Increasing O2 Partial Pressure Research Articles

Chlorine Fixing Ability of Electric Arc Furnace Dust During the Thermal Degradation of Polyvinyl Chloride under Oxidative Conditions

Electric arc furnace dust (EAFD) and polyvinyl chloride (PVC) are two hazardous wastes that are accumulated world-wide at an alarming rate. Utilising these two wastes simultaneously towards a sustainable recycling loop can greatly mitigate their environmental impact. Herein, EAFD was studied as a potential emission fixator of evolved gaseous HCl generated from the thermal decomposition of PVC under different operational conditions: EAFD-PVC mass ratio, solid reactants geometry, O2 partial pressure, holding temperature, holding time and heating rate. The highest chlorine fixation percentage was calculated to be 78.9% and was obtained at an EAFD-PVC mass ratio of 1:1 (thin disks geometry), while the rest escaped in the form of HCl/Cl2. No significant variation was observed on the percentage of fixed chlorine when the thermal treatment was performed using different geometries: long cylinder, thin disks, and powder forms with a maximum difference in fixation of only 5.6% between extremities. Increasing O2 partial pressure positively affected the chlorine fixation percentage increasing it from 39.9 to 48.4% at 0 and 21 kPa partial pressures, respectively. Increasing both the holding temperature and holding time under oxidative conditions negatively affected the percentage of fixed chlorine due to oxidation of formed FeCl2 back to Fe2O3. The heating rate did not show any significant effect on the amount of fixed HCl, suggesting that the speed of chlorination reactions can be identical to or faster than the decomposition rate of PVC. Overall, EAFD is believed to be an excellent candidate for capturing HCl contained in PVC upon thermal degradation.

Low-temperature PECVD silicon-nitride passivation for perovskite solar cell

Low temperature PECVD Si-nitride was investigated as passivation layer for Ag electrode of perovskite solar cell, which is highly sensitive to H2O. FTIR analysis verified that, with H2O in aging ambient, hydrolysis and oxidation reaction occurred on Si-nitride films, which weakened and cracked Si-nitride film. Adding O2 in aging ambients, surface Si–N bonds could be passivated by adsorbed O and hydrolysis reaction of Si-nitride could be reduced. It is confirmed by FTIR spectrum of aged Si-nitirde films in O2/N2/H2O ambient. With further increasing O2 partial pressure (over 25% O2) in O2/N2/H2O ambient, surface-adsorbed O diffused into Si-nitride and accumulated at Si-nitride/Ag interface, which built-up pressure and cracking Si-nitride film. Thus, it is concluded that the pressure built-up from O2 accumulation and hydrolysis and oxidation reactions of Si-nitride are key factors for the reliability of Si-nitride passivation films.

XANES and XRR study on phase evolution of TiO2 films developed using HiPIMS

High power impulse magnetron sputtering (HiPIMS) is one of the recent advanced techniques for the development of high quality TiO2 thin films. Due to the formation of high energetic ions in the discharge, HiPIMS can produce various crystalline phases of TiO2 (anatase and rutile) with low roughness as compared to conventional direct current magnetron sputtering (DCMS). This work emphasizes on the effect of oxygen partial pressure in the evolution of phases and oxidation states of TiO2 films deposited using HiPIMS along with a comparative study against DCMS grown films under similar oxygen environment. TiO2 thin films were prepared with DCMS and HiPIMS, as a function of oxygen content in the sputter gas flow. Thickness, density and roughness were calculated using XRR fitting and analysis. It was observed that HiPIMS deposited films were smoother and denser than DCMS grown films. Crystallite sizes of HiPIMS deposited films were significantly lower than DCMS. Phase growth analyses were performed using X-ray diffraction (XRD), Raman and XANES (X-ray absorption near-edge spectroscopy of the Ti L2,3 and O K-edges) spectroscopy. In HiPIMS grown films, the increase in O2 partial pressure changed the phase from rutile to mixed and then to anatase phase whereas only rutile and mixed phases were detected in DCMS grown film under similar oxygen environment. HiPIMS developed films were smooth, uniform free from cracks as observed in FESEM and Atomic Force microscope (AFM) morphological images. Lognormal crystallite size distribution values decreased with increasing O2 partial pressure. Crystal field splitting values of (Δo) between ∼1.9 and 2.2 eV indicate crystalline phase formation by XANES Ti L2,3-edge analysis. These findings point to better crystalline growth TiO2 thin films as compared to DC-MS. HiPIMS grown films shows phase transformation of rutile into mix phase and anatase with increase in oxygen partial pressure.

Internal Referencing Photoluminescence Probes for Simultaneous Sensing of O2 Gas and Temperature Based on Mn:MAPb(Br/Cl)3 Perovskite

The ratiometric photoluminescence (PL)‐based O2 sensitive probes provide built‐in self‐calibration for the correction of various target‐independent influencing factors. They attract particular attention to be used for O2 gas sensing and imaging. Herein, internal referencing ratiometric PL probes are fabricated that not only detect O2 concentration and temperature simultaneously but also remove the destructive effect of temperature on O2 sensing. A dual‐emission thin film of Mn‐doped halide perovskite nanocrystals (PNCs) (Mn:MAPb(Br/Cl)3) with a 50% PL quantum yield is used as the sensing layer, which is synthesized in situ. Through the sensing process, excitonic PL and the PL caused by Mn are used for detecting temperature and O2 partial pressures, respectively. Remarkably, the Mn PL intensity shows 40% decrement with increasing O2 partial pressures from 0% to 20%, while for the excitonic PL, intensity changes are less than 5%. As the temperature undesirably affects the sensing quantity, the O2 PL is used as an internal reference signal to achieve good accuracy and selectivity. Furthermore, the temperature variation is determined by measuring PL peak intensity change and wavelength shift. In addition to the O2 gas sensitivity of 1.55, a relative temperature sensitivity of −9.36% K−1 is also achieved.

Electron scattering at Co(0001) surfaces: Effects of Ti and TiN capping layers

In situ transport measurements on epitaxial 7.6-nm-thick Co(0001)/Al2O3(0001) films with and without Ti and TiN capping layers during O2 exposure are used to investigate the effects of surface chemistry on electron scattering at Co(0001) surfaces. The Co sheet resistance Rs increases with increasing thickness dTi and dTiN of the Ti and TiN capping layers, saturating at 8% and 31% above the uncoated Co(0001) for dTi > 0.2 nm and dTiN > 0.1 nm, respectively. This increase is attributed to electron scattering into local surface states, which is less pronounced for Ti than TiN. In situ resistance measurements taken during a continuously increasing O2 partial pressure from 0 Pa to 40 Pa indicate a relatively steep 24% increase in Rs at an exposure of ∼50 Pa s, which can be attributed to Co surface oxidation that leads to atomic level roughness and a decrease in the electron scattering specularity p. Ti and TiN cap layers with dTi ≥ 0.5 nm and dTiN ≥ 0.13 nm exhibit no resistance change upon air exposure, indicating suppression of Co oxidation. These results indicate a promising Co–Ti interface with an electron scattering specularity of p = 0.4–0.5, which is retained during oxygen exposure, while, in contrast, electron scattering at the Co–TiN interface is completely diffuse (p = 0), suggesting that Ti barrier layers facilitate higher-conductivity Co interconnects than TiN barriers, as long as the Ti layer is sufficiently thick (dTi ≥ 0.5 nm) to suppress Co oxidation.

Oxygen partial pressure-dependent growth mechanism of low-dimensional zinc oxide on indium tin oxide glass

The influence of O2 partial pressure on the growth mechanism of quasi-one-dimensional thermal-evaporated ZnO structure was explained by the preferential interface nucleation. At the relatively low temperature of 550 °C, the growth was governed by different growth mechanisms as the O2 partial pressure increased. At a very low O2 partial pressure of 0.3 Pa, the growth of ZnO nanowire on indium-tin oxide glass was Au-catalyzed vapor-liquid-solid (VLS) mechanism instead of vapor-solid (VS) mechanism. As increasing O2 partial pressure to 3 and 6 Pa, the ZnO needle-like structure was grown by self-catalyzed VLS mechanism. While, the VS mechanism was suggested for ZnO micropillar and two-dimensional ZnO sheet grown with the O2 partial pressure of 9 Pa and above. The near band edge (NBE) at 3.26 eV from the photoluminescence (PL) spectra strongly depended on the as-grown structure. In addition, PL at 2.32 eV corresponded to the ZnO defects due to the oxygen vacancies within 14 nm beneath the one-dimensional ZnO surface.

Effect of Post-Annealing on Structural and Electrical Properties of ZnO:In Films**Supported by the National Natural Science Foundation of China under Grant Nos 51472038 and 51502030, the Natural Science Foundation of Chongqing City under Grant Nos CSTC2016jcyjA and 2018jcyjA2923, the Education Commission of Chongqing under Grant Nos KJ1500319, 1501112 and KJ1600314, and the PhD Scientific Research Fund under Grant No 16XlB002.

Indium-doped ZnO (ZnO:In) films are deposited on quartz substrates by rf magnetron sputtering. The effects of post-annealing on structural, electrical, optical and Raman properties are investigated by x-ray diffraction, Raman scattering, Hall measurement and first-principles calculation. The results indicate that all of the ZnO:In films have excellent crystallinity with a preferred ZnO (002) orientation. It is found that the incorporation of In can dramatically increase the intensity of the 274 cm−1 Raman mode. However, both post-annealing treatment and increasing O2 partial pressure in the process of preparing thin films can reduce the intensity of the 274 cm−1 mode or even eliminate it, and relax compressive stress of the ZnO:In film judged by analyzing the shifts of the (002) Bragg peaks and E2 (high) mode. Finally, the origin of the 274 cm−1 mode is inferred to be the vibration of Zn interstitial (Zni) defects, which play a crucial role in the high electron concentration and low resistivity of ZnO:In films annealed in an appropriate temperature range (450–600°C).

Insulator-to-metal transition of vanadium oxide-based metal-oxide-semiconductor devices at discrete measuring temperatures

In this article, crystallinity and phase dependent insulator-to-metal transition (IMT) of vanadium oxide (VO)-based metal-oxide-semiconductor (MOS) devices is studied at higher measuring temperatures where the sputtered VOs are deposited in different Ar:O2 ratios at room temparture. The VO phases were identified by differential scanning calorimetry and synchrotron-based grazing incidence x-ray diffraction techniques. A change in the crystalline to amorphous nature of the as-deposited films is observed with increasing O2 partial pressure (pO2) at elevated substrate temperatures. The I-V trends reveal an electrically-triggered insulator-to-metal transition phenomena at higher temperatures. The IMT has been ascribed to both the increase in carrier concentration in the gate dielectric due to electric-field induced carrier injection and structural phase transition (SPT). The effect of Joule heating also plays a role in the IMT. It is further observed that IMT is absent at certain intermediate temperatures. The temperature dependent quantized IMT suggests a trade-off between various crystalline and amorphous phases of VO.

Investigation on electrical properties of indium tin oxide thin films by effective control of crystallographic orientation

Although indium tin oxide (ITO) film has been widely used in optoelectronic devices, it remains difficult to systemically determine the structural properties' influence on electrical properties for ITO. In this work, ITO films are grown by metal organic chemical vapor deposition (MOCVD). By introducing nucleation layers, the structural properties could be controlled effectively so that the dependence of electrical properties on crystallographic orientation and O2 partial pressure could be investigated separately. It is found that (1) for the samples grown with the same doping level, the decrease in carrier concentration with increasing oxygen flow rate is purely attributed to the increasing O2 partial pressure rather than different crystallographic orientation; (2) electron mobility of the ITO films is strongly affected by crystallographic orientation and it decreases with (100)-grain density. Analysis by using carrier's transport theory reveals that the averaged barrier height of grain boundary scattering increases with the (100)-grain density.

Influence of oxygen partial pressure on microstructure, optical properties, residual stress and laser induced damage threshold of amorphous HfO2 thin films

HfO2 thin films were deposited by electron beam evaporation technique at different oxygen (O2) partial pressures. The films are characterized using x-ray diffraction, x-ray reflectivity, spectrophotometry, atomic force microscopy, substrate curvature measurement and laser induced damage threshold (LIDT) measurement techniques. All the films show amorphous structure and are optically homogeneous. The film density decreases from 8.53 to 6.99 gm/cm3, while both the grain size and surface roughness increase with increasing oxygen partial pressure. Film refractive index decreases from 1.96 to 1.82, and the band gap increases from 5.59 eV to 5.67 eV with increasing O2 partial pressure. The variation of refractive index is correlated with the grain size and density of the films. The measured residual stress for all the films is tensile in nature, and its variation with oxygen pressure is correlated with the film microstructure. The measured LIDT value decreases from 9.89 to 8.83 J/cm2 for 1064 nm laser and 5.97 to 4.52 J/cm2 for 532 nm laser, with increasing O2 partial pressure. The variation of laser damage threshold with oxygen partial pressure has been explained through density of the film.

Effects of O2 Partial Pressure on Composition and Infrared Emissivity of PtO x Films Prepared by Reactive Magnetron Sputtering

PtO x films have been prepared by reactive magnetron sputtering on glass substrates without external heating and characterized by x-ray diffraction (XRD) analysis, x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The resulting PtO x films mainly consisted of amorphous PtO and PtO2, and the composition largely depended on the O2 partial pressure during sputtering. In this study, the effects of the O2 partial pressure on the deposition rate, composition, surface morphology, structure, electrical resistivity, and infrared emissivity of the as-deposited PtO x films were evaluated. It was found that, with increase in the O2 partial pressure, the O/Pt atomic ratio, resistivity, and infrared emissivity of the as-deposited PtO x film increased, while the deposition rate first increased then decreased with increasing O2 partial pressure. In addition, the O2 partial pressure had little influence on the structure or surface morphology of the as-deposited PtO x film.

Defects and properties of cadmium oxide based transparent conductors

Transparent conductors play an increasingly important role in a number of semiconductor technologies. This paper reports on the defects and properties of Cadmium Oxide, a transparent conducting oxide which can be potentially used for full spectrum photovoltaics. We carried out a systematic investigation on the effects of defects in CdO thin films undoped and intentionally doped with In and Ga under different deposition and annealing conditions. We found that at low growth temperatures (<200 °C), sputter deposition tends to trap both oxygen vacancies and compensating defects in the CdO film resulting in materials with high electron concentration of ∼2 × 1020/cm3 and mobility in the range of 40–100 cm2/V s. Thermal annealing experiments in different ambients revealed that the dominating defects in sputtered CdO films are oxygen vacancies. Oxygen rich CdO films grown by sputtering with increasing O2 partial pressure in the sputter gas mixture results in films with resistivity from ∼4 × 10−4 to >1 Ω cm due to incorporation of excess O in the form of O-related acceptor defects, likely to be O interstitials. Intentional doping with In and Ga donors leads to an increase of both the electron concentration and the mobility. With proper doping CdO films with electron concentration of more than 1021 cm−3 and electron mobility higher than 120 cm2/V s can be achieved. Thermal annealing of doped CdO films in N2 ambient can further improve the electrical properties by removing native acceptors and improving film crystallinity. Furthermore, the unique doping behavior and electrical properties of CdO were explored via simulations based on the amphoteric defect model. A comparison of the calculations and experimental results show that the formation energy of native donors and acceptors at the Fermi stabilization energy is ∼1 eV and that the mobility of sputtered deposited CdO is limited by a background acceptor concentration of ∼5–6 × 1020/cm3. The calculations offer an insight into understanding of the effects of defects on electrical properties of undoped and doped CdO and offer a potential to use similar methods to analyze doping and defect properties of other semiconductor materials.

Oxygen partial pressure effects on the magnetron sputtered WO3 films

Electrochromism is changing color of a substance in response to the applied an external electric field and the phenomenon is reversible. WO3 is very attractive material due to its electrochromic properties as well as it is also attractive for many different applications such as gas sensors, phosphorous screen, textile, glass industry. In this study, it is aimed to provide optimization of the optical and structural characteristics of WO3 by changing the growth parameters mainly the oxygen partial pressure. The partial pressure of oxygen was changed with increments of 0.7 mTorr. For the analysis, X-ray Diffraction (XRD), absorption, Raman spectroscopy measurements were used. When O2 gas increased, peaks belong to the WO3 was observed in XRD patterns at the 2 theta angles of 23.0, 11.0, 23.5 and 28.5 angles corresponding to the (002), (020) and (220) planes, respectively. This shows that there is a significant effect of increasing O2 partial pressure in the formation of WO3 films. The bandgap energy of the WO3 thin films are found to be around 3.0 eV. Raman measurements showed vibrational modes of W-O-W stretching and bending modes which shows small shifts depending on the partial pressures of the O2. Obtained results indicated that better crystal structure is obtained with higher O2 gas partial pressure.

The effect of O2 partial pressure on the photoluminescence of ZnO thin films grown by pulsed laser deposition

In this paper, photoluminescence (PL) of ZnO thin films prepared on c-Al2O3 substrates by the pulsed laser deposition (PLD) method at different O2 partial pressures is investigated. For all samples, a narrow ultraviolet (UV) emission and a broad visible emission can be observed at room-temperature (RT). With increasing O2 partial pressures from 0.2 to 5Pa, the intensity ratio of the UV to visible emissions increases, and the energy positions of the UV emission band shift to the high energy side. It is noted that the visible part includes two emission bands of green luminescence (GL) and yellow luminescence (YL), in which the GL emission is strong at low oxygen pressure and the YL emission becomes dominant at high O2 partial pressures. The temperature-dependent PL spectra show that the UV emission is composed of two bands labeled FX and FA. The dependences and possible assignments of these PL bands are briefly discussed.

High-quality nonpolar ZnO thin films grown on r-plane sapphire by radio frequency-magnetron sputtering

Nonpolar, a-plane 112¯0 ZnO thin films were epitaxially grown on r-plane 11¯02 sapphire substrate by radio frequency magnetron sputtering. The influence of oxygen partial pressure was studied. With increasing O2 partial pressure of the Ar/O2 sputtering gas, the ridge-like facet structure of the ZnO film altered to a smooth film. Full width half maximum of X-ray rocking curves for the on-axis 112¯0 reflections were 0.45°, 0.36°, 0.09° and 0.25° for samples grown at Ar/O2 ratios of 2/1, 1/1, 1/2 and 1/3, respectively. A smooth surface could be obtained under oxygen rich conditions (Ar/O2 ratio: 1/2), enhancing the lateral growth along the c-axis direction.

Effect of O2 gas partial pressure on mechanical properties of Al2O3 films deposited by inductively coupled plasma-assisted radio frequency magnetron sputtering

The effect of O2 partial pressure on the mechanical properties of Al2O3 films is studied. Using films prepared by inductively coupled plasma-assisted radio frequency magnetron sputtering, the deposition rate of Al2O3 decreases rapidly when oxygen is added to the argon sputtering gas. The internal stresses in the films are compressive, with magnitude decreasing steeply from 1.6 GPa for films sputtered in pure argon gas to 0.5 GPa for films sputtered in argon gas at an O2 partial pressure of 0.89 × 10−2 Pa. Stress increases gradually with increasing O2 partial pressure. Using a nanoindentation tester with a Berkovich indenter, film hardness was measured to be about 14 GPa for films sputtered in pure argon gas. Hardness decreases rapidly on the addition of O2 gas, but increases when the O2 partial pressure is increased. Adhesion, measured using a Vickers microhardness tester, increases with increasing O2 partial pressure. Electron probe microanalyzer measurements reveal that the argon content of films decreases with increasing O2 partial pressure, whereas the O to Al composition ratio increases from 1.15 for films sputtered in pure argon gas to 1.5 for films sputtered in argon gas at O2 partial pressures over 2.4 × 10−2 Pa. X-ray diffraction measurements reveal that films sputtered in pure argon gas have an amorphous crystal structure, whereas γ-Al2O3 is produced for films sputtered in argon gas with added O2 gas. Atomic force microscopy observations reveal that the surface topography of sputtered Al2O3 films changes from spherical to needlelike as O2 partial pressure is increased. Fracture cross sections of the films observed by scanning electron microscopy reveal that the film morphology exhibits no discernible features at all O2 partial pressures.

Mechanistic aspects of photo-induced formation of peroxide ions on the surface of cubic Ln2O3 (Ln = Nd, Sm, Gd) under oxygen

The photo-induced formation of peroxide ions on the surface of cubic Ln2O3 (Ln = Nd, Sm, Gd) was studied by in situ microprobe Raman spectroscopy using a 325 nm laser as excitation source. It was found that the Raman bands of peroxide ions at 833-843 cm(-1) began to grow at the expense of the Ln(3+)-O(2-) bands at 333-359 cm(-1) when the Ln2O3 samples under O2 were continuously irradiated with a focused 325 nm laser beam at temperatures between 25-150 °C. The intensity of the peroxide Raman band was found to increase with increasing O2 partial pressure, whereas no peroxide band was detected on the Ln2O3 under N2 as well as on the samples first irradiated with laser under Ar or N2 followed by exposure to O2 in the dark. The experiments using (18)O as a tracer further confirmed that the peroxide ions are generated by a photo-induced reaction between O2 and the lattice oxygen (O(2-)) species in Ln2O3. Under the excitation of 325 nm UV light, the transformation of O2 to peroxide ions on the surface of the above lanthanide sesquioxides can even take place at room temperature. Basicity of the lattice oxygen species on Ln2O3 also has an impact on the peroxide formation. Higher temperature or laser irradiation power is required to initiate the reaction between O2 and O(2-) species of weaker basicity.

'Royal Gala' apple quality stored under ultralow oxygen concentration and low temperature conditions

The objective of this work was to evaluate the interaction of ultralow oxygen concentrations (ULO) with storage temperatures and carbon dioxide partial pressures and its influence on fruit quality preservation and on the occurrence of physiological disorders in 'Royal Gala' apples. The experiment was carried out in a completely randomized design, with four replicates 25-fruit. ULO conditions (1.0 kPa O2 + 2.0 kPa CO2; 0.8 kPa O2 + 1.5 kPa CO2; 0.8 kPa O2 + 1.0 kPa CO2; 0.6 kPa O2 + 1.5 kPa CO2; and 0.6 kPa O2 + 1.0 kPa CO2) were tested at 0, 0.5 and 1.0°C, in a 5x3 factorial arrangement. Fruit quality and ripening analyses were performed after eight-month storage plus seven days of shelf-life at 20°C. Oxygen partial pressures below 0.8 kPa increased the occurrence of internal breakdown and mealiness. The best ULO condition was 1.0 kPa O2 + plus 2.0 kPa CO2 at 1.0°C. The interaction of ULO conditions and storage temperatures shows the need of increasing O2 partial pressure at higher storage temperatures.

Gas‐phase reaction of Cl with dimethyl sulfide: Temperature and oxygen partial pressure dependence of the rate coefficient

AbstractThe kinetics of the reaction of Cl atoms with dimethyl sulfide has been investigated using a relative rate technique. Experiments were performed with oxygen partial pressures of 0, 200, and 500 mbar at a total pressure of 1000 mbar (N2 + O2) over the temperature range 283–308 K in a 1080 L reactor using long path in situ Fourier transform infrared absorption spectroscopy to monitor the reactants. The 254 nm photolysis of trichloroacetyl chloride was used as the Cl atom source. Three reference hydrocarbons, cyclohexane, n‐butane, and propene were employed. Good agreement was found between the rate coefficients determined using the different reference compounds. The rate coefficients were found to decrease with increasing temperature at constant O2 pressure and increase moderately with increasing O2 partial pressure at constant temperature. The temperature dependences of the Cl atom reaction with dimethyl sulfide for the three O2 partial pressure investigated can be expressed by the simple Arrhenius expressions: k = (4.22 ± 1.78) × 10−13 exp((1968 ± 379)/T), k = (5.42 ± 1.85) × 10−13 exp((1946 ± 381)/T), and k = (6.90 ± 2.04) × 10−13 exp((1912 ± 381)/T). The errors are a combination of the 2σ statistical errors from the kinetic data analysis plus an estimated systematic error that includes the error in the reference hydrocarbon. The mechanistic implications of the results are discussed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 66–73, 2005

Performance of seminal and nodal roots of wheat in stagnant solution: K+ and P uptake and effects of increasing O2 partial pressures around the shoot on nodal root elongation.

Roots of intact wheat plants were grown for 7-12 d in stagnant nutrient solution, containing 0.1% agar, to mimic the lack of convection in waterlogged soil. Net K+ and P uptakes by seminal and nodal roots were measured separately using a split root system. For seminal roots in stagnant solution, net uptakes as a percentage of aerated roots were between 0% and 16% for P, while K+ ranged between 15% uptake and 54% loss. For the more waterlogging-tolerant nodal roots, net uptakes in stagnant nutrient solution, as a percentage of aerated roots, were 31-73% for P and 69-115% for K+. Elongation rates of nodal roots in stagnant nutrient were about 35-43% of those for roots in aerated solution. This partial inhibition occurred in these nodal roots despite their 15% porosity (v/v). Elevation of O2 partial pressures around the shoots to 40 kPa and then to 80 kPa substantially accelerated nodal root elongation in stagnant solution, demonstrating that most of the inhibition seen with ambient O2 around the shoots was associated with a restricted O2 supply to these nodal roots. Thus, in wheat nodal roots, with a partial pressure of 20 kPa O2 around the shoots, O2 diffusion from the shoots did not completely relieve the restrictions on elongation resulting from stagnancy in the nutrient solution. These results contrast with those in the literature for rice, in which roots function efficiently in stagnant solutions (0.1% agar). So, when wheat roots are aerenchymatous there are still restrictions to O2 diffusion in the gas space continuum between the atmosphere and the functional tissues of the roots. This poor acclimation must have been due to inefficiency of the aerenchymatous axes, which may include persistence of anoxic steles, and/or restricted O2 diffusion in other parts of the gas space continuum, in either the shoots and shoot-root junction or in the root tip.