2007 Fiscal Year Final Research Report Summary
Room temperature spin-dependent single-electron-tunneling in nanostructures with controlled Fermi levels
| Project/Area Number |
17360003
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied materials science/Crystal engineering
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| Research Institution | Tohoku University |
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Principal Investigator |
MITANI Seiji Tohoku University, Tohoku University, IMR, Associate Professor (20250813)
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| Co-Investigator(Kenkyū-buntansha) |
SHIMA Toshiyuki Tohoku Gakuin University, Faculty of Engineering, Associate Professor (50261508)
TAKANASHI Koki Tohoku University, IMR, Professor (00187981)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Nanomaterials / Tunnel effect / Quantum dot / Spin electronics / Electron device / Coulomb blockade |
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| Research Abstract |
Aiming at the observation of spin dependent single electron tunneling phenomena at room temperature, experimental and theoretical studies were carried out on material properties, including Fermi levels, and device structures etc. In this study, the key issues were low resistive and low capacitive tunnel barriers and optimization of the whole device structures for the clear observation of spin dependent single electron tunneling.
In the experiments using MgO barriers, fairly good MgO barriers with the barrier height of ~ 1 eV were obtained, with good reproducibility and suitability for device applications, by choosing appropriate growth conditions. The obtained barrier height for MgO barrier layers is much lower than a half of the band gap for bulk MgO, and this suggests that the Fermi level shifts upward by about 2 eV, compared to that for bulk. While relatively low barrier heights were obtained, we found a problem for MgO barriers with a very low barrier height (typically < ~ 0.5 eV). Although low resistive barriers with a very low barrier height is useful for high temperature operation of single electron devices, their resistance ratio between on and off states for the devices is too small to be used for practical applications. In the experiments using AlO barriers, it was found that a multiple oxidation process is useful for preparation of flat tunnel barriers.
In addition, large tunnel magnetoresistance was observed for Fe and FeCo nanopartices embedded in a monocrystalline MgO matrix. This is almost the first observation of large tunnel magnetoresistance in monocrystalline granular systems, and the magnitude is consistent with the value predicted from spin polarization in Fe and FeCo.
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