Catalin Harnagea

Bio: Catalin Harnagea is an academic researcher from Institut national de la recherche scientifique. The author has contributed to research in topics: Ferroelectricity & Pulsed laser deposition. The author has an hindex of 41, co-authored 133 publications receiving 5296 citations. Previous affiliations of Catalin Harnagea include Université du Québec & Max Planck Society.

Bandgap tuning of multiferroic oxide solar cells

Abstract: Tuning the bandgap of multiferroic solar cells made from Bi2FeCrO6 is achieved by cationic ordering and is shown to dramatically improve their performance.

Impact of misfit dislocations on the polarization instability of epitaxial nanostructured ferroelectric perovskites.

Abstract: Defects exist in almost all materials and defect engineering at the atomic level is part of modern semiconductor technology Defects and their long-range strain fields can have a negative impact on the host materials In materials with confined dimensions, the influence of defects can be even more pronounced due to the enhanced relative volume of the 'defective' regions Here we report the dislocation-induced polarization instability of (001)-oriented Pb(Zr(052)Ti(048))O(3) (PZT) nanoislands, with an average height of approximately 9 nm, grown on compressive perovskite substrates Using quantitative high-resolution electron microscopy, we visualize the strain fields of edge-type misfit dislocations, extending predominantly into a PZT region with a height of approximately 4 nm and width of approximately 8 nm The lattice within this region deviates from the regular crystal structure Piezoresponse force microscopy indicates that such PZT nanoislands do not show ferroelectricity Our results suggest that misfit engineering is indispensable for obtaining nanostructured ferroelectrics with stable polarization

High dielectric constant and frozen macroscopic polarization in dense nanocrystalline BaTiO3 ceramics

Abstract: Theoretical models for small ferroelectric particles predict a progressive decrease of the Curie temperature, spontaneous lattice strain, and polarization until the critical size corresponding to t ...

Polarization imprint and size effects in mesoscopic ferroelectric structures

Abstract: Piezoresponse scanning force microscopy measurements performed on lead zirconate titanate mesoscopic structures revealed a negative shift of the initial piezoelectric hysteresis loop. The shift is dependent on the size of the structure and is most probably due to the pinning of ferroelectric domains at the free lateral surface and ferroelectric–electrode interface. Considering a simple model, the thickness of the pinned domain layers is found to be about 15 and 70 nm at the ferroelectric–electrode interface and lateral free surface, respectively.

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

Abstract: Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

Applications of Modern Ferroelectrics

Abstract: Long viewed as a topic in classical physics, ferroelectricity can be described by a quantum mechanical ab initio theory. Thin-film nanoscale device structures integrated onto Si chips have made inroads into the semiconductor industry. Recent prototype applications include ultrafast switching, cheap room-temperature magnetic-field detectors, piezoelectric nanotubes for microfluidic systems, electrocaloric coolers for computers, phased-array radar, and three-dimensional trenched capacitors for dynamic random access memories. Terabit-per-square-inch ferroelectric arrays of lead zirconate titanate have been reported on Pt nanowire interconnects and nanorings with 5-nanometer diameters. Finally, electron emission from ferroelectrics yields cheap, high-power microwave devices and miniature x-ray and neutron sources.

Physics of thin-film ferroelectric oxides

Abstract: This review covers important advances in recent years in the physics of thin-film ferroelectric oxides, the strongest emphasis being on those aspects particular to ferroelectrics in thin-film form. The authors introduce the current state of development in the application of ferroelectric thin films for electronic devices and discuss the physics relevant for the performance and failure of these devices. Following this the review covers the enormous progress that has been made in the first-principles computational approach to understanding ferroelectrics. The authors then discuss in detail the important role that strain plays in determining the properties of epitaxial thin ferroelectric films. Finally, this review ends with a look at the emerging possibilities for nanoscale ferroelectrics, with particular emphasis on ferroelectrics in nonconventional nanoscale geometries.

1000 at 1000: The effect of electric field and pressure on the synthesis and consolidation of materials: a review of the spark plasma sintering method.

Abstract: The use of electric current to activate the consolidation and reaction-sintering of materials is reviewed with special emphasis of the spark plasma sintering method. The method has been used extensively over the past decade with results showing clear benefits over conventional methods. The review critically examines the important features of this method and their individual roles in the observed enhancement of the consolidation process and the properties of the resulting materials.

2D Homologous Perovskites as Light-Absorbing Materials for Solar Cell Applications

Abstract: We report on the fabrication and properties of the semiconducting 2D (CH3(CH2)3NH3)2(CH3NH3)n–1PbnI3n+1 (n = 1, 2, 3, and 4) perovskite thin films. The band gaps of the series decrease with increasing n values, from 2.24 eV (CH3(CH2)3NH3)2PbI4 (n = 1) to 1.52 eV CH3NH3PbI3 (n = ∞). The compounds exhibit strong light absorption in the visible region, accompanied by strong photoluminescence at room temperature, rendering them promising light absorbers for photovoltaic applications. Moreover, we find that thin films of the semi-2D perovskites display an ultrahigh surface coverage as a result of the unusual film self-assembly that orients the [PbnI3n+1]− layers perpendicular to the substrates. We have successfully implemented this 2D perovskite family in solid-state solar cells, and obtained an initial power conversion efficiency of 4.02%, featuring an open-circuit voltage (Voc) of 929 mV and a short-circuit current density (Jsc) of 9.42 mA/cm2 from the n = 3 compound. This result is even more encouraging con...