2006 Fiscal Year Final Research Report Summary
Study on Liquid Crystalline Organic Semiconductors
| Project/Area Number |
16205023
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Functional materials/Devices
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
HANNA Jun-Ichi Tokyo Institute of Technology, Graduate School of Engineering, Professor (00114885)
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| Project Period (FY) |
2004 – 2006
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| Keywords | Smectic Liquid Crystal / Discotic Liquid Crystal / Mobility / Electronic Conduction / Organic Semiconductor / Liquid Crystalline Semiconductor / Ionic Conduction |
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| Research Abstract |
We have investigated liquid crystalline materials including both discotic and calamitic liquid crystals in order to establish the scientific basis as a new type of organic semiconductors exhibiting self-organization for opto-electronic device applications in the future : we tried to get the answers to the following questions thorough this research on the basis of both experimental and theoretical approaches :
1. What are the most important factors that influence charge mobility in SOMS?
2. How can the carrier transport in SOMS be understood theoretically?
3. What are the theoretical or practical limits of charge mobility in SOMS?
4. How can SOMS be designed with both high mobility and other important ancillary properties?
5. How can the carrier injection at the interface with the electrode materials be controlled and optimized?
6. What are the most unique phenomena and device structures involving SOMS?
7. What are the most promising technological applications for exploitation of SOMS?
After th
… More
e three years research, we have obtained the following results on the charge carrier transport properties of the liquid crystals, which are described in the final research report in detail, and some of them have been published in 32 papers in scientific journals.
1. The carrier mobility in mesophases is determined by a reduced molecular distance in a smectic layer in the smectic mesophases when the molecular order is sophisticated, while determined by the reduced disorder in a column in the discotic mesophases.
2. As for the relationship between the chemical structure of liquid crystals and mobility, we haven't come to a final conclusion yet, but we have observed that dipole in the liquid crystal molecule affected the charge carrier mobility, in addition to a π-conjugated core size.
3. The carrier transport in the mesophase was modeled as a hoping transport in the narrowly Gaussian-distributed localized density of states, whose the standard deviation was 40 to 60 meV, and it made possible to estimate the highest mobility in the mesophase, which was 0.1〜1 cm^2/Vs.
4. The dipoles and a size of π-conjugate aromatic affected charge carrier mobility, but we haven't come to the final conclusion about a relationship between the chemical structure and charge carrier transport properties yet because of less samples characterized.
5. The electrical properties at the interface of a liquid crystal/an electrode material were determined by charge injection through a Schottky type of barrier, which was well established in solid materials systems, and the charge injection was varied by surface-modification of electrode surface with thiols.
6. The grain boundaries of polycrystalline thin films were well controlled by utilizing pre-formed molecular alignment in mesophases, making it possible to prepare high crystallinity polycrystalline thin films of liquid crystalline materials. Less
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