OAJ Materials and Devices

What is the weight: how and why it occurs for gaseous matter

2024-02-01T16:19:42+00:00

A pure mechanical approach is proposed to gain a more penetrating insight into the physical meaning of the body’s weight, in deducing its notion just from the Newton’s equation for the body moving along the gravitational field. In that view, the body is weighty when its acceleration along the g-field is other than g. The approach was used for to account the occurrence of the gaseous matter weight that was regarded by us as some sort of experimentum crucis capable of estimating its validity. According to the results obtained, the body’s weight is a physical reality fundamentally different from the force of gravity, and represents the inevitable factor assuring the fulfilment of the momentum conservation law in the body – Earth system.

Insight into negative trions binding energy behavior inside type-I and reversed type-I core/shell quantum dots: A variational analysis

2023-06-01T16:36:51+00:00

Many body interactions between single particles inside low-dimensional semiconducting materials play a critical role in their optical characteristics. Within this context, tuning trionic and excitonic binding energy enables tailoring of the optical band gap of a given material. In this paper, we theoretically investigated the binding energy (Eb) of negatively charged excitons inside GaN/AlN type-I, and AlN/GaN inverted type-I core/shell quantum dots. Firstly, we started our study by examining the variation in the energy of electrons (holes) according to the change in the internal and external radii { as a means to obtain an insight into the energetic behavior of non-correlated single particles inside the two understudied nanosystems. The feature of the radial probability density distribution of confined single particles and negative trions is also discussed. Afterwards, we examined the impact of the heteronanodot spatial parameters (core radius and shell thickness) on the binding energy of confined trions. A comparison between the Eb behavior of negative trions inside core/shell type-I, and reversed type-I nanodots is also highlighted. Our results exhibit a strong dependence of the negative trion binding energy on the core material size and the shell thickness, and on the core-to-shell band mismatch as well. The obtained data also show the opportunity of modulating the negatively charged exciton correlation energy in a broad range extending from 220 to 650 meV . That paves the way for new optoelectronic devices based on III-Nitride core/shell quantum dots.

Theoretical study of structural phase transition and soft mode behavior in moganite

2024-02-06T22:23:56+00:00

Changes in the structure and lattice dynamics of the moganite during crystal expansion were studied using ab initio calculations within the framework of density functional theory. The obtained results shed light on many anomalies in the temperature behavior of this crystal, such as the presence of a phase transition, soft mode condensation, elastic anomalies and negative thermal expansion. Comparison of the structural and dynamic properties of moganite and quartz opens up new possibilities for their identification in natural samples of mixed composition.

Book: Perovskites and other Framework Structure crystalline materials

2023-10-18T18:15:24+00:00

Perovskites are among the most famous materials due to their exceptional properties : they
present nearly all existing types of ferroic and multiferroic properties (ferroelectric,
ferromagnetic, antiferroelectric, antiferromagnetic, magnetoelectric, etc), they may be
insulators, (super)conductors, or semiconductors, are used in numerous devices, they present
hundreds of variants and different crystalline phases, and recently appeared as probably the
most promising materials for photovoltaics. With a crystal structure characterized by octahedra
that share their corners, these materials belong to the wider category of « Framework Structure
(FWS) materials » the structure of which is based on units (octahedra, tetrahedra, ...) that
share some of their corners with their neighbours. This particular feature of FWS materials
confers to them unique properties.
This review volume is constituted of 26 chapters on different aspects, and is divided in two
parts, « Fundamental aspects and general properties », and « Elaborated materials and
applied properties ». Its main purpose is to attempt to identify the properties common to all
members of the vast family of FWS materials, and understand their differences. Besides
perovskites, derived compounds as 2D perovskites, Dion-Jacobson, Ruddlesden-Popper,
Aurivillius, tungsten-bronzes, and others, predominantly oxides, are presented, and their
preparation and/or properties as single crystals, ceramics, thin films, multilayers, nanomaterials,
nanofibers, nanorods, etc, are discussed. We focus on new trends and important recent
developments by leaving somewhat aside more classical aspects which can be easily found in
older textbooks or review articles.
Among most recent applications, this volume focuses on applications related with interactions
with other molecules, on photovoltaics, and on memories, with a special attention to perovskite
solar cells that have certainly attracted the most attention of researchers in recent years,
opening extremely promising routes in photovoltaics.
In conclusion, this book presents a collection of texts elucidating various aspects of the
phenomena related to the structural instabilities and singular properties of framework crystals ;
it proposes a reasonable balance between experimental and theoretical results, and between
fundamental aspects and applied properties.
This volume can be approached on several levels (each chapter initially assumes that the reader
is not a specialist in the subject, and is presented in a pedagogical way) : it is accessible to
master or doctoral students, as well as to researchers who want to enter the subject, or have
informations on recent developments, who will find excellent detailed introductions up to hot
subjects. It may also be used by undergraduate students who should approach given subjects. The volume contains 800 pages written by about 70 authors from different countries, it has an indexn and is completed by numerous figures to illustrate the text.

Template for Opinion and Methods articles

2023-05-10T17:12:59+00:00

Updated file to be used to write an Opinion article or a Methods article

Standard template

2023-05-10T16:49:57+00:00

Updated template to be used.

Template

2023-05-10T16:55:32+00:00

Updated template to be used for review articles.

Real Solar Cell and Determination Methods of Electrical Parameters

2023-01-17T23:13:23+00:00

In this work, we develop methods to determine the characteristic electrical parameters of a photovoltaic cell such as the photocurrent density (J_ph), the saturation current density (J₀), the short-circuit current density (J_sc), the open-circuit voltage (V_oc), the maximum power density point (J_m , V_m), the fill factor (FF) and the electrical conversion efficiency (eta_C) according to the irradiance spectrum. The real solar cell model is considered for the determination of these various parameters. This model takes into account the effect of shunt and series resistances (parasitic resistances). Notions of semiconductor physics, continuity equation of charge carriers combined to optoelectronic and geometrical properties of the materials, numerical resolution method to solve implicit equations based on characteristic equation of a photodiode, are notions mainly exploited to determine electrical parameters of the real solar cell. The results are applied to the heterostructures ZnO(n⁺)/CdS(n)/CuInS₂(p)/ CuInSe₂(p⁺) named CIS and ZnO(n⁺)/CdS(n)/CuInSe₂(p)/CuInS₂(p⁺) named CISE to evaluate their performances according to the considered parameters. The results obtained for each structure, photocurrent density ~ 17 mA.cm^-2 (CIS) and 31 mA.cm^-2(CISE), short-circuit current density ~ 16.79 - 17 mA.cm^-2 (CIS) and 30.62 - 31 mA.cm^-2 (CISE), open-circuit voltage ~ 0.76 V (CIS) and 0.52 V (CISE), fill factor ~ 0.648 - 0.745 (CIS) and 0.545 - 0.677 (CISE), maximum power density ~ 8.28 - 9.69 mW.cm^-2 (CIS) and 8.72 - 11.02 mW.cm^-2 (CISE), saturation current ~ 4.117×10^-8 mA.cm^-2 (CIS) and 1.169×10^-3 mA.cm^-2 (CISE), are in the same magnitude order as the values published in the literature. We obtain under AM 1.5 solar spectrum and taken into account the parasitic resistances, a theoretical conversion efficiency ranging from 9.93% to 11.62% for the model CIS and from 10.46% to 13.22% for the model CISE. Thus, these results allow to validate the various models established to model the phenomena studied.

A critical view on citation index

2023-03-21T20:27:21+00:00

This “opinion article” presents the “dialogue”, namely the series of questions addressed to chatGPT and its outputs, on the question of citation index and other metrics associated with scientific publication. The AI is asked to explain basic quantities (citation index, impact factor of journals, h-index, etc) and through different questions, to give outputs on different important problems, mainly related with citation index and its biases. The AI clearly expresses that the citation index alone should not be used for evaluation purposes, and is led to predict that in certain situations a high quality scientific article would be with a low citation index. The AI also replies that the citation index depends on several factors in a complex way, and is probably not defined in an unambiguous way from a mathematical point of view, but it appears unable to explain evolutions in the field of informetrics that occurred following issues with citation index. The article concludes that the citation index is irrelevant as it is not normalized and strongly depends on the publishing journal and databases, and that it is potentially dangerous for science.