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High carrier mobility and uniform device performance are of crucial importance for organic field-effect transistor (OFET)-based device and integrated circuit applications. However, strategies for achieving high device performance with small variations from batch to batch are still desired. Here, we report a thin liquid crystal-like film of 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (dif-TES-ADT) grown on a N,N′-ditridecylperylene-3,4,9,10-tetra-carboxylic diimide (PTCDI-C13) template, confirmed by atomic force microscopy and polarized fluorescence microscopy. The liquid crystal-like films with large crystalline domains are further employed as carrier transport channels for OFETs. As a result, we achieved high-performance OFETs with a saturation carrier mobility of 1.62 ± 0.26 cm2 V−1 s−1 and a small variation of 16% among three batches. This finding provides a new strategy to design materials and device structures to simultaneously achieve high carrier mobility and device uniformity.

Non-contact atomic force microscopy (AFM) with CO-functionalized tips allows visualization of the chemical structure of adsorbed molecules and identify individual inter- and intramolecular bonds. This technique enables in-depth studies of on-surface reactions and self-assembly processes. Herein, we analyze the suitability of qPlus sensors, which are commonly used for such studies, for the application of modern multifrequency AFM techniques. Two different qPlus sensors were tested for submolecular resolution imaging via actuating torsional and flexural higher eigenmodes and via bimodal AFM. The torsional eigenmode of one of our sensors is perfectly suited for performing lateral force microscopy (LFM) with single bond resolution. The obtained LFM images agree well with images from the literature, which were scanned with customized qPlus sensors that were specifically designed for LFM. The advantage of using a torsional eigenmode is that the same molecule can be imaged either with a vertically or laterally oscillating tip without replacing the sensor simply by actuating a different eigenmode. Submolecular resolution is also achieved by actuating the 2nd flexural eigenmode of our second sensor. In this case, we observe particular contrast features that only appear in the AFM images of the 2nd flexural eigenmode but not for the fundamental eigenmode. With complementary laser Doppler vibrometry measurements and AFM simulations we can rationalize that these contrast features are caused by a diagonal (i.e. in-phase vertical and lateral) oscillation of the AFM tip.

QPlus sensors are non-contact atomic force microscope probes constructed from a quartz tuning fork and a tungsten wire with an electrochemically etched tip. These probes are self-sensing and offer an atomic-scale spatial resolution. Therefore, qPlus sensors are routinely used to visualize the chemical structure of adsorbed organic molecules via the so-called bond imaging technique. This is achieved by functionalizing the AFM tip with a single CO molecule and exciting the sensor at the first vertical cantilever resonance mode. Recent work using higher-order resonance modes has also resolved the chemical structure of single organic molecules. However, in these experiments, the image contrast can differ significantly from the conventional bond imaging contrast, which was suspected to be caused by unknown vibrations of the tip. This work investigates the source of these artefacts by using a combination of mechanical simulation and laser vibrometry to characterize a range of sensors with different tip wire geometries. The results show that increased tip mass and length cause increased torsional rotation of the tuning fork beam due to the off-center mounting of the tip wire, and increased flexural vibration of the tip. These undesirable motions cause lateral deflection of the probe tip as it approaches the sample, which is rationalized to be the cause of the different image contrast. The results also provide a guide for future probe development to reduce these issues.

The synthesis of cycloarenes in solution is challenging because of their low solubility and the often hindered cyclodehydrogenation reaction of their nonplanar precursors. Using an alternative on-surface synthesis protocol, we achieved an unprecedented double-stranded hexagonal cycloarene containing 108 sp2 carbon atoms. Its synthesis is based on hierarchical Ullmann coupling and cyclodehydrogenation of a specially designed precursor on a Au(111) surface. The structure and other properties of the cycloarene are investigated by scanning tunneling microscopy/spectroscopy, atomic force microscopy, and density functional theory calculations.

Various two-dimensional (2D) carbon allotropes with nonalternant topologies, such as pentaheptites and phagraphene, have been proposed. Predictions indicate that these metastable carbon polymorphs, which contain odd-numbered rings, possess unusual (opto)electronic properties. However, none of these materials has been achieved experimentally due to synthetic challenges. In this work, by using on-surface synthesis, nanoribbons of the nonalternant graphene allotropes, phagraphene and tetra-penta-hepta(TPH)-graphene, have been obtained by dehydrogenative C-C coupling of 2,6-polyazulene chains. These chains were formed in a preceding reaction step via on-surface Ullmann coupling of 2,6-dibromoazulene. Low-temperature scanning probe microscopies with CO-functionalized tips and density functional theory calculations have been used to elucidate their structural properties. The proposed synthesis of nonalternant carbon nanoribbons from the fusion of synthetic line-defects may pave the way for large-area preparation of novel 2D carbon allotropes.

Journal peer review information: Nature Communications thanks Mingdong Dong and other anonymous reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available., [EN] The structure and the role of the interfacial water in mediating the interactions of extended hydrophobic surfaces are not well understood. Two-dimensional materials provide a variety of large and atomically flat hydrophobic surfaces to facilitate our understanding of hydrophobic interactions. The angstrom resolution capabilities of three-dimensional AFM are exploited to image the interfacial water organization on graphene, few-layer MoS2 and few-layer WSe2. Those interfaces are characterized by the existence of a 2 nm thick region above the solid surface where the liquid density oscillates. The distances between adjacent layers for graphene, few-layer MoS2 and WSe2 are ~0.50 nm. This value is larger than the one predicted and measured for water density oscillations (~0.30 nm). The experiments indicate that on extended hydrophobic surfaces water molecules are expelled from the vicinity of the surface and replaced by several molecular-size hydrophobic layers., This work was funded by the European Research Council ERC-AdG-340177 (3DNanoMech) and the Ministerio de Economía, Industria y Competitividad (MAT2016-76507-R).

The chemical structure and orientation of molecules on surfaces can be visualized using low temperature atomic force microscopy with CO-functionalized tips. Conventionally, this is done in constant-height mode by measuring the frequency shift of the oscillating force sensor. However, this method is unsuitable for analyzing 3D objects. We are using the tunneling current to track the topography while simultaneously obtaining submolecular resolution from the frequency shift signal. Thereby, the conformation of 3D molecules and the adsorption sites on the atomic lattice can be reliably determined.

The bond imaging atomic force microscopy (AFM) technique has become an invaluable tool for studying organic molecules on surfaces. The key feature of this technique is the functionalization of the AFM-tip with a single CO molecule, which improves the lateral resolution and allows us to visualize the chemical structure of adsorbed organic molecules. Such experiments are usually performed at low temperatures in an ultrahigh vacuum environment in the frequency modulation (FM) mode. Here, we use the Q-controlled amplitude modulation (AM) mode for imaging organic molecules with CO-functionalized tips in constant-height mode. By reducing the effective quality factor (Qeff) of the sensor from about 20 000–30 000 to 1500–4000, we are able to image molecules with atomic resolution. Detailed instructions for determining the optimum Qeff and oscillation amplitude are given. To compare the phase and frequency shift images of the Q-controlled AM and the FM mode, we define an effective signal-to-noise ratio (SNR) that relates the observed contrast between the bonds and centers of imaged carbon rings to the noise in the respective image regions. This effective SNR is systematically analyzed in different regions of the imaged molecule for different oscillation amplitudes and average tip-substrate distances. By using appropriate imaging parameters, an increased effective SNR is achieved in the Q-controlled AM mode (on the order of 30–60%). This advantage over the conventional FM mode might, e.g., be used for increasing the experimental throughput.

Force microscope provides atomically resolved images of surfaces immersed in a liquid. The presence of different chemical species in the interface (cations, anions, water, neutral atoms) complicates the adscription of the observed features to a given species. We develop a 3D atomic force microscopy method to identify the cations adsorbed on a mica surface from a potassium chloride solution. The method is based on measuring the peak value of the attractive force within the Stern layer. The maximum of the attractive force shows site-specific variations. The positions with the highest attractive force values are associated with the presence of adsorbed potassium ions, while the other positions are associated with a local depletion of the hydration layer. This criterion provides a surface coverage of K cations that is consistent with the one reported by other techniques., This work was funded by the European Research Council ERC-AdG-340177 (3DNanoMech) and the Ministerio de Economía, Industria y Competitividad (MAT2016-76507-R).

Supplementary information: 1. Supplementary Figures 1-7, Supplementary Methods and Supplementary References [pdf file].-- 2. Supplementary Movie 2: 3D AFM image of the mical-KCl aqueous solution (~ 4 M) was obtained by exciting the cantilever at 838 kHz (2nd eigenmode); k= 921 N/m, Q= 24; A0= 0.11 nm. Data points= 1984000 [movie].-- 3. Supplementary Movie 3: 3D AFM image of the mical-NaCl aqueous solution (~ 5 M) was obtained by exciting the cantilever at 159 kHz (1st eigenmode), k= 24 N/m, Q= 7; A0= 0.23 nm. Data points = 2400000 [movie]., Interfacial liquid layers play a central role in a variety of phenomena ranging from friction to molecular recognition. Liquids near a solid surface form an interfacial layer where the molecular structure is different from that of the bulk. Here we report atomic resolution three-dimensional images of electrolyte solutions near a mica surface that demonstrate the existence of three types of interfacial structures. At low concentrations (0.01–1 M), cations are adsorbed onto the mica. The cation layer is topped by a few hydration layers. At higher concentrations, the interfacial layer extends several nanometres into the liquid. It involves the alternation of cation and anion planes. Fluid Density Functional calculations show that water molecules are a critical factor for stabilizing the structure of the interfacial layer. The interfacial layer stabilizes a crystal-like structure compatible with liquid-like ion and solvent mobilities. At saturation, some ions precipitate and small crystals are formed on the mica., This work was funded by the European Research Council ERC-AdG-340177 (3DNanoMech) and Spanish Ministry of Science and Innovation (CSD2010-00024, FIS2013-47350-C5, MDM-2014-0377).

Fast, accurate, and robust nanomechanical measurements are intensely studied in materials science, applied physics, and molecular biology. Amplitude modulation force microscopy (tapping mode) is the most established nanoscale characterization technique of surfaces for air and liquid environments. However, its quantitative capabilities lag behind its high spatial resolution and robustness. We develop a general method to transform the observables into quantitative force measurements. The force reconstruction algorithm has been deduced on the assumption that the observables (amplitude and phase shift) are slowly varying functions of the tip–surface separation. The accuracy and applicability of the method is validated by numerical simulations and experiments. The method is valid for liquid and air environments, small and large free amplitudes, compliant and rigid materials, and conservative and non-conservative forces., This work was funded by the Spanish Ministry of Economy (MINECO) through grant CSD2010–00024 and the European Research Council ERC-AdG-340177 (3DNanoMech).