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The supramolecular organization of a new polychlorotriphenyl (PTM) radical bearing three long alkyl chains is analyzed by scanning tunneling microscopy (STM) at the liquid-solid interface. The radical has self-assembled hierarchically on graphite forming head-to-head dimers that is organized in rows following a spin-containing two-leg molecular ladder topology, in which the alkyl chains have determined the space between the radical rows and have acted as diamagnetic barriers.

We successfully identified native point defects that occur in Bi 2 Te 3 crystals by combining high-resolution bias-dependent scanning tunneling microscopy and density functional theory based calculations. As-grown Bi 2 Te 3 crystals contain vacancies, antisites, and interstitial defects that may result in bulk conductivity and therefore may change the insulating bulk character. Here, we demonstrate the interplay between the growth conditions and the density of different types of native near-surface defects. In particular, scanning tunneling spectroscopy reveals the dependence on not only the local atomic environment but also on the growth kinetics and the resulting sample doping from n-type toward intrinsic crystals with the Fermi level positioned inside the energy gap. Our results establish a bias-dependent STM signature of the Bi 2 Te 3 native defects and shed light on the link between the native defects and the electronic properties of Bi 2 Te 3 , which is relevant for the synthesis of topological insulator materials and the related functional properties.

The key steps of a transfer of two-dimensional (2D) materials are the delamination of the as-grown material from a growth substrate and the lamination of the 2D material on a target substrate. In state-of-the-art transfer experiments, these steps remain very challenging, and transfer variations often result in unreliable 2D material properties. Here, it is demonstrated that interfacial water can insert between graphene and its growth substrate despite the hydrophobic behavior of graphene. It is understood that interfacial water is essential for an electrochemistry-based graphene delamination from a Pt surface. Additionally, the lamination of graphene to a target wafer is hindered by intercalation effects, which can even result in graphene delamination from the target wafer. For circumvention of these issues, a direct, support-free graphene transfer process is demonstrated, which relies on the formation of interfacial water between graphene and its growth surface, while avoiding water intercalation between graphene and the target wafer by using hydrophobic silane layers on the target wafer. The proposed direct graphene transfer also avoids polymer contamination (no temporary support layer) and eliminates the need for etching of the catalyst metal. Therefore, recycling of the growth template becomes feasible. The proposed transfer process might even open the door for the suggested atomic-scale interlocking-toy-brick-based stacking of different 2D materials, which will enable a more reliable fabrication of van der Waals heterostructure-based devices and applications.

Topological insulators (TIs) are renowned for their exotic topological surface states (TSSs) that reside in the top atomic layers, and hence, detailed knowledge of the surface top atomic layers is of utmost importance. Here we present the remarkable morphology changes of Bi2Te3 surfaces, which have been freshly cleaved in air, upon subsequent systematic annealing in ultrahigh vacuum and the resulting effects on the local and area-averaging electronic properties of the surface states, which are investigated by combining scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and Auger electron spectroscopy (AES) experiments with density functional theory (DFT) calculations. Our findings demonstrate that the annealing induces the formation of a Bi bilayer atop the Bi2Te3 surface. The adlayer results in n-type doping, and the atomic defects act as scattering centers of the TSS electrons. We also investigated the annealing-induced Bi bilayer surface on Bi2Te3 via voltage-dependent quasi-particle-interference (QPI) mapping of the surface local density of states and via comparison with the calculated constant-energy contours and QPI patterns. We observed closed hexagonal patterns in the Fourier transform of real-space QPI maps with secondary outer spikes. DFT calculations attribute these complex QPI patterns to the appearance of a "second" cone due to the surface charge transfer between the Bi bilayer and the Bi2Te3. Annealing in ultrahigh vacuum offers a facile route for tuning of the topological properties and may yield similar results for other topological materials.

Membranes and their size-selective filtering properties are universal in nature and their behavior is exploited to design artificial membranes suited for, e.g., molecule or nanoparticle filtering and separation. Exploring and understanding penetration and transmission mechanisms of nanoparticles in thin-film systems may provide new opportunities for size selective deposition or embedding of the nanoparticles. Here, we demonstrate an unexpected finding that the sieving of metal nanoparticles through atomically thin nonporous alkali halide films on a metal support is size dependent and that this sieving effect can be tuned via the film thickness. Specifically, relying on scanning tunneling microscopy and spectroscopy techniques, combined with density functional theory calculations, we find that defect-free NaCl films on a Au(111) support act as size-dependent membranes for deposited Au nanoclusters. The observed sieving ability is found to originate from a driving force toward the metal support and from the dynamics of both the nanoparticles and the alkali halide films.

Co-rich ZnCoO nanoparticles embedded in wurtzite Zn0.7Co0.3O thin films are grown by pulsed laser deposition on a Si substrate. Local superconductivity with an onset Tc at 5.9 K is demonstrated in the hybrid system. The unexpected superconductivity probably results from Co3+ in the Co-rich ZnCoO nanoparticles or from the interface between the Co-rich nanoparticles and the Zn0.7Co0.3O matrix.

During the last 20 years, using scanning tunneling microscopy (STM) and atomic force microscopy, scientists have successfully achieved vertical and lateral repositioning of individual atoms on and in different types of surfaces. Such atom manipulation allows the bottom-up assembly of novel nanostructures that can otherwise not be fabricated. It is therefore surprising that controlled repositioning of virtual atoms, i.e., atomic vacancies, across atomic lattices has not yet been achieved experimentally. Here we use STM at liquid helium temperature (4.5 K) to create individual Cl vacancies and subsequently to laterally manipulate them across the surface of ultrathin sodium chloride films. This allows monitoring the interactions between two neighboring vacancies with different separations. Our findings are corroborated by density functional theory calculations and STM image simulations. The lateral manipulation of atomic vacancies opens up a new playground for the investigation of fundamental physical properties of vacancy nanostructures of any size and shape and their coupling with the supporting substrate, and of the interaction of various deposits with charged vacancies.

Ultrafine ZnO nanocrystals with a thickness down to 0.25 nm are grown by a metalorganic chemical vapor deposition method. Electronic band structures and native point defects of ZnO nanocrystals are studied by a combination of scanning tunneling microscopy/spectroscopy and first-principles density functional theory calculations. Below a critical thickness of ∼1 nm ZnO adopts a graphitic-like structure and exhibits a wide band gap similar to its wurtzite counterpart. The hexagonal wurtzite structure, with a well-developed band gap evident from scanning tunneling spectroscopy, is established for a thickness starting from ∼1.4 nm. With further increase of the thickness to 2 nm, VO-VZn defect pairs are easily produced in ZnO nanocrystals due to the self-compensation effect in highly doped semiconductors.

Nowadays molecular nanoporous networks have numerous uses in surface nanopatterning applications and in studies of host-guest interactions. Trimesic acid (TMA), a benzene derivative with three carboxylic groups, is a marvelous building block for forming 2D H-bonded porous networks. Here, we report a low-temperature study of the nanoporous "chicken-wire" superstructure formed by TMA molecules adsorbed on a Au(111) surface. Distinct preferential orientations of the porous networks on Au(111) lead to the formation of peculiar TMA polymorphs that are stabilized only at the boundary between rotational molecular domains. Scanning tunneling microscopy (STM) and spectroscopy are used to investigate the electronic properties of both the molecular building blocks and the pores. Sub-molecular-resolution imaging and spatially resolved electronic spectroscopy reveal a remarkable change in the appearance of the molecules in the STM images at energies in the range of the lowest unoccupied molecular orbital, accompanied by highly extended molecular wave functions into the pores. The electronic structure of the pores reflects a weak confinement of surface electrons by the TMA network. Our experimental observations are corroborated by density-functional-theory-based calculations of the nanoporous structure adsorbed on Au(111).

We introduce the use of ferromagnetic resonance (FMR) to actuate mechanical resonances in as grown arrays of carbon nanotubes (CNTs) loaded with Ni particles (Ni-CNTs). This contactless method is closely related to the magnetic resonance force microscopy technique and provides spatial selectivity of actuation along the array. The Ni-CNT arrays are grown by chemical vapor deposition and are composed of homogeneous CNTs with uniform length (~600 nm) and almost equal diameter (~20 nm), which are loaded with Ni catalyst particles at their tips due to the tip growth mode. The vibrations of the Ni-CNTs are actuated by relying on the driving force that appears due to the FMR excited at about 2 GHz in the Ni particles (diameter ~100 nm). The Ni-CNT oscillations (frequency ~40 MHz) are detected mechanically by atomic force microscopy. The acquired oscillation images of the Ni-CNT uniform array reveal clear maxima in the spatial distribution of the oscillation amplitudes. We attribute these maxima to the "sensitive slices", i.e., the spatial regions of the Ni-CNT array where the FMR condition is met. Similar to magnetic resonance imaging, the sensitive slice is determined by the magnetic field gradient and moves along the Ni-CNT array as the applied magnetic field is ramped. Our excitation method does not require the presence of any additional microfabricated electrodes or coils near the CNTs and is particularly advantageous in cases where the traditional electrical actuation methods are not effective or cannot be implemented. The remote actuation can be effectively implemented also for arrays of other magnetic nanomechanical resonators.

The deposition of n-octylphosphonic acid on aluminum oxide was studied. The substrate was pretreated in order to achieve a root-mean-square roughness of <1 nm, a hydroxyl fraction of 30%, and a thickness of approximately 170 nm. It was proven using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) that, rather than a monolayer, an organic multilayer was formed. The growth mechanism was identified as a Stranski-Krastanov one. It was also shown that the use of AFM, probing the surface topography, is essential for a reliable quantification and interpretation of data obtained with XPS.