355 research outputs found
High-frequency performance of Schottky source/drain silicon pMOS devices
A radio-frequency performance of 85-nm gate-length p-type Schottky barrier (SB) with PtSi source/drain materials is investigated. The impact of silicidation annealing temperature on the high-frequency behavior of SB MOSFETs is analyzed using an extrinsic small-signal equivalent circuit. It is demonstrated that the current drive and the gate transconductance strongly depend on the silicidation anneal temperature, whereas the unity-gain cutoff frequency of the measured devices remains nearly unchanged
Nutrient relations in calcareous grassland under elevated CO2
Plant nutrient responses to 4 years of CO2 enrichment were investigated in situ in calcareous grassland. Beginning in year 2, plant aboveground C:N ratios were increased by 9% to 22% at elevated CO2 (P > 0.01), depending on year. Total amounts of N removed in biomass harvests during the first 4 years were not affected by elevated CO2 (19.9 +/- 1.3 and 21.1 +/- 1.3 g N m(-2) at ambient and elevated CO2), indicating that the observed plant biomass increases were solely attained by dilution of nutrients. Total aboveground P and tissue N:P ratios also were not altered by CO2 enrichment (12.5 +/- 2 g N g(-1) P in both treatments). In contrast to non-legumes (<98% of community aboveground biomass), legume C/N was not reduced at elevated CO2 and legume N:P was slightly increased. We attribute the less reduced N concentration in legumes at elevated CO2 to the fact that virtually all legume N originated from symbiotic N-2 fixation (%N-dfa approximate to 90%), and thus legume growth was not limited by soil N. While total plant N was not affected by elevated CO2, microbial N pools increased by +18% under CO2 enrichment (P = 0.04) and plant available soil N decreased. Hence, there was a net increase in the overall biotic N pool, largely due increases in the microbial N pool. In order to assess the effects of legumes for ecosystem CO2 responses and to estimate the degree to which plant growth was P-limited, two greenhouse experiments were conducted, using firstly undisturbed grassland monoliths from the field site, and secondly designed 'microcosm' communities on natural soil. Half the microcosms were planted with legumes and half were planted without. Both monoliths and microcosms were exposed to elevated CO2 and P fertilization in a factored design. After two seasons, plant N pools in both unfertilized monoliths and microcosm communities were unaffected by CO2 enrichment, similar to what was found in the field. However, when P was added total plant N pools increased at elevated CO2. This community-level effect originated almost solely from legume stimulation. The results suggest a complex interaction between atmospheric CO2 concentrations, N and P supply. Overall ecosystem productivity is N-limited, whereas CO2 effects on legume growth and their N2 fixation are limited by P
Composite fermions in the Fractional Quantum Hall Effect: Transport at finite wavevector
We consider the conductivity tensor for composite fermions in a close to
half-filled Landau band in the temperature regime where the scattering off the
potential and the trapped gauge field of random impurities dominates. The
Boltzmann equation approach is employed to calculate the quasiclassical
transport properties at finite effective magnetic field, wavevector and
frequency. We present an exact solution of the kinetic equation for all
parameter regimes. Our results allow a consistent description of recently
observed surface acoustic wave resonances and other findings.Comment: REVTEX, 4 pages, 1 figur
Ohmic contacts to n-type germanium with low specific contact resistivity
A low temperature nickel process has been developed that produces Ohmic contacts to n-type germanium with specific contact resistivities down to (2.3 ± 1.8) x10<sup>-7</sup> Ω-cm<sup>2</sup> for anneal temperatures of 340 degC. The low contact resistivity is attributed to the low resistivity NiGe phase which was identified using electron diffraction in a transmission electron microscope. Electrical results indicate that the linear Ohmic behaviour of the contact is attributed to quantum mechanical tunnelling through the Schottky barrier formed between the NiGe alloy and the heavily doped n-Ge.<p></p>
Regeneration in gap models: priority issues for studying forest responses to climate change
Recruitment algorithms in forest gap models are examined with particular regard to their suitability for simulating forest ecosystem responses to a changing climate. The traditional formulation of recruitment is found limiting in three areas. First, the aggregation of different regeneration stages (seed production, dispersal, storage, germination and seedling establishment) is likely to result in less accurate predictions of responses as compared to treating each stage separately. Second, the relatedassumptions that seeds of all species are uniformly available and that environmental conditions are homogeneous, are likely to cause overestimates of future species diversity and forest migration rates. Third, interactions between herbivores (ungulates and insect pests) and forest vegetation are a big unknown with potentially serious impacts in many regions. Possible strategies for developing better gap model representations for the climate-sensitive aspects of each of these key areas are discussed. A working example of a relatively new model that addresses some of these limitations is also presented for each case. We conclude that better models of regeneration processes are desirable for predicting effects of climate change, but that it is presently impossible to determine what improvements can be expected without carrying out rigorous tests for each new formulation
Application of Bryan's algorithm to the mobility spectrum analysis of semiconductor devices
A powerful method for mobility spectrum analysis is presented, based on Bryan's maximum entropy algorithm. The Bayesian analysis central to Bryan's algorithm ensures that we avoid overfitting of data, resulting in a physically reasonable solution. The algorithm is fast, and allows the analysis of large quantities of data, removing the bias of data selection inherent in all previous techniques. Existing mobility spectrum analysis systems are reviewed, and the performance of the Bryan's algorithm mobility spectrum (BAMS) approach is demonstrated using synthetic data sets. Analysis of experimental data is briefly discussed. We find that BAMS performs well compared to existing mobility spectrum methods
Reflecting on the experiential journey: Creating, developing and understanding leadership in Equality, Diversity and Inclusion within a Faculty
London South Bank University (LSBU) appointed equality, diversity and inclusion (EDI) leads
in each of its Schools in 2021/22. The leadersâ remit was to deliver and embed LSBUâs EDI
strategy cognisant of the uniqueness of the Schools. LSBUâs pioneering EDI strategy has
been recognised as a symbol of excellence and shortlisted for two national EDI awards. The
composition of LSBUâs academic senior management does not yet fully reflect the
intersectional diversity of the organisation. Therefore, this session aims to share the
experience of LSBUâs EDI leads and facilitate discussion about the benchmarks for
achieving leadership in EDI within a School
A study of temperature-related non-linearity at the metal-silicon interface
In this paper, we investigate the temperature dependencies of metal-semiconductor interfaces in an effort to better reproduce the current-voltage-temperature (IVT) characteristics of any Schottky diode, regardless of homogeneity. Four silicon Schottky diodes were fabricated for this work, each displaying different degrees of inhomogeneity; a relatively homogeneous NiV/Si diode, a Ti/Si and Cr/Si diode with double bumps at only the lowest temperatures, and a Nb/Si diode displaying extensive non-linearity. The 77â300âK IVT responses are modelled using a semi-automated implementation of Tung's electron transport model, and each of the diodes are well reproduced. However, in achieving this, it is revealed that each of the three key fitting parameters within the model display a significant temperature dependency. In analysing these dependencies, we reveal how a rise in thermal energy âactivatesâ exponentially more interfacial patches, the activation rate being dependent on the carrier concentration at the patch saddle point (the patch's maximum barrier height), which in turn is linked to the relative homogeneity of each diode. Finally, in a review of Tung's model, problems in the divergence of the current paths at low temperature are explained to be inherent due to the simplification of an interface that will contain competing defects and inhomogeneities
Implications of incorporating N cycling and N limitations on primary production in an individual-based dynamic vegetation model
The LPJ-GUESS dynamic vegetation model uniquely combines an individual- and
patch-based representation of vegetation dynamics with ecosystem
biogeochemical cycling from regional to global scales. We present an updated
version that includes plant and soil N dynamics, analysing the implications
of accounting for CâN interactions on predictions and performance of the
model. Stand structural dynamics and allometric scaling of tree growth
suggested by global databases of forest stand structure and development were
well reproduced by the model in comparison to an earlier multi-model study.
Accounting for N cycle dynamics improved the goodness of fit for broadleaved
forests. N limitation associated with low N-mineralisation rates reduces
productivity of cold-climate and dry-climate ecosystems relative to mesic
temperate and tropical ecosystems. In a model experiment emulating free-air
CO<sub>2</sub> enrichment (FACE) treatment for forests globally, N limitation
associated with low N-mineralisation rates of colder soils reduces CO<sub>2</sub>
enhancement of net primary production (NPP) for boreal forests, while some
temperate and tropical forests exhibit increased NPP enhancement. Under a
business-as-usual future climate and emissions scenario, ecosystem C storage
globally was projected to increase by ca. 10%; additional N requirements
to match this increasing ecosystem C were within the high N supply limit
estimated on stoichiometric grounds in an earlier study. Our results
highlight the importance of accounting for CâN interactions in studies of
global terrestrial N cycling, and as a basis for understanding mechanisms on
local scales and in different regional contexts
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