Vedoucí výzkumné skupiny
- Plasma processing of materials, plasma diagnostics, process monitoring and simulations
- Functional plasma polymer coatings
- Inorganic and hybrid (organic/inorganic) coatings and nanomaterials
- Carbon nanostructured materials and their functionalization
- Development of methods for the characterization of optical and mechanical properties of materials
- Development of the scanning probe microscopy (SPM) data analysis software, Gwyddion
The aim is to develop procedures for plasma processing of materials (plasma enhanced chemical vapor deposition - PECVD, plasma polymerization, plasmachemical synthesis of nanomaterials, plasma treatment and reduction) enabling the preparation of advanced materials and surfaces with additional functionalities and applications in sensing, tissue engineering, tribology, optics, smart textiles, batteries etc. One of the objectives is the understanding of interaction of reactive plasmas with a solid surface using thin film and surface characterization methods, plasma diagnostics, process monitoring and simulations. Additionally, our goal is to further develop physical methods and software for the characterization of materials, namely for the characterization of optical and mechanical properties and scanning probe microscopy.
Plasma processing of materials, plasma diagnostics, process monitoring and simulations
We develop and investigate low and atmospheric pressure plasma processing of materials. The understanding of the processes and interaction of plasma with surfaces is achieved by plasma diagnostics, process monitoring and simulations of related phenomena (electromagnetic field, gas flow, heat transport, plasma).
In our numerical models, we focus exclusively on plasma devices which have direct material or biomedical applications. We simulate plasma in close-to-real geometries in relevant gas mixtures. This does, sometimes, pose a big challenge because the coupling of the plasma, the gas dynamics and mixing and the electromagnetic field is very strong. The numerical modelling is, always, complemented with plasma diagnostics in order to verify the validity of our models. The most interesting models that we have developed include:
- Coupled model of gas dynamics and the electromagnetic field in a microwave plasma torch operating at the atmospheric pressure in an inhomogeneous argon/hydrogen mixture.
- Gas dynamics model of gas flow and heat transfer in a radio-frequency jet for bioapplications.
- A model of gas dynamics and precursor consumption in a dielectric barrier discharge with the aim of gas supply optimization.
- Currently, our main focus lies on self-consistent modelling of atmospheric discharges with bioapplications.
Knowing the conditions in the plasma discharges, especially the gas and electron temperatures and the electron density) is absolutely crucial for transferring our plasma processes to different setups or for upscaling them. In addition, measurements of plasma properties are very useful for validation of the numerical models developed in our group. So far, we have employed the following techniques to characterize our discharges:
- Optical emission spectroscopy for electron denisty and gastemperature measurements.
- Thomson scattering for electron density and temperature measurements and Rayleigh scattering for gas temperature measurements (in collaboration with Technische UniversiteitEindhoven).
- Laser schlieren deflectometry for gas temperature measurement.
- Capacitively coupled radio frequency (RF) discharges
- Cold RF plasma jet
- Dielectric barrier discharges (DBD)
Microwave plasma torch is atmospheric pressure device that provides high temperature, electron and energy density. In applications it is most suitable for conversion and synthesizing processes where it can achieve full breakdown of the precursor molecules to active radicals. We have successfully utilized this device for synthesis of nanoparticles and nanotubes and also studied by diagnostic methods and modeling.
The glide arc or gliding arc is a type of a plasma discharge, where the arc channel is moving along slanted electrodes. When external forces (buoyancy, gas flow) act on the plasma channel, it is pushed from this optimal position. The discharge channel starts to glide and consecutively changes its properties from the ones nearly identical to a standard arc discharge at short channel lengths to a non-equilibrium plasma at longer channels. The non-equilibrium stage begins when the length of the plasma column exceeds its critical value and heat losses from the plasma begin to exceed the energy supplied by source. The maximum length of the glide arc channel is related to the supplied voltage. After the quenching of one discharge at maximum elongation a new discharge appears at minimal electrode distance and the whole evolution is repeated. Advantageous properties of the glide arc plasma can be used for various applications such as decontamination, methane transformation or CO2 dissociation. Reference: Hypergravity effects on glide arc plasma
Functional plasma polymer coatings
The plasma (co)polymerization is applied for a surface modification by coatings containing (bio)active groups (carboxyls, amines, ...). We develop plasmachemical processes that utilize non-toxic monomers. The coatings can be applied to different substrates because the processes take places at temperatures closed to the room temperature. The coatings are tested in sensors, for immobilization of biomolecules and for the modification of biodegradable electrospun polymer nanofibers aiming at the applications in tissue engineering.
- Plasma polymerization of cyclopropylamine
- Preparation of immunosensor with the help of plasma polymerization
- Modification of polycaprolactone electrospun nanofibers
Hard and hybrid (organic/inorganic) coatings
Organic/inorganic organosilicon coatings with tuned hybrid structure are deposited by PECVD from organosilicon monomers (e.g. hexamethyldisiloxane - HMDSO) in low pressure RF discharges, atmospheric pressure DBD and RF plasma jet. We develop and investigate hard coatings based on diamond like carbon (DLC) prepared by low pressure PECVD.
- Organosilicon protective films prepared by low pressure PECVD
- Organosilicon films prepared in atmospheric pressure discharges
- SiOx and nitrogen doped DLC films
Multilayer amorphous diamond-like carbon films with graded silicon and oxygen content exhibiting hardness in the range from 16 to 24 GPa were deposited using low pressure PECVD. Gradients in elastic properties of a coating can provide substantial improvements in the resistance to indentation. The variation in elastic properties of the thin film were achieved by composition change, simply adjusting the deposition conditions during the film growth. The films were optimised for deposition on steel substrates. To evaluate the impact resistance of graded amorphous carbon films in dynamic loading wear applications an impact test has been used. During testing the specimen was cyclically loaded by tungsten carbide ball that impacts against the coating surface. The results demonstrate the usability of these coatings in dynamic load and enables the optimization of the coating/substrate system design for a particular use. The films with optimum structure exhibited very good resistance against delamination, high fracture toughness and low friction coefficient. The principal new finding concerns the fracture toughness of the film and the interfacial adhesion. Upon impact testing the films remain attached to the substrate, even at impact loads exceeding 200 N. The films can sustain compression strains without debonding or spalling.
Reference: V. BURŠÍKOVÁ, J. SOBOTA, T. FOŘT, J. GROSSMAN, A. STOICA, J. BURŠÍK, P. KLAPETEK, V. PEŘINA. Optimisation of mechanical properties of plasma deposited graded multilayer diamond-like carbon coatings. JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, Vol. 10, No. 12, December 2008, p. 3229 - 3232.
Metal oxide coatings and nanomaterials
Very thin films of TiO2, HfO2 and other oxides are prepared by atomic layer deposition (ALD) or plasma ALD. Additionally, we investigate the structure of TiO2-based ternary oxides prepared by PECVD. In MW torch, a fast synthesis of iron oxide (maghemite, hematite) nanoparticles and nanostructured coatings can be tuned to desired applications including in-flight coating of nanoparticles for a core-shell structure.
- ALD and plasma ALD of oxides
- Ab-initio calculations of structure and optical properties of TiO2-based ternary oxides and HfO2
Iron oxide nanoparticles (NPs) have a wide range of applications that can be generally divided into two branches with respect to either their magnetic or chemical properties. The magnetic applications often utilize the superparamagnetic behavior of NPs and include for example; selective drug delivery, magnetic resonance imaging or hypertermia treatment. The chemical applications include carbon nanotube synthesis, pollutant degradation and water remediation, molecular imprinting of polymers, analytical fluorescence techniques and solid phase extraction.
Iron can occur in several oxidation states, FeO, Fe3O4 and Fe2O4, with several corresponding polymorphs. Ferrimagnetic magnetite (Fe3O4) and maghemite (gama-Fe3O4) NPs with the size below 20 nm exhibit superparamagnetic behavior. Hematite alfa-Fe3O4 has been widely known for its catalytic properties. epsilon- Fe3O4 was found to exhibit a huge coercive field of 20 kOe at the room temperature.
We have developed novel methods for synthesizing and characterization of NP which allow us to produce tailored size and phase of NPs in single step plasmachemical synthesis. Synthesis takes place in atmospheric pressure plasma torch described in (Plasma processing of materials, plasma diagnostics, process monitoring and simulations). Characterization methods include Raman spectroscopy, XRD powder diffraction and Infrared spectroscopy.
- Study of Microwave Torch Plasmachemical Synthesis of Iron Oxide Nanoparticles Focused on the Analysis of Phase Composition
- epsilon-Fe2O3 nanoparticles synthesized in atmospheric-pressure microwave torch
- Plasmachemical synthesis of maghemite nanoparticles in atmospheric pressure microwave torch
- Iron-Based Nanopowders Containing alpha-Fe, Fe3C, and gamma-Fe Particles Synthesised in Microwave Torch Plasma and Investigated with Mossbauer Spectroscopy
- Synthesis of Carbon Nanotubes and Iron Oxide Nanoparticles in MW Plasma Torch with Fe(CO)5 in Gas Feed
Carbon nanostructured materials and their functionalization
Carbon nanotubes (CNTs) and graphene nanowalls are synthesized directly on the functional devices, e.g. sensors, using the MW plasma torch or by CVD using iron catalytic nanoparticles synthesized in the torch. Graphene is grown on copper foils by CVD. The CNTs or graphene are functionalized by plasmachemical method for enhanced sensing properties, imobilization of biomolecules, better dispersion in liquids (e.g. for spraying) or improved dispersion and covalent bonding in polymer matrixes (for composites). Plasmachemical modified carbon nanomaterials can find applications in smart textiles, multifunctional polymer composites, (bio)sensors, supercapacitors, batteries etc.
- Growth of CNTs in MW torch
- Polyurethane composites filled by plasma-functionalized CNTs
- Field emission pressure sensor based on CNTs grown in MW torch
- Modifications of working electrodes of electrochemical sensors using CNTs and plasma treatment
Enhanced adsorption properties of carbon nanomaterials make it possible to create novel gas sensors with improved performance. High surface area of porous CNTs and carbon nanofibers increase the response of the gas sensors. Unique and fast plasma-assisted technique of making of the gas sensors based on carbon nanomaterials (carbon nanotubes, carbon nanofibers, graphene etc.) was created to investigate and produce high quality devices. Advantages of the gas sensors based on carbon nanomaterials:
- Excellent sensing properties allow to use the sensors at room temperature;
- Low detection limit (e.g. lower than 10 ppm);
- Possibility to engineer the sensing properties precisely;
- Possibility to use the gas sensors for a wide range of industrial and toxic gases or gas mixtures (CO, CO2, CxHy, NH3, NO2 etc.).
Development of methods for the characterization of optical properties of materials
The optical characterization of thin films and surfaces is performed by the combination of ellipsometric and spectrophotometric measurements in the wide spectral range. We develop own software (newAD) for the solution of advanced and complex problems. The characterization provides information not only about the thickness and optical properties (refractive index and extinction coefficient) but also about non-uniformity, inhomogeneity, existence of interlayers, roughness, changes in chemical composition and electronic band structure.
A unique normal-incidence imaging spectrophotometer in UV-visible-NIR spectral range with spatial resolution of 37 µm was built at Institute of Physical Engineering FSI BUT. Our group develops data processing methods and software for this instrument and applies them to optical characterisation of highly non-uniform thin films, with focus on precise mapping of film thickness. The applications include for instance characterisation plasma jet-deposited films and mapping of roughness of non-uniform rough ZnTe films.
- Complex modelling of dielectric response in wide spectral range
- Efficient numerical methods for modelling of roughness and other defects in thin film optics
Development of methods for the characterization of mechanical properties of materials
The advanced studies of mechanical properties of thin films and nanomaterials is carried out by instrumented micro/nanoindentation and nanoscratch tests. The complex analysis of relation between nanoindentation response and material structure is performed for thin films, multilayered and nanocomposite materials. Recently, the measurement in liquids for the samples with potential bioapplications and the measurements at the temperatures up to 800 oC are investigated.
The Hysitron TI 950 TriboIndenter is a nanomechanical test instrument with a high degree of sensitivity and excellent performance. Its Advanced Control Module improves the precision of feedback-controlled nanomechanical testing, provides dual head testing capability for nano/micro scale connectivity, and offers very good noise floor performance. Several different nanomechanical testing techniques are currently possible, making the TI 950 nano-indenter system an effective nanomechanical characterization tool for a wide range of applications.
Hysitron's TI 950 TriboIndenter Features:
- Quasistatic nanoindentation – Measure Young’s modulus, hardness, fracture toughness and other mechanical properties via nanoindentation.
- Scratch testing – Quantify scratch resistance, critical delamination forces, and friction coefficients with simultaneous normal and lateral force and displacement monitoring.
- Top-down optics – High- resolution, color CCD camera for individual structure identification and coarse test positioning.
- SPM imaging – In-situ imaging using the indenter tip provides nanometer precision test positioning and surface topography information
- Dual head testing capability for true nano/micro scale connectivity
- Active vibration isolation systemproviding environmental separation
- nanoDMA – Investigate time-dependent properties of materials using a dynamic testing technique designed specifically for polymers and biomaterials
- Modulus Mapping – Obtain quantitative maps of the storage and loss stiffness and moduli from a single SPM scan 3D OmniProbe – Provides forces up to 10 N and scratch lengths up to 150 mm for depth- sensing micro-indentation and tribological studies
- nanoECR – Conductive nanoindentation system capable of providing simultaneaous in-situ electrical and mechanical measurements for investigating material deformation and stress induced transformation behavior
- Thermal control – Heating/cooling stages can be added for the investigation of mechanical properties at non-ambient temperatures
- Vacuum stage – Wafer mounting system that eliminates necessity of gluing or cutting wafers prior to testing
- Long probes that allow to safely investigate the mechanical properties of samples imersed in water.
Photo during testing of a sample immersed in water.
Development of the scanning probe microscopy (SPM) data analysis software, Gwyddion
The open source software Gwyddion is developed in close collaboration with the CEITEC RG Development of Methods for Analysis and Measuring and a large number of participants from other institutions throughout the world. It has become a standard software in the field and is used by thousands of scientists.
Gwyddion was designed as a cross-platform and extensible. It consits of three main parts: libraries providing core data processing routines, GUI elements and utility functions; modules that provide specific data processing and file functions; and a small and simple application itself that primarily serves as a glue connecting everything else together.
Notable features of Gwyddion include:
- Support for more than 100 SPM file formats.
- Processing of data under arbitrarily shaped masks.
- Calibration and metrology support.
- Single point spectra and volume data support.
- Generation of artificial surfaces and measurement simulation.
- Python scripting.
For further information contact David Nečas mail: firstname.lastname@example.org
The development of Gwyddion is naturaly connected to development of data processing methods in SPM. Examples includes methods for the analysis of nanoparticles under non-ideal conditions or statistical characterisation of roughness in irregular rough regions. Quantitative analysis of SPM data should also include uncertainties of the obtained parameters. This requires the characterisation of measurement errors in SPM, both systematic and random, and their propagation through data processing calculations.
For quantitative analysis of data acquired using novel SPM scanning modes, such as fast point spectroscopy and imaging, it is crucial to have available independent data processing methods that can be applied off-line (after acquisition) and consistently to data measured using different instruments. Thanks to the open-source nature of Gwyddion, all algorithms implemented there can be examined and verified at the source code level, which is key for comparablity of results and further progress to standardisation in nanometrology.