Effects of phonon scattering on the electron transport and photocurrent of graphene quantum dot structures

The nonequilibrium Green’s function (NEGF) on the basis of unitary transformation is used to study the effects of phonon scattering on the electron transport and photocurrent of rectangular Armchair graphene quantum dots (GQD) in different lengths and widths. Applying the Landauer–Buttiker formalism, the electron current and photocurrent is calculated. The noninteracting Hamiltonian is interpreted as nearest neighbor tight-binding model, and electron–phonon interaction contribution to the earlier Hamiltonian is written using the Holstein model. The obtained results show that electron–phonon coupling has three major effects: (i) phonon-assisted and phonon-restricted effect on the electron transport and photocurrent, (ii) increasing the band gap in the absence of photon radiation, and (iii) increasing and decreasing the band gap in the presence of photon radiation

Comparison of alkali metal cationmetal cation (Rb/K) doping effect on the structural, optical and photovoltaic behavior of methylammonium lead triiodide perovskite thin films

Metal cation doping is an established strategy to increase the efficiency of perovskite solar cells. However, the underlying mechanism is less discussed regarding the doping site. In this paper, the effect of rubidium/potassium as dopant has been evaluated on the CH3NH3PbI3 (MAPbI(3)) perovskite lattice. At the 5% doping level, K cations have significantly improved photovoltaic properties by promoting crystallinity, releasing the strain, reducing the trap states, and boosting all key photovoltaic parameters. Moreover, this study provides a rough description of Rb/K doping mechanisms in the MAPbI(3) lattice, where K cations occupy the interstitial sites while both interstitial and substitutional occupancies may occur for Rb cations. Our findings help to adjust the properties of perovskite layers to design new materials with better photovoltaic performance.Funding Agencies|Ferdowsi University of Mashhad [3/45854]; Ministry of Science, Research and Technology of Iran</p

Reduced graphene oxide/TiO2/NiFe2O4 nanocomposite as a stable photocatalyst and strong antibacterial agent

Abstract In this study, we prepared reduced graphene oxide (rGO)/titanium dioxide (TiO2)/nickel ferrite (NiFe2O4) nanocomposites with different mass ratios of rGO, TiO2, and NiFe2O4 by a simple hydrothermal method. These nanocomposites were found to exhibit enhanced visible light harvesting, reduced electron–hole recombination, and improved magnetic properties compared to rGO, TiO2, and NiFe2O4. The study evaluated the photocatalytic and antibacterial activity of the nanocomposites, with particular emphasis on the GTN211 (with a mass ratio of 2:1:1 for rGO:TiO2:NiFe2O4) nanocomposite. The results showed that the GTN211 nanocomposite exhibited the best photocatalytic performance under both UV and visible light irradiation, achieving 95 and 89% degradation of Methylene Blue dye in 15 min, respectively. The study also investigated the photodegradation mechanism using various scavengers and found that holes were the main active species in the process. In addition to photocatalytic activity, the GTN211 nanocomposite also showed good antibacterial activity against Escherichia coli and Staphylococcus aureus bacteria, with the minimum inhibitory concentration of 1 mg mL−1 for both bacteria and a minimum bactericidal concentration of 0.8 and 1 mg mL−1, respectively. Hence, the GTN211 nanocomposite has potential as a material for environmental remediation and biomedical applications. The combination of photocatalytic and antibacterial activity makes this material a promising candidate for a wide range of applications

Topological phase in oxidized zigzag stanene nanoribbons

First-principles and semi-empirical tight binding calculations were performed to understand the adsorption of oxygen on the surface of two dimensional (2D) and zigzag stanene nano-ribbons. The intrinsic spin-orbit interaction is considered in the Kane-Mele tight binding model. The adsorption of an oxygen atom or molecule on the 2D stanene opens an electronic energy band gap. We investigate the helical edge states and topological phase in the pure zigzag stanene nano-ribbons. The adsorption of oxygen atoms on the zigzag stanene nano-ribbons deforms the helical edge states at the Fermi level which causes topological (non-trivial) to trivial phase transition. The structural stability of the systems is checked by performing Γ-point phonon calculations. Specific arrangements of adsorbed oxygen atoms on the surface of zigzag stanene nano-ribbons conserve the topological phase which has potential applications in future nano-electronic devices

Interaction of longitudinal phonons with discrete breather in strained graphene

We numerically analyze the interaction of small-amplitude phonon waves with standing gap discrete breather (DB) in strained graphene. To make the system support gap DB, strain is applied to create a gap in the phonon spectrum. We only focus on the in-plane phonons and DB, so the issue is investigated under a quasi-one-dimensional setup. It is found that, for the longitudinal sound waves having frequencies below 6 THz, DB is transparent and thus no radiation of energy from DB takes place; whereas for those sound waves with higher frequencies within the acoustic (optical) phonon band, phonon is mainly transmitted (reflected) by DB, and concomitantly, DB radiates its energy when interacting with phonons. The latter case is supported by the fact that, the sum of the transmitted and reflected phonon energy densities is noticeably higher than that of the incident wave. Our results here may provide insight into energy transport in graphene when the spatially localized nonlinear vibration modes are presented

Antibacterial Evaporator Based on Wood-Reduced Graphene Oxide/Titanium Oxide Nanocomposite for Long-Term and Highly Efficient Solar-Driven Wastewater Treatment

Herein, we developed antifouling and highly efficient solar absorbers consisting of poplar wood coated with titanium dioxide (TiO2) and reduced graphene oxide (RGO) nanocomposites (with different weight ratio of TiO2 to RGO). The antibacterial activity of all prepared nanocomposites against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) was investigated. The results showed that T2G1 (a nanocomposite in which the weight ratio of TiO2 to RGO is 2:1) has the highest antibacterial activity among all nanocomposites (MIC of 0.08 and 0.08 mg mL–1 and MBC of 0.6 and 0.8 mg mL–1 for E. coli and S. aureus, respectively). Therefore, it was considered to be the most efficient photothermal material for interfacial solar desalination and solar-driven treatment of wastewater. Because of the broad-band solar absorption by T2G1, the solar absorber composed of T2G1 and wood (denoted as T2G1-w) showed a high energy conversion efficiency of 90.12% under 1 sun (1 kW m–2). T2G1-w also had a high stability for long-term cycles. T2G1-w also showed great performance of freshwater production from contaminated water containing dye or heavy metals. The concentration of heavy metals of Zn2+, Pb2+, Fe2+, Ni2+, and Cr6+ reduced from 1000 mg L–1 to near zero in the presence of the prepared solar absorber, indicating its great potential application for sewage treatment