Joel van Embden

Electronic Tuning of 2D MoS2 through Surface Functionalization

The electronic properties of thiol-functionalized 2D MoS2 nanosheets are investigated. Shifts in the valence and conduction bands and Fermi levels are observed while bandgaps remain unaffected. These findings allow the tuning of energy barriers between 2D MoS2 and other materials, which can lead to improved control over 2D MoS2 -based electronic and optical devices and catalysts.

Synthesis and characterisation of famatinite copper antimony sulfide nanocrystals

The method to synthesise monodisperse copper antimony sulfide (CAS) nanocrystals is reported for the first time. This material opens up a new class of I–V–VI semiconductor nanocrystals and antimony-based nanocrystals in general. The novel CAS nanocrystals synthesised here absorb over UV-vis-NIR wavelengths and are suitable for application in near infrared detectors, as well as telecommunication, thermoelectric, and solar photovoltaic devices.

Exfoliation Solvent Dependent Plasmon Resonances in Two-Dimensional Sub-Stoichiometric Molybdenum Oxide Nanoflakes.

Few-layer two-dimensional (2D) molybdenum oxide nanoflakes are exfoliated using a grinding assisted liquid phase sonication exfoliation method. The sonication process is carried out in five different mixtures of water with both aprotic and protic solvents. We found that surface energy and solubility of mixtures play important roles in changing the thickness, lateral dimension, and synthetic yield of the nanoflakes. We demonstrate an increase in proton intercalation in 2D nanoflakes upon simulated solar light exposure. This results in substoichiometric flakes and a subsequent enhancement in free electron concentrations, producing plasmon resonances. Two plasmon resonance peaks associated with the thickness and the lateral dimension axes are observable in the samples, in which the plasmonic peak positions could be tuned by the choice of the solvent in exfoliating 2D molybdenum oxide. The extinction coefficients of the plasmonic absorption bands of 2D molybdenum oxide nanoflakes in all samples are found to be high (ε > 10(9) L mol(-1) cm(-1)). It is expected that the tunable plasmon resonances of 2D molybdenum oxide nanoflakes presented in this work can be used in future electronic, optical, and sensing devices.

Optically monitored spray coating system for the controlled deposition of the photoactive layer in organic solar cells

A spray deposition process equipped with an in situ optical thickness monitoring system has been developed to fabricate the photoactive layer of solar cells. Film thickness is monitored by a photodiode–LED couple after each deposition cycle. Using optimized conditions, the thickness of the spray deposited photoactive films can be tuned to increase linearly with the number of deposition cycles over a wide range of deposition conditions. After instrument calibration, optimization of the active layer thickness can be accomplished by simply setting the desired absorbance of the film. The simple process outlined here may be used for the rapid optimization of thin film photovoltaic devices. As proof of this, we fabricate a poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester as well as a P3HT and indene-C60 bis-adduct organic solar cells, which achieve a champion power conversion efficiency of 4.2%.

Oxygen-deficient photostable Cu2O for enhanced visible light photocatalytic activity

Oxygen vacancies in inorganic semiconductors play an important role in reducing electron-hole recombination, which may have important implications in photocatalysis. Cuprous oxide (Cu2O), a visible light active p-type semiconductor, is a promising photocatalyst. However, the synthesis of photostable Cu2O enriched with oxygen defects remains a challenge. We report a simple method for the gram-scale synthesis of highly photostable Cu2O nanoparticles by the hydrolysis of a Cu(i)-triethylamine [Cu(i)-TEA] complex at low temperature. The oxygen vacancies in these Cu2O nanoparticles led to a significant increase in the lifetimes of photogenerated charge carriers upon excitation with visible light. This, in combination with a suitable energy band structure, allowed Cu2O nanoparticles to exhibit outstanding photoactivity in visible light through the generation of electron-mediated hydroxyl (OH˙) radicals. This study highlights the significance of oxygen defects in enhancing the photocatalytic performance of promising semiconductor photocatalysts.

The formation mechanism of Janus nanostructures in one-pot reactions: the case of Ag–Ag8GeS6

Herein we describe a large-scale, non-injection “one-pot” batch method for producing large quantities of novel colloidal Ag–Ag8GeS6 heteronanostructures. Using a suite of analytical techniques, including high resolution TEM, HAADF-STEM, XEDS mapping, and XRD, the formation mechanism of the nanostructures is elucidated. The formation is discovered to occur in three stages comprising nucleation, phase separation of the metal and semiconductor components, and the final segregation of the metal and semiconductor components to form the Janus nanostructure. The high ionic mobility and chemical reactivity of Ag enables the self-regulated formation of Janus nanostructures in optimized one-pot reactions – a phenomenon that is almost unique to silver-based systems. As such, silver-based systems are ideal candidates to study the formation of Janus nanostructures.

Functional three-dimensional nonlinear nanostructures in a gold ion nanocomposite

We developed a novel nanocomposite consisting of an organic-inorganic hybrid polymer and gold ion nanoparticles. The nanocomposite has been proven to be suitable for functional three-dimensional nanostructure fabrication due to the fact that dominant formation of the nanoparticles is triggered in the post bake process after nanofabrication. The nanocomposite has high third-order nonlinearity due to the local field enhancement of the gold nanoparticles.