arXiv subjects

Ian Underwood

Publications and source records attributed to Ian Underwood.

4 recordsLinked to original sources

arXiv2026

Methods for an Electron Emission Digital Twin

The effective design and operation of electron emitters is the core of critical technologies such as high-resolution electron imaging and spectroscopy or X-ray production for medical imaging. Despite 100 years of theoretical development in thermo- and field-electron emission models, the analysis of experimental data and design of electron emitters remains an art more than a science. This is due to the many processes that are involved in electron emission, which result in an extremely complex phenomenon. Here we describe and develop the Methods for an Electron Emission Digital Twin (MEEDiT), which integrates state-of-the-art thermo-field electron emission models and experimental data characterisation. By applying MEEDiT to silicon electron emitters, we demonstrate an approach that bridges the gap between simple experimental measurements and 'hidden' physical quantities like temperature and field enhancement. MEEDiT provides the physical consistency of a 3D simulation with the speed of a neural network, enabling resource-effective, real-time characterization and the extraction of critical data that is otherwise inaccessible during operation.

physics.ins-det↗

arXiv2025

Towards 4D modelisation of thermal-field emission from semiconductors

The theoretical picture of thermal field-emission (TFE) from semiconductors has been limited to 1D and 2D models. This can be attributed to the complex and interdependent phenomena that is involved in TFE from semiconductors which makes the calculations cumbersome. Such limitations result in a partial understanding of the underlying physics of semiconducting surfaces under high electrical fields, which requires the addition of the temporal dimension (4D) to yield a realistic model. Here we develop a 3D model of TFE from semiconductors that can take arbitrary geometries and doping levels. Our model successfully reproduces the characteristic saturation plateau of some semiconductors, as well as its dependence in temperature. The model is found to be in good agreement with experimental data from ntype Germanium at a qualitative level. We propose this model as a platform for future extensions into the full 4D framework, incorporating temporal dynamics for a more complete and predictive description of thermal-field emission from semiconductors.

cond-mat.mtrl-sci↗

arXiv2025

Theory and computation of thermal-field emission from semiconductors

Semiconducting field emitters present some interesting features (e.g.; self-limited electron emission) for both scientific interest and industrial applications. The analysis of experimental results and device design has been restrained by the lack of accurate 3D models for the simulation of thermal-field emission from semiconductors. Here we review and correct the equations of field emission from semiconductors and include them to expand GETELEC (General Tool for Electron Emission Calculations). Our method covers all electron emission regime (field, thermal, and intermediate), aiming to maximise the calculation accuracy while minimising the computational cost. GETELEC-2.0 is able to reproduce the characteristic non-linear I-V curves in Fowler-Nordheim coordinates obtained from semiconductors, giving insights about their nature. As well as providing an explanation to the lack of experimental observation of valence band electrons from semiconductors.

cond-mat.mtrl-sci↗

arXiv2021

A pulse oximeter based on Time-of-Flight histograms

A pulse oximeter is an optical device that monitors tissue oxygenation levels. Traditionally, these devices estimate the oxygenation level by measuring the intensity of the transmitted light through the tissue and are embedded into everyday devices such as smartphones and smartwatches. However, these sensors require prior information and are susceptible to unwanted changes in the intensity, including ambient light, skin tone, and motion artefacts. Previous experiments have shown the potential of Time-of-Flight (ToF) techniques in measurements of tissue hemodynamics. Our proposed technology uses histograms of photon flight paths within the tissue to obtain tissue oxygenation, regardless of the changes in the intensity of the source. Our device is based on a 45ps time-to-digital converter (TDC) which is implemented in a Xilinx Zynq UltraScale+ field programmable gate array (FPGA), a CMOS Single Photon Avalanche Diode (SPAD) detector, and a low-cost compact laser source. All these components including the SPAD detector are manufactured using the latest commercially available technology, which leads to increased linearity, accuracy, and stability for ToF measurements. This proof-of-concept system is approximately 10cmx8cmx5cm in size, with a high potential for shrinkage through further system development and component integration. We demonstrate preliminary results of ToF pulse measurements and report the engineering details, trade-offs, and challenges of this design. We discuss the potential for mass adoption of ToF based pulse oximeters in everyday devices such as smartphones and wearables.

physics.med-ph↗