Synthesis and characterization of nanomaterials

Focus

The research team "Preparation and characterization of nanomaterials" focuses on the study of electronic and optical phenomena at surfaces and interfaces of nanomaterials caused by the impact of photons, ions, electrons and absorption of gases to their use for sensor applications, such as sources of light and to enhance the nano-diagnostic capabilities of analytical methods.

Current work

Study of the metal-semiconductor interface

Compound semiconductors are nowadays indispensable in many electronic and photonic components. A number of them are based on metal-semiconductor interfaces. This type of interface has been the subject of study for several decades. New possibilities for its implementation emerged with the development of nanotechnologies.

Metal nanoparticles (KNCs) the size of several nanometers are applied on the surface of the semiconductor. These structures exhibit unique properties.

Surface plasmons of itinerant electrons of metal nanoparticles, which are excited due to the impact of electromagnetic radiation, can amplify light absorption and the Raman scattering intensity of the luminescence from the semiconductor pads. We try to theoretically describe and experimentally verify the luminescence intensification of the semiconductor materials decorated by KNC.

A large part of compound semiconductors suffer from a high density of surface states, which causes fixation of the Fermi level. Such Fixation of the Fermi level leads to low Schottky barrier height and the independence of the deposited metal, if the metal is deposited by conventional methods such as vacuum evaporation.

We have shown that the deposition of organized KNC from reverse micelles together with colloidal graphite on the surface of the InP leads to the elimination of the fixation of the Fermi level in InP and reproducible preparation of the Pd-InP interface with a high Schottky barrier. These structures exhibit excellent sensitivity to low concentrations of hydrogen. We focus on the application of KNC on to polished boards and other epitaxial layers of compound semiconductors (GaAs, GaN, ZnO) in order to prepare high-quality Schottky barriers describe electrical transport through the interface KNC / semiconductor. We also aim to explain the chemical processes that take place in atoms and molecule during absorption and we implement structures for detection of dangerous gases.

Application of nanoparticles onto surfaces

We mainly use the technology of electrophoretic deposition (EFD) and vacuum evaporation for the KNC application onto surfaces. The EFD technology is based on the deposition of charged colloid nanoparticles made from the colloidal solution which is applied onto the surface of conductive solids. The KNC solutions in polar and nonpolar solvents with different surfactants are prepared with keeping in mind their subsequent depositions and the consequent execution of plasmonic or Schottky structures. We study the influence of the composition of the colloids and the EPD parameters, in both the DC and time- varying electric fields, on the quality of the deposited layers in order to gain control over the degree of coverage. In the case of thicker layers we want to achieve growth layer by layer. Semiconductor substrates are modified ( patterning ) with the use of an electron and ion beam lithography in order to not only understand the mechanisms of KNC deposition but also to prepare the appropriate structures to their characterization and application in gas sensors .

Characterization of Nanomaterials

The research focuses on the study of physical processes that occur in the interaction of light ions and electrons with solid surfaces in order to characterize nanostructured materials. The analytical methods used ( SEM, FIB , SIMS , EDX , AFM , STM , BEEM / BEES , Raman, optical microscopy , photoluminescence, cathodoluminescence ) or develop their own detailed studies of three of them : photoluminescence , ballistic electron microscopy and spectroscopy ( BEEM / BEES ) , secondary ion mass spectrometry (SIMS ) . The study also focuses on whether photoluminescence can be increased by application of metallic nanoparticles on the surface of semiconductor samples. We are also trying to understand the structure of electronic levels of quantum dots using BEEM / BEES. The FIB SIMS method focuses on the effect of letting in reactive gases, such as oxygen , in order to increase the yield of secondary ions  which have a major effect on the sensitivity and resolution of the  ion-imaging method.