Composition and thickness of surface layer on molybdenum tips for scanning tunnelling microscopy (STM) studied by SEM/AES/(AR)XPS

Abstract

A combination of SEM, AES and angle-resolved XPS (ARXPS) has been applied to analyse the distribution of chemical compounds in the surface region of electrochemically etched molybdenum tips and to determine the contamination layer thickness. Carbon monoxide, graphite, molybdenum carbide and molybdenum oxide were found to be the main surface contaminants on molybdenum tips. Auger line profiling revealed a significant enrichment of carbon and oxygen upon the tip. The thickness of the oxygebcarbon contamination layer on the tip was estimated to be 135 & 1.0 nm as measured by AES. The thickness of the contamination layer on a molybdenum sheet was found to be 8.0 f 15 and 6.8 am using AES and ARXPS respectively. Quantitative analysis of the surface concentrations of carbon, oxygen and molybdenum has been performed.

Generation and Characteristics of IV-VI transition Metal Nitride and Carbide Nanoparticles using a Reactive Mesoporous Carbon Nitride

“…XPS spectra of the obtained samples for core levels of N 1 s, C 1 s, O 1 s, and metal (Ti 2p, V 2p, Nb 3d, Ta 4 f, Cr 2p, Mo 3d, W 4 f) are shown in Figure . First, it was noticeable that strong signals of the O 1 s peaks at 530–531 eV were obtained, which are assigned to metal oxides in all the samples . Due to the passivation step at the end of the synthetic procedure in addition to the exposure of the sample to ambient air, an oxide layer was formed on the surface even though the samples were completely cooled to room temperature .…”

“…There is a small peak in the Ti 2p spectrum at 456.4 eV that is difficult to identify due to the overlap of the signals emitted from the Ti 2p 3/2 of TiO 2 and TiN. As a result, this binding energy was attributed to the intermediate phase of Ti−O−N, associated with the peak at 395.8 eV in the N 1 s spectrum . The XPS spectrum of the V 2p core level shows the presence of two dominant peaks at binding energies of 517.0 eV for V 2p 3/2 and 524.6 eV for V 2p 1/2 , which were assigned to V 5+ in V 2 O 5.…”

Molybdenum carbide–carbon nanocomposites synthesized from a reactive template for electrochemical hydrogen evolution

“…40 For the samples synthesized at 1123, 1223, and 1323 K, the Mo 3d 5/2 signal observed at 228.1 eV increased in intensity with increasing reaction temperature. 41 This peak became prominent and shied to 228.0 eV at 1573 K, which conrms the formation of Mo 2 C. 39,41 In addition to this peak, a Mo 3d 3/2 signal was observed at 231.3 eV in the spectrum of the sample prepared at 1573 K; this signal was close to 231.1 eV characteristic value of Mo 2 C. 42 The O 1s spectrum (Fig. 5B) for samples prepared at temperatures from 1023 to 1323 K contained a characteristic signal at 530.4 that was assigned to O 2À in MoO 3 ; the intensity of this signal decreased with increasing reaction temperature.…”

“…5B) for samples prepared at temperatures from 1023 to 1323 K contained a characteristic signal at 530.4 that was assigned to O 2À in MoO 3 ; the intensity of this signal decreased with increasing reaction temperature. 39 The C 1s XPS spectra (Fig. 5C) contained a characteristic peak attributed to graphite at 284.4 eV.…”

“…These peaks were observed at the following binding energies: 235.6 and 232.5 eV for Mo 3d 3/2 and Mo 3d 5/2 , which were assigned to Mo 6+ (MoO 3 ). 38,39 An additional peak at 228.7 eV for Mo 3d 5/2 was observed for the sample synthesized at 1023 K and was assigned to Mo 4+ (MoO 2 ). 40 For the samples synthesized at 1123, 1223, and 1323 K, the Mo 3d 5/2 signal observed at 228.1 eV increased in intensity with increasing reaction temperature.…”