There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Power dissipation is a fundamental problem for nanoelectronic circuits. Scaling the supply voltage reduces the energy needed for switching, but the field-effect transistors (FETs) in today's integrated circuits require at least 60 mV of gate voltage to increase the current by one order of magnitude at room temperature. Tunnel FETs avoid this limit by using quantum-mechanical band-to-band tunnelling, rather than thermal injection, to inject charge carriers into the device channel. Tunnel FETs based on ultrathin semiconducting films or nanowires could achieve a 100-fold power reduction over complementary metal-oxide-semiconductor (CMOS) transistors, so integrating tunnel FETs with CMOS technology could improve low-power integrated circuits.

Tunnel field-effect transistors as energy-efficient electronic switches

Tin dioxide is a widely used sensitive material for gas sensors. Many research and development groups in academia and industry are contributing to the increase of (basic) knowledge/(applied) know-how. However, from a systematic point of view the knowledge gaining process seems not to be coherent. One reason is the lack of a general applicable model which combines the basic principles with measurable sensor parameters. The approach in the presented work is to provide a frame model that deals with all contributions involved in conduction within a real world sensor. For doing so, one starts with identifying the different building blocks of a sensor. Afterwards their main inputs are analyzed in combination with the gas reaction involved in sensing. At the end, the contributions are summarized together with their interactions. The work presented here is one step towards a general applicable model for real world gas sensors.

Conduction Model of Metal Oxide Gas Sensors

The surface and materials science of tin oxide

In this paper, we look into the scaling issues of a vertical tunnel field-effect transistor (FET). The device, a gated p-i-n diode based on silicon, showed gate-controlled band-to-band tunneling from the heavily doped source to the intrinsic channel. An exponentially increasing input characteristics, perfect saturation in the output characteristics, and off-currents of the order of 1 fA//spl mu/m for sub-100-nm channel lengths were observed. Further, with a /spl delta/p/sup +/ SiGe layer at the p-source end, improvements in the device performance in terms of on-current, threshold voltage and subthreshold swing were shown, albeit trading off the off-currents which increase with Ge content x. We show here that the tunnel FET performance is nearly independent of channel length scaling L and with /spl delta/p/sup +/ SiGe layer, scaling t/sub ox/ is not critical to tunnel FET scaling. Further, with gate workfunction engineering, the tunnel FET can be tuned to achieve a high on-current as well as very low off-currents. Due to the perfect saturation in the output characteristics, the device looks good for sub-100-nm low-power analog devices.

Scaling the vertical tunnel FET with tunnel bandgap modulation and gate workfunction engineering

The gas sensing characteristics and the morphology of cobalt oxide thin films have been investigated. The thin films were prepared by reactive electron beam evaporation of cobalt on “pure” and surface-oxidised silicon wafers respectively followed by an additional thermal treatment. Structural and morphological analyses of the thin Co3O4 films were performed by X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and Rutherford backscattering (RBS). Two gas-sensitive parameters of the Co3O4 films were investigated: the shift of the work function and change of conductivity during gas exposure. The gas measurements were carried out with ammonia, methane, carbon monoxide, hydrogen, chlorine (only GasFET) and nitric dioxide as test gases in synthetic air at different humidities. The work function measurements were carried out with suspended gate GasFETs as transducer, the resistive measurements with single chip thin-film sensor arrays.

Cobalt oxide based gas sensors on silicon substrate for operation at low temperatures

The metal–oxide–semiconductor (MOS)-based vertical tunnel field effect transistor (FET) on silicon has been proposed earlier and which showed gate-controlled band-to-band tunneling from the valence band in the heavily doped δp+ layer at source to the conduction band in the inversion channel. In this work, using 2D computer simulation, we further investigate the device performance enhancement with SiGe in the δp+ layer. On-current as well as threshold voltage are seen to improve considerably and meet the roadmap technology requirements. We also show that unlike the conventional MOSFET, the subthreshold swing of the vertical tunnel FET is not limited to the theoretical value of 60 mV/dec at room temperature.

https://iopscience.iop.org/article/10.1143/JJAP.43.4073/pdf

Performance Enhancement of Vertical Tunnel Field-Effect Transistor with SiGe in the δp+ Layer

We develop the theory for grazing incidence small-angle x-ray scattering (GISAXS) from nanometer-sized naked islands on a flat substrate in the framework of the distorted-wave Born approximation (DWBA). The scattered wave amplitude is composed of four terms, including all combinations of scattering from the islands and reflection from the substrate. We apply this theory to x-ray measurements on Ge islands grown on Si(111), and show that we can determine the full triangular symmetry of these islands. The results also show that the DWBA must be used for smooth substrates near the angle of total external reflection. We finally discuss the advantages of GISAXS as compared to transmission small angle x-ray scattering for determining the symmetry of nanostructures.

Grazing incidence small angle x-ray scattering from free-standing nanostructures

Using two-dimensional device simulations, the electrical parameters of gated tunnel field-effect transistor (FET) are optimized with a SiGe delta doped layer in the source region. In order to prove the validity of the simulation models we compare simulation results with the experimentally realized tunnel FET on silicon and show that it gives a good match. It is shown that the incorporation of pseudomorphic strained-Si/sub 1-x/Ge/sub x/ layers leads to a significant performance increase. Furthermore, it becomes evident that the improvements are not a direct consequence of bandgap lowering but rather an indirect consequence of tunnel barrier width lowering. This leads to an asymmetry in the n- and the p-channel performance.

Ignaz Eisele

Papers

Scaling the vertical tunnel FET with tunnel bandgap modulation and gate workfunction engineering

Cobalt oxide based gas sensors on silicon substrate for operation at low temperatures

Performance Enhancement of Vertical Tunnel Field-Effect Transistor with SiGe in the δp+ Layer

Grazing incidence small angle x-ray scattering from free-standing nanostructures

A simulation approach to optimize the electrical parameters of a vertical tunnel FET