Browsing by Subject "DENSIFICATION"

Sort by: Order: Results:

Now showing items 1-2 of 2
  • Djurabekova, F.; Fridlund, C.; Nordlund, K. (2020)
    We present molecular dynamics simulations of atomic mixing over a Si/SiO2 heterostructure interface, induced by focused Ne+ and broad Si(+ )ion-beam irradiations, using a speed-up scheme that significantly reduces the relaxation time of the cascading recoils. To assess the qualitative reliance of the chosen method, two different potential models for Si-O, Si-Si, and O-O interactions were used: the Stillinger-Weber-like Watanabe-Samela potential and the Tersoff-like Munetoh potential. Furthermore, the molecular dynamics simulations were assessed by simulating a similar case, at a total fluence of 1 x10(15) cm(-2), with the binary collision approximation. The same general atomic density profile distributions were achieved with both models; however, the binary collision approach showed shallower penetration of Si into the SiO(2 )layer. Coordination analysis of the molecular dynamics results provides strong evidence that ion mixing at high fluences leads to coordination defects, which will affect the electronic properties of the structures unless removed with annealing.
  • Heikinheimo, Vuokko Vilhelmiina; Tenkanen, Henrikki; Bergroth, Claudia; Järv, Olle; Hiippala, Tuomo; Toivonen, Tuuli (2020)
    Parks and other green spaces are an important part of sustainable, healthy and socially equal urban environment. Urban planning and green space management benefit from information about green space use and values, but such data are often scarce and laborious to collect. Temporally dynamic geographic information generated by different mobile devices and social media platforms are a promising source of data for studying green spaces. User-generated data have, however, platform specific characteristics that limit their potential use. In this article, we compare the ability of different user-generated data sets to provide information on where, when and how people use and value urban green spaces. We compare four types of data: social media, sports tracking, mobile phone operator and public participation geographic information systems (PPGIS) data in a case study from Helsinki, Finland. Our results show that user-generated geographic information sources provide useful insights about being in, moving through and perceiving urban green spaces, as long as evident limitations and sample biases are acknowledged. Social media data highlight patterns of leisure time activities and allow further content analysis. Sports tracking data and mobile phone data capture green space use at different times of the day, including commuting through the parks. PPGIS studies allow asking specific questions from active participants, but might be limited in spatial and temporal extent. Combining information from multiple user-generated data sets complements traditional data sources and provides a more comprehensive understanding of green space use and preferences.