ELECTRON MICROSCOPY AND NANOMATERIALS – Research

A wide range of nanomaterials are studied by SEM and TEM techniques including HRTEM, EELS and EFTEM in order to optimize their growth conditions and tailor their properties, including nanomaterials for nanoelectronics, photovoltaics, catalysis, biomedical, energy and environmental applications.

Zinc oxide nanostructures

ZnO is a wide band gap (3.3 eV) semiconductor, which has been the subject of intense interest in recent years. The attractive features of ZnO for optoelectronic applications, in addition to its wide band gap are its high exciton binding energy (60 meV) and the high electron mobility.These -among others- properties are the reason that ZnO is envisaged for a variety of applications concerning solar cells, photocatalytic cells, sensors and optoelectronics to mention but a few.

ZnO nanorods grown on flexible kapton substrate.

Typical SEM cross-section view of ZnO nanorods

We have engaged in the growth of ZnO nanostructures (nanorods and nanoparticles) employing low cost, low temperature wet chemical and electrochemical methods on a variety of substrates and their characterization by electron microscopy, optical and electrical methods.

PL spectra, obtained at T=4.2 K, of ZnO nanorods with various concentrations of intrinsic defects.

The intrinsic point defects, which play a profound role in the electrical behavior of ZnO, have extensively been studied in nanostructures specifically grown with large concentrations of such defects.

Cross-section SEM image of high-density Cu2O grown on ZnO nanorods.

HRTEM image of Cu2O/ZnO heterojunction with corresponding SAED pattern.

We have developed a new two-step, low-cost, non-toxic and low temperature electrochemical deposition method for the synthesis of ZnO/Cu2O heterojunctions in an effort to improve Cu2O solar cell performance.

ZnO nanoparticles were grown using zinc acetate dehydrate (Zn(O2CCH3)2(H2O)2) as a Zn precursor. The size of the ZnO nanoparticles was tailored between 3 and 17nm through appropriate adjustment of the growth parameters. More over 1 at% Al-doped ZnO nanoparticles were synthesized utilizing aluminum acetylacetonate (Al(C₅H₇O₂)₃). Structural analysis showed that the Al-doped ZnO nanoparticles retained the wurzite hexagonal structure of ZnO, while no other Al containing phase was detected. The ZnO and Al-doped ZnO nanoparticles were spin coated on glass substrates to form smooth thin films for transparent conductive oxides applications and the fabrication of memristor devices.

Bright field TEM images of 1 at% Al-doped ZnO nanoparticles

Nanostructures for memory applications

We have fabricated nanoparticles of various metals on the interface between the 2 oxides of Si/ SiO2 / HfO2, withthe use of electron beam evaporation. We have studied their electrical properties for applications in non volatile memories

Memory effects under various applied voltages