Scanning Auger microscopy techniques are used to study the effects of hydrofluoric acid on the surface chemical composition of STM W tips prepared by electrochemical etching in base solution. Auger point spectra performed on a series of ad hoc prepared samples allow us to evaluate how the separate chemical and electrochemical processes involved in the making and cleaning of a tip contribute to its content in surface tungsten oxides. We find that HF attack in large part removes the oxides left at the surface of the tip after the electrochemical etching. HF-treated samples are much more oxidized at the apex region than at the trunk region, whereas the reverse is found in untreated tips. These findings are interpreted as arising from the local efficiency of the electrochemical etching in dissolving the oxides as well as from the different surface-to-volume ratios associated with the two regions of the tip. Chemical speciation is attempted in high-energy resolution W N4,5N67N7 and W M5N67N67 spectra. While the former proves to be of little diagnostic consequence, the latter clearly shows that the apex is heavily covered with W6+ oxides as well as lower-valence tungsten oxides, and these oxides are nearly completely removed upon HF attack. Elemental imaging highlights lateral chemical inhomogeneities at the surface of these materials with a spatial resolution of ~0.4 ?m.
Effects of HF attack on the surface and interface microchemistry of W tips for use in the STM microscope: a scanning Auger microscopy (SAM) study
Paparazzo E;Selci S;Righini M;
1999
Abstract
Scanning Auger microscopy techniques are used to study the effects of hydrofluoric acid on the surface chemical composition of STM W tips prepared by electrochemical etching in base solution. Auger point spectra performed on a series of ad hoc prepared samples allow us to evaluate how the separate chemical and electrochemical processes involved in the making and cleaning of a tip contribute to its content in surface tungsten oxides. We find that HF attack in large part removes the oxides left at the surface of the tip after the electrochemical etching. HF-treated samples are much more oxidized at the apex region than at the trunk region, whereas the reverse is found in untreated tips. These findings are interpreted as arising from the local efficiency of the electrochemical etching in dissolving the oxides as well as from the different surface-to-volume ratios associated with the two regions of the tip. Chemical speciation is attempted in high-energy resolution W N4,5N67N7 and W M5N67N67 spectra. While the former proves to be of little diagnostic consequence, the latter clearly shows that the apex is heavily covered with W6+ oxides as well as lower-valence tungsten oxides, and these oxides are nearly completely removed upon HF attack. Elemental imaging highlights lateral chemical inhomogeneities at the surface of these materials with a spatial resolution of ~0.4 ?m.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
