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For the wafer-scale fabrication of diamond devices, the growth of diamond substrates by heteroepitaxial chemical vapor deposition is the most promising option currently available. However, the transfer of growth and also structuring processes from small homoepitaxial to larger heteroepitaxial samples is not straightforward and requires adaptation. In this study, we present an approach for the fabrication of functional microstructures including pyramids and mesas as well as more complex structures with hollow centers. The associated methods were previously demonstrated by homoepitaxial growth and are now evaluated on heteroepitaxially grown diamond films. After optimizing the growth procedures to ensure a sufficient quality of the bare diamond substrates, precursor structures for overgrowth were fabricated by e-beam lithography and plasma etching. In the overgrowth of nanopillars, a truncated pyramidal shape was achieved. The characterization with scanning electron microscopy revealed the growth of higher-index facets. Nevertheless, photoluminescence spectroscopy reveals localized doping on the sides of the microstructures. In addition, optically detected magnetic resonance reaches a contrast of 6 % of one preferred nitrogen vacancy orientation per facet and a transverse relaxation time T 2 ∗ of 96 ns. [ABSTRACT FROM AUTHOR]

Heteroepitaxial chemical vapor deposition is the most promising option to fabricate wafer-scale monocrystalline diamonds for quantum applications. Previously, we demonstrated the feasibility to manufacture functional micrometer-sized pyramids on as-grown heteroepitaxial diamond as well as their quantum optical characteristics. Due to high background signals and microfabrication challenges, these pyramids could not compete with homoepitaxially grown structures. In this study, we overcame these problems with a nominally undoped buffer layer between the heteroepitaxial substrate and the pyramidal microstructure to reduce the signal-to-noise ratio from the substrate on the spin measurements of the nitrogen-vacancy (NV) center. Moreover, the microfabrication was improved to reach a higher angle of the pyramidal side plane, corresponding to the {111} facets. These improvements lead to pyramids on which each facet contains almost purely only one of the four possible NV orientations as shown by optically detected magnetic resonance (ODMR). ODMR shows a very high contrast of 19% without an external magnet and of 13% for a single spin resonance in the presence of a magnetic field. The contrast is more than doubled compared to our previous study. The T 2 * dephasing time of the NV centers of the samples ranges from 0.02 to 0.16 μs. The P1 center is a single substitutional nitrogen center, and the P1 densities range from 1.8 to 5 ppm. [ABSTRACT FROM AUTHOR]

Temperature Programmed Desorption (TPD) spectroscopy was used to determine the binding energies of polycyclic aromatic hydrocarbons CnHm (22 ≤ n ≤ 60) with highly oriented pyrolytic graphite. These energies were then used to estimate the dispersive graphite interlayer cohesion by means of a refined extrapolation method proposed by Björk et al. This yields a cohesion energy of 44.0 ± 3.8 meV per carbon atom. We discuss some limits of the TPD-based approach and contrast our values with previous determinations of the interlayer cohesion energy of graphite. [ABSTRACT FROM AUTHOR]

Films comprising the endohedral fullerene Er3N@C80 are deposited onto highly oriented pyrolytic graphite (HOPG) substrates in high purity enabled by performing mass‐selected low‐energy deposition from a cation beam. In the initial stage, the growth on HOPG is dominated by spontaneous nucleation of small 2D islands both on intact terraces as well as the step edges. The island growth exhibits strong differences from films comprising other fullerenes grown by the same method. This behavior can be explained by the surface‐diffusion‐mediated nucleation model presented in previous work: Dominant components in the behavioural differences are a high intercage dispersion interaction and a lower kinetic energy of cages migrating on the surface in comparison with previously deposited materials. When annealed, the films undergo several competing processes: A small fraction desorbs in the temperature range 700–800 K, another fraction forms covalent intercage bonds instead of the previous purely dispersive bonding mode, and a third fraction probably decomposes to small fragments. [ABSTRACT FROM AUTHOR]

Due to fascinating physical properties powered by remarkable progress in chemical vapor deposition of high-quality epilayers, diamond thin films attract great attention for fabrication of nitrogen-vacancy-based solid-state spin systems capable of operating in ambient conditions. To date, diamond heteroepitaxy via bias-enhanced nucleation is an unavoidable method for reliable wafer-scale film manufacturing. In this work, we analyze the coalescence phenomena in nitrogen doped, heteroepitaxial diamond epilayers, with a particular focus on their specific role in the annihilation of macroscopic crystal irregularities such as grain boundaries, non-oriented grains, and twinned segments. Here, we also report on the growth mechanism for the "primary" crystal orientation along with a predominant formation of two different types of boundaries highlighting the {011}-type as a main source of the crystal lattice irregularities. [ABSTRACT FROM AUTHOR]

The non-IPR fulleride compound CsxC68 was investigated in analogy to previous experiments on CsxC58. While the vibrational properties as well as the electronic structure in the valence band range appear to be pretty similar to CsxC58, a striking difference could be observed by XPS and Photoemission Microscopy analysis: apparently, C68 forms different phases within a thick film including islands in which it is able to store more than 70 Cs atoms per fullerene cage and to keep these amounts even after annealing over 1100 K. This means that CsxC68 constitutes the highest alkali metal doping degree of any Fullerene species known so far. Spatially resolved photoemission analysis also revealed that the Cs-rich fulleride phases constitute a unique chemical state that has never been observed before. [ABSTRACT FROM AUTHOR]

Wafer‐scale heteroepitaxial diamond thin films demonstrate multiple advantages for a further development of integrated optical and quantum devices based on impurity–vacancy color centers. The main obstacle here is a high structural defect density characteristic for heteroepitaxial epilayers. In this work, technological methods of stress control, NV formation, and defect density reduction in diamond epilayers, which are based on principles of epitaxial lateral overgrowth (ELO) are reported on. Herein, material and quantum properties of NV‐doped diamond thin films obtained by patterned nucleation growth and by ELO of microstructured epilayers, are compared. It is demonstrated that a combination of both methods might have a significant potential for the wafer‐scale production of heteroepitaxial diamond for quantum devices. [ABSTRACT FROM AUTHOR]

A combination of low energy ion beam deposition and mass resolved thermal desorption spectroscopy is applied to analyze the binding behavior of two nonplanar polycyclic aromatic hydrocarbons (PAHs) to highly oriented pyrolytic graphite (HOPG) surfaces—also concerning their lateral dispersion interactions. In particular, the fullerene precursor C60H30 (FPC) and rubrene C42H28 are studied. Due to their smaller contact areas, both molecules exhibit significantly weaker binding energies to the HOPG surface compared to planar PAHs of similar size: C60H30 is bound to the surface by 3.04 eV, which is 0.6 eV lower than for a fully planar homologue. For rubrene, an isolated molecule–substrate binding energy of 1.59 eV is found, which is about 1 eV less than that of the corresponding planar homologue hexabenzocoronene C42H18. In contrast to FPC, rubrene shows a significant (intermolecular) lateral dispersion contribution to the binding energy as the submonolayer coverage increases. [ABSTRACT FROM AUTHOR]

Cs doped non‐IPR fullerides (IPR: isolated pentagon rule) have been grown by co‐depositing C58 cations and Cs atoms on highly oriented pyrolytic graphite (HOPG). The C58 cages, as building blocks of the material, form a predominantly covalently stabilized scaffold, C58–C58, which is doped by Cs atoms thermally diffusing across the bulk. The heating of the solid CsxC58 sample is accompanied by sublimation of Cs, C58, and C60 species from the topmost layers of the sample. However, the major part (>94%) of the material survives the heating procedure and constitutes a doped high‐temperature carbon solid, HT‐CsxC58. The new non‐IPR material exhibits surprisingly high thermal stability. It survives a heating flash up to 1100 K at which the classic IPR‐CsxC60 phase does not exist anymore. However, the thermally treated HT‐CsxC58 phase exhibits a considerably depleted Cs content (x < 2) and a significantly modified carbon scaffold. The apparent stability of the scaffold results from covalent C–C bonds interlinking adjacent carbon cages. Cs atoms in the HT‐CsxC58 phase contribute to this stability only as minority species, forming comparably weak ionic bonds with C58–C58 oligomers. However, this interaction facilitates the formation of structural defects (new non‐IPR sites) in carbon cages. The surface topography of the HT‐CsxC58 as monitored by scanning photoemission microscopy, atomic force microscopy, and scanning electron microscopy is governed by islands standing out by their elevated Cs/C ratio. The properties of macroscopic films comprising the non‐IPR fulleride CsxC58 are described: Cs catalyzes the thermally activated transfer of C2 units between fullerene cages thus leading to a new phase, HT‐CsxC58. This work describes the electronic and vibrational properties of this new phase and presents an analysis of chemical inhomogeneities mirrored by spectral photoemission microscopy. [ABSTRACT FROM AUTHOR]

In focus of this report are the mechanisms of formation, propagation, and interaction of growth defects in heteroepitaxial diamond films along with their impact on the optical emission properties of N- and Si-vacancy (NV and SiV) color centers. Here, we analyze and discuss the properties of incoherent grain boundaries (IGBs) and extended defects in a nitrogen- and boron-doped heterodiamond nucleated and grown on Ir(001) via bias-enhanced nucleation and chemical vapor deposition techniques. We show that the low-angle IGBs alter the structural and optical emission properties of NV and SiV complexes by subduing NV emission and supporting the formation of interstitial Si-vacancy complexes dominating in the faulted IGB regions. We also demonstrate that the IGB-confined threading dislocations are responsible for the vertical transport and incorporation of Si impurities in thick layers, leading to an enhanced SiV emission from the IGBs. [ABSTRACT FROM AUTHOR]

Multiply twinned particles (MTPs) are fascinating crystallographic entities with a number of controllable properties originating from their symmetry and cyclic structure. In the focus of our studies are diamond MTPs hosting optically active defects—objects demonstrating high application potential for emerging optoelectronic and quantum devices. In this work, we discuss the growth mechanisms along with the microstructural and optical properties of the MTPs aggregating a high-density of "silicon-vacancy" complexes on the specific crystal irregularities. It is demonstrated that the silicon impurities incite a rapid growth of MTPs via intensive formation of penetration twins on {100} facets of regular octahedral grains. We also show that the zero-phonon-line emission from the Si color centers embedded in the twin boundaries dominates in photo- and electroluminescence spectra of the MTP-based light-emitting devices defining their steady-state optical properties. [ABSTRACT FROM AUTHOR]

A combination of mass spectrometry, collision-induced dissociation, ion mobility mass spectrometry (IM-MS), and density functional theory (DFT) has been used to study the evolution of anionic species generated by laser-desorption of the near-planar, fluorinated polycyclic aromatic hydrocarbon (PAH), C60H21F9 (s). The dominant decay process for isolated, thermally activated C60H21F9- species comprises a sequence of multiple regioselective cyclodehydrofluorination and cyclodehydrogenation reactions (eliminating HF and H2, respectively, while forming additional pentagons and/or hexagons). The DFT calculations allow us to set narrow bounds on the structures of the resulting fragment ions by fitting structural models to experimentally determined collision cross sections. These show that the transformation of the precursor anion proceeds via a series of intermediate structures characterized by increasing curvature, ultimately leading to the closed-shell fullerene cage C60- as preprogrammed by the precursor structure. [ABSTRACT FROM AUTHOR]