Fysiikan jättitapahtuma Yhdysvalloissa

Amerikan fyysikkoseuran satavuotisjuhlakonferenssi Atlantassa maaliskuussa oli kaikkien aikojen suurin fyysikkojen kokoontuminen. Rekisteröityneiden osanottajien määrä oli noin 11500 henkilöä. Näkyvimmät osanottajat olivat yli 20 fysiikan Nobelin palkinnon saajaa, Yhdysvaltain presidenttien kahdeksan tiedepoliittista neuvonantajaa presidentti Kennedyn ajoista alkaen, National Science Foundationin (NSF) pääjohtaja, pari kongressiedustajaa ja Stephen Hawking. Ohjelma antoi kuvan tämän hetken fysiikan tutkimuksesta ja historiallisen perspektiivin Yhdysvaltain tiedepolitiikkaan. Järjestäjät toivoivat sen sisällöllä olevan vaikutusta suureen yleisöön, poliitikkoihin, julkiseen sanaan ja opiskelijoihin. Tavoitteena oli osoittaa kuinka fysiikka on vaikuttanut Yhdysvaltain kansalliseen turvallisuuteen, talouteen ja hyvinvointiin

Infrastruktuurit ja suomalaiset tutkijat

Useissa maissa käynnissä ollut pitkän aikavälin tutkimuksen infrastruktuurien suunnittelu vauhdittaa kehitystä myös Suomessa. Erityisessä asemassa on Euroopan tutkimusinfrastruktuurien strategisessa suunnittelussa (European Strategy Forum on Research Infrastructures, ESFRI) laadittu pitkän tähtäyksen suunnitelma eli tiekartta, jonka laatimiseen myös suomalaiset osallistuivat. Siinä tarkastellaan Euroopan tason tutkimusinfrastruktuurien rakentamis- ja päivitystarpeita. EU:n kilpailukykyneuvosto on suositellut jäsenmaille myös omien kansallisten tiekarttojen laatimista

Julkaisu- ja konferenssiavustusten linjauksista

Tieteellisten seurain valtuuskunta on päättänyt viime vuosina tieteelliseen julkaisutoimintaan ja tieteellisiin konferensseihin tarkoitetun valtionavustuksen jakamisesta. Suomen Akatemia on delegoinut näiden valtionavustusten jakamisen Tieteellisten seurain valtuuskunnalle. Tällä puheenvuorolla valtuuskunta haluaa informoida hakijoita ja rohkaista keskustelua siitä, mitä seikkoja avustuksia myönnettäessä tulisi painottaa

Characterization of ion-irradiation-induced defects in multi-walled carbon nanotubes

Peer reviewe

Non-invasive transmission electron microscopy of vacancy defects in graphene produced by ion irradiation

Irradiation with high-energy ions has been widely suggested as a tool to engineer properties of graphene. Experiments show that it indeed has a strong effect on its transport, magnetic and mechanical characteristics. However, to use ion irradiation as an engineering tool requires understanding of the type and detailed characteristics of the produced defects which is still lacking, as the use of high-resolution transmission electron microscopy (HRTEM) - the only technique allowing direct imaging of atomic-scale defects - often modifies or even creates defects during imaging, thus making it impossible to determine the intrinsic atomic structure. Here we show that encapsulating the studied graphene sample between two other (protective) graphene sheets allows non-invasive HRTEM imaging and reliable identification of atomic-scale defects. Using this simple technique, we demonstrate that proton irradiation of graphene produces reconstructed monovacancies, which explains the profound effect that such defects have on magnetic and transport properties. This finding resolves the existing uncertainty with regard to the effect of ion irradiation on the electronic structure of graphene.Comment: 18 pages, 6 figures and Supplementary Information (4 supplementary figures

Ion irradiation of multi-walled boron nitride nanotubes

Non Peer reviewe

Absence of single critical dose for the amorphization of quartz under ion irradiation

In this work, we first simulated the amorphization of crystalline quartz under 50 keV Na-23 ion irradiation with classical molecular dynamics (MD). We then used binary collision approximation algorithms to simulate the Rutherford backscattering spectrometry in channeling conditions (RBS-C) from these irradiated MD cells, and compared the RBS-C spectra with experiments. The simulated RBS-C results show an agreement with experiments in the evolution of amorphization as a function of dose, showing what appears to be (by this measure) full amorphization at about 2.2 eV.atom(-1). We also applied other analysis methods, such as angular structure factor, Wigner-Seitz, coordination analysis and topological analysis, to analyze the structural evolution of the irradiated MD cells. The results show that the atomic-level structure of the sample keeps evolving after the RBS signal has saturated, until the dose of about 5 eV.atom(-1). The continued evolution of the SiO2 structure makes the definition of what is, on the atomic level, an amorphized quartz ambiguous.Peer reviewe

Ni+-irradiated InGaAs/GaAs quantum wells: picosecond carrier dynamics

Room-temperature carrier dynamics as functions of heavy-ion implantation and subsequent thermal annealing were investigated for technologically important InGaAs/GaAs quantum wells (QWs) by means of a time-resolved up-conversion method. Sub-picosecond lifetimes were achieved at 10 MeV Ni+ doses of (20-50) x 1010 ions cm-2. The decay rates reached a maximum at the highest irradiation dose, yielding the shortest lifetime of the confined QW states of 600 fs. A simple theoretical model is proposed for the photodynamics of the carriers. The relaxation rate depended on the irradiation dose according to a power law of 1.2, while the irradiated and subsequently annealed samples exhibited a power law of 0.35. The results are qualitatively interpreted.Room-temperature carrier dynamics as functions of heavy-ion implantation and subsequent thermal annealing were investigated for technologically important InGaAs/GaAs quantum wells (QWs) by means of a time-resolved up-conversion method. Sub-picosecond lifetimes were achieved at 10 MeV Ni+ doses of (20-50) x 1010 ions cm-2. The decay rates reached a maximum at the highest irradiation dose, yielding the shortest lifetime of the confined QW states of 600 fs. A simple theoretical model is proposed for the photodynamics of the carriers. The relaxation rate depended on the irradiation dose according to a power law of 1.2, while the irradiated and subsequently annealed samples exhibited a power law of 0.35. The results are qualitatively interpreted.Room-temperature carrier dynamics as functions of heavy-ion implantation and subsequent thermal annealing were investigated for technologically important InGaAs/GaAs quantum wells (QWs) by means of a time-resolved up-conversion method. Sub-picosecond lifetimes were achieved at 10 MeV Ni+ doses of (20-50) x 1010 ions cm-2. The decay rates reached a maximum at the highest irradiation dose, yielding the shortest lifetime of the confined QW states of 600 fs. A simple theoretical model is proposed for the photodynamics of the carriers. The relaxation rate depended on the irradiation dose according to a power law of 1.2, while the irradiated and subsequently annealed samples exhibited a power law of 0.35. The results are qualitatively interpreted.Peer reviewe