1,598 research outputs found

    Environmental aspects related to nanomaterials : A literature survey

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    Nanomaterials and nanotechnologies offer great opportunities for almost all sectors of society. New materials and applications are invented all the time. Benefits are obvious in many cases, such as enhanced energy use, improved electronic devices, lighter products, higher hygiene level, or increased storage time. The motive for manufacturing nanomaterials lies in the chemical and physical characteristics, which are different from material in bulk. Due to these new properties environmental effects assessment is challenging. We are only at the beginning of understanding how nanomaterials will behave in actual environmental conditions

    Development of radiation hard radiation detectors : differences between Czochralski silicon and float zone silicon

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    The purpose of this work was to develop radiation hard silicon detectors. Radiation detectors made of silicon are cost effective and have excellent position resolution. Therefore, they are widely used for track finding and particle analysis in large high-energy physics experiments. Silicon detectors will also be used in the CMS (Compact Muon Solenoid) experiment that is being built at the LHC (Large Hadron Collider) accelerator at CERN (European Organisation for Nuclear Research). This work was done in the CMS programme of Helsinki Institute of Physics (HIP). Exposure of the silicon material to particle radiation causes irreversible defects that deteriorate the performance of the silicon detectors. In HIP CMS Programme, our approach was to improve the radiation hardness of the silicon material with increased oxygen concentration in silicon material. We studied two different methods: diffusion oxygenation of Float Zone silicon and use of high resistivity Czochralski silicon. We processed, characterised, tested in a particle beam, and irradiated silicon detectors and test structures. Samples were processed at the clean room facilities of Helsinki University of Technology Microelectronics Centre (MEC) where our group has the status of a member laboratory. Electrical characterisations were done mainly at CERN at the premises of our collaborators from CERN RD39 and RD50 research and development programmes, where our group is participating as a member institute. Defect characterisations were carried out using PCD (Photoconductivity Decay) and SPV (Surface Photovoltage) methods at Helsinki University of Technology Electron Physics Laboratory. Detection performance was measured with a Helsinki Silicon Beam telescope at CERN using muon beam. Radiation hardness was studied in irradiation tests at Jyväskylä University Accelerator Laboratory. Our research on the radiation hardness of diffusion oxygenated Float Zone silicon resulted in several previously unreported findings. We found an evident correlation between silicon oxygenation and detector leakage current after irradiations. Additionally, we found that the oxygenation has a positive effect on the long-term stability of irradiated silicon. Furthermore, we successfully applied alternative methods for the characterisation of silicon detectors, i.e. PCD (Photoconductivity Decay) and SPV (Surface Photovoltage). The most important results of our research were obtained in our work on high resistivity Czochralski silicon. Although the advantages of Czochralski silicon had been known for some time, we were the first group to process, characterise, test in a particle beam, and irradiate full-size Czochralski silicon detectors. In proton irradiations, Czochralski silicon was found to be more radiation hard than any other silicon material.reviewe

    Synteettisten nanomateriaalien ympäristövaikutukset: Kokeellisen tutkimuksen nykytila

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    Nanomateriaaleja käytetään nykyään monissa kuluttajatuotteissa ja teollisuuden sovelluksissa. Teollisen tuotannon ja käytön voimakkaaseen kasvuun liittyy uhka nanomateriaalien tahattomasta vapautumisesta ympäristöön. Sen vuoksi on tehty jo paljon tutkimusta, jossa pyritään arvioimaan nanomateriaalien turvallisuutta ihmisten terveyden ja ympäristön kannalta. Tämä raportti on katsaus synteettisten nanomateriaalien ympäristötutkimukseen, ja se pohjautuu viimeaikaiseen tieteelliseen kirjallisuuteen. Lähteinä on käytetty 2000-luvulla ja pääasiassa viimeisen viiden vuoden aikana ilmestyneitä alkuperäisiä artikkeleita ja katsauksia. Selvityksessä käsitellään nanomateriaalien ympäristötutkimukseen liittyviä teemoja, kuten aineiden vapautumista ympäristöön, mittaustekniikoita, mittaamiseen ja analysoimiseen liittyviä haasteita, nanomateriaalien ympäristökohtaloa ja biologisia vaikutuksia. Tarkastelun kohteeksi valittiin ominaisuuksiltaan kuusi erilaista nanomateriaalia tai nanomateriaaliryhmää (sinkkioksidi, titaanidioksidi, hopea, hiilipohjaiset aineet, nanoselluloosa ja kvanttipisteet). Katsauksen lopussa on joitakin huomioita tärkeimmistä tietoaukoista. Tässä raportissa keskitytään käsittelemään nanomateriaaleja vesiympäristössä, aerosolihiukkaset jätettiin kokonaan huomiotta, ja maaperäasioita on käsitelty vain rajoitetusti

    Characterization of Heavily Irradiated Dielectrics for Pixel Sensors Coupling Insulator Applications

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    An increase in the radiation levels during the high-luminosity operation of the Large Hadron Collider calls for the development of silicon-based pixel detectors that are used for particle tracking and vertex reconstruction. Unlike the conventionally used conductively coupled (DC-coupled) detectors that are prone to an increment in leakage currents due to radiation, capacitively coupled (AC-coupled) detectors are anticipated to be in operation in future collider experiments suitable for tracking purposes. The implementation of AC-coupling to micro-scale pixel sensor areas enables one to provide an enhanced isolation of radiation-induced leakage currents. The motivation of this study is the development of new generation capacitively coupled (AC-coupled) pixel sensors with coupling insulators having good dielectric strength and radiation hardness simultaneously. The AC-coupling insulator thin films were aluminum oxide (Al2O3) and hafnium oxide (HfO2) grown by the atomic layer deposition (ALD) method. A comparison study was performed based on the dielectric material used in MOS, MOSFET, and AC-coupled pixel prototypes processed on high resistivity p-type Magnetic Czochralski silicon (MCz-Si) substrates. Post-irradiation studies with 10 MeV protons up to a fluence of 10(15) protons/cm(2) suggest HfO2 to be a better candidate as it provides higher sensitivity with negative charge accumulation on irradiation. Furthermore, even though the nature of the dielectric does not affect the electric field within the AC-coupled pixel sensor, samples with HfO2 are comparatively less susceptible to undergo an early breakdown due to irradiation. Edge-transient current technique (e-TCT) measurements show a prominent double-junction effect as expected in heavily irradiated p-type detectors, in accordance with the simulation studies.Peer reviewe

    Impact of GEM foil hole geometry on GEM detector gain

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    Detailed 3D imaging of Gas Electron Multiplier (GEM) foil hole geometry was realized. Scanning White Light Interferometry was used to examine six topological parameters of GEM foil holes from both sides of the foil. To study the effect of the hole geometry on detector gain, the ANSYS and Garfield ++ software were employed to simulate the GEM detector gain on the basis of SWLI data. In particular, the effective gain in a GEM foil with equally shaped holes was studied. The real GEM foil holes exhibited a 4% lower effective gain and 6% more electrons produced near the exit electrode of the GEM foil than the design anticipated. Our results indicate that the GEM foil hole geometry affects the gain performance of GEM detectors.Peer reviewe
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