The electronic properties and the function of hybrid inorganic-organic systems (HIOS) are intimately linked to their interface geometry. Here we show that the inclusion of the many-body collective response of the substrate electrons inside the inorganic bulk enables us to reliably predict the HIOS geometries and energies. This is achieved by the combination of dispersion-corrected density-functional theory (the DFT+ van der Waals approach) [Phys. Rev. Lett. 102, 073005 (2009)], with the Lifshitz-Zaremba-Kohn theory for the nonlocal Coulomb screening within the bulk. Our method yields geometries in remarkable agreement (≈0.1 Å) with normal incidence x-ray standing wave measurements for the 3, 4, 9, 10-perylene-tetracarboxylic acid dianhydride (C(24)O(6)H(8), PTCDA) molecule on Cu(111), Ag(111), and Au(111) surfaces. Similarly accurate results are obtained for xenon and benzene adsorbed on metal surfaces.

Optoelectronic applications require materials both responsive to objective photons and able to transfer carriers, so new two-dimensional (2D) semiconductors with appropriate band gaps and high mobilities are highly desired. A broad range of band gaps and high mobilities of a 2D semiconductor family, composed of monolayer of Group 15 elements (phosphorene, arsenene, antimonene, bismuthene) is presented. The calculated binding energies and phonon band dispersions of 2D Group 15 allotropes exhibit thermodynamic stability. The energy band gaps of 2D semiconducting Group 15 monolayers cover a wide range from 0.36 to 2.62 eV, which are crucial for broadband photoresponse. Significantly, phosphorene, arsenene, and bismuthene possess carrier mobilities as high as several thousand cm(2)  V(-1)  s(-1) . Combining such broad band gaps and superior carrier mobilities, 2D Group 15 monolayers are promising candidates for nanoelectronics and optoelectronics.

The adsorption of aromatic molecules on metal surfaces plays a key role in condensed matter physics and functional materials. Depending on the strength of the interaction between the molecule and the surface, the binding is typically classified as either physisorption or chemisorption. Van der Waals (vdW) interactions contribute significantly to the binding in physisorbed systems, but the role of the vdW energy in chemisorbed systems remains unclear. Here we study the interaction of benzene with the (111) surface of transition metals, ranging from weak adsorption (Ag and Au) to strong adsorption (Pt, Pd, Ir, and Rh). When vdW interactions are accurately accounted for, the barrier to adsorption predicted by standard density-functional theory (DFT) calculations essentially vanishes, producing a metastable precursor state on Pt and Ir surfaces. Notably, vdW forces contribute more to the binding of covalently bonded benzene than they do when benzene is physisorbed.Comparison to experimental data demonstrates that some of the recently developed methods for including vdW interactions in DFT allow quantitative treatment of both weakly and strongly adsorbed aromatic molecules on metal surfaces, extending the already excellent performance found for molecules in the gas phase.

A nanostructured platform that combines electrospun TiO(2) nanofibers (TiNFs)-deposited substrate and cell-capture agent realizes significant capture of circulating tumor cells (CTCs). The enhanced local topographic interactions between the horizontally packed TiNFs deposited substrates and extracellular matrix scaffolds, in addition to anti-EpCAM/EpCAM biological recognition, contributes to the significantly enhanced capture efficiency compared to flat surfaces.

The adsorption of benzene on metal surfaces is an important benchmark system for hybrid inorganic/organic interfaces. The reliable determination of the interface geometry and binding energy presents a significant challenge for both theory and experiment. Using the Perdew-Burke-Ernzerhof (PBE), PBE+vdW (van der Waals) and the recently developed PBE+vdW surf (densityfunctional theory with vdW interactions that include the collective electronic response of the substrate) methods, we calculated the structures and energetics for benzene on transition-metal surfaces: Cu, Ag, Au, Pd, Pt, Rh and Ir. Our calculations demonstrate that vdW interactions increase the binding energy by more than 0.70 eV for physisorbed systems (Cu, Ag and Au) and by an even larger amount for strongly bound systems (Pd, Pt, Rh and Ir). The collective response of the substrate electrons captured via the vdW surf method plays a significant role for most substrates, shortening the equilibrium distance by 0.25 Å for Cu and decreasing the binding energy by 0.27 eV for Rh. The reliability of our results is assessed by comparison with calculations using the random-phase approximation including renormalized single excitations, often hard to interpret, or even lacking. For example, due to the relative difficulty of controlling and measuring weakly bound systems, no experimental adsorption height has been reported so far for Bz physisorbed on noble metals. The only experimentally deduced adsorption height, to the best of our knowledge, was determined for the disordered Bz chemisorbed on the Pt(111) surface at a coverage close to or less than one [36].The binding energy, which reflects the strength of the interaction between an adsorbate and the substrate, is another key parameter for the description of HIOS. Experimental binding energies are mainly obtained by temperature-programmed desorption (TPD) [22][23][24][25]27] and microcalorimetry measurements [32,[37][38][39]. TPD is the most extensively used method for determining the kinetic and thermodynamic parameters of desorption processes and decomposition reactions. The desorbing molecular species are selected by their mass, while the amount of adsorbate is determined by integrating the peaks of the desorption spectrum. The Redhead formula is typically used to calculate the adsorption energy based on three parameters: the desorption temperature, the heating rate and a pre-exponential factor [40]. The wide range of empirical pre-exponential factors (10 13 -10 19 s −1 ) that are typically used for molecular desorption may cause a notable uncertainty in the determined binding energy [41][42][43]. TPD experiments have been carried out to study the interaction of Bz with the Cu [13], Ag [24] and Au surfaces [29]. However, special attention must be paid to the interpretation of TPD spectra for the Pd, Pt and Rh surfaces, because the adsorbed Bz molecules may decompose during heating, in particular at low coverage [44]. Here, we revisit the adsorption energies from the measured TPD spectra for Bz on Cu(111), A...

Exploring the role of van der Waals (vdW) forces on the adsorption of molecules on extended metal surfaces has become possible in recent years thanks to exciting developments in density functional theory (DFT). Among these newly developed vdW-inclusive methods, interatomic vdW approaches that account for the nonlocal screening within the bulk [V. G. Ruiz, W. Liu, E. Zojer, M. Scheffler, and A. Tkatchenko, Phys. Rev. Lett. 108, 146103 (2012)] and improved nonlocal functionals [J. Klimeš, D. R. Bowler, and A. Michaelides, J. Phys.: Condens. Matter 22, 022201 (2010)] have emerged as promising candidates to account efficiently and accurately for the lack of long-range vdW forces in most popular DFT exchange-correlation functionals. Here we have used these two approaches to compute benzene adsorption on a range of close-packed (111) surfaces upon which it either physisorbs (Cu, Ag, and Au) or chemisorbs (Rh, Pd, Ir, and Pt). We have thoroughly compared the performance between the two classes of vdW-inclusive methods and when available compared the results obtained with experimental data. By examining the computed adsorption energies, equilibrium distances, and binding curves we conclude that both methods allow for an accurate treatment of adsorption at equilibrium adsorbate-substrate distances. To this end, explicit inclusion of electrodynamic screening in the interatomic vdW scheme and optimized exchange functionals in the case of nonlocal vdW density functionals is mandatory. Nevertheless, some discrepancies are found between these two classes of methods at large adsorbate-substrate separations.

ConspectusThe understanding of adsorption and reactions of (large) organic molecules at metal surfaces plays an increasingly important role in modern surface science and technology. Such hybrid inorganic/organic systems (HIOS) are relevant for many applications in catalysis, light-emitting diodes, single-molecule junctions, molecular sensors and switches, and photovoltaics. Obviously, the predictive modeling and understanding of the structure and stability of such hybrid systems is an essential prerequisite for tuning their electronic properties and functions. At present, density-functional theory (DFT) is the most promising approach to study the structure, stability, and electronic properties of complex systems, because it can be applied to both molecules and solids comprising thousands of atoms. However, state-of-the-art approximations to DFT do not provide a consistent and reliable description for HIOS, which is largely due to two issues: (i) the self-interaction of the electrons with themselves arising from the Hartree term of the total energy that is not fully compensated in approximate exchange-correlation functionals, and (ii) the lack of long-range part of the ubiquitous van der Waals (vdW) interactions. The self-interaction errors sometimes lead to incorrect description of charge transfer and electronic level alignment in HIOS, although for molecules adsorbed on metals these effects will often cancel out in total energy differences. Regarding vdW interactions, several promising vdW-inclusive DFT-based methods have been recently demonstrated to yield remarkable accuracy for intermolecular interactions in the gas phase. However, the majority of these approaches neglect the nonlocal collective electron response in the vdW energy tail, an effect that is particularly strong in condensed phases and at interfaces between different materials.Here we show that the recently developed DFT+vdWsurf method that accurately accounts for the collective electronic response effects enables reliable modeling of structure and stability for a broad class of organic molecules adsorbed on metal surfaces. This method was demonstrated to achieve quantitative accuracy for aromatic hydrocarbons (benzene, naphthalene, anthracene, and diindenoperylene), C60, and sulfur/oxygen-containing molecules (thiophene, NTCDA, and PTCDA) on close-packed and stepped metal surfaces, leading to an overall accuracy of 0.1 Å in adsorption heights and 0.1 eV in binding energies with respect to state-of-the-art experiments. An unexpected finding is that vdW interactions contribute more to the binding of strongly bound molecules on transition-metal surfaces than for molecules physisorbed on coinage metals. The accurate inclusion of vdW interactions also significantly improves tilting angles and adsorption heights for all the studied molecules, and can qualitatively change the potential-energy surface for adsorbed molecules with flexible functional groups. Activation barriers for molecular switches and reaction precursors are modified as well.

We measured the adsorption geometry of single molecules with intramolecular resolution using noncontact atomic force microscopy with functionalized tips. The lateral adsorption position was determined with atomic resolution, adsorption height differences with a precision of 3 pm, and tilts of the molecular plane within 0.2 . The method was applied to five -conjugated molecules, including three molecules from the olympicene family, adsorbed on Cu(111). For the olympicenes, we found that the substitution of a single atom leads to strong variations of the adsorption height, as predicted by state-ofthe-art density-functional theory, including van der Waals interactions with collective substrate response effects. DOI: 10.1103/PhysRevLett.111.106103 PACS numbers: 68.37.Ps, 34.20.Gj, 68.35.Àp, 68.43.Àh In noncontact atomic force microscopy (AFM), the crucial factors affecting the image contrast are the chemical interaction between probe and sample [1], the tip termination [2][3][4], and the adsorbate geometry [5]. For organic molecules on metal substrates, the adsorption geometry (adsorption site, height, tilt) is intimately linked to the electronic properties of the adsorbate and the interaction between adsorbate and substrate [6]. In other words, the adsorption geometry is a direct indicator of the adsorbatesubstrate interaction. The adsorption height of molecules above the substrate is traditionally measured using the x-ray standing wave method (XSW) [7,8]. While the XSW allows us to determine the adsorption height with high precision and chemical sensitivity, it does not (yet) provide information about the lateral adsorption position or tilt angle. Because XSW values are averaged over large ensembles, individual molecules are not distinguished. In contrast, using scanning probe microscopy, molecules are treated individually, and therefore the molecular adsorption geometry can be measured as a function of molecular conformation [5] or the adsorption site [9]. The adsorption site of single adsorbates can be determined by scanning tunneling microscopy (STM) using marker atoms [10,11] or inelastic electron tunneling spectroscopy [12] or by directly resolving substrate and adsorbate by AFM [5,13,14]. However, to date, adsorption heights could not be quantified by scanning probe microscopy.In this Letter, we present a novel experimental approach to extract the molecular adsorption geometry in full detail by AFM and compare our results to densityfunctional theory (DFT) calculations. First, the method of determining heights is exemplified for pentacene and diindeno½1; 2; 3-cd : 1 0 ; 2 0 ; 3 0 -lmperylene (DIP), and the role of our tip termination, carbon monoxide (CO) and Xe, is discussed. Thereafter, we apply the method to three molecules of the olympicene family, 6H-benzo[cd]pyrene (olympicene), benzo[cd]pyrene (radical), and 6H-benzo[cd]pyren-6-one (ketone), which differ in their chemical structure only by one atom. Finally, adsorption sites of the olympicenes are determined by atomically resolving the substrate an...