Resistive switching offers a promising route to universal electronic memory, potentially replacing current technologies that are approaching their fundamental limits. In many cases switching ...originates from the reversible formation and dissolution of nanometre-scale conductive filaments, which constrain the motion of electrons, leading to the quantisation of device conductance into multiples of the fundamental unit of conductance, G0. Such quantum effects appear when the constriction diameter approaches the Fermi wavelength of the electron in the medium - typically several nanometres. Here we find that the conductance of silicon-rich silica (SiOx) resistive switches is quantised in half-integer multiples of G0. In contrast to other resistive switching systems this quantisation is intrinsic to SiOx, and is not due to drift of metallic ions. Half-integer quantisation is explained in terms of the filament structure and formation mechanism, which allows us to distinguish between systems that exhibit integer and half-integer quantisation.
Resistive random access memory (RRAM) is considered an attractive candidate for next generation memory devices due to its competitive scalability, low-power operation and high switching speed. The ...technology however, still faces several challenges that overall prohibit its industrial translation, such as low yields, large switching variability and ultimately hard breakdown due to long-term operation or high-voltage biasing. The latter issue is of particular interest, because it ultimately leads to device failure. In this work, we have investigated the physicochemical changes that occur within RRAM devices as a consequence of soft and hard breakdown by combining full-field transmission x-ray microscopy with soft x-ray spectroscopic analysis performed on lamella samples. The high lateral resolution of this technique (down to 25 nm) allows the investigation of localized nanometric areas underneath permanent damage of the metal top electrode. Results show that devices after hard breakdown present discontinuity in the active layer, Pt inclusions and the formation of crystalline phases such as rutile, which indicates that the temperature increased locally up to 1000 K.
Abstract This paper presents a study of quartz sand grain surface textures using atomic force microscopy (AFM) to image the surface. Until now scanning electron microscopy (SEM) has provided the ...primary technique used in the forensic surface texture analysis of quartz sand grains as a means of establishing the provenance of the grains for forensic reconstructions. The ability to independently corroborate the grain type classifications is desirable and provides additional weight to the findings of SEM analysis of the textures of quartz grains identified in forensic soil/sediment samples. AFM offers a quantitative means of analysis that complements SEM examination, and is a non-destructive technique that requires no sample preparation prior to scanning. It therefore has great potential to be used for forensic analysis where sample preservation is highly valuable. By taking quantitative topography scans, it is possible to produce 3D representations of microscopic surface textures and diagnostic features for examination. Furthermore, various empirical measures can be obtained from analysing the topography scans, including arithmetic average roughness, root-mean-square surface roughness, skewness, kurtosis, and multiple Gaussian fits to height distributions. These empirical measures, combined with qualitative examination of the surfaces can help to discriminate between grain types and provide independent analysis that can corroborate the morphological grain typing based on the surface textures assigned using SEM. Furthermore, the findings from this study also demonstrate that quartz sand grain surfaces exhibit a statistically self-similar fractal nature that remains unchanged across scales. This indicates the potential for a further quantitative measure that could be utilised in the discrimination of quartz grains based on their provenance for forensic investigations.
•Alq3 chemisorbs onto magnetic transition metal surfaces.•Alq3 changes the surface magnetisation of the NiFe film.•Alq3 chemisorbs stronger onto the oxide rich FeCo surface.
The interface between the ...organic semiconductor tris(8-hydrixyquinolate) aluminium (Alq3) and two different magnetic electrodes has been investigated using X-ray photoelectron spectroscopy (XPS), Kelvin Probe, atomic force microscopy (AFM) and magneto-optic Kerr effect (MOKE) magnetometry. The transition metal magnetic electrode/Alq3 films were first measured using a XPS, and then washed and remeasured. It was found that Alq3 still existed on the magnetic electrode after washing. This suggests that the Alq3 chemisorbs onto the transition metal electrode surfaces. Using MOKE magnetometry, the surface magnetisation of the transition metal electrodes was studied. It was found that the surface magnetisation of the NiFe electrode changed with the Alq3 layer on top, which was taken to be due to the Alq3 chemisorption onto the NiFe electrode, so changing the electronic states at the interface.
This paper describes the application of atomic force microscopy (AFM) for the imaging of collagen denaturation as observed in parchment. Parchment is prepared from processed animal skin and collagen ...is the main component. Large collections in national archives, libraries and religious
institutions contain numerous documents written on parchment. Their preservation presents an unsolved problem for conservators. The main challenge is to assess the state of collagen and to detect what conservators refer to as the pre-gelatinised state, which can cause surface cracking resulting
in a loss of text and can increase the vulnerability of parchment to aqueous cleaning agents. Atomic force microscopy (AFM) was first used within the Improved Damage Assessment of Parchment (IDAP) project, enabling the characterisation of the collagen structure within parchment at the nanoscale.
Damage categories were also established based on the extent of the ordered collagen structure that was observed in the AFM images. This paper describes the work following the IDAP project, where morphological changes in the fibres due to both artificial and natural ageing were observed and
linked to observations made by AFM. It also explores the merits and drawbacks of different approaches used for sample preparation and the possibility of using a portable AFM for imaging directly on the surface of documents. A case study on a manuscript from the 18th century is presented.
DC magnetoresistive effects were observed in above-percolation-threshold loaded Fe-filled carbon nanotube/polyurethane-urea composite samples. A phenomenological model is derived from interpretation ...of resistance relaxation for a range of axial strains. The large instantaneous magnetoresistance of + 90% observed at low axial strain was a result of conduction pathway breaking caused by preferential orientation of the conducting nanotubes perpendicular to the axial current flow: a result of the magnetic torque experienced by the ferromagnetic nanotube core. At large strain the observed large instantaneous change in resistance of - 90% resulted from voltage-driven relaxation in the conducting nanotube network. At high axial strain the competition between voltage-driven relaxation and a magnetic torque gave rise to an oscillatory component of resistance relaxation.
Resistive switching in a metal-free silicon-based material offers a compelling alternative to existing metal oxide-based resistive RAM (ReRAM) devices, both in terms of ease of fabrication and of ...enhanced device performance. We report a study of resistive switching in devices consisting of non-stoichiometric silicon-rich silicon dioxide thin films. Our devices exhibit multi-level switching and analogue modulation of resistance as well as standard two-level switching. We demonstrate different operational modes that make it possible to dynamically adjust device properties, in particular two highly desirable properties: nonlinearity and self-rectification. This can potentially enable high levels of device integration in passive crossbar arrays without causing the problem of leakage currents in common line semi-selected devices. Aspects of conduction and switching mechanisms are discussed, and scanning tunnelling microscopy (STM) measurements provide a more detailed insight into both the location and the dimensions of the conductive filaments.
As flash memory approaches its scaling limit, resistive RAM devices show promise for next generation memories due to their small size and low operating voltages enabling denser packing and lower ...power consumption. Many materials have shown desirable active layer properties, yet silicon based memories are particularly appealing as they allow for facile integration into CMOS infrastructures. Our devices are composed of silicon suboxide sandwiched between conductive electrodes. Here, we present results probing the three-dimensional structure of conducting pathways following the application of an electric field. These pathways, or filaments, give dielectric materials memory functionality yet are difficult to image with conventional techniques owing to low imaging contrast. Our results highlight the importance of conductive atomic force microscopy for three-dimensional analyses and show that filamentation conforms to the pristine dielectric structure. We also present findings showing that multiple growths can compete during the filament growth process.
Personality traits have been found to be related to a variety of health outcomes. The aim of this study was to examine how personality traits were associated with adjustment to the COVID pandemic in ...college students. The sample included 484 first-year university students (76% female) attending a northeastern university who completed the Big Five Inventory (BFI) personality assessment at the beginning of a semester that was disrupted by the COVID pandemic. Using a phone-based app, students completed daily ratings of mood, perceived stress levels, and engagement in a number of health promotion activities (exercise, mindfulness, adequate sleep, etc.) throughout the semester both before and after the onset of the pandemic (e.g., a within-person longitudinal design). Results, as expected, showed that mood and wellness indices generally declined during the COVID period, although stress levels actually decreased. Further, irrespective of COVID, improved mood, less perceived stress and greater participation in health promotion activities were significantly associated with a number of personality traits including neuroticism (lower), extraversion (higher), agreeableness (higher), and conscientiousness (higher). Of primary interest, mixed-effects models were used to test how major personality traits interacted with any changes in daily ratings from the pre-COVID to COVID period. Significant interactions terms were found suggesting differential impacts of the COVID epidemic for students with low versus high levels of particular traits. Higher levels of extraversion, for example, were found to be related to decreases in mood as the pandemic progressed in contrast to those with lower extraversion, for whom there was a slight increase in mood over time. These data support the conclusion that personality traits are related to mental health and can play a role in a person's ability to cope with major stressful events. Different traits may also be more adaptive to different types of stressors.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
To test the impact of the coronavirus disease 2019 (COVID) pandemic on the emotions, behavior, and wellness behaviors of first-year college students.
A total of 675 first-year university students ...completed a full assessment of behavioral and emotional functioning at the beginning of the spring semester 2020. Of these, 576 completed the same assessment at the end of the spring semester, 600 completed at least 1 item from a COVID-related survey after the onset of COVID pandemic, and 485 completed nightly surveys of mood and wellness behaviors on a regular basis before and after the onset of the COVID crisis.
Externalizing problems (mean = -0.19, 95% CI = -0.06 to 0.33, p = .004) and attention problems (mean = -0.60, 95% CI = -0.40 to 0.80, p < .001) increased after the onset of COVID, but not internalizing symptoms (mean = 0.18, 95% CI = -0.1 to 0.38, p = .06). Students who were enrolled in a campus wellness program were less affected by COVID in terms of internalizing symptoms (β = 0.40, SE = 0.21, p = .055) and attention problems (β = 0.59, SE = 0.21, p = .005) than those who were not in the wellness program. Nightly surveys of both mood (β = -0.10, SE = 0.03, p = .003) and daily wellness behaviors (β = -0.06, SE = 0.03, p = .036), but not stress (β = 0.02, SE = 0.03, p = .58), were negatively affected by the COVID crisis. The overall magnitude of these COVID-related changes were modest but persistent across the rest of the semester and different from patterns observed in a prior year.
COVID and associated educational/governmental mitigation strategies had a modest but persistent impact on mood and wellness behaviors of first-year university students. Colleges should prepare to address the continued mental health impacts of the pandemic.
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