ConspectusCarbon-based materials─often with superlative electronic, mechanical, chemical, and thermal properties─are often categorized by dimensionality and hybridization. Most of these categories are produced in high-temperature conditions that afford equilibrium-dictated structures, but limit their diversity. In contrast, an emerging class of one-dimensional (1D) carbon materials, coined nanothreads, are accessible through kinetically controlled solid-state reactions of small multiply unsaturated molecules. While abundant in molecular organic synthesis, exerting kinetic control over reactivity is a revolutionary approach to access dense carbon networks. Owing to their internal diamond-like core, these materials are calculated to span a wide range of mechanical and optical properties, with the introduction of functional groups and/or heteroatoms leading to tailorable band gaps and the potential to access electronic states that are not featured in traditional polymers or nanomaterials. Accessing these properties requires the ability to precisely control solid-state molecular reaction pathways, chemical connectivity, and heteroatom/functional group density. Carbon nanothreads are often synthesized through the pressure-induced polymerization of aromatic molecules (e.g., benzene, pyridine, and thiophene) upon compression to 23-40 GPa. While the high pressures required to achieve these crystalline materials often preclude making synthetically viable quantities of product, the use of lessened aromatic reactants, along with light and/or heat, enables more mild reaction pressures. Success to date in forming nanothreads from diverse reactants suggests that physical organic principles govern the reaction, along with topochemical relationships, enabling the emergence of a new field of carbon chemistry that combines the control of organic chemistry with the range of physical properties only possible in extended periodic solids.In this Account, we describe our efforts to rationally synthesize carbon nanothreads with desired structures and present our approaches to dictate reactivity in the organic solid state that enable the formation of crystalline 1D carbon materials. In particular, we focus on the principles being pursued by our group to expand the chemical diversity of materials being accessed, while highlighting efforts that both enhance selectivity over reaction pathways and reduce pressure requirements for polymerization. We begin by leveraging starting materials with lessened or no aromaticity (relative to benzene) to design new backbones while enabling lower pressures such as 15-20 GPa to achieve nanothread formation. Next, we discuss efforts to utilize photochemical activation as a means to dictate the reaction pathway and/or affect the mechanism while also achieving ordered crystalline solids at reduced pressures. Lastly, we highlight efforts to demonstrate kinetic control in solid-state reactions by leveraging supramolecular chemistry (e.g., aryl/perfluoroaryl interactions, hydrogen bonds, π-π stacking) to preorganize starting materials into polymerizable molecular stacks. The resultant design principles provide multiple opportunities to attain previously inaccessible sp3-rich 1D polymeric carbon nanomaterials with unique structures and properties from widely available small molecules. Moreover, the kinetic control provided in the organic solid state enables a priori functionalization and the design of a rich diversity of materials with emergent properties in stark contrast to many well-developed carbon materials.

Carbon nanothreads are a rapidly growing class of 1D nanomaterials with sp3-hybridized diamond-like backbones. They are typically synthesized through pressure-induced polymerizations of aromatics, resulting in diverse structures and functionalities. Aside from precursor selection, there are limited means to control reaction pathway or polymerization outcome. Analogous to selection rules that govern outcomes in molecular chemistry, we investigated thermally and photochemically mediated pressure-induced polymerizations of 1,4-cyclohexadiene and explored the resultant products. Thermally mediated polymerization of 1,4-cyclohexadiene yields a crystalline product; yet identification of the backbone architecture is complicated by the product's less ordered packing in which only two Friedel pairs are observed. Support for cyclobutane-based structures is present when comparing experimentally-obtained data to computed structures, yet further evidence suggesting eliptical cross-sections consistent with anti-cyclobutanes is obtained when comparing experimental data obtained from a Paris Edinburgh (PE) synthesis. In contrast, the recovered product obtained from the photochemically mediated polymerization exhibits different d-spacings and is consistent with simulations that support a single pathway toward highly elliptical syn-cyclobutane-linked nanothreads. These results suggest that photochemistry can enable reaction selectivity in nanothread synthesis.

Topological magnetic monopoles (TMMs), also known as hedgehogs or Bloch points, are three-dimensional (3D) non-local spin textures that are robust to thermal and quantum fluctuations due to the topology protection 1 – 4 . Although TMMs have been observed in skyrmion lattices 1 , 5 , spinor Bose–Einstein condensates 6 , 7 , chiral magnets 8 , vortex rings 2 , 9 and vortex cores 10 , it has been difficult to directly measure the 3D magnetization vector field of TMMs and probe their interactions at the nanoscale. Here we report the creation of 138 stable TMMs at the specific sites of a ferromagnetic meta-lattice at room temperature. We further develop soft X-ray vector ptycho-tomography to determine the magnetization vector and emergent magnetic field of the TMMs with a 3D spatial resolution of 10 nm. This spatial resolution is comparable to the magnetic exchange length of transition metals 11 , enabling us to probe monopole–monopole interactions. We find that the TMM and anti-TMM pairs are separated by 18.3 ± 1.6 nm, while the TMM and TMM, and anti-TMM and anti-TMM pairs are stabilized at comparatively longer distances of 36.1 ± 2.4 nm and 43.1 ± 2.0 nm, respectively. We also observe virtual TMMs created by magnetic voids in the meta-lattice. This work demonstrates that ferromagnetic meta-lattices could be used as a platform to create and investigate the interactions and dynamics of TMMs. Furthermore, we expect that soft X-ray vector ptycho-tomography can be broadly applied to quantitatively image 3D vector fields in magnetic and anisotropic materials at the nanoscale.

Nanostructured semiconductors are interesting because of their varied electronic and optical properties compared to the bulk. Using ordered porous materials as templates is an appealing approach to prepare nanostructured materials. However, the very small pore sizes (< 10 nm) of many mesoporous silicas make traditional deposition methods for germanium difficult, resulting in aggregated particles or voids in the deposited material. To overcome this challenge, high-pressure chemical vapor deposition (HPCVD) has been used to deposit germanium within the pore network of KIT-5 mesoporous silica. This technique allows for smooth, continuous deposition within small, tortuous pore networks. Both crystalline and amorphous materials can be produced, expanding the applicability of the resulting materials for various uses. The resulting nanocrystalline germanium has 5-nm features derived from the parent KIT-5 and is the smallest templated material prepared using HPCVD to date. This work represents the first time a three-dimensional mesoporous silica, with features ≤ 5 nm, has been uniformly filled with a semiconductor.

Understanding topological spin textures is important because of scientific interests and technological applications. However, observing nanoscale magnetization and mapping out their interactions in 3D have been challenging–due to the lack of nondestructive vector nanoimaging techniques that penetrate thick samples. Recently, we developed a new characterization technique, soft x-ray vector ptycho-tomography, to image spin textures with a 3D vector spatial resolution of 10 nm. Using 3D magnetic metamaterial as an example, we demonstrated the creation and observation of topological magnetic monopoles and their interactions. We expect this method to be applied broadly to image vector fields in magnetic samples and beyond.

The pressure-induced polymerization of aryl/perfluoroaryl co-crystals offers a strategic route to obtain sequence-defined polymeric architectures, such as diamond nanothreads, that feature a stiff sp3 hybridized backbone.

We developed soft x-ray vector ptychography at 10 nm spatial resolution without requiring a priori knowledge, which is then used to quantitatively image 3D magnetization vector fields of topological magnetic monopoles and their interactions.

Semiconductor metalattices consisting of a linked network of three-dimensional nanostructures with periodicities on a length scale <100 nm can enable tailored functional properties due to their complex nanostructuring. For example, by controlling both the porosity and pore size, thermal transport in these phononic metalattices can be tuned, making them promising candidates for efficient thermoelectrics or thermal rectifiers. Thus, the ability to characterize the porosity, and other physical properties, of metalattices is critical but challenging, due to their nanoscale structure and thickness. To date, only metalattices with high porosities, close to the close-packing fraction of hard spheres, have been studied experimentally. Here, we characterize the porosity, thickness, and elastic properties of a low-porosity, empty-pore silicon metalattice film (∼500 nm thickness) with periodic spherical pores (∼tens of nanometers), for the first time. We use laser-driven nanoscale surface acoustic waves probed by extreme ultraviolet scatterometry to nondestructively measure the acoustic dispersion in these thin silicon metalattice layers. By comparing the data to finite element models of the metalattice sample, we can extract Young's modulus and porosity. Moreover, by controlling the acoustic wave penetration depth, we can also determine the metalattice layer thickness and verify the substrate properties. Additionally, we utilize electron tomography images of the metalattice to verify the geometry and validate the porosity extracted from scatterometry. These advanced characterization techniques are critical for informed and iterative fabrication of energy-efficient devices based on nanostructured metamaterials.

Nanothreads are emerging one-dimensional sp3- hybridized materials with high predicted tensile strength and a tunable band gap. They can be synthesized by compressing aromatic or nonaromatic small molecules to pressures ranging from 15-30 GPa. Recently, new avenues are being sought that reduce the pressure required to afford nanothreads; the focus has been placed on the polymerization of molecules with reduced aromaticity, favorable stacking, and/or the use of higher reaction temperatures. Herein, we report the photochemically mediated polymerization of pyridine and furan aromatic precursors, which achieves nanothread formation at reduced pressures. In the case of pyridine, it was found that a combination of slow compression/ decompression with broadband UV light exposure yielded a crystalline product featuring a six-fold diffraction pattern with similar interplanar spacings to previously synthesized pyridine-derived nanothreads at a reduced pressure. When furan is compressed to 8 GPa and exposed to broadband UV light, a crystalline solid is recovered that similarly demonstrates X-ray diffraction with an interplanar spacing akin to that of the high-pressure synthesized furan-derived nanothreads. Our method realizes a 1.9-fold reduction in the maximum pressure required to afford furan-derived nanothreads and a 1.4-fold reduction in pressure required for pyridine derived nanothreads. Density functional theory and multiconfigurational wavefunction-based computations were used to understand the photochemical activation of furan and subsequent cascade thermal cycloadditions. The reduction of the onset pressure is caused by an initial [4+4] cycloaddition followed by increasingly facile thermal [4+2]-cycloadditions during polymerization.

Topological magnetic monopoles, also known as hedgehogs or Bloch points, are three-dimensional (3D) nonlocal spin textures that are robust to thermal and quantum fluctuations due to their topology 1-4 . Understanding their properties is of both fundamental interest and practical applications 1-9 . However, it has been difficult to experimentally produce topological magnetic monopoles in a controlled manner and directly observe their 3D magnetization vector field and interactions at the nanoscale. Here, we report the creation of 138 stable topological magnetic monopoles at the specific sites of a ferromagnetic meta-lattice at room temperature. We further develop 3D soft x-ray vector ptychography to determine the magnetization vector and emergent magnetic field of the topological monopoles with a 3D spatial resolution of 10 nm. This spatial resolution is comparable to the magnetic exchange length of transition metals 10 , enabling us to probe monopole-monopole interactions. We find that the topological monopole pairs with positive and negative charges are separated by 18.3±1.6 nm, while the positively and negatively charged pairs are stabilized at comparatively longer distances of 36.1±2.4 nm and 43.1±2.0 nm, respectively. We also observe virtual topological monopoles created by magnetic voids in the meta-lattice. This work demonstrates that ferromagnetic meta-lattices could be used as a new platform to create and investigate the interactions and dynamics of topological magnetic monopoles. Furthermore, we expect that soft x-ray vector ptychography can be broadly applied to quantitatively image 3D vector fields in magnetic and anisotropic materials at the nanoscale.

High pressure chemical vapor deposition (HPCVD) has shown to be a promising method for producing Cr2+:ZnSe and Fe2+:ZnSe mid-IR optical fiber lasers. The oxidation state of the dopants and their spatial homogeneity are critical for the characterization of effective fiber laser performance; however, this is challenging for small fiber cores and small doping concentrations. We demonstrate using synchrotron micro X-ray fluorescence (XRF) mapping to study the distribution of the dopants throughout the fiber cross-sections. Furthermore, we study the local chemical environment of these unique fiber structures using micro X-ray near edge absorption spectroscopy (XANES). Our study reveals that transition metal doped ZnSe deposited using HPCVD has nanoscale dopant aggregation although the material is chemically identical to the commercially produced diffusion doped laser crystals, as indicated by the presence +2 oxidation state of the dopants. This work demonstrates the power of synchrotron-based X-ray techniques for use as metrology tools for improving the performance of laser materials in fiber geometry.

HPCVD ZnSe optical fibers support hundreds to thousands of modes because they lack an appropriate cladding layer. Here, we demonstrate HPCVD deposited ZnS x Se 1–x claddings to tune the number of supported modes.

Magnetic topological defects are energetically stable spin configurations characterized by symmetry breaking. Vortices and skyrmions are two well-known examples of 2D spin textures that have been actively studied for both fundamental interest and practical applications. However, experimental evidence of the 3D spin textures has been largely indirect or qualitative to date, due to the difficulty of quantitively characterizing them within nanoscale volumes. Here, we develop soft x-ray vector ptychography to quantitatively image the 3D magnetization vector field in a frustrated superlattice with 10 nm spatial resolution. By applying homotopy theory to the experimental data, we quantify the topological charge of hedgehogs and anti-hedgehogs as emergent magnetic monopoles and probe their interactions inside the frustrated superlattice. We also directly observe virtual hedgehogs and anti-hedgehogs created by magnetically inert voids. We expect that this new quantitative imaging method will open the door to study 3D topological spin textures in a broad class of magnetic materials. Our work also demonstrates that magnetically frustrated superlattices could be used as a new platform to investigate hedgehog interactions and dynamics and to exploit optimized geometries for information storage and transport applications.

13C-enrichment of furan by customsynthesis followed by modest-pressure synthesis of 13C-enrichednanothreads enabled a detailed characterization of the reaction products by afull complement of advanced solid-state NMR techniques, with validation by abinitio calculation of chemical shifts. The 13C NMR spectrum wascomplex, with more than a dozen distinct features, but almost all (> 95%)represented CH moieties are as expected in nanothreads, with only 2–4% CH2,0.3% C=O, and 0.3% COO groups, according to spectral editing. Differentcomponents were quantified by integration of the fully equilibrateddirect-polarization spectrum. Symmetric andasymmetric alkene-containing rings as well as trapped furan were identified by 13C-13Cand 1H-13C NMR. The most intriguing component observed wasfully saturated perfect anti furan-derived nanothread segments, with twodistinct, sharp peaks, accounting for ca. 10% of the material. The bondingpatterns in these periodic structures deduced from DQ/SQ NMR was that of a [4+2]cycloaddition product. While the small number of chemically inequivalent carbonsites eliminated low-symmetry syn/anti threads, the large number ofmagnetically inequivalent ones (i.e., distinct C-H orientations) inCODEX NMR was incompatible with the high-symmetry syn threads. Antithreads with two chemically and eight magnetically inequivalent sites providethe only consistent fit of the experimental data. These conclusions were convincinglycorroborated by quantum-chemical simulations, which showed good agreement ofisotropic chemical shifts only for the anti threads. This represents thefirst molecular-level identification of a specific type of nanothread. Thetypical length of the perfect, fully saturated thread segments was around 14bonds and they accordingly constitute small clusters (according to 13Cand 1H spin diffusion analyses) which likely reside within anoverall hexagonal thread packing along with other, less-perfect orless-saturated brethren. The relatively slow T1C relaxationconfirms the nanometer-scale length of the periodic perfect structure,indicates that the perfect threads are particularly rigid, and enables theirselective observation in 13C NMR.

Carbon nanothreads, which are unique one-dimensional sp3-rich polymers, combine high tensile strength with flexibility owing to subnanometer widths and diamond-like cores. These extended carbon solids are constructed through pressure-induced polymerization of sp2 molecules such as benzene. Whereas a few examples of carbon nanothreads have been reported, the need for high onset pressures ( ≥ 17 GPa) to synthesize them precludes scalability and limits scope. Herein, we report the scalable synthesis of carbon nanothreads based on molecular furan, which can be achieved through ambient temperature pressure-induced polymerization with an onset reaction pressure of only 10 GPa due to its lessened aromaticity relative to other molecular precursors. When slowly compressed to 15 GPa and gradually decompressed to 1.5 GPa, a sharp six-fold diffraction pattern is observed in situ, indicating a well‐ordered crystalline material formed from liquid furan. Single-crystal X-ray diffraction of the reaction product exhibits three distinct d-spacings from 4.75 to 4.9 Å, whose size, angular spacing, and degree of anisotropy are consistent with our atomistic simulations for crystals of furan nanothreads. Further evidence for polymerization was obtained by powder XRD and Raman/IR spectroscopy. Comparison of the IR spectra with computed vibrational modes provides identification of spectral features characteristic of specific nanothreads, namely syn, anti, and syn/anti configurations. Furan therefore presents a strategic entry toward scalable carbon nanothreads.

A set of novel potassium-calcium-aluminosilicate glasses are developed to serve as the cladding material for a doped ZnSe core infrared fiber laser. The compositions exhibit high glass transition temperatures between 753 degrees C and 918 degrees C and high thermal expansion coefficients between 5.75 ppm/degrees C and 8.21 ppm/degrees C. We demonstrate successful application of these glass compositions as a cladding for a ZnSe tunable fiber laser.

Transmission electron microscopy, scanning transmission electron tomography, and electron energy loss spectroscopy were used to characterize three-dimensional artificial Si nanostructures called "metalattices", focusing on Si metalattices synthesized by high-pressure confined chemical vapor deposition in 30-nm colloidal silica templates with ~7 and ~12 nm "meta-atoms" and ~2 nm "meta-bonds". The "meta-atoms" closely replicate the shape of the tetrahedral and octahedral interstitial sites of the face-entered cubic colloidal silica template. Composed of either amorphous or nanocrystalline silicon, the metalattice exhibits long-range order and interconnectivity in two-dimensional micrographs and three-dimensional reconstructions. Electron energy loss spectroscopy provides information on local electronic structure. The Si L2,3 core-loss edge is blue-shifted compared to the onset for bulk Si, with the meta-bonds displaying a larger shift (0.55 eV) than the two types of meta-atoms (0.30 and 0.17 eV). Local density of state calculations using an empirical tight binding method are in reasonable agreement.

Metalattices are crystalline arrays of uniform particles in which the period of the crystal is close to some characteristic physical length scale of the material. Here, we explore the synthesis and properties of a germanium metalattice in which the ∼70 nm periodicity of a silica colloidal crystal template is close to the ∼24 nm Bohr exciton radius of the nanocrystalline Ge replica. The problem of Ge surface oxidation can be significant when exploring quantum confinement effects or designing electronically coupled nanostructures because of the high surface area to volume ratio at the nanoscale. To eliminate surface oxidation, we developed a core-shell synthesis in which the Ge metalattice is protected by an oxide-free Si interfacial layer, and we explore its properties by transmission electron microscopy (TEM), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The interstices of a colloidal crystal film grown from 69 nm diameter spherical silica particles were filled with polycrystalline Ge by high-pressure confined chemical vapor deposition (HPcCVD) from GeH4. After the SiO2 template was etched away with aqueous HF, the Ge replica was uniformly coated with an amorphous Si shell by HPcCVD as confirmed by TEM-EDS (energy-dispersive X-ray spectroscopy) and Raman spectroscopy. Formation of the shell prevents oxidation of the Ge core within the detection limit of XPS. The electronic properties of the core-shell structure were studied by accessing the Ge 3d edge onset using STEM-EELS. A blue shift in the edge onset with decreasing size of Ge sites in the metalattices suggests quantum confinement of the Ge core. The degree of quantum confinement of the Ge core depends on the void sizes in the template, which is tunable by using silica particles of varying size. The edge onset also shows a shift to higher energy near the shell in comparison with the Ge core. This shift along with the observation of Ge-Si vibrational modes in the Raman spectrum indicate interdiffusion of Ge and Si. Both the size of the voids in the template and core-shell interdiffusion of Si and Ge can in principle be tuned to modify the electronic properties of the Ge metalattice.

Metalattices are artificial 3D solids, periodic on sub-100 nm length scales, that enable the functional properties of materials to be tuned. However, because of their complex structure, predicting and characterizing their properties is challenging. Here we demonstrate the first nondestructive measurements of the mechanical and structural properties of metalattices with feature sizes down to 14 nm. By monitoring the time-dependent diffraction of short wavelength light from laser-excited acoustic waves in the metalattices, we extract their acoustic dispersion, Young's modulus, filling fraction, and thicknesses. Our measurements are in excellent agreement with macroscopic predictions and potentially destructive techniques such as nanoindentation and scanning electron microscopy, with increased accuracy over larger areas. This is interesting because the transport properties of these metalattices do not obey bulk predictions. Finally, this approach is the only way to validate the filling fraction of metalattices over macroscopic areas. These combined capabilities can enable accurate synthesis of nanoenhanced materials.