Kaikki aineistot
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We have applied positron annihilation spectroscopy combined with sheet resistance measurements to study the electrical isolation of thin ZnO layers irradiated with 2 MeV O+ ions at various fluences. Our results indicate that Zn vacancies, the dominant defects detected by positrons, are produced in the irradiation at a relatively low rate of about 2000 cm−1 when the ion fluence is at most 1015 cm−2 and that vacancy clusters are created at higher fluences. The Zn vacancies introduced in the irradiation act as dominant compensating centers and cause the electrical isolation, while the results suggest that the vacancy clusters are electrically inactive.
The Master Thesis studied the liquid-assisted laser ablation of ceramics. Six alumina ceramics materials with different composition (Al2O3 from 16% to 98%, SiO2 up to 72%) were exposed to pulsed and continuous wave irradiation in near IR and IR regions. The effect of bulging of melt bath during ablation and expansion to the glass sphere above crater after cessation of laser action were observed, recorded and analyzed. The samples mostly prone to this effect were defined. In addition, thickness, hardness, chemical and optical properties of spheres were measured. The overall mechanism and modeling were presented according to high-speed camera and thermal imaging monitoring data.
We have used positron annihilation spectroscopy to determine the nature and the concentrations of the open volume defects in as-grown and electron irradiated (Eel=2 MeV, fluence 6×1017 cm−2) ZnO samples. The Zn vacancies are identified at concentrations of [VZn]≃2×1015 cm−3 in the as-grown material and [VZn]≃2×1016 cm−3 in the irradiated ZnO. These concentrations are in very good agreement with the total acceptor density determined by temperature dependent Hall experiments. Thus, the Zn vacancies are dominant acceptors in both as-grown and irradiated ZnO.
We investigate the antisite formation in GaAs by molecular dynamics simulation with a realistic many-atom potential. The recoil energies are chosen to correspond to the values encountered in electron irradiation experiments. The probability of forming antisites directly during the cascade is substantial. The antisite defects are stable and are likely to survive during long-term annealing. We estimate the angle-dependent threshold for antisite formation and discuss the creation mechanism. The cross sections for antisite and vacancy formation are compared.
InN layers have been implanted with helium at 158 keV at various fluences to study the nature of the generated defects. The defects have been probed using positron annihilation spectroscopy. The first measurements showed that at least two different kinds of defects are created depending of the implantation fluence. The second measurements performed two years later gave different results suggesting that at least one of these defects is not stable at room temperature.
We have used positron annihilation spectroscopy to study the introduction and recovery of point defects in electron-irradiated n-type ZnO. The irradiation (Eel=2MeV, fluence 6×1017cm−2) was performed at room temperature, and isochronal annealings were performed from 300 to 600 K. In addition, monochromatic illumination of the samples during low-temperature positron measurements was used in identification of the defects. We distinguish two kinds of vacancy defects: the Zn and O vacancies, which are either isolated or belong to defect complexes. In addition, we observe negative-ion-type defects, which are attributed to O interstitials or O antisites. The Zn vacancies and negative ions act as compensating centers and are introduced at a concentration [VZn]≃cion≃2×1016cm−3. The O vacancies are introduced at a 10-times-larger concentration [VO]≃3×1017cm−3 and are suggested to be isolated. The O vacancies are observed as neutral at low temperatures, and an ionization energy of 100 meV could be fitted with the help of temperature-dependent Hall data, thus indicating their deep donor character. The irradiation-induced defects fully recover after the annealing at 600 K, in good agreement with electrical measurements. The Zn vacancies recover in two separate stages, indicating that the Zn vacancies are parts of two different defect complexes. The O vacancies anneal simultaneously with the Zn vacancies at the later stage, with an activation energy of EmV,O=1.8±0.1eV. The negative ions anneal out between the two annealing stages of the vacancies.
We use positron annihilation spectroscopy to study 2MeV 4He+-irradiated InN grown by molecular-beam epitaxy and GaN grown by metal-organic chemical-vapor deposition. In GaN, the Ga vacancies act as important compensating centers in the irradiated material, introduced at a rate of 3600cm−1. The In vacancies are introduced at a significantly lower rate of 100cm−1, making them negligible in the compensation of the irradiation-induced additional n-type conductivity in InN. On the other hand, negative non-open volume defects are introduced at a rate higher than 2000cm−1. These defects are tentatively attributed to interstitial nitrogen and may ultimately limit the free-electron concentration at high irradiation fluences.
A unique experimental setup at the Accelerator Laboratory of the University of Helsinki enables in situ positron annihilation spectroscopy (PAS) analysis on ion irradiated samples. In addition, the system enables temperature control (10–300 K) of the sample both during irradiation and during subsequent positron annihilation measurements. Using such a system for defect identification and annealing studies comes with a plethora of possibilities for elaborate studies. However, the system also poses some restrictions and challenges to these possibilities, both related to irradiation and to the PAS analysis. This review tries to address these issues.
C60 donor dyads in which the carbon cage is covalently linked to an electron-donating unit have been discussed as one possibility for an electron-transfer system, and it has been shown that spherical [Ge9] cluster anions show a close relation to fullerenes with respect to their electronic structure. However, the optical properties of these clusters and of functionalized cluster derivatives are almost unknown. We now report on the synthesis of the intensely red [Ge9] cluster linked to an extended π-electron system. [Ge9{Si(TMS)3}2{CH3C=N}-DAB(II)Dipp]− (1−) is formed upon the reaction of [Ge9{Si(TMS)3}2]2− with bromo-diazaborole DAB(II)Dipp-Br in CH3CN (TMS=trimethylsilyl; DAB(II)=1,3,2-diazaborole with an unsaturated backbone; Dipp=2,6-di-iso-propylphenyl). Reversible protonation of the imine entity in 1− yields the deep green, zwitterionic cluster [Ge9{Si(TMS)3}2{CH3C=N(H)}-DAB(II)Dipp] (1-H) and vice versa. Optical spectroscopy combined with time-dependent density functional theory suggests a charge-transfer excitation between the cluster and the antibonding π* orbital of the imine moiety as the cause of the intense coloration. An absorption maximum of 1-H in the red region of the electromagnetic spectrum and the corresponding lowest-energy excited state at λ=669 nm make the compound an interesting starting point for further investigations targeting the design of photo-active cluster compounds.
Using first-principles and analytical potential atomistic simulations, production of defects in epitaxial graphene (EG) on SiC upon ion irradiation for ion types and energies accessible in helium-ion microscope is studied. Graphene-SiC systems consisting of the buffer (zero) graphene layer and SiC substrate, as well as one (monolayer) and two (bilayer) additional graphene layers, are focused on. The probabilities for single, double, and more complex vacancies to appear upon impacts of energetic ions in each graphene layer as functions of He- and Ne-ion energies are calculated and the data are compared with those obtained for free-standing graphene. The results indicate that the role of the substrate is minimal for He-ion irradiation with energies above 5 keV, which can be associated with a low sputtering yield from this system upon ion irradiation, as compared with the common Si/SiO2 substrate. In contrast, SiC substrate has a significant effect on defect production upon Ne-ion irradiation. The results can serve as a guide to the experiments on ion irradiation of EG to choose the optimum ion beam parameters for defect-mediated engineering of such systems, for example, for creating nucleation centers to grow other 2D materials, such as h-BN, on top of the irradiated EG.
Two-dimensional (2D) transition metal dichalcogenides (TMDs), like MoS2, have unique electronic and optical properties, which can further be tuned using ion bombardment and post-synthesis ion-beam mediated methods combined with exposure of the irradiated sample to precursor gases. The optimization of these techniques requires a complete understanding of the response of 2D TMDs to ion irradiation, which is affected by the reduced dimensionality of the system. By combining analytical potential molecular dynamics with first-principles calculations, we study the production of defects in free-standing MoS2 sheets under noble gas ion irradiation for a wide range of ion energies when nuclear stopping dominates, and assess the probabilities for different defects to appear. We show that depending on the incident angle, ion type and energy, sulfur atoms can be sputtered away predominantly from the top or bottom layers, creating unique opportunities for engineering mixed MoSX compounds where X are chemical elements from group V or VII. We study the electronic structure of such systems, demonstrate that they can be metals, and finally discuss how metal/semiconductor/metal junctions, which exhibit negative differential resistance, can be designed using focused ion beams combined with the exposure of the system to fluorine.
The interpretation of helium ion microscopy (HIM) images of crystalline metal clusters requires microscopic understanding of the effects of He ion irradiation on the system, including energy deposition and associated heating, as well as channeling patterns. While channeling in bulk metals has been studied at length, there is no quantitative data for small clusters. We carry out molecular dynamics simulations to investigate the behavior of gold nanoparticles with diameters of 5-15 nm under 30 keV He ion irradiation. We show that impacts of the ions can give rise to substantial heating of the clusters through deposition of energy into electronic degrees of freedom, but it does not affect channeling, as clusters cool down between consecutive impact of the ions under typical imaging conditions. At the same time, high temperatures and small cluster sizes should give rise to fast annealing of defects so that the system remains crystalline. Our results show that ion-channeling occurs not only in the principal low-index, but also in the intermediate directions. The strengths of different channels are specified, and their correlations with sputtering-yield and damage production is discussed, along with size-dependence of these properties. The effects of planar defects, such as stacking faults on channeling were also investigated. Finally, we discuss the implications of our results for the analysis of HIM images of metal clusters.
Recent experiments have demonstrated the formation of free-standing Au monolayers by exposing the Au–Ag alloy to electron beam irradiation. Inspired by this discovery, we used semi-empirical effective medium theory simulations to investigate monolayer formation in 30 different binary metal alloys composed of late d-series metals such as Ni, Cu, Pd, Ag, Pt, and Au. In qualitative agreement with the experiment, we find that the beam energy required to dealloy Ag atoms from the Au–Ag alloy is smaller than the energy required to break the dealloyed Au monolayer. Our simulations suggest that a similar method could also be used to form Au monolayers from the Au–Cu alloy and Pt monolayers from Pt–Cu, Pt–Ni, and Pt–Pd alloys.
Abstract This study concentrates on the preparation and characterization of some ionic liquids and their use in dimerization reaction of 2-methylpropene. Ionic liquids consist of cations and anions, and are commonly understood as green solvents. By definition their melting points should be lower than 100 °C. Prepared ionic liquids were used as catalytic solvents in dimerizations of 2-methylpropene to a high octane compound, isooctene. The monograph consists of two parts: the literature survey and the practical work. The literature survey reviews the preparation and characterization of ionic liquids as well as their environmental aspects, such as toxicity, biodegradability and recyclability. In addition, the acid catalyzed dimerization of butenes is discussed together with the dimerizations of light olefins carried out in ionic liquids. The practical work consists of three entities: The environmentally benign preparation of 1-alkyl-3-methylimidazolium-based ionic liquids under microwave activation, the characterization of ionic liquids and the use of the ionic liquids in the dimerization reaction. Ionic liquids absorb efficiently microwave irradiation and the most beneficial aspect in the microwave-assisted preparations was the considerably shortened reaction time compared to the conventional methods. In addition to the microwave-assisted preparations, [Cnmim][InCl4] ionic liquids were prepared successfully without microwave irradiation. A special attention was paid to the characterization of ionic liquids since impurities are known to affect on the properties of the ionic liquids. Ionic liquids were analysed with the following methods: 1H and 13C NMR, MS(ESI+ and ESI-), GC and elemental analysis. Characterization of ionic liquids was done by determining the thermal stability, the melting point and the crystal structure of each solid ionic liquid. The determination of the liquid range of ionic liquid is necessary in order to know the temperature limits for each ionic liquid. Novel InCl3-based ionic liquids revealed to be the more efficient than Brønsted acidic ILs as a catalytic reaction media in the dimerization of 2-methylpropene. It was preferable to apply [C6mim]Cl/InCl3 (x(InCl3) = 0.55) as a catalytic IL since then the conversion of 2-methylpropene and the product distribution revealed to be good. In order to maximize the production and the separation of dimers reaction should be carried out continuously at temperature high enough, such as 160 °C. Neutral InCl3-based ionic liquid did not catalyze reaction of 2-methylpropene, but it had to be acidic x(InCl3) > 0.5. Excess of InCl3 did not leach out from the IL and the recycling of IL was possible.
Controlled production of defects in hexagonal boron nitride (h-BN) through ion irradiation has recently been demonstrated to be an effective tool for adding new functionalities to this material, such as single-photon generation, and for developing optical quantum applications. Using analytical potential molecular dynamics, we study the mechanisms of vacancy creation in single-and multi-layer h-BN under low-and high-fluence ion irradiation. Our results quantify the densities of defects produced by noble gas ions in a wide range of ion energies and elucidate the types and distribution of defects in the target. The simulation data can directly be used to guide the experiment aimed at the creation of defects of particular types in h-BN targets for single-photon emission, spin-selective optical transitions and other applications by using beams of energetic ions.
Background: Oxidative stress induced by radiation causes variable expression of antioxidant enzymes in a tissue-specific manner. Testicular tissues carry out the complex process of spermatogenesis, and studies indicate that testicular damages due to irradiation require long-term recovery before complete resumption. Ionizing radiation also causes oxidative stress in tissues, leading to testicular damage. Aims and Objectives: This study measured differential expression of antioxidant enzymes following administration of C. borivilianum root extract (CRB) in response to irradiation-induced oxidative stress. The activity of various important endogenous enzymatic defense systems was evaluated and correlated for strength of association. Materials and method: Two forms of C. borivilianum (CB) extracts [CB alone and CB-silver nanoparticles (AgNPs)] were administered at a dose of 50 mg/kg body weight to Swiss albino male mice for 7 consecutive days. After that, they were irradiated with 6 Gy irradiation and further used to study various parameters of antioxidant enzymes. Results: Results indicate a significant increase in the level of glutathione (GSH) and the activity of GSH-related antioxidant enzymes in irradiated mice treated with CRE and CRE-AgNPs (silver nanoparticles biosynthesized using C. borivilianum root extract) in comparison to non-pretreated ones (groups I and II). Reciprocal elevation was observed in related enzymes, that is, glutathione S-transferase activity (GST), glutathione reductase (GR), and glutathione peroxidase activity (GPx). Elevation in the activity of catalase (CAT) and superoxide dismutase (SOD) was also evident in both the irradiated groups pretreated with CRE-AgNPs. However, expression of CAT in the CRE-treated irradiated group was similar to that of the non-treated irradiated group. Higher association among CAT-SOD, CAT-GPx, and GR-GST was observed. Conclusion: Overall, it was observed that testicular cells post-irradiation in all groups go through intense oxidative stress; however, groups pretreated with CRE or CRE-AgNPs indicated better toleration and resumption of antioxidant capacity. CRE or CRE-AgNPs pretreated non-irradiated groups mostly remained within the control range indicating stimulated expression of antioxidants.
Tässä työssä on tutkittu galliumnitridin ja indiumgalliumnitridin käyttäytymistä kun niitä säteilytetään matalaenergisella elektronisuihkulla (engl., low energy electron beam irradiation, LEEBI). Tämän lisäksi tutkittiin ja valmistettiin periodisia hopearaidoituksia, jonka tavoitteena oli aikaansaada plasmonikytkentään perustuva valon emission lisäys. Sekä hopearaitojen, että LEEBI:n vaikutusta tutkittiin fotoluminesenssiin (engl., photoluminescence, PL) perustuvin mittauksin. Lisäksi hopearaitojen ominaisuuksia mitattiin käyttäen reflektometriaa. On osoitettu, että LEEBI aiheuttaa selvän vaimenemisen valon emission intensiteetissä metallo-orgaanisella kaasufaasiepitaksialla valmistetuissa InGaN kvanttikaivoissa (engl., quantum well, QW) sekä GaN-kalvoissa. Vaimeneminen on voimakkaampaa LEEBI-säteilyannoksen kasvaessa. Vaimeneminen on myös voimakkaampaa pienemmillä elektronien liike-energioilla. Tämä täsmää hyvin elektronisäteen energian tunkeutumisprofiilin kanssa. Vaimenemisen aiheuttavaa mekanismia on tutkittu positroniannihilaatiospektroskopialla (PAS). Mittaukset paljastavat, että LEEBI aktivoi valmistuksen aikana muodostuneita galliumvakansseja (VGa), jotka ovat muuten passiivisia. Toisin sanoen ne eivät vaikuta PL-signaaliin eivätkä näy PAS:ssa. Vakanssien passivaatiomekanismismi liittynee kompleksien muodostumiseen vedyn kanssa. Erityisesti VGa -3H kompleksi ei näy PAS-mittauksissa ja on neutraali. Koska vaimeneminen on identtistä näytteiden välillä, jotka on kasvatettu vedyssä ja typessä, voidaan todeta että vedyn lähde ei ole kantajakaasu. Näytteiden lämmittäminen palauttaa osan luminesenssin intensiteetistä. Todennäköisesti näytteen sisäinen vetydiffuusio uudelleenpassivoi vakansseja. Olemme kehittäneet pintarakenteen (poly)vinyyliakoholilla (PVA) peitetyistä hopeananoraidoista InGaN QW-rakenteen päälle. Hopearaidat voivat difraktoida valokanavamoodeja GaN- ja PVA-kerroksista, lisäten näin merkittävästi valon ulospääsyä rakenteesta. Tällä yksinkertaisella tekniikalla on saavutettu lähes 3-kertainen valon intensiteetti verrattuna käsittelemättömään näytteeseen.
Hyperdoped silicon (hSi) fabricated via femtosecond laser irradiation has emerged as a promising photoelectric material with strong broadband infrared (IR) absorption. In this work, we measured the optical absorptance of the hSi in the wavelength of 0.3–16.7 µm. Unlike the near to mid wavelength IR absorption, the mid-long wavelength IR (M–LWIR) absorption is heavily dependent on the surface morphology and the dopants. Furthermore, calculations based on coherent potential approximation (CPA) reveal the origin of free carrier absorption, which plays an important role in the M–LWIR absorption. As a result, a more comprehensive picture of the IR absorption mechanism is drawn for the optoelectronic applications of the hSi.
Two-dimensional (2D) materials with nanometer-size holes are promising systems for DNA sequencing, water purification, and molecule selection/separation. However, controllable creation of holes with uniform sizes and shapes is still a challenge, especially when the 2D material consists of several atomic layers as, e.g., MoS2, the archetypical transition metal dichalcogenide. We use analytical potential molecular dynamics simulations to study the response of 2D MoS2 to cluster irradiation. We model both freestanding and supported sheets and assess the amount of damage created in MoS2 by the impacts of noble gas clusters in a wide range of cluster energies and incident angles. We show that cluster irradiation can be used to produce uniform holes in 2D MoS2 with the diameter being dependent on cluster size and energy. Energetic clusters can also be used to displace sulfur atoms preferentially from either top or bottom layers of S atoms in MoS2 and also clean the surface of MoS2 sheets from adsorbents. Our results for MoS2, which should be relevant to other 2D transition metal dichalcogenides, suggest new routes toward cluster beam engineering of devices based on 2D inorganic materials.
The spread of the invasive species via ballast water is one of the most serious global environment threats. International Maritime Organization IMO adopted in 2004 ‘the International Convention for the Control and Management of Ships’ Ballast Water and Sediments’ for the purpose of prevents the spread of species. The Convention binds ships to treat their ballast water and it also contains requirements for the treatment systems. Even though the Convention hasn’t yet come into effect, there is already dozens of IMO’s approved treatment systems in the market. These systems utilize different kinds of mechanical, physical and chemical techniques. One of the most used techniques for the treatment of ballast water is ultra-violet irradiation. UV radiation is created by mercury lamps, which however consume a lot of energy and contain toxic mercury. The object of this thesis was to find out, is it possible to substitute UV LED lamps for mercury lamps in the near future. Among other things advantages of the UV LED lamps are energy efficiency and a resistant and non-toxic structure. The main aim of this study was to research with laboratory tests, what will be the UV dose that is needed to inactivate 10-50 µm sized phytoplankton species. Setup of measurements met largely the requirements of IMO. In the laboratory tests it was used UV LED lamps, which wavelength of light was 265 nm. Samples were analysed with PAM-fluorometer and flow cytometer. Based on the results it was needed approximately 600 mJ/cm2 UV dose to inactivate species Asterionellopsis glacialis and Thalassiosira sp., which were used in the study. The result was similar to expectations and it was comparative with the other studies, which have been published on the topic. As present UV LED lamps are very inefficient, they are not yet suitable for ballast water treatment. UV LED lamps’ development work is however underway and it has been estimated, that high water flow rates will be treated with UV LED lamps in 5-10 years.
CASP8 mutations occur most commonly in head and neck squamous cell carcinoma (HNSCC), with a mutation frequency of 10,7 %. Alterations in this gene have been shown to impair the effects of radiotherapy in HNSCC patients and are associated with poor overall survival. Thus, it is of great importance to identify the means cancer cells use to escape cell death and develop resistance to cancer therapies in order to find predictive markers. Caspase-8 is a cysteine protease, encoded by the CASP8 gene that plays a crucial role in both extrinsic apoptosis and inflammatory signaling, while acting as an inhibitor of necroptosis. In apoptotic signaling, the catalytic activation of Caspase-8 by cleavage and dimerization is required, while in inflammatory signaling, procaspase-8 acts as a scaffold for FADDosome formation independently from its catalytic activity. CASP8 mutations have a complex role in HNSCC; mutations have been shown to impair and inhibit death receptor-mediated cell death as well as to promote activation of NF-κB-dependent inflammatory signaling. Previous studies have shown that HNSCC-associated CASP8 mutations could inhibit the activation of apoptotic signaling and cell death following death receptor stimulation. Moreover, mutations have been shown to both impair and enhance the NF-κB- dependent inflammatory signaling, depending on the mutation site. These findings indicate the diverse functional properties of HNSCC-associated CASP8 mutations, rather than only being loss- of-function mutations. This thesis aimed to investigate the contributions of nine HNSCC-associated CASP8 mutations (L7V, L62P, R71T, S99F, L105H, D303G, S375*, T441I and Q465*) to radiotherapy response in cancer cells. In addition, the effects of CASP8 mutations on inflammatory signaling mediated by death receptor stimulation in cancer cells were studied. CASP8 mutations were generated by site-directed mutagenesis and cloned using Gateway cloning. HeLa CASP8-/- cells were then virally transduced with mutation plasmids. Created stable CASP8 mutation cell lines were irradiated, after which cell viabilities were measured using the MTT assay. The effects of CASP8 mutations on the cytokine and chemokine expression following irradiation and TRAIL treatment were analysed by qPCR. Based on the findings from this study, mutations T441I and Q465* exhibited higher cell viability following irradiation compared to WT CASP8, suggesting that these mutations could potentially impair the activation of cell death signaling after irradiation. Moreover, seven out of nine CASP8 mutants were more sensitive to irradiation than WT CASP8. This study also showed that most of the CASP8 mutants retained their ability to activate NF-κB-dependent inflammatory signaling following irradiation or death receptor stimulation by TRAIL. However, further studies are required to determine whether mutations T441I and Q465* have potential to act as predictive markers in HNSCC.
The focused ion beam (FIB) has proven to be an extremely powerful tool for the nanometer-scale machining and patterning of nanostructures. In this work, we experimentally study the behavior of AISI 420 martensitic stainless steel when bombarded by Ga+ ions in a FIB system. The results show the formation of nanometer sized spiky structures. Utilizing the nanospiking effect, we fabricated a single-tip needle with a measured 15.15 nanometer curvature radius and a microneedle with a nanometer sized spiky surface. The nanospikes can be made straight or angled, depending on the incident angle between the sample and the beam. We also show that the nanospiking effect is present in ferritic AISI 430 stainless steel. The weak occurrence of the nanospiking effect in between nano-rough regions (nano-cliffs) was also witnessed for austenitic AISI 316 and martensitic AISI 431 stainless steel samples.
A 3-dimensional mathematical model of asphalt pavement system was developed, based on the fundamental energy balance, to calculate temperatures beneath asphalt surface using hourly measured solar radiation, air temperature and wind velocity data. The modelling was conducted to predict the heat retention under the asphalt surface to seek an optimum position of pipe tubing to maximise the heat extraction considering the Nordic winter conditions for future infrastructure projects. The model results show good agreement with the experimental results conducted in a span of three months (June–Sept) notwithstanding the simplification of the model i.e. thermal properties unaffected by changing moisture content, perfect contact between different layers and homogeneous and isotropic thermal properties of materials (asphalt, sand and gravel). The findings indicated that the positioning of the heat extraction tubes under the asphalt layer will be dictated by the application. For heat extraction, pipes closer to the surface are ideal for maximal heat absorption during summer, however, in winter the outer temperature may effect properties the pipes. Parameters including pipe diameter, positioning of the pipes and flow rate were analysed. Temperature increase of up to 10 °C gain was observed for piping closer to the asphalt layer and 6 °C for pipes position at deeper from the asphalt layer. This model could be used in future to optimise critical variables for successful implementation of asphalt heating concepts.
By combining scanning tunneling microscopy, low-energy electron diffraction, photoluminescence and Raman spectroscopy experiments with molecular dynamics simulations, a comprehensive picture of the structural and electronic response of a monolayer of MoS 2 to 500 eV Xe + irradiation is obtained. The MoS 2 layer is epitaxially grown on graphene/Ir(1 1 1) and analyzed before and after irradiation in situ under ultra-high vacuum conditions. Through optimized irradiation conditions using low-energy ions with grazing trajectories, amorphization of the monolayer is induced already at low ion fluences of 1.5 × 10 14 ions cm -2 and without inducing damage underneath the MoS 2 layer. The crystalline-to-amorphous transformation is accompanied by changes in the electronic properties from semiconductor-to-metal and an extinction of photoluminescence. Upon thermal annealing, the re-crystallization occurs with restoration of the semiconducting properties, but residual defects prevent the recovery of photoluminescence.
Background and purpose: The interplay efect of respiratory motion on the planned dose in free-breathing rightsided whole-breast irradiation (WBI) were studied by simulating hypofractionated VMAT treatment courses. Materials and methods: Ten patients with phase-triggered 4D-CT images were included in the study. VMAT plans targeting the right breast were created retrospectively with moderately hypofractionated (40.05 Gy in 15 fractions of 2.67 Gy) and ultra-hypofractionated (26 Gy 5 fractions of 5.2 Gy) schemes. 3D-CRT plans were generated as a reference. All plans were divided into respiratory phase-specifc plans and calculated in the corresponding phase images. Fraction-specifc dose was formed by deforming and summing the phase-specifc doses in the planning image for each fraction. The fraction-specifc dose distributions were deformed and superimposed onto the planning image, forming the course-specifc respiratory motion perturbed dose distribution. Planned and respiratory motion perturbed doses were compared and changes due to respiratory motion and choice of fractionation were evaluated. Results: The respiratory motion perturbed PTV coverage (V95%) decreased by 1.7% and the homogeneity index increased by 0.02 for VMAT techniques, compared to the planned values. Highest decrease in CTV coverage was 0.7%. The largest dose diferences were located in the areas of steep dose gradients parallel to respiratory motion. The largest diference in DVH parameters between fractionation schemes was 0.4% of the prescribed dose. Clinically relevant changes to the doses of organs at risk were not observed. One patient was excluded from the analysis due to large respiratory amplitude. Conclusion: Respiratory motion of less than 5 mm in magnitude did not result in clinically signifcant changes in the planned free-breathing WBI dose. The 5 mm margins were sufcient to account for the respiratory motion in terms of CTV dose homogeneity and coverage for VMAT techniques. Steep dose gradients near the PTV edges might decrease the CTV coverage. No clinical signifcance was found due to the choice of fractionation.
The usage of PV batteries nowadays became more and more widely spread. Due to the fact that the efficiency of modern PV is rising every year the prevalence of this source of energy is increasing. As the source of the energy is sunlight, these batteries need to be complimented by storage capacitors which will store energy for future use. Nevertheless the less the calculation of demanded amount of energy according the load and capacity of a storage battery that will keep the end consumer in work during certain time still is not overviewed. In this thesis the overall system will be considered and there will be made economic calculations for configurations of such system that will depend from the load. Also the behavior of the system in different geographical and climate conditions that influence of the amount of energy produced will be overviewed.
The main objective of the present study was to design an agricultural robot, which work is based on the generation of the electricity by the solar panel. To achieve the proper operation of the robot according to the assumed working cycle the detailed design of the main equipment was made. By analysing the possible areas of implementation together with developments, the economic forecast was held. As a result a decision about possibility of such device working in agricultural sector was made and the probable topics of the further study were found out.
This topic is a cooperation project between Helsinki University of Technology (TKK) and Uppsala University (UU). Multiple quantum wells (MQWs) were grown and characterized in Department of Micro and Nanosciences of TKK. The samples were irradiated in Ångström Laboratory of UU. In this thesis, quantum well (QW) structures based on InGaN/GaN material system have been grown by using metalorganic vapor phase epitaxy (MOVPE). The samples grown had 5 and 10 quantum wells with 6 and 10% of indium, respectively. Iodine and bromine have been used as irradiations ions. The irradiation fluences of these ions were varied from 109 to 1012 ions/cm2. Our X-ray diffraction results have shown no signs of a major crystal damage on the quantum wells. The photoluminescence results indicate a strong dependence of the optical properties on the type and fluence of ions used for irradiation.
We demonstrate that the instability of the Sb vacancy in GaSb leads to a further increase in the acceptor-type defect concentration in proton irradiated undoped, p-type GaSb. Using positron annihilation spectroscopy in situ with 10 MeV proton irradiation at 35 K, we find that the irradiation produces both native vacancy defects in GaSb. However, the Sb vacancy is unstable above temperatures of 150 K and undergoes a transition resulting in a Ga vacancy and a Ga antisite. The activation energy of this transition is determined to be 0.6 eV +/- 0.1 eV. Our results are in line with the established amphoteric defect model and prove that the instability of the Sb vacancy in GaSb has a profound role on the native defect concentration in GaSb.
In this work pine sawdust was converted into levulinic acid (LA) and furfural. Sawdust was first pre-treated with sulfuric acid-catalysed mechanical depolymerization. The conversion reactions were then performed with microwave heating at 180 °C. To enhance the furfural yield and the efficient separation of furfural and LA, a biphasic water-toluene reaction system was used. The effect of an additional catalyst, AlCl3, on the yield of LA and furfural was also studied. According to the results the pre-treatment method enhanced the yields of LA. In addition, due to the microwave heating the reaction times were short. Additional AlCl3 catalyst enhanced the LA yield, however excellent furfural yields were achieved even without it. Best LA yield (38%) was achieved with 6 h of milling combined with 30 min of microwave heating while the best furfural yield (85%) was achieved with 4 h of milling and 20 min of microwave heating.
Solar power forecasting has become an important factor in Europe in the recent past, particularly in the middle Europe as well as in the Nordic countries such as Denmark and Finland. The need for accurate forecasting has played a pivotal role in planning the operations of photovoltaic (PV) systems as well as in achieving power grid balance. In this thesis, a statistical model for solar power forecasting is computed, studied, investigated and used to predict solar power. The model uses past power measurements and meteorological forecasts of temperature, solar irradiation, relative humidity and wind speed as inputs. The weather forecast parameters used to compute power are obtained from Aladin Research Model on Nonhydrostatic forecast Inside Europe (HARMONIE) representing Lappeenranta region. The computed estimate power is then compared with the real power produced from Lappeenranta University of Technology (LUT) solar power plant. Normalized Root Mean Square Error (NRMSE) is used as the evaluation criteria. The results indicate that solar power production can be forecasted using the model with small NRMSE errors captured indicating better performance of the model.
Abstract The rapid increase of energy demand for transportation generates a rise of environmental pollution, stimulating the development of alternative sources of energy. Biomass is considered as the main organic carbon source of energy to substitute petroleum permitting sustainable production of chemicals and transportation fuels. Biowastes, residues and non-edible feedstock possess high potential resources avoiding food competition. This research aims to convert starch-based industrial waste, potato peels, into reducing sugars and platform molecules, such as glucose. These high added-value chemicals can further be transformed into chemicals and fuels. Catalytic conversion of starch, the main constituent of potato peels, was activated with non-conventional technologies to enhance the depolymerisation rate and to reduce energy consumption according to the principles of green chemistry. Depolymerisation of starch was first performed in acidic water as reaction medium assisted with ultrasonic and/or microwave irradiation. Ultrasonic irradiation enhanced mass transfer of heterogeneous system, whereas the use of microwaves improved heat transfer in the reaction medium. The frequency applied leads to different effects on heterogeneous systems: low frequencies irradiation (below 100 kHz) generates turbulences resulting in enhanced transport properties, whereas higher frequencies produce chemical effects. Catalytic conversion of starch into reducing sugars required more energy than individual irradiation could provide. Simultaneous irradiation, combining ultrasound and microwave or several ultrasonic frequencies, on potato peels led to 50% yield of sugars without former separation processes, at moderate temperature. A weak synergetic effect was only observed with potato peels. The second part of this research is dedicated to study the effect of catalytic reaction medium (acids, ionic liquids). More appropriate systems possess the ability to dissolve and hydrolyse carbohydrates: specific ionic liquids. A room-temperature ionic liquid and a task-specific ionic liquid were selected for their solvability properties to dissolve and depolymerise starch present in potato peels. The depolymerisation of starch in the task-specific ionic liquid generated a yield of 43% of sugars, without former separation process.
SiGe HBTs have emerged to meet the burgeoning demand of wireless communication and high-speed niche applications at a compelling cost advantage. The high integration capability of SiGe technology with CMOS provides a favorable opportunity to leverage the advantages of both technologies. But in recent years, the fast scaling of transistor dimensions has increased the 1/f noise and sets a minimum signal level of electronic devices. In addition, the detrimental effects of radiation on the performance and reliability of electronic devices have been an issue in the radiation society. Consequently, this is my main motivation to characterize, model and analyze the SiGe:C HBT devices to design rad-hard devices and to find a solution that reduces low-frequency noise. I have evaluated the impacts of x-ray irradiation on the DC characteristics and low-frequency noise of 55 nm advanced SiGe:C HBTs. The HBTs, which exhibit a fT/fMax of 320/370 GHz, are issued by STMicroelectronics. Three samples, which covers an emitter area range of 0.2\times 5 µm² to 0.42 \times 10 µm² were irradiated to 240 krad(air), 280 krad(air) and 520 krad(air), which is far more than the prior study on this device (i.e., 151 krad (air)). The DC parameters such as forward Gummel characteristics, current gain (hFE), relative excess base current (∆ib/ib) and relative excess collector current (∆ic/ic) were examined before and after irradiation. Moreover, the impacts of annealing at 100 \degc and 130 \degc have been evaluated to examine the possible recovery mechanisms of induced radiation traps. Concerning low frequency noise (LFN) the dependence of base current noise spectral density (Sib) of 1/f noise and generation-recombination noise (g-r noise) on base current is evaluated. To extract Kb, a figure of merit representing the 1/f noise amplitude, and locate the low-frequency noise sources, the impact of emitter geometry and collector doping is analyzed using compact SPICE modeling. I present that the radiation- induced traps majorly affect the low injection region of the base current. This is confirmed by the plot of ∆ib/ib with TID at different base emitter voltages, Vbe, and our post-irradiation model. In addition, the dependence of ∆ib/ib with emitter geometry locates the induced-radiation trap centers. The compact SPICE modeling of the 1/f noise of the device under test (DUT) shows that Sib is proportional to the quadratic dependence of base current and Kb is in the range of 10-9 µm².
Enormous amounts of fiber sludge are generated annually by the pulp industry as a by-product. As a cellulose-rich material, its current usage, mainly as fuel, is inefficient from a material efficiency point of view. This work studied the utilization of fiber sludge from a Finnish and a Swedish pulp mill as a potential feedstock to produce levulinic acid, a valuable platform chemical. The conversion experiments of fiber sludge to levulinic acid were performed in a microwave reactor with a mixture of H2SO4 and Lewis acid as the catalyst. The reaction conditions, which included reaction time and temperature as well as the H2SO4 and Lewis acid concentrations, were studied in detail. The highest levulinic acid yield, 56%, was obtained with Swedish fiber sludge after 60 min at 180 °C with the H2SO4 concentration of 0.3 mol/L and a CrCl3 concentration of 7.5 mmol/L which indicated that the fiber sludge had the potential to be used as feedstock for levulinic acid production.
The radiation tolerance of isotopic enriched and natural silicon carbide junction barrier Schottky diodes are compared under heavy ion irradiation. Both types of devices experience leakage current degradation as well as single event burnout events. The results were comparable, although the data may indicate a marginally lower thresholds for the isotopic enriched devices at lower LET. Slightly higher reverse bias threshold values for leakage current degradation was also observed compared to previously published work.
Water, typically used as the primary coolant in facilities such as fusion and fission reactors, could be exposed to a large amount of neutrons causing water activation. This phenomenon could cause radiation damage to electrical components and increase the dose to personnel. As there are only few sources of gamma rays with energies in the range of 6 MeV and 7 MeV, an irradiation system using activated cooling water as a source of energetic gamma rays is proposed at the Jozef Stefan Institute (JSI) TRIGA Mark II research reactor. A water activation irradiation loop design is proposed, inserted into a radial piercing port of a research reactor. In this thesis, a numerical model of the irradiation loop was developed and a CFD analysis was performed using ANSYS CFX. Pressure and velocity profiles were established and will serve as design limits and criteria reference for assembling the actual facility. Moreover, the 16N concentration inside the loop was studied. Its formation and decay inside the loop were predicted. This shall serve as reference for future experimental designs and further studies to be conducted using the proposed facility.
High sensitivity of SiC power MOSFETs has been observed under heavy ion irradiation, leading to permanent increase of drain and gate leakage currents. Electrical postirradiation analysis confirmed the degradation of the gate oxide and the blocking capability of the devices. At low drain bias, the leakage path forms between drain and gate, while at higher bias the heavy ion induced leakage path is mostly from drain to source. An electrical model is proposed to explain the current transport mechanism for heavy-ion degraded SiC power MOSFETs.
Nowadays, the application of human-made construction materials leads to a tremendous amount of energy consumption and non-recycled waste generation. The quantity of harmful chemicals and other components used in construction is astonishing and continues to increase constantly. Wood is one of the organic construction materials and the only one considered a renewable one. Therefore, wood becomes a preferable construction material to build safe low-energy structures which do not cause detrimental environmental impact. However, the building of wooden prefabricated residential units is mainly limited by legislation, standards, and safety requirements. The fact that wood can ‘’breathe’’, absorb, and release moisture makes this material not very durable and, consequently, not always relatively reliable. Therefore, many new different coatings and other technologies developed nowadays to achieve the greater mechanical properties of wood operated under weathering conditions such as moisture, UV irradiation, fungi, et cetera. The main target of this thesis was to assess and compare the durability of ceramic and polymeric wood coatings, which are developed to enhance wood resistance to ambient conditions and, as a result, prevent wood structure degradation. The artificial accelerated weathering and cycling tests have been carried out to imitate environmental conditions under which the wood should be operated. The tape method was performed to estimate the adhesion properties of the coatings under study. The most favorable conditions for the application of ceramic and polymeric coatings have been revealed, and the potential improvements which can be done in this field of study also have been suggested.
Three SDRAMs from the same manufacturer with technology node sizes 110, 72, and 63 nm, were investigated under proton irradiation and using scanning electron microscopy (SEM). The radiation-induced faults were characterized and compared between the different part types. The devices under test (DUT) were irradiated with protons and experienced single event effects (SEE) in the form of stuck bits and single bit upsets (SBU). Analysis of the data retention times of bits which had SBU and were stuck during irradiation, showed similar patterns of retention time degradation, suggesting that the SBUs and stuck bits in all three part types could be induced by the same mechanism. Detailed data retention time analyses were also performed before and after irradiation to investigate the evolution of data retention times after irradiation, and after periods of annealing. The largest radiation-induced retention time losses were found to anneal, but the bits least affected directly after irradiation experienced decreasing data retention time as a function of annealing time. SEM imaging showed differences in the memory cell structure between the tested part types. The largest node size device was the most sensitive to the radiation, both for SEE and cumulative radiation effects.
This study explores the optimization of electricity supply to mobile base station with the modelling of a hybrid system configuration in Accra, the capital city of Ghana. The hybrid system deployed is to enhance sustainability, reliability and stability of electricity supply to meet the telecom load. The proposed hybrid system incorporated solar photovoltaic (PV) with utility grid and a battery storage backup, (PV/Grid/Battery) with a converter conversion. The objective of the study is to reduce operational cost, emissions and cost of energy when compared with the existing system operation (Grid/DG/Battery). The tool deployed in the simulation process is HOMER software, with sensitivity variables computed into the system to attain the optimum result. The sensitivity variables were fixed around diesel prices pegged between €1 and €2. Another sensitivity variable was the nominal discount fixed between 8 and 10 %. Thus, random power outages were infused into the system from the utility grid. Knowing the load consumption of selected cell sites, Achimota_1, Taifa_2, High Street and Tetteh Quarshie, the simulated results were compared with two different configurations: (PV/Grid/DG/Battery) and (PV/Grid/Battery). The simulation resulted in cost of energy for Achimota_1 of €0.425 with a renewable penetration of 41.4%. Taifa_2 optimum simulated results indicated COE €0.299 with 40.2% renewable fraction. The renewable share for High Street cell sites was 53.2 % and resulted in €0.313 cost of the energy. Lastly, the outcome of the simulation for Tetteh Quarshie revealed that with 17% renewable energy penetration, the cost of energy for the hybrid system was €0.345. Clearly, the hybrid system will sustainably improve electricity supply to the base stations, reduce GHG emissions, and cost of energy. This will enhance quality services from telecom operators.
The investigation of the noble metal ions photoreduction to nanoparticles was conducted in this Master Thesis. Four types of graphitic carbon nitride powders were synthesized through the thermal polycondensation reaction of four different precursors (melamine, dicyandiamide, urea and melamine-cyanuric complex). The chemical and physical properties of synthesized materials were studied by XRD, SEM, TEM, EDS, UV-VIS spectroscopy, BET and BJH methods. Photocatalytic properties of the samples were tested in the photoreduction of Au3+ and Pt4+ to Au and Pt-nanoparticles from tetrachloroauric and hexachloroplatinic acids aqueous solutions, respectively. Ethanol and water were used as hole scavengers. DRS and UV-VIS spectroscopy were applied to control the reaction efficiency in solid and liquid phases of the experiments, respectively. The analysis of the thermodynamic parameters of the process, experiment conditions development, experimental data interpretation and correlation of those to the materials’ parameters were conducted and future directions of the research in related area were proposed.
Grafeenikvanttipisteet (GQDs) ovat viime aikoina herättäneet suurta kiinnostusta niiden ainutlaatuisten ominaisuuksien ja mahdollisten sovellusten vuoksi. Tämä ainutlaatuinen komponentti voidaan syntetisoida alhaalta ylöspäin sekä ylhäältä alaspäin suuntautuvalla lähestymistavalla käyttämällä halpoja, ekologisia ja helposti hankittavia raaka aineita. Tämän työn tavoitteena on löytää optimaaliset olosuhteet, jotta halutun kokoisten GQD:iden tuottaminen olisi kontrolloitua, ekologista sekä taloudellista, tutkimalla miten raaka aineen koostumus, käytetty reaktio lämpötila/säteilytys sekä reaktioaika vaikuttavat GQD:iden syntetisointiin. Tuloksista voi huomata, kuinka veden läsnäolo vähentää sivureaktioita ja tuottaa enemmän GQDs, mutta syntetisoidut GQDs omaavat pienemmän koon. Tämän lisäksi voi huomata kuinka katalyytti kompensoi veden vaikutuksen tuottamalla suuremman kokoisia GQDs, mutta katalyyttiä on lisättävä pienissä määrin, muuten synteesi muuttuu kontrolloimattomaksi