Unravelling charge separation via surface built-in electric fields within single particulate photocatalysts

2017 ◽  
Vol 198 ◽  
pp. 473-479 ◽  
Author(s):  
Ruotian Chen ◽  
Jian Zhu ◽  
Hongyu An ◽  
Fengtao Fan ◽  
Can Li
Keyword(s):  
Electric Fields ◽  
Charge Separation ◽  
Energy Conversion Efficiency ◽  
Single Particles ◽  
Kelvin Probe ◽  
Force Microscopy ◽  
Transfer Processes ◽  
Spatially Resolved ◽  
P Type

Kelvin Probe Force Microscopy (KPFM) and spatially resolved surface photovoltage (SRSPV) techniques were employed to reveal built-in electric fields and surface photogenerated charge distribution on single particulate photocatalysts. The photogenerated holes and electrons spread over the whole surface of the particulate photocatalyst are imaged on n-type BiVO4 and p-type Cu2O single particles, respectively. It is demonstrated that the built-in electric field in the surface Space Charge Region (SCR) dictates the charge separation/transfer processes and allows the drift of one kind of the photogenerated carriers to the surface, while holding another kind of the carriers in the bulk. The results emphasize the role of the SCR played in the unidirectional charge transport between the bulk and surface in the particulate photocatalyst, which may be the crucial reason for low solar energy conversion efficiency.

scholarly journals Quantification of electron accumulation at grain boundaries in perovskite polycrystalline films by correlative infrared-spectroscopic nanoimaging and Kelvin probe force microscopy

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Ting-Xiao Qin ◽  
En-Ming You ◽  
Mao-Xin Zhang ◽  
Peng Zheng ◽  
Xiao-Feng Huang ◽  
...  
Keyword(s):  
Solar Cell ◽  
Grain Boundaries ◽  
Cell Performance ◽  
Kelvin Probe Force Microscopy ◽  
Light Illumination ◽  
Kelvin Probe ◽  
Solar Cell Performance ◽  
Force Microscopy ◽  
Infrared Spectroscopic

AbstractOrganic–inorganic halide perovskites are emerging materials for photovoltaic applications with certified power conversion efficiencies (PCEs) over 25%. Generally, the microstructures of the perovskite materials are critical to the performances of PCEs. However, the role of the nanometer-sized grain boundaries (GBs) that universally existing in polycrystalline perovskite films could be benign or detrimental to solar cell performance, still remains controversial. Thus, nanometer-resolved quantification of charge carrier distribution to elucidate the role of GBs is highly desirable. Here, we employ correlative infrared-spectroscopic nanoimaging by the scattering-type scanning near-field optical microscopy with 20 nm spatial resolution and Kelvin probe force microscopy to quantify the density of electrons accumulated at the GBs in perovskite polycrystalline thin films. It is found that the electron accumulations are enhanced at the GBs and the electron density is increased from 6 × 1019 cm−3 in the dark to 8 × 1019 cm−3 under 10 min illumination with 532 nm light. Our results reveal that the electron accumulations are enhanced at the GBs especially under light illumination, featuring downward band bending toward the GBs, which would assist in electron-hole separation and thus be benign to the solar cell performance.

Laser cleaning of exfoliated graphene

2012 ◽  
Vol 1455 ◽  
Author(s):  
Oliver Ochedowski ◽  
Benedict Kleine Bußmann ◽  
Marika Schleberger
Keyword(s):  
Local Heating ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Ambient Conditions ◽  
Kelvin Probe ◽  
Structural Modifications ◽  
Force Microscopy ◽  
Exfoliated Graphene ◽  
Atomic Force ◽  
P Type

ABSTRACTWe have employed atomic force and Kelvin-Probe force microscopy to study graphene sheets exfoliated on TiO2 under the influence of local heating achieved by laser irradiation. Exfoliation and irradiation took place under ambient conditions, the measurements were performed in ultra high vacuum. We show that after irradiation times of 6 min, an increase of the surface potential is observed which indicates a decrease of p-type carrier concentration. We attribute this effect to the removal of adsorbates like water and oxygen. After irradiation times of 12 min our topography images reveal severe structural modifications of graphene. These resemble the nanocrystallite network which form on graphene/SiO2 but after much longer irradiation times. From our results we propose that short laser heating at moderate powers might offer a way to clean graphene without inducing unwanted structural modifications.

Surface displacements and surface charges on Ba2CuWO6 and Ba2Cu0.5Zn0.5WO6 ceramics induced by local electric fields investigated with scanning-probe microscopy

2007 ◽  
Vol 22 (1) ◽  
pp. 193-200
Author(s):  
Ralf-Peter Herber ◽  
Gerold A. Schneider
Keyword(s):  
Electric Fields ◽  
Ferroelectric Properties ◽  
Piezoresponse Force Microscopy ◽  
Ferroelectric Material ◽  
Relaxor Ferroelectrics ◽  
Surface Charges ◽  
Kelvin Probe ◽  
Force Microscopy ◽  
Atomic Force ◽  
Surface Displacements

Ba2CuWO6 (BCW) was first synthesized in the mid 1960s, and it was predicted to be a ferroelectric material with a very high Curie temperature of 1200 °C [N. Venevtsev and A.G. Kapyshev: New ferroelectrics. Proc. Int. Meet. Ferroelectr.1, 261 (1966)]. Since then, crystallographic studies were performed on the compound with the result that its crystal structure is centrosymmetric. Thus for principal reason, BCW cannot be ferroelectric. That obvious contradiction was examined in this study. Disk-shaped ceramic samples of BCW and Ba2Cu0.5Zn0.5WO6 (BCZW) were prepared. Because of the low electrical resistivity of the ceramics, it was not possible to perform a typical polariszation hysteresis loop for characterization of ferroelectric properties. Scanning electron microscopy investigations strongly suggest that the reason for the conductivity is found in the impurities/precipitations within the microstructure of the samples. With atomic force microscopy (AFM) in piezoresponse force microscopy (PFM) mode, it is possible to characterize local piezoelectricity by imaging the ferroelectric domains. Neither BCW nor BCZW showed any domain structure. Nevertheless, when local electric fields were applied to the surfaces of the ceramics topographic displacements, imaged with AFM, and surface charges, imaged with Kelvin probe force microscopy (KFM) and PFM, were measured and remained stable on the surface for the time of the experiment. Therefore BCW and BCZW are considered to be electrets and possibly relaxor ferroelectrics.

Band bending in conjugated polymer films: role of morphology and implications for bulk charge transport characteristics

2017 ◽  
Vol 5 (30) ◽  
pp. 7446-7451 ◽  
Author(s):  
J. K. Wenderott ◽  
Ban Xuan Dong ◽  
Peter F. Green
Keyword(s):  
Charge Transport ◽  
Polymer Films ◽  
Conjugated Polymer ◽  
Kelvin Probe Force Microscopy ◽  
Kelvin Probe ◽  
Band Bending ◽  
Force Microscopy ◽  
Bending Effect ◽  
Bulk Charge

The band bending effect depends on the morphology of the conjugated polymer as studied by Kelvin probe force microscopy.

scholarly journals Application of AFM-Based Techniques in Studies of Corrosion and Corrosion Inhibition of Metallic Alloys

2020 ◽  
Vol 1 (3) ◽  
pp. 345-372
Author(s):  
Kiryl Yasakau
Keyword(s):  
Metallic Materials ◽  
Kelvin Probe ◽  
Force Microscopy ◽  
Atomic Force ◽  
Current State ◽  
Corrosion Susceptibility ◽  
Corrosion Mechanisms ◽  
Microscopy Techniques ◽  
Corrosion Research

In this review several scanning probe microscopy techniques are briefly discussed as valuable assets for corrosionists to study corrosion susceptibility and inhibition of metals and alloys at sub-micrometer resolution. At the beginning, the review provides the reader with background of atomic force microscopy (AFM) and related techniques such as scanning Kelvin probe force microscopy (SKPFM) and electrochemical AFM (EC-AFM). Afterwards, the review presents the current state of corrosion research and specific applications of the techniques in studying important metallic materials for the aircraft and automotive industries. Different corrosion mechanisms of metallic materials are addressed emphasizing the role of intermetallic inclusions, grain boundaries, and impurities as focal points for corrosion initiation and development. The presented information demonstrates the importance of localized studies using AFM-based techniques in understanding corrosion mechanisms of metallic materials and developing efficient means of corrosion prevention.

Photoassisted Kelvin probe force microscopy at GaN surfaces: The role of polarity

2010 ◽  
Vol 97 (17) ◽  
pp. 172111 ◽  
Author(s):  
J. D. Wei ◽  
S. F. Li ◽  
A. Atamuratov ◽  
H.-H. Wehmann ◽  
A. Waag
Keyword(s):  
Kelvin Probe Force Microscopy ◽  
Kelvin Probe ◽  
Force Microscopy

scholarly journals Atomic Force Microscope Study of Ag-Conduct Polymer Hybrid Films: Evidence for Light-Induced Charge Separation

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1819
Author(s):  
Yinghui Wu ◽  
Dong Wang ◽  
Jinyuan Liu ◽  
Houzhi Cai ◽  
Yueqiang Zhang
Keyword(s):  
Charge Separation ◽  
Electrostatic Force ◽  
High Sensitivity ◽  
Kelvin Probe ◽  
Ag Nps ◽  
Kelvin Probe Microscopy ◽  
Force Microscopy ◽  
Atomic Force ◽  
Material Systems ◽  
Induced Charge

Scanning Kelvin probe microscopy (SKPM), electrostatic force microscopy (EFM) are used to study the microscopic processes of the photo-induced charge separation at the interface of Ag and conductive polymers, i.e., poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-bʹ]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and poly(3-hexylthiophene-2,5-diyl) (P3HT). They are also widely used in order to directly observe the charge distribution and dynamic changes at the interfaces in nanostructures, owing to their high sensitivity. Using SKPM, it is proved that the charge of the photo-induced polymer PCPDTBT is transferred to Ag nanoparticles (NPs). The surface charge of the Ag-induced NPs is quantified while using EFM, and it is determined that the charge is injected into the polymer P3HT from the Ag NPs. We expect that this technology will provide guidance to facilitate the separation and transfer of the interfacial charges in the composite material systems and it will be applicable to various photovoltaic material systems.

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