Fundamental processes in organic spintroncis

Introduction. When heating with high-frequency currents (HFCs) at high speeds, more significant strengthening effects can be observed compared to using machine generators. Therefore, hardening at high frequencies is more efficient. However, the increase in the generator frequency results in a decrease in the depth of penetration of eddy currents and an increased unevenness of heating across the cross-section. The application of a constant external magnetic field during HFC hardening can increase the depth of eddy current penetration and create more uniform heating. Unfortunately, there is not enough information available on the effect of the external magnetic field on HFC heating processes and phase transformations in steel. Currently, there are no quantitative estimates for the impact of an external magnetic field on changes in the kinetics of electric heating and the penetration depth of eddy currents. In connection with the above, the aim of this paper is to investigate changes in the kinetics of high-frequency heating of iron-carbon alloys when an external constant magnetic field is applied and, and, based on this, to consider the potential for technological applications. Materials and Methods. Theoretical assessment of the influence of an external magnetic field on the change in the kinetics of electric heating and the penetration depth of eddy currents is based on the general theory of induction heating kinetics. An experimental study of the influence of a magnetic field on the kinetics of high-frequency current heating was performed on samples of 45 steel, pearlitic gray (SCh30), and ferritic malleable cast iron (KCh30-6). The temperature distribution over the cross-section of ferromagnetic materials during induction heating with an external magnetic field has been studied using special samples of iron, 45 steel, and SCh30 gray pearlitic cast iron. Electric tempering processes have been investigated on samples of U8A steel using a vacuum tube generator (heating temperature — 450℃, heating rate — 750℃/s). Changes in austenite grain size after high-speed heating with external magnetization have been examined on samples of reduced-hardenability 55PP steel. To study the processes of thermal treatment in a magnetic field during experiments involving heating samples using high-frequency currents, a specially designed electromagnet was created to apply an external constant magnetic field. Results. Theoretical curves were constructed for heating conditions with and without an external constant magnetic field. Experimental data on the effect of an external constant magnetic field on induction heating in the surface layer of various materials were summarized in kinetic diagrams. Evidence that the observed changes were due to increased depth of penetration of eddy currents came from experiments on cylindrical samples of 45 steel with different wall thicknesses. Kinetic curves were provided for estimating the temperature field (at 6 points at different depths) during high-frequency current heating with and without external magnetization. The paper presents experimental data on the micro-hardness distribution across the cross-section of a U8 steel sample after quenching, quenching and electric tempering, quenching and electric tempering with external magnetization, and quenching and bulk tempering. It also includes the results of the study of the austenite grain size of 55PP steel after high-speed heating with external magnetization and conventional (slow) deep heating. Discussion. The application of a high-intensity external constant magnetic field during the first quasi-stationary process resulted in a decrease in the rate of induction heating of the ferromagnetic material and an increase in the depth of its uniform heating. However, above the Curie point, the effect of the magnetic field was negligible due to the low magnetic susceptibility of the material, and the heating rate remained unchanged as if there was no field present. In addition, due to the insignificant difference in the values of magnetic permeability below and above the Curie point during heating in the field, the thermal curve did not exhibit the characteristic inflection typical of kinetic curves observed during the transition of the surface layer to a paramagnetic state. Experiments with electric tempering have demonstrated that by applying an external field, it was possible to temper a material to the desired depth and it could be done on a single high-frequency current setup. The size of the austenite grains after high-speed heating with magnetization was reduced compared to conventional deep heating of steel with low hardenability, eliminating the issue of induction heating for low-hardenability steel. Conclusion. The results of the study demonstrated that the use of an external magnetic field enabled the achievement of strengthening effects during heating at higher frequencies, thereby eliminating the drawbacks of such heating methods.

Plastic spintronics : spin transport and intrinsic magnetoresistance in organic semiconductors

The effects of the intense laser and magnetic fields on the group velocity of light in GaAs/Al0.3Ga0.7As near-surface quantum well

Recently there has been much interest in combining the fields of organic electronics and spintronics. This has been motivated by the fact that low atomic mass of organic materials are predicted to have long spin lifetimes. Also, spintronic devices could benefit from the chemical tunability, ease of fabrication, and mechanical flexibility of organic semiconductors. The nascent field of organic spintronics has already presented many new phenomena which must be explained with novel physics, here we explore one of these phenomena, organic magnetoresistance (OMAR). OMAR is a room temperature spintronic effect in organic devices without any magnetic materials. OMAR is a large change in resistance (up to 25%) at low magnetic fields ( 20mT). OMAR represents a scientific puzzle since no traditional magnetoresistance mechanisms can explain the combination of properties listed above. Another one of the remarkable properties of OMAR is that the sign of the MR can change based operating conditions of the device, like temperature and voltage. In this dissertation we focused in particular on resolving the origin of the sign change since understanding this unique property should be a major step in unraveling the microscopic origin of OMAR. We have explored the properties of the sign change experimentally with bipolar semiconducting small molecule and polymer devices, in which we observed sign changes as functions of voltage and temperature. These devices showed a strong correlation between the sign change and the onset of minority charge carrier injection and we could describe the lineshape and MR(V) behavior as a superposition of two MR effects of opposite sign. From this work we concluded the separate MR effects were from the mobilities of holes and electrons having different responses to magnetic fields, which is best described by the bipolaron model for OMAR. To test this conclusion, we employed analytical and numerical device models assigning separate magnetomobilities to holes and electrons. The models show, counter-intuitively, that in the case when the minority charge carrier contact is injection limited, a decrease in minority charge carrier mobility increases the current. This is a result of the minority carrier contact acting like a constant current source, and of the compensation of the majority carrier space charge by the oppositely charged minority carriers. We show that these models describe the observed MR(V) behavior very well, and if one assumes the magnetic field acts to reduce the mobility of electrons and holes, we observe that our models can reproduce all the sign changes observed in literature. The device model also predicts how different device parameters affect the observed MR, to test its predictions we performed experiments in which we increased the charge recombination by dye doping the organic active layer, we also observed how changing the charge injection by altering the organic semiconductor/ metal contacts experimentally compared with the device model. The fact that the current can increase when the minority carrier mobility decreases may explain the fact that in experiments the magnitude of the negative MR features has been much larger than the positive MR features, even though, microscopically, the bipolaron model predicts the opposite. Therefore, the presence of both signs of magnetoresistance may be related only to the device physics and not to the microscopic mechanism which causes OMAR.

view Abstract Citations (9) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Effect of a Vertical Magnetic Field on the Propagation of Gravity Waves Along the Plane Surface of a Semi-Infinite Viscous, Electrically Conducting Fluid. Roberts, P. H. ; Boardman, A. D. Abstract The basic equations and boundary conditions governing the effect of vertical magnetic and gravitational fields on small-amplitude perturbations of the free equilibrium surface of a viscous, electrically conducting fluid are presented Normal modes are examined. A dispersion relationship is derived which relates the complex "frequency" n of the normal mode to the Allven velocity, V, the viscosity, , the magnetic diffusivity, X, and the horizontal wave number, k. This dispersion relationship is solved in nine extreme cases In six of these, the magnetic field is too weak to modify substantially the familiar gravity- wave solution holding in the absence of a magnetic field. The influence of the field is so strong in the remaining three cases that they have no parallel in the zero-field case One of these holds for any k if the magnetic field is sufficiently strong In this case n = gV-l(X/ l/2 i e, the effect of the magnetic field is so great that the disturbance is attenuated aperiodically as the Aliven waves radiate energy away from the free surface. Another interesting feature demonstrated is the existence (if V is sufficiently large) of a band of wave numbers k for which no normal-mode solution exists It is nevertheless demonstrated that the associated initial-value problem can be solved for such values of k. In addition to the nine extreme cases mentioned above, three special cases are solved for all k for particular values of V, namely, p = p = 0, and X = 0. Publication: The Astrophysical Journal Pub Date: March 1962 DOI: 10.1086/147291 Bibcode: 1962ApJ...135..552R full text sources ADS |

Organic materials with attractive electronic and optoelectronic properties are in high demand for functional electro-optical device applications. Research on synthetic polymer and organic small molecules has gained a great deal of attention due to their potential applications in low cost, ultra-thin, and flexible products and are expected to have a revolutionary role in modern day life. Basically, organic semiconductors are imperative for a range of optoelectronic applications including organic photovoltaic devices, light-emitting diodes, organic light-emitting transistor and organic field effect transistor-driven photonics since they possess photoluminescence, electroluminescence, and nonlinear optical properties in addition to liquid crystalline, structural patterning, printing and solution casting abilities. Electronic devices based on organic materials can be fabricated by simple processing techniques and are under intense investigation in academic and industrial laboratories because of their potential for mass production of flexible and cost-effective devices models. Organic devices also possess light-weight and transparent advantages compared to silicon-based devices. Significant progress has been achieved in the development of novel materials and new device engineering in the last decade. In this regard, arylene diimide families have shown high promise as useful building blocks for the fabrication of next-generation electronic and optoelectronics devices, providing deeper insight into their transistor characteristics at the molecular scale to practical applications ranging from medicine to high end security systems. These organic compounds are being developed for improved resistance to thermal and environmental stresses, which is one of the major challenges in the field. Several other classes of compounds based on fullerene (C60) and chemically modified thiophenes are also being explored and developed for use in a plethora of devices encompassing interdisciplinary research areas. These devices, owing to their low-cost, ease of synthesis and processing, are expected to pave the way for next-generation electronics with energy-efficient security systems, sensors, photonics, and spintronic memories. In this chapter we present a brief review on the different types of organic devices, their fabrication processes, and recent applications by citing examples of oligomers and polymers.

Magnetic Field Effects in Organic Semiconducting Materials and Devices

Molecular doping is an effective tool to enhance bulk conductivity, increase carrier injection and de-activate electron or hole traps in organic molecular and polymer semiconductors. Considerable effort has been directed toward the synthesis of powerful and stable p-type and n-type molecular dopants over the past decade.[1,2] This talk reviews a range of molecular redox agents used in organic electronics, with focus on strong reductants and oxidants for organic semiconductors with low electron affinity (EA) and large ionization energy (IE), respectively. In particular, we look at air-stable dimers, e.g. [RuCp*Mes]2, formed of 19-electron organometallic sandwich compounds able to reduce organic semiconductors with EA well below 3 eV.[3] We review powerful single-electron molecular oxidants, e.g. F6-TCNNQ and CN6-CP, which can introduce holes in organic semiconductors with IE larger than 5.6 eV. Applications of these n- and p-dopants to improve the conductivity of carrier injection layers and create large gap semiconductor p-i-n structures are described.[4] The last part of the talk focuses on recent work on adduct-based p-doping of organic semiconductors, applicable to a range of hole transport materials.[5][1]S. Barlow, S.R. Marder, X. Lin, F. Zhang and A. Kahn, Electrical Doping of Organic Semiconductors with Molecular Oxidants and Reductants, Handbook of Conducting Polymers (2019)[2] G. Song, S.B. Kim,S. Mohapatra, Y. Qi, T. Sajoto, A. Kahn, S.R. Marder, S. Barlow, n-Doping of Organic Electronic Materials Using Air-Stable Organometallics, Adv. Mat. 24, 699 (2012)[3] X. Lin, B. Wegner, K. M. Lee, M. A. Fusella, F. Zhang, K. Moudgil, B. P. Rand, S. Barlow, S. R. Marder, N. Kochand A. Kahn, Beating the Thermodynamic Limit: Photo-Activation of n-Doping in Organic Semiconductors, Nature Materials 16, 1209 (2017)[4] H. L. Smith, J. T. Dull, S. Mohapatra, S. Barlow, S. Marder, B. P. Rand, and A. Kahn, Powerful organic molecular oxidant and reductant enable a large gap, blue light-emitting organic homojunction diode, ACS Appl. Mat. Int. 14, 2381 (2022)[5] N. Sakai, R. Warren, F. Zhang, S. Nayak, S. V. Kesava, Y.-H. Lin, H. S. Biswal, X. Lin, A. Kahn, M. Riede, P. K. Nayak and H. J. Snaith, Adduct-based p-doping of Organic Semiconductors, Nature Materials, 20, 1248 (2021)

Organic semiconductors devices, such as, organic solar cells (OSCs), organic light-emitting diodes (OLEDs) and organic field-effect transistors (OFETs) have drawn increasing interest in recent decades. As organic materials are flexible, light weight, and potentially low-cost, organic semiconductor devices are considered to be an alternative to their inorganic counterparts. This dissertation will focus mainly on OSCs and OLEDs. As a clean and renewable energy source, the development of OSCs is very promising. Cells with 9.2% power conversion efficiency (PCE) were reported this year, compared to < 8% two years ago. OSCs belong to the so-called third generation solar cells and are still under development. While OLEDs are a more mature and better studied field, with commercial products already launched in the market, there are still several key issues: (1) the cost of OSCs/OLEDs is still high, largely due to the costly manufacturing processes; (2) the efficiency of OSCs/OLEDs needs to be improved; (3) the lifetime of OSCs/OLEDs is not sufficient compared to their inorganic counterparts; (4) the physics models of the behavior of the devices are not satisfactory. All these limitations invoke the demand for new organic materials, improved device architectures, low-cost fabrication methods, and better understanding of device physics. For OSCs, we attempted to improve the PCE by modifying the interlayer between active layer/metal. We found that ethylene glycol (EG) treated poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT: PSS) improves hole collection at the metal/polymer interface, furthermore it also affects the growth of the poly(3- hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) blends, making the phase segregation more favorable for charge collection. We then studied organic/inorganic tandem cells. We also investigated the effect of a thin LiF layer on the hole-collection of copper phthalocyanine (CuPc)/C70-based small molecular OSCs. A thin LiF layer serves typically as the electron injection layer in OLEDs and electron collection interlayer in the OSCs. However, several reports showed that it can also assist in holeinjection in OLEDs. Here we first demonstrate that it assists hole-collection in OSCs, which is more obvious after air-plasma treatment, and explore this intriguing dual role. For OLEDs, we focus on solution processing methods to fabricate highly efficient phosphorescent OLEDs. First, we investigated OLEDs with a polymer host matrix, and enhanced charge injection by adding hole- and electron-transport materials into the system. We also applied a hole-blocking and electron-transport material to prevent luminescence quenching by the cathode. Finally, we substituted the polymer host by a small molecule, to achieve more efficient solution processed small molecular OLEDs (SMOLEDs); this approach is cost-effective in comparison to the more common vacuum thermal evaporation. All these studies help us to better understand the underlying relationship between the organic semiconductor materials and the OSCs and OLEDs’ performance and will subsequently assist in further enhancing the efficiencies of OSCs and OLEDs. With better efficiency and longer lifetime, the OSCs and OLEDs will be competitive with their inorganic counterparts.

An irreversible electrochemical reaction from material interaction with the environment and causing degradation is known as corrosion. The electrolyte changes significantly affect the corrosion's reaction kinetics. Unknown factors and various notable factors influence the corrosion rate of a particular material in the environmental system. Significant interest in magnetic fields and their effects on electrochemical reactions have recently been gained. This paper studies the effect of an external magnetic field on the electrochemical oxidation of Aluminum (Al) in a 3,5% NaCl solution. The magnetic field 0; 0,8; 1,4; and 2,1 Tesla were used to expose the samples during corrosion testing. We found that the effect of a magnetic field on electrochemical oxidation shifts the oxidation potential to higher or lower than the oxidation potential without a magnetic field. Moreover, the oxidation potential's value depends on the magnetic field's intensity.

Organic electronics has made great progress in the past decades, which is inseparable from the innovative development of organic electronic devices and the diversity of organic semiconductor materials. It is worth mentioning that both of these great advances are inextricably linked to the development of organic high-performance semiconductor materials, especially the representative n-type organic small-molecule semiconductor materials with high electron mobilities. The n-type organic small molecules have the advantages of simple synthesis process, strong intermolecular stacking, tunable molecular structure, and easy to functionalize structures. Furthermore, the n-type semiconductor is a remarkable and important component for constructing complementary logic circuits and p-n heterojunction structures. Therefore, n-type organic semiconductors play an extremely important role in the field of organic electronic materials and are the basis for the industrialization of organic electronic functional devices. This review focuses on the modification strategies of organic small molecules with high electron mobility at molecular level, and discusses in detail the applications of n-type small-molecule semiconductor materials with high mobility in organic field-effect transistors, organic light-emitting transistors, organic photodetectors, and gas sensors.

Effects of magnetic field on the viscosity of molten Cu–Sn alloys

The deployment of organic semiconducting materials for radiation detection is an emerging and highly attractive area of materials science research. These organic materials offer the enticing vision of technologies created from low-cost materials that can be printed on-demand with a range of different tailored optoelectronic functionalities. An explosion in the number of available materials, improved functionality of materials, and sophistication of solution-based device fabrication techniques for organic semiconductors in recent years have led to considerable opportunities for the utilization of organic materials in the detection of ionizing radiation. While the potential of organic semiconducting materials for low-cost radiation detection is clear, transitioning these printable materials to a commercial reality presents a significant scientific challenge. In this work, we provide a comprehensive analysis of the use of organic semiconductors for radiation detection. We discuss the fundamental physics of these materials and how their conduction mechanisms, including charge generation and charge transport, differ significantly from established inorganic semiconductors. Various strategies employed to control the nanostructure in organic semiconductors to optimize charge generation and transport for radiation detection are discussed. We provide insights into the strategies employed to fabricate organic semiconducting devices at industrially relevant scales using roll-to-roll solution processing and finally discuss existing examples of organic semiconducting materials utilized in the radiation detection arena.

Studies of spin current injection, transport, and interface control have drawn attention recently for efficient organic spintronic devices. In this study, we apply both spin pumping (SP) and the longitudinal spin Seebeck effect (LSSE) to inject spin currents into a π-conjugated organic semiconductor, perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), and characterize injection and transport by measuring inverse spin Hall voltage VISHE in spin detectors. A normalization factor introduced to SP analysis eliminates a contribution provoked by deviation of spin sources and leads to a more accurate determination of the spin diffusion length in PTCDA. While SP with Permalloy as a spin source is effective in generating detectable VISHE, the LSSE from yttrium iron garnet shows no convincing sign of spin injection. In addition, spin-flip scattering induced by hybrid states undermining electrical spin injection is negligible in SP. These results are attributed to interfaces between spin sources and PTCDA, indicative of the importance of injection methods and material choices.

The influence of the magnetic field on the convective heat transfer characteristics of Fe3O4/water nanofluids