Influence of aluminium annealing on the galvanoluminescent properties of anodic oxide films

Rezultati spektralnih istraživanja predstavljeni u ovom radu prikazuju dva različita uzroka postojanja galvanoluminescencije: karboksilne jone koji su inkorporirani u oksidni film za vreme anodizacije i molekule AlH, AlO, Al2, AlH2 takođe formiranih tokom anodizacionog procesa i već prepoznatih u slučaju neorganskih elektrolita. Anodizacijom uzoraka u organskim elektrolitima, odgrejanih na temperaturama T ≥ 525 oC, GL spektar se takođe menja, dobija identičan oblik kao i onaj u neorganskim elektrolitima i za red veličine je veći od onih odgrejanih na T < 500 oC. Ova promena inteziteta GL je posledica, kao i u neorganskim elektrolitima, prisustva većeg broja i veličine zrnaca γ-alumine i ovaj mehanizam je dominantan u doprinosu inteziteta GL spektra. Analiza GL spektra dobijenog usled prisustva većeg broja zrnaca γ-alumine na površini uzorka, pokazuje da je on posledica elektronsko-vibracionih prelaza molekula: Al2, AlH, AlO, AlH2. Znajući da su Al2, AlO, AlH i AlH2 veoma nestabilni radikali u okruženju kakvo je u oksidnom sloju pri procesu anodizacije, predpostavljamo da nanopore predstavljaju mesta za njihovu egzistenciju i ekscitaciju sa elektronskom lavinom, nastale usled jakog električnog polja. U elektrolitima u kojima se stvaraju porozni oksidni slojevi, zrnca γ-alumine su izložena elektronskoj lavini sve dok su ta zrnca u barijernom delu oksidnog sloja. Dalji rast oksidnog sloja i stvaranje pora koje se dešava na granici metal-oksid dovodi do toga da termički stvorena zrnca γ-alumine prelaze u zidove pora što za posledicu ima gašenje GL. Zatim, prezentovan je galvanoluminescentni spektar dobijen u ultraljubičastoj oblasti za vreme anodizacije visokočistih aluminijumskih uzoraka odgrevanih na temperaturi iznad 525 oC. Naime, u dosadašnjim istraživanjima GL kao fenomena koji prati anodizaciju ventilnih metala, nisu primećeni efekti vezani za doprinos GL u UV oblasti za neodgrejane ili odgrevane uzorke ispod 500 oC, nego su dobijani signali reda šuma. Ranije je rečeno da temperaturski predtretman odgrevanja na temperaturi T ≥ 525 oC uzrokuje nagli porast broja i veličine kristalnih zrnaca γ-alumine, a to upravo dovodi do pojave GL i u UV oblasti optičkog spektra. Snimljeni GL spektar u UV oblasti je kontinualan sa jasno izraženom trakom u intervalu talasnih brojeva (32 100 - 34 800) cm-1 sa maksimumom na 313 nm (31 949 cm-1). Došlo se do zaključka da jasno izraženi maksimum na 313 nm pripada molekulu AlO i odgovara prelazu C2Π→X2Ʃ+ . Prilikom analize dobijenih spektara uzeta je u obzir i mogućnosti postojanja bliske trake koje odgovaraju prelazu A2Ʃ+→X2Π sistema OH, čije prisutvo ne može biti isključeno pri ovakvim eksperimentalnim uslovima. Najistaknutija traka (0-0) ovog elektronskog prelaza leži na oko 32 640 cm-1. Naime, osnovni vibracioni nivoi u X2Ʃ+ i C2Π stanjima za AlO su na 979 cm-1 i 856.5 cm-1 a dužine ravnotežne veze su 1.618 Å i 1.685 Å. Koristeći ove rezultate i, opet, harmonijsku aproksimaciju, dobijamo Franck-Condon-ove faktore za nisko postavljene vibracione prelaze u X2Ʃ+ i C2Π stanjima. U ovom slučaju je promena dužine veze značajnija nego u prvom slučaju za prelaz A2Ʃ+ →X2Π u molekulu OH. Posledica je da za Δ ν = ± 1, a za veće vrednosti ν čak Δ ν = ± 2 prelazi imaju intezitete koji se mogu porediti. Zbog ovoga je moguće očekivati kompleksniji spektar sa slabim lokalnim pikovima. Iz tog razloga smo pažnju usmerili na spektralni sistem AlO i prelaze X2Ʃ+ i C2Π . Da bi objasnili strukturu snimljenog pika, simulirali smo spektar koji se očekuje kao posledica elektronskog prelaza C2Π→X2Ʃ+ u molekulu AlO. Na osnovu brojeva iz tablica i termskih vrednosti, izračunali smo termske vrednosti za elektronsko stanje C2Π koje odgovara uočenim maksimumima traka. Može da se primeti da se rezultati simuliranog spektra slažu u svim pojedinačnim slučajevima sa odgovarajućim eksperimentalnim podacima (do na nekoliko cm-1). To je od veoma velike važnosti za unutrašnju konzistentnost i pouzdanu interpretaciju publikovanih eksperimentalnih rezultata. Samo u jednom slučaju, za granu R2 9-11, neslaganje je veliko i iznosi 23 cm- 1. Moguće je da razlog ovom neslaganju moguće je da leži u predisocijativnom ponašanju stanja C2Π. U ovom radu je takođe po prvi put: 1. Konstruisan i upotrebljen optičko-detekcioni sistem sa CCD kamerom kao detektorom za snimanje dinamike GL procesa u ultraljubičastoj oblasti spektra. 2. Urađena je kalibracja istog tog sistema, tj. određena kvantna efikasnosti celog sistema i zavisnost kolone piksela po talasnim dužinama za date položaje difrakcione rešetke.The results of spectral studies presented in this dissertation show two different causes for the existance of galvanoluminescence (GL) existence: carboxyl ions, which are incorporated in the oxide film during anodization and AlH, AlO, Al2 and AlH2 molecules which are also formed during the process of anodization and are already identified in the case of inorganic electrolytes. Anodization of the samples in organic electrolytes, annealed at temperatures T ≥ 525 °C, results in a change of GL intesity , given the identical form receives an identical shape as the inorganic electrolytes and an order of magnitude higher than those heated at T < 500 °C. This change intensity of GL is related toincreased number and size of grains of γ-alumina and this mechanism is the dominant contribution to the intensity of GL spectrum. This is confirmed in the case of inorganic electrolyte. Analysis of the GL spectrum obtained from the presence of a large number of grains of γ-alumina on the surface of the sample, shows that the spectrum is a consequence of electronic-vibrational transitions of molecules: Al2, AlH, AlO and AlH2. Knowing that the Al2, AlO, AlH and AlH2 are very unstable radicals in the oxide layer enviroment during the anodization process, we assume that the nanopores are places of their existence and excitation by the electron avalanche, caused by the strong electric field. In the electrolytes in which a porous oxide layers are formed, γ-alumina particles are exposed to electronic avalanche until the grains are part of the barrier oxide layer. Further growth of the oxide layer and pore creation on the metal-oxide interference causes the γ-alumina particles to transfer into the walls of the pores resulting in GL quenching. Subsequently, the GL spectrum obtained in the ultraviolet region during the anodization of high purity aluminum samples, annealed at temperatures above 525 °C is presented. It is important to mention that previous research results of the GL as a phenomenon that accompanies the anodization of valve metals showed no presence of GL in the UV region for either annealed or non-annealed samples. Thermal pretreatment by annealing at temperatures T ≥ 525 °C causes a sharp increase in the number and size of crystal grains of γ-alumina and it leads to GL in the UV range of the optical spectrum. Observed GL spectrum in the UV region is continuous with a well defined band in the range of wave numbers (32,100-34,800) cm-1 with a maximum at 313 nm (31,949 cm-1). It was concluded that clearly defined maximum at 313 nm belongs to the molecule AlO and it corresponds to C2Π→X2Ʃ+ transition. When the obtained spectrum was analyzed the possibility of close bands corresponding to transition A2Ʃ+→X2Π of system OH was taken into account.The presence of this transition can not be excluded under prepared experimental conditions. The most prominent band (0-0) of this electronic transitions lies at about 32,640 cm-1. The basic vibrational levels in X2Ʃ+ and C2Π states for AlO are at 979 cm-1 and 856.5 cm-1 and the equilibrium bond lengths are 1618 Å and 1685 Å. Using these results and the harmonic approximation, we obtain the Franck-Condon factors for the low vibrational transition placed in X2Ʃ+ and C2Π states. In this case the change in bond length is more important than in the first case of the transition A2Ʃ+ →X2Π in the OH molecule. The result is that for the Δ ν = ± 1 (or even higher) transitions have intensities that can be comparable. This makes it possible to expect a more complex spectrum with weak local peaks. For this reason, we focused our attention on the AlO spectral system and its X2Ʃ+ and C2Π transitions . To explain the structure of the observed peak, we simulated a spectrum that can be expected as a result of electronic transitions C2Π → X2Ʃ+ in the AlO molecule. Based on tabular and term values, we calculated values for term C2Π electronic state corresponding to the observed maximal bands. The results of the simulated spectrum agree in all individual cases with the corresponding experimental data (up to several cm- 1). This is of great importance for the internal consistency and a reliable interpretation of published experimental results. Only in the case of R2 9-11 branch, the disagreement is larger than stated and it is 23 cm-1.The reason for this discrepancy may be in predissociative behavior of the C2Π state. Other important results reported for the first time in this dissertation are: 1. Design, construction, and experimental validation of the new optical-detection system with CCD camera as a detector for capturing the dynamics of the GL process in the ultraviolet spectral range. 2. The calibration of the optical-detection system was performed, i.e. quantum efficiency of the whole system was determined, as well as the dependence of the column of pixels per wavelength for given positions of diffraction gratings

Supramolecular insight into the substitution of sulfur by selenium, based on crystal structures, quantum-chemical calculations and biosystem recognition

Statistical analysis of data from crystal structures extracted from the Cambridge Structural Database (CSD) has shown that S and Se atoms display a similar tendency towards specific types of interaction if they are part of a fragment that corresponds to the side chains of cysteine (Cys), methionine (Met) selenocysteine (Sec) and selenomethionine (Mse). The most numerous are structures with C-H..Se and C-H..S interactions (∼80%), notably less numerous are structures with Se..Se and S..S interactions (∼5%), and Se..π and S..π interactions are the least numerous. The results of quantum-chemical calculations have indicated that C-H..Se (∼-0.8 kcal mol-1) and C-H..S interactions are weaker than the most stable parallel interaction (∼-3.3 kcal mol-1) and electrostatic interactions of σ/π type (∼-2.6 kcal mol-1). Their significant presence can be explained by the abundance of CH groups compared with the numbers of Se and S atoms in the crystal structures, and also by the influence of substituents bonded to the Se or S atom that further reduce their possibilities for interacting with species from the environment. This can also offer an explanation as to why O-H..Se (∼-4.4 kcal mol-1) and N-H..Se interactions (∼-2.2 kcal mol-1) are less numerous. Docking studies revealed that S and Se rarely participate in interactions with the amino acid residues of target enzymes, mostly because those residues preferentially interact with the substituents bonded to Se and S. The differences between Se and S ligands in the number and positions of their binding sites are more pronounced if the substituents are polar and if there are more Se/S atoms in the ligand. © 2020 International Union of Crystallography

A multidisciplinary study on magnesium

During plasma electrolytic oxidation of a magnesium alloy (96% Mg, 3% Al, 1% Zn) we obtained a luminescence spectrum in the wave number range between 19 950 and 20 400 cm-1. The broad peak with clearly pronounced structure was assigned to the v’-v” = 0 sequence of the B 1Σ+ → X 1Σ+ electronic transition of MgO. Quantum-mechanical perturbative approach was applied to extract the form of the potential energy curves for the electronic states involved in the observed spectrum, from the positions of spectral bands. These potential curves, combined with the results of quantum-chemical calculations of the electric transition moment, were employed in subsequent variational calculations to obtain the Franck-Condon factors and transition moments for the vibrational transitions observed. Comparing the results of these calculations with the measured intensity distribution within the spectrum we derived relative population of the upper electronic state vibration levels. This enabled us to estimate the plasma temperature. Additionally, the temperature was determined by analysis of the recorded A 2Σ+ (v’ = 0) - X 2П (v” = 0) emission spectrum of OH. The composition of plasma containing magnesium, oxygen, and hydrogen under assumption of local thermal equilibrium was calculated in the temperature range up to 12 000 K and for pressures of 105, 106, 107, and 108 Pa, in order to explain the appearance of the observed spectral features and to contribute to elucidation of processes taking place during the electrolytic oxidation of Mg. [Projekat Ministarstva nauke Republike Srbije, br. 172040

Substitution of S by Se. Supramolecular Insight.

The study includes the crystallographic analysis of interactions of S and Se from Cys, Met, Sec and Mse side chains, based on crystal structures from the Cambridge Structural Database (CSD), and quantum-chemical insight in the strength of their individual interactions. CSD statistical analyses have shown a similar tendency of sulfur and selenium atoms towards the specified types of interactions. The most numerous are C−H···Se (for Se fragments) and C−H···S (for S fragments) interactions (~80%), while the second group in numerosity are structures with Se···Se and S···S interactions (~5%). The results of quantum-chemical calculations have revealed that C−H···S and C−H···Se interactions (about −0.8 kcal/mol) are weaker than the most stable parallel Se/Se interaction (about −3.3 kcal/mol) and electrostatic Se/Se interaction of σ/π type (around −2.6 kcal/mol). The numerosity of C−H···S and C−H···Se interactions was explained by an abundance of CH groups compared to the numbers of Se and S atoms in the analyzed crystal structures. The substituents bonded to Se or S atom sterically reduce the possibilities of Se and S atoms to interact with species from the environment. The numerosity of crystal structures explains the lower values of O−H···Se (around −4.4 kcal/mol) and N−H…Se interactions (around −2.2 kcal/mol)

Испитивање утицаја геометријских параметара на интеракције између атома флуора и атома кисеоника (F∙∙∙O)

As a continuation of our investigation into fluorine interactions [1], initially focusing on F-F interactions, crystalographic analysis, and quantum mechanical calculations were employed to systematically investigate the nature and strength of fluorine-oxygen (F···O) interactions using a model system.У наставку истраживања интеракција атома флуора, а са циљем да се испита природа и јачина F···O интеракција, урађени су кристалографска студија и квантномеханички прорачуни на моделу

Fluorination of aromatic groups. The effects of coordination on fluorine interactions

Statistical analysis of crystal structures obtained from Cambridge Structural Database (CSD) showed that the most numerous are structures in which carbon atom is bound to interacting fluorine atom.Statistička analiza kristalnih struktura iz Kembričke baze strukturnih podataka pokazuje da su najbrojnije one strukture kod kojih je ugljenikov atom vezan za interagujući atom fluora. One u kojima je fluor vezan za aromatičnu grupu su malo manje zastupljene

Испитивање F…F интеракција у кристалним структурама: Увид у геометријско уређење

Analysis of crystal structures from the Cambridge Structural Database reveals a significant prevalence of F∙∙∙F contacts, with 136431 contacts involving alkyl groups (C(sp3)–F∙∙∙F–C(sp3) interactions) and 111336 contacts involving unsaturated carbon atoms (C(sp2)–F∙∙∙F–C(sp2) interactions).Анализом кристалних структура из Кембричке струклтурне базе података уочен је велики број F∙∙∙F контаката, од којих се 136431 контакт успоставља између алкилних група (интеракције C(sp3)–F∙∙∙F–C(sp3), док је 111336 контаката између група са незасићеним C-атомима (интеракције C(sp2)–F∙∙∙F–C(sp2))

Natural radionuclides in bottled mineral water at the Serbian market

Natural radionuclides are present in mineral water as a result of geochemical processes that influence its final composition. The quality of mineral water varies and, apart from the natural disasters such as droughts and floods, it is also affected by industrial activities. The aim of our investigation is to determine the activity concentrations of 40K, 238U, 226Ra and 232Th in mineral waters available at the Serbian market. Nine samples of carbonated mineral water and five samples of non-carbonated natural spring water, collected during 2016, are analyses by standard gamma spectrometry. The maximum 40K specific activity measured in the samples is 3.6 Bq/l, while the 238U, 226Ra and 232Th specific activities are below minimal detectable activity. These results show that according to the national regulations, all samples are radiologically safe for human consumption

Innovative optical method for sensing the nutritional stress in hydroponically cultivated plants

Well-balanced nutrition is important for the successful cultivation of healthy plants. In this paper, we demonstrate a nondestructive optical method that can sense a deficiency of certain nutrients. The setup was tested on hydroponically grown Ocimum basilicum. The plants were subjected to nutrient deficiency by the exclusion of one of the essential elements (Fe, Mg, P, N) from the hydroponic solution. A control group of plants, fed by the balanced hydroponic solution, was also grown under the same conditions. The proposed method tracks and records the optical transmittance of the plants' leaves. All groups exhibit clearly defined day-night Circadian rhythms. When compared to the control group, the treated plants exhibited modified circadian rhythms of the optical transmission, suggesting an early indicator of the plants' stress. The condition of the plants under test was also assessed by the more common (destructive) methods such as: measurements of the determination of the photosynthetic pigment content, dray weight determination and the efficiency of PSII. Several biological parameters were observed, calculated and compared to the graphs of optical transmission dependence in real time. Presented results have demonstrated a significant potential of the proposed optical method for the early detection of plants' stress in hydroponic cultivation