Microwave (Photo)Electrochemistry

Microwave Enthrakometric Labs-On-A-Chip and On-Chip Enthrakometric Catalymetry: From Non-Conventional Chemotronics Towards Microwave-Assisted Chemosensors

“…This is partially true, as similar work was carried out before, while the first English-language papers really became available in this period. For example, microwave photoelectrochemistry or electro-photochemistry go back to 1993 [86], and the review of 1999 on this topic referenced mainly links from the 1980-1990s to 1998 [87]. Microwave electrochemistry is essentially capable of operating with locally superheated liquids-electrolytes of different phase composition (two-phase and multiphase systems) and heterogeneous, partially structured soft-matter media such as micellar systems [88,89].…”

Microwave Reflectance Studies of Photoelectrochemical Kinetics at Semiconductor Electrodes. 1. Steady-State, Transient, and Periodic Responses

“…Perturbation of the semiconductor|electrolyte system by light alters the local dielectric properties primarily as the result of changes in the local concentration of free carriers (electrons and holes). The change in the reflected microwave power Δ R M can be related to the change in the conductivity of the sample . Δ R M is defined as Here Δ P r is the change in reflected microwave power, and P in is the incident microwave power.…”

“…The mean value of this conductivity change, 〈Δ σ 〉, can be calculated by integrating the profiles of excess electrons and holes in the sample: (Δ n ( x ) and Δ p ( x )). It has been proposed that the measured microwave response is a linear function of the mean conductivity change, so that Here S is the sensitivity factor with units Ω cm, 〈Δ σ 〉 is the mean conductivity change, Δ σ ( x ) is the position dependent change in conductivity, d is the sample thickness, and μ n and μ p are the electron and hole mobilities. It should be noted here that the mobilities could be lower than the values characteristic of the bulk semiconductor if accumulation or inversion layers are formed. − In principle, S can be calculated using the Fresnel equations 17 (see below), but it is usually more convenient to measure it experimentally.…”

“…The key point recognized by Tributsch and co-workers , is the fact that microwave reflectance methods can detect the buildup and decay of minority carriers near the surface of a semiconductor electrode. When a photoelectrode is illuminated under depletion conditions, minority carriers in the space charge region are driven toward the semiconductor|solution interface, where their concentration builds up until a steady-state situation is achieved.…”

Microwave Reflectance Studies of Photoelectrochemical Kinetics at Semiconductor Electrodes. 2. Hydrogen Evolution at p-Si in Ammonium Fluoride Solution

“…The theory of light-induced microwave reflectance changes at the semiconductor|electrolyte junction was developed initially by Kunst and Tributsch, together with their collaborators. − In a preceding paper in this series, we have reviewed the theoretical foundations for the interpretation of light-induced microwave reflectivity measurements, including the responses to transient and periodic illumination. Profiles of the electron and hole concentrations computed numerically from a Hall Shockley Read model of the semiconductor|electrolyte junction were used to calculate the mean change in electronic conductivity, 〈Δ σ 〉, of the silicon sample as a function of photon flux, band bending, and rate constant for interfacial electron transfer.…”