stability were used to validate the developed technique. According to the standards of the International Council for Harmonization, all of the experimental parameters were found to be within allowable bounds (ICH). The simultaneous concentrations of clindamycin phosphate, tretinoin, methylparaben, and imidazolidinyl urea in pharmaceutical formulations were successfully determined using the suggested approach. The proposed RP-HPLC method detected no interfering peaks in the chromatogram. We may conclude from the data that the new RP-HPLC method can be utilized in pharmaceutical laboratories to simultaneously assess clindamycin phosphate, tretinoin, and two preservatives, methylparaben and imidazolidinyl urea, for both qualitative and quantitative analyses

The Interrelation of Synthesis Conditions and Wettability Properties of the Porous Anodic Alumina Membranes

The results of studies on the wettability properties and preparation of porous anodic alumina (PAA) membranes with a 3.3 ± 0.2 μm thickness and a variety of pore sizes are presented in this article. The wettability feature results, as well as the fabrication processing characteristics and morphology, are presented. The microstructure effect of these surfaces on wettability properties is analyzed in comparison to outer PAA surfaces. The interfacial contact angle was measured for amorphous PAA membranes as-fabricated and after a modification technique (pore widening), with pore sizes ranging from 20 to 130 nm. Different surface morphologies of such alumina can be obtained by adjusting synthesis conditions, which allows the surface properties to change from hydrophilic (contact angle is approximately 13°) to hydrophobic (contact angle is 100°). This research could propose a new method for designing functional surfaces with tunable wettability. The potential applications of ordinary alumina as multifunctional films are demonstrated