Nanometre scale electron beam processing andin situatomic observation of vacuum-deposited MgO films in high-resolution transmission electron microscopy

Abstract

Nanometre scale processing was performed on vacuum-deposited single crystalline magnesium oxide films by using a nanometre-sized electron beam in highresolution transmission electron microscopy (HRTEM). Two kinds of processing, drilling and edge-flattening, were demonstrated. The resolution of the present processing was demonstrated by the minimum size of the hole being about 4 nm and the minimum distance between holes being 14nm. The shape modulation during the processing was observed for the first time in situ dynamically,at atomic resolution. The dynamic observations in HRTEM showed that the processing is caused by desorption of constituent atoms from the solid state surface of the magnesium oxide films. It was found that the size of the processing area could be controlled at the atomic scale by adjusting the irradiation time during the in situ observation of the processing. 1. INTRODUCTIONVarious kinds of nanometre scale processing are required to be applied to advanced materials. Materials which need to be processed and artificially modified at the atomic scale, are exemplified by the semiconductor (Esaki and Tsu 1970), metal (Grunberg, Shreiber, Pang, Brodsky and Sowers 1986) and ceramic (Shigematsu, Ushigome, Bando and Takada 1980) superlattices, and nanometre-grained polycrystalline materials (Birringer 1989). Recently, electron beam processing at the nanometre scale (by drilling, line-writing and structure-modification due to the direct irradiation effect and the electron stimulated chemical reaction) has been attempted using scanning transmission electron microscopy (STEM) (Mochel, Humphreys, Eades, Mochel and Petford 1983, Muray, Scheinfein, Isaacson and Adesida 1985, Macaulay and Berger 1987, Turner, Bullough, Devenish, Maher and Humphreys 1990, Pan and Broers 1992, Chen, Boothroyd and Humphreys 1993. These studies have focused on the improvement of the processing resolution and the evaluation of the suitability of some irradiation-sensitive materials for electron beam processing. The minimum size of the processed area was 1 nm for MgO smoke particles (Turner et al. 1990), and 2 nm for p-alumina (Mochel et al. 1983) and SiO, (Chen et al. 1993); the minimum line width was 5 nm and the minimum distance between the lines was 17 nm for AIF, (Macaulay et al. 1987, Macaulay, Allen, Brown andBerger 1989) during direct electron beam processing. Areas 2 nm in diameter separated by 4 nm in AlF, (Muray et al. 1985) and lines of 10 nm width and 15 nm pitch in SiO, (Pan and Broers 1992) were processed using a chemical reaction in addition to the direct electron 0141-8610/95 $10~00 0 1995 Taylor

Self-Organized Nanostructures Generated on Metal Surfaces under Electron Irradiation

“…For the generation of aligned nanogrooves, we did not use a convergent nanosized electron beam as has been done for the generation of nanoholes [10] but a homogeneous electron beam of about 200-800 nm in diameter. In this case, the phenomena occurring on the electron exit surface may be as follows (Figure 18).…”

“…Electron irradiation, which can induce back sputtering on the surface of thin foil specimens, is also one of the techniques used for nanometer scale etching, lithography and hole formation, and intense convergent electron beams have been utilized, so far. Deep nanoholes have been formed in MgO using a convergent nanosized electron beam, the smallest widths so far achieved being about 1 nm [9,10]. Parallel electron beams, on the other hand, of 500-1000 nm diameter have been shown to produce pits on the exit surface of Au(111) foils by sputtering over the electron energy range of 0.4-1.1 MeV [11].…”