Visualization of steps and surface reconstructions in Helium Ion Microscopy with atomic precision

Abstract

Helium Ion Microscopy is known for its surface sensitivity and high lateral resolution. Here, we present results of a Helium Ion Microscopy based investigation of a surface confined alloy of Ag on Pt(111). Based on a change of the work function of 25 meV across the atomically flat terraces we can distinguish Pt rich from Pt poor areas and visualize the single atomic layer high steps between the terraces. Furthermore, dechanneling contrast has been utilized to measure the periodicity of the hcp/fcc pattern formed in the 2-3 layers thick Ag/Pt alloy film. A periodicity of 6.65 nm along the ⟨112⟩ surface direction has been measured. In terms of crystallography a hcp domain is obtained through a lateral displacement of a part of the outermost layer by 1/ √ 3 of a nearest neighbour spacing along ⟨112⟩. This periodicity is measured with atomic precision: coincidence between the Ag and the Pt lattices is observed for 23 Ag atoms on 24 Pt atoms. The findings are perfectly in line with results obtained with Low Energy Electron Microscopy and Phase Contrast Atomic Force Microscopy.

Comparative study of image contrast in scanning electron microscope and helium ion microscope

“…This may be attributed to the de‐channelling of the ions in the top amorphous layer, which increases the backscattered yield of the implanted regions compared with the 110 crystalline Si. Note that very thin surface layers were reported to result in strong contrast due to dechannelling in HIM (Hlawacek et al ., ).…”

Alloying, Dealloying, and Reentrant Alloying in (Sub)monolayer Growth of Ag on Pt(111)

“…The LEEM offers a capability of recording spatial maps of relative changes of the surface WF change (see also Ref. [20] for more details) during deposition of thin films. Figure 14 shows a sequence of LEEM images and the corresponding spatial maps of the surface role in determining the work function.…”

“…">IntroductionThe growth of ultra-thin Ag films on Pt(111) has received much attention in the past few decades [1,2,3,4,5,6,7], caused mainly by complex surface alloying [8,9,10] resulting in the formation of stress stabilized surface nanostructures [11,12,13,14]. The interest was further raised by the possibility to generate and tune novel chemical and physical properties by varying stoichiometry at the surface and careful control of the Ag growth conditions [14,15,16], and the formation of periodic dislocation networks [17,18,19,20] used as nano-templates [21] for the growth of organic films [22,23,24,25].Low-energy electron diffraction (LEED) [2], thermal energy atom scattering (TEAS) [7] and scanning tunnelling microscopy (STM) [3] experiments revealed that at room temperature the first Ag layers grew through the formation of large pseudomorhic and thus strained Ag islands. This strain is caused by an about 4% lattice mismatch between the lattice constants of bulk Ag and Pt.…”

“…Further deposition of Ag induced the formation of a triangular dislocation network which allows relief of the surface strain [17]. The third layer was reported to be a pure silver layer [18] with a propagation of a height undulation originating from the dislocation network at the buried interface [18,19,20].Much important microscopic work on the growth of ultra-thin silver films on Pt (111) has been done since this system has become a prototype of surface confined alloying.However, in-situ spatio-temporal information during deposition is still completely Alloying, de-alloying and reentrant alloying in (sub-)monolayer growth of Ag on Pt (111) 4 lacking. The present study fills this remarkable gap.…”

Defect formation in multiwalled carbon nanotubes under low-energy He and Ne ion irradiation

“…In this context, it is to be noted that helium ion microscopy (HIM) has received increasing attention recently as a high-resolution imaging tool [ 32 – 33 ]. A He + or Ne + ion beam can be used to irradiated the samples with an impact energy in the range of 5 to 30 keV, either for imaging or nano-machining [ 34 – 35 ], or for doing both simultaneously [ 33 ].…”