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15–16 December 2015 University of Nottingham, Nottingham, UK http://SAMM.iopconfs.org UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy Abstract book
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15–16 December 2015 University of Nottingham, Nottingham, UK

http://SAMM.iopconfs.org

UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel

Current in Scanning Probe Microscopy

Abstract book

FORTHCOMING INSTITUTE CONFERENCESJANUARY 2016 – SEPTEMBER 2017

20166–7 January Topical Research Meeting: Physical Principles of Biological and Active Systems University of Edinburgh, Edinburgh, UK Organised by the Institute of Physics and the Higgs Centre for Theoretical Physics

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21–23 March Joint Annual HEPP and APP Conference University of Sussex, Brighton, UK Organised by the IOP Astroparticle Physics and High Energy Particle Physics groups

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3–6 April Advanced School in Soft Condensed Matter “Solutions in the Spring” Homerton College, Cambridge, UK Organised by the IOP Liquids and Complex Fluids Group

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Institute of Physics 76 Portland Place, London W1B 1NT, UK Tel +44 (0)20 7470 4800 E-mail [email protected] Web www.iop.org/conferences

Conference Programme

Tuesday 15 December 2015

08:30 Registration

09:00 Introduction With opening remarks by Chigusa Ogaya, Deputy Director JSPS London, UK

09:30 (invited) Atom switch assembly by atom manipulation Yoshiaki Sugimoto, University of Tokyo, Japan

10:10 High-resolution DFM imaging of CaFx/Si(111) Philipp Rahe, University of Nottingham, UK

10:30 Theoretical study of the intermolecular potential between C60 molecules Mohammad Abdur Rashid, University of Nottingham, UK

10:50 Effects of flexibility and entropy: Adsorption and self-assembly of functionalised organic molecules David Gao, University College London, UK

11:10 Morning refreshments

11:30 (invited) Structures of phosphorous adsorbed on and incorporated into the Si(100) surface Keisuke Sagisaka, National Institute for Materials Science, Japan

12:10 The role of entropic forces in the dynamics of a molecular rotor Hans J Hug, Swiss Federal Laboratories for Materials Testing and Research, Switzerland

12:30 Lunch

14:00 (invited) Submolecular imaging and atomic species identification on the anatase TiO2 (101) surface by simultaneous AFM and STM Tomoko Shimizu, National Institute for Materials Science, Japan

14:40 (invited) Manipulation of adatoms on Cu(2x1):O surface: An insight from theoretical simulations Lev Kantorovich, King's College London, UK

15:20 Afternoon refreshments

15:40 Rapid and quantitative measurements of 3D force maps and the reconstruction of water density distributions over fluorite surfaces Matt Watkins, University of Lincoln, UK

UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy 1

16:00 Investigating atomic contrast in atomic force microscopy and Kelvin probe force microscopy on ionic systems using functionalised tips Mats Persson, University of Liverpool, UK

16:20 (invited) Overview of JSPS Activities Chigusa Ogaya, JSPS, Japan

16:40 (invited) JSPS Fellowship Programmes Takeshi Kamezawa, JSPS, Japan

17:00 Poster session and buffet dinner

18:30 Close of Symposium Day 1

2 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

Wednesday 16 December 2015

08:45 Registration

09:20 (invited) Inducing on-demand final-state control in a metal bound molecular switch involving H- tautomerism Renald Schaub, University of St Andrews, UK

10:00 Force-induced tautomerisation in a single molecule Janina Ladenthin, Fritz-Haber Institute of the Max-Planck Society, Germany

10:20 Cascade manipulation of hybrid (C60)m−(Au)n clusters with STM tip Dogan Kaya, University of Birmingham, UK

10:40 STM manipulation of phthalocyanine molecules on Cu(111) and Ag(111) surfaces Taylor Stock, University College London, UK

11:00 Morning refreshments

11:20 High resolution qPlus® NC-AFM with a new cryogen-free variable temperature UHV SPM Björn Piglosiewicz, Scienta Omicron GmbH, Germany

11:40 Break out discussions

12:30 Lunch

14:00 (invited) Atomic and molecular-scale modification of semiconductor surfaces Steven Schofield, University College London, UK

14:40 (invited) Atomic manipulation and force spectroscopy on Cu(110)-O surface with low temperature FM-AFM Yasuhiro Sugawara, Osaka University, Japan

15:20 Afternoon refreshments

15:40 (invited) Real space imaging of the post tunnelling behaviour of electrons injected into a silicon surface from an STM tip Peter Sloan, University of Bath, UK

16:20 Close of Symposium Day 2

UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy 3

Poster Programme

P01. Development and integration of a universal SPM head: Design criteria and challenges Andreas Bettac, Sigma Surface Science GmbH, Germany P02. Dangling bond quantum states on the Si(111):B surface Manuel Siegl, University College London, UK P03. Quantum states of dangling bond defect structures on H-terminated Si(001) Asif Suleman, University College London, UK P04. An electrically-detected read out device for optically driven donor excitations defined by STM hydrogen lithography Koelker Alexander, University College London, UK P05. Tautomeric molecular switches adsorbed on Au(111): A low temperature STM study Grant Simpson, University of Graz, Austria P06. Recent technology advancements in SPM based electrical probing at low temperatures Björn Piglosiewicz, Scienta Omicron GmbH, Germany P07. qPlus® NC-AFM and STM imaging of C60 encapsulated H2O molecules Simon Taylor, University of Nottingham, UK P08. A combined Monte Carlo and Hückel theory simulation of C60 molecular rotations in C60 assemblies on Cu(111), Au(111) and NaCl Jeremy Leaf, University of Nottingham, UK P09. Structure determination of Au on Pt(111) surface: LEED, STM and DFT study Aleksander Krupski, University of Portsmouth, UK P10. Mechanochemical manipulation of Pb dimers on Si(100) Ioannis Lekkas, University of Nottingham, UK

P11. Templating of electronically decoupled molecules using domain boundaries of the 2D material silicene on ZrB2

Ben Warner, University College London, UK

4 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

Oral Abstracts

Tuesday 15 December 2015

Atom switch assembly by atom manipulation

Y Sugimoto

University of Tokyo, Japan

Supported nanoclusters have attracted considerable attention in recent years, by virtue mainly of their unique size-dependent properties. Various novel approaches have been developed to create nano-clusters with different functionalities on surfaces. To unveil the unique properties of these clusters in practical applications, it is essential to control their size and uniformity. Although the uniformity of cluster arrays has been achieved using the template-induced cluster formation method1, the precise determination of the cluster size and hence of the number of atoms involved in a cluster structure remains a challenging task.

The scanning probe method offers precise positioning capabilities with atomic precision. These capabilities have led to the creation of various artificial nanostructures atom-by-atom. This method, when combined with atomic force microscopy (AFM), provides an opportunity to directly measure the forces that induce the atomic motion in the manipulation process2.

In this study, we propose an alternative approach to the assembly of various nano-clusters atom-by-atom using the tip of a scanning probe microscope (SPM) at room temperature3. Half-unit cells of the Si(111)-(7x7) surface serve as nanospace (NS) arrays to confine individual adsorbates diffusing on the surface. This method is based on the transfer of single diffusing atoms among NSs governed by gates that can be opened in response to the chemical interaction force with the SPM tip (Fig. a-c). The clusters with predetermined compositions, such as Au12, Ag12, Au5Pb, and Pb3Si can be formed by collecting single atoms from the surrounding NSS into a pre-defined NS with successive gate controls (Fig. d-g). This method provides a way to assemble some atom clusters that work as atom switch. We demonstrate that Pb3 cluster works as a chiral switch caused by carrier injection4 and Si4 works as a switch caused by both current and force5.

[1] H. Brune, et al., Nature 394, 451 (1998) [2] Y. Sugimoto, et al., ACS Nano 7, 7370 (2013) [3] Y. Sugimoto, A. Yurtsever, N. Hirayama, M. Abe and S. Morita, Nat. Commun. 5, 4360 (2014) [4] E. Inami, I. Hamada, K. Ueda, M. Abe, S. Morita, and Y. Sugimoto, Nat. Commun. 6, 6231 (2015) [5] S. Yamazaki, et al., Nano Letters, 15, 4356 (2015)

UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy 5

High-resolution DFM imaging of CaFx/Si(111)

P Rahe and P J Moriarty

University of Nottingham, UK

Besides their essential presence in semiconducting device technology, thin insulating films have played a key role in the study of single atoms or molecules, where reduced electronic coupling of the adsorbates to an underlying substrate was revealed using scanning probe techniques1. The NaCl-on-metal system has been investigated extensively in this context, but to date a similar thin barrier for single molecule decoupling from semiconductor substrates has not been exploited. Insulating CaF2 grows epitaxially on the Si(111) surface in a wide variety of growth modes, and enables the interface and bonding between a covalent and ionic material to be examined in detail2,3.

We present high-resolution dynamic force microscopy (DFM) data to study this important analogue to the NaCl-on-metal prototype. Data were acquired at 77K using a tuning fork setup in imaging and force mapping mode. We shall discuss contrast modes on different phases of the CaFx-on-Si(111) system and will investigate step edge structures.

[1] Repp et al., Phys. Rev. Lett. 94, 026803 (2005) [2] Olmstead, in: Series Dir. Cond. Matter Phys. Vol. 15 (1999), ed. W.K. Liu, M.B. Santos (World Scientific) [3] Wollschläger, Rec. Res. Dev. Appl. Phys. 5-III, 621 (2002)

Theoretical study of the intermolecular potential between C60 molecules

M A Rashid, S P Jarvis, A Sweetman, P Moriarty and J L Dunn

University of Nottingham, UK

We study the interaction between fullerene (C60) molecules using a sum of pairwise Lennard-Jones (12-6) potentials, and investigate how flexibility in the tip can produce a bond like feature between the molecules in a C60 island where there is no chemical bond present except the weak van der Waals bond. We also investigate how the potential between the molecules is dependent on their relative orientations. For a given configuration of the tip and the sample molecules, our results allow us to predict the form of the intermolecular potential that would be observed using dynamic atomic force microscopy (AFM). For appropriate choices of the parameters of the analytic potential and of relative tip-sample orientations, the results are seen to closely resemble results we have obtained in AFM experiments. Our theoretical approach has the potential to be applied to a wide variety of different systems; due to the simplicity of the method, results can be obtained very quickly and at a very low computational cost.

Effects of flexibility and entropy: Adsorption and self-assembly of functionalised organic molecules

D Z Gao1, J Gaberle1, F Federici Canova1, 2, M B Watkins1, L Nony3, C Loppacher3, A Amrous3, F Bocquet3, F Para3, S Lamare4, F Palmino4, F Cherioux4 and A L Shluger1,2 1University College London, UK, 2Tohoku University, Japan, 3Aix-Marseille Université, France, 4Université de Franche-Comté, France

Non-contact atomic force microscopy (NC-AFM) experiments combined with theoretical simulations were used to study the adsorption, diffusion, and self-assembly of functional organic molecules on KCl(001). Our results highlight

6 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

the importance of molecular mobility and flexibility in order to provide insight into the mechanisms that drive self-assembly in these systems.

1,3,5-tri-(4-cyano-4,4 biphenyl)-benzene (TCB) and 1,4-bis(cyanophenyl)-2,5-bis(decyloxy)benzene (CDB) molecules, were synthesised, deposited, and annealed on the KCl (001) and imaged using NCAFM. DFT calculations were performed to study the adsorption of single molecules and the competing molecule-molecule and molecule-surface interactions for CDB and TCB molecules on KCl (001). These results were used to parameterise classical force fields for both the TCB and CDB molecules1. We then used these force fields to perform molecular dynamics (MD) simulations of CDB and TCB molecules on the KCl (001) surface, predict monolayer structures, and calculate the entropic contributions to adsorption energy. We demonstrate that the flexibility of the molecule changes its interactions with step edges which in turn qualitatively changes growth mechanisms. Finally, we highlight the importance of accounting for dynamics within these systems by discussing how adsorption height and geometry can change depending on temperature.

Figure 1: A single CDB molecule (a) and TCB molecule (b)s adsorbed at a step edge on the KCl (001) surface.

[1] D. Z. Gao, F. Federici Canova, M. B. Watkins, A. L. Shluger, Journal of Computational Chemistry, (2015)

Structures of phosphorous adsorbed on and incorporated into the Si(100) surface

K Sagisaka

National Institute for Materials Science, Japan

The characterisation of individual dopant atoms in silicon is one of the key issues to sustain miniaturisation in the semiconductor industry. Scanning tunneling microscopy (STM) and spectroscopy (STS) with atomic resolution are excellent lab-based tools for this purpose. Using STM, we study structural and electronic properties of different states of individual phosphorous in the Si(100) surface [Fig. 1]. In this talk, we discuss the structures of adsorbed phosphorous molecules [Fig. 1(b)] and of incorporated phosphorous [Fig. 1(c)] in the surface. Phosphorous molecules evaporated from a piece of InP wafer onto the Si(100) surface have been found to form five adsorption states1. Incorporation of phosphorous in the surface is achieved by annealing to 550°C. In this process, a phosphorous atom replaces with one of silicon atom of a silicon dimer to form a P-Si heterodimer. Identification of the structures of the adsorbates and the heterodimer are accomplished by bias-dependent imaging and structural manipulation in STM with the support of STM simulations based on density functional theory calculations.

UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy 7

Fig.1 Illustration of samples used for the studies of phosphorous in the Si(100) surface.

[1] K. Sagisaka, M. Marz, D. Fujita, D. Bowler, Phys. Rev. B 87, 155316 (2013)

The role of entropic forces in the dynamics of a molecular rotor

H J Hug1,2, J C Gehrig1, M Penedo-Garcia1, M Parschau1, J Schwenk1, M A Marioni1 and E W Hudson1 1Swiss Federal Laboratories for Materials Science and Technology, Switzerland, 2University of Basel, Switzerland

The tendency of systems with many degrees of freedom to increase their entropy manifests as so-called “entropic” forces associated with changes of a system attribute. Particularly in biochemical and biological processes1, and in heterogeneous catalysis2 entropic forces play an important role. Recently entropic forces have even been invoked to describe fundamental interactions such as gravity3. Studying them at the level of individual molecules would improve our understanding of chemical reaction- and transformation kinetics, and this possibility can be addressed with scanning probe microscopy (SPM). To date the conservative forces of an AFM or STM tip on molecules have been studied in some detail4,5, but the possibility that it also affects the stochastic forces on molecules has not been addressed.

Here we demonstrate that the proximity of an STM tip to a dibutyl-sulfide molecular rotator6 adsorbed on Au(111) results in both conservative- and entropic forces that substantially change its rotation dynamics. The former alters the energy-barrier to hopping and the latter the apparent hopping attempt rates, even though the topograph of a stationary molecule is not substantially modified in the process.

These effects partially compensate, but can be observed as a function of relative tip-molecule position in the hopping rate. Based on this insight, SPM measurements of the tip-position dependent molecular transition kinetics seem particularly useful in the study of catalytic reactions or molecular self-assembly processes on surfaces.

8 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

(a) Measurement principle: The DBS molecule adsorbed on the Au(111) surface is scanned at a rate of 602 s/line. z-feedback keeps the average tunnelling current constant at 20 pA, and telegraph noise recorded at a high measurement bandwidth allows measurement of the molecular hopping rate at various temperatures. From these site-specific energy barriers and attempt rates were obtained and maps of entropic (b) and conservative forces (c) were calculated. Locations with a stronger restoring conservative force (high energy barrier) show a correspondingly increased entropic force facilitating a transition of the molecule over the energy barrier (compensation effect).

[1] H. Dong, R. Lund, and T. Xu. Micelle Stabilisation via Entropic Repulsion: Balance of Force Directionality and Geometric Packing of Subunit. Biomacromolecules, 16 (2015) 743

[2] G. C. Bond, M. A. Keane, H. Kral, and J. A. Lercher. Compensation Phenomena in Heterogeneous Catalysis: General Principles and a Possible Explanation. Catalysis Reviews, 42 (2000) 323

[3] E. Verlinde. On the origin of gravity and the laws of Newton. Journal of High Energy Physics 4 (2011) 29 [4] J. A. Stroscio, F. Tavazza, J. N. Crain, R. J. Celotta, and A. M. Chaka. Electronically Induced Atom Motion in

Engineered CoCun Nanostructures. Science, 313 (2006) 948 [5] M. Ternes, C. P. Lutz, C. F. Hirjibehedin, F. J. Giessibl, and A. J. Heinrich. The force needed to move an atom

on a surface. Science, 319 (2008) 1066 [6] A. E. Baber, H. L. Tierney, and E. C. H. Sykes. A Quantitative Single-Molecule Study of Thioether Molecular

Rotors. ACS Nano, 2 (2008) 2385

Submolecular imaging and atomic species identification on the anatase TiO2 (101) surface by simultaneous AFM and STM

T K Shimizu1,2, C Moreno1, O Stetsovych1 and O Custance1 1National Institute for Materials Science (NIMS), Japan, 2JST PRESTO, Japan

Submolecular imaging using atomic force microscopy (AFM) has recently been established as a stunning technique to reveal the chemical structure of unknown molecules, to characterise intra-molecular charge distributions, and to observe chemical transformations. So far, most of these feats were achieved on planar molecular systems using specially designed quartz AFM sensors. Here, we present a method for high-resolution imaging of non-planar molecules and 3D surface systems using silicon cantilever based AF1. We demonstrate this method by imaging pentacene and C60 molecules adsorbed on the anatase TiO2(101) surface. This anatase substrate was also precisely characterised by simultaneous AFM and scanning tunneling microscopy (STM) measurements. Comparison of experimental results with first principle calculations enables us to identify the atomic species responsible for the atomic contrast in AFM and STM images as well as common defects observed at this surface such as subsurface oxygen vacancies, individual water molecules, and surface hydroxyl2.

UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy 9

Our results show the potential of simultaneous AFM-STM measurements with atomic and intra-molecular resolution to investigate more complex phenomena such as photovoltaic effect and catalytic reactions not only on the anatase surface but also on various types of nano materials.

Fig. (a) 1st-pass AFM topography image and (b) 2nd-pass Δf image of a C60 molecule on anatase TiO2(101).1

Fig.2 (a) 2nd-pass Δf image of pentacene adsorbed anatase TiO2(101). Red dotted line indicates a step.

(b) Model of adsorption geometry of pentacene at the step edge.

[1] C. Moreno, O. Stetsovych, T. K. Shimizu, and O. Custance, Nano Lett. 15, 2257 (2015) [2] O. Stetsovych et al., Nat. Commun. 6, 7265 (2015)

Manipulation of adatoms on Cu(2x1):O surface: An insight from theoretical simulations

L Kantorovich1, J Bamidele1, S H Lee2, Y Kinoshita2, J Brndiar3, R Turansky3, Y Naitoh3, Y J Li3, Y Sugawara3 and I Stich3 1King’s College London, UK, 2Osaka University, Japan, 3Slovak Academy of Sciences, Slovakia

In this talk I’d like to discuss two types of manipulation of adatoms on the same Cu(110):O surface with AFM which has been a result of a fruitful collaboration of theoretical groups in London and Bratislava, and the experimental group in Osaka: in one case dynamics of the vertical manipulation process appeared to be crucial for understanding the observations, while in the other a strikingly unusual potential energy surface of the adatom combined with long-range interactions between adatoms on the surface.

10 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

Firstly, I’ll present low temperature NC-AFM experiments of vertical manipulations of “super”-Cu atoms on the p(2 × 1) phase of oxidised Cu(110) surface, both extractions to and depositions from the tip, which leave the imaging contrast unchanged after each manipulation event. Experimental observations are rationalised by an original model revealing a novel multistep manipulation mechanism combining activated jumps of “super”-Cu atoms to/from the tip with their drag by and diffusion on the tip. We show how important it is to be able for the theory to consider the manipulation events dynamically in order to evaluate the probabilities of extraction (from the surface) and deposition (from the tip) of the adatom. For describing the observed vertical manipulations, a novel kinetic Monte Carlo algorithm has been developed which was used in conjunction with ab initio density functional theory (DFT) calculations.

Secondly, I’ll discuss a novel type of manipulation, which harnesses both short-range interaction of adatoms with the surface and long-range interactions between adatoms, whereby the manipulated adatoms can be kept in a metastable state, which is delocalised above several surface unit cells. These adatoms then manifest themselves as smeared out “large” features on the images that “survive” over macroscopic times. The principle is demonstrated on NC-AFM manipulation of Co atoms on the p(2 × 1) Cu(110):O surface in UHV at 78K. Using ab initio DFT calculations, we show that the manipulation is possible due to a peculiar potential energy surface of the Co atoms on the substrate, which contains large flat plateaus. In addition, when manipulated to those plateaus by the tip, the Co atom spin state is to be modified stabilising it in this metastable state. Geometrically the state extends over several surface cells and is stabilised even further due to long-range interaction with neighbouring Co adatoms via Friedel oscillations mechanism. We hence demonstrate the possibility of prediction and mechanical control of the spin state of the Co atom as a result of this manipulation.

Rapid and quantitative measurements of 3D force maps and the reconstruction of water density distributions over fluorite surfaces

M Watkins, K Miyazawa, T Fukuma and A Shluger

University of Lincoln, UK

Hydration plays important roles in various solid-liquid interfacial phenomena. Very recently, three-dimensional scanning force microscopy (3D-SFM) has been proposed as the tool to visualise solvated surfaces and their hydration structures with lateral and vertical (sub)molecular resolution. However, the relationship between the 3D force map obtained and the equilibrium water density, ρ(r), distribution above the surface remains an open question. Here, we investigate this relationship at the interface of an inorganic mineral, fluorite, and water using a combination of refined experimental techniques and computational modelling.

Using new developments in 3D-SFM, we can obtain quantitative force maps Fexp(r) in pure water less than 20 minutes from submersion. This increase in the speed of measurement greatly expands the number of systems the method should be applicable to. Additionally, measurements in pure water can be directly compared to simulated data. Previous measurements1 were greatly complicated by sample dissolution and the complex electrolyte environment that was needed to maintain stable imaging conditions.

We compare force images generated using the Solvent Tip Approximation (STA) model2 and from explicit molecular dynamics simulations to the new experimental data. The results show that the simulated STA force map reproduces the major features of the experimentally obtained force image. The agreement between the STA data and experiment strongly implies that the water density used as an input to the STA model is close to the experimental hydration structure and thus provides a tool to bridge between the experimental force data and atomistic solvation structures.

UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy 11

The proposed method should improve the accuracy and reliability of interpretation of this measurement technique, with applications in all fields dependent on solid-liquid interfacial phenomena. Obtaining full 3D force maps also raises the possibility of obtaining quantitative hydration free energy maps and, indeed, measuring free energy barriers for water diffusion. These are the tools that in UHV were needed for controlled and reproducible manipulation of molecules and defects.

[1] N. Kobayashi et al, J. Phys. Chem. C, 2013, 117 (46), pp 24388–24396; http://dx.doi.org/10.1021/jp4076228

[2] M. Watkins, B. Reischl, J. Chem. Phys. 138, 154703 (2013); http://dx.doi.org/10.1063/1.4800770

Investigating atomic contrast in atomic force microscopy and Kelvin probe force microscopy on ionic systems using functionalised tips

M Persson1, L Gross2, B Schuler2, F Mohn2, N Moll2, N Pavliček2, W Steurer2, I Scivetti1, K Kotsis1 and G Meyer2 1University of Liverpool, UK, 2IBM Research–Zurich, Switzerland

Non-contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM) have become important tools for nanotechnology; however, their contrast mechanisms on the atomic scale are not entirely understood. Here we used chlorine vacancies in NaCl bilayers on Cu(111) as a model system to investigate atomic contrast as a function of applied voltage, tip height, and tip functionalisation1. We demonstrate that the AFM contrast on the atomic scale decisively depends on both the tip termination and the sample voltage. On the contrary, the local contact potential difference acquired with KPFM showed the same qualitative contrast for all tip terminations investigated, which resembled the contrast of the electrostatic field of the sample. We find that the AFM contrast stems mainly from electrostatic interactions but its tip dependence cannot be explained by the tip dipole alone. With the aid of a simple electrostatic model and by density functional theory, we investigate the underlying contrast mechanisms.

[1] Phys. Rev. B 90, 155455 (2014)

12 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

Wednesday 15 December 2015

Inducing on-demand final-state control in a metal bound molecular switch involving H-tautomerism

R Schaub, J A Garrido Torres, G J Simpson and H Früchtl

University of St Andrews, UK

A potential end-point in the miniaturisation of electronic devices lies in the field of molecular electronics, where molecules perform the function of single components. Molecular switches display stability in two or more states (“zero” and “one”), and the use of such molecules as electronic devices has been the focus of many recent studies. The mechanism responsible for switching in molecules can take various forms, including metal-ligand complexation1, cis/trans isomerisation2 or H-tautomerism. To date, H-tautomerism in surface bound molecular switches has only been observed in the macrocycle system of a porphyrin-type molecule3,4. The restriction of the active hydrogens to this moiety is, however, not compulsory as we will show here. The present work reveals how H-tautomerism is the mechanism for switching in substituted quinone derivatives – a novel class of molecules with a different chemical structure.

STM measurements are carried out at 5K on azophenine - a prototypical quinone derivative. When adsorbed on a Cu(110) surface, the molecular switch remains in one of two stable H-tautomeric states and can be made to switch between them, at will, by applying a bias exceeding a threshold voltage of approximately 0.3 eV. By recording many switch events the activation energy of the process is measured and shown to be induced by inelastic electron excitations. Computational modelling shows that the mechanism underlying this process is tautomerisation of protons belonging to two amino groups5. This property is retained upon functionalisation by the addition of side groups, meaning that the switch can be chemically modified to fit specific applications.

By combining microscopy with single-molecule spectroscopy and density functional theory (DFT) calculations, we unravel an asymmetric behaviour in the preference of the tautomeric states depending on the precise injection location of the inelastic electron excitation within the molecule, without affecting the rate of the reaction. This spatial dependence allows to selectively favour on demand one or the other tautomeric states, achieving controllability in the final state up to 98%. This result is surprising considering that the final states remain degenerate. We will propose an explanation and further devise alternative strategies to allow for final state control in unimolecular bistable switches6.

STM image showing switching between the two tautomeric states of azophenine

[1] Ohmann R., et al. Nano Lett. 2010, 10, 2995 [2] Choi B.-Y., et al. Phys. Rev. Lett. 2006, 96, 156106 [3] Liljeroth P., et al. Science 2007, 317, 1203 [4] Auwärter W., et. al. Nat. Nanotechnol. 2012, 7, 41

UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy 13

[5] Simpson G.J., et al., Nano Lett. 2014, 14, 634 [6] Torres J. A. G., et al., Submitted 2014

Force-induced tautomerisation in a single molecule

J N Ladenthin1, S Gawinkowski2, J Waluk2 and T Kumagai1 1Fritz-Haber Institute of the Max-Planck Society, Germany, 2Polish Academy of Sciences, Poland

Mechanochemical reactions, in which directional mechanical forces induce selective rupture and reformation of covalent bonds1, have a prominent application potentiality not only in mechanoresponsive materials to technology, but also in nanoscale science and chemistry, e.g. control of molecular machines. However, it still remains a significant challenge to reveal the mechanism how macroscopic forces can be transferred to molecules. Here we present the mechanically-induced intramoleculer H-atom transfer (tautomerisation) within a single porphycene molecule adsorbed on a Cu(110) surface by using non-contact atomic force microscopy (NC-AFM). Tautomerisation of a single porphycene molecule on Cu(110) has been studied by using STM (Figure 1)2, 3. The tautomerisation can also be induced by approaching a metallic tip through a distortion of the potential landscape, and the interaction acting between the tip apex and molecule is quantified by force spectroscopy (Figure 2). It is also found that a Xe terminated tip cannot induce the tautomerisation because of a weaker interaction with a molecule. These results provide a fundamental insight into the mechanism of mechanochemical reactions at the single molecule level.

Figure 1 (a) - (b) STM image of a porphycene molecule on Cu(110) at 5 K. Switching corresponds to (c) cis‒cis tautomerisation

Figure 2 (a) Force curve during tip approach (black) and retraction (grey). (b) Schematic illustration of tip-induced tautomerisation process through potential distortion.

[1] C. R. Hickenboth et al. Nature 446, 423 (2007) [2] T. Kumagai et al. Nature Chemistry 6, 41 (2014) [3] T. Kumagai et al. Phys. Rev. Lett. 111, 246101 (2013)

14 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

Cascade manipulation of hybrid (C60)m−(Au)n clusters with STM tip

D Kaya, R E Palmer and Q Guo

University of Birmingham,UK

Fullerenes draw a lot of interest for fundamental investigations and diverse potential applications in e.g. solar cells, organic electronics, or single molecule devices in nanoelectronics, due to their electronic properties1. In our recent work2, we demonstrated the production of hybrid (C60)m−(Au)n clusters such as (C60)7−(Au)19, (C60)10−(Au)35, (C60)12−(Au)49, and (C60)14−(Au)63 on the Au(111) surface at RT.

These (C60)m−(Au)n clusters show a clear magic number effect that only certain combinations of m and n are allowed. Here we report a cascade manipulation of these hybrid clusters by the STM tip and demonstrate that a (C60)m−(Au)n cluster can be tailor modified by downsizing it from one magic number cluster to another. The manipulation process is explained with the STM images in Figure 1. In Fig. 1A, we start with a (C60)12−(Au)49 cluster which consists of three C60 molecules sitting on top of a Au49 island. The edges of the Au island are decorated by 9 C60 molecules. The STM tip driven towards the molecule highlighted with a circle by 1.2 nm, temporarily disrupting the cluster. The atoms and molecules are able to re-group forming a (C60)10−(Au)35 cluster which is a magic number cluster “one size smaller” than (C60)12−(Au)49. Hence, this manipulation process has removed two C60 molecules and 14 Au atoms simultaneously from the initial (C60)12−(Au)49 cluster. In Fig. 1B, we show that the (C60)10−(Au)35 cluster can be changed further to (C60)7−(Au)19 which is the smallest stable cluster. This manipulation process is highly efficient because there is no need to remove atoms/molecules one-by-one by the STM tip and yet the final product is “error-free” due to the stability of the magic number cluster.

Figure 1: Manipulation images showing before, during and after manipulation of (C60)12−(Au)49, (C60)10−(Au)35 clusters A and B, respectively. Manipulation is performed on the site of clusters shown white circle. All images are

acquired using a -1.67 V and 47 pA. Manipulation is achieved by driving the tip toward the surface by 1.2 nm.

[1] L. Sanchez, R. Otero, J. M. Gallego, R. Miranda, and N. Martin, Chem. Rev. 109, 2081-2091 (2009) [2] Y-C. Xie, L. Tang, and Q. Guo, Phys. Rev. Lett. 111, 186101 (2013)

UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy 15

STM manipulation of phthalocyanine molecules on Cu(111) and Ag(111) surfaces

T Stock and J Nogami

University of Toronto, Canada

The room temperature adsorption of up to one monolayer (ML) of metal-free phthalocyanine (H2Pc) and copper phthalocyanine (CuPc) molecules on Cu(111) and Ag(111) has been studied using STM and STS. In all four systems, at coverages below 1 ML, the molecules are found to be in a fluid state and are mobile on the surface. At approximately 1 ML coverage the fluid molecules become immobilised and transition into highly ordered 2D crystal phases. At sub-ML coverages, immobilisation of the fluid molecules can be induced through exposure to tunneling electrons at positive sample bias voltages exceeding specific threshold values. This STM induced immobilisation effect is only found to be stable in the case of the Cu(111)-CuPc system. A variety of related STM manipulations are however also observed in the other three systems, including manipulation of the molecules in the 2D crystal phase. The STM induced immobilisation effect in the Cu(111)-CuPc allows for a novel variety of molecular STM lithography as illustrated in Figure 11.

Figure 1: Tunneling electron induced immobilisation of CuPc on Cu(111) used to perform molecular STM lithography: The letters "CUPC" have been patterned in a 0.75 ML CuPc layer, with a single pass of the STM tip at a sample bias V = +4.5 V, and tunneling current I = 1.5 nA. The inset shows the final “C” in greater detail, where the

individual immobilised molecules are observed lying flat on the substrate.

[1] T. Stock and J. Nogami, Appl. Phys. Lett. 104, 071601 (2014)

16 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

High resolution qPlus® NC-AFM with a new cryogen-free variable temperature UHV SPM

B Piglosiewicz1, C Troeppner1, D Jedamzik2, A Adams2, R Brzakalik2, A Sulikowska2, M Atabak1, S Molitor1, J Koeble1 and J Chrost1

1Scienta Omicron GmbH, Germany, 2Oxford Instruments NanoScience, UK

We present first qPlus®1 NC-AFM results of a new cryogen-free cooled ultra-high vacuum compatible scanning probe microscope (SPM). This Cryofree SPM is capable of high stability STM and qPlus® NC-AFM operation at sample temperatures down to 10K. Overcoming the limits of hold time of cryogenic liquids this microscope provides access to new classes of experiments. Decoupling the strong mechanical vibrations induced by the closed cycle cooler represents a major technical challenge. Our design of the Cryofree SPM effectively decouples the inherent mechanical vibrations to a level of state-of-the art low temperature SPMs utilising cryogenic liquids. The results presented here clearly demonstrate the stability of the microscope and its capability of atomic resolution imaging and spectroscopy at low temperatures in the qPlus® NC-AFM mode.

Fig.1: Cooling concept of the Cryofree Fermi SPM

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Fig.2: STM measurements on Au(111) and drift measurements at T=13K with the Cryofree Fermi SPM

Fig.3: qPlus® measurements on NaCl(100) and Si(111) at the base temperature of T=10K

with the Cryofree Fermi SPM [1] Patented, cf. Franz J. Giessibl, APL, Vol. 73, No. 26 (1998) [2] B. Uder: Cold Tip SPM: A New Generation of Variable Temperature SPM for Spectroscopy. International

Conference on Nanoscience + Technology (2014) [3] P. Chomiuk et. al.: A New Generation of Variable Temperature Scanning Probe Microscope for

Spectroscopy.Acta Physica Polonica A, Vol. 125, 1049-1051 (2014)

18 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

Atomic and molecular-scale modification of semiconductor surfaces

S Schofield

University College London, UK

Scanning tunnelling microscopy and spectroscopy (STM/STS) can be used to introduce atomic-scale defects in semiconductors1 and to characterise their structural and electronic properties at the atomic-scale2. Similarly, STM and complementary techniques can be used to manipulate and characterise molecules attached to semiconductor surfaces3,4, and together these capabilities allow us to explore the fundamental physics and chemistry of semiconductor surfaces at the atomic scale. Such investigations may facilitate the future fabrication of atomic and molecular scale devices where individual atoms and molecules form the individual components of the device. Here I present recent work exploring the fabrication and characterisation of atomic-scale defects in silicon and the organic functionalisation of silicon surfaces. In particular, we have explored the properties of isolated and interacting point defects due to dangling bonds on chemically passivated Si(001) and Si(111) surfaces, as well as isolated subsurface dopant atoms. This STM/STS data was analysed using both simple toy-model and first principles density functional theory calculations. We have also explored the attachment of small organic molecules, e.g., acetophenone and benzonitrile onto clean Si(001), and we show the ability to manipulate these molecules into favourable bonding configurations. For these investigations we have used both STM and complementary synchrotron-based techniques (XPS and NEXAFS).

[1] Schofield et al., Nature Commun. 4, 1649 (2013) [2] Sinthiptharakoon et al., J. Phys.: Condens. Matter 26 , 012001 (2014) [3] O’Donnell et al., J. Phys. Condens. Matter 27, 054002 (2015) [4] Schofield and Brázdová, J. Phys.: Condens. Matter 27, 050301 (2015)

Atomic manipulation and force spectroscopy on Cu(110)-O surface with low temperature FM-AFM

Y Sugawara, Y Kinoshita, S H Lee, Y Naitoh and Y J Li

Osaka University, Japan

Manipulation of single atoms and molecules is an innovative experimental technique of nanoscience. Recently, an atomic force microscopy (AFM) has been used to manipulate single atoms and molecules. Atom manipulation with an AFM is particularly promising, because it allows the direct measurement of the required forces.

In the present study, we investigated the forces in AFM lateral manipulation for a top single Cu atom (super Cu atom) on the Cu(110)-O surface. The AFM tip apex was coated with Cu or O atoms in situ by slightly making a tip-sample mechanical contact on the Cu(110)-O surface prior to the imaging. In the case of O-adsorbed AFM tip1, the super Cu atom on the surface was pulled at a lateral tip position on the adjacent binding site. In contrast, in the case of Cu-adsorbed AFM tip1, the super Cu atom was pushed over the top of the super Cu atom. Thus, we found that the forces (attractive or repulsive forces) to move an atom laterally on the surface strongly depend on the atom species of the AFM tip apex and the surface. Furthermore, in order to clarify the manipulation process, we investigated the full tip-sample potential landscape necessary to manipulate atoms. The tip-sample potentials were determined by the frequency shift versus distance curves by mathematical analysis. We found that the tip-sample potentials which move the super Cu atom laterally on the surface strongly depended on the atom species of the AFM tip apex and the surface. These results strongly suggest that the chemical nature of tip-sample interaction plays an important role in lateral atom manipulation. Furthermore, we discuss the pathways for moving the super Cu atom.

UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy 19

Fig. 1 (a) AFM image and (b) two-dimensional map of force curves measured with Cu-adsorbed tip on Cu(110)-O surface

[1] J. Bamidele, Y. Kinoshita, R. Turanský, S. H. Lee, Y. Naitoh, Y. J. Li, Y. Sugawara, I. Štich, and L. Kantorovich, Phys. Rev. B 86, 155422 (2012)

20 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

Real space imaging of the post tunnelling behaviour of electrons injected into a silicon surface from an STM tip.

P A Sloan

University of Bath, UK

The tip of a scanning tunnelling microscope can be considered an atomic-scale source of hot electrons (or holes). This beam of tuneable electrical energy has been used to instigate single molecule dynamics (chemistry) in many surface/molecule systems. Such conventional atomic-manipulation is restricted to the tunnel junction; the STM tip directly injects charge into a single atom or molecule. Nonlocal manipulation, whereby atoms or molecules some distance remote from the tunnel junction are also induced to react, has been reported for several surface/adsorbate systems1. This mode of atomic manipulation is fundamentally different as it involves three steps, (1) injection of charge from tip to substrate, (2) charge transport across the substrate and (3) charge induces manipulation of a molecule. The spatial spread of the effect has encoded in its form details about all of these processes, but perhaps most intriguing it offers the possibility of mapping the transport of hot electrons on the true nanoscale.

Here I will report on the Si(111)-7x7 surface with various chemisorbed benzene and benzene derivatives and their nonlocal manipulation properties. First, by careful energy and position resolved injections, we mapped out the probability of inducing nonlocal desorption of chlorobenze on Si(111)-7x7. We find that the nonlocal probability of manipulation is an analogue of the LDOS of a Si(111)-7x7 electronic surface resonance giving insight into the initial tip-to-substrate injection process2. Second I will report variable temperature and voltage measurements of the nonlocal manipulation. The range of the nonlocal effect increases with temperature and, at constant temperature, is invariant over a wide range of electron energies3. We propose that our measurements probe, in real space, the underlying hot electron dynamics on the 10 nm scale. These results are well described by a two-dimensional diffusive model with a single decay channel, consistent with 2PPE measurements of the real time (~200 fs) dynamics. Finally I will report on the initial coherent expansion of an electron after injection into the surface and the evidence we find in the radial dependence of nonlocal manipulation4. A simple model of initial coherent expansion of a wavepacket in a 2D surface state followed by diffusion is developed and shown to (nearly) fully describe our results with the minimum of fitting parameters.

Nonlocal manipulation offers the possibility to map out, in real space, the fate of high energy hot charge carriers and hence couple the atomic length scale resolution of the STM to the atomic time scale of atomic processes.

[1] Jennifer M. MacLeod, Josh Lipton-Duffin, Chaoying Fu and Federico Rosei, 2009, Inducing Nonlocal Reactions with a Local Probe. ACSNano, 3 (11) pp 3347–3351

[2] Sloan, P. A., Sakulsermsuk, S. and Palmer, R. E., 2010. Nonlocal desorption of chlorobenzene molecules from the Si(111)-(7×7) surface by charge injection from the tip of a scanning tunneling microscope: remote control of atomic manipulation. Physical Review Letters, 105 (4), 048301.

[3] Lock, D., Rusimova, K., Pan, T., Palmer, R. E. and Sloan, P., 2015. Atomically resolved real-space imaging of hot electron dynamics. Nature Communications, 6 (8365), 8365.

[4] K. R. Rusimova, N. Bannister, P. Harrison, D. Lock, R. E. Palmer, P. A. Sloan, 2015. Imaging the room-temperature coherent inflation of a localised charge carrier at a semiconductor surface, in preparation.

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Poster Abstracts

P01. Development and integration of a universal SPM head: Design criteria and challenges

A Bettac, B Guenther and A Feltz

SIGMA Surface Science GmbH, Germany

Recently we have developed a SPM microscope head that merges the needs for high resolution STM/QPlus1-AFM and at the same time satisfies the requirements for integration into different cryogen environments including tip and sample handling.

The new SPM head was integrated into different platforms, e.g. in an UHV Helium Flow Cryostat system for temperatures <10K and in a 3He Magnet Cryostat UHV system for high magnetic fields (±12T) and temperatures <400mK.

This contribution focuses on design aspects and challenges for the new SPM head with respect to spatial restrictions, sample sizes/standards, QPlus – and STM signal shielding as well as on first results (STM, STS and QPlus) obtained with the different instrumental setups.

Figure: SPM and STS measurements on Au(111) (a & b) and NbSe2 (c & d) at low temperatures. The atomically resolved images were taken in combination with different cryostats: a) Helium Flow cryostat with tip & sample at

T<10K and b-d) with a 3He Magnet Cryostat UHV system.

[1] F. J. Giessibl, Applied Physics Letters 73 (1998) 3956

22 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

P02. Dangling bond quantum states on the Si(111):B surface

M Siegl, H Hedgeland, D R Bowler and S R Schofield

University College London, UK

Scanning tunnelling microscopy (STM) is notable for its application in the creation of quantum structures such as quantum corrals showing bound electron states across multiple lattice sites on a metal surface1. Extending STM, we use spatially resolved scanning tunnelling spectroscopy (CITS)2 to investigate the electronic structure of point defect induced quantum bound states on the Fermi‐level pinned boron passivated Si(111)-sqrt(3) x sqrt(3) R30° surface. Further, we explore the site dependent interaction of these atomically sized quantum dots in varying arrangements and thus changing distance between the dangling bond (DB) sites. Comparing the experimental results to first principle density function theory (DFT) calculations we find a non-‐‐linear constructive interference of the positively charged DB excited states3.

[1] M. F. Crommie et al., Science 262, 218 (1998) [2] R. J. Hamers et al., PRL 56, 18 (1986) [3] H. Hedgeland, M. Siegl et al. In preparation (2015)

P03. Quantum states of dangling bond defect structures on H-terminated Si(001)

A M Suleman, K A Rahnejat, C F Hirjibehedin, N J Curson, G Aeppli, D R Bowler and S R Schofield

University College London, UK

Atomic point defects in semiconductors have the potential to form the next generation nano‐ and quantum-electronic devices. However, to achieve this the fundamental physics of their interactions with each other and their local environment must be understood at the atomic-scale. Scanning tunnelling microscopy (STM) has been used over the past two decades to investigate, and in some cases create and manipulate, atomic point defects on semiconductor surfaces. Here we present measurements of the dangling bond orbital point defect on the hydrogen-terminated silicon (001) surface. The STM tip is used to selectively desorb individual H atoms to create interacting DBs1,2. We show that pairs and two‐dimensional arrangements of DBs on H‐terminated Si(001) exhibit energy dependent quantum bound states analogous to molecular orbitals1,2.

[1] S. R. Schofield et al. Nat. Commun. 4, 1649 (2013) [2] A. M. Suleman et al. In preparation (2015)

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P04. An electrically-detected read out device for optically driven donor excitations defined by STM hydrogen lithography

K Alexander

University College London, UK

Devices capable of probing quantum information processes in the solid state will be indispensable for future quantum electronics1. Via STM hydrogen lithography patterning, single dopants can be placed in the Si(100) surface with atomic precision2. The patterned structure is encapsulated with a few nanometers of silicon, grown by molecular beam epitaxy3. After the contacting of these buried structures4, transport measurements can determine how optical driven donor and spin excitations effect the carrier mobility and scattering in the device.

[1] Morello, Andrea, et al. "Single-shot readout of an electron spin in silicon." Nature 467.7316 (2010): 687-691

[2] Ruess, Frank J., et al. "Toward atomic-scale device fabrication in silicon using scanning probe microscopy." Nano Letters 4.10 (2004): 1969-1973

[3] Schofield, S. R., et al. "Atomically precise placement of single dopants in Si." Physical review letters 91.13 (2003): 136104

[4] Fuechsle, Martin, et al. "Surface gate and contact alignment for buried, atomically precise scanning tunneling microscopy–patterned devices." Journal of Vacuum Science & Technology B 25.6 (2007): 2562-2567

P05. Tautomeric molecular switches adsorbed on Au(111): A low temperature STM study

G Simpson

University of Graz, Austria

Molecular electronics seeks to realise the function of conventional electronic components in single molecules, switching being one of the most important ones. Tautomeric molecular switches, which are based on intramolecular proton transfer, hold promise in that the movement of a single hydrogen atom brings about a measurable change in the conductance of the molecule while avoiding substantial conformational changes. Moreover, the proton transfer itself is of great interest in fundamental physics and chemistry. Until recently, tautomeric molecular switches were confined to the use of porphyrin type molecules. However, a recent paper1 demonstrated the switching of a molecule based on hydrogen transfer between an amino group in close proximity to an imino group, namely azophenine. The work presented here is preliminary work on a project aimed at expanding the utility of this new tautomeric switching moiety to other species. Low temperature scanning tunneling microscopy (LT-STM) data of a switching aminotroponimine derivative will be presented. When adsorbed on a Au(111) surface, bistability in the tunneling current measured through the molecule is observed both when the molecule is isolated and in close-packed configurations. We seek to understand the mechanism for this behavior through temperature dependent and spectroscopic STM measurements.

[1] G. J. Simpson, S. W. L. Hogan, M. Caffio, C. J. Adams, H. Früchtl, T. van Mourik and R. Schaub, Nano Lett., 2014, 14, 634–639

24 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

P06. Recent technology advancements in SPM based electrical probing at low temperatures

B Piglosiewicz, M Maier, J Köble, J Chrost and A Ettema

Scienta Omicron GmbH, Germany

A major challenge in the development of novel devices in nano- and molecular electronics is their interconnection with larger scaled electrical circuits. Local electrical probing by multiple probes with precision on the atomic scale can significantly improve efficiency in analyzing electrical properties of individual structures on the nano-scale without the need of a full electrical integration.

The LT NANOPROBE is a dedicated microscope stage that merges the requirements of a SEM navigated 4-probe STM and at the same time satisfies the needs for high performance SPM. Besides SEM/SPM probe fine navigation, the excellent STM/NC-AFM imaging performance with atomic resolution at T<5K, expands applications to tunneling spectroscopy and even the creation of atomically precise structures. We will present measurements that prove the performance level of the instrument, specifically the low thermal drift, which allows for sufficient measurement time on extremely small structures as well as QPlus AFM measurements, which become important if nanostructures are deposited on an insulating substrate for a better electrical decoupling. We will also show the newest technology improvements and challenges as well as application and scientific drivers for this type of scientific instrumentation.

a) STM atom manipulation on Au(111) @ T<5K. Data Courtesy by Ch. Joachim et al., PicoLab, CNRS, France

b) Drift measurements STM on Au(111) @ T<5K. Image size 20 nm2 , Ugap = 0.5 V, IT = 0.5 nA. Total measurement time of approx. 2hrs, resulting in a lateral drift < 1.3Å/h

c) Picture of the LT NANOPROBE stage, showing thermal shields, spring suspension, and 4 dedicated shared stack SPM scanners

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P07. qPlus® NC-AFM and STM imaging of C60 encapsulated H2O molecules

S Taylor1, S P Jarvis1, S Mamone2, B Meier2, A J Horsewill1, R J Whitby2, M H Levitt2 and P Moriarty1 1University of Nottingham, UK, 2University of Southampton, UK

The encapsulation of molecules within a C60 cage provides a unique opportunity to study their properties unperturbed by interactions with the environment. Encapsulating H2O within a C60 molecule provides an ideal system to isolate and study a single water molecule due to its weak interaction with the C60 cage. Here we present an extensive STM/NC-AFM investigation of sub-monolayer and multilayer H2O@C60 molecules on the Cu(111) surface. By controlling the filling factor of the C60 cage we investigate a mixed film of both empty C60 and the filled H2O@C60. We find that, despite reports of significant changes in the electronic structure of the C60 cage due to the encapsulated water1, the appearance of both filled and empty molecules is very similar.

[1] B. Ensing et. al, J. Phys. Chem. A, 116, 12184 (2012)

P08. A combined Monte Carlo and Hückel theory simulation of C60 molecular rotations in C60 assemblies on Cu(111), Au(111) and NaCl

J Leaf, A Stannard, S Jarvis, P Moriarty and J Dunn

University of Nottingham, UK

Orientational order of C60 molecules within monolayer and multilayer islands is a regularly observed phenomenon in STM studies1. Here, these rotational structures are simulated via a novel use of Monte Carlo and Hückel theory methods. A unitless repulsive interaction energy between two adjacent molecules is pre-calculated for every possible combination of molecular orientations. Repulsive intermolecular interaction energies are calculated by integrating the repulsive electron density overlap between the two molecules. These energies are then inputted into a simulated C60 island where the molecules positions are fixed, but are allowed to rotate freely. A variety of different substrates have been simulated with varying surface interaction strengths. Results show significant correlation with observed features in both mono and multilayered islands (Fig. 1).

Fig. 1: A 10 x 10 simulation is compared to two STM images and similar features identified

[1] F. Rossel, et. al. Phys.Rev. B, vol. 84, no. 7, 2011

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P09. Structure determination of Au on Pt(111) surface: LEED, STM and DFT study

A Krupski

University of Portsmouth, UK

Low-energy electron diffraction (LEED), scanning tunnelling microscopy (STM) and density functional theory (DFT) calculations have been used to investigate the atomic and electronic structure of gold deposited (between 0.8 and 1.0 monolayer) on the Pt(111) face in ultrahigh vacuum at room temperature1. The analysis of LEED and STM measurements indicates two-dimensional growth of the first Au monolayer. Change of the measured surface lattice constant equal to 2.80 Å after Au adsorption was not observed. Based on DFT, the distances between the nearest atoms in the case of bare Pt(111) and Au/Pt(111) surface equal to 2.83 Å, which gives 1% difference in comparison with STM values. The first and second interlayer spacings of the clean Pt(111) surface are expanded by +0.87% and contracted by -0.43%, respectively. The adsorption energy of the Au atom on the Pt(111) surface is dependent of the adsorption position, and there is a preference for a hollow fcc site. For the Au/Pt(111) surface the top interlayer spacing is expanded by +2.16% with respect to the ideal bulk value. Changes in the electronic properties of the Au/Pt(111) system below the Fermi level connected to the interaction of Au atoms with Pt(111) surface are observed.

[1] K. Krupski, M. Moors, P. Jóźwik, T. Kobiela, A. Krupski, Materials (2015) 8(6), 2935-2952

P10. Mechanochemical manipulation of Pb dimers on Si (100)

I Lekkas, A Sweetman and P Moriarty

University of Nottingham, UK

Semiconducting substrates, particularly silicon, are the bedrock of the micro-/nanoelectronics industry. Consequently, there is an exceptionally strong drive to develop atomically precise protocols for the modification and control of semiconductor surfaces (and devices based on those surfaces). Particularly impressive levels of precision using scanning tunnelling microscope (STM)-driven surface medication have recently been achieved by, for example, Simmons et al. who have used hydrogen atom desorption from the H:Si(100) surface to realise atomic wires and single atom transistors1,2.

As compared to STM, NC-AFM enables manipulation of semiconductor surfaces using purely mechanical – or, more accurately, mechanochemical – force. This has a number of potential advantages over STM-driven protocols which often involve relatively high current densities and/or electric fields. A number of years ago our group demonstrated that it was possible to toggle the bond angle (i.e. the conformation) of silicon dimers on Si(100) using an NC-AFM probe3. Here we discuss the extension of NC-AFM manipulation to a heterodimer, namely Pb-Si(100). The introduction of Pb, which has a much larger covalent radius than silicon, enables the effects of strain and steric hindrance to be explored in the context of mechanochemical manipulation at the single bond level.

Juré et al.4 have previously used STM to study the Pb/Si(100) system, where the Pb atoms form dimer chains on the underlying Si dimer rows (Fig1 a). We have used a combination of NC-AFM imaging and spectroscopy to explore the extent to which a Pb dimer can be controllably manipulated parallel, and perpendicular to the Si(100) rows using the NC-AFM tip (Fig. 1(b), (c), (d)). We will discuss the central influence of the tip apex on the manipulation process.

UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy 27

Figure 1: Pb dimer and Pb dimer chain on Si(100). a) STM image; b) AFM constant Δf image showing the lateral manipulation of the Pb dimer; c) similar manipulation to (b) in over a shorter distance; d) Pb dimer manipulation along the Si(100) rows and e) Final image of extended Pb chain.

[1] B. Weber et al. - Science.(6064), 64-67 (2012) [2] M. Fuechsle et al. - Nature Nanotechnology, 7(4), 242–246 (2012) [3] Sweetman et al. - Phys. Rev. Lett. 106 136101 (2011) [4] Juré L. et al. Phys. Rev. B, 61(24), 902–910 (2000)

P11. Templating of electronically decoupled molecules using domain boundaries of the 2D material silicene on ZrB2

B Warner1, T G Gill1,2, A Fleurence2, Y Yamada-Takamura2 and C F Hirjibehedin1

1University College London, UK, 2Japan Advanced Institute of Science and Technology (JAIST), Japan

In order for molecular electronics to become a reality, it will be necessary to electrically contact single molecules, a process that will require precise control of the position of molecules on a surface1. One method for achieving this is to exploit spatial variations in the interactions between molecules and surfaces to produce a nanoscale template2. However, a careful balance in the strength of the interaction between the molecule and the substrate is necessary because in addition to controlling the confinement the interaction can also destroy the functionality of the molecule3. An ideal surface for templating single molecules is therefore one that couples to the molecule strongly enough to control its position4,5 but weakly enough to retain single molecule functionality.

In this work, we utilise the striped domains of silicene on ZrBr2 to template linear arrays of molecules. Silicene, the silicon analogue of graphene, is a particularly interesting 2D material because it may be possible to easily integrate it with current silicon based technology6. STM measurements of iron phthalocyanine (FePc) molecules on silicene allow for the binding configuration to be measured and show that molecules stick to the edges of the stripe domains, enabling the formation of linear chains that remain stable up to room temperature. Through the use of

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both bias dependent imaging and spatially resolved STM-based spectroscopic measurements, we resolve the frontier orbitals of the molecules, suggesting that these orbitals are only weakly electronically coupled to the surface and underlying conducting substrate3,4,7. This work demonstrates that silicene on ZrB2 can be used to pin molecules in well-ordered configurations at room temperature while retaining their single molecule functionality, thus satisfying the conditions for an ideal molecular template4,5.

Room temperature STM topographic image of FePc on silicene on ZrB2. STM topographic images show that FePc is pinned to the domain boundaries forming chains at room temperature. (Vset = ‐1.0V, Iset = 1.0 nA)

[1] Joachim et. al., Nature. 408, 541-‐‐448, (2000). [2] Corso et. al., Science, 303, 217–220, (2004). [3] Repp et. al., Phys, Rev. Letts, 94, 026803, (2005). [4] Münnich et. al., J. Appl .Phys., 112, 034312, (2012). [5] Dil et. al., Science, 319, 1824–1826, (2008). [6] Tao et al., Nature Nano., 10, 227 –231, (2015). [7] Sessi et. al., Nano Letts., 14, 5092–5096, (2014).

UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy 29

Notes

30 UK–Japan Symposium on Atomic and Molecular Manipulation: Force and Tunnel Current in Scanning Probe Microscopy

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