New Developments in Cathodoluminescence Spectroscopy for the Study of Luminescent Materials.

Herein, we describe three advanced techniques for cathodoluminescence (CL) spectroscopy that have recently been developed in our laboratories. The first is a new method to accurately determine the CL-efficiency of thin layers of phosphor powders. When a wide band phosphor with a band gap (Eg > 5 eV) is bombarded with electrons, charging of the phosphor particles will occur, which eventually leads to erroneous results in the determination of the luminous efficacy. To overcome this problem of charging, a comparison method has been developed, which enables accurate measurement of the current density of the electron beam. The study of CL from phosphor specimens in a scanning electron microscope (SEM) is the second subject to be treated. A detailed description of a measuring method to determine the overall decay time of single phosphor crystals in a SEM without beam blanking is presented. The third technique is based on the unique combination of microscopy and spectrometry in the transmission electron microscope (TEM) of Brunel University London (UK). This combination enables the recording of CL-spectra of nanometre-sized specimens and determining spatial variations in CL emission across individual particles by superimposing the scanning TEM and CL-images.

Ultrahigh-current field emission from sandwich-grown well-aligned uniform multi-walled carbon nanotube arrays with high adherence strength.

We describe a new method to grow multi-walled carbon nanotube (MWCNT) arrays, which enable very high and stable macroscopic emission current density of 3.55 A cm(-2) along with a scalable total emission current of more than 710 mA. A sandwich-growth technology was employed to synthesize vertically well-aligned MWCNT arrays in large areas and patterned uniformly by using microwave plasma chemical vapour deposition. A thick nickel layer was inserted between the silicon substrate and catalyst layer to achieve good adhesion between the MWCNTs and the substrate. Scanning electron microscope and transmission electron microscope investigations showed that well-structured, vertically aligned and uniform MWCNTs with perfect crystal lattices had been grown on lithographically predetermined sites. The root ends of MWCNTs adhered firmly to the nickel layer, establishing high electrical and thermal conductance of the MWCNTs to the substrate. This feature largely explains the large and stable emission current density of the MWCNT arrays.