Janina Maultzsch’s research while affiliated with Friedrich-Alexander-University Erlangen-Nürnberg and other places

Connecting two‐dimensional (2D) material layers via interface linkers represents a new avenue for fabricating 2D heterostructures. Utilizing light to remotely modulate this interface function allows for seamless assembly and patterning in a single run. Here, an efficient method for fabricating patterned 2D heterostructures using direct laser writing is demonstrated, drawing a conceptual parallel to laser printing. In the approach, functionalized transition metal dichalcogenide (TMD) dispersions serve as inks, graphene as the substrate, and a Raman laser as the patterning tool. Unlike laser printing's electrostatic interactions, the method achieves patterned assembly through covalent bonding between TMDs and graphene. Selective Raman laser irradiation of functionalized TMD/graphene heterostructures triggers localized reactions, forming chemically modified domains exclusively in the laser‐irradiated regions, as confirmed by Raman spectroscopy, Kelvin probe force microscopy (KPFM), and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). Experimental and theoretical analyses of the interface composition and structure provide new insights into laser‐induced chemistry. The work demonstrates the potential for high‐throughput assembly of customizable 2D heterostructures, with enhanced compatibility for subsequent patterning through photolabile linkers and photoinduced coupling. Additionally, the results provide deeper insights into chemistry within confined 2D spaces, offering a novel approach to nanoscale heterostructure engineering.

Theoretical simulations of the electronic properties of graphene‐like 2D carbon networks with a periodic arrangement of defect lines formed by alternating four‐ and eight‐membered rings are presented. These networks can be seen as arrays of armchair‐edged nanoribbons (AGNRs), which are covalently connected at the edges. Using a combination of density functional theory and a simple tight binding model, it is shown that the electronic properties of these networks can be understood to arise from the family behavior of the constituting AGNRs, plus a rigid shift due to an “inter‐ribbon” coupling across the defect lines. As a result, one class of zero‐bandgap semiconducting 2D networks and two classes of semimetallic networks with quasilinear band close to the Fermi energy are found. The formation of closed‐ring electron‐ and hole‐like Fermi surfaces due to hybridization across the defect lines offers interesting perspectives of using such defective 2D networks for transport applications or the realization of carbon‐based nodal‐line semimetals.

We present theoretical simulations of the electronic properties of graphene-like two-dimensional (2D) carbon networks with a periodic arrangement of defect lines formed by alternating four- and eight-membered rings. These networks can be seen as arrays of armchair-edged nanoribbons (AGNRs), which are covalently connected at the edges. Using a combination of density functional theory and a simple tight binding model, we show that the electronic properties of these networks can be understood to arise from the family behaviour of the constituting AGNRs, plus a rigid shift due to an 'inter-ribbon' coupling across the defect lines. As a result, we find one class of zero-band-gap semiconducting 2D networks, and two classes of semimetallic networks with quasi-linear band close to the Fermi energy. The formation of closed-ring electron- and hole-like Fermi surfaces due to hybridization across the defect lines offers interesting perspectives of using such defective 2D networks for transport applications or the realization of carbon-based nodal line semimetals.

Graphene nanoribbons (GNRs) have garnered significant interest due to their highly customizable physicochemical properties and potential utility in nanoelectronics. Besides controlling widths and edge structures, the inclusion of chirality in GNRs brings another dimension for fine-tuning their optoelectronic properties, but related studies remain elusive owing to the absence of feasible synthetic strategies. Here, we demonstrate a novel class of cove-edged chiral GNRs (CcGNRs) with a tunable chiral vector (n,m). Notably, the bandgap and effective mass of (n,2)- CcGNR show a distinct positive correlation with the increasing value of n, as indicated by theory. Within this GNR family, two representative members, namely, (4,2)- CcGNR and (6,2)-CcGNR, are successfully synthesized. Both CcGNRs exhibit prominently curved geometries arising from the incorporated [4]helicene motifs along their peripheries, as also evidenced by the single-crystal structures of the two respective model compounds (1 and 2). The chemical identities and optoelectronic properties of (4,2)- and (6,2)-CcGNRs are comprehensively investigated via a combination of IR, Raman, solid-state NMR, UV-vis, and THz spectroscopies as well as theoretical calculations. In line with theoretical expectation, the obtained (6,2)-CcGNR possesses a low optical bandgap of 1.37 eV along with charge carrier mobility of 8 cm2/Vs, whereas (4,2)-CcGNR exhibits a narrower bandgap of 1.26 eV with increased mobility of 14 cm2/Vs. This work opens up a new avenue to precisely engineer the bandgap and carrier mobility of GNRs by manipulating their chiral vector.

Stacking orders and topological defects substantially influence the physical properties of 2D van der Waals (vdW) materials. However, the inherent features of 2D materials challenge the effectiveness of single characterization techniques in identifying stacking sequences, necessitating correlative approaches. Using bilayer MoS2 as a benchmark, we differentiate its polytypism and specific dislocations through transmission electron microscopy (TEM) and Raman spectroscopy. Perfect and partial dislocations were revealed in TEM, which are closely linked to the stacking sequences, thus indirectly indicating the 2H and 3R polytypes. 3D electron diffraction reconstruction on relrods and low-frequency Raman spectroscopy further validated these polytypes owing to their reliance on crystal symmetry. Surprisingly, we unexpectedly resolved both polytypes despite starting with 2H bulk crystal, pointing to a possible phase transition during mechanical exfoliation. The correlative TEM-Raman approach can be extended to other 2D materials, paving the way for property alteration via stacking and defect engineering.

We present a novel approach to achieve spatial variations in the degree of non‐covalent functionalization of twisted bilayer graphene (tBLG). The tBLG with twist angles varying between ~5° and 7° was non‐covalently functionalized with 1,4,5,8,9,11‐hexaazatriphenylenehexacarbonitrile (HATCN) molecules. Our results show a correlation between the degree of functionalization and the twist angle of tBLG. This correlation was determined through Raman spectroscopy, where areas with larger twist angles exhibited a lower HATCN peak intensity compared to areas with smaller twist angles. We suggest that the HATCN adsorption follows the moiré pattern of tBLG by avoiding AA‐stacked areas and attach predominantly to areas with a local AB‐stacking order of tBLG, forming an overall ABA‐stacking configuration. This is supported by density functional theory (DFT) calculations. Our work highlights the role of the moiré lattice in controlling the non‐covalent functionalization of tBLG. Our approach can be generalized for designing nanoscale patterns on two‐dimensional (2D) materials using moiré structures as a template. This could facilitate the fabrication of nanoscale devices with locally controlled varying chemical functionality.

We present a novel approach to achieve spatial variations in the degree of non‐covalent functionalization of twisted bilayer graphene (tBLG). The tBLG with twist angles varying between ~5° and 7° was non‐covalently functionalized with 1,4,5,8,9,11‐hexaazatriphenylenehexacarbonitrile (HATCN) molecules. Our results show a correlation between the degree of functionalization and the twist angle of tBLG. This correlation was determined through Raman spectroscopy, where areas with larger twist angles exhibited a lower HATCN peak intensity compared to areas with smaller twist angles. We suggest that the HATCN adsorption follows the moiré pattern of tBLG by avoiding AA‐stacked areas and attach predominantly to areas with a local AB‐stacking order of tBLG, forming an overall ABA‐stacking configuration. This is supported by density functional theory (DFT) calculations. Our work highlights the role of the moiré lattice in controlling the non‐covalent functionalization of tBLG. Our approach can be generalized for designing nanoscale patterns on two‐dimensional (2D) materials using moiré structures as a template. This could facilitate the fabrication of nanoscale devices with locally controlled varying chemical functionality.

Solution-processable 2D materials are promising candidates for a range of printed electronics applications. Yet maximizing their potential requires solution-phase processing of nanosheets into high-quality networks with carrier mobility (μNet) as close as possible to that of individual nanosheets (μNS). In practice, the presence of internanosheet junctions generally limits electronic conduction, such that the ratio of junction resistance (RJ) to nanosheet resistance (RNS), determines the network mobility via μNS/μNet ≈ RJ/RNS + 1. Hence, achieving RJ/RNS < 1 is a crucial step for implementation of 2D materials in printed electronics applications. In this work, we utilize an advanced liquid-interface deposition process to maximize nanosheet alignment and network uniformity, thus reducing RJ. We demonstrate the approach using graphene and MoS2 as model materials, achieving low RJ/RNS values of 0.5 and 0.2, respectively. The resultant graphene networks show a high conductivity of σNet = 5 × 10⁴ S/m while our semiconducting MoS2 networks demonstrate record mobility of μNet = 30 cm²/(V s), both at extremely low network thickness (tNet < 10 nm). Finally, we show that the deposition process is compatible with nonlayered quasi-2D materials such as silver nanosheets (AgNS), achieving network conductivity close to bulk silver for networks <100 nm-thick.

Solution-processable 2D materials are promising candidates for a range of printed electronics applications. Yet maximising their potential requires solution-phase processing of nanosheets into high-quality networks with carrier mobility ({\mu}Net) as close as possible to that of individual nanosheets ({\mu}NS). In practise, the presence of inter-nanosheet junctions generally limits electronic conduction, such that the ratio of junction resistance (RJ) to nanosheet resistance (RNS), determines the network mobility via . Hence, achieving RJ/RNS<1 is a crucial step for implementation of 2D materials in printed electronics applications. In this work, we utilise an advanced liquid-interface deposition process to maximise nanosheet alignment and network uniformity, thus reducing RJ. We demonstrate the approach using graphene and MoS2 as model materials, achieving low RJ/RNS values of 0.5 and 0.2, respectively. The resultant graphene networks show a high conductivity of {\sigma}Net = 5 \times 104 S/m while our semiconducting MoS2 networks demonstrate record mobility of {\mu}Net = 30 cm2/Vs, both at extremely low network thickness (tNet <10 nm). Finally, we show that the deposition process is compatible with non-layered quasi-2D materials such as silver nanosheets (AgNS), achieving network conductivity close to bulk silver for networks <100 nm thick. We believe this work is the first to report nanosheet networks with RJ/RNS<1 and serves to guide future work in 2D materials-based printed electronics.