OBJECTIVES

• Investigation of functional molecules as core components of hybrid molecular-semiconductor and molecular-metal devices. So fat we have tested molecules in the classes of polyoxometalates, phthalocyanines, cyclodextrines and carbon nanotubes.
• Fabrication of hybrid devices on semiconducting and/or metal surfaces as a test bed for molecular layers, while they can be directly exploited for fast switching, diode and memory applications as well as for chemical sensors or bio-sensors.
• Development of consistent evaluation methods based on the electronic transport properties at the nanolevel for the characterization of molecular few layered systems.

ACTIVITIES AND MAIN RESULTS

1. Molecular memory cells based on tungsten polyoxometalates and high-k dielectrics

Polyoxometalates are complex inorganic anions that may be considered as the molecular analog of transition metals oxides. In this application we developed a hybrid molecular/semiconductor capacitor type memory cell based on the redox properties of a Keggin type Tungsten polyoxometalate. The molecular layer is the charging part of the structure. A thin silicon bottom oxide is for the control of the cell (write/erase operations) and a high-k tantalum oxide serves as a gate. The performance of the cell depends on the quality of the gate oxide.

2. In plane molecular nanotransistors

We fabricated planar nanotransistors based on monolayers of tungsten polyoxometalates. The device was fabricated with electron beam lithography with two opposite electrodes acting as source and gate and two side electrodes for gate control. Transistor action was successfully demonstrated

3. Electronic properties of phthalocyanine/gold nanoparticle networks

We studied the electronic transport properties of hybrid networks based on semiconducting conjugated oligomers and metal nanoparticles (NPs). Spherical gold (Au) NPs were linked by means of copper 3-diethylamino-1-propylsulphonamide sulfonic acid substituted phthalocyanine (CuPcSu) molecules to form a network confined between Au nanodistant electrodes. It was possible to discriminate between various transport mechanisms typical for such structures (i.e. tunnelling and hopping), to evaluate conduction thresholds and to reveal charging effects involving few electrons, at lower temperatures. The interpretation was assisted by AFM, FE-SEM and TEM imaging techniques.

4. Carbon nanotube photodetector

We are currently working on a new type of photodetector using carbon nanotubes. The device is a complex heterojunction built on a Si substrate with Au electrodes with Si3N4 insulating layers and an ITO sealing electrode. The nanotube layer is grown at high CVD temperature. The aim is to develop a sensitive photodevice in the range from UV to medium IR. The thickness of the CNT layer monitors the sensitivity and the response rate of the device.