Gregory Owen

Nano-crystalline SnO2 gas sensor response to O2 and CH4 at elevated temperature investigated by XPS

Abstract The electronic changes occurring at the surface of a nano-crystalline SnO 2 sensor upon exposure to O 2 and CH 4 at elevated temperature have been investigated by X-ray photoelectron spectroscopy (XPS). Gas exposures and subsequent XPS scanning were conducted at 120 and 250 °C to simulate the working conditions of the sensor. Exposure to O 2 at 120 °C resulted in a 0.2 eV upward band bending while subsequent exposure to CH 4 resulted in a 0.1 eV downward band bending, as expected from oxidising and reducing gases, respectively. Similar changes in surface band bending were observed at 250 °C, although quantitative analysis suggests that oxygen absorption might be enhanced. The results clearly indicate the electronic nature of the gas sensing mechanism when exposed to O 2 and CH 4 and the very high sensitivity of the sensor.

Charge writing on the nanoscale: From nanopatterning to molecular docking

The drive towards nanotechnology has highlighted the need to engineer the properties of surfaces in unprecedented detail. Here, we report the modification of nanocrystalline SnO2 surfaces using the tip of a scanning tunneling microscope (STM) to inject electrons into individual 8 nm SnO2 nanocrystals. The surface displays a characteristic consistent with charge retention within the grains producing dramatic enhancements in the effective height of the nanoparticles, as observed by STM imaging. This allows the production of modified surfaces where patterns can be written onto a surface with a spatial resolution limited by the size of tip and the nanoparticles, 8 nm in this case. It is also possible to selectively erase the features on the surface using the STM tip under reverse bias. The pattern remains for up to three weeks and therefore opens the door to applications such as patterned nanoscale catalysis, molecular docking, and even ultrahigh density analog data storage.

Evolution of the Grain Boundary Network as a Consequence of Deformation and Annealing

Iterative processing, involving sequential deformation and annealing, has been carried out on copper specimens with the aim of grain boundary engineering (GBE) them. The data have provided some interesting insights into the mechanisms of GBE. The results have demonstrated that development of a high proportion of Σ3s is beneficial to properties, as shown by improved strain-to-failure for the same strength. The proportion of Σ3s saturates at approximately 60% length fraction. Analysis of the data indicates that iterative processing is not always necessary for the development of beneficial properties, and it is further suggested that the condition of the starting specimen has a large influence on the subsequent microstructural development. The present, new data are also compared with previous research on copper where all five parameters of the grain boundary network population have been measured.

A Comparison of Grain Boundary Engineering Mechanisms in Copper and Brass

Grain boundary engineering (GBE) has been carried out on copper and brass. A comparison of the resulting microstructure and grain boundary characteristics from the two specimens revealed that the brass specimen had approximately the same number fraction of Σ3s as the copper specimen (38%), but a lower number fraction of Σ9s and Σ27s and a markedly different microstructure. In the brass specimen twins were not incorporated into the grain boundary network, whereas in the copper specimen Σ3s replaced portions of the grain boundary network. These two mechanisms are discussed in detail.