Effect of an External Applied Potential on the Photocatalytic Properties of Manganese-Doped Titanium Dioxide
Gracien Bakambo Ekoko,
Joseph Kanza-Kanza Lobo,
Omer Muamba Mvele,
Jérémie Lunguya Muswema,
Jean-Félix Senga Yamambe
Issue:
Volume 3, Issue 4, August 2014
Pages:
41-46
Received:
14 August 2014
Accepted:
19 August 2014
Published:
30 August 2014
Abstract: The electrochemical anodic oxidation method was used to prepare thin films of titanium dioxide (TiO2) semiconductors (undoped and doped with Mn). These films were used to test the oxidation of methanol (CH3OH), the degree of which was quantified by measuring the current density produced as a function of an applied potential between 0.5 V and 5.0 V. The value of the potential to be applied in order to prevent fast electron-hole recombination was determined. The observed phenomenon is explained by considering the wave nature of the electron.
Abstract: The electrochemical anodic oxidation method was used to prepare thin films of titanium dioxide (TiO2) semiconductors (undoped and doped with Mn). These films were used to test the oxidation of methanol (CH3OH), the degree of which was quantified by measuring the current density produced as a function of an applied potential between 0.5 V and 5.0 V....
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First-Principles Calculations of the Formation and Structures of Point Defects on GaN (0001) Surface
Chun Yang,
Weiwei Jie,
Ping Huang,
Xiaoqing Liang,
Xiaoxiao Pan
Issue:
Volume 3, Issue 4, August 2014
Pages:
47-53
Received:
29 August 2014
Accepted:
18 September 2014
Published:
30 September 2014
Abstract: We studied the structures and energies associated with 8 types of point defects on the [0001] surface of hexagonal gallium nitride (GaN) by modeling: (1) Ga vacancies (VGa), (2) N vacancies (VN), (3) substitution of N by Ga (GaN), (4) substitution of Ga by N (NGa), (5) Ga octahedral interstitial defects (GaO), (6) Ga tetrahedral interstitial defects (GaT), (7) N octahedral interstitial defects (NO), and (8) N tetrahedral interstitial defects (NT). Using a plane-wave ultrasoft pseudopotential method, we calculate these defect structures, simulate the shift, bonding, and relaxation reconstruction of surface atoms in response to the formation of these defects and also calculate the formation energies of these defects. We find that the Ga-related defects only slightly affect the surface, whereas all N-related defects induce substantial surface reconstruction. In particular, the formation of NT not only induces distortion of the surface structure, but also significantly influences the structure of the deeper lattice space. Calculations of formation energies suggest that, in Ga-rich conditions, GaO forms most easily, followed by GaN, VN, and GaT. In comparison, in N-rich conditions, VGa forms most easily. In all environments, GaO, GaN, and VGa form more easily than VN, and the formation of octahedral interstitial defects requires less energy than tetrahedral interstitial defects, which suggests it is difficult to form tetrahedral interstitial defects in the GaN (0001) surface.
Abstract: We studied the structures and energies associated with 8 types of point defects on the [0001] surface of hexagonal gallium nitride (GaN) by modeling: (1) Ga vacancies (VGa), (2) N vacancies (VN), (3) substitution of N by Ga (GaN), (4) substitution of Ga by N (NGa), (5) Ga octahedral interstitial defects (GaO), (6) Ga tetrahedral interstitial defect...
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