The reactions of oxygen at dark and irradiated zinc oxide surfaces

1960 ◽  
Vol 255 (1280) ◽  
pp. 124-144 ◽  
Keyword(s):  
Zinc Oxide ◽  
Previous History ◽  
Ultra Violet ◽  
Normal Behaviour ◽  
Adsorption And Desorption ◽  
Kinetics Of Adsorption ◽  
Temperature Range ◽  
Interstitial Zinc ◽  
Chemisorbed Oxygen ◽  
Type Semiconductor

Studies of the kinetics of adsorption of oxygen on zinc oxide over the temperature range from 25 to 390°C have provided evidence for two distinct types of chemisorption, one prevalent below 200 and the other above 300°C. This pattern of activity has been confirmed by measurements of desorption rates over the same temperature range. The mode of preparation and pretreatment of the oxide exert a strong influence on the adsorption behaviour, and these differences are accentuated when the processes of adsorption and desorption are studied in the presence of irradiation in the ultra-violet and visible. Photodesorption of oxygen is confirmed to be the normal behaviour for zinc oxide, but photo-adsorption has been observed under conditions of high excess zinc concentration. The photo-effects are especially marked below 300°C. The adsorption studies have been followed up by experiments on the rate of the intermolecular oxygen reaction 18 O 2 + 16 O 2 ⇌2 18 O 16 O, and on the influence of irradiation on this catalysis. It is evident that irradiation stimulates both adsorption and desorption, but the balance between them depends on the previous history of the specimen. The experiments with heavy oxygen have also included a brief study of oxygen exchange with zinc oxide at 400 to 500°C. The results as a whole are discussed in terms of the model of zinc oxide as an n -type semiconductor with interstitial zinc, and oxygen chemisorbed as O¯ and O 2¯ , respectively, are held to be mainly responsible for the phenomena observed. The relationship with conductivity studies is emphasized and the depletive chemisorption of oxygen, forming a boundary layer, is discussed in some detail. The depletion of electrons is not exhaustive for normal specimens of zinc oxide, and the treatment of this case leads to an expression consistent with the observed kinetics. Several possible mechanisms for photo-adsorption are put forward, and the association with high donor concentrations is discussed. Interstitial zinc diffusing under the influence of the electric field of chemisorbed oxygen is considered to play an important role in specimens heated above 300°C.

The distribution of interstitial zinc in zinc oxide

1967 ◽  
Vol 20 (1) ◽  
pp. 85 ◽  
Author(s):  
VJ Norman
Keyword(s):  
Zinc Oxide ◽  
Zinc Content ◽  
Surface Fraction ◽  
Interstitial Zinc ◽  
Oxide Powders ◽  
Convenient Means ◽  
Chemisorbed Oxygen ◽  
Excess Zinc

A method is described which enables the position of interstitial zinc within the crystals of zinc oxide powders to be determined. The crystals are etched to various depths with acid, and the excess zinc content of each fraction is estimated. It is shown that the distribution of the interstitial zinc is dependent upon the species of chemisorbed oxygen prevalent, and that a marked concentration of excess zinc in the surface fraction of the crystals is apparent only in those samples of zinc oxide on which the oxygen chemisorbed is predominantly of the reactive variety. The method provides a convenient means of following the diffusion of interstitial zinc on heating. The changes in the distribution of interstitial zinc in both types of zinc oxide that occur on heating in air are shown and discussed.

Study of C2H5O2 using modulated photolysis: ultra-violet spectrum and self-reaction kinetics in the temperature range 233-363 K

1997 ◽  
Vol 94 ◽  
pp. 484-502
Author(s):  
S Fauvet ◽  
JP Ganne ◽  
J Brion ◽  
D Daumont ◽  
J Malicet ◽  
...  
Keyword(s):  
Reaction Kinetics ◽  
Ultra Violet ◽  
Temperature Range

Synthesis of Zn1−xCdxO Nanoparticles by Co-Precipitation: Structural, Optical and Photodetection Analysis

2017 ◽  
Vol 17 (01n02) ◽  
pp. 1760015 ◽  
Author(s):  
Anju Anna Jacob ◽  
L. Balakrishnan ◽  
S. R. Meher ◽  
K. Shambavi ◽  
Z. C. Alex
Keyword(s):  
Zinc Oxide ◽  
Energy Dispersive Spectrometer ◽  
Ultra Violet ◽  
Wide Bandgap ◽  
Precipitation Method ◽  
Cutoff Wavelength ◽  
X Ray ◽  
Wide Bandgap Semiconductor ◽  
Co Precipitation ◽  
Scanning Electron

Zinc oxide (ZnO) is a wide bandgap semiconductor with excellent photoresponse in ultra-violet (UV) regime. Tuning the bandgap of ZnO by alloying with cadmium can shift its absorption cutoff wavelength from UV to visible (Vis) region. Our work aims at synthesis of Zn[Formula: see text]CdxO nanoparticles by co-precipitation method for the fabrication of photodetector. The properties of nanoparticles were analyzed using X-ray diffractometer, UV–Vis spectrometer, scanning electron microscope and energy dispersive spectrometer. The incorporation of cadmium without altering the wurtzite structure resulted in the red shift in the absorption edge of ZnO. Further, the photoresponse characteristics of Zn[Formula: see text]CdxO nanopowders were investigated by fabricating photodetectors. It has been found that with Cd alloying the photosensitivity was increased in the UVA-violet as well in the blue region.

Kinetics of Adsorption and Desorption of Non-Covalent Self-Assembling Systems

2020 ◽  
Vol MA2020-01 (12) ◽  
pp. 927-927
Author(s):  
K W Hipps ◽  
Kirill Gurdumov ◽  
Ursula Mazur
Keyword(s):  
Adsorption And Desorption ◽  
Kinetics Of Adsorption ◽  
Self Assembling ◽  
Kinetics Of

The Effect of Sintering Temperature to the Properties of Zinc Oxide

2013 ◽  
Vol 795 ◽  
pp. 419-423 ◽  
Author(s):  
J.H. Lim ◽  
C.K. Yeoh ◽  
Pei Leng Teh ◽  
W.M. Arif ◽  
A. Chik
Keyword(s):  
Thermal Conductivity ◽  
Zinc Oxide ◽  
Thermal Properties ◽  
Solid State ◽  
Sintering Temperature ◽  
Solid State Method ◽  
Influence Of Temperature ◽  
Temperature Range ◽  
Influence Of Temperature On ◽  
State Method

In this paper, different sintering temperature used to study the influence of temperature on the structural and thermal properties of zinc oxide (ZnO). On this research, the sample was prepared by solid-state method for zinc oxide (ZnO) at different sintering temperature which was 700°C, 800°C and 900°C. It was observed that the density of bulk ZnO that sintering at 900°C had the higher value of density 5.03 g/cm3. The microhardness of the bulk ZnO had a higher measurement 397.3 Hv after sintered at 900°C. ZnO that sintering at 900°C had been observed that had thermal conductivity 1.1611W/cm-K in the sintering temperature range 700°C to 900°C.

Oxygen chemisorbed on zinc oxide: The determination of reactive oxygen

1966 ◽  
Vol 19 (7) ◽  
pp. 1133
Author(s):  
VJ Norman
Keyword(s):  
Zinc Oxide ◽  
Potassium Iodide ◽  
Reactive Oxygen ◽  
Zinc Content ◽  
Photometric Method ◽  
Chemisorbed Oxygen ◽  
Published Evidence ◽  
Excess Zinc ◽  
Acid Reduction

The changes in excess zinc content which occur on heating zinc oxide in air are discussed, and are suggested as a means of estimating oxygen chemisorbed on zinc oxide. The published evidence for the existence of at least two varieties of chemisorbed oxygen is confirmed, and it is established that only one of these varieties is reactive chemically. The results deduced from the heating experiments are confirmed directly by a rapid photometric method which is described for the determination of reactive oxygen chemisorbed on zinc oxide. Oxygen is desorbed from the surface of the zinc oxide by etching with ammonium chloride solution in the presence of potassium iodide. By complexing the iodine liberated by reactive oxygen with starch prior to dissolution of the sample in acid, reduction of iodine by excess of zinc in the sample is avoided. Atmospheric oxidation of potassium iodide is overcome by close control of acid concentration (pH 5.2) throughout the determination. A reference solution is employed in which iodide is added only after dissolution of the sample in acid has been completed. The necessary compensation for oxidizable matter present in the zinc oxide and reagents is achieved by the addition of standardized hydrogen peroxide to both sample and reference solutions.��� Reactive chemisorbed oxygen on a number of samples of zinc oxide ranged from 0 to 1.5 p.p.m. by weight. The method gives good reproducibility, and is sensitive to 0.03 p.p.m. of oxygen by weight.

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