Robert Bryl

Observation of vertex-rounding transition for a crystal in equilibrium: Oxygen-covered tungsten

Equilibrium crystal shape of oxygen-covered tungsten is followed as a function of temperature using field ion microscopy. In the vicinity of the (111) region, at the temperature

The interaction of water with surfaces of Pt and Ir field emitters

970\pm70

Diffusion of H2O on surfaces of clean and Au covered tungsten field emitters

K, the system undergoes a phase transition from a polyhedral form (sharp edges and sharp vertex) to a rounded form (sharp edges, rounded vertex).

Interaction of water with clean and gold-precovered tungsten field emitters: adsorption and desorption

Abstract Some results of a study of the adsorption and thermal desorption of H 2 O on Pt and Ir surfaces, using field emission methods, are presented. At a substrate temperature of 78 K H 2 O admolecules reduced the total field emission current both from the Pt and Ir tips in a wide range of coverages whereas the local emission current, e.g. from the (001) and (113) faces of Ir, was increased. Water was desorbed from thermally cleaned Pt in the temperature range 140–160 K with an average desorption energy of E des = 54kJ/mol. The possible behavior of H 2 O molecules on the crystallographically diversified surfaces of Pt and Ir under the conditions of field emission is discussed.

Atomically Sharp Field Emitters and Oxygen Caused Thermal Faceting of W[111] Tip

Abstract The results of field emission microscopy measurements of the diffusion of water deposited on a thermally clean and a gold covered tungsten emitter are presented. The diffusion of water from a multilayer to a submonolayer H 2 O was observed on clean W in the temperature range 126–147 K and on Au W ( Θ ≥ 2) in the range 113–123 K, with activation energies for diffusion of 27 ± 2 kJ/mol in both cases. It is suggested that water in the low coverage range can diffuse on clean W and Au surfaces at temperatures as low as 78 K.

The Interaction of Platinum with W[111] Tip: Diffusion, Desorption and Changes of Tip Morphology

Abstract The results of field emission microscopy investigation of the adsorption and thermal desorption of water deposited on a thermally clean and gold-covered tungsten emitter are presented. The desorption experiments indicate that H2O molecules dissociate in contact with surfaces of the clean tungsten emitter, but no traces of dissociation of water adsorbed on Au W were found, if only the gold coverage was sufficiently high (Θ ≥ 2). H2O is probably adsorbed in two adsorption states on Au W . Water desorption from the first state was carried out in the temperature range 145–155 K with an activation energy of 51.5 ± 1.5 kJ/mol, whereas the desorption from the second state was observed at 220–240 K. Generally, the adsorption of water causes the reduction of the emission current at a constant high voltage, both for W and Au W , but for the second adsorption state in the system H2O/Au/W a slight increase of the emission current was noticed. The behaviour of water adlayer in the presence of the high electric field is discussed.

A comparison of adsorbate-induced faceting on flat and curved crystal surfaces

This paper demonstrates and summarises both temperature and oxygen exposure limitations of faceting in the system O/W[111], including facets evolution with-oxygen exposure leading to globally or steplike faceted tip, for intermediate O2 exposures 0.3 L-3 L (31 L at elevated annealing temperature 1700 K). The results presented here were obtained using FIM technique. Results show that after annealing at temperatures lower than 800 K, higher than 1850 K or for Oa exposures lower than 0.5 L the oxygen caused faceting of W[111] tip was not observed. For exposures 0.5-1.9 L and annealing temperatures 800-1600 K well developed {112} facets with sharp edges formed, and the globally faceted tip topography formed mainly after exposing the emitter to 1-1.9 L of oxygen and annealing it at temperatures 1400-1600 K. For exposures higher than 2.0 L edges of the {112} facets were broadening and disappearing, what has been attributed to the formation of 3-dimensional tungsten oxides. The oxides could be easily removed by annealing the tip at 1700 K, what lead to the formation of sharp facet edges. On the basis of these results a method of atomically sharp field emitter preparation is proposed

Oxygen-Induced Thermal Faceting of Pd Nanosized Crystals

Summary form only given. Adsorption, diffusion and desorption of platinum on W[111] oriented tip has been studied using field electron microscopy technique. The diffusion of platinum in submonolayer range on clean W tip was studied at temperatures 630-750 K. Mean activation energy for diffusion was established for Ediff=112plusmn7 kJ/mol. The layer equilibrated in diffusion process was stable at temperatures up to 1150-1200 K where some changes of tip morphology, likely due to alloying of Pt with W, started to be visible. Submonolayer of platinum started to desorb from the tip at temperatures as high as 1850-1900 K. The measurements of activation energy for desorption of Pt from W were carried out at temperatures 2050-2150 K and yield the value of Edes=425plusmn40 kJ/mol