Tomohide Murase

Ligand Control of Semiconductor Nanocrystals for Efficient Carrier Injection

Inorganic/organic hybrid material of CdSe/ZnS core/shell nanocrystals (NCs) covered with organic ligands was prepared with ligand exchange reaction in order to facilitate carrier injection into NCs through the organic ligands. The organic ligands used in this study, 2-naphtalenethiol and bathophenanthroline, were selected as model compounds according to adjustment of highest occupied molecular orbital and lowest unoccupied molecular orbital of the ligand to valence band maximum and conduction band minimum of the CdSe NCs, respectively. The prepared hybrid NCs easily disperse in polar organic solvents such as CHCl 3 and show photoluminescence only from the CdSe/ZnS core/shell NCs. Current-voltage characteristics of the ligand exchanged NCs thin films sandwiched between electrodes were investigated. It was shown that conductivity of the film was improved by the introduction of carrier injecting ligands in comparison to the ligand unexchanged trioctylphosphine oxide-capped CdSe/ZnS NC thin film.

Improved Height Measurement of Single CdSe Colloidal Quantum Dots by Contact-Mode Atomic Force Microscopy Using Carbon Nano-Tube Tips; for the Investigation of Current-Voltage Characteristics

We have investigated the distribution of measured heights of single CdSe colloidal quantum dots (QDs) by contact-mode atomic force microscopy. The dot heights measured with metal-coated Si tips, with which large adhesive force is measured between the tip and sample, are much smaller than that expected from optical absorption. This discrepancy could be due to the dot position fluctuation that occurs when the tip is in contact with the dot because the height distribution of the QDs covered with very thin SiO2 layer is in agreement with the optical measurement. On the other hand, when conductive carbon nano-tube (CNT) tips are used, the adhesive force is reduced significantly, and the measured dot heights become close to the expected value. Thus, the measurement of QD height is greatly improved in accuracy with CNT tips. As a result, the current flowing through the QD can be measured, and conductance changes attributed to electron resonant tunneling through the QD are observed.

Thermotropic liquid crystalline polyimides toward high heat conducting materials for 3D chip stack

Novel thermotropic liquid crystalline semi-aliphatic polyimide containing polysiloxane unit has been developed. The polyimide film exhibits high thermal stability and liquid crystallinity with lower transition temperature. Poly(amic acid) solution used as a precursor of the polyimide has very good surface wetting properties for a silicon wafer, resulting in homogeneous polyimide thin film formation on the wafer after thermal imidization below 200 °C. The silicon wafer coated with the polyimide thin film can be bonded to another silicon wafer, or to another polyimide film on heating at 270 °C with relatively low pressure. Moreover the bonding is repairable on heating again. It is proposed that the polyimide can be utilized as a polymer adhesive for three dimensional chip stack.