Symmetry Breakdown of 4,4″-Diamino-p-Terphenyl on a Cu(111) Surface by Lattice Mismatch

Result of the Month

Different adsorption geometries of DATP on Cu(111). a Constant Current AFM frequency shift image showing two terraces (upper terrace in right and lower in left part) separated by monoatomic step. The tunneling current was used for tip-sample feedback. Imaging parameters: gap voltage = 10 mV, tunneling set point = 100 pA. Type I and II adsorption structures are indicated by red and orange arrows. Red arrows are pointing towards the fuzzy side of the type I structures. Symmetry reduction from six-fold to three-fold is observed, i.e., orientations that correspond to the three dashed white arrows are not observed on neither terrace. b Chemical structure of DATP. c, d Constant height AFM zoom-in images of type I and type II adsorption structures. e Transition from type II to type I during constant height upward scan. Parameters: the tip-heights Δz are c + 20 pm, d −85 pm, e −85 pm, relative to a STM set point of 100 mV, 10 pA on bare Cu surfaces. The +/− signs represent increase/decrease of the tip-sample distance. Scale bars: a 10 nm, c–e 0.5 nm

Dynamics and energy barrier of the observed hopping mechanism. a–d AFM images of type I DATP molecule taken at 5.2 K, 7.0 K, 9.3 K, and 14.0 K. The tip-heights Δz are a −90 pm, b −85 pm, c −100 pm, d −90 pm, relative to a STM set point of 100 mV, 10 pA on bare Cu surfaces.

Dynamics and energy barrier of the observed hopping mechanism. e–h Current vs time traces recorded at the fuzzy end at 5.2 K, 7.0 K, 9.3 K, and 14.0 K. Parameters: Vbias = 60 mV, tip height Δz = −10 pm with respect to the STM tunneling set point of 100 mV, 10 pA on bare Cu(111) surface.

Dynamics and energy barrier of the observed hopping mechanism. i Arrhenius type plot of natural logarithm of the jumping rate ln(k) vs 1/T. Displayed are the jumping rates for all jumping events (total jumps, red circles) and the rates for jumps into the upper (blue circles) and into the lower current states (black circles), respectively. An energy barrier (Eα) of 5.15 ± 0.13 meV and a pre-exponential factor (A) of e9.40±0.22 s−1 for the total jumps is determined by fitting the Arrhenius’ equation (ln(k)=(−Eα/kB)(1/T)+ln(A), where kB is the Boltzmann constant) to the right three points (at 5.2 K, 7.0 K, and 9.3 K). Jumps into lower state: Eα = 5.00 ± 0.09 meV, A = e(8.69±0.16) s−1. Jumps into upper state: Eα = 4.98 ± 0.04 meV, A = e(9.46±0.08) s−1. Please note, the data point at 14.0 K has not been taken into account since the observed jumping rate for this temperature exceeds the bandwidth of our tunneling amplifier setup. The vertical error bars in i are derived from the standard deviation of k (see Supplementary Fig. 3). Scale bar: 0.5 nm

Author: Prof. Dr. André Schirmeisen Institute: ''Institute of Applied Physics, Justus-Liebig University, Heinrich-Buff-Ring 16, 35392, Giessen, Germany '' Nature Communications
URL: https://www.nature.com/articles/s41467-018-05719-y
Date: 10/2020 Instruments: LT STM Lab

Site-selective functionalization of only one of two identical chemical groups within one molecule is highly challenging, which hinders the production of complex organic macromolecules. Here we demonstrate that adsorption of 4,4″-diamino-p-terphenyl on a metal surface leads to a dissymmetric binding affinity. With low temperature atomic force microscopy, using CO-tip functionalization, we reveal the asymmetric adsorption geometries of 4,4″-diamino-p-terphenyl on Cu(111), while on Au(111) the symmetry is retained. This symmetry breaking on Cu(111) is caused by a lattice mismatch and interactions with the subsurface atomic layer. The dissymmetry results in a change of the binding affinity of one of the amine groups, leading to a non-stationary behavior under the influence of the scanning tip. Finally, we exploit this dissymmetric binding affinity for on-surface self-assembly with 4,4″-diamino-p-terphenyl for side-preferential attachment of 2-triphenylenecarbaldehyde. Our findings provide a new route towards surface-induced dissymmetric activation of a symmetric compound. 

AFM Measurements 

The measurements were performed with a commercial combined low temperature AFM/STM (Scienta Omicron, Germany). All STM/AFM images were acquired at 5 K (Except for Fig. 2b–d) under ultra-high vacuum (base pressure < 1.0 × 10–10 mbar). For STM imaging, the tip was connected to the ground while the sample was in contact with the bias voltage. For AFM imaging, a small offset gap voltage (a few uV) was used to minimize the tunneling current. The AFM imaging was realized with a force sensor based on the qPlus quartz tuning fork design. Two different force sensors were used—for Fig. 4b, Supplementary Fig. 9a,b: resonance frequency fres ≈ 19.4 kHz, Q-factor ≈ 6300, oscillation amplitude Amp = 94 pm; for all other AFM images: resonance frequency fres ≈ 27.0 kHz, Q-factor > 10,000, oscillation amplitude Amp ≈ 60 pm (the oscillation amplitude for Fig. 1c is 143 pm). A PLL bandwidth of 10 Hz and a scanning speed of 380–630 pm/s were applied to all the AFM images. (Exceptions: scanning speeds are 1750 pm/s, 2000 pm/s, and 1130 pm/s for Supplementary Fig. 1, Fig. 5a, and Supplementary Fig. 9a, respectively.) To achieve submolecular resolution, the tip apex of the metal tip was functionalized with single CO molecules. 

Authors: 

Qigang Zhong, Daniel Ebeling, Jalmar Tschakert, Yixuan Gao, Deliang Bao, Shixuan Du, Chen Li, Lifeng Chi & André Schirmeisen 

Affiliations:

1. Qigang Zhong & Lifeng Chi: Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou, 215123, P. R. China 

2. Daniel Ebeling, Jalmar Tschakert & André Schirmeisen: Institute of Applied Physics, Justus-Liebig University, Heinrich-Buff-Ring 16, 35392, Giessen, Germany 

3. Yixuan Gao, Deliang Bao & Shixuan Du: Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, P. R. China 

4. Chen Li: School of Environment and Civil Engineering, Dongguan University of Technology, Dongguan, 523808, P. R. China 

Name and email of corresponding author(s):

• Daniel Ebeling  
• Shixuan Du  
• Lifeng Chi