Fabrication of Nanostructures on the Base of Oxides of Mixed Valence Metals and Investigation of their Structural, Magnetic and Electron Properties
Tech Area / Field
- MAT-SYN/Materials Synthesis and Processing/Materials
- PHY-SSP/Solid State Physics/Physics
8 Project completed
Senior Project Manager
Latynin K V
Institute of Microelectronics Technology and High Purity Materials, Russia, Moscow reg., Chernogolovka
- NPO Lutch, Russia, Moscow reg., Podolsk
- URA 0073/Universite Paris-Sud / Laboratoire de Physique des Solides, France, Orsay
Project summaryMixed-valence perovskite oxides are materials displaying a number of interesting and important in practice phenomena such as metal-insulator transitions, magnetic ordering of different nature (ferromagnetism and antiferromagnetism), superconductivity. Because of this, they are of interest of a wide circle of researches throughout the world, which carry out both fundamental investigations aimed to reveal the nature of the above phenomena and applied research to develop manufacturing technology of perovskite oxides and creation of a variety of devices whose operation is based on electronic properties of the oxides. The latter direction of the research is given the title oxide electronics.
Since one of the most important tendencies of modern electronics is increasing of operation rate and recorded information density, it is currently central to create objects of decreasingly lower dimensions down to a few nanometers and to explore their properties. Creation and exploration of such objects give, on the one hand, a possibility to establish the fundamental lateral limitation for the existence of physical properties observed on microscopic size. On the other hand, it is probable to discover new physical effects only inherent to nm-sized objects and use them for elaborating the new types of electronic devices.
This project is directed to combine these two directions of investigations. Using achievements of modern microfabrication technology, a new fabrication technology of nanostructures of mixed-valence oxides will be developed. New information about their properties and perspectives of practical application will be obtained. Investigation of fundamental properties of oxide nanostructures is important for understanding the natures of physical phenomena observed both in nm-sized structures and in macroscopic samples as well, as it allows verifying theoretical models of electronic phenomena observed on a macroscopic scale.
The basic aims of the project are:
- investigation of phase equilibria at synthesis of perovskite oxides, revealing the origins of formation of non-homogeneous structure of metal-oxide materials,
- creation of metal-oxide nanostructures with the use of electron-beam lithography, thin film deposition technology and the original techniques of microfabrication developed in the Participating Institutions,
- studying electrical and magnetic properties of nanostructures in a wide range of temperatures and intensities of external magnetic field,
- diagnostics of nanostructures by scanning and transmission electron microscopy,
- development of physical models of electronic transport in oxide nanostructures on the base of obtained experimental data.
Nanostructures on the base of the following perovskite oxides considered as perspective materials for practical application will be fabricated in the project:
- rear-earth manganites Re1-xAxMnO3, where Re – a rear-earth element (La, Y etc.), A – an alkaline-earth element (Ca, Sr, Ba), manganese resides in Re1-xAxMnO3 in two valence states Mn3+ and Mn4+;
- yttrium-barium cuprates YBa2Cu3Oy (YBCO) containing mixed valence ions Cu2+ and Cu3+.
Manganites are actively studied because of the effect of colossal magnetoresistance (CMR), which nature has not clearly understood yet. This effect occurs, when a rear-earth element is substituted partially by an alkaline-earth one in the original perovskite ReMnO3, which is an insulator and antiferromagnetic, that leads to appearance of metallic and ferromagnetic properties of Re1-xAxMnO3 oxides. A sharp decrease of electrical resistance observed under applying external magnetic field depends strongly on preparation technology and may achieve of 104-105% in value. YBCO is a high-temperature superconductor with the critical temperature (Tc=90K) well above liquid nitrogen temperature (77K). Revealing the mechanism of high temperature superconductivity is an issue of the day.
The results of experiments obtained in the recent years indicate that manganites and oxide superconductors as well have non-homogeneous electronic and crystalline structures. From the known spatial resolutions of employed structural methods it follows that the inhomogeneity size lies in the range of a few nm (10-9 m), which explains the impossibility to detect such fine inhomogeneity by standard long-range structural methods. The understanding of the nature of non-homogeneous state of perovskite oxides and its possible relation with the CMR effect in manganites and the superconductivity mechanism in YBCO will be promoted extensively through studying properties of nanometer-sized samples. A relative contribution of separate inhomogeneities increases in such samples in comparison with macroscopic samples where the contributions are averaged.
To meet the project aims, a fabrication technology of nanostructures, which assures stability and reproduction of electrical and magnetic properties of nanostructures, will be developed. An important condition is the avoidance of essential degradation of oxide materials during technological operations. This is necessary, in particular, to provide for certain that properties of oxide nanostructures are determined exactly by the lateral effect, but not due to defects introduced during fabrication of nanostructures. A series of technological procedures, including thin film deposition by magnetron and laser sputtering, electron-beam lithography to form nanostructures topology, plasmachemical and ion etching, will be used. The basic method of diagnostics of investigated materials and nanostructures made of them will be scanning and transmission electron microscopy, which combine the ability to provide a large information data with a high spatial resolution.
Two types of oxide nanostructures are planned to fabricate and investigate: 1) one-dimensional conductors of 100-1000 nm in size lying on massive substrates; 2) freely suspending self-supporting conductors of 50-1000 nm in size. It will be studied electrical conductivity and magnetoresistance of manganite nanostructures in a wide range of temperatures and intensities of external magnetic field. Experimental data on the existence and magnitude of the effect of CMR and spin-polarized tunneling in nm-sized samples will be obtained. Expected results are important for revealing the nature of the CMR and for creation of nm-sized electronic devices on the base of manganites for magnetic systems of data recording and reading. The use of physical effects of strong response like as the CMR in electronic devices is important because it makes possible to maintain their operation stability despite the fact that the influence of thermal noise and spread of parameters increases with decrease of active elements of the devices down to nanometer sizes. Noise spectra and fluctuations of conductivity of YBCO nanostructures in the normal (non-superconducting) state and critical current in the superconducting state will be studied. The influence of static and dynamic magnetic field on electric current in YBCO nanostructures will be studied as well. The experiments should deliver the information on the possible existence of bosons (paired electrons) being in a non-correlated (non-superconducting) state at temperatures higher than the critical one. Besides, the information about possible fabrication of nanometer-sized superconducting sensors of magnetic field will be obtained.
The Participating Institutions have in disposal all the necessary equipment for fabrication of nm-sized nanostructures and studying electrophysical properties thereof. To fulfill the project tasks experimental set-ups devised for fabrication and investigation of nanostructures of different materials will be used. The project participants have elaborated the original techniques for fabrication of nanostructures on thin membranes and self-supporting nanostructures, thin films deposition. It has been fulfilled fundamental studies of phase formation in metal-oxide systems and structures of perovskite oxides of Y-Ba-Cu-O and Ba-K-Bi-O superconducting systems. Crystal structure of perovskite manganites has been studied, it discovered principally important features of crystalline state of these materials related to their electronic properties. On the base of established experimental facilities, the important results on studies of electronic transport in metallic nanostructures, carbon nanotubes, biological molecules and manganite nanostructures have been obtained.
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