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Research topics
Last Update
28.10.2017

The general research field of the laboratory is studies of the influence of the amorphous state on the optical, electrical and chemical properties of solid materials.

The main research objects are: (1) silicon dioxide (SiO2) in its multiple crystalline, glassy and amorphous forms, (2) Various amorphous oxide materials related to SiO2, such as germanosilicate glasses and multicomponent silicate glasses. These materials are studied in bulk (monocrystals, polycrystals, glasses) , thin film, fiber and nanoparticle forms.

Silicon dioxide is selected as the main research object due to two aspects:

1) Fundamental aspect. Silicon dioxide is one of the few existing simple compounds, which exists both in crystalline and glassy states. This property allows to elucidate the effects of amorphous disorder on optical, electric and other properties of the material.

2) Application-related aspect. Silicon dioxide has a number of outstanding properties, which make it one of the presently most widely used materials in optics, photonics and microelectronics. It is the material of choice for low-loss optical communication fibers and for a plethora of specialty-fibers, for example, fibers for high power laser transmission in medicine or material processing, UV-transmitting fibers for analytical optical instrumentation, radiation-tough fibers for nuclear and space environments, fiber Bragg gratings for information processing and sensors, photonic fibers. High purity SiO2 glass is used in the vast majority of UV bulk optical elements (lenses, prisms, windows). SiO2 films on silicon serve as passivating, masking and dielectric layers in the Si-based microelectronics. Crystalline SiO2 in α-quartz form is used as a resonator in virtually any electronic timekeeping device.

The main directions of research in the laboratory are the following:

1) The studies of optically active point defects in crystalline and glassy SiO2. Silicon dioxide is distinguished by an excellent optical transmissivity in the spectral range from the near infrared (1300nm) up to vacuum UV region (that is why it is No 1 in optical fibers). However, its optical properties are degraded by “point defects” – local deviations from the ideal interconnectivity between Si and O atoms in SiO2 network. Understanding of their structure, optical properties and formation processes is essential for many applications.

2) Spectroscopic studies of SiO2 crystalline polymorphs. At the room temperature and at normal pressure SiO2 can exist in various polymorphic forms: stable form - α-quartz and metastable forms (α-tridymite, α-cristobalite, coesite, stishovite). It is usually assumed that the closest crystalline counterpart of glassy SiO2 is α-quartz. However, it is considered that in small local regions of amorphous SiO2, in particular, around point defects, there may exist structures, bearing resemblance to other crystalline polymorphs of SiO2.

3) Studies of doped SiO2 and multicomponent SiO2-related glasses. SiO2 is often doped to obtain the necessary properties, for example, by Ge to increase the refraction coefficient in fiber waveguides and to create fiber optic Bragg gratings, by fluorine to decrease the refraction index or to increase the vacuum-UV transmission, or by rare earth ions to create fiber lasers.

4) Studies of interstitial molecules in SiO2. Amorphous SiO2 and some crystalline forms of SiO2 (zeolites) have nanosized interstitial spaces in their structure, which can accommodate small molecules. They can be introduced by diffusion (e.g., H2) or created internally by photochemical reactions (O2), or introduced during synthesis (Cl2). Their presence significantly affects the optical properties of SiO2 and their studies are of direct practical interest.

5) Studies of SiO2 nanoparticles and photochemical properties on surfaces of SiO2. Different SiO2 related nanoparticles and core-shell structures are widely studied for biological applications, e.g., drug transport, photodynamic therapy, sensors. Compared to the crystalline polymorphs, amorphous SiO2 is characterized by large interstitial spaces, which can be considered as internal surfaces. Defects on these internal surfaces bear many similarities to defects on outer surfaces of SiO2, which affect the photo- chemical processes in applications involving SiO2 nanoparticles.

The studies in the laboratory are performed mainly by spectroscopic methods. The available equipment allows using optical absorption and luminescence spectroscopy, time-resolved and luminescence kinetics spectroscopy, infrared absorption, Raman scattering (at several wavelengths) and vacuum-ultraviolet spectroscopy. Low temperature (down to 14K) measurements are available. In cooperation with other laboratories and partners many other investigation methods (e.g., XRD, XRF, EPR...) are available.