Defended Dissertations in 2014

Rolandas Verbickas
Author: Rolandas Verbickas
Dissertation title: Investigation of heavy metal determination using electroanalytical stripping analysis
Fields of science: Physical sciences, Chemistry (03P)
Scientific supervisor: Prof. Habil. Dr. Eugenijus Norkus
Defence of the dissertation: 2014-01-17
The aim of the work is to investigate gallium and bismuth film plating in situ and ex situ processes as well as to optimize metal film plating conditions for determination of
Novelty and actuality of the work
With the development of industry and technology, the growth in consumption of  environmental resources rises heavily, while there is also the problem of various wastes containing heavy metals. It is important to monitor heavy metals in various systems. This work investigates bismuth and gallium film electrodes as an alternative tool for  determination of heavy metals in water samples. Industrially gallium and bismuth are considered one of the less toxic of the heavy metals, but have not been studied enough for suitability for determination of heavy metals. Especially, there are no many investigations of gallium film electrodes. The electrochemical and microscopic properties of bismuth film electrode were investigated. It has been shown that bismuth film electrode can be used for determination of heavy metals. Gallium film plating conditions were optimized on glassy carbon substrate. Gallium influence on Pb(II) and Cd(II) deposition was studied. It has been shown that gallium film plated in situ and preferably onto the carbon paste-based support can be employed as a detection tool in anodic stripping voltammetry of Zn(II) at the trace concentration level.
  • When depositing Bi films on glassy carbon electrode it was found, that the addition of Br-1 changes the BiFE morphology making it more uniform and forming crystalline aggregates. The reoxidation peak of Bi was shifted to more negative potentials showing the electrocatalytic effect of bromide for the bismuth film.
  • The addition of the other metal ions to the deposition solutions caused changes in the morphology of the Bi film. Moreover, the morphology of Bi film with Cd was different from that with Pb. CVs at these films had rather low peaks of Cd or Pb and lower peak of Bi than that without additional metals. However, the SWASV this effect was observed only for the Bi-Cd film but in the case of Bi-Pb film the Pb peak was much higher than the Bi one, as well as Bi peak was similar to that without any additional metal. Cd was slowing the Bi film deposition and Pb was catalyzing this deposition.
  • Nanoparticle-structured film was obtained when Bi film was deposited together with both Cd and Pb. Although, the CVs showed even lower reoxidation peaks of all metals than at Bi-Cd or Bi-Pb films but SWASVs had bigger peak of Cd, the same peak was of Pb, and Bi was similar to the peak without any metals. Pb is catalyzing deposition of other metals on the electrode surface.
  • Zn(II), Cd(II), Cu(II) and Pb(II) ions were determined in the water samples using bismuth film electrode. The linear calibration curve of each metal was obtained from SWASV measurements with increasing concentrations of Zn(II), Cd(II), Cu( II) and Pb(II) in the acetate buffer (pH 4.5). Good linear responses of the peak area vs. concentration were obtained for Zn(II), Cd(II), Pb(II) and Cu (II) up to the concentration level of 150, 130, 90 and 100 µL-1 and correlation coefficients of 0.997, 0.997, 0.999 and 0.998 respectively.
  • The possibilities of gallium film plating were studied. The glassy carbon substrate was chosen for optimization. The optimized deposition conditions were: supporting electrolyte 0.1 M acetate buffer, deposition potential -1.7 V, deposition time 120 s, deposition temperature 40°C.
  • The gallium influence on Pb(II) and Cd(II) deposition at the glassy carbon electrode was studied. The Ga(III), Cd(II) and Pb(II) were deposited in situ and ex situ. It has been shown that Pb(II) and Cd(II) peaks increased significantly in the presence of gallium when deposited in situ. It could be explain due to gallium possibility to form intermetallic compounds with other metals.
  • The possibilities to determine Zn(II) on gallium film electrode using different carbon substrates were studied. It has been shown that gallium film plated in situ and preferably onto the carbon paste-based support can be employed as a detection tool in anodic stripping voltammetry of zinc(II) at the trace concentration level (in an interval of 10-50 µM Zn(II)).
Inga Garbarienė
Author: Inga Garbarienė
Dissertation title: Origin, chemical composition and formation of submicron aerosol particles in the atmosphere
Fields of science: Physical  sciences, Physics (02 P)
Scientific supervisor: Dr. Kęstutis Kvietkus
Defence of the dissertation: 2014-05-15
The effect of aerosol particles on the atmosphere, climate and public health is among the central topics in the current environmental research. Atmospheric aerosol particles have significant local, regional and global impacts. Local impacts  include  vehicular emissions, wood burning fires and industrial processes that can greatly affect the urban air quality. Regionally, aerosols can be transported from areas of high emissions  to  relatively  clean remote regions. Aerosol particles have the potential to  significantly  influence  the composition of gaseous species in the atmosphere through their role in heterogeneous chemistry in the troposphere and stratosphere, as well as their effect on the Earth's climate as they scatter sunlight and serve as condensation nuclei for cloud droplet formation. At present, the radiative effects of aerosols have the largest uncertainties in global climate predictions to quantify climate forcing due to man-made changes in the composition of the atmosphere. A better understanding of the formation, composition and transformation of aerosols in the atmosphere is of great importance in order to better quantify these effects.
The concentration and composition of aerosol particles in Lithuania were investigated before, but due to lack of the sampling equipment and measuring technique, traditionally more attention was given to the coarse aerosol particle fraction, whereas it  is  well established that submicron aerosol fraction has a larger impact on the human health and climate. Due to adverse health effects comprehensive studies of submicron aerosol particles composition, concentration and sources become more and more releyant.  Thus, this  work will give quantitative data for global aerosol and climate model in assessing its impact on the climate change as well as provide information  for setting new air quality standards.


Evaldas Stankevičius
Author: Evaldas Stankevičius
Dissertation title: Fabrication of periodic micro-structures in polymers by interference lithography and modification of their properties by photo- grafting technique
Fields of science: Physical  sciences, Physics (02 P)
Scientific supervisor: dr. Gediminas Račiukaitis
Defence of the dissertation: 2014-05-22
Here we present results of our experimental work to create periodic micro-structures in polymers by using interference lithography (IL) and their photo-modification by photo­ grafting. Interference lithography is a powerful technique which allows fabrication of periodic micro-structures over a large area by a single laser exposure.  This  technique  is based on the recording of the interference  pattern  into  a  photosensitive  material. Interference lithography technique enables fabricating 2D and 3D periodic structures which can be used as functional devices in  many fields: photonics (photonics crystals), tissue engineering (scaffolds for cell growth), micro-fluidics,  micro-optics (micro lens arrays), sensors, etc.

Other technique demonstrated  in this work is photo-grafting.  Photo-grafting  is a method utilizing light activation for covalent incorporation of functional molecules to a polymer surface or polymer matrix. It has been widely applied as a simple and versatile method for tailoring physical-chemical properties of various surfaces.

Viktor Novičenko
Author: Viktor Novičenko
Dissertation title: Development  and application of phase reduction and averaging methods to nonlinear  oscillators
Fields of science: Physical  sciences, Physics (02 P)
Scientific supervisor: prof. habil. dr. Kęstutis Pyragas
Defence of the dissertation: 2014-06-02

Oscillatory systems are common in nature and man-made equipments. The behavior of such systems is usually described by nonlinear differential equations. The oscillations in the conservative systems with infinite number of close periodic solutions are well investigated in theoretical physics, since this problem arises when considering the motion of planets. Whereas the oscillators containing limit cycles when in the neighborhood of a periodic solution there are no other such solutions, have been considered only for the last century. Such oscillators can be encountered e.g. in electronics, robotics, lasers, chemical reactions, biological systems and economical models. A great interest about limit cycle oscillators has been boosted in the last two decades with the development of neuroscience. It considers the mechanism of suppression and activation of the neuron, and control of synchronization and desynchronization in the neural networks. In nonlinear dynamics one may obtain the analytical results by means of linearization of underlying equations around the specific solution. In the case of the limit cycle, such linearization is described by the Floquet theory, which was formulated at the end of the 19th century. However, the main achievement has been made by I. Malkin in the middle of the 20th century, when the phase reduction method was formulated. Later, it was rediscovered by A. Winfree, who investigated the biological rhythms. The method is based on the idea that one is dealing only with a scalar phase instead of all the system variables. Such an approach enables to obtain analytical results for a weakly perturbed limit cycle oscillator or for several coupled oscillators with a weak interaction. In biological systems, in lasers and electronics, one often has to deal with the delay effect, when the system dynamics depends not only on the current value of dynamic variables but also on their delayed values. Such systems are described by delayed differential equations which are infinite-dimensional, in contrast to ordinary differential equations. Therefore, it is convenient to perform a phase reduction of these systems since an infinite-dimensional system is reduced to a system with a single dimension. In this work we will pay attention to this issue. viii Introduction The dynamical systems with an irregular behavior, called as chaotic systems, are hard to predict but relatively easy to control. One of the recent problems in the control theory is stabilization of the unstable periodic orbits embedded in a chaotic attractor. For solving this problem, K. Pyragas proposed in 1992 a control method using the delayed feedback. This method showed itself as very attractive in various experimental situations. Here the controlled orbits are described by equations with delay, and thus the phase reduction method such systems is also relevant since it may show whether the orbit is stabilizible, and reveal the other properties of the orbit. Another significant problem in nonlinear dynamics is the treatment of systems under a high frequency external force. The frequency is high in comparison with the intrinsic system frequencies. The vibrational mechanics is a field of science devoted to mechanical systems subject to high frequency perturbations. The high frequency of the external force can drastically change the system’s behavior. For example, the classical problem of the vibrational mechanics is the stabilization of the upside-down position of a rigid pendulum by vibrating its pivot up and down with a quite small amplitude. The stabilization can be achieved if the amplitude and the frequency satisfy some conditions. Another example – a sand spilled on an inclined plane, which is moved by high frequency force. The sand can start climb up if the angle of the plane, the frequency and the amplitude satisfy some conditions. These crazy experimental results can be explained by the mathematical analysis of the system’s equations. Here the phase reduction is not the appropriate tool for the theoretical analysis, since oscillator changes it’s behavior drastically. Therefore, here it is more useful to apply the averaging method which is based on the eliminating of the fast oscillating terms in order to get the equations determining the system behavior averaged over the period of high frequency oscillations. For patients with Parkinson’s disease, when the illness can’t be removed by drugs, there is applied a surgical procedure called deep brain stimulation. The electrode is implanted directly into the brain and the high frequency electrical current stimulates some parts of the brain. From the experiments we know that this leads to the positive results – involuntary movements are decreased or they disappear absolutely. But still it is not clear what happens with the synchronized neurons, which are responsible for the unwanted movement, under the high frequency electrical current. Therefore here we need to use the averaging method in order to analyze the system’s dynamical equations.

Zita Sukackienė
Author: Zita  Sukackienė
Dissertation title: Investigation of peculiarities of cobalt and its alloys electroless deposition
Fields of science: Physical sciences, Chemistry (03P)
Scientific supervisor: Prof. Habil. Dr. Eugenijus Norkus
Defence of the dissertation: 2014-06-30
Co alloy thin films play a major role in development of magnetic devices and microelectromechanical systems. Renewed interest to the Co electroless deposition process is due to the application of the CoP or  CoB  thin films as  barrier layers for protection of Cu layer in microelectronical systems. Though a CoP film was found to be an effective barrier against Cu diffusion, it was proposed that introduction of a third alloying element, especially a refractory metal (W, Mo, Re), may improve the barrier efficiency. An application of ternary Cobased films as diffusion barriers for Cu solves some problems preventing contamination by copper. The solutions for electroless deposition of the CoPW alloys commonly  contain citrate ions as a complexing agent. The possibility of the use of glycine as a complexing agent for Co(II) ions in a wide pH range, leading to the deposition of films with different composition and microstructure, was also  demonstrated. Glycine serves  as a complexing agent as well as a  buffering additive.
Boron containing compounds borohydrides or borazanes are stronger  reducing agents as compared to sodium hypophosphite. A commonly used boron-containing reducing agent borazane dimethylamine borane (DMAB), enables deposition of  the cobalt films at a markedly lower pH (5-9). The advantage of boron-containing reducing agents is the so-called 'self-activated' cobalt deposition. This means the beginning of electroless deposition on copper without a prior Pd activation step. Data concerning the use of other boranes for the electroless deposition of metals are scarce. The suitability of morpholine borane for cobalt and nickel deposition is mentioned only in some patents, however, there are no data concerning this process and properties of the coatings obtained. Therefore, it was important to investigate electroless cobalt deposition with morpholine borane as a reducing agent in the solutions containing an alkaline metal-free ligand glycine.
In this study we also present a simple way for preparation of the gold-cobalt and gold-cobalt-boron catalysts with low Au loadings deposited on the copper surface. The electrocatalytic activity of the mentioned catalysts towards the oxidation of BH4 ions is compared with that of bare Au, Co/Cu and CoB/Cu electrodes.
Irma Liaščukienė
Author: Irma Liaščukienė
Dissertation title: Lipid films on nanostructured aluminum substrate: mechanism of formation, stability and effect on surface properties
Fields of science: Physical sciences, Chemistry (03P)
Scientific supervisor: Dr. Svajus Asadauskas
Defence of the dissertation: 2014-07-04
Lipids interact with metallic materials in various fields of applied sciences and technologies. For instance, vegetable oils are extensively used in food industries and more recently as environmentally friendly lubricants, fatty acid methyl esters as biodiesel, and a variety of phospholipids for the design of biomaterials and biosensors, for the drug delivery, and cosmetic products.
Lipids, one of the four mam  classes  of  biomolecules,  constitute  the molecular architecture of biomembranes and play key functional roles in biochemical processes. They include a  wide  range  of  amphiphilic molecules which generally possess one  or  several  hydrophobic  alkyl  chains and hydrophilic groups such as phosphate  in  phospholipids,  carboxylate  in fatty acids (FA), hydroxyl in cholesterol, and amino  alcohol  in sphingolipids. The ability of lipids to self-assemble and self-organize at interfaces has attracted much interest, leading to the design of biomimetic materials with tailored properties and functions. In particular, the ability to tailor both head and tail groups of lipid molecules may help to better understand relevant phenomena at the molecular  level, such as wetting, adhesion, lubrication, and corrosion processes.
The mechanism of adsorption of lipids on solid surfaces is complex as it involves multiple interfacial processes, including self-assembly, self­ organization, hydration, desorption, etc. Furthermore, the adsorbed phase is sensitive to physicochemical conditions of the medium (temperature, ionic strength, etc.) and the properties  of the substrate (hydrophobicity, charge, etc.).
The adsorption ofFA on solid surfaces often creates major technical hurdles, when "clean" surfaces are necessary. The propensity ofFA and their derivative esters to bind chemically to metal surfaces makes them difficult to remove. Fm1hermore, most fatty acids are not soluble in water and are not  volatile. When washed with water, detergents must be used for their removal, but this typically  leads  to  even  further  surface  contamination  with  soaps,  detergents, etc. Indeed, even a simple touch of bare hands immediately leaves a trac human sebum and epidermal lipids, which are mainly constituted  of fre.  Surface  contamination  with  FA  can  also  occur  due  to  the  mi' lubricants,  exposure  to vacuum  pump  grease,  soldering  flux, incidental etc. Once  adsorbed  on  the  metal surface,  the  removal  of  FA  requir chemically  aggressive  technique,  such as  treatment  in H202,  acid etchin reagent-free methods such as thermal annealing or UV/03 treatment. 
In the present study, we focus on the adsorption behavior of two categ of lipids on Al substrate: FA and phopholipid. Indeed, the self-assembly a on  Al  oxides  has  attracted  particular  interest.  This  is  due  tc relevance  of the Al oxides/hydroxides  chemistry, from the  fundam point of view, but also to the importance of this material in many technolo applications  such as lubrication,  water/oil  repellency  and corrosion  inhil. Moreover,  Al foil is widely used  in food  industry  and  many packaging  applications. Free oleic and linoleic acids are widespread  in 1 types of food, because oils and fats easily hydrolyze during food storag1 processing, producing free FA along with mono- or di-glycerides.  Oleic a by far the most widespread fatty acid in foods, while linoleic acid is nem abundant as stearic or palmitic acids.   Consequently,  adsorption  of olei< linoleic  acids  on Al  surface occurs almost  inevitably  when  food is wn into AI foil.   Previous  reports showed significant  increase of Al conte1 foods, which were processed while wrapped  into the aluminum foil. So far possible  Al  intake  levels  were  reported  to be  far below  l  mg bodyweight per  day,  established  as  a  safe  dose  by  WHO  (World  1 Organization,   1989).  Nevertheless,  bearing   in  mind the  magnitude  a exposure  to  Al  foil,  possibilities  of  chemical  transformations  of  olei1 linoleic acids, when adsorbed on AI, deserve much more significant attent.
Kęstutis Juškevičius
Author: Kęstutis Juškevičius
Dissertation title: Investigation of optical and physical properties of dielectric tidn films and optimisation of their deposition technologies
Fields of science: Physical  sciences, Physics (02 P)
Scientific supervisor: dr. Ramutis Drazdys
Defence of the dissertation: 2014-09-04
In the doctoral thesis experimental results are presented in 3 parts. In the first part we report an experimental investigation of subsurface damage (SSD) in conventionally polished fused silica (FS) substrates, which are widely used in laser applications and directly influence performances of optical elements. Subsurface damages are defined as residual digs and scratches, some of which arc filled with polishing slurry and covered with so­ called Bielby layer (polished layer). Acid etching procedure of FS substrates was developed, which allows removing polished layer and eliminating SSD. Surface roughness and laser induced damage threshold (LIDT measurements were perfonned to find con·elation between the main surface properties as circumstantial evidence of elimination  of SSD. Different durations of acid etching have been used to study LIDT of FS substrates. These experiments revealed that the optimal etching time is ~1 min for a given acid concentration. Laser induced damage threshold of etched FS samples increased -4 times.
In second part, we  investigate  a LIDT  in  LiB305  (LBO) crystals coated  with different types of (single AR@355 nm and triple AR@355+532+ I 064 nm wavelength) anti­ reflective coatings while optimizing the refractive  index. All these  coatings were produced of different  oxide materials (Zr02, Al203, and  Si02)  and  Zr02-Si02 mixtures  by using  the ion beam sputtering (IBS) deposition technique. The Noch filter with gradient refractive index profile were designed and deposited on FS substrate.
In  third part, we present  explorations  of reactive  magnetron  sputtering technology for deposition of Zr02and Nb20s/Si02 mixture thin films at low substrate temperature. A high deposition rate (64% of the pure Zr metal rate) process of zirconium oxide is obtained by employing active  feedback  reactive  gas  control  which  creates  a  stable and  repeatable deposition processes  in the transition region.  Substrate heating at 200°C was found to have no significant effect  on  the  optical  Zr02 film  properties.  The  addition  of  nitrogen  to  a closed-loop controlled   process  was  found  to  have  mostly  negative  effects  in  terms  of deposition rate and optical properties.  Constant reactive gas flow 02 gas regulated Zr02 film deposition  is slow and requires  elevated  (200°C)  substrate  temperature or post-deposition annealing  to  reduce absorption  losses.  X-ray  diffraction  analysis  showed  crystalline Zr02 films consisted of monoclinic + tetragonal piJases when produced  in Arlo, atmosphere and monoclinic +rhombohedral or a single rhombohedral phase when produced  in Arl0 + N Niobia!silica mixture thin films were deposited using a reactive DC - RF magnetron c2o­ sputtering of Nb and Si metal targets at room temperature. The reactive gas llow during the sputtering processes  was controlled  by constant reactive gas flow or by an active feedback process control system. The deposition rates of an Nb20, and Si02 layers higher  by 61% and   137%,  respectively,   were  obtained   using  the latter echnique.  All  mixture  films produced  in  this  study had  amorphous  structure.  Substantially less inhomogeneity  of mixture coatings was found in feedback controlled reactive sputtering processes.
Simonas Kecorius
Author: Simonas Kecorius
Dissertation title: Application  of aerosol  spectrometry to define processes which  change atmospheric aerosol particle properties
Fields of science: Physical  sciences, Physics (02 P)
Scientific supervisor: dr. Vidmantas Ulevičius
Defence of the dissertation: 2014-12-19
In this dissertation the aerosol spectrom etry method was used to defint the processes which change  the phy sical properties of atmospheric  aeroso particles. It presents the results from both, long term  and field campaigr measurements. State of art instrumentation was used to determine sub-micror aerosol particle number size distribution (Neutral cluster and Air lor Spectrometer, NAIS, and Scanning Mobility Pmiicle Sizer, SMPS) volatilit) (Volatility Tandem Differential Mobi lity Analyzer, V-TDMA), anc hygroscopicity (Hygroscopicity Tandem Differential Mobility Analyzer, R TDMA) properties of an aerosol. In this work volatility and hygroscopicit) technique s, which link aerosol size to chemical composition, were combined tc determine aerosol particle mixing state and to understand factors favourin nocturnal new particle formation.
Long term measurement s at the Preila Environmental Research Statior (Lithuania) indicated periodic , exclusively high aerosol particle number anc black carbon (BC) mass concentration episodes. The processes altering the physical properties of the background environment aerosol particles were found to be bioma ss burning and emissions from the ships. It was shown thai high levels of black  carbon and high accumulation mode particle numbe1 concentrat ion are related to the transport of air masses rich in bioma ss burnin g product s arriving from Kaliningrad region, Ukraine and south western part oJ Russia. One hour aerosol particle numb er and (BC) mass concentrations during such episodes exceed 40000 ± 4000 cm-3 and 11000 ± 550 ng/m3, respectively While the average concentration values are about 3800 ± 380 cm-3 and 340 ± 20 ng/m3 , respectively. Ångstrom exponent of the absorption coefficient was 2.4. Moreover, during the situation of connected atmospheric  flow  between three atmospheric observation stations along the Baltic Sea coast: Vavihill (upwind, Sweden), Utö (upwind, Finland), and Preila  (downwind , Lithuania)  a clear increase in particle number concentration (diameter interval 50 - 400 nm) by a factor of 2.1 from Utö (NUtö = 870 ± 90 cm to Preila, and by a factor of 1.7 from Vavihill  (NVavihill = 870 ±  90 cm-3 to Preila, was found. Likewise, the aerosol pmticle light absorption coefficient (A.= 530 nm) was 2.7 times greater at Preila than at Vavihill (babs vavihill = 0.9 ± 0.05 Mm-1 ) than at Utö ( babs Utö = 2.2 ± 0.1 Mm-1) During the periods of connected flow, the absorption Angstrom exponent at Preila was found to be near unity, further supporting the conclusion that ship-emitted, particulate matter contributed to the background aerosol properties in Lithuania.
A one month long field campaign was carried out in Xianghe, China, as a part of "Campaign of Air Quality Research in Beijing and Surrounding Region 2013" (CAREBeijing-2013). The results indicate that during the observation period, 19 of 32 nights experienced rapid bursts of ultra-fine pmticle number concentration   which   were   attributed   to   new
particle   formation   with   a condensation sink (for particles in the range of 2 - 750 nm) of CS = 0.055 s-1. The lower limit of the nocturnal new particle fonnation rate was 45± 5 cm-3 s-1, which is 1.25 times higher than a daytime value. Several factors were found to favour a new particle formation, including relative humidity, wind speed and most impmtant- wind direction. The upwind life-stock lofts were found to be the main source of possibly high concentrations of NH3 and condensable organics (amines), all contributing to nochtrnal new particle fonnation and rapid growth. It was also concluded that such nocturnal events intensify particle aging and effectively change the mixing state of aerosol particles.