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Abstract: A cathodic needle growth which is possibly associated with the temperature-field (T-F) electron emission is described. Experimental data disclosed that densely populated needle crystals exhibiting a dendritic configuration growth at the tip area of a pointed cathode when it is operated in an Mo(CO)6 or Cr(CO)6 atmosphere at a field strength just insufficient to draw field electrons. The needle growth occurs always at elevated temperatures of ∼600–∼700 K, indicating that it is triggered by T-F electrons emitted from the cathode tip. Needle crystals produced are not single crystals but composed of linearly packed micro-crystals, and those crystals obtainable from Mo(CO)6 are a face-centered cubic phase of Mo2C. Needles arising from Cr(CO)6 have not been identified, but they are believed to be an unknown phase of chromium carbide.

Conical Si projections generated on Si wafers bombarded with obliquely incident Ar+ ions were studied by high-resolution transmission electron microscopy. The cones were composed of an [111]-oriented bulk phase covered with a disordered thin layer, but the bulk phase was not perfectly ordered, containing an amorphous domain underneath the outermost area. Such a multi-phase structure is inexplicable in terms of ion erosion, suggesting interplay of the redeposition of sputtered Si atoms on the bombarded area with the ion-erosion process so as to promote cone evolution. The cones were also characterized by the development of web-like platelets at their acute angles, an indication of a crystal growth process involved in the surface phenomenon observed.

It is shown that metallic needle crystals grow on electron emitting areas of field emission cathodes working in Mo(CO)6 vapor. The growth is driven by ions impinging from a field emission arc plasma, and the products are classified into two categories depending on the thermal energy supplied externally to the substrate: 1) Mo particles are agglomerated in dendritic shapes at ~ 300-1300 K, and 2) whisker-like crystals with an unknown structure are obtained at ~ 1300-1500 K. The high-temperature needles are capped with Taylor cones during the growth, and it is shown that they are a metastable phase of Mo.

Ar+ sputtering of an Cu(111) surface while simultaneously supplying Mo atoms is known to induce an oriented growth of Mo thin crystals, or “seed-layers”, on evolving conical Cu protrusions. The seed-layers thus formed are shown to be dual-oriented, or bicrystalline, consisting of columnar crystallites grown homo-epitaxially. The orientation relationship between the two types of crystallites was (100)I ? (111)II with [001]I ? [110]II, and this bicrystallinity probably resulted from a non-uniform charge-up of the layers' growth front. As concluded from high-resolution electron microscopy, the Mo(100) stacking is elastically converted into the Mo(111) stacking and vice versa, under the influence of tensile stress. The homo-epitaxy that the seed-layers exhibited is believed to reflect the mutual convertibility of the Mo(100) and (111) stackings.

The carburization of tungsten single crystals through chemical reaction with gaseous acetone at pressure 10--5-10--6 torr and at temperature 1500-1800 K has been studied by means of a field emission and a transmission electron microscope. A single-crystal field emitter tip of tungsten is wholly converted into a W2C single crystal after a full carburization : a single-crystal overlayer of W2C initially forms at the tip surface, increasing in thickness until the entire tip is carburized into a W2C single crystal. The carburization takes place in a definite crystallographic orientation and is accompanied by a slight volume expansion and a remarkable change in the tip geometry.

The dependence of the field ionization behaviour of olefines on field-induced surface reactions is demonstrated using 1-Hexene as an example. Different emitter- and field strength dependent reaction mechanisms leading to the production of (M+1)+and (M-1)+ions may be distinguished. The characteristics of define spectra taken using activated emitters are determined largely by surface induced reactions which appear at higher field strengths. These have as their starting point an ionic field adsorption of the olefine. In particular the field enhancement of the organic microneedles is strongly influenced by field adsorbed ions so that field dissociation products are also measured with increased intensity.