Effect Of Oxygen Flow Rate Research Articles

Degradation of MoOx Thin‐Films Properties in Excessive Oxygen Environments and Its Influence on Dopant‐Free Silicon Solar Cells

Transition metal oxides such as molybdenum oxide (MoOx) demonstrate significant potential as efficient hole‐selective passivating contacts in silicon heterojunction solar cells. Achieving efficient hole collection necessitates precise control over the optical and electrical properties of MoOx films. In this study, the effects of oxygen flow rate () on the growth, optical properties, and electrical properties of thermally evaporated MoOx films are investigated. In the Kelvin probe force microscopy results, it is indicated that MoOx thin‐film deposition followed an island‐to‐layer growth model. X‐ray photoelectron spectroscopy shows that MoOx films exhibit stoichiometric composition with fully oxidized Mo6+ ions, without additional oxygen. Notably, the O 1s orbital peak shifts toward higher binding energy with increased , indicating defect introduction. Consequently, the work function of MoOx films decreases from 5.93 to 5.51 eV as increases from 0 to 8 sccm. The maximum optical bandgap of the MoOx films exceeds 3.60 eV. As a proof of concept, 's impact on MoOx as a front buffer layer for dopant‐free silicon solar cells is analyzed. An efficiency of 20.8% was achieved for dopant‐free silicon solar cells after optimized MoOx film deposition, with an open‐circuit voltage of 713.7 mV, short‐circuit current density of 39.1 mA cm−2, and fill factor of 74.6%.

Effect of Oxygen Flow Rate, Post-annealing Temperature, and Different Electrolyte Concentrations on WO3 Thin Films Deposited by DC Magnetron Sputtering For Electrochromic Applications

Effect of Oxygen Flow Rate, Post-annealing Temperature, and Different Electrolyte Concentrations on WO3 Thin Films Deposited by DC Magnetron Sputtering For Electrochromic Applications

Performance evaluation and mathematical model of pipeline diffused aeration for recirculating aquaculture system

High requirement of aerating to increase dissolved oxygen is essential for improving the level of intensive recirculating aquaculture system (RAS). A simple, low-cost and maintainable pipeline diffused aeration (PDA) was proposed and designed for pure oxygen to increase the dissolved oxygen. It mainly consists of a diffused aeration stone, a union tee and an interior plug joint. The aim of this article was to study effects of oxygen flow rate (OFR) or inlet dissolved oxygen (IDO) combined with pipe length (PL) on PDA performance, and to construct a referable mathematical model of outlet dissolved oxygen (ODO) with IDO and gas-liquid contact time (CT) for actual recirculating aquaculture water. Results indicated that the oxygen increment rate and the oxygen utilization rate increased with the increase of PL for tap water, and that increased with the decrease of IDO for actual recirculating aquaculture water. PDA is mainly influenced by PL and thus suitably applied in the treated circulating water back flow to culture ponds, especially for RAS with long pipelines. Under the experimental conditions with OFR of 3 L/min, IDO of 3.92 mg/L, and PL of 10 m, the best oxygen increment rate was 149.02% and the best oxygen utilization rate was 11.60%. The linearly mathematical model of ODO=3.8464+0.6237*IDO+0.2705*CT (R2=0.97) can be referred to develop a controllable PDA system for predicting or regulating the dissolved oxygen of water in culture ponds. In particular, PDA combined with liquid oxygen supply will be further studied to promote its application in RAS.

Effect of oxygen flow on electrical and optical properties of ITO films synthesized by magnetron sputtering method

The tin-doped indium oxide thin films were synthesized by DC magnetron sputtering on the surface of polished silicon samples and glass slides in a mixed argon-oxygen atmosphere. The other deposition parameters: operating pressure, magnetron power and substrate rotation speed were kept constant. Thickness and density of thin films were measured by X-ray Reflectometry. The effects of oxygen flow rate and substrate temperature on the optical and electrical properties were investigated. The electrical properties (resistivity, Hall mobility and charge concentration) of the thin films were measured by the Van der Pauw method using the Hall effect. The minimum value of resistivity 0.52 × 10-3 Ohm·cm, and maximum charge mobility 28 cm2V-1s-1 was achieved at an oxygen proportional gas mixture of 2.6% (0.71 sccm). The transmission spectra of the films were measured in the wavelength range from 300 to 1100 nm. The transmittance of all films exceeds 75% in the visible and near-infrared spectral ranges. It was found that increasing the oxygen flow rate and heating of the substrate up to optimal value 150°C led to an increase in the crystallinity of the films and, consequently, to an increase in the Hall mobility and the transmittance.

Effect of oxygen flow rate on properties of multilayer aluminum-doped indium saving ITO thin films produced by sputtering method

Multilayer aluminum-doped indium saving indium-tin oxide (ITO) thin films with low volume resistivity and high transmittance in the visible spectrum have been designed and fabricated by sputtering method. Double-layered structures consisting of very thin layer of conventional indium tin oxide (In2O3-10 mass % SnO2) and aluminum-doped indium saving indium-tin oxide layer with reduced to 50 mass % In2O3 content are discussed. Multilayer aluminum-doped ITO were deposited on glass substrates preheated at 523 K. Thin films deposited in pure argon demonstrate volume resistivity of 445 µΩcm, mobility of 26 cm2/V·s, carrier concentration of 5.6 × 1020 cm−3 and average transmittance larger than 85% in the visible range. Introducing oxygen to sputtering gas allowed increasing average transmittance of as-deposited multilayer aluminum-doped indium saving ITO thin films over 90% in the visible range. As-deposited multilayer aluminum-doped ITO thin films showed significantly higher transmittance in comparison with undoped ML ITO50/ITO90 and crystallized in In4Sn3O12 structure.

Effects of Oxygen Flow Rate on Metal-to-Insulator Transition Characteristics in NbOx-Based Selectors.

In this work, NbOx-based selector devices were fabricated by sputtering deposition systems. Metal-to-insulator transition characteristics of the device samples were investigated depending on the oxygen flow rate (3.5, 4.5, and 5.5 sccm) and the deposition time. The device stack was scanned by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). The yields, including MIT, nonlinear, and Ohmic, in working devices with different deposition conditions were also evaluated. Moreover, we observed the trend in yield values as a function of selectivity. In addition, the current-voltage (I-V) curves were characterized in terms of DC and pulse endurance. Finally, the switching speed and operating energies were obtained by applying a triangular pulse on the devices, and the recovery time and drift-free characteristics were obtained by the paired pulses.

Effect of Oxygen Flow Rate on PECVD Prepared ZnO Thin Films Physical Properties: Experiments Associated with DFT Calculations

Effect of Oxygen Flow Rate on PECVD Prepared ZnO Thin Films Physical Properties: Experiments Associated with DFT Calculations

Mathematical model for the forced oxygen blowing decarburization process of ultra-low carbon steel during RH treatment

A new mathematical model for the RH forced oxygen blowing decarburization process which takes the influence of post combustion on decarburization into account is established. Decarburization reactions are considered to take place at four reaction sites. The simulated results of carbon and oxygen contents show relatively good agreement with the experimental data under different oxygen flow rates. At the rapid decarburization stage including the O2 blowing process, 66.1% of the total decarburization amount is removed. By using the forced oxygen blowing decarburization process, the decarburization rate in the bulk steel is improved most significantly. Additionally, the effects of oxygen flow rates on carbon, oxygen and total decarburization rate are evaluated in detail. At 1500 m3 · h−1, the oxygen content is adequate to completely remove carbon of molten steel in the vacuum vessel during the O2 blowing. Combining with the analysis of oxygen flow rates on the decarburization rate at each site, 1500 m3 · h−1 is chosen as the critical oxygen flow rate to achieve the best decarburization performance. The influences of other parameters including initial carbon and oxygen contents and oxygen utilization rate on decarburization are also investigated.

Total Subgap Range Density of States-Based Analysis of the Effect of Oxygen Flow Rate on the Bias Stress Instabilities in a-IGZO TFTs

In this study, the oxygen flow rate (OFR) dependence of negative bias illumination stress (NBIS) and positive bias stress (PBS) in amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) devices was investigated. Unlike in previous studies, our study simultaneously considered and analyzed the bias stress-induced degradation mechanisms by charge trapping and defect creation. NBIS and PBS instability were measured according to the OFR splits of bottom-gate (BG) IGZO TFTs and the behavior of full subgap range density of states (DOS) was experimentally tracked with especial emphasis on deep-level oxygen vacancy ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {O}}$ </tex-math></inline-formula> ) peak. It was found that the observed DOS variation was consistent with the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {O}}$ </tex-math></inline-formula> ionization model during NBIS. In addition, the threshold voltage shift by charge trapping ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Delta } {V}_{\text {T,CT}}$ </tex-math></inline-formula> ) and the threshold voltage shift by defect creation, i.e., change of DOS, ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Delta } {V}_{\text {T,DOS}}$ </tex-math></inline-formula> ) were separated and extracted through the subthreshold slope decomposition method. After NBIS, the threshold voltage shift ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Delta } {V}_{\text {T}}$ </tex-math></inline-formula> ) was composed of a component by charge trapping and a component with the ionization of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {O}}$ </tex-math></inline-formula> . After PBS, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Delta } {V}_{\text {T}}$ </tex-math></inline-formula> was dominated by a component arising due to charge trapping. Fitting through the stretched exponential function (SEF) was performed for each separately extracted <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Delta } {V}_{\text {T}}$ </tex-math></inline-formula> , and the activation energy for each <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Delta } {V}_{\text {T}}$ </tex-math></inline-formula> was extracted using the inverse Laplace transform method through the extracted <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Delta } {V}_{\text {T0}}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\tau $ </tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> . Activation energy by charge trapping and DOS was extracted from NBIS and PBS, respectively. As a result of simultaneously considering the two degradation mechanisms, the extracted activation energy was located between the previous values. Experimentally extracted sets of DOS-specific parameters before and after bias stress were applied to technology computer-aided design (TCAD) simulations. Accurate reproduction of TFT current–voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> ) curves before and after bias stress and recovery suggests that the methodology and parameter set used in this study are reasonable and potentially useful for a more robust and systematic analysis of the bias stress-induced instability in a-IGZO BG TFTs.

Effect of Oxygen Flow Rate on Properties of Aluminum-Doped Indium-Saving Indium Tin Oxide (ITO) Thin Films Sputtered on Preheated Glass Substrates

Amorphous aluminum-doped indium tin oxide (ITO) thin films with a reduced indium oxide content of 50 mass% were manufactured by co-sputtering of ITO and Al2O3 targets in a mixed argon–oxygen atmosphere onto glass substrates preheated at 523 K. The oxygen gas flow rate and heat treatment temperature effects on the electrical, optical and structural properties of the films were studied. Thin films were characterized by means of a four-point probe, ultraviolet–visible-infrared (UV–Vis-IR) spectroscopy and X-ray diffraction. Transmittance of films and crystallization temperature increased as a result of doping of the ITO thin films by aluminum. The increase in oxygen flow rate led to an increase in transmittance and hindering of the crystallization of the aluminum-doped indium saving ITO thin films. It has been found that the film sputtered under optimal conditions showed a volume resistivity of 713 µΩ cm, mobility of 30.8 cm2/V·s, carrier concentration of 2.9 × 1020 cm−3 and transmittance of over 90% in the visible range.

A Study on the Effect of Oxygen Flow Rate on Optical Properties of RF Sputtered a-GaOx Thin Films on Corning Glass Substrate

Transparent amorphous thin films of ultra-wide band gap (Eg ≈ 4.5–5.3 eV) gallium oxide (a-GaOx) were deposited on Corning glass substrates by radio frequency (RF) magnetron reactive sputtering under different oxygen flow rates. Amorphous nature of the deposited films was confirmed using X-ray diffraction method. Surface properties of the films were obtained from field emission scanning electron and atomic force microscopic images. Compositional and surface chemistry analyses were done using energy-dispersive X-ray and X-ray photoelectron spectroscopic techniques respectively. Optical characteristics of the films deposited under varying oxygen flow rates were investigated. UV-visible transmittance spectra showed excellent transparency in the visible region for all the films. Optical band gap values were found to increase with the increase of oxygen flow rates. Thickness of the films and refractive index dispersion relation were studied using spectroscopic ellipsometry by utilizing a Cauchy dispersion model. Refractive index dispersion parameters were obtained using Wemple-DiDomenico model. The results indicate that the presence of oxygen in the sputtering environment significantly alter the deposition rate and thereby optical properties of the films.

Effect of Oxygen Flow Rate on Combustion Time and Temperature of Underground Coal Gasification

Underground Coal Gasification (UCG) is a process of converting coal in the ground into synthetic gas that has economic value. In the UCG process which will be carried out in the UCG prototype assisted by the presence of oxygen as a gasification agent, which this gasification agent will help the process of burning coal in the ground. The flow rate of oxygen in the process of UCG affecting the coal combustion temperature and effective flame from burning coal. The highest temperature at a flow rate of 5 l/min is 240oC, at an oxygen flow rate of 3 l/min the highest temperature is 143oC and at an oxygen flow rate of 2 l/min the highest temperature is 135oC and time effective flame at a flow rate of 5 l / min ie 80 minutes, effective burning time on the speed of the flow rate of 3 l / min ie for 120 minutes and time effective flame at a flow rate of 2 l / min ie for 165 minutes. This study proves that the greater the oxygen flow rate is used as the gasification agent at UCG process the lignite coal combustion temperatures will be high and effective flame coal combustion process will be more brief.

High-performance Ti and W co-doped indium oxide films for silicon heterojunction solar cells prepared by reactive plasma deposition

Titanium and tungsten co-doped indium oxide (IWTO) films are deposited via low-damage reactive plasma deposition technique at room temperature (RT) and heating temperature (HT). The effects of oxygen flow rates (FO2) on the structural, optical and electrical properties of the IWTO films are investigated after air annealing. X-ray diffraction and scanning electron microscopy results show that the IWTO films are polycrystalline structure exhibiting a preferred (222) crystal plane orientation. As FO2 increases from 10 sccm to 80 sccm, carrier concentration decreases by an order of magnitude for both RT and HT condition, while carrier mobility first increases and then decreases. It is noteworthy that films fabricated at HT show highest mobility (92.1 cm2 V−1 s−1) and lowest resistivity (2.13 × 10−4 Ω cm) due to better crystallinity and hence decreased grain boundary scattering. In addition, the average transmittance of the IWTO films exceeds 89.5% in the wavelength range of 400–1200 nm. Finally, silicon heterojunction solar cells with a high efficiency of 23.8% (with open-circuit voltage (Voc) of 0.746 V, short-circuit current density (Jsc) of 38.7 mA cm−2 and fill factor (FF) of 82.9%) is achieved with the application of the high-performance IWTO film.

Growth of InGaN-based blue-LED on AlN/sapphire sputtered with different oxygen flow rate.

Indium gallium nitride (InGaN) based blue light-emitting diodes (LEDs) suffer from insufficient crystal quality and serious efficiency droop in large forward current. In this paper, the InGaN-based blue LEDs are grown on sputtered aluminum nitride (AlN) films to improve the device light power and weaken the efficiency droop. The effects of oxygen flow rate on the sputtering of AlN films on sapphire and device performance of blue LEDs are studied in detail. The mechanism of external quantum efficiency improvement is related to the change of V-pits density in multiple quantum wells. The external quantum efficiency of 66% and 3-V operating voltage are measured at a 40-mA forward current of with the optimal oxygen flow rate of 4 SCCM.

Impact of oxygen flow rate on performance of indium-tin-oxide-based RRAMs

This paper investigates the effect of oxygen flow rates on the performance of the resistive random access memory (RRAM) of indium-tin-oxide (ITO)/ITO(O2)/TiN configuration. By using a co-sputtering deposition system with oxygen gas at different flow rates, oxygen-rich ITO thin films, such as the RRAM switching layer, can be realized. The relationship between oxygen flow rates and electrical characteristics is provided in this research. Further, the material analyses indicate that the oxygen exhibits different bonding characteristics. As a result, the device with the lower oxygen flow rate has better electrical characteristics and reliability. In addition, to explain the experimental results, the Schottky emission conduction mechanism for the high-resistance state and the Ohmic conduction mechanism for the low-resistance state are determined through the current fitting results, and appropriate models are proposed.

Effect of Oxygen Flow Rate on the Characteristics of RF Sputtered ZnO Thin Films

Zinc Oxide (ZnO) thin films were deposited on glass substrate by radio frequency (RF)reactive magnetron sputtering technique at variable Oxygen flow rates while Argon flow rates waskept constant. The effect of oxygen flow rate on structural, electrical, optical properties of nanostructured ZnO thin films were investigated by X-ray diffractometer, scanning eletron microscopy(SEM), Hall effect measurements and UV-Visible spectrophotometer. X-ray diffraction (XRD) datareveals films are polycrystalline hexagonal structure with (002) peak as a preferred orientation andcrystallite size was found to be in range12 nm-16 nm.The electrical resistivity of films decreasesfrom 10-1 Ω-cm to 10-2 Ω-cm. All deposited ZnO thin films shows high transmittance above 95% inthe visible range 360 nm-800 nm. The optical band gap and refractive indices have been calculatedusing UV-Vis transmission spectra. Oxygen gas flow rates found to have large impact onoptoelectronic properties of ZnO films.

Kinetic Study of Manganese Precipitation of Nickel Laterite Leach Based-solution by Ozone Oxidation

ABSTRACT The increase in nickel and cobalt consumption encourages the exploration of different resources. Limonite ore exploration is carried out through the hydrometallurgical route. After nickel and cobalt separation, the remaining solution contains manganese to be recovered. The present study aimed at the kinetic modeling of manganese precipitation by ozonation. The experiments were carried out in a 250 mL reactor containing an 8-metals sulfated synthetic solution fed by an ozone-oxygen mixture with a bubble diffusor at 21.6–26.0 mg.L−1.min−1 to a total of 2186 mg.L−1 over 90 min. The effects of oxygen flow rate (0.8–10 L.L−1.min−1) and pH (0.5–1.5) varying the ozone dosages and time were studied. Kinetic modeling was performed using linear, Higbie, and pseudo-homogeneous orders. Results showed that the best oxygen flow rate for MnO2 was 2.0 L.L−1.min−1 achieving 97% of efficiency after dosing 24.3 mg.L−1.min−1 O3 or 2186 mg.L−1 (ozone applied) for 90 min at pH 1.5 with a power consumption of 80 W.L−1. The reaction was more selective at pH 0.5 in which the highest manganese precipitation of 55.4% and lower amount of contaminants in the solid phase were obtained. The kinetic model study has demonstrated that manganese precipitation using ozone fitted better on the pseudo-homogeneous model, suggesting that the process is controlled by mass transfer, where the calculated constant rates were 0.035, 0.033, and 0.042 min−1 for the experiments carried out at pH 0.5, 1.0 and 1.5, respectively.

Effect of Oxygen Flow Rate in Zinc Oxide Radio Frequency Magnetron Sputtering on the Structural and Optical Properties of ZnO|PEDOT:PSS Inorganic|Organic Hetero-Junction

Effect of Oxygen Flow Rate in Zinc Oxide Radio Frequency Magnetron Sputtering on the Structural and Optical Properties of ZnO|PEDOT:PSS Inorganic|Organic Hetero-Junction

The effect of oxygen flow rate on metal–insulator transition (MIT) characteristics of vanadium dioxide (VO2) thin films by pulsed laser deposition (PLD)

Vanadium dioxide (VO2), because of its unique metal–insulator phase transion around room temperature, has enormous potential for applications in thermochromic, electrochromic, microbolometery, and non-volatile switches. However, obtaining phase-pure VO2 has been challenging due to its narrow window of thermodynamic stability. Pulsed laser deposition (PLD) is considered to be one of the most promising technique to deposit phase-pure VO2 thin films. While optimizing PLD processing parameters, (such as oxygen pressure (PO2), substrate temperature (Ts), laser energy (EL), target-substrate distance (dT-S), and laser repetition rate (RR)) is crucial, and their effects have been reported, the effect of gas flow rate (QO2) has been largely neglected. Since the QO2 and PO2 of the PLD system are intertwined at the outset, most reports are focused only on either QO2 or PO2. We report on the effect of gas flow rate under constant PO2, on the quality of the VO2 thin films. Controlling flow rate affected the resistivity contrast between the metallic and insulator phases, the temperature ranges of the transition, and the width of hysteresis. We anticipate that this study will help set the standard for obtaining high quality VO2 thin films.

Effect of oxygen flow rate on physical properties of Al-doped ZnO transparent conducting films prepared by reactive dc magnetron sputtering using metallic Zn:Al target

In this work, Al-doped ZnO transparent conducting thin films were prepared by a reactive dc magnetron sputtering method on slide glass substrate using single metallic Zn:Al (2 wt.% Al) target with the oxygen flow rate 1, 3, 5, 7 and 9 sccm, respectively. From XRD patterns, the films prepared at R(O2) of 1 sccm showed amorphous characteristics. In contrast, the films prepared at R(O2) of 3, 5, 7 and 9 sccm showed the preferred orientation (002) plane of hexagonal structure. Surface morphology and diameter of nanocolumns of the films were observed by AFM and FESEM. From transmittance spectra, energy gap value was found to vary between 3.24 and 3.32 eV. Electrical resistivity and Hall effect measurements were performed on the films with van der Pauw configuration. The temperature-dependent conductivity was performed in the range 20-300 K. Three types of conduction mechanisms were expected. Thermally activated band conduction at the high temperature range (250-300 K), Mott variable-range hopping (Mott-VRH) at the low temperature range (100-210 K) and Efros-Shklovskii variable-range hopping (ES-VRH) at the very low temperature range (<100 K) can be found in the films prepared with different oxygen flow rate conditions. Except for the oxygen flow rate at 5 sccm, the behavior of weakly localized electrons was observed. Then, the sets of parameters explaining the properties of localized electrons in each conduction regime were determined. The results indicated that the reactive dc magnetron sputtering using a single metallic Zn:Al (2 wt.% Al) target is suitable for TCO films since it can be easily obtained at low temperatures with good physical properties.