To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
The development of more sustainable construction materials is a crucial step toward the reduction of CO2 emissions to mitigate climate change issues and minimize environmental impacts of the associated industries. Therefore, there is a growing demand for bio-based binders which are not only safer toward human and environmental health but also facilitate cleaner disposal of the construction materials and enable their compostability. Here, we summarize the most relevant bio-based polymers and molecules with applications in the construction sector. Due to the biologic nature of these materials, the existing biotechnologic processes, including synthetic biology, for their development and production have been evaluated.
Thomas Rickman has been credited, perhaps for too long, as the first figure to ‘discriminate’ the styles of medieval architecture and create a chronological analysis of Gothic architectural forms. Not only were there several authors who published on the subject immediately before Rickman, but there was also, as early as the mid-seventeenth century, considerable interest in the discernment and classification of periods in medieval architecture. One of the chief figures in this was John Aubrey, who pioneered a method for deducing the date of a medieval building by analysing the shapes of its windows. This intellectual initiative, 150 years before Rickman, has been either overlooked or interpreted as a ‘false start’ in Gothic revivalism. It is, however, worthy of fresh appraisal as a significant development in historical method and as an indicator of one way in which architecture was understood in the seventeenth century. Aubrey’s idea was that objects of a given type, in this case medieval windows, had a particular shape during a particular historical period, and that their morphology could be used to create a system for establishing the date of any given building. The context for this scheme was the innovative proposal of several early modern antiquaries that shapes in themselves could convey historical information, and that specific historical periods had their own distinctive forms. These scholars, many of whom were associated with the Royal Society, took faltering steps towards taxonomies of historical form which foreshadowed the methods of analysis that became — and arguably remain — central to the discipline of architectural history. That their interest focused upon medieval architecture at a time when the Gothic was largely rejected as irregular and barbarous is also notable. Examining the origins of a technique for dating historic buildings through visual analysis reveals how an intellectual circle of the seventeenth century perceived and understood architecture at a time when in England architectural commentary and criticism were still in their infancy.
The hunt for Virgil’s sources has been, by unspoken agreement among Latinists, largely abandoned. This regrettable development may in part have been a by-product of the justifiable revulsion against the excesses of Quellenforschung as practised c. 1880-c. 1930 (everyone read Posidonius and Varro; no-one else was read), in part by the opening of alluring new vistas in Virgilian studies, where apparent progress might be made without the need of painstaking consultation of HRR,GRF,FGH,FHG and similar collections. It has therefore escaped notice that just as the detailed examination of Virgil’s use of Homer (Knauer, Die Aeneis und Homer) or even of the Homer scholia (Schlunk, Virgil and the Homeric Scholia) can lead to immensely valuable advances in our understanding of the poet’s compositional techniques, so the survey of Virgil’s prose sources and the analysis of how he handles the material available to him can be employed to precisely comparable ends. It is the purpose of this paper to indicate some ways in which such a survey may be put into effect.
We present the characteristics of a high temperature CMOS integrated circuit process based on 4H silicon carbide designed to operate at temperatures beyond 300°C. N-channel and P-channel transistor characteristics at room and elevated temperatures are presented. Both channel types show the expected low values of field effect mobility well known in SiC MOSFETS. However the performance achieved is easily capable of exploitation in CMOS digital logic circuits and certain analogue circuits, over a wide temperature range.
Data is also presented for the performance of digital logic demonstrator circuits, in particular a 4 to 1 analogue multiplexer and a configurable timer operating over a wide temperature range. Devices are packaged in high temperature ceramic dual in line (DIL) packages, which are capable of greater than 300°C operation. A high temperature “micro-oven” system has been designed and built to enable testing and stressing of units assembled in these package types. This system heats a group of devices together to temperatures of up to 300°C while keeping the electrical connections at much lower temperatures. In addition, long term reliability data for some structures such as contact chains to n-type and p-type SiC and simple logic circuits is summarized.
We have investigated, using density functional simulations, the energetics and the electronic properties of oxides of selected transition metals, TMs, adsorbed onto a dia-mond (001) surface. We find that stoichiometric oxides of TMs, particularly Ti and Zn,influence the electron affinity of diamond strongly. The electron affinities of stoichiomet-ric oxides of Ti and Zn are calculated to be around −3 eV, significantly higher than 1.9 eV of commonly used H–termination. The reactions of TMs with an oxygenated diamond are found to be highly exothermic. Based upon the energetics and the electronic properties, we propose that in the regime of ultra thin films, oxides of TMs are promising options for surface coating of diamond–based electron emitters, as these coatings are compatible with semiconductor device fabrication processes, while having the benefit of inducing a large negative electron affinity.
The output power-density and the efficiency of thermo-tunnel devices are examinedas a function of inter-electrode separation, electrode work-function, and temperature. We find that these physical parameters dramatically influence the device characteristics, and under optimal conditions a thermo-tunnel device is capable of delivering a very high output power-density of ∼ 103Wcm−2. In addition, at higher temperatures, the heat-conversion efficiency of the thermo-tunnel device approaches ∼ 10%, comparable to that of a thermoelectric generator. We therefore propose that thermo-tunnel devices are promising for solid-state thermal energy conversion.
The effects of post-implant anneal conditions on the level of residual damage resulting from nitrogen and boron implants after different anneal processes are investigated using the Positron Annihilation Spectroscopy (PAS) technique. It is shown that after implantation there is a substantial defect concentration significantly below the range of the implants. However such damage is almost completely recovered after anneal in contrast with the damage close to the implant range point. Such residual damage has a strong effect on the electrical characteristics of double implanted bipolar transistors - principally though reduction in carrier mobility and lifetime. It is shown that the precise implant and anneal conditions play a strong role in the level of such damage and the subsequent electrical performance of bipolar devices.
A simple ion-implanted bipolar transistor technology in 4H-SiC is presented. Suitable for both high-voltage vertical devices and lateral high-temperature transistors (for circuit applications), the technology is based on an implanted boron p-well with nitrogen and boron (or aluminium) implanted n+ and p+ regions respectively. The effects of base doping and carrier lifetime on device performance have been studied using TCAD techniques. It is shown that understanding the strong variation of carrier concentration with temperature (due to deep activation levels) and applied field (so-called field ionization) is critical in device design optimisation. The effects of post-implant anneal conditions on the physical and electrical characteristics of the junctions are investigated. It is shown that annealing can remove much of the damage induced by high dose nitrogen implantation but that residual damage is still present. The electrical characteristics of simple BJT transistors with breakdown voltages in excess of 1000V and common-emitter gains of ∼2 is related to the level of such residual damage.
As the trend for miniaturisation in the microelectronics field continues, metallisation connecting components has smaller and smaller dimensions, especially width and thickness. The mechanical properties of the deposited metal are very different from those of the bulk material and it is important to evaluate them accurately if the reliability of the metallisation is to be optimised. The assessment of the mechanical properties of thin aluminium metallisation is possible by nanoindentation but to extract properties useful for lifetime prediction such as yield stress or creep relaxation behaviour additional modelling is necessary using finite elements analysis (FEA). In this study evaporated aluminium layers from 50nm to 600nm thick on (100) silicon were indented to various depths. Proportional loading was used to minimise the effect of creep. The loading curves were then simulated by FEA and the results compared to identify the yield properties of the coating. Modelling data for thicker samples closely follows experimental data but for thinner coatings there is a considerable gradient in properties through the film thickness.
Schottky barrier diodes fabricated on Silicon carbide have been demonstrated as gas sensors for deployment in extreme environments. It has been shown that the interfacial layer formed at the Metal – Semiconductor junction, determines both the sensitivity and the reliability of the device. Hence, accurate knowledge of the thickness and interfacial trap density of this layer is required to make predictions of the behaviour of the sensor in the environment under investigation and to predict its variation with time. Diode parameters, such as the ideality factor, barrier height and series resistance have been extracted from experimental measurements on Palladium Schottky Barrier diodes on 4H SiC, over a range of temperatures. The comparison of the parameters extracted from modified Norde function, Cheung's method and Thermonic Emission model has been performed. The variation in the barrier height obtained is quite marked between the different techniques. The reverse I-V characteristics have been used to extract thickness of the interfacial layer, by fitting to the experimental data using the TEBIL model to extract the value of Dit from ä and the ideality factor, assuming the interfacial layer is stoichiometric SiO2 . This allows a comparison between the effective interfacial layer behaviour for the different parameter extraction techniques and demonstrates that knowledge of this interfacial layer is influenced by the technique selected.
HfO2 films were grown on SiO2/4H-SiC and SiON/4H-SiC layers by evaporation of metallic Hf in an electron beam deposition system followed by thermal oxidation. X-ray photoelectron spectroscopy confirmed the formation of HfO2 films. There is no evidence of formation of hafnium silicide or carbon pile up at the surface as well as at the interfacial layer. Electrical measurements show the presence of fewer slow traps in the HfO2/SiON gate dielectric stack on 4H-SiC and comparable values of interface state density. The HfO2/SiON stack layer improves leakage current characteristics with a higher breakdown field and has better reliability under electrical stress.
The dimensions of microelectronic devices are constantly being reduced due to the increasing operational demands imposed such as higher working frequencies, higher component density and lower power consumption. This affects the geometrical dimensions of the metallisation, i.e. its width and thickness. The mechanical properties of very thin films are considerably different from those of bulk materials and, also, the deposition method may influence the mechanical behaviour of the components. In order to obtain reliable metallisation it is therefore important to assess accurately the mechanical parameters of the interconnecting lines. As part of designing, developing and manufacturing of a stress micro-sensor there is a need to extract properties useful for performance prediction such as yield stress or creep relaxation behaviour. Part of the data may be obtained by nanoindentation but to have a more complete view, finite element analysis of the indentation cycle has to be employed. In this study nanoindentation testing was carried out at various depths on sputtered and evaporated aluminium layers with different thicknesses deposited on (100) silicon. The loading curves were then simulated by FEA and the results compared to identify the yield properties of the coating. Modelling data for thicker samples closely follows experimental data but for thinner coatings there is a considerable gradient in properties through the film thickness. By incorporating a peak load hold the creep behaviour of the metallization can also be assessed and modelling parameters developed.
The scaling of contemporary metal-insulator-metal (MIM) capacitors requires oxides of higher dielectric constant (>10), such as hafnium oxide (∼18) and titanium oxide (∼40). Intensive research of these oxides and oxide stacks is needed to develop them into high quality electronic materials for their application as capacitors in high temperature environments. High-k dielectrics such as HfO2 and HfO2/TiO2/HfO2 have been grown by thermal oxidation to fabricate MIM capacitors on SiO2/Si substrates and on sapphire substrates also. The thermally grown Al/HfO2/TiO2/HfO2/Pt/Ti/SiO2/Si MIM capacitor is reported here for the first time. The MIM capacitor using HfO2/TiO2/HfO2 dielectric film shows a similar frequency dependence using HfO2 dielectric on a SiO2/Si substrate, whilst its voltage linearity coefficients, leakage current and temperature coefficient are higher than the capacitor employing HfO2 dielectric. The MIM capacitor with HfO2 dielectric fabricated on sapphire substrate shows the strongest frequency dependence, voltage linearity coefficient and temperature dependence which is related to the surface roughness of substrate. The high capacitance density of these capacitors, ranging from 5.21 fF/µm2, meets the ITRS requirements for analog capacitor up to 2012. The MIM capacitor using 30nm HfO2 dielectric film illustrates highest capacitance density, 5.21 fF/µm2, a VCC of 236 ppm/V2, a temperature coefficient of 290 ppm/ºC, measured up to 300 ºC, and leakage current density which is 1.3 × 10−7 A/cm2 at 1V.
The process-induced stress in interconnects within integrated circuits (IC) has a direct influence on the mean time to failure of the devices. Since measurement of stress in individual metallised lines is not possible by existing techniques, another approach has been adopted where a test structure is generated during fabrication based on a micro-rotating cantilever sensor. To support the design, finite element modeling (FEM) has been performed. By comparing the rotation predicted by FEM simulations and that observed experimentally, a clear discrepancy is observed which is critically dependent on the details of the sensor design, the pattern transfer of the lithographic process and on the dry etching processing.
This paper provides a new interpretation of the date, form, meanings and theological sources of the former painted cycle on the vaults of Salisbury Cathedral. As the cycle is now known predominantly from antiquarian evidence, we begin with a discussion of the nature and significance of that evidence, namely the series of sketches, drawings and notes produced by Jacob Schnebbelie in the late eighteenth century before the whitewashing of the medieval paintings. Through consideration of the archaeological and stylistic evidence, we propose a date for the cycle between c 1235 and 1245, thus contemporary with the new building campaign begun in 1220. Two connected interpretations of the cycle are offered: first, we argue that the painted cycle was designed to function as a map of the major liturgical sites of the eastern arm; second, we suggest that the imagery was designed to structure an allegory of religious experience and personal salvation in accord with reform-minded thinking in the post-Lateran period.
This Working Party has considered the pensions implications of a prolonged period of low inflation. Experience in the United States of America suggests weaker correlation between equity and bond returns and greater overall volatility of returns. Without a further significant increase in the valuation of equities relative to their underlying economic activity, the cost of pensions will rise, possibly as much as doubling within the next 15 years. It follows that for defined contribution schemes and personal pensions, current contribution levels are likely to produce disappointing and generally inadequate results. Similarly, the costs of defined benefit promises will increase. Future defined benefit provision is also vulnerable to the mismatch of mainly equity assets with mainly fixed liabilities and is therefore difficult to control. Many practical issues of scheme design still reflect past inflation and need to be addressed.