The instability of isolate catalysts during metal-assisted chemical etching is a major hindrance to achieve high aspect ratio structures in the vertical and directional etching of silicon (Si). In ...this work, we discussed and showed how isolate catalyst motion can be influenced and controlled by the semiconductor doping type and the oxidant concentration ratio. We propose that the triggering event in deviating isolate catalyst motion is brought about by unequal etch rates across the isolate catalyst. This triggering event is indirectly affected by the oxidant concentration ratio through the etching rates. While the triggering events are stochastic, the doping concentration of silicon offers a good control in minimizing isolate catalyst motion. The doping concentration affects the porosity at the etching front, and this directly affects the van der Waals (vdWs) forces between the metal catalyst and Si during etching. A reduction in the vdWs forces resulted in a lower bending torque that can prevent the straying of the isolate catalyst from its directional etching, in the event of unequal etch rates. The key understandings in isolate catalyst motion derived from this work allowed us to demonstrate the fabrication of large area and uniformly ordered sub-500 nm nanoholes array with an unprecedented high aspect ratio of ∼12.
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IJS, KILJ, NUK, PNG, UL, UM
In this work, we investigate the transport processes governing the metal-assisted chemical etching (MacEtch) of silicon (Si). We show that in the oxidation of Si during the MacEtch process, the ...transport of the hole charges can be accomplished by the diffusion of metal ions. The oxidation of Si is subsequently governed by a redox reaction between the ions and Si. This represents a fundamentally different proposition in MacEtch whereby such transport is understood to occur through hole carrier conduction followed by hole injection into (or electron extraction from) Si. Consistent with the ion transport model introduced, we showed the possibility in the dynamic redistribution of the metal atoms that resulted in the formation of pores/cracks for catalyst thin films that are ≲30 nm thick. As such, the transport of the reagents and by-products are accomplished via these pores/cracks for the thin catalyst films. For thicker films, we show a saturation in the etch rate demonstrating a transport process that is dominated by diffusion via metal/Si boundaries. The new understanding in transport processes described in this work reconcile competing models in reagents/by-products transport, and also solution ions and thin film etching, which can form the foundation of future studies in the MacEtch process.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Using the small polaron model, we show clearly that oxygen vacancy defects are detrimental to the electrochromic responses of molybdenum oxide (MoO3). The observed phenomenon is explained by studying ...the oxidation states of the molybdenum (Mo) metal, which is central to the site specific small polaron model. First, we used the small polaron pair to explain the red-shift between the absorption peak induced by the vacancy defects and the inserted lithium (Li). Next, we show that any Mo5+ defects results in either a poor cathodic optical pair, or forms a site that is inactive for Li insertion. The main reason for the latter is due to the inability to generate Mo4+ in the reported optimal potential range. Finally, if the oxide starts with any intrinsic Mo4+ defect, we provided evidence to show that Mo6+–Mo4+ remains the only possible site for Li insertion, thereby greatly reducing available active sites. This optical modulation from Li insertion into this aforementioned pair is also low when compared with the Mo6+–Mo6+ pair. We therefore conclude that the most effective modulation is achieved by the Mo6+–Mo6+ pair and defects creation will be detrimental to the electrochromic performance of MoO3.
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Molybdenum oxide (MoO3) is a promising anode buffer layer (ABL) for high-performance organic photovoltaic (OPV) devices. However, the reasons for the enhanced performances remain unclear. In this ...work, we show that defect states play an important, if not dominating, role in improving the OPV performances. The changes in both the density of defect states and the work function of MoO3 with annealing are shown and correlated with the OPV device performance. The increased defect densities improve the OPV performance through an enhanced hole extraction rate at the MoO3/organic interface. The reduction in work function, however, reduces the interface field that can possibly lower mobility near the interface and reduce the electron-blocking effect. This plays a role in saturation of the device performance. This work, therefore, shows the importance of the defects in MoO3 as an ABL and a dominance of defect-enhanced extraction over a field-enhanced extraction process.
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The aim of this thesis is to investigate the fabrication and characterization of molybdenum oxide, with focus on three specific properties in its stochiometric and sub-stochiometric forms. These are ...the electronic properties, the ability to reversibly intercalate positive ions, and the associated optical property changes and surface reactivity. In addition, the use of molybdenum oxide in four related but distinct applications, which takes advantage of these unique properties, are also investigated. These four applications are in organic photovoltaics, electrochromic devices, secondary batteries, and gas sensing. These investigations will then help to elucidate the details of these properties, in the hope of achieving a more comprehensive understanding of the properties of molybdenum oxide in its various stoichiometries.
Layered nickel hydroxide thin films with mesoporous structure were prepared on ITO substrates by a facile chemical bath deposition method. The electrochemical properties of the nickel ...hydroxide/oxyhydroxide films were investigated in both potassium hydroxide and lithium perchlorate in propylene carbonate electrolytes. We show that the high reversible charge cycling capability of the material is enabled by the redox reaction involving hydroxyl ions, especially in the oxidative cycle. Li ion reversible charge cycling requires available reaction or adsorption sites that can be provided by sub-stoichiometry or defective films. Raising the defect concentration, the cyclic reversibility is shown to increase by similar to 5 times. The effects of intercalated water in the interlayers are also discussed. We show that the presence of water in the interlayers can lead to a passivating reaction during the charge cycling and also cause optical efficiency losses through unwanted charge trapping.
Abstract The growing interest in utilizing waste for composite development has prompted investigations across social, economic, and environmental domains. This study focuses on utilizing recyclable ...waste plastic materials and micro-sized ground tire rubber (GTR) of varying sizes (600 µm, 300 µm, and 150 µm) to create a polymer matrix composite (PMC). Employing a thermal blending technique, the manufacturing process adjusts the composition ratios of polymer and GTR from 90:10 to 50:50. Subsequently, Energy Dispersive Spectroscopy (EDS) is utilized to analyze the PMC composition, while Fourier-transform infrared spectroscopy confirms functional group and chemical structure. The study demonstrates significant improvements in various properties upon adding GTR to High-Density Polyethylene (HDPE) and Low-Density Polyethylene (LDPE) composite materials. For HDPE-GTR composites, the melting temperature (Tm) ranged from 120.29°C to 138.53°C, crystallization temperature (Tc) from 102.84°C to 127.14°C, and enthalpy of melting (ΔHm) from 70.96 to 139.67 J/g. Crystallinity (Xc) varied from 48.43% to 52.96%. In LDPE-GTR composites, Tm ranged from 106.08°C to 129.57°C, Tc from 90.27°C to 112.20°C, ΔHm from 75.59 to 142.53 J/g, and Xc from 51.59% to 54.05%. Moreover, mechanical properties such as tensile strength, flexural modulus, and impact strength exhibited enhancements with GTR addition to the polymer matrix. These findings underscore the potential of sustainable waste utilization, advancing environmentally friendly and resource-efficient composite materials.
Depression is common in diabetes and has significant impact on health outcomes. Suicidal ideation also forms a part of the spectrum of diabetes and coexistent depression. To assess the predictors of ...depression as well as its prevalence in Type 2 Diabetes Mellitus (T2DM) patients, we conducted a cross sectional study entitled “DEPression in DIABetes” (DEPDIAB).
A cohort of consecutive 1371 T2DM patients from Eastern India suffering from diabetes greater than 1 year was assessed in a cross- sectional survey in 9 different hospitals and medical polyclinics in Kolkata, India for depression by administering the 9-item PHQ – 9 and Beck depression scales. Socioeconomic status was assessed by the “Revised Kuppuswamy and B G Prasad socio-economic scales for 2016”, a validated scoring system for assessing the socioeconomic status of Indian patients.
In our study 836 patients (60.9%) were male and 535 (39.02%) were female. 56 patients (4.1%) met the criteria for major depression and 494 patients (36.16%) for minor depression. No sign of depression was found in 816 patients (59.74%). Depression was strongly associated with younger age (18–40 years vs. >60 years) OR-2.09; 95% CI 1.11–3.96, female sex OR-1.31; 95% CI 1.11–2.01, low socioeconomic status OR-2.69; 95% CI 1.34–3.79, poor compliance OR- 5.05; 95% CI 2.79–8.13, hypoglycemia OR 1.466; 95% CI 1.076–1.999 and difficulty in managing day-to-day activities OR- 4.648; 95% CI 3.450–6.262 Suicidal ideation was detected in 201 patients (14.8%). Among patients who had repeated attacks of hypoglycemia (>1 episode per month), 22% experienced suicidal ideation. This was significantly higher than in patients who had not suffered from hypoglycemia (12%) (p < 0.0001). Patients with HbA1C of 7% or lower experienced statistically significantly lesser suicidal ideation than patients with a higher HbA1C (12% vs. 16.8% {p = 0.016}). Suicidal ideation did not correlate withbody mass index (BMI), fasting plasma glucose (FPG) or insulin usage.
We found a high prevalence of depression in T2DM patients in Eastern India. Younger age, female sex, lower socio-economic status, poor compliance, hypoglycemia, and difficulty in managing day to day activities emerged as significant predictors of depression in this study. Recurrent episodes of hypoglycemia were an independent risk factor for suicidal ideation in patients with depression. Depression was not significantly associated with co morbidities associated with T2D and surprisingly insulin usage was not associated with increased depression.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Knowledge of soil hydraulic parameters and their spatiotemporal variation is crucial for estimating the water and solute fluxes across the land-atmosphere boundary and within the vadose zone at ...different scales. The objective of this study was to determine soil hydraulic conductivities saturated hydraulic conductivity, K(sat), and unsaturated hydraulic conductivity, K(psi) and their spatial and temporal variations in a clay-dominated biporous Vertisol near College Station, TX, using tension infiltrometers. The study was conducted within a 20- by 16-m plot across several seasons during a 21-mo period (May 2003-January 2005) to investigate the impact of varying disk sizes (measurement support) on K(psi), and the spatial and temporal variations of K(psi) under natural environmental conditions due to pore space evolution. Infiltration occurred in a bimodal fashion consisting of preferential flow (occurring at soil water pressure heads psi = -0.05 to 0 m) and matrix flow (at psi = -0.2 to -0.1 m). Biological and structural macropores present in the soil resulted in gravity-dominated flow near saturation (psi = -0.05 to 0 m) for all experiments. The Student's t-test of analysis of variance indicated that hydraulic conductivities were not affected by changes in the infiltration disk sizes. Although the K(psi) values at four different locations within the plot did not show significant spatial variability, they demonstrated strong temporal variation during the 21-mo period based on the evolution of natural environmental conditions due to seasonal precipitation, root growth and decay, and structural pore space dynamics. Temporal trends of K(psi) indicated that hydraulic conductivities close to saturation were positively correlated with antecedent moisture conditions reflecting liquid cohesion, water films bridging across cracking peds, and the activation of flow in biological and structural macroporosity in the biporous soil system.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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