Improving ALD-Al2O3 Surface Passivation of Si using Native SiOx

Al2O3 has rapidly become the surface passivation material of choice for the n-type Si solar cells with p + emitter due to its high negative fixed charge, good long-term and thermal stability, and no parasitic absorption. In this study, the surface saturation current density, fixed charge, and interface state density is compared for Al2O3 grown on Si substrates where the native SiOx was not removed, with substrates where the SiOx was removed by hydrofluoric acid. The depositions are performed by atomic layer deposition at temperatures in the 150–300 ˚C range, using trimethylaluminium, H2O, and O3 as precursors. The samples where the native oxide was not removed achieve a higher level of surface passivation for every tested deposition temperature, with the sample deposited at 200 ˚C exhibiting a surface saturation current density of only 1.9 fA/cm2, a fixed charge of 4.2×1012 cm− 2, and a density of interface states of 9.8×109 cm− 2 ev− 1. Capacitance and conductance voltage characteristics reveal a strong correlation between the surface saturation current density and the density of interface states and fixed charges. It is also determined that the long-term stability of the surface passivation depends on the deposition temperature, with higher deposition temperatures resulting in improved long-term stability.

Medusa–Aqua system: simultaneous measurement and evaluation of novel potential halogenated transient tracers HCFCs, HFCs, and PFCs in the ocean

This study evaluates the potential usefulness of the halogenated compounds HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14, and PFC-116 as oceanographic transient tracers to better constrain ocean ventilation processes. We do this mainly in terms of four aspects of the characteristics of the potential tracers: input function (including atmospheric history and historical surface saturation), seawater solubility, feasibility of measurement, and stability in seawater; of these, atmospheric history and seawater solubility have been investigated in previous work. For the latter two aspects, we collected seawater samples and modified an established analytical technique for the Medusa–Aqua system to simultaneously measure these compounds. HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, and HFC-125 have been measured in depth profiles in the Mediterranean Sea for the first time and for reproducibility in the Baltic Sea. We found that the historical surface saturation of halogenated transient tracers in the Mediterranean Sea is estimated to have been nearly constant at 94 % based on historical data. Of the investigated compounds, HCFC-142b, HCFC-141b, and HFC-134a are found to currently be the most promising transient tracers in the ocean. The compounds that have the greatest potential as future tracers are PFC-14 and PFC-116, mainly hampered by the low solubility in seawater that creates challenging analytical conditions, i.e., low concentrations. HCFC-22 is found to be likely unstable in warm seawater, which compromises the potential as an oceanic transient tracer, although it is possibly useful in colder water. For the compounds HFC-125 and HFC-23, we were not able to fully evaluate their potential as tracers due to inconclusive results, especially regarding their solubility and stability in seawater, but also with regard to potential analytical challenges. On the other hand, HFC-125, HFC-23, and HCFC-22 might not need to be considered because there are alternative tracers with similar input histories that are better suited as transient tracers.

REVIEW ON THE ROLE OF EARTHWORMS ON HILLSLOPE HYDROLOGY AND SOIL EROSION WITH SPECIAL REFERENCE TO DANUM VALLEY, SABAH, MALAYSIA

Hydrological routes exist through active burrowing of soil fauna, and in numbers improve soil drainage systems. Earthworms are of particular interest because their presence is known widely to increase infiltration and reduce erosion rates by creating macropores and stable casts. Ideally during non-extreme rainfall events on flatlands, earthworm macropores lengthens the time prior to soil surface saturation thus slowing down occasions of overland flow resulting in runoff. Hypothesizing similar effects on hillslopes with gradients can be misleading whereas laboratory experiments which try to recreate and simulate field consistency cannot match the natural soil architecture which is vital in the dissection of the many bio-geophysical processes involved in the rainfall-runoff process. This review paper aims to summarize past studies conducted around the world and highlighting possible gaps on earthworm’s studies related to hillslopes and erosion.

Influence of Water on the Oxidation of NO on Pd/TiO2 Photocatalysts

Two series of new photocatalysts were synthesized based on modification with Pd of the commercial P25 photocatalyst (EVONIK®). Two techniques were employed to incorporate Pd nanoparticles on the P25 surface: photodeposition (series Pd-P) and impregnation (series Pd-I). Both series were characterized in depth using a variety of instrumental techniques: BET, DRS, XRD, XPS, TEM, FTIR and FESEM. The modified series exhibited a significant change in pore size distribution, but no differences compared to the original P25 with respect to crystalline phase ratio or particle size were observed. The Pd0 oxidation state was predominant in the Pd-P series, while the presence of the Pd2+ oxidation state was additionally observed in the Pd-I series. The photoactivity tests were performed in a continuous photoreactor with the photocatalysts deposited, by dip-coating, on borosilicate glass plates. A total of 500 ppb of NO was used as input flow at a volumetric flow rate of 1.2 L·min−1, and different relative humidities from 0 to 65% were tested. The results obtained show that under UV-vis or Vis radiation, the presence of Pd nanoparticles favors NO removal independently of the Pd incorporation method employed and independently of the tested relative humidity conditions. This improvement seems to be related to the different interaction of the water with the surface of the photocatalysts in the presence or absence of Pd. It was found in the catalyst without Pd that disproportionation of NO2 is favored through its reaction with water, with faster surface saturation. In contrast, in the catalysts with Pd, disproportionation took place through nitro-chelates and adsorbed NO2 formed from the photocatalytic oxidation of the NO. This different mechanism explains the greater efficiency in NOx removal in the catalysts with Pd. Comparing the two series of catalysts with Pd, Pd-P and Pd-I, greater activity of the Pd-P series was observed under both UV-vis and Vis radiation. It was shown that the Pd0 oxidation state is responsible for this greater activity as the Pd-I series improves its activity in successive cycles due to a reduction in Pd2+ species during the photoactivity tests.

Colorimetric detection and adsorption of mercury using silver nanoparticles: A bibliographic and patent review

: Mercury (Hg) contamination is a problem that currently affects not only the environment but also human health. Various types of commercial adsorbents have been proposed for its removal. Silver is a noble element that can chemically adsorb mercury, forming amalgams. However, its use as an adsorbent presents the following disadvantages: rapid surface saturation and high cost. These limitations can easily be overcome using silver nanoparticles (AgNPs). With a size of less than 100 nm, their reactivity, their high surface area, and a minimal amount of metallic precursor, they are ideal candidates for mercury removal. This study presents a compendium of the use of conventional mercury adsorbents and the use of AgNPs for their colorimetric detection and removal in different matrices, in both the aqueous and gas phases of Hg0 and Hg2+ . In addition, the number of patents available in each case is analyzed. AgNPs as colorimetric sensors allow for quick detection of mercury in-situ. Additionally, the adsorption systems formed with AgNPs, allow for the obtaining of stable and chemically inert complexes, facilitating their recycling. It is concluded that the use of AgNPs is particularly efficient for the detection and removal of mercury, presenting a removal percentage of over 90%. As a result of the patents analyzed, its use is perfectly applicable at an industrial level.

Experimental and Numerical Investigation of the Catalytic Gas Carburization of Steel

The carbon surface saturation process of the steel plates during the catalytic gas carburization was under consideration. The rate of the carburization was determined, as well as the hardness of the diffusion layer, after quenching. A mathematical model based on experimental and numerical modeling data had been obtained. The carbon concentration profile of the surface layer was estimated depending on the carburization process parameters. A simplified simulation technique of the steel carburization was proposed.

Intra-catchment variability of surface saturation – insights from physically based simulations in comparison with biweekly thermal infrared image observations

In this study, we explored the spatio-temporal variability of surface saturation within a forested headwater catchment using a combined simulation–observation approach. We simulated the occurrence of surface saturation in the Weierbach catchment (Luxembourg) with the physically based model HydroGeoSphere. We confronted the simulation with thermal infrared images that we acquired during a 2-year mapping campaign for seven distinct riparian areas with weekly to biweekly recurrence frequency. Observations and simulations showed similar saturation dynamics across the catchment. The observed and simulated relation of surface saturation to catchment discharge resembled a power law relationship for all investigated riparian areas but varied to a similar extent, as previously observed between catchments of different morphological and topographical characteristics. The observed spatial patterns and frequencies of surface saturation varied between and within the investigated areas and the model reproduced these spatial variations well. The good performance of the simulation suggested that surface saturation in the Weierbach catchment is largely controlled by exfiltration of groundwater into local topographic depressions. However, the simulated surface saturation contracted faster than observed, the simulated saturation dynamics were less variable between the investigated areas than observed, and the match of simulated and observed saturation patterns was not equally good in all investigated riparian areas. These mismatches between observations and simulation highlight that the intra-catchment variability of surface saturation must also result from factors that were not considered in the model set-up, such as differing subsurface structures or a differing persistence of surface saturation due to local morphological features like perennial springs.