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Electric field calibration method for scanning electron microscope
No full textThis paper proposes a calibration method which can be utilized for the analysis of SEM images. The field of application of the developed method is a calculation of surface potential distribution of biased silicon edgeless detector. The suggested processing of the data collected by SEM consists of several stages and takes into account different aspects affecting the SEM image. The calibration method doesn’t pretend to be precise but at the same time it gives the basics of potential distribution when the different biasing voltages applied to the detector
Nanorakenteiden ja fotoniikan komponenttien uudet valmistustekniikat
No full textThis thesis introduces novel micro- and nanofabrication methods and their applications developed in Micronova, the clean room facilities of Aalto University. The work is performed with silicon, which is robust, stable, and easy to process material with good electrical and optical properties. The developed fabrication methods facilitate technologically challenging types of nanostructures and their fabrication on non-planar surfaces.
The presented research consists of two parts. The first part is focused on nanofabrication, mostly via top-down fabrication approach. The second one describes the modification of photonic devices and waveguides by \mbox{atomic-layer-deposited} thin films. The three main types of processing involved in the thesis are: atomic layer deposition, exposure by focused ion beam, and dry etching.
As a result of this study, several fabrication methods were developed. One of them utilizes focused ion beam lithography for nanofabrication on multilevel and strongly corrugated surfaces. This process has a great potential for general 3D integration and for micro- and nanofluidics. The same approach enables the fabrication of suspended nanostructures and gives a platform for accurate measurement of material properties and realization of lab-on-a-chip concepts. Another separately developed process is a grayscale lithography that provides a control over the height of patterned features at nanometer scale. It gives an effective way to fabricate miniature diffractive optics components for extreme ultraviolet and soft X-ray radiation. It also allows for new designs and improved performance of photonic grating couplers. Finally, the work shows how atomic layer deposition can be used to tune the operational parameters of photonic components. In particular, the dispersion properties of photonic nanostrip waveguides were optimized, and micro ring resonators were tuned towards polarization-independent regime in a broad wavelength range.
In summary, the work extends the applications of nanotechnology for sensing and integrated optics. The shown nanofabrication methods provide fast prototyping due to the minimized number of process steps. Atomic layer deposition of thin films was demonstrated to be very effective for tuning of photonic waveguides and devices. The presented techniques and methods have a showcase character and provide a room for further research focused on other materials and applications.Tässä väitöskirjassa tarkastellaan Aalto-yliopiston Micronova-puhdastilaympäristössä kehitettyjä uusia mikro- ja nanotekniikan valmistusmenetelmiä ja niiden sovelluksia. Valmistusmateriaaliksi valittiin pii, koska se on kestävä ja stabiili materiaali, jolla on suotuisat sähköiset ja optiset ominaisuudet ja jota on verrattain helppo prosessoida.
Työ koostuu kahdesta osasta. Ensimmäinen osa käsittelee nanovalmistusta, pääosin ns. "topdown"-valmistustekniikoita, joihin kuuluu menetelmiä, joilla materiaalia poistetaan ennalta suunnitellun kuvion mukaisesti. Toisessa osassa tutkitaan fotoniikan komponenttien ominaisuuksien räätälöintiä atomikerroskasvatettujen ohutkalvojen avulla. Tässä tutkimustyössä on kolme keskeistä prosessia: atomikerroskasvatus, fokusoidun ionisuihkun avulla suoritettu kuviointi ja kuivaetsaus.
Tutkimuksen tuloksena on kehitetty useita piimateriaalin muokkaamiseen tarkoitettuja valmistusmenetelmiä. Merkittävä osa tuloksista saatiin hyödyntämällä fokusoidun ionisuihkun (FIB) avulla suoritettua litografiaa, jolloin oli mahdollista saada aikaan nanorakenteita myös epätasaisille ja kalteville pinnoille. Tätä prosessia voi hyödyntää sekä 3Dintegraatiossa että mikro- ja nanofluidistiikassa. Samoja periaatteita voidaan soveltaa myös vapautettujen nanorakenteiden valmistamiseen. Tämäntyyppisiä rakenteita käytetään mm. materiaalien ominaisuuksien tutkimuksissa ja "lab-on-a-chip"- sovelluksissa. Tutkimuksessa on myös kehitetty fokusoidun ionisuihkun käyttöön perustuva ns. "harmaasävy"- litografia, jolla kyetään aikaansaamaan erilaisia nanorakenteiden korkeusprofiileja. Tätä menetelmää voi käyttää pienten integroitujen diffraktiivisen optiikan komponenttien valmistukseen, jotka toimivat ultraviolettiaallonpituuksilla. Työssä kehitetty litografia mahdollistaa uuden tavan tehdä piipohjaisia fotoniikan hilakytkimiä. Lisäksi tässä väitöskirjassa esitellään tapoja käyttää atomikerroskasvatusta fotoniikassa aaltojohteiden ja mikroresonaattorien virittämiseen esimerkiksi siten, että niiden toiminta on polarisaatiosta riippumatonta.
Tässä työssä saavutetut tulokset laajentavat nanoteknologian mahdollisuuksia sekä nanorakenteiden valmistamisessa että optiikan sovelluksissa. Kehitetyissä valmistusmenetelmissä prosessivaiheiden määrä on minimoitu, joten ne sopivat erityisesti prototyyppien valmistamiseen. Työssä esitetään myös suuntaviivoja miten näitä kehitettyjä perustekniikoita voisi jatkossa edelleen tehostaa
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
Numerical optimization of grating couplers in nanophotonic waveguides
Get PDFOptisten taajuuksien käyttö tietotekniikassa voi mahdollistaa nykyistä suuremmat kaistanleveydet ja pienemmän energian kulutuksen. Piifotoniikka pyrkii ohjaamaan ja manipuloimaan näitä taajuuksia piialustalla. Piifotoniikalla on sovelluksia esimerkiksi sensoritekniikassa ja tietoverkoissa. Epäsuora energia-aukko estää tehon tuottamisen suoraan piialustalla, jolloin optinen teho täytyy tuoda piihin ulkoisesta lähteestä. Tämä edellyttää kytkennän rakentamista teholähteen ja sirun välille. Kytkentä voidaan toteuttaa esimerkiksi diffraktiohilan avulla. Diffraktiohilan etuja ovat joustava sijoitus piirilevylle ja samanaikainen kytkeytyminen useisiin signaalilähteisiin. Hilan aallonpituusriippuvuus vaikuttaa kytkentään, joka on tehokas ainoastaan hilalle ominaisella resonanssitaajuudella. Kytkentähyötysuhde riippuu diffraktiohilan geometriasta, kuten sen koosta, jaksollisuudesta ja hilaelementtien muodoista. Hyötysuhteen maksimointi voidaankin toteuttaa hilan geometriaa optimoimalla. Tämä työ käsittelee kytkentähyötysuhteen parantamista geometrian avulla. Optimointi perustuu numeeriseen mallinnukseen FEM-menetelmällä (Finite Element Method). FEM-menetelmän käyttö on perusteltua, koska äärellisen kokoisten hilarakenteiden analyyttinen mallintaminen on vaikeaa mielivaltaisille geometrioille. Riittävän suuri parametrisilmukka pystyy käymään useimmat geometriat läpi, jolloin erilaisten vaihtoehtojen joukosta löydetään optimaalinen geometria. Tällainen laskenta hyötyy FEM-menetelmän eduista, joihin kuuluu lyhyt laskenta-aika. Tämän työn laskennassa hyödynnettiin COMSOL Multiphysics ohjelmistoa, koska kyseinen ohjelmisto mahdollistaa parametrisilmukoiden automatisoinnin. Optimoinnin jälkeen saavutettuja taajuusvasteita verrattiin alkuperäiseen taajuusvasteeseen. Näin voitiin varmistua siitä, että saavutettu aallonpituusriippuvuus vastaa teoriaa parantuneella maksimihyötysuhteella. Taajuusvasteella on voimakas maksimi resonanssiaallonpituudella, mikä havaittiin kaikilla optimoiduilla geometrioilla.Use of optical frequencies in information technology can provide increased bandwidth and reduced energy consumption compared to modern applications. In silicon photonics, optical signals are processed in circuits that are mainly based on silicon and silica structures. Silicon photonic applications can be utilized, for example, in sensors and in telecommunication networks. The indirect bandgap of silicon prevents the construction of a laser type power source on a silicon substrate. Hence, power in silicon photonics has to be produced outside the chip. This demands a device, which can couple signal power to silicon. One example of such a device is a diffraction grating. Gratings can be flexibly placed on the chip and they can couple to multiple power sources simultaneously. When a grating coupler is utilized, one crucial parameter that defines its performance is the coupling efficiency. This figure denotes the fraction of source power, which can be transmitted to the chip. Many studies have been performed to maximize this fraction. Coupling efficiency depends on the grating geometry, which can be optimized by altering the grating parameters, such as period or groove depth. In this work, such optimization was performed by simulating the grating structure while varying the geometric dimensions. Numerical simulation is necessary because finite sized gratings cannot be modelled analytically for arbitary shapes. The simulations were performed on finite element method (FEM) using the COMSOL Multiphysics software. An advantage of the FEM is fast calculation, essential when computing large scale parametric sweeps required by the optimization procedure. The main objective of this study was to compare the initial and optimized frequency responses as they define the coupling efficiency and the operation bandwidth. The comparison revealed an improved coupling at the resonance wavelength for certain geometries found by the sweeps. The achieved frequency responses around this maximum are in agreement with grating theory and previous studies made on the topic
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
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