Genetic algorithm for design of reflective filters: Application to AlxGa1-xN based Bragg reflectors

A genetic algorithm (GA) with adaptive mutations has been employed for the design of Bragg reflectors. The algorithm enables three different design types a) composition and thickness of two layers are chosen and the pair is repeated b) two compositions are chosen for the two alternating materials, and thickness of each layer is optimized c) composition and thickness of each layer are optimized. In all cases, the wavelength and composition dependence of the index of refraction is taken into account. Also, it is possible to impose constraints on the composition difference of the neighbouring layers, either with a penalty function or with narrowing the boundaries for possible compositions. This feature is important because the large lattice mismatch between GaN and AlN can cause poor surface morphology, so measured reflectivity would be lower than the calculated one due to the surface roughness. The algorithm enables finding the optimal design for two chosen incident and final media, and it is capable of taking into account the existence of a finite, optically thick substrate. We have investigated two systems: air/sapphire/AlxGa1-xN reflector/GaN and GaN/AlxGa1-xN/air.published_or_final_versio

Minimum površinske hrapavosti: tanki sloj Ag deponovan na staklu

In this paper the results of an examination of the surface roughness and morphology dependence of silver thin films up to 100 nm thick deposited on a microscope glass on the deposition rate and on the deposition time are presented. It was found that, for a constant deposition rate, the surface roughness exhibits minimum at a certain layer thickness. This coincides with the turning point when the influence of the substrate surface on the deposition process becomes negligible, i.e., to the change in the nature of the system substrate/deposit from Ag/glass to Ag/Ag. For a constant layer thickness, the surface roughness minimum, achieved at a certain deposition rate, coincides to the turning point when the average free path for vertical adatom mobility becomes zero

Effect of the magnetic field on the operation of ionisation gauges

Funding Information: The support of the Portuguese Foundation for Science and Technology via the grants UIDB/00068/2020 and UIDP/00068/2020 is gratefully acknowledged. One of the authors (R. Silva) would like also to express his gratitude to the Portuguese Foundation for Science and Technology for his scholarship UI/BD/150626/2020. Publisher Copyright: © 2022 Elsevier LtdHot cathode ionisation gauges are the only reliable pressure measurement devices suitable for both high and ultra-high vacuum measurement. These devices are characterized by low accuracy that is hardly better than 20%. The sources of loss of accuracy are documented in the literature although their quantification and details are not fully understood. In the present work, simulations of Bayard-Alpert and extractor gauges were performed under the influence of uniform magnetic fields up to 30 Gs. Results are in qualitative agreement with measurements taken previously with the Bayard-Alpert gauge. Both gauges are sensitive to low intensity magnetic fields which may be present in vacuum chambers. However, the extractor gauge proved to be more stable in the presence of a magnetic field due to its ring-shaped cathode.publishersversionpublishe

Experimental and theoretical insights on charge transfer and cluster formation in co-doped N-TiO2

Inroduction Among various applications of TiO2, hydrogen generation from methanol/ethanol solutions or ultimately water, is one of the big interest for renewable energy applications. One of approaches in modifying properties of titania in order to bring this cheap material one step closer to these applications is oxide doping and co-doping as a way of stimulating charge transfer between the metal and oxide surface [1]. We consider charge transfer and optical properties of doped and co-doped TiO2 surfaces, as well as deposition of platinum and palladium at the 001 anatase TiO2 surface, to study influence of nitrogen doping on metal clustering and metal-support interaction.3rd International Meeting MATERIALS SCIENCE FOR ENERGY RELATED APPLICATIONS; September 25-26, 2018; Belgrade, Serbi

Thermal Desorption of 2,4,6-Trichloroanisole from Cork

PT109878B) authored by Orlando Manuel Neves Duarte Teodoro with royalties paid by Amorim Cork S.A. Publisher Copyright: © 2023 by the authors.While extensive efforts have been made over the past two decades to understand how cork becomes contaminated by 2,4,6-trichloroanisole (TCA), the nature of its bond to cork remains unclear. A deeper understanding of this interaction is crucial in designing processes to effectively remove TCA from cork stoppers. This study presents an investigation into the thermal desorption of TCA from cork under vacuum conditions. To facilitate detection by a quadrupole mass spectrometer, samples were artificially contaminated with sufficient TCA. A calibration system was developed to determine the absolute rate of TCA released from the cork. Desorption spectra revealed two peaks at 80 °C and 170 °C. Despite the known variability of cork, repeated measurements demonstrated reasonable repeatability. The low-temperature peak decreased with time and after preheating the sample to 50 °C. It is proposed that the high-temperature peak corresponds to TCA bonded to the cork material. Experiments with naturally contaminated cork stoppers revealed a significant reduction in the amount of releasable TCA following a vacuum-heating process. This study provides an insightful discussion on the adsorption of TCA on cork and proposes an estimate for the adsorption energy. Furthermore, it discloses a process capable of removing TCA from natural cork stoppers.publishersversionpublishe

Changes in the physicochemical properties of geopolymer gels as a function of NaOH concentration

In the present paper, polymerization of alkali activated metakaolin (MK) and its structural changing, using 2M NaOH, 8M NaOH, and 16M NaOH solutions were followed by means of X-ray photoelectron spectroscopy (XPS), Diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), Raman spectroscopy and Scanning electron microscopy (SEM). XPS analysis revealed that changing of NaOH concentration did not affect the types of formed bonds in the material. At the same time, the amount of sodium and aluminum increased with the NaOH molarity. The latter steps could be especially interesting because it may indicate the possibility of 'dosing' the amount of Al incorporated by changing the NaOH concentration in the solution. DRIFT analysis revealed that the absorption band for AlIV located at 800 cm-1 is shifted towards the smaller values. Changing the concentration of NaOH, the chemical content did not change, but the structural changes are observed. Raman spectroscopy detected that the most dominant peaks at ∼400 cm-1 and 519 cm-1 originate from Si-O-Al and Si-O-Si bending modes. With increasing the NaOH concentration, peaks at 1019-1060 cm-1 become more prominent as a result of polymerization. Both analyzes (DRIFT and Raman) confirmed the presence of quartz. SEM analysis showed that different structures are created by changing the concentration of NaOH.У овом раду, праћена је полимеризација алкално активираног метакаолина (МК) и његове структурне промене, коришћењем 2М NaOH, 8М NaOH и 16М раствора NaOH. Промене су праћене рендгенском фотоелектронском спектроскопијом (XPS), дифузном рефлексијом инфрацрвене Фуријеове трансформације (DRIFT), Рамановом спектроскопијом и скенирајућом електронском микроскопијом (SEM). XPS анализа је показала да промена концентрације NaOH није утицала на типове формираних веза у материјалу. Истовремено, количина натријума и алуминијума се повећавала са моларношћу NaOH. Последњи кораци могу бити посебно интересантни јер могу указивати на могућност 'дозирања' количине Al инкорпорираног променом концентрације NaOH у раствору. DRIFT анализа је открила да је опсег апсорпције за AlIV који се налази на 800 cm-1 померен ка мањим вредностима. Променом концентрације NaOH, хемијски садржај се није мењао, али су уочене структурне промене. Раманова спектроскопија је открила да најдоминантнији пикови на 400 cm-1 и 519 cm-1 потичу из Si-О-Al и Si-О-Si начина савијања хемијских веза. Са повећањем концентрације NaOH, пикови на 1019-1060 cm-1 постају све израженији као резултат полимеризације. Обе анализе (DRIFT и Раман) потврдиле су присуство кварца. SEM анализа је показала да се променом концентрације NaOH стварају различите структуре

Detailed characterization of the Ti-O based thin films obtained by cathodic arc evaporation

Physicochemical properties of thin films on the base of titanium oxides, obtained by a cathodic arc evaporation on the surface of glass substrate are analysed in details. The analysis of these films was made by using XRD, FTIR, SEM, XPS analysis and ellipsometry. On the basis of these analyses, particularly analysis obtained by XPS, the oxidative state Ti and corresponding phases are determined through various film layers from the surface to the substrate. The depth of the various levels and their extinction coefficients and refractory indexes are estimated by ellipsometry

XPS and FTIR studies of DC reactive magnetron sputtered TiO2 thin films on natural based-cellulose fibers

FEDER, through Programa Operacional Factores de Competitividade - COMPETE and Fundacao para a Ciencia e a Tecnologia - FCT by the project UID/FIS/00068/2019; FEDER, through POACORES - Valorizacao e Desenvolvimento de Produtos da Conteira (Hedychium gardnerianum) - 01-0247-FEDER-000011; Regional Government of the Azores-Fundo Regional da Ciencia e Tecnologia (Fellowship M3.1.a/F/040/2015).Natural based-cellulosic fibers are trending due to the global awareness regarding environmental health and because their properties make them a great alternative to the synthetic fibers. However, these fibers also have some hindrances that can be solved with their functionalization. The present study concerns modification of the surface of natural based-cellulosic fibers extracted from stems of the ginger lily plant (Hedychium gardnerianum) with TiO2 films deposited by DC magnetron sputtering using a titanium (Ti) target. A detailed characterization of the TiO2-coated fibers was investigated by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results revealed that the sputtered TiO2 films can be attached to the ginger lily fibers mainly by their OH groups. XPS analysis further shows that C-OH group is not dominant, which means that no pure cellulose is present at the surface.publishersversionpublishe

A review on hot cathode ionisation gauges with focus on a suitable design for measurement accuracy and stability

project 16NRM05 'Ion gauge'A literature review starting from 1950 is given on the design and geometry of ionisation gauge types with hot cathodes. Considerations on the material of the electrodes and of surface effects are included. The review focuses on the design issues for measurement accuracy, linearity, repeatability, reproducibility, and stability of sensitivity. Also, the attempts to reduce the lower measurement limit are reviewed to some extent.publishersversionpublishe

Ispitivanje promena na površini nakon dugotrajnog izlaganja vazduhu polazeći od prvih principa-XPS

Within the scope of this paper, a potential impact of noble metal particles on the surface of N-TiO2 and its catalytic properties is observed through correlation with contamination layer thickness. Owing to 'first principle' approach study, without additional experimental measurements or permanent damage to the surface of the samples, it is possible to obtain significant novel information based on a single measurement of the XPS spectra. Presented research demonstrated how the surface contamination layer in the case of samples based on N-TiO2 is related to the nature of two studied noble metals, indicating that Pd might serve as an important co-modifier to suppress surface contamination.Kroz ovaj rad će biti sagledan uticaj čestica plemenitih metala na strukturu površine titanijum dioksida dopiranog azotom i katalitička svojstva kroz uticaj na debljinu sloja nečistoća. U ovakvom pristupu koji polazi od „prvih principa“ je bez dodatnih eksperimentalnih merenja i trajnog oštećenja površine uzoraka moguće dobiti značajne nove informacije korišćenjem rezultata jednom izvedenog merenja rendgenskog fotoelektronskog spektra. Dobijeni rezultati ukazuju na to da promene na površini uzoraka na bazi N-TiO2, do kojih dolazi zbog prisustva Pd, utiču na suzbijanje površinskih organskih nečistoća