Valence band modification of Cr2O3 by Ni-doping: creating a high figure of merit p-type TCO

p-Type transparent conductors and semiconductors still suffer from remarkably low performance compared to their more widespread n-type counterparts, despite extensive investigation into their development. In this contribution, we present a comparative study on the defect chemistry of potential p-type transparent conducting oxides Mg-doped and Ni-doped Cr 2 O 3 . Conductivities as high as 28 S cm -1 were achieved by Ni-doping. By benchmarking crystallography and spectroscopy characterization against density functional theory calculations, we show that the incorporation of Ni into Cr 2 O 3 contributes to the composition of the valence band, making the formed holes more delocalized, while Mg states do not interact with the valence band in Mg-doped Cr 2 O 3 . Furthermore, it is experimentally proven that Ni has a higher solubility in Cr 2 O 3 than Mg, at least in the highly non-thermodynamic deposition conditions used for these experiments, which directly translates into a higher acceptor concentration. The combination of these two effects means that Ni is a more effective acceptor in Cr 2 O 3 than Mg and explains the improved conductivity observed for the former

Percolating metallic structures templated on laser-deposited carbon nanofoams derived from graphene oxide: applications in humidity sensing

Carbon nanofoam (CNF) is a low-density, high-surface-area material formed by aggregation of amorphous carbon nanoparticles into porous nanostructures. We report the use of a pulsed infrared laser to prepare CNF from a graphene oxide (GO) target material. Electron microscopy shows that the films consist of dendritic strings that form web-like three-dimensional structures. The conductivity of these structures can be modified by using the CNF as a nanostructured scaffold for gold nanoparticles deposited by sputter coating, controllably increasing the conductivity by up to 4 orders of magnitude. The ability to measure the conductivity of the porous structures allows electrochemical measurements in the environment. Upon decreasing humidity, the pristine CNF exhibits an increase in resistance with a quick response and recovery time. By contrast, the gold-sputtered CNF showed a decrease in resistance, indicating modification of the doping mechanism due to water adsorption. The sensitivity to humidity is eliminated at the percolation threshold of the metal on the CNF

Sonochemical edge functionalisation of molybdenum disulfide

Liquid-phase exfoliation (LPE) has been shown to be capable of producing large quantities of high-quality dispersions suitable for processing into subsequent applications. LPE typically requires surfactants for aqueous dispersions or organic solvents with high boiling point. However, they have major drawbacks such as toxicity, aggregation during solvent evaporation or the presence of residues. Here, dispersions of molybdenum disulfide in acetone are prepared and show much higher concentration and stability than predicted by Hansen parameter analysis. Aiming to understand those enhanced properties, the nanosheets were characterised using UV-visible spectroscopy, zeta potential measurements, atomic force microscopy, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and scanning transmission microscopy combined with spatially-resolved electron energy loss spectroscopy. Also, the performance of the MoS2 nanosheets exfoliated in acetone was compared to those exfoliated in isopropanol as a catalyst for the hydrogen evolution reaction. The conclusion from the chemical characterisation was that MoS2 nanosheets exfoliated in acetone have an oxygen edge-functionalisation, in the form of molybdenum oxides, changing its interaction with solvents and explaining the observed high-quality and stability of the resulting dispersion in a low boiling point solvent. Exfoliation in acetone could potentially be applied as a pretreatment to modify the solubility of MoS2 by edge-functionalisation

GWAS of random glucose in 476,326 individuals provide insights into diabetes pathophysiology, complications and treatment stratification

Conventional measurements of fasting and postprandial blood glucose levels investigated in genome-wide association studies (GWAS) cannot capture the effects of DNA variability on ‘around the clock’ glucoregulatory processes. Here we show that GWAS meta-analysis of glucose measurements under nonstandardized conditions (random glucose (RG)) in 476,326 individuals of diverse ancestries and without diabetes enables locus discovery and innovative pathophysiological observations. We discovered 120 RG loci represented by 150 distinct signals, including 13 with sex-dimorphic effects, two cross-ancestry and seven rare frequency signals. Of these, 44 loci are new for glycemic traits. Regulatory, glycosylation and metagenomic annotations highlight ileum and colon tissues, indicating an underappreciated role of the gastrointestinal tract in controlling blood glucose. Functional follow-up and molecular dynamics simulations of lower frequency coding variants in glucagon-like peptide-1 receptor (GLP1R), a type 2 diabetes treatment target, reveal that optimal selection of GLP-1R agonist therapy will benefit from tailored genetic stratification. We also provide evidence from Mendelian randomization that lung function is modulated by blood glucose and that pulmonary dysfunction is a diabetes complication. Our investigation yields new insights into the biology of glucose regulation, diabetes complications and pathways for treatment stratification

Transmission electron imaging and diffraction characterisation of 2D nanomaterials

Following the discovery of graphene, 2D nanostructures have been noted for their potential in a range of high-impact applications, such as sensing, catalysis, and composite reinforcement. Liquid-phase exfoliation and chemical vapour deposition have been demonstrated and indicate the feasibility of mass-scale production. With the advent of mass-produced 2D nanostructures a key focus of research is to characterise these materials. This thesis is concerned with imaging and structural properties of the 2D nanomaterials, hexagonal boron nitride (h-BN), molybdenum disulfide (MoS2), tungsten disulfide (WS2), titanium disulfide (TiS2) and hexabenzocoronene (HBC), produced via liquid phase exfoliation. HBC strictly speaking is not 2D nanomaterial, however, it can be viewed as transition molecule from benzene to graphene. The data used for characterisation is based primarily on electron diffraction and, in particular, aberration corrected annular dark field (ADF) scanning transmission electron microscopy (STEM). The incoherent nature of ADF STEM provides direct atomic imaging without the contrast reversals upon focus changes seen in conventional high-resolution transmission electron microscopy (HRTEM). The main structural feature investigated in this thesis was the stacking sequences in few-layers h-BN, MoS2, WS2 and TiS2. Simple stacking (AAA) can be distinguished from Bernal (ABA) and rhombohedral (ABC) on the basis of intensity ratio, I{10̅10}/I{11̅20} , in diffraction patterns and indirectly in HRTEM images. Nonetheless acquisition of the diffraction patterns suitable for analysis can be challenging due to the sample issues. Non-bulk stacking sequences were reliably confirmed for all above 2D nanomaterials on the basis of atomically resolved ADF STEM. 20 h-BN, 28 MoS2, 5 WS2 and 6 TiS2 nanoflakes were imaged and analysed. Amongst them 2 h-BN, 9 MoS2, 4 WS2 and 1 TiS2 nanoflakes displayed non-bulk stacking. Hence, it appears that 2D WS2 has the greatest affinity for non-bulk stacking. Finally, an interesting structural transformation was observed in HBC molecules. Under the influence of electron beam HBC agglomerates were transformed into crystalline phase with 90o symmetry</p

Transmission electron imaging and diffraction characterisation of 2D nanomaterials

Following the discovery of graphene, 2D nanostructures have been noted for their potential in a range of high-impact applications, such as sensing, catalysis, and composite reinforcement. Liquid-phase exfoliation and chemical vapour deposition have been demonstrated and indicate the feasibility of mass-scale production. With the advent of mass-produced 2D nanostructures a key focus of research is to characterise these materials. This thesis is concerned with imaging and structural properties of the 2D nanomaterials, hexagonal boron nitride (h-BN), molybdenum disulfide (MoS2), tungsten disulfide (WS2), titanium disulfide (TiS2) and hexabenzocoronene (HBC), produced via liquid phase exfoliation. HBC strictly speaking is not 2D nanomaterial, however, it can be viewed as transition molecule from benzene to graphene. The data used for characterisation is based primarily on electron diffraction and, in particular, aberration corrected annular dark field (ADF) scanning transmission electron microscopy (STEM). The incoherent nature of ADF STEM provides direct atomic imaging without the contrast reversals upon focus changes seen in conventional high-resolution transmission electron microscopy (HRTEM). The main structural feature investigated in this thesis was the stacking sequences in few-layers h-BN, MoS2, WS2 and TiS2. Simple stacking (AAA) can be distinguished from Bernal (ABA) and rhombohedral (ABC) on the basis of intensity ratio, I{10̅10}/I{11̅20} , in diffraction patterns and indirectly in HRTEM images. Nonetheless acquisition of the diffraction patterns suitable for analysis can be challenging due to the sample issues. Non-bulk stacking sequences were reliably confirmed for all above 2D nanomaterials on the basis of atomically resolved ADF STEM. 20 h-BN, 28 MoS2, 5 WS2 and 6 TiS2 nanoflakes were imaged and analysed. Amongst them 2 h-BN, 9 MoS2, 4 WS2 and 1 TiS2 nanoflakes displayed non-bulk stacking. Hence, it appears that 2D WS2 has the greatest affinity for non-bulk stacking. Finally, an interesting structural transformation was observed in HBC molecules. Under the influence of electron beam HBC agglomerates were transformed into crystalline phase with 90o symmetryThis thesis is not currently available in ORA

Colloidal core-satellite supraparticles via preprogramed burst of nanostructured micro-raspberry particles

Colloidal molecules, or more general supraparticles, i.e., particles which are themselves assembled of smaller nanoparticles in a defined way, are known to be synthesizable via bottom‐up assembly techniques in colloidal dispersion. The amount of synthesizable particles is mostly limited to milligrams. Herein, a bottom‐up‐programed, triggerable top‐down process is reported to obtain core–satellite supraparticles, i.e., particles composed of a larger core particle surrounded by smaller satellite particles. The key is to prepare a nanostructured, microparticulate powder into which defined burst behavior is preprogramed. Once the system is mechanically triggered, it bursts into well‐defined nanosized core–satellite supraparticles. Scale‐up is easily feasible and several hundred grams per batch can be demonstrated. The product is a ready‐to‐use and flexibly processible powder. Upon simple mixing with a polymer, it disintegrates into the preprogramed core–satellite supraparticles, thus forming a highly sophisticated nanocomposite with the polymer matrix. A pure silica nanoparticle system and a silica–iron oxide nanoparticle hybrid system are presented to demonstrate the versatility of the approach. Enhanced mechanical and unexpected magneto‐optical properties with the particle system are found. The disintegration of the microparticles into individual core–satellite colloidal supraparticles is confirmed via in situ liquid cell transmission electron microscopy

Hollow superparamagnetic microballoons from lifelike, self-directed pickering emulsions based on patchy nanoparticles

Herein, the formation of hollow microballoons derived from superparamagnetic iron oxide nanoparticles with silica patches is reported. Depending on the experimental conditions, single- or multishelled superparamagnetic microballoons as well as multivesicular structures were obtained. We show how such structural changes follow a lifelike process that is based on self-directing Pickering emulsions. We further demonstrate that the key toward the formation of such complex architectures is the patchy nature of the nanoparticles. Interestingly, no well-defined ordering of patches on the particles surface is required, unlike what theorists formerly predicted. The resultant hollow microballoons may be turned into hollow carbonaceous magnetic microspheres by simple pyrolysis. This opens the way to additional potential applications for such ultralightweight (density: 0.16 g·cm–3) materials