Band gap reduction and dielectric function of Ga1−xZnxN1−xOx and In1−xZnxN1−xOx alloys

Dou, Maofeng; Persson, Clas

doi:10.1002/pssa.201100148

Cited by 24 publications

(21 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In particulate heterogeneous photocatalyst systems, charge separation only relies on the formation of an effective semiconductor-electrolyte Schottky type of contact, and the efficient diffusion of charge carriers. The data points in Figure 2B represent experimentally measured absorption coefficients at different wavelengths, [11][12][13][50][51][52][53][54][55] where the inverse of this magnitude represents the penetration depth of the light into the semiconductor absorber. Thus, Figure 2A provides a qualitative and quantitative expectation of this charge collection region into the semiconductor photocatalyst based on carrier density.…”

Section: Resultsmentioning

confidence: 99%

A simplified theoretical guideline for overall water splitting using photocatalyst particles

Garcia‐Esparza

Takanabe

2016

J. Mater. Chem. A

View full text Add to dashboard Cite

Particulate photocatalytic water splitting is the most disruptive and competitive solution for the direct production of solar fuels. Despite more than four decades of work in the field of photocatalysis using powder semiconductors decorated with catalyst particles, there is no clear consensus on the factors limiting the solar-to-hydrogen efficiency (STH). To understand the intrinsic limitations of the system, we numerically simulated simplified two-dimensional photocatalytic models using classical semiconductor device equations. This work presents the sensitivity of quantum efficiency (QE) to the various semiconductor properties, such as absorption properties and carrier mobilities, and to the dispersion of catalyst particles, which create heterojunctions, the driving force for charge separation. As a result, a pinch-off effect was prevalent underneath the hydrogen evolution site, suggesting an undesired energetic barrier for electron diffusion to the catalyst. The simulation using the values reported in the literature revealed that the QE was exclusively governed by recombination in the bulk of the photocatalyst particles, hindering the charge separation efficiency before reaching the catalysts on the surface. Using some of the reported parameters, our simulation shows that a typical defective n-type semiconductor particle (~100 nm) ideally exhibits a QE of <5% in the visible light range per particle, which reaches only approximately 10% in a slurry after 4 consecutive absorbing units (1.4% STH, from simulated solar irradiation). Although the present model contains rigid limitations, we use these trends as an initial guideline to pursue a photocatalysis by design strategy, which may result in possible alternatives to achieve higher efficiencies. 9

show abstract

Section: Resultsmentioning

confidence: 99%

A simplified theoretical guideline for overall water splitting using photocatalyst particles

Garcia‐Esparza

Takanabe

2016

J. Mater. Chem. A

View full text Add to dashboard Cite

show abstract

“…The imaginary part of the dielectric function was calculated in the long wavelength limit from the joint density of states and the optical momentum matrix. Since the dielectric function in polar materials can depend strongly on the electron-phonon coupling, The results for ZnO and HfO2 are from calculations in this work using the GW0 method based on the DFT [28,32]; the first ZnO version neglects and the second includes phonon contributions. For SiO2 the first version is from an oscillator model [26], while the second is the present GW0 results.…”

Section: Calculation Of Dielectric Permittivitiesmentioning

confidence: 99%

Casimir attractive-repulsive transition in MEMS

et al. 2012

View full text Add to dashboard Cite

Unwanted stiction in micro-and nanomechanical (NEMS/MEMS) systems due to dispersion (van der Waals, or Casimir) forces is a significant hurdle in the fabrication of systems with moving parts on these length scales. Introducing a suitably dielectric liquid in the interspace between bodies has previously been demonstrated to render dispersion forces repulsive, or even to switch sign as a function of separation. Making use of recently available permittivity data calculated by us we show that such a remarkable nonmonotonic Casimir force, changing from attractive to repulsive as separation increases, can in fact be observed in systems where constituent materials are in standard NEMS/MEMS use requiring no special or exotic materials. No such nonmonotonic behaviour has been measured to date. We calculate the force between a silica sphere and a flat surface of either zinc oxide or hafnia, two materials which are among the most prominent for practical microelectrical and microoptical devices. Our results explicate the need for highly accurate permittivity functions of the materials involved for frequencies from optical to far-infrared frequencies. A careful analysis of the Casimir interaction is presented, and we show how the change in the sign of the interaction can be understood as a result of multiple crossings of the dielectric functions of the three media involved in a given set-up.

show abstract

“…The electronic structure neglecting electronphonon coupling is then obtained from the partial self-consistent GW 0 method where the Green's functions are updated iteratively, whereas the screened Coulomb potential W is fixed [14,15]. The imaginary part of the dielectric function is calculated in the long wavelength limit from the joint density of states and the optical momentum matrix.…”

mentioning

confidence: 99%

Casimir quantum levitation tuned by means of material properties and geometries

et al. 2014

Self Cite

View full text Add to dashboard Cite

The Casimir force between two surfaces is attractive in most cases. Although stable suspension of nano-objects has been achieved, the sophisticated geometries make them difficult to be merged with well-established thin film processes. We find that by introducing thin film surface coating on porous substrates, a repulsive to attractive force transition is achieved when the separations are increased in planar geometries, resulting in a stable suspension of two surfaces near the force transition separation. Both the magnitude of the force and the transition distance can be flexibly tailored though modifying the properties of the considered materials, that is, thin film thickness, doping concentration, and porosity. This stable suspension can be used to design new nanodevices with ultralow friction. Moreover, it might be convenient to merge this thin film coating approach with micro-and nanofabrication processes in the future. If the distance of two neutral objects is very close (typically nanoscale), the Casimir force, which arises from quantum fluctuations, becomes dominant and increases rapidly as the distance decreases. The force is generally attractive in configurations with vacuum separated dielectrics or metallic objects. By properly choosing the materials, such as magnetic compounds [1], fluid-separated dielectrics [2], or topological insulators [3], the force can, however, turn out to be repulsive. Although the fundamental theory of Casimir force has been well studied, tuning this force for potential technology applications is still in its infancy and has recently attracted considerable attention. As microelectromechanical systems [4,5] evolve into nanoelectromechanical systems, the attractive Casimir stiction phenomenon becomes important and has to be faced. On the other hand, such phenomena may also be of significant interest when designing new nanodevices, such as the Casimir anharmonic oscillator [6,7] or the ultrasensitive sensor [8]. Several interesting works have appeared regarding the use of repulsive Casimir force to achieve stable levitation of nano-objects, such as cylinder in cylinder [9], sphere on surface [10], or rotated hockey pucks [11]. Most of them are, however, achieved in sophisticated geometries that are difficult to fabricate using well-established micro-and nanofabrication technologies. In this work, we demonstrate by means of multilayer modeling that the Casimir induced quantum levitation can be achieved in traditional planar geometry containing nanosheets. Moreover, this configuration could be further extended to thin film cladding on a mesoporous substrate without destroying the quantum levitation. Remarkably, both the magnitude of the force and the levitation distance are tunable through modifying the properties of the involved materials, that is, the thickness of the film, the doping concentration, and the porosity.In this Rapid Communication we consider a configuration of four layers, labeled as m, j , s, and l. The retarded Casimir force acting on layer j per unit area include...

show abstract

Band gap reduction and dielectric function of Ga_1−xZn_xN_1−xO_x and In_1−xZn_xN_1−xO_x alloys

Cited by 24 publications

References 23 publications

A simplified theoretical guideline for overall water splitting using photocatalyst particles

A simplified theoretical guideline for overall water splitting using photocatalyst particles

Casimir attractive-repulsive transition in MEMS

Casimir quantum levitation tuned by means of material properties and geometries

Contact Info

Product

Resources

About