C. Laube, T. Oeckinghaus, J. Lehnert, J Griebel, W. Knolle, A. Denisenko, A. Kahnt, J. Meijer, J. Wrachtrup, B. Abel
Nanoscale  11 (2019) 1770-1783
https://doi.org/10.1039/C8NR07828A

Control over the formation and fluorescence properties of nitrogen vacancy (NV) centers in nano- diamonds (NDs) is an important factor for their use in medical and sensor applications. However, reports providing a deep understanding of the potential factors influencing these properties are rare and focus only on a few influencing factors. The current contribution targets this issue and we report a comprehen- sive study of the fluorescence properties of NVs in nanodiamonds as a function of electron irradiation fluence and surface termination. Here we show that process parameters such as defect center inter- actions, in particular, different nitrogen defects and radiation induced lattice defects, as well as surface functionalities have a strong influence on the fluorescence intensity, fluorescence lifetime and the charge state ratio of the NV centers. By employing a time-correlated single photon counting approach we also established a method for fast macroscopic monitoring of the fluorescence properties of ND samples. We found that the fluorescence properties of NV centers may be controlled or even tuned depending upon the radiation treatment, annealing, and surface termination.

Y. Mindarava, R. Blinder, C. Laube, W. Knolle, B. Abel, C. Jentgens, J. Isoya, J. Scheuer, J. Lang, I. Schwartz, B. Naydenov, F. Jelezko
Carbon  170 (2020) 182-190
https://doi.org/10.1016/j.carbon.2020.07.077

Fluorescent nanodiamonds containing negatively-charged nitrogen-vacancy (NV^_) centers are promising for a wide range of applications, such as for sensing, as fluorescence biomarkers, or to hyperpolarize nuclear spins. NV^_ centers are formed from substitutional nitrogen (P1 centers) defects and vacancies in the diamond lattice. Maximizing the concentration of NVs is most beneficial, which justifies the search for methods with a high yield of conversion from P1 to NV^_. We report here the characterization of surface cleaned fluorescent micro- and nanodiamonds, obtained by irradiation of commercial diamond powder with high-energy (10 MeV) electrons and simultaneous annealing at 800 OC. Using this tech- nique and increasing the irradiation dose, we demonstrate the creation of NV^_ with up to 25% conversion yield. Finally, we monitor the creation of irradiation-induced spin-1 defects in microdiamond particles, which we associate with W16 and W33 centers, and investigate the effects of irradiation dose and particle size on the coherence time of NV^_.

J.Y. Zhou, C. Laube, W. Knolle, S. Naumov, A. Prager, F.D. Kopinke, B. Abel
Diam. Relat. Mater. 82 (2018) 150-159
https://doi.org/10.1016/j.diamond.2018.01.012

Surface functionality of nanodiamonds is of crucial importance for their desired chemical, optical and electro- magnetic properties. Chlorinated surfaces are expected to enable an easy further modification of diamond surfaces via various substitution reactions for targeted molecule grafting, particularly interesting for biochemical applications. Previously reported chlorination approaches of diamonds required troublesome handling of ha- zardous chemicals, such as chlorine gas, and long chlorination time or high temperature. Here, we describe a radiation chemistry approach using electron beam irradiation for efficient surface chlorination of nanodiamonds (with averaged diameter of ca. 30 nm) at ambient temperature. Nanodiamonds with hydrogenated and gra- phitized surfaces were used for chlorination in CCl4, CHCl3 and CH2Cl2 at increasing radiation doses. A com- prehensive set of measurements, including XPS, ATR-FTIR and in-source thermal desorption mass spectrometry (IS-TD-MS) was applied to characterize the chlorinated products. Density functional theory (DFT) calculations were performed to assist the discussion of reaction mechanisms. It is confirmed that remarkable covalently chlorine-covered surfaces bearing adequate stability against air and water were achieved for hydrogenated nanodiamonds in CCl4 by applying doses ≥500 kGy.

C. Laube, J. A. Taut, J. Kretzschmar, S. Zahn, W. Knolle, S. Ullmann, A. Kahnt, B. Kersting, B. Abel
Inorg. Chem. Front. 7 (2020) 4333-4346
https://doi.org/10.1039/D0QI00980F

The application of supramolecular host–guest chemistry for controlled photoreactivity and molecular sensing is a highly important field of modern inorganic and physical chemistry. One key aspect is the formation of the triplet state after photoexcitation. Applications of zinc ion Schiff-base derivatives for this purpose are rarely reported in the literature and there is still a lack of investigation into the triplet state formation of these supramolecular complexes. In this paper, triplet state formation and photosensitization is demonstrated for Zn(II) salicylaldiminato-functionalized calixarene complexes. We show that the photoinduced triplet state formation and the photoreactivity is a direct consequence of the Zn2+ complexation. Herein, the photochemical reactivity, as well as the mechanistic details of the photooxidation were deduced from a comprehensive set of steady state and time resolved spectroscopic as well as radiation chemistry data, respectively. The metal center (Zn2+) controlled photoreactivity observed here may lead to novel applications in the direction of photodynamical therapy or may open new avenues in catalysis, selective reactions and sensor applications.

M. F. Crook, C. Laube, I. A. Moreno-Hernandez, A. Kahnt, S. Zahn, J. C. Ondry, A. Liu, A. P. Alivisatos
J. Am. Chem. Soc. 143 (2021) 11703-11713
https://doi.org/10.1021/jacs.1c05099

Graphene liquid cell transmission electron microscopy (TEM) has enabled the observation of a variety of nanoscale transformations. Yet understanding the chemistry of the liquid cell solution and its impact on the observed transformations remains an important step toward translating insights from liquid cell TEM to benchtop chemistry. Gold nanocrystal etching can be used as a model system to probe the reactivity of the solution. FeCl3 has been widely used to promote gold oxidation in bulk and liquid cell TEM studies, but the roles of the halide and iron species have not been fully elucidated. In this work, we observed the etching trajectories of gold nanocrystals in different iron halide solutions. We observed an increase in gold nanocrystal etch rate going from Cl–- to Br–- to I–-containing solutions. This is consistent with a mechanism in which the dominant role of halides is as complexation agents for oxidized gold species. Additionally, the mechanism through which FeCl3 induces etching in liquid cell TEM remains unclear. Ground-state bleaching of the Fe(III) absorption band observed through pulse radiolysis indicates that iron may react with Cl2·– radicals to form an oxidized transient species under irradiation. Complete active space self-consistent field (CASSCF) calculations indicate that the FeCl3 complex is oxidized to an Fe species with an OH radical ligand. Together our data indicate that an oxidized Fe species may be the active oxidant, while halides modulate the etch rate by tuning the reduction potential of gold nanocrystals

S. Riedel, P. Hietschold, K. Krömmelbein, T. Kunschmann, R. Konieczny, W. Knolle, C. Mierke, M. Zink, S. G. Mayr
Materials & Design 168 (2019) 107606
https://doi.org/10.1016/j.matdes.2019.107606

Elektronenbestrahlung ermöglicht auch die Quervernetzung von Kollagen-Matrizen, wodurch sich maßgeschneiderte Netzwerktopologien und mechanische Eigenschaften einstellen lassen. Diese Erkenntnisse münden in die Entwicklung neuartiger Gewebe-Scaffolds ein.