Ultraflat Cu(111) foils by surface acoustic wave-assisted annealing.

Ultraflat metal foils are essential for semiconductor nanoelectronics applications and nanomaterial epitaxial growth. Numerous efforts have been devoted to metal surface engineering studies in the past decades. However, various challenges persist, including size limitations, polishing non-uniformities, and undesired contaminants.

Triggered integer charge transfer: energy-level alignment at an organic-2D material interface.

Weakly interacting systems such as organic molecules on monolayers of hexagonal boron nitride (h-BN) offer the possibility of single integer charge transfer leading to the formation of organic ions. Such open-shell systems exhibit unique optical and electronic properties which differ from their neutral counterparts. In this study, we used a joint experimental and theoretical approach to investigate the charge transfer of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecules on h-BN/Ni(111) by using differential reflectance spectroscopy (DRS), scanning tunneling spectroscopy (STS), and photoelectron orbital tomography (POT) measurements in combination with density functional theory (DFT) calculations.

Partial restoration of aromaticity of pentacene-5,7,12,14-tetrone on Cu(111).

The π-conjugation of organic molecules can be strongly influenced when functional groups are added to a molecule, for example when pentacene is converted into pentacene-5,7,12,14-tetrone (P4O) by substitution of four H-atoms with four O-atoms, leading to four CO double bonds. In fact, although free P4O resembles the parent hydrocarbon pentacene structurally at a first glance, its electronic properties differ drastically and can be more accurately described by three benzene units connected four carbonyl groups. If P4O is deposited onto Cu(111), the electronic interaction across the interface has previously been reported to fully restore the π-conjugation through a weakening of the CO double bonds and a redistribution of electrons, both of which have been explained with the model of surface-induced aromatic stabilization.

Structural and electronic properties of MoS and MoSe monolayers grown by chemical vapor deposition on Au(111).

The exceptional electronic and photonic properties of the monolayers of transition metal dichalcogenides including the spin-orbit splitting of the valence and conduction bands at the points of the Brillouin zone make them promising for novel applications in electronics, photonics and optoelectronics. Scalable growth of these materials and understanding of their interaction with the substrate is crucial for these applications. Here we report the growth of MoS and MoSe monolayers on Au(111) by chemical vapor deposition at ambient pressure as well as the analysis of their structural and electronic properties down to the atomic scale.

Sustainable catalysts for efficient triazole synthesis: an immobilized triazine-based copper-NNN pincer complex on TiO.

The multistep synthesis of a hybrid material based on a TiO core with an immobilized triazine-based copper(II)-NNN pincer complex is reported. The formation of the material was confirmed by FT-IR spectroscopy and elemental and thermogravimetric analyses, and the loading by copper ions was quantified by ICP/OES analysis. The properties of the hybrid material were further investigated by X-ray photoelectron spectroscopy (XPS), contiuous wave electron spin resonance (CW-ESR), UV-vis spectroscopy, and argon sorption.

Atomically Thin Metal-Dielectric Heterostructures by Atomic Layer Deposition.

Heterostructures increasingly attracted attention over the past several years to enable various optoelectronic and photonic applications. In this work, atomically thin interfaces of Ir/AlO heterostructures compatible with micro-optoelectronic technologies are reported. Their structural and optical properties were determined by spectroscopic and microscopic techniques (XRR, XPS, HRTEM, spectroscopic ellipsometry, and UV/vis/NIR spectrophotometry).

Performance of Common Density Functionals for Excited States of Tetraphenyldibenzoperiflanthene.

Time-dependent density functional theory is the method of choice to efficiently calculate excitation spectra with the functional and basis set choice allowing one to compromise between accuracy and computational cost. In this work, the performance of different functionals as well as the second-order approximate coupled cluster singles and doubles model CC2 is evaluated by comparing the results to experimental results of the example molecule tetraphenyldibenzoperiflanthene (DBP). The choice of the functional has a significant impact on the calculated spectrum of DBP.

Correlation between two- and three-dimensional crystallographic lattices for epitaxial analysis. II. Experimental results.

While the crystal structure of the polymorph phase can be studied in three dimensions conveniently by X-ray methods like grazing-incidence X-ray diffraction (GIXD), the first monolayer is only accessible by surface-sensitive methods that allow the determination of a two-dimensional lattice. Here, GIXD measurements with sample rotation are compared with distortion-corrected low-energy electron diffraction (LEED) experiments on conjugated molecules: 3,4;9,10-perylenetetracarboxylic dianhydride (PTCDA), 6,13-pentacenequinone (P2O), 1,2;8,9-dibenzopentacene (trans-DBPen) and dicyanovinyl-quaterthiophene (DCV4T-Et2) grown by physical vapor deposition on Ag(111) and Cu(111) single crystals. For these molecular crystals, which exhibit different crystallographic lattices and crystal orientations as well as epitaxial properties, the geometric parameters of the three-dimensional lattice are compared with the corresponding geometry of the first monolayer.

Correlation between two- and three-dimensional crystallographic lattices for epitaxial analysis. I. Theory.

The epitaxial growth of molecular crystals at single-crystalline surfaces is often strongly related to the first monolayer at the substrate surface. The present work presents a theoretical approach to compare three-dimensional lattices of epitaxially grown crystals with two-dimensional lattices of the molecules formed within the first monolayer. Real-space and reciprocal-space representations are considered.

Plasma-Enhanced Atomic Layer Deposition of HfO with Substrate Biasing: Thin Films for High-Reflective Mirrors.

Tuning ion energies in plasma-enhanced atomic layer deposition (PEALD) processes enables fine control over the material properties of functional coatings. The growth, structural, mechanical, and optical properties of HfO thin films are presented in detail toward photonic applications. The influence of the film thickness and bias value on the properties of HfO thin films deposited at 100 °C using tetrakis(dimethylamino)hafnium (TDMAH) and oxygen plasma using substrate biasing is systematically analyzed.

Wafer-scale single-crystal monolayer graphene grown on sapphire substrate.

The growth of inch-scale high-quality graphene on insulating substrates is desirable for electronic and optoelectronic applications, but remains challenging due to the lack of metal catalysis. Here we demonstrate the wafer-scale synthesis of adlayer-free ultra-flat single-crystal monolayer graphene on sapphire substrates. We converted polycrystalline Cu foil placed on AlO(0001) into single-crystal Cu(111) film via annealing, and then achieved epitaxial growth of graphene at the interface between Cu(111) and AlO(0001) by multi-cycle plasma etching-assisted-chemical vapour deposition.

Nonintuitive Surface Self-Assembly of Functionalized Molecules on Ag(111).

The fabrication of nanomaterials involves self-ordering processes of functional molecules on inorganic surfaces. To obtain specific molecular arrangements, a common strategy is to equip molecules with functional groups. However, focusing on the functional groups alone does not provide a comprehensive picture.

Optical bandgap control in AlO/TiO heterostructures by plasma enhanced atomic layer deposition: Toward quantizing structures and tailored binary oxides.

Atomically thin heterostructures and superlattices are promising candidates for various optoelectronic and photonic applications. Different combinations of AlO/TiO composites are obtained by plasma enhanced atomic layer deposition (PEALD). Their growth, composition, dispersion relation, and optical bandgap are systematically studied by means of UV/VIS spectrophotometry, spectroscopic ellipsometry (SE), x-ray reflectometry (XRR), scanning transmission electron microscopy(STEM) and x-ray photoelectron spectroscopy (XPS).

Searching for New Polymorphs by Epitaxial Growth.

The formation of unknown polymorphs due to the crystallization at a substrate surface is frequently observed. This phenomenon is much less studied for epitaxially grown molecular crystals since the unambiguous proof of a new polymorph is a challenging task. The existence of multiple epitaxial alignments of the crystallites together with the simultaneous presence of different polymorphs does not allow simple phase identification.

Hybridization vs decoupling: influence of an h-BN interlayer on the physical properties of a lander-type molecule on Ni(111).

2D materials such as hexagonal boron nitride (h-BN) are widely used to decouple organic molecules from metal substrates. Nevertheless, there are also indications in the literature for a significant hybridization, which results in a perturbation of the intrinsic molecular properties. In this work we study the electronic and optical properties as well as the lateral structure of tetraphenyldibenzoperiflanthene (DBP) on Ni(111) with and without an atomically thin h-BN interlayer to investigate its possible decoupling effect.

An efficient method for indexing grazing-incidence X-ray diffraction data of epitaxially grown thin films.

Crystal structure identification of thin organic films entails a number of technical and methodological challenges. In particular, if molecular crystals are epitaxially grown on single-crystalline substrates a complex scenario of multiple preferred orientations of the adsorbate, several symmetry-related in-plane alignments and the occurrence of unknown polymorphs is frequently observed. In theory, the parameters of the reduced unit cell and its orientation can simply be obtained from the matrix of three linearly independent reciprocal-space vectors.

Effect of an electric field during the deposition of silicon dioxide thin films by plasma enhanced atomic layer deposition: an experimental and computational study.

The growth, chemical, structural, mechanical, and optical properties of oxide thin films deposited by plasma enhanced atomic layer deposition (PEALD) are strongly influenced by the average-bias voltage applied during the reaction step of surface functional groups with oxygen plasma species. Here, this effect is investigated thoroughly for SiO2 deposited in two different PEALD tools at average-bias voltages up to -300 V. Already at a very low average-bias voltage (< -10 V), the SiO2 films have significantly lower water content than films grown without biasing together with the formation of denser films having a higher refractive index and nearly stoichiometric composition.

: a comprehensive software tool for geometry-independent grazing-incidence X-ray diffraction data analysis and pole-figure calculations.

is a software package based on MATLAB specialized for, but not limited to, the visualization and analysis of grazing-incidence thin-film X-ray diffraction data obtained during sample rotation around the surface normal. allows the user to perform detector calibration, data stitching, intensity corrections, standard data evaluation ( cuts and integrations along specific reciprocal-space directions), crystal phase analysis . To take full advantage of the measured data in the case of sample rotation, pole figures can easily be calculated from the experimental data for any value of the scattering angle covered.

The role of initial and final states in molecular spectroscopies.

Interpreting experimental spectra of thin films of organic semiconductors is challenging, and understanding the relationship between experimental data obtained by different spectroscopic techniques requires a careful consideration of the initial and final states for each process. The discussion of spectroscopic data is frequently mired in confusion that originates in overlapping terminology with however distinct meaning in different spectroscopies. Here, we present a coherent framework that is capable of treating on equal footing most spectroscopies commonly used to investigate thin films of organic semiconductors.

Fraternal twins: distinction between PbPc and SnPc by their switching behaviour in a scanning tunnelling microscope.

In this contribution, we compare the optical absorbance behaviour and the structural properties of lead(II)-phthalocyanine (PbPc) and tin(II)-phthalocyanine (SnPc) thin films. To this end, we employ a Ag(1 1 1) substrate terminated with a monolayer of 3,4,9,10-perylene tetracarboxylic dianhydride constituting an internal interface whose main effect is an electronic decoupling of the phthalocyanine adlayer from the metal surface. As deduced from low-energy electron diffraction and scanning tunnelling microscopy (STM) measurements, the epitaxial relations and unit cell compositions of the prevailing PbPc monolayer and multilayer domains are confusingly similar to those of SnPc on PTCDA/Ag(1 1 1).

Fully Atomistic Understanding of the Electronic and Optical Properties of a Prototypical Doped Charge-Transfer Interface.

The current study generates profound atomistic insights into doping-induced changes of the optical and electronic properties of the prototypical PTCDA/Ag(111) interface. For doping K atoms are used, as KPTCDA/Ag(111) has the distinct advantage of forming well-defined stoichiometric phases. To arrive at a conclusive, unambiguous, and fully atomistic understanding of the interface properties, we combine state-of-the-art density-functional theory calculations with optical differential reflectance data, photoelectron spectra, and X-ray standing wave measurements.

Contorted polycyclic aromatic hydrocarbons with cove regions and zig-zag edges.

A series of tetrapyrene-fused benzocoronenes was synthesized by a "bottom-up" approach, which offers a facile access to extended polycyclic aromatic hydrocarbons with concave π-surfaces, cove regions and zig-zag edges.

Influence of Film and Substrate Structure on Photoelectron Momentum Maps of Coronene Thin Films on Ag(111).

Angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) was measured for one-monolayer coronene films deposited on Ag(111). The ( , )-dependent photoelectron momentum maps (PMMs), which were extracted from the ARUPS data by cuts at fixed binding energies, show finely structured patterns for the highest and the second-highest occupied molecular orbitals. While the substructure of the PMM main features is related to the 4 × 4 commensurate film structure, various features with three-fold symmetry imply an additional influence of the substrate.

Classification of epitaxy in reciprocal and real space: rigid versus flexible lattices.

Early investigations of epitaxy focused on inorganic adsorbates consisting of atoms or few-atom molecules, where commensurate registries are predominantly encountered. Expanding such studies to larger (organic) molecules has revealed hitherto unknown types of epitaxy with coherence between adlayer and substrate lattices in just one direction. Here we review recent contributions to the fundamental understanding and modeling of epitaxy.

Insight into the unit cell: Structure of picene thin films on Ag(100) revealed with complementary methods.

We study the molecular structure of one monolayer of picene on a Ag(100) surface. Low energy electron diffraction and scanning tunneling microscopy experiments show that the molecules arrange in a highly ordered manner exhibiting a point-on-line epitaxy with two differently arranged molecules per unit cell. Comparing measured and simulated photoelectron momentum maps allows further conclusions about the composition of the unit cell.