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Neelduvate lainepikkuste määramine päikesepaneeli nanomaterjalides – ZnO nanoosakesed
No full textBachelor’s Thesis
Engineering curriculumIn this thesis the absorbance and band gap properties of ZnO nanoparticles (NP), which is a
solar cell and photocatalytic material, have been investigated. The absorbance of the ZnO NP
were measured using a UV-Vis spectrophotometer and their band gap properties were
calculated. Four different samples of ZnO NP were already synthesized. Several steps after
synthesis of these NP were carried out before obtaining a powder of ZnO NP, explained in
this thesis. To measure the absorbance of these nanomaterials, ZnO NP were spread
homogeneously in isopropanol. For absorbance studies, a UV-Vis II Nanocolor
spectrophotometer by MACHEREY-NAGEL was used to measure the absorbance with a
measurement range of 190–1100 nm. Isopropanol was also used as reference during the
measurements. The UV-Vis spectrophotometershows the maximum absorbance of these ZnO
NP in 356.8-363.1 nm range. All the results were plotted using software Origin and MS Excel.
Energy band gaps were calculated using tauc plot method. The calculated band gap of ZnO
NP were in 3.160-3.288 eV range which is comparable with the direct bandgap 3.37 eV of
bulk ZnO. These variations in band gap are attributed to the synthesis conditions of these NP.Selles lõputöös uuriti valguse energia neeldumist ZnO nanoosakestes. Mõõdetud valguse
neeldumist ja spektri vahemikke võrreldi kirjanduses olevaga. ZnO nanoosakesed olid juba
eelnevalt valmistatud sünteesi teel. ZnO nanoosakesi oli 4 erinevat proovi. Töö alguses olid
ZnO nanoosakesed teralise struktuuriga ja vajasid purustamist. Peale purustamist jäi alles
väga peene pulber nanoosakestest. Purustamine võttis aega kuni 20 minutit. Valguse
neeldumise mõõtmiseks oli vaja teha ZnO nanoosakeste lahus, lahustiks oli isopropanool.
Neeldumise mõõtmiseks kasutati spektrofotomeetrit UV-Vis II Nanocolor tootjalt
MACHEREY-NAGEL. Valguse neeldumine oli mõõdetav 190-1100 nm vahemikus.
Spektrofotomeeter võimaldas 2 täpsusel mõõtmist: normaalne ja maksimaalne. Kõik
mõõtmised siin töös said tehtud maksimaalsel režiimil, andmed olid palju täpsemad.
Mõõdetud neeldumise suurimad väärtused jäid 356.8 ja 363.1 nm lainepikkuse vahemikku.
Saadud andmeid töödeldi tarkvaraga Origin ja MS Excel. Kasutades tauc plot meetodit
arvutati energia vahemik. Energia vahemik oli 3.160-3.288 eV, mis on võrreldav kirjanduses
leitava ZnO energia vahemikuga 3.37 eV-ga
ZnO nanovarraste fotoelektrilisted omadused
No full textMaster’s Thesis
Energy Application Engineering CurriculumIn this study, electrical and photoelectrical properties of ZnO nanorods were investigated.
This study is the continuation of my bachelor’s work where I studied absorption and band gap
properties of ZnO nanoparticles. The aim of the current study was to investigate electrical
properties of ZnO nanostructures. It was found that ZnO nanoparticles studied in my
bachelor’s do not show electrical characteristics due to high amount of grain boundaries and
non-uniformity. Therefore, the nanorods structure of ZnO was investigated for the electrical
measurements. In this study, four samples of ZnO nanorods were investigated, and are
classified according to the solvent used for preparing the seeding layer. The nanorods were
prepared by a two-step method. The first step includes seeding of zinc precursor. The seeding
solution was prepared in four different solvents: ethanol, methanol, isopropanol and 70%
ethanol. The second step was the hydrothermal method to grow ZnO nanorods on pre-seeded
indium tin oxide (ITO) substrate. The ITO substrate, which consists of 100 nm thick ITO
layer deposited on 0.5 mm thick quartz glass substrate were purchased from Ossila [1]. The current-voltage (I-V) characteristics of all four ZnO nanorod samples were studied for two
types of contacts: Ohmic and Schottky. The measurements were carried out in two different
conditions: in dark and under light exposure, for both type of contacts. A source measure unit
(SMU) was used to measure ZnO nanorods conductivity. The measurement range was set to
-3 V to +3 V for both Ohmic and Schottky contacts. The data was plotted with Origin Pro
software. The Ohmic I-V measurements in dark and room light suggested that methanol
seeded ZnO nanorod sample is highly photosensitive to room light itself. The experiments
with Schottky behavior were not conclusive for all the nanorod samples. However, sample
with isopropanol seeding showed Schottky-like characteristics for the silver (Ag) Schottky
contact. The study of Schottky contact needs further investigations and is beyond the scope
of this thesis. In conclusion, the enhancement in the current under room light for ohmic
contacts for all the nanorod samples suggested that these samples are sensitive to photons
emitted by room light. It was expected that room light emits some UV radiation coming from
the neon light that excites electrons from ZnO nanorods and resulted in the enhancement of
current. As mentioned earlier, the highest enhancement was shown by ZnO nanorods with
methanol solution seeding, which suggests that this sample is a good UV light absorber
compared to others and is a potential candidate to be used in applications such as solar cells
and photo detectors.Käesolevas magistritöös uuriti ZnO nanovarraste elektrilisi ja fotoelektrilisi omadusi. See töö
on jätkuks minu bakalaureusetööle, kus ma uurisin ZnO nanoosakeste valguse neeldumist ja
selle energia vahemikke. Antud teadustöö eesmärk oli uurida ZnO nanostruktuuride elektrilisi
omadusi ja valgustundlikkust. Selgus, et minu bakalaureusetöös uuritud ZnO nanoosakesed
ei näita elektrilisi omadusi kasutusmeetodil uurides. Seetõttu sai valitud uurimisobjektiks
ZnO nanovardad, et teostada valguse mõju tuvastamiseks vajalikke elektrimõõtmisi.
Käesolevas töös uuriti nelja ZnO nanovarraste proovi, mis on klassifitseeritud vastavalt
sünteesi aluskihi valmistamiseks kasutatud lahustile. Nanovardaid valmistati kaheastmelisel
meetodil. Esimene samm hõlmas tsinki sisaldava sünteesi aluskihi valmistamist. Aluskihi
tekitamiseks kasutatav lahus valmistati neljas erinevas lahustis: etanool, metanool,
isopropanool ja 70% etanool. Teiseks etapiks oli hüdrotermiline meetod: ZnO nanovarraste
kasvatamine eelnevalt kaetud indiumtinaoksiidiga (ITO) substraadil. 100 nm paksuse ITOkihtiga on kaetud 0,5 mm paksune kvartsklaasi tükk. Substraat osteti Ossilalt [1]. Kõigi nelja ZnO nanovarraste proovi voolu ja pinge (I-V) omadusi uuriti kahe tüüpi kontaktide puhul:
Ohmic ja Schottky. Mõlema kontakti tüübi mõõtmised viidi läbi kahes erinevas olukorras:
pimedas ja valguse käes. ZnO- nanovarraste juhtivuse mõõtmiseks kasutati mõõteseadet
Source measure unit X200 (SMU). Mõõtmisvahemikuks määrati -3 V kuni +3 V nii Ohmickui ka Schottky-kontaktide puhul. Andmetöötlus sai tehtud Origin Pro tarkvaraga. Ohmic IV mõõtmised pimedas ja toavalguses näitasid, et metanooliga sünteesitud ZnO nanovarraste
proov on toavalgusele väga valgustundlik. Katsed Schottky kontaktidega polnud kõigi
nanovarraste proovide puhul veenvad. Isopropanooli proov näitas ainsana paremaid Schottkytaolisi omadusi hõbeda (Ag) Schottky- kontaktidega. Schottky- kontaktide uurimine vajab
täiendavaid uuringuid ja väljub käesoleva lõputöö raamidest. Kokkuvõtteks võib öelda, et
toavalguses toimuv voolu suurenemine kõigi nanovarraste proovide Ohmic kontaktide puhul
viitas sellele, et need on tundlikud toavalguse poolt kiiritatud footonite suhtes. Eeldasin, et
toavalgus kiirgab neoon valgust ja vähesel määral ka UV-kiirgust, mis ergastab ZnO
nanovarraste elektrone ja põhjustas voolu suurenemise. Nagu varem mainitud, näitas kõige
suuremat muutust metanooliga sünteesitud ZnO nanovardad. Antud proov on teistega
võrreldes hea neoon valguse ja UV-kiirguse neelaja ja potentsionaalne kandidaat
kasutamiseks päikesepaneelide ja fotodetektorite rakendustes
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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