Negative Oxygen Research Articles

On the solubility of oxygen and xenon in n-hexane and n-perfluorohexane at room temperature

Experimental measurements have shown that, at room temperature, xenon has a good solubility in both n-hexane and n-perfluorohexane, whereas oxygen is poorly soluble in both liquids. However, oxygen proves to be more soluble in n-perfluorohexane than in n-hexane, in contrast with xenon behavior. This difference is investigated by calculating the reversible work of cavity creation in both liquids and estimating the solute–solvent attractive interactions. The magnitude of the reversible work of cavity creation in n-hexane is larger than in n-perfluorohexane, and also the strength of the solute–solvent dispersion attraction is larger in n-hexane. However, it emerges that the dispersion attractions between oxygen and n-perfluorohexane are stronger than expected due to specific interactions between partially negative fluorine atoms and oxygen molecules.

Imaging spectroscopy of polymer ablation plasmas for laser propulsion applications

A number of polymers have been proposed for use as propellants in space launch and thruster applications based on laser ablation, although few prior studies have either evaluated their performance at background pressures representative of the upper atmosphere or investigated interactions with ambient gases other than air. Here, we use spatially and temporally resolved optical emission spectroscopy to compare three polymers, poly(ethylene), poly(oxymethylene), and glycidyl azide polymer, ablated using a 532 nm, nanosecond pulsed laser under Ar and O2 at pressures below 1 Torr. Emission lines from neutrally and positively charged atoms are observed in each case, along with the recombination radiation at the interaction front between the plasma plume and the background gas. C2 radicals arise either as a direct fragmentation product or by a three-body recombination of C atoms, depending on the structure of the polymer backbone, and exhibit a rotational temperature of ≈5000 K. The Sedov–Taylor point blast model is used to infer the energy release relative to the incident laser energy, which for all polymers is greater in the presence of O2, as to be expected based on their negative oxygen balance. Under Ar, plume confinement is seen to enhance the self-reactivity of the ejecta from poly(oxymethylene) and glycidyl azide polymer, with maximum exothermicity close to 0.5 Torr. However, little advantage of the latter, widely considered one of the most promising energetic polymers, is apparent under the present conditions over the former, a common engineering plastic.

Effects of negative oxygen ions on sleep quality

This paper aims to investigate the effects of negative oxygen ions on sleep quality. An experiment was held using both subjective and physiological methods on 33 subjects (16 females and 17 males). The subjective assessment on sleep quality was surveyed and the duration of every sleep stage was determined. The results of this experiment indicate that the negative oxygen ions have a significant effect on sleep quality. The subjective results indicate that with negative oxygen ions subjects fell asleep easier, meanwhile, the objective results indicate that the duration of sleep onset latency was shortened and the slow-wave sleep was lengthened. All these results show that negative oxygen ions can improve people’s sleep quality.

Formation of amorphous calcium carbonate in caves and its implications for speleothem research.

Speleothem deposits are among the most valuable continental formations in paleoclimate research, as they can be dated using absolute dating methods, and they also provide valuable climate proxies. However, alteration processes such as post-depositional mineralogical transformations can significantly influence the paleoclimatic application of their geochemical data. An innovative sampling and measurement protocol combined with scanning and transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy is presented, demonstrating that carbonate precipitating from drip water in caves at ~10 °C contains amorphous calcium carbonate (ACC) that later transforms to nanocrystalline calcite. Stable oxygen isotope fractionations among calcite, ACC and water were also determined, proving that ACC is 18O-depleted (by >2.4 ± 0.8‰) relative to calcite. This, in turn, has serious consequences for speleothem-based fluid inclusion research as closed system transformation of ACC to calcite may induce a negative oxygen isotope shift in fluid inclusion water, resulting in deterioration of the original compositions. ACC formation increases the speleothems’ sensitivity to alteration as its interaction with external solutions may result in the partial loss of original proxy signals. Mineralogical analysis of freshly precipitating carbonate at the studied speleothem site is suggested in order to determine the potential influence of ACC formation.

Modeling Corneal Oxygen with Scleral Gas Permeable Lens Wear.

The main goal of this current work is to use an updated calculation paradigm, and updated boundary conditions, to provide theoretical guidelines to assist the clinician whose goal is to improve his or her scleral gas permeable (GP) contact lens wearing patients' anterior corneal oxygen supply. Our model uses a variable value of corneal oxygen consumption developed through Monod equations that disallows negative oxygen tensions within the stroma to predict oxygen tension at the anterior corneal surface of scleral GP contact lens wearing eyes, and to describe oxygen tension and flux profiles, for various boundary conditions, through the lens, tears, and cornea. We use several updated tissue and boundary parameters in our model. Tear exchange with GP scleral lenses is considered nonexistent in this model. The majority of current scleral GP contact lenses should produce some levels of corneal hypoxia under open eye conditions. Only lenses producing the thinnest of tear vaults should result in anterior corneal surface oxygen tensions greater than a presumed critical oxygen tension of 100 mmHg. We also find that corneal oxygen tension and flux are each more sensitive to modification in tear vault than to changes in lens oxygen permeability, within the ranges of current clinical manipulation. Our study suggests that clinicians would be prudent to prescribe scleral GP lenses manufactured from higher oxygen permeability materials and especially to fit without excessive corneal clearance.

Quantitative secondary ion mass spectrometric analysis of secondary ion polarity in GaN films implanted with oxygen

Quantitative analyses of N and O ions in GaN thin films implanted with oxygen ions (16O+) were conducted by secondary ion mass spectrometry (SIMS). Positive (CsM+) and negative secondary ions extracted by Cs+ primary ion bombardment were analyzed for oxygen quantitative analysis. The oxygen depth profiles were obtained using two types of primary ion beams: a Gaussian-type beam and a broad spot beam. The oxygen peak concentrations in GaN samples were from 3.2 × 1019 to 7.0 × 1021 atoms/cm3. The depth profiles show equivalent depth resolutions in the two analyses. The intensity of negative oxygen ions was approximately two orders of magnitude higher than that of positive ions. In contrast, the O/N intensity ratio measured using CsM+ molecular ions was close to the calculated atomic density ratio, indicating that the SIMS depth profiling using CsM+ ions is much more effective for the measurements of O and N ions in heavy O-implanted GaN than that using negative ions.

Transparent Conducting Oxide Layer By Thermal Evaporation for Cu(In,Ga)Se2 Solar Cell with Chemical Bath Deposited-ZnS Buffer Layer

Chemical-bath-deposited (CBD) ZnS buffer layer is being steadily studied in Cu(In,Ga)Se2 (CIGS) thin-film solar cell because of their beneficial properties, for examples, good transparency with large direct bandgap, less toxicity and cost effectiveness. CBD-ZnS buffer layer, however, is easily affected during subsequent sputtering process for window layer and the conversion efficiency decreases with sputtering power. The decrease of efficiency in CBD-ZnS/CIGS thin-film solar cells is known to be related to plasma damage originated from high energy negative oxygen ions or neutral particles at the interface. In typical CIGS solar cell, ITO/i-ZnO bilayer deposited by sputtering process has been used as a conventional window layer and then interface properties between window layer and buffer is considered as an important key to determine the cell efficiency. In this paper, to know actual effects of interface property between window layer and buffer on cell performance, we applied the two types of window layer and fabricated CIGS solar cell with CBD-ZnS buffer; (i) typical structure of ITO/i-ZnO/CBD-ZnS/CIGS, and (ii) thermally grown-IZO/i-ZnO/CBD-ZnS/CIGS. To completely exclude plasma damage from sputtering, two types of CIGS solar cell were also fabricated without i-ZnO layer. As a result, the cell performance interestingly shows the opposite tendency depending on presence or absence of i-ZnO layer; cell efficiency with IZO layer is higher than that with ITO layer in the presence of i-ZnO layer, while the former is lower than the latter in the absence of i-ZnO layer. To understand these phenomena, interfacial properties between window and buffer layer are characterized by various analysis tools.

Reconstruction of Holocene paleohydrological and sedimentological characteristics of Umm Ar-Rimam basin (northern Kuwait)

The paleohydrological and sedimentological characteristics of a playa lake in northern Kuwait (Arabian Gulf) are reconstructed using sedimentological, geochemical, and isotopic techniques. The sequence consists of up to 8 cycles of S-poor, alluvial sediments capped by a thin organic soil interbedded with gravity-fall calcrete sediments. The succession is locally derived from mainly Quaternary sediments and is regressive with upsection filling of the subsiding basin by cycles of sheetwash flow in response to climatic change. There is no natural, open-water lake water as indicated by low total organic carbon (TOC) data, but the presence of incised calcrete yardangs suggests that more extensive open-water conditions were operative in the past. Stable isotope (δ18O‰ and δ13C‰) values of the authigenic carbonates indicate the following three distinct processes: evaporation, meteoric fluid infiltration, and rapid per-descensum flow (rapid downward movement of water and playa sediment through pipes) through a porous, clastic sequence. Because evaporites are scarce, other factors besides evaporation action control chemical and isotopic compositions of the per-decensum lake fluids. Consequently, the isotopic composition cannot be interpreted exclusively as an indicator of salinity or evaporation ratio. The degassing of CO2 during groundwater discharge may explain the enriched carbon isotope values for the authigenic carbonates precipitated in the sediments. Hydrologically closed lake water bodies tend to show low negative carbonate oxygen and carbon isotopic signatures. Isotopically negative δ13C values imply a strong input of soil-zone carbon to the groundwater of the top 60 cm of the sediment. Lakes that are hydrologically closed and evaporate or equilibrate with atmospheric CO2 will tend to have low negative δ18O and δ13C values in the carbonates as reported by Talbot (Chem Geol: Isotope Geosci Sect 80(4):261–279, 1990). Biologically active lakes will tend toward lower δ13C of dissolved carbon due to the photosynthetic effects of 12C withdrawal as reported by Dunagan and Driese (J Sed Res 69:772–783, 1999). Increased biological activity during sedimentation may account for low carbon isotope values where plants were abundant, but in shrinkage-dominated systems (those of clay-rich soil subjecting to wet-dry conditions), carbon isotopes will be largely inherited from the calcretic limestones in the land extending landward of the coast and not influenced by coastal processes (known as hinterland), such as Umm Ar-Rimam depression. This basin does not fit the classic shallow playa-type basins of the Arabian Peninsula but rather the recharge playas of the southwestern USA.

Anomalous Positive Ion Formation in Negative Ion Collisions with HOPG

Charge transfer on graphite, a typical substrate and one of the fusion first wall materials, is of great importance in the plasma–wall interaction, thin-film growth, and surface catalysis. We present an experimental study of 8.5–22.5 keV energy carbon, oxygen, and fluorine negative ions scattering from a highly oriented pyrolytic graphite (HOPG) surface at a scattering angle of 8°. It is found that the positive ion fraction decreases monotonically with the increase of both incident velocity and angle. In particular, these dependences are very different from those presented in previous studies. A molecular dynamics simulation reveals that, around the critical condition for planar surface channeling, a number of projectiles may penetrate into the subsurface and become energetic atoms when they emerge from the surface. Hence, an exponential scaling related to the penetration probability has been proposed to well describe the velocity and angle dependences of positive ion fractions.

Characterization of Ar–O2DC Discharge Employing Langmuir Probe in Conjunction With Photodetachment

Negative oxygen ions (O2− + O−) in the bulk of a dc discharge for Ar/O2 gas mixture have been determined employing Langmuir probe-assisted laser photodetachment. Electron density and temperature were obtained for the mixture at discharge powers between 2 and 15 W and pressure between 75 and 375 mtorr. Electron temperature shows very minimum dependence on pressure, while electron number density is increasing with power and decreasing as a function of pressure. Total negative ion number density showed an increasing trend as a function of power, while decreasing as the pressure was increased at a constant discharge power. Equally negative ion density was found to decrease as the O2 percentage in the mixture was increased under the same conditions of discharge pressure and power. The maximum negative ion number density was found to be about 6.5 E14 at 75 mtorr and 5.5 W of power with 25% O2 in the mixture. The electronegativity at 150 mtorr pressure and 5 W of discharge power was found to decrease from 0.21 to a minimum of 0.06 and increase again to 0.11 as the O2 partial pressure was varied from 25% to 100% with the minimum at 75% O2.

Highly negative oxygen isotopes in precipitation in southwest China and their significance in paleoclimatic studies

The moisture carried by the Indian summer monsoon (ISM) is increasingly believed to have an important effect on oxygen isotope in precipitation (δ18Op) in the East Asian summer monsoon (EASM) region. This is mainly based on the spatially coherent variability in the stalagmite oxygen isotopic records (δ18Os) from both the ISM and EASM regions. Based on the comparison of δ18Os records with variable time scales, including the last glacial (36–54 ka BP) and the mid–late Holocene (2–6.5 ka BP), in this paper, we show that the δ18Os values in southwest China were much more negative than in the EASM region of east China, and the behavior of modern δ18Op values is similar. Detailed analyses demonstrated that the highly negative δ18Os and δ18Op values in southwest China could not be explained by any of the altitude, latitude, amount, and temperature effects, and therefore the only interpretation for this phenomenon was might the different moisture sources. The different major moisture sources for southwest and east China were supported by further analyses of the deuterium excess (d-excess) parameter of modern δ18Op and δD values for both the ISM and EASM regions. The results suggested that the moisture sources for the ISM and EASM regions were might essentially different. Our findings could contribute to a better understanding of the paleoclimatic history in the ISM and EASM regions and their possible interactions.

Simulation of nonstationary phenomena in atmospheric-pressure glow discharge

Nonstationary processes in atmospheric-pressure glow discharge manifest themselves in spontaneous transitions from the normal glow discharge into a spark. In the experiments, both so-called completed transitions in which a highly conductive constricted channel arises and incomplete transitions accompanied by the formation of a diffuse channel are observed. A model of the positive column of a discharge in air is elaborated that allows one to interpret specific features of the discharge both in the stationary stage and during its transition into a spark and makes it possible to calculate the characteristic oscillatory current waveforms for completed transitions into a spark and aperiodic ones for incomplete transitions. The calculated parameters of the positive column in the glow discharge mode agree well with experiment. Data on the densities of the most abundant species generated in the discharge (such as atomic oxygen, metastable nitrogen molecules, ozone, nitrogen oxides, and negative oxygen ions) are presented.

Cell type specificity of neurovascular coupling in cerebral cortex

Identification of the cellular players and molecular messengers that communicate neuronal activity to the vasculature driving cerebral hemodynamics is important for (1) the basic understanding of cerebrovascular regulation and (2) interpretation of functional Magnetic Resonance Imaging (fMRI) signals. Using a combination of optogenetic stimulation and 2-photon imaging in mice, we demonstrate that selective activation of cortical excitation and inhibition elicits distinct vascular responses and identify the vasoconstrictive mechanism as Neuropeptide Y (NPY) acting on Y1 receptors. The latter implies that task-related negative Blood Oxygenation Level Dependent (BOLD) fMRI signals in the cerebral cortex under normal physiological conditions may be mainly driven by the NPY-positive inhibitory neurons. Further, the NPY-Y1 pathway may offer a potential therapeutic target in cerebrovascular disease.

Environmental dynamics during the Paleocene–Eocene thermal maximum (PETM) in the northeastern Peri-Tethys revealed by high-resolution micropalaeontological and geochemical studies of a Caucasian key section

The sedimentary record of the Paleocene–Eocene Thermal Maximum (PETM) in the wide epeiric sea of the NE Peri-Tethys contains a sapropelitic bed (SBD) characterized by a specific microfossil assemblage and negative oxygen and carbon isotope excursions (CIE). New results obtained from a high-resolution sampling of this interval in the Kheu section, central Caucasus, allows us to explore the succession, interrelationships and consequences of global and regional palaeoenvironmental events during the PETM. The CIE apparently lasted twice as long as the SBD accumulation period; thus, the SBD represents a response to the early and most dramatic phase of the PETM related to rapid transgression and greatly enhanced eutrophication of the basin. The lithological architecture of the SBD represents four bands, each of which consists of a dark, low-calcareous TOC-rich clay and relatively paler calcareous clays. The highest TOC concentrations are found in the lower and upper bands of the SBD; however, the lower band mostly consists of basinal organic matter, while the upper band represents mixed, basinal and terrestrial, organic matter. Pre-PETM events include the initial evolution of the Rhomboaster nannofossil lineage with the early first appearance of a short-arm species, relatively reduced calcareous plankton productivity, changes in the ratios of dinocyst ecological groups, and minor fluctuations in δ13C and δ18O. The onset of the CIE corresponds to the base of the SBD, which exhibits a dramatic decrease in total nannofossil abundance and an increase in total dinoflagellate abundance, the occurrence of “excursion taxa” of nannofossils (rhomboasters, asymmetric discoasters) and dinocysts (Axiodinium augustum, Epelidinium pechoricum), and significant variations in the species ratios of both nannoplankton and dinoflagellate communities, with widespread dominance of warm-water and eutrophic species. Above the SBD but during the late phase of CIE, the nannofossil abundance and species composition show a slight recovery, but most Paleocene taxa become extinct during the CIE recovery. Apectodinium spp. significantly decrease in abundance above the SBD, but rare specimens of Ax. augustum persist higher in the section after the end of the CIE. Thus, the major extinction of the Paleocene nannofossil taxa occurs after the termination of the most critical conditions during the CIE recovery phase, while the dinocyst “excursion taxa” survive even later.

Post-annealing-free, room temperature processed nanocrystalline indium tin oxide thin films for plastic electronics

In this study, we confirm that bombardment by high energy negative oxygen ions (NOIs) is the key origin of electro-optical property degradations in indium tin oxide (ITO) thin films formed by conventional plasma sputtering processes. To minimize the bombardment effect of NOIs, which are generated on the surface of the ITO targets and accelerated by the cathode sheath potential on the magnetron sputter gun (MSG), we introduce a magnetic field shielded sputtering (MFSS) system composed of a permanent magnetic array between the MSG and the substrate holder to block the arrival of energetic NOIs. The MFSS processed ITO thin films reveal a novel nanocrystal imbedded polymorphous structure, and present not only superior electro-optical characteristics but also higher gas diffusion barrier properties. To the best of our knowledge, no gas diffusion barrier composed of a single inorganic thin film formed by conventional plasma sputtering processes achieves such a low moisture permeability.

Negative Oxygen Ions Production by Superamphiphobic and Antibacterial TiO2/Cu2O Composite Film Anchored on Wooden Substrates.

According to statistics, early in the 20th century, the proportion of positive and negative air ions on the earth is 1 : 1.2. However, after more than one century, the equilibrium state of the proportion had an obvious change, which the proportion of positive and negative air ions became 1.2 : 1, leading to a surrounding of positive air ions in human living environment. Therefore, it is urgent to adopt effective methods to improve the proportion of negative oxygen ions, which are known as “air vitamin”. In this study, negative oxygen ions production by the TiO2/Cu2O-treated wood under UV irradiation was first reported. Anatase TiO2 particles with Cu2O particles were doped on wooden substrates through a two-step method and further modification is employed to create remarkable superamphiphobic surface. The effect of Cu2O particles dopant on the negative oxygen ions production of the TiO2-treated wood was investigated. The results showed that the production of negative oxygen ions was drastically improved by doping with Cu2O particles under UV irradiation. The wood modified with TiO2/Cu2O composite film after hydrophobization is imparted with superamphiphobicity, antibacterial actions against Escherichia coli, and negative oxygen ions production under UV irradiation.

Defect-Free Amorphous Indium Gallium Zinc Oxide Deposition Process By Magnetic Field Shielded Sputtering

The amorphous InGaZnO (a-IGZO) is widely accepted as a promising channel material for thin-film transistor (TFT) applications owing to their outstanding electrical properties [1, 2]. However, a-IGZO TFTs have still suffer from their bias instability with illumination [1-4]. Up to now, many researchers have studied the sub-gap density of states (DOS) as the root cause of instability. It is well known that defect states can influence on the performances and stabilities of a-IGZO TFTs. The defects states should be closely related with the deposition condition, including sputtering power, and pressure. Nevertheless, it has not been reported how these defects are created during conventional RF magnetron sputtering. In general, during conventional RF magnetron sputtering process, negative oxygen ions (NOIs) can be generated by electron attachment in oxygen atom near target surface and then accelerated up to few hundreds eV by a self-bias; at this time, the high energy bombardment of NOIs induce defects in oxide thin films. Recently, we have reported that the properties of IGZO thin films are strongly related with effects of NOIs which are generated during the sputtering process [5]. From our previous results, the electrical characteristics and the chemical bonding states of a-IGZO thin films were depended with the bombardment energy of NOIs. And also, we suggest that the deep sub-gap states in a-IGZO as well as thin film properties would be influenced by the bombardment of high energetic NOIs during the sputtering process.In this study, we have studied the gate bias instability and their density of states (DOSs) of a-IGZO TFTs as depending on the bombardment of NOIs during conventional magnetron sputtering. Finally, we will introduce our novel technology named as Magnetic Field Shielded Sputtering (MFSS) process to prevent the NOIs bombardment effects and present how much to be improved the instability of a-IGZO TFTs by this new deposition method. 1. M.G. Kim, M.G. Kanatzidis, A. Facchetti, and T.J. Marks, Nat. Mater. 10, 382 (2011). 2. K.K. Banger, Y. Yamashita, K. Mori, R.L. Peterson, T. Leedham, J. Rickard, and H. Sirringhaus, Nat. Mater. 10, 45 (2011). 3. M.D.H. Chowdhury, P. Migliorato, and J. Jang, Appl. Phys. Lett. 98, 153511 (2011). 4. X. Xiao, W. Deng, S. Chi, Y. Shao, X. He, L. Wang, and S. Zhang, IEEE Trans. Electron Devices 60, 4159 (2013). 5. D.H. Kim, J.N. Jang, S.B. Yoon, and MunPyo Hong, Appl. Phys. Express 7, 031401 (2014).

A Method to Fabricate Biaxially Textured MgO Buffer Layer for HTS Coated Conductor

In this paper, a radio-frequency magnetron sputtering system without any assisting ion source was employed to fabricate biaxially textured MgO films on the substrates of amorphous Y 2 O 3 /Al 2 O 3 /Hastelloy stacks. During the deposition process, the growing MgO film was bombarded by an off-normal energetic particle flux mainly composed of oxygen atoms and negative oxygen ions, which originated from the target surface. MgO obtained a biaxial texture due to such bombardment; thus, this method is named energetic particle self-assist deposition (EPSAD). The texture of EPSAD-MgO films was evaluated via the X-ray diffraction measurement of the postdeposited homoepitaxial MgO layers. An out-of-plane orientation of MgO(111) and a three-fold symmetric in-plane alignment were observed. The MgO texture was optimal when the EPSAD-MgO thickness was about 10 nm. The formation of biaxial texture during the EPSAD process was verified by a control study, and the influences of targetinclined angle and target-substrate distance were also investigated. Furthermore, the mechanism of the EPSAD-MgO method was compared with those of the inclined substrate deposition and ion beam assisted deposition. This study proposed a new method to fabricate a biaxially textured MgO buffer layer for high temperature superconducting (HTS) coated conductors. More optimization research will be conducted in our future study.

Positive Allosteric Modulator of GABA Lowers BOLD Responses in the Cingulate Cortex.

Knowledge about the neural underpinnings of the negative blood oxygen level dependent (BOLD) responses in functional magnetic resonance imaging (fMRI) is still limited. We hypothesized that pharmacological GABAergic modulation attenuates BOLD responses, and that blood concentrations of a positive allosteric modulator of GABA correlate inversely with BOLD responses in the cingulate cortex. We investigated whether or not pure task-related negative BOLD responses were co-localized with pharmacologically modulated BOLD responses. Twenty healthy adults received either 5 mg diazepam or placebo in a double blind, randomized design. During fMRI the subjects performed a working memory task. Results showed that BOLD responses in the cingulate cortex were inversely correlated with diazepam blood concentrations; that is, the higher the blood diazepam concentration, the lower the BOLD response. This inverse correlation was most pronounced in the pregenual anterior cingulate cortex and the anterior mid-cingulate cortex. For subjects with diazepam plasma concentration > 0.1 mg/L we observed negative BOLD responses with respect to fixation baseline. There was minor overlap between cingulate regions with task-related negative BOLD responses and regions where the BOLD responses were inversely correlated with diazepam concentration. We interpret that the inverse correlation between the BOLD response and diazepam was caused by GABA-related neural inhibition. Thus, this study supports the hypothesis that GABA attenuates BOLD responses in fMRI. The minimal overlap between task-related negative BOLD responses and responses attenuated by diazepam suggests that these responses might be caused by different mechanisms.

The gas metallicity gradient and the star formation activity of disc galaxies

We study oxygen abundance profiles of the gaseous disc components in simulated galaxies in a hierarchical universe. We analyse the disc metallicity gradients in relation to the stellar masses and star formation rates of the simulated galaxies. We find a trend for galaxies with low stellar masses to have steeper metallicity gradients than galaxies with high stellar masses at z ~0. We also detect that the gas-phase metallicity slopes and the specific star formation rate (sSFR) of our simulated disc galaxies are consistent with recently reported observations at z ~0. Simulated galaxies with high stellar masses reproduce the observed relationship at all analysed redshifts and have an increasing contribution of discs with positive metallicity slopes with increasing redshift. Simulated galaxies with low stellar masses a have larger fraction of negative metallicity gradients with increasing redshift. Simulated galaxies with positive or very negative metallicity slopes exhibit disturbed morphologies and/or have a close neighbour. We analyse the evolution of the slope of the oxygen profile and sSFR for a gas-rich galaxy-galaxy encounter, finding that this kind of events could generate either positive and negative gas-phase oxygen profiles depending on their state of evolution. Our results support claims that the determination of reliable metallicity gradients as a function of redshift is a key piece of information to understand galaxy formation and set constrains on the subgrid physics.