Single crystal electrodes

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Single crystal electrodes are conductive materials characterized by a uniform crystal structure throughout their volume, allowing for consistent electrochemical properties. They are used in various applications, including electrochemistry and materials science, to study fundamental processes at the atomic level and to enhance the performance of electrochemical devices.

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On the vibrational behaviour of cyanide adsorbed at Pt(111) and Pt(100) surfaces in alkaline solutions

by FRANCISCO JAVIER GALINDEZ MONTILLA

2024, Surface Science

This communication deals with the vibrational behaviour of cyanide adlavers formed on Pt(lll) and Pt(100) surfaces in the electrochemical environment. In situ FTIR spectroscopy can be employed to follow the potential dependence of the C-N... more

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The adsorption of methylamine on Pt single crystal surfaces

by Cesar Quijada

2023, Journal of Electroanalytical Chemistry

The irreversible adsorption of methylamine at platinum single-crystal electrodes has been studied by a combination of electrochemical and in situ spectroscopic techniques. From purely electrochemical data, it has been stated that the... more

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Restructuring of an Ir(210) electrode surface by potential cycling

by khaled soliman

2022, Beilstein Journal of Nanotechnology

This study addresses the electrochemical surface faceting and restructuring of Ir(210) single crystal electrodes. Cyclic voltammetry measurements and in situ scanning tunnelling microscopy are used to probe structural changes and... more

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In-situ STM characterisation of the surface morphology of platinum single crystal electrodes as a function of their preparation

by Angel Cuesta Ciscar

2021, Journal of Electroanalytical Chemistry

A systematic study of the surface morphology of Pt(111) and Pt(100) electrodes as prepared by flame-annealing and cooling in different atmospheres (air, N 2 , H 2 +N 2 and CO +N 2) is presented. The electrodes were characterised by cyclic... more

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In-situ STM characterisation of the surface morphology of platinum single crystal electrodes as a function of their preparation

by Mike Kleinert

2016, Journal of Electroanalytical Chemistry

A systematic study of the surface morphology of Pt(111) and Pt(100) electrodes as prepared by flame-annealing and cooling in different atmospheres (air, N 2 , H 2 +N 2 and CO +N 2 ) is presented. The electrodes were characterised by... more

Fig. 1. (A) Cyclic voltammogram of a Pt(111) electrode, prepared by flame-annealing and cooling in air. 0.1 M H,SO,; scan rate: 50 mV s~!. (B) Corresponding STM image (500 x 500 nm?) obtained at 0.35 V with a tungsten tip. 4, = 10 nA; U,;=0.35 V (tip negative). Regarding the results for cooling in N,, we noted that, if the N,-stream during cooling was not strong enough, STM images partially revealed the morphology observed when cooling in air. Accordingly, the intensity of the current peaks associated with hydrogen adsorp- tion on defect sites and the sharpness of the ‘butterfly’ in the cyclic voltammograms changed slightly. We at- tribute this observation to the presence of traces of oxygen in the cooling atmosphere. Obviously, such An interesting effect was observed when the Pt(111) electrode was cooled in an atmosphere with a high H, concentration. In these experiments, a strong H, stream in a rather dangerous ex had reached room tempera the STM images (Fig. 3) s quality) to an increased sur periment!) until the sam with straight triangular step edges. We attribute t feature (which, in turn, is indicative of a high surface face mobility induced by the mixed with some N,) was blown onto the hot crystal ple ure. Under such conditions, how atomically flat terraces his high H, concentration used. We believe that a simi ar effect would be seen when cooling the sample in an atmosphere of high CO concentration. but we refrained

Fig. 2. (A) Cyclic voltammogram of a Pt(111) electrode, prepared by flame-annealing and cooling in a CO + N, mixture. 0.1 M H,SO,; scan rate: 50 mV s~!. (B) Corresponding STM image (500 x 500 nm?) obtained at 0.35 V with a tungsten tip. ,=10 nA; U,;=0.35 V (tip negative).

Fig. 3. STM image (1000 x 1000 nm?) at 0.35 V in 0.1 M H,SO, of a Pt(111) electrode, prepared by flame-annealing and cooling under a strong H, stream. W-tip; J; = 10 nA; U;=0.35 V (tip negative).

Fig. 4. (A) Cyclic voltammogram of a Pt(100) electrode, prepared by flame-annealing and cooling in air. 0.1 M H,SO,; scan rate: 50 mV s~!. (B and C) Corresponding STM images (150 x 150 and 200 x 200 nm?) obtained at — 0.15 V with a tungsten tip. J-=10 nA; U;=0.10 V (tip positive). Cooling in CO should also result in a Pt(100)—(1 x 1) surface, as suggested by the well-known fact that CO adsorption lifts the hex-reconstruction under UHV con- ditions [28]. However, no islands were seen in this case on the surface (Fig. 7B). In order to check that CO An interesting aspect of Figs. 5A and 7A is that the two voltammograms are very similar, despite significant differences in surface morphologies as revealed by

Fig. 5. (A) Cyclic voltammogram of a Pt(100) electrode, prepared by flame-annealing and cooling in a H, + N, mixture. 0.1 M H,SO,; scan rate: 50 mV s~!. (B) Corresponding STM image (225 x 225 nm?) obtained at 0.55 V with a Pt/Ir tip. 4; =2 nA; U;=0.10 V (tip negative).

Fig. 6. STM image (730 x 730 nm?), at — 0.15 V in 0.1 M H,SO, of a Pt(100) electrode, prepared by flame-annealing and cooling under a strong H, stream. W-tip; = 10 nA; U;=0.10 V (tip positive). In order to obtain further information about the structure of the surface (reconstructed or unrecon- structed?), the following experiment was carried out: the electrode was flame-annealed, cooled down in N, and immersed into 0.1 M H,SO, under potential con- trol, where a cyclic voltammogram was recorded (see

Fig. 7. (A) Cyclic voltammogram of a Pt(100) electrode, prepared by flame-annealing and cooling in a CO + N, mixture. 0.1 M H,SO,; scan rate: 50 mV s~!. (B) Corresponding STM image (800 x 800 nm?) obtained at — 0.15 V with a tungsten tip. 7; =10 nA; U;=0.10 V (tip positive).

Fig. 8. (A) Cyclic voltammogram of a Pt(100) electrode, prepared by flame-annealing and cooling in N,. 0.1 M H,SO,; scan rate: 50 mV s~!. (B) Corresponding STM image (314 x 314 nm?) obtained at 0.45 V with a tungsten tip. 7-=10 nA; U;=0.5 V (tip negative).

Fig. 9. (A) Cyclic voltammogram for a freshly prepared, initially CO-covered Pt(110) electrode in 0.1 M H,SO, showing the anodic stripping of CO (dashed line) and the subsequent cycle (solid line). (B) Steady state voltammogram of a Pt(110) electrode prepared by flame-annealing and cooling in N,. Scan rate: 20 mV s~!. Although we are currently not in a position to present STM data of flame-annealed Pt(110) electrodes, we include for the sake of completeness our results from a voltammetric study of Pt(110). Since the use of CO as the cooling atmosphere after flame-annealing has certain advantages when handling rather big Pt(111) and Pt(100) single crystals (see above), it was also applied to Pt(110). Formation of the unreconstructed surface was expected, because CO ad- sor ption from the gas phase is known to lift the recon- struction [31]. In contrast to CO adsorbed on Pt(111) and air, on Pt(100), a CO layer on Pt(110) is oxidised by as was shown by a partial blocking of the voltam- me ric peaks in the hydrogen adsorption region. For this reason, the Pt(110) crystal was cooled in a CO atmosphere inside the electrochemical cell for 10 min directly after flame-annealing and subsequently im- mersed into the electrolyte at —0.2 V. Pure nitrogen was then bubbled for 30 min in order to free the

Fig. 10. Cyclic current—potential curves for differently prepared Pt(110) electrodes in 0.1 M H,SO,+ 5 mM CuSO, showing the underpotentia deposition of Cu. After flame-annealing the crystal was cooled in: (A) CO+N;; (B) pure N3. Scan rate: 1 mV s~!.

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Probing the electronic transport on the reconstructed Au/Ge(001) surface

by Christian Bobisch and

2015, Beilstein Journal of Nanotechnology

By using scanning tunnelling potentiometry we characterized the lateral variation of the electrochemical potential µ ec on the goldinduced Ge(001)-c(8 × 2)-Au surface reconstruction while a lateral current flows through the sample. On the... more

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Probing the electronic transport on the reconstructed Au/Ge(001) surface

by P. Indyka

2015, Beilstein Journal of Nanotechnology

Figure 1: a) Scheme of the potentiometry setup using a multiprobe STM. Two STM tips (1 and 2) in contact with the sample surface are used to drive a lateral current. The third STM tip (3) simultaneously images the topography and the electrochemical potential of the surface. b) HRSEM image of the 6 ML Au/Ge(001) sample surface exhibiting the Au clusters and some terrace edges. Most clusters are of asymmetric octagonal shape as depicted by the colour contour in c). d) HRSTM image of an area between the Au clusters showing two differently oriented domains of the Au induced wires (/7 = 200 pA, Vsample = -2V). We deposited 6 monolayers (MLs) of Au on the reconstructed Ge(001) from a resistively heated crucible. The deposition rate of 0.2 ML/min is monitored by using a quartz crystal microbal- ance and the substrate temperature during the deposition of Au is kept at 150 K. After the deposition, no ordered structure is observed until the sample is annealed. After annealing to 770 K for about 10 min the Au-induced wire-like Ge(001)-c(8 x 2)-Au structure emerges [1,3]. The excess amount of Au aggregates into Au clusters. We intentionally deposited this excess amount of Au since the Au clusters may serve as metallic leads to contact the surface structure by STM tips [12,13]. In Figure 1b an overview of the sample surface is provided by a high resolu- tion SEM image exhibiting several Au clusters together with the terrace edges. The Au clusters are of about 150 nm size and they are of an asymmetric octagonal shape at their base (see Figure 1b and Figure Ic). A high resolution STM image of the area between the Au clusters exhibits Au reconstructed terraces separated by single layer steps, exemplarily shown in Figure 1d. At most step edges the wire structure is rotated by 90° resulting from the reconstructed Ge(001) substrate. The domains exhibit some structural defects within the atomic wires. For the struc- Scanning tunnelling microscopy (STM) and various STM-based methods are excellent tools to study the topographic structure. the electronic structure, and electron transport phenomena of conducting surfaces at the limit of lateral resolution. By performing scanning tunnelling potentiometry (STP) [11] we tried to study the lateral variation of the electrochemical poten- tial lee (called potential in the following) at the boundary between two rotated Au wire-like domains while a lateral current was flowing through the Au/Ge(001) sample (see also the scheme in Figure la below). By using a multiprobe STM setup (Omicron Nanoprobe) individually controlled STM tips are used to establish well defined electric contacts to the recon- structed surface. We applied a voltage between two contacts leading to a current flow across the surface. Thus, if the main contribution of the total current is flowing through the Au reconstructed 1D domains, the impact of the predicted conductance anisotropy should be observed as a variation of the electrochemical potential in the vicinity of the domain bound- aries.

Figure 2: a) STM image of the Au/Ge(001) surface showing both different types of Au wire-like domains and several Au clusters. b) Corresponding image of the potential, exhibiting a constant gradient on the terraces (Au wire-like domains). The Au clusters appear with constant potential and rather sharp transitions at their borders. c) Line profiles of the topography (red) and potential (green) as marked in a) and b). As a guide to the eye a linear function was fitted to the overall gradient of the potential. d) Potential near a Au cluster. Sharp transitions of the potential at the perimeter of the cluster are easily recognized. e) and f) show the topography and the corresponding potential for a small area near a step edge, i.e., domain boundary. The directions of the atomic wires are marked by white lines in a) and e) (Vpat = 9 V, trans = 3 MA).

Figure 3: Resistivity, as evaluated from the gradient of the potential in the STP images, as a function of the temperature of the sample. Figure 2b. On the reconstructed surface the potential exhibits strong fluctuations (+2.5 mV) but no direct correlation to steps in the topography. The potential on the Au clusters appears rather flat and smooth, only limited by the resolution of our STP setup (+5 nV) and is constant within the experimental error. At the edge of the Au clusters a discontinuity of the potential occurs. The resistivity, i.e., the corresponding gradient of the potential on the terraces scales about linearly as a function of the absolute sample temperature (Figure 3) indicating that the measured conductivity for the present Au/Ge(001) system is metallic. Although it may be assumed that the transverse current may heat the Ge sample, we do not see any indications for this in our data. As sample heating would result in a temperature difference between the tunnelling tip and the sample, a thermo- voltage in the tunnelling gap would occur. This voltage would also be measured by our STP setup and would be independent of the polarity of the transverse current. Since we do not observe this effect, heating of the sample seems to be negli- gible.

Figure 4: a) Exemplary TEM image of a lamella of Au grown on Ge(001) after the deposition of 6 ML of Au and annealing at 770 K. The apparent sample surface is exemplarily marked by black arrows on the right hand side of the image. b) EDX line scan analysis through the Au cluster. The Au cluster is reaching far into the Ge substrate. The non-zero Ge signal from the Au cluster is due to secondary fluorescence (excitations of “bulk” Ge caused by the X-ray emission from Au), which is a well-known effect (artefact) in the EDX spectroscopy. c) HAADF HRSTEM image through the Au/Ge lamella taken along the line on the right hand side in a). The results of the line scan EDX analysis are also shown. The Au concentration is found to reach its maximum of approx. 10% underneath the apparent sample surface (see circle). On the lower side of the image the atomic structure of Ge(001) bulk is visible.

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