N-heterocyclic carbenes (NHCs) continue to attract interest as ligands for self-assembled monolayers on metals due to their propensity to form strong bonds to a variety of metals. However, understanding of the effect of NHC structural elements on adsorption geometry, NHC mobility, and on-surface intermolecular interactions remains limited. Herein, we report the self-assembly of 1,3-diisopropyl imidazolylidene I-NHC iPr on the Au(111) surface. This relatively simple NHC has never previously been examined on Au surfaces experimentally. We combine scanning tunnelling microscopy (STM) and density functional theory (DFT) calculations to provide detailed insight into this NHC-based SAM, which is the densest packed NHC-based SAM reported to date, utilizing approximately 14.5% of the available binding sites of the Au(111) surface. STM interrogations of the surface show the occasional formation of brighter adsorbates that we suggest can be attributed to metalation at the backbone C-4, rather than the expected C-2 site. This type of '' abnormal '' or mesoionic bonding mode is commonly observed in related organometallic compounds, suggesting that such complexes can provide a useful analogy for surface reactivity. The high density of the I-NHC iPr SAM and the generally high thermal and chemical robustness of NHC-based SAMs make this molecule ideally suited for a range of applications, providing an exciting platform for more complex surface functionalization.

N-Heterocyclic carbenes (NHCs) that have wingtip groups with low steric bulk, such as 1,3-dimethyl-benzimidazol-2-ylidene (NHCMe), form bis-complexes with metal atoms when they are deposited onto Au(111) surfaces in vacuo. These complexes self-assemble into three different lattices: a herringbone, a double-herringbone, and a chiral kagome lattice. The static properties of these lattices have been studied with scanning tunneling microscopy and ab initio theoretical methods. Dynamic processes including complex center displacement and hindered monomer motion have also been observed. Our results suggest that in addition to surface hopping, exchange processes are important, providing a facile mechanism for atom exchange between the overlayer and the metal. These dynamic processes are well-known from studies of metal epitaxy but have not previously been discussed in the context of NHC self-assembly.

We investigated physics students' learning experience and behaviour in a second-year laboratory by analyzing transcribed audio recordings of laboratory sessions. One student group was given both a problem and procedure and asked to analyze and explain their results. Another was provided with only the problem and asked to design and execute the experiment, interpret the data, and draw conclusions. These two approaches involved different levels of student inquiry and they have been described as guided and open inquiry respectively. The latter gave students more opportunities to practice designing experiments, one of the six major learning outcomes in the recommendations for the undergraduate physics laboratory curriculum by the American Association of Physics Teachers (AAPT). Qualitative analysis was performed of the audio transcripts to identify emergent themes and it was augmented by quantitative analysis for a richer understanding of students' experiences. An important finding is that significant improvements can be made to undergraduate laboratories impacting both student learning experience and behaviour by increasing the level of inquiry in laboratory experiments. This is most easily achieved by requiring students to design their own experimental procedures.

The production of ordered arrays of organic molecules onmetallic surfaces by means of self-assembly is one of themost powerful methods for controlled patterning on thenanometer scale. Although the self-assembly of sulfurbased ligands has been studied for decades, the thermaland oxidative instability of these systems introduceschallenges in many potential applications. In recentyears, it has been shown that a new ligand class,N-heterocyclic carbenes (NHCs), bind to metal surfacesvia a metal–carbon covalent bond, resulting inmonolayers with much greater stability. However,fundamental questions surrounding self-assembly in thisnew ligand class remain unanswered, including the simplequestions of what controls NHC orientation on thesurface and under what conditions they self-assemble.Herein we describe how NHC structure, surface density,deposition temperature, and annealing temperaturecontrol mobility, thermal stability, NHC surfacegeometry, self-assembly, and the exact chemical nature ofthe surface structures. These data provide the first generalset of guidelines to enable the rational design of highlyordered NHC-based monolayers. Considering that NHCsmay supplant thiols as the functionalization agent ofchoice in a wide range of applications, a detailedunderstanding of their surface chemistry is crucial for thesuccess of these next-generation monolayers.

It has recently been demonstrated that N-heterocyclic carbenes (NHCs) form self-assembled monolayers (SAMs) on metal surfaces. Consequently, it is important to both characterize and understand their binding modes to fully exploit NHCs in functional surface systems. To assist with this effort, we have performed first-principles total energy calculations for NHCs on Au(111) and simulations of X-ray absorption near edge structure (XANES). The NHCs we have considered are N,N-dimethyl-, N,N-diethyl-, N,N-diisopropylbenzimidazolylidene (BNHCX, with X = Me, Et, and iPr, respectively) and the bis-BNHCX-Au complexes derived from these molecules. We present a comprehensive analysis of the energetic stability of both the BNHCX and the complexes on Au(111) and, for the former, examine the role of the wing group in determining the attachment geometry. Further structural characterization is performed by calculating the nitrogen K-edge X-ray absorption spectra. Our simulated XANES results give insight into (i) the relationship between the BNHCX/Au geometry and the N(1s) → π*/σ*, pre-edge/near-edge, absorption intensities, and (ii) the contributions of the molecular deformation and molecule-surface electronic interaction to the XANES spectrum. These simulated spectra work not only as a map to the BNHCX conformation, but also, combined with electronic structure calculations, provide a clear understanding of recent experimental XANES findings on BNHCX/Au.

The interplay of adsorption geometry and interface dipoles of the transition-metal complex Ir(ppy)3 on Cu(111) was studied using low-temperature scanning probe microscopy and density-functional-theory calculations. We find that the orientation of the molecule's intrinsic dipole moment with respect to the surface has a strong influence on the total energy of the different configurations, where the most stable one has the molecular dipole moment pointing out of the surface plane along the surface normal. Adsorption-induced redistribution of charges results in an additional dipole moment that also points out of the surface plane for all configurations. Submolecularly resolved maps of the resulting local contact potential difference suggest that any in-plane dipole moment is very effectively screened.

The formation of organic films on gold employing N-heterocyclic carbenes (NHCs) has been previously shown to be a useful strategy for generating stable organic films. However, NHCs or NHC precursors typically require inert atmosphere and harsh conditions for their generation and use. Herein we describe the use of benzimidazolium hydrogen carbonates as bench stable solid precursors for the preparation of NHC films in solution or by vapour-phase deposition from the solid state. The ability to prepare these films by vapour-phase deposition permitted the analysis of the films by a variety of surface science techniques, resulting in the first measurement of NHC desorption energy (158±10 kJ mol −1 ) and confirmation that the NHC sits upright on the surface. The use of these films in surface plasmon resonance-type biosensing is described, where they provide specific advantages versus traditional thiol-based films.

We report first-principles calculations of the energetic stability and electronic properties of metalphthalocyanine (MPc) molecules (M = Cr, Mn, Fe, Co, Ni, Cu, and Zn) adsorbed on the delta-doped Si(111)-B( root 3 x root 3) reconstructed surface. (i) It can be seen that CrPc, MnPc, FePc, and CoPc are chemically anchored to the topmost Si atom. (ii) Contrastingly, the binding of the NiPc, CuPc, and ZnPc molecules to the Si(111)-B(root 3 x root 3) surface is exclusively ruled by van der Waals interactions, the main implication being that these molecules may diffuse and rearrange to form clusters and/or self-organized structures on this surface. The electronic structure calculations reveal that in point (i), owing to the formation of the metal-Si covalent bond, the net magnetic moment of the molecule is quenched by 1 mu(B), remaining unchanged in point (ii). In particular, the magnetic moment of CuPc (1 mu(B)) is preserved after adsorption. Finally, we verify that the formation of ZnPc, CuPc, and NiPc molecular (self-assembled) arrangements on the Si(111)-B(root 3 x root 3) surface is energetically favorable, in good agreement with recent experimental findings.

The B/Si(1 1 1)- (√3 x √3)R30° surface reconstruction has recently been used as a platform for supramolecular assembly. However, our understanding of the native defects in this delta-doped system and their corresponding scanning tunnelling microscopy (STM) signatures is incomplete. So we have studied this system using ab initio total energy calculations and scanning tunneling microscopy. We find that although perturbations to the equilibrium geometry of the surface are in general weak, the perturbations to the electronic structure can be quite strong due to the presence of dangling bonds composed of Si-3p(z) orbitals. Additionally, we propose a possible structure for a previously unidentified defect that appears in positive bias constant-current STM images as an equilateral triangular arrangement of Si adatoms with attenuated intensity.

Nature Chemistry 6, 409–414 (2014); published online 23 March 2014; corrected after print 21 May 2014.10.1038/nchem.1891 In the version of this Article originally published, ref. 40 was incorrect, it should have read: Rodríguez-Castillo, M. et al. Reactivity of gold nanoparticles towards N-heterocyclic carbenes.

We have studied the near surface defects of the delta-doped B:Si(111)-(√3 × √3)R30° system using a combination of scanning tunneling microscopy, non-contact atomic force microscopy, Kelvin probe force spectroscopy, total energy DFT, and STM theoretical simulations. We positively identify and characterize two near surface defects: the adatom vacancy and a B substitutional defect located in the second Si bilayer. We also confirm the assignment of the dangling-bond defect. Additionally, the influence that the subsurface B dopants have on the surface electronic structure, the modulation of the surface potential and the chemical activity of the surface is investigated.

In this paper, we show that simultaneous noncontact atomic force microscopy (nc-AFM) and scanning tunneling microscopy (STM) is a powerful tool for molecular discrimination on the Si(111)-7 × 7 surface, even at room temperature. Using density functional theory modeling, we justify this approach and show that the force response allows us to distinguish straightforwardly between molecular adsorbates and common defects, such as vacancies. Finally, we prove that STM/nc-AFM method is able to determine attachment sites of molecules deposited on semiconductor surface at room temperature.

Because of their compact form factor and rigidity, piezoelectric motors are used in scanning probe microscopes that operate at low temperature and high magnetic field. Here we present detailed information to facilitate the assembly, operation, and characterization of inertial motors. Specifically, a model of the motor is developed and used to identify different regions of operation. Drive electronics with high slew rate and large output current are described and a step-by-step procedure for assembling piezoelectric shear stacks is detailed. Additionally, a novel reflective object sensor is described and used to characterize a Pan-style inertial motor that was designed and assembled using the concepts presented in this paper.

The most commonly occurring boundary separating Ge-5 x 5 domains grown on Si(111) is the B[(2) over bar 2] domain boundary. We demonstrate that this boundary can be used to template one-dimensional arrays of identical In and Ga magic clusters with a lattice constant of 3.3 nm. This is larger than the lattice constant of the two-dimensional magic cluster arrays templated by the Si(111)-7 x 7 surface reconstruction (2.7 nm), although the magic clusters have the same structure. We also demonstrate that a necessary condition for cluster growth at the domain boundary is the presence of faulted dimer-adatom-stacking-fault-7 x 7 half unit cells. The relatively unexplored possibility of exploiting the unique structural and electronic properties of domain boundaries in nanostructured materials is discussed.

The Si(111)-7 x 7 surface reconstruction can be used to template an array of mesitylene (1,3,5-trimethylbenzene) molecules in which each molecule bridges a corner Si adatom and a neighboring Si rest atom. The molecules adsorb in corner sites to minimize a weak steric interaction associated with nearest-neighbor bridging sites. We demonstrate that the formation of the molecular array can be blocked by adding submonolayer amounts of Ge to the surface. The Ge atoms block the formation of the array because they substitute preferentially for Si adatoms located in corner sites, and the Ge-C bond strength is approximate to 0.8 eV weaker than the Si-C bond strength.

We present a theoretical investigation of the influence of domain boundaries on the Ge/Si(111)-5 × 5 phase using both large-scale DFT simulations and an analytical model. It is shown that different boundary types modify the atomic and electronic structure of the adjoining 5 × 5 domains in very different ways. A simple theoretical model, that describes the energy interaction J between the boundaries and the 5 × 5 phase, is presented and the interaction energy decay J(x) ≈ x(-n) for different domain boundaries is estimated. Additionally, the influence of the boundaries on the atomic and electronic structure of adatoms in the parental 5 × 5 phase is analyzed and it is argued that the presence of domain boundaries may strongly affect not only the physical but also the chemical properties of the Ge/Si(111)-5 × 5 phase.

We show that the Si(111)-7 x 7 surface reconstruction can be used to template an ordered array of 1,3,5-trimethyl benzene (mesitylene) molecules. The disorder that normally derives from the multiplicity of admissible adsorption geometries, for small aromatic molecules on 7 x 7, is suppressed, and the molecules are found to occupy both halves of the 7 x 7 unit cell with equal probability. It is argued that a steric interaction, associated with the methyl groups, hinders nearest neighbor adsorption and this leads to the formation of an array that has the molecules at the corners of the 7 x 7 half unit cells. To understand the ordering kinetics we used: scanning tunneling microscopy to study site occupancy as a function of coverage, ab initio total energy calculation to study the stability of the attachment sites and kinetic Monte Carlo modeling to investigate the emergence of translational order in the overlayer.[GRAPHICS]When two mesitylene molecules adsorb in nearest neighbor bridging geometries on the 7 x 7 reconstruction, the hydrogen atoms located on the methyl groups interact. To reduce the interaction energy, the molecules form an ordered array that places each molecule at the corner of the half cell. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We demonstrate that nearest neighbor molecular adsorption can be sterically hindered on the Si(111)-7×7 surface reconstruction. This breaks the energetic equivalence of corner and edge di-σ attachment geometries and allows a translationally ordered organic layer to be templated directly on the 7×7 reconstruction.

The adsorption of ethylene on the bridge adatom-restatom position of the Si(111)-7 x 7 surface was studied with scanning tunneling microscopy, photoelectron spectroscopy, and theoretical calculations. The electronic structure and the corresponding vibrational states were calculated for a single molecule adsorbed in different binding sites located within the 7 x 7 unit cell. We found that there is no significant difference in the electronic structure between the absorption sites that were considered: center and corner adatom-restatom. Moreover, the different electron occupation of the restatoms and adatoms has a strong effect on the electronic structure of the adsorbed molecule near the Fermi level, and this leads to the reduction of the molecular symmetry to C-s or even to C-1. In the case of the Si 2p core level, beside the previously reported continuous quenching of the restatom state, we found clear evidence of existence of a peak corresponding to the Si-C bond separated by 044 eV from the bulk component Furthermore, for the vibrational analysis, isotopic substitution of C2H4 with C2D4, gave Us More insight into the correct assignment of the modes in the experiment. Specifically; exceptional care Must be taken with the allocation of the C-H wagging, twisting, and C-C stretching modes.

We demonstrate that the Si(111)-7 x 7 surface reconstruction can be used to template an ordered array of 1,3,5-methyl benzene molecules that are uniformly distributed over both the faulted and the unfaulted halves of the 7 x 7 unit cell by covalent attachment in vacuo. An intermolecular steric interaction, which hinders nearest-neighbor adsorption, is shown to play an important role in the formation of the ordered array. The stable equilibrium structure is shown to be one where the molecules are located at the corner of the half unit cells maximizing the intermolecular separation. In addition to the intermolecular steric interaction, there is an interaction between the molecule and the surface that plays a important role in reducing disorder in the array. Moreover, as the coverage is increased, there is a switch in site preference, from edge to corner, that mitigates the effect of the intermolecular interaction. To investigate this system we used scanning tunneling microscopy to study site occupancy as a function of coverage, ab initio total energy calculation to study the stability of the attachment sites, and Monte Carlo modeling to examine the emergence of translational order in the overlayer. The switch in site preference from edge to corner is faithfully reproduced by the kinetic Monte Carlo model when an interaction term is included.