36 research outputs found
Defect detection in nano-scale transistors based on radio-frequency reflectometry
Radio-frequency reflectometry in silicon single-electron transistors (SETs)
is presented. At low temperatures (<4 K), in addition to the expected Coulomb
blockade features associated with charging of the SET dot, quasi-periodic
oscillations are observed that persist in the fully depleted regime where the
SET dot is completely empty. A model, confirmed by simulations, indicates that
these oscillations originate from charging of an unintended floating gate
located in the heavily doped polycrystalline silicon gate stack. The technique
used in this experiment can be applied for detailed spectroscopy of various
charge defects in nanoscale SETs and field effect transistorsComment: 3 pages, 3 figure
Dopant effects on the photoluminescence of interstitial-related centers in ion implanted silicon
The dopant dependence of photoluminescence(PL) from interstitial-related centers formed by ion implantation and a subsequent anneal in the range 175–525 °C is presented. The evolution of these centers is strongly effected by interstitial-dopant clustering even in the low temperature regime. There is a significant decrease in the W line (1018.2 meV) PL intensity with increasing B concentration. However, an enhancement is also observed in a narrow fabrication window in samples implanted with either P or Ga. The annealtemperature at which the W line intensity is optimized is sensitive to the dopant concentration and type. Furthermore, dopants which are implanted but not activated prior to low temperature thermal processing are found to have a more detrimental effect on the resulting PL. Splitting of the X line (1039.8 meV) arising from implantation damage induced strain is also observed.This work is supported by a grant from the Australian
Research Council. B.C.J. is partially supported by the Japan
Society for the Promotion of Science (JSPS) (Grant-in-aid
for Scientific Research, 22.00802)
Understanding resonant charge transport through weakly coupled single-molecule junctions
Off-resonant charge transport through molecular junctions has been
extensively studied since the advent of single-molecule electronics and it is
now well understood within the framework of the non-interacting Landauer
approach. Conversely, gaining a qualitative and quantitative understanding of
the resonant transport regime has proven more elusive. Here, we study resonant
charge transport through graphene-based zinc-porphyrin junctions. We
experimentally demonstrate an inadequacy of the non-interacting Landauer theory
as well as the conventional single-mode Franck-Condon model. Instead, we model
the overall charge transport as a sequence of non-adiabatic electron transfers,
the rates of which depend on both outer and inner-sphere vibrational
interactions. We show that the transport properties of our molecular junctions
are determined by a combination of electron-electron and electron-vibrational
coupling, and are sensitive to the interactions with the wider local
environment. Furthermore, we assess the importance of nuclear tunnelling and
examine the suitability of semi-classical Marcus theory as a description of
charge transport in molecular devices.Comment: version accepted in Nature Communications; SI available at
https://researchportal.hw.ac.uk/en/publications/understanding-resonant-charge-transport-through-weakly-coupled-s
Corrigendum: Coherent creation and destruction of orbital wavepackets in Si:P with electrical and optical read-out
The ability to control dynamics of quantum states by optical interference, and subsequent
electrical read-out, is crucial for solid state quantum technologies. Ramsey interference has
been successfully observed for spins in silicon and nitrogen vacancy centres in diamond, and
for orbital motion in InAs quantum dots. Here we demonstrate terahertz optical excitation,
manipulation and destruction via Ramsey interference of orbital wavepackets in Si:P with
electrical read-out. We show milliradian control over the wavefunction phase for the two-level
system formed by the 1s and 2p states. The results have been verified by all-optical echo
detection methods, sensitive only to coherent excitations in the sample. The experiments
open a route to exploitation of donors in silicon for atom trap physics, with concomitant
potential for quantum computing schemes, which rely on orbital superpositions to, for
example, gate the magnetic exchange interactions between impurities
Brain-behaviour modes of covariation in healthy and clinically depressed young people.
Understanding how variations in dimensions of psychometrics, IQ and demographics relate to changes in brain connectivity during the critical developmental period of adolescence and early adulthood is a major challenge. This has particular relevance for mental health disorders where a failure to understand these links might hinder the development of better diagnostic approaches and therapeutics. Here, we investigated this question in 306 adolescents and young adults (14-24 y, 25 clinically depressed) using a multivariate statistical framework, based on canonical correlation analysis (CCA). By linking individual functional brain connectivity profiles to self-report questionnaires, IQ and demographic data we identified two distinct modes of covariation. The first mode mapped onto an externalization/internalization axis and showed a strong association with sex. The second mode mapped onto a well-being/distress axis independent of sex. Interestingly, both modes showed an association with age. Crucially, the changes in functional brain connectivity associated with changes in these phenotypes showed marked developmental effects. The findings point to a role for the default mode, frontoparietal and limbic networks in psychopathology and depression.Wellcome Trus
Preserved cognitive functions with age are determined by domain-dependent shifts in network responsivity
Healthy ageing has disparate effects on different cognitive domains. The neural basis of these differences, however, is largely unknown. We investigated this question by using Independent Components Analysis to obtain functional brain components from 98 healthy participants aged 23-87 years from the population-based Cam-CAN cohort. Participants performed two cognitive tasks that show age-related decrease (fluid intelligence and object naming) and a syntactic comprehension task that shows age-related preservation. We report that activation of task-positive neural components predicts inter-individual differences in performance in each task across the adult lifespan. Furthermore, only the two tasks that show performance declines with age show age-related decreases in task-positive activation of neural components and decreasing default mode (DM) suppression. Our results suggest that distributed, multi-component brain responsivity supports cognition across the adult lifespan, and the maintenance of this, along with maintained DM deactivation, characterizes successful ageing and may explain differential ageing trajectories across cognitive domains
Multiple determinants of lifespan memory differences
Memory problems are among the most common complaints as people grow older. Using structural equation modeling of commensurate scores of anterograde memory from a large (N = 315), population-derived sample (www.cam-can.org), we provide evidence for three memory factors that are supported by distinct brain regions and show differential sensitivity to age. Associative memory and item memory are dramatically affected by age, even after adjusting for education level and fluid intelligence, whereas visual priming is not. Associative memory and item memory are differentially affected by emotional valence, and the age-related decline in associative memory is faster for negative than for positive or neutral stimuli. Gray-matter volume in the hippocampus, parahippocampus and fusiform cortex, and a white-matter index for the fornix, uncinate fasciculus and inferior longitudinal fasciculus, show differential contributions to the three memory factors. Together, these data demonstrate the extent to which differential ageing of the brain leads to differential patterns of memory loss
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Brain-behaviour modes of covariation in healthy and clinically depressed young people
Abstract: Understanding how variations in dimensions of psychometrics, IQ and demographics relate to changes in brain connectivity during the critical developmental period of adolescence and early adulthood is a major challenge. This has particular relevance for mental health disorders where a failure to understand these links might hinder the development of better diagnostic approaches and therapeutics. Here, we investigated this question in 306 adolescents and young adults (14–24 y, 25 clinically depressed) using a multivariate statistical framework, based on canonical correlation analysis (CCA). By linking individual functional brain connectivity profiles to self-report questionnaires, IQ and demographic data we identified two distinct modes of covariation. The first mode mapped onto an externalization/internalization axis and showed a strong association with sex. The second mode mapped onto a well-being/distress axis independent of sex. Interestingly, both modes showed an association with age. Crucially, the changes in functional brain connectivity associated with changes in these phenotypes showed marked developmental effects. The findings point to a role for the default mode, frontoparietal and limbic networks in psychopathology and depression