The present work considers engineering of the flat band potential, FBP, of metal oxides in a controlled manner. The aim is to minimise the energy losses related to recombination. The related experimental approaches include imposition of a chemically-induced electric field using the phenomena of segregation, diffusion and the formation of multilayer systems. This paper considers several basic phenomena that allow the modification of the surface charge and the space charge at the gas/solid and solid/liquid interfaces.
Titanium dioxide is a promising candidate for high-performance photocatalysts. Defect engineering may be
applied for the modification of its properties, including the functional-related properties, in a controlled manner
in order to achieve the desired/optimized performance. The present work reports the application of defect
engineering for the modification of semiconducting properties of undoped TiO2. The defect disorder is considered
in terms of the predominant defect reactions. The related equilibrium constants are used to derive the defect
disorder diagram for undoped TiO2 in equilibrium (1273 K) in the gas phase of controlled oxygen activity
(10−13 Pa < p(O2) < 105 Pa). The obtaind data on the concentration of electronic charge carriers have been
used for the determination of the effect of p(O2) on the change of Fermi energy within the band gap. The
determined diagram may be applied for the selection of processing conditions of undoped TiO2 with controlled
semiconducting properties and the ability to donate or accept electrons.
The present work considers the application of defect chemistry for engineering of semiconducting properties of metal oxides in general and TiO2 in particular. The performance-related functional properties of TiO2-based photoelectrode for hydrogen generation through water splitting using solar energy (solar-hydrogen) are considered in terms of (i) electronic structure, (ii) charge transport, (iii) near-surface charge distribution and the related electric fields, and (iv) defect disorder of the outermost surface layer. The present work considers the modification of these functional properties for TiO2 through the imposition of controlled defect disorder. The defect disorder is considered in terms of defect equilibria and the defect diagram describing the effect of oxygen activity on the concentration of both ionic and electronic defects.
The semiconducting properties of TiO2 single crystal and their changes during oxidation and reduction at elevated
temperatures (1073 - 1323 K) under controlled oxygen activity (10-9 - 105 Pa) were monitored using measurements of
electrical conductivity and thermoelectric power. The experimental data obtained in equilibrium led to a TiO2 defect
disorder model. According to this model, oxygen vacancies are the predominant defect species in TiO2 across a wide
range of oxygen activities. This work has discovered the diffusion of Ti vacancies, which are formed during prolonged
oxidation at elevated temperatures and in a gas phase of high oxygen activity. Observations indicate that appreciable
concentrations of Ti vacancies are formed on the TiO2 surface and then are very slowly incorporated into the bulk. The
obtained diffusion data has shown that in the commonly studied temperature range (1000-1400 K) the Ti vacancy
concentration is quenched and can be considered as constant. Prolonged oxidation involves two kinetic regimes that are
related to the transport of defects of different mobilities. The defect disorder model derived in this work may be
beneficial for engineering TiO2 for enhanced water splitting through the selection of optimal processing conditions,
including temperature and oxygen activity.
The present paper considers the effect of segregation on the performance of photo-electrode materials for
photo-electrochemical water splitting. This phenomenon, which alters the surface composition of a material
during processing at elevated temperatures, has the capacity to dominate interfacial charge transfer between
the photo-electrode and the electrolyte. As the present understanding of segregation in metal oxides is
limited, this paper aims at addressing the need to collect empirical data which can be used for the
development of novel materials.
In the present investigation, Nb surface segregation was investigated at 1273 K under high and low oxygen
activity using secondary ion mass spectrometry (SIMS). A calibration procedure was used to enable
quantifiable data and Nb was observed to segregate strongly, especially at high oxygen activity. While this
was attributed to the defect disorder, it remained unclear whether gas/solid equilibrium was achieved, and
consequently whether the observed behaviour represents equilibrium segregation. Irrespectively, the
observed behaviour clearly illustrates how the surface composition of a metal oxide can be altered through
the control of segregation. This must be considered in the pursuit of high performance photo-electrode
materials for water splitting under sunlight.
This paper considers the impact of segregation on the charge transfer at the oxygen/zirconia interface. Specifically, the effect of segregation-induced low dimensional interface structures on the performance of electrochemical devices based on zirconia as a solid electrolyte is discussed.
This paper considers the impact of segregation on the charge transfer at the oxygen/zirconia interface. Specifically, the effect of segregation-induced low dimensional interface structures on the performance of electrochemical devices based on zirconia as a solid electrolyte is discussed.
Detailed investigations of the projection moire and grid projection methods used for the computer aided studies of the shape of the muscle-osseous system and postural deformities are presented. The shape determination process is readily automated using the phase methods for analyzing the fringe patterns. The issue of subtracting the reference surface inherent to the measurement-by-comparison methods is discussed. Specialized medical software for studying the deformity of the back and front of the human body illustrated by clinical examples is presented.
Two basic optical triangulation systems for routine studies of postural deformities among youths and adults are described. They use projection moire with temporal phase stepping and grating projection with carrier frequency spatial phase stepping for the automatic analysis of fringe patterns. The operation parameters of both systems are discussed and compared. The special medical software developed for analyzing the back and front of the human body is presented.
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