1,152 research outputs found
Simulating Spatial Distributions, Variability and Uncertainty of Soil Arsenic by Geostatistical Simulations in Geographic Information Systems
No full textVLSI compatible parallel fabrication and characterisation of down-scaled multi-configuration Silicon quantum dot devices
No full textElectron spins in semiconductor quantum dots (QDs) have been increasingly shown in recent years to be a promising platform for realising the qubit – the basic unit of information in quantum computing. A crucial advantage of silicon QDs over alternative platforms is the potential for scalability in a quantum system to contain large numbers of qubits. Electron spins in Si-based QDs also have the benefit of a much longer spin coherence time relative to their extensively researched GaAs based counter parts – a prerequisite which gives the essential time needed for successful quantum gate operations and quantum computations.In this work, we propose and realise the first very large scale integration (VLSI) compatible process capable of fabricating scalable repeatable QD systems in parallel using silicon on insulator (SOI) technology. 3D finite element method (FEM) capacitance and single electron circuit simulations are first utilised to demonstrate the suitability of our double quantum dot (DQD) design dimensions in supporting single electron operation and detection. Here, we also present a new method of detection for single electron turnstile operations which makes use of the periodicity present in the charge stability diagram of a DQD.Through process optimisation, we fabricate 144 high density lithographically defined Si DQDs for the first time in parallel with 80% of the fabricated devices having dimensional variations of less than 5 nm. The novel use of hydrogen silsesquioxane (HSQ) resist with electron beam lithography (EBL) enabled the realisation of lithographically defined reproducible QD dimensions of an average of 51 nm with a standard deviation of 3.4 nm. Combined with an optimised thermal oxidation process, we demonstrate the precise fabrication of different QDs ranging from just 10.6 nm to over 20 nm. These are the smallest lithographically defined high density intrinsic SOI based QDs achieved to date. In addition, we demonstrate the flexibility of our fabrication process in its ability to realise a wide variety of complex device designs repeatedly. A key advantage of our process is its ability to support the scalable fabrication of QD devices without significantly affecting fabrication turnover time.Repeatable characteristic QD Coulomb oscillations and Coulomb diamonds signifying single electron tunnelling through our system are observed in electrical characteristics. Here we achieve precise independent simultaneous control of different QD’s single electron occupation as well as demonstrate evidence suggesting charge detection between QD channels. The unmatched level of clarity observed within Coulomb blockade diamond characteristics at 4.2K enables observations of line splitting of our QD’s excited states at this temperature, and readout of the spin orientation of sequential single electrons filling the QD. Through this spin readout, we gained an idea of the number of electrons stored on the QD and in turn, our ability to control the QD with precision down to the single electron limit.Statistically, we realise a parallel fabrication yield of 69% of devices demonstrating the ability to switch on and off repeatedly at 4K cryogenic temperatures with no leakage and sufficient channel resistances for single electron turnstile operations. This is the highest achieved yield observed to date for fabrication of intrinsic SOI based QD systems
Comparison of sequential Gaussian simulation, simulated annealing simulation and kriging methods for characterizing soil lead
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Multivariate Analysis of the soil heavy metal pollution and Landscape patterns analysis in Changhua County in Taiwan
No full textPartial concordance between nuclear and organelle DNA in revealing the genetic divergence among Quercus glauca (Fagaceae) populations in Taiwan
No full textTwo genetic divergence centers revealed by chloroplastic DNA variation in populations of Cinnamomum kanehirae Hay
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The lin-3/let-23 pathway mediates inductive signalling during male spicule development in Caenorhabditis elegans
Full text linkDuring Caenorhabditis elegans male spicule development, four pairs of precursor cells respond to multiple positional cues and establish a pattern of fates that correlates with relative anterior-posterior cell position. One of the extracellular cues is provided by the F and U cells, which promote anterior fates. We show that the genes in the lin-3/let-23 signalling pathway required for hermaphrodite vulval induction also mediate this F/U signal. Reduction-of-function mutations in lin-3, let-23, sem-5, let-60 or lin-45 disrupt the fate of anterior cells. Likewise, activation of the pathway with ubiquitously produced signal results in posterior cells inappropriately adopting the anterior fates even in the absence of F and U. We have further used this genetic pathway to begin to understand how multiple positional cues are integrated to specify cell fate. We demonstrate that lin-15 acts in spicule development as it does in vulval induction, as a negative regulator of let-23 receptor activity. A second extracellular cue, from Y.p, also acts antagonistically to the lin-3/let-23 pathway. However, this signal is apparently integrated into the lin-3/let-23 pathway at some step after lin-45 raf and is thus functionally distinct from lin-15. We have also investigated the role of lin-12 in forming the anterior/posterior pattern of fates. A lin-12 gain-of-function defect is masked by redundant positional information from F and U
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