Limits...
Rough gold films as broadband absorbers for plasmonic enhancement of TiO 2 photocurrent over 400 – 800   nm

View Article: PubMed Central - PubMed

ABSTRACT

Recent years have witnessed an increasing interest in highly-efficient absorbers of visible light for the conversion of solar energy into electrochemical energy. This study presents a TiO2-Au bilayer that consists of a rough Au film under a TiO2 film, which aims to enhance the photocurrent of TiO2 over the whole visible region and may be the first attempt to use rough Au films to sensitize TiO2. Experiments show that the bilayer structure gives the optimal optical and photoelectrochemical performance when the TiO2 layer is 30 nm thick and the Au film is 100 nm, measuring the absorption 80–90% over 400–800 nm and the photocurrent intensity of 15 μA·cm−2, much better than those of the TiO2-AuNP hybrid (i.e., Au nanoparticle covered by the TiO2 film) and the bare TiO2 film. The superior properties of the TiO2-Au bilayer can be attributed to the rough Au film as the plasmonic visible-light sensitizer and the photoactive TiO2 film as the electron accepter. As the Au film is fully covered by the TiO2 film, the TiO2-Au bilayer avoids the photocorrosion and leakage of Au materials and is expected to be stable for long-term operation, making it an excellent photoelectrode for the conversion of solar energy into electrochemical energy in the applications of water splitting, photocatalysis and photosynthesis.

No MeSH data available.


Simulation results.(a) Perspective view, top cross-sectional view (XY plane) and side cross-sectional view (XZ plane) of the model for the TiO2-Au bilayer sample; (b) comparison of the measured absorption spectrum with the calculated one using the FDTD method for the TiO2-Au bilayer sample whose TiO2 film is 30-nm thick; The electric field distributions on the transverse cross-sections located at (c) Z = 0 nm, (d) Z = 30 nm, (e) Z = 60 nm and (f) Z = 90 nm, here Z = 0 is at the upper surface of the flat Au layer.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5016800&req=5

f5: Simulation results.(a) Perspective view, top cross-sectional view (XY plane) and side cross-sectional view (XZ plane) of the model for the TiO2-Au bilayer sample; (b) comparison of the measured absorption spectrum with the calculated one using the FDTD method for the TiO2-Au bilayer sample whose TiO2 film is 30-nm thick; The electric field distributions on the transverse cross-sections located at (c) Z = 0 nm, (d) Z = 30 nm, (e) Z = 60 nm and (f) Z = 90 nm, here Z = 0 is at the upper surface of the flat Au layer.

Mentions: Based on the physical structure and materials of the actual TiO2-Au bilayer sample, the simulation model is built up as depicted in Fig. 5a, with the Au portion and the TiO2 portion denoted by yellow and blue color, respectively. The model consists of three layers, from bottom to top, a flat Au film layer, an Au NPs layer and a TiO2 layer. The FTO thin film is not included in the simulation since there is almost no transmission of light through the Au layer. As an approximation, the thickness of the flat Au film layer is 100 nm in the simulation. Considering the roughness of the Au film (see the AFM image in Fig. 3b), the rough surface is represented by randomly-distributed particles28. In the simulation, the particles are randomly scattered on the surface in a space of 1 μm × 1 μm × 30 nm, with their diameters varying from 60 to 120 nm. The vertical positions of the particles are adjusted so that the highest particles are always attached to the upper boundary of the flat Au layer while the other particles may be partially embedded into the flat Au layer. The Au nanoparticles can be overlapped with each other, in which some larger domain can be formed occasionally to further account for the randomness of the distribution, the shape and the size. To mimic the TiO2 film, the template method is adopted29. Each Au NPs is embraced by a shell layer of TiO2, whose thickness is equal to the ALD deposition thickness approximately. For the bare area without the Au NPs covered, a flat TiO2 film layer with the deposition thickness is also added above the flat Au layer. The meshing order of these Au NPs has higher priority than the TiO2 layers to ensure the coverage by TiO2 at only the outer boundaries. The transverse dimension of the model structure is 1 μm × 1 μm and the number of Au NPs is 320 in the simulation. With the random positioning, the number of Au NPs is essential for simulating the surface roughness of the Au film, and a relatively small number generally implies a larger surface roughness. In this way, the roughness of Au surface of the real TiO2-Au bilayer can be well represented.


Rough gold films as broadband absorbers for plasmonic enhancement of TiO 2 photocurrent over 400 – 800   nm
Simulation results.(a) Perspective view, top cross-sectional view (XY plane) and side cross-sectional view (XZ plane) of the model for the TiO2-Au bilayer sample; (b) comparison of the measured absorption spectrum with the calculated one using the FDTD method for the TiO2-Au bilayer sample whose TiO2 film is 30-nm thick; The electric field distributions on the transverse cross-sections located at (c) Z = 0 nm, (d) Z = 30 nm, (e) Z = 60 nm and (f) Z = 90 nm, here Z = 0 is at the upper surface of the flat Au layer.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016800&req=5

f5: Simulation results.(a) Perspective view, top cross-sectional view (XY plane) and side cross-sectional view (XZ plane) of the model for the TiO2-Au bilayer sample; (b) comparison of the measured absorption spectrum with the calculated one using the FDTD method for the TiO2-Au bilayer sample whose TiO2 film is 30-nm thick; The electric field distributions on the transverse cross-sections located at (c) Z = 0 nm, (d) Z = 30 nm, (e) Z = 60 nm and (f) Z = 90 nm, here Z = 0 is at the upper surface of the flat Au layer.
Mentions: Based on the physical structure and materials of the actual TiO2-Au bilayer sample, the simulation model is built up as depicted in Fig. 5a, with the Au portion and the TiO2 portion denoted by yellow and blue color, respectively. The model consists of three layers, from bottom to top, a flat Au film layer, an Au NPs layer and a TiO2 layer. The FTO thin film is not included in the simulation since there is almost no transmission of light through the Au layer. As an approximation, the thickness of the flat Au film layer is 100 nm in the simulation. Considering the roughness of the Au film (see the AFM image in Fig. 3b), the rough surface is represented by randomly-distributed particles28. In the simulation, the particles are randomly scattered on the surface in a space of 1 μm × 1 μm × 30 nm, with their diameters varying from 60 to 120 nm. The vertical positions of the particles are adjusted so that the highest particles are always attached to the upper boundary of the flat Au layer while the other particles may be partially embedded into the flat Au layer. The Au nanoparticles can be overlapped with each other, in which some larger domain can be formed occasionally to further account for the randomness of the distribution, the shape and the size. To mimic the TiO2 film, the template method is adopted29. Each Au NPs is embraced by a shell layer of TiO2, whose thickness is equal to the ALD deposition thickness approximately. For the bare area without the Au NPs covered, a flat TiO2 film layer with the deposition thickness is also added above the flat Au layer. The meshing order of these Au NPs has higher priority than the TiO2 layers to ensure the coverage by TiO2 at only the outer boundaries. The transverse dimension of the model structure is 1 μm × 1 μm and the number of Au NPs is 320 in the simulation. With the random positioning, the number of Au NPs is essential for simulating the surface roughness of the Au film, and a relatively small number generally implies a larger surface roughness. In this way, the roughness of Au surface of the real TiO2-Au bilayer can be well represented.

View Article: PubMed Central - PubMed

ABSTRACT

Recent years have witnessed an increasing interest in highly-efficient absorbers of visible light for the conversion of solar energy into electrochemical energy. This study presents a TiO2-Au bilayer that consists of a rough Au film under a TiO2 film, which aims to enhance the photocurrent of TiO2 over the whole visible region and may be the first attempt to use rough Au films to sensitize TiO2. Experiments show that the bilayer structure gives the optimal optical and photoelectrochemical performance when the TiO2 layer is 30 nm thick and the Au film is 100 nm, measuring the absorption 80–90% over 400–800 nm and the photocurrent intensity of 15 μA·cm−2, much better than those of the TiO2-AuNP hybrid (i.e., Au nanoparticle covered by the TiO2 film) and the bare TiO2 film. The superior properties of the TiO2-Au bilayer can be attributed to the rough Au film as the plasmonic visible-light sensitizer and the photoactive TiO2 film as the electron accepter. As the Au film is fully covered by the TiO2 film, the TiO2-Au bilayer avoids the photocorrosion and leakage of Au materials and is expected to be stable for long-term operation, making it an excellent photoelectrode for the conversion of solar energy into electrochemical energy in the applications of water splitting, photocatalysis and photosynthesis.

No MeSH data available.