Dr Adam Fahy

Resolution is a key parameter for microscopy, but methods for standardizing its definition are often poorly defined. For a developing technique such as scanning helium microscopy, it is critical that a consensus-based protocol for determining instrument resolution is prepared as a written standard to allow both comparable quantitative measurements of surface topography and direct comparisons between different instruments. In this paper we assess a range of quantitative methods for determining instrument resolution and determine their relative merits when applied to the specific case of the scanning helium microscope (SHeM). Consequently, we present a preliminary protocol for measuring the resolution in scanning helium microscopy based upon utilizing appropriate test samples with sets of slits of well-defined dimensions to establish the quantitative resolution of any similar instrument.

Nanoengineered, eco-friendly, solution-processable electroactive materials are in demand for the growing field of printed electronics, and these material requirements can be achieved by the development of waterborne colloidal dispersions. Functionality in these composite materials can be tuned by thermodynamically modifying the material nanomorphology, often by creation of kinetically stabilized aqueous nanoparticle dispersions. In this work we demonstrate that the internal structure of organic nanoparticles is controlled by the surface energy difference between the polymeric donor material and the non-fullerene acceptor (NFA) material. Nanoparticles of the following donor-acceptor combinations, suitable for printed organic photovoltaics, have been synthesized: TQ1:N2200, TQ1:PNDIT10, P3HT:N2200, P3HT:o-IDTBR and P3HT:eh-IDTBR. Advanced synchrotron-based X-ray spectroscopy and microscopy are used to correlate the formation of core-shell nanoparticle morphology to the material surface energy. We subsequently present a viable avenue for customizing the blended nanoparticle structure into (i) core-shell, (ii) molecularly intermixed, or (iii) inverted shell-core structures. Our results showed that TQ1:PNDIT10 and P3HT:o-IDTBR nanoparticles were comprised of a donor-rich shell and an NFA-rich core, however, interestingly we show a reversal to the inverse NFA shell/donor core structure for TQ1:N2200, P3HT:N2200 and P3HT:eh-IDTBR nanoparticles, driven by the low surface energy of N2200 (23.7 mJ m-2) and eh-IDTBR (18.3 mJ m-2). This article is the first report of a flipped nanoparticle core-shell morphology comprising an NFA-rich shell for the miniemulsion synthesis route. The composition of the shells and cores was able to be controlled by the differential mismatch in the surface energy of the donor and acceptor materials, with ?Gsurface > 0, ?Gsurface = 0, and ?Gsurface < 0 for acceptor core-donor shell, molecularly intermixed, and acceptor shell-donor core, respectively. Accordingly, we introduce an entirely overlooked new figure of merit (FoM) for customizing nanoparticulate colloidal inks: tunable surface energy of non-fullerene-based semiconductors. The establishment of this FoM opens up electroactive material design to a wide range of functional printing applications with varying device and ink structure requirements, thereby reshaping the nanoengineering toolkit for waterborne colloidal dispersions and hence printed electronics.

Adsorption is a promising technology for removal of organic and inorganic contaminants from soil and water system. In this study, magnetically separable mesoporous polymeric beads (NiZnFe4O4-HNT@alg) were synthesised for efficient removal of methylene blue (MB, cationic dye) under broad solution pH (from pH 3.41 to pH 8.43). Alginate biopolymer were used to stabilize halloysite nanotubes (HNTs) and nickel zinc iron oxide nanoparticles (NiZnFe4O4 < 100 nm). NiZnFe4O4 was incorporated onto the polymer beads to generate the adsorbents' magnetic properties and catalytic degradability. The adsorbent (NiZnFe4O4-HNT@alg) have higher surface area (122.43 m2/g), suitable mesoporosity (~6.68 nm), larger pore volume (0.11 cm3/g), and abundance of active sites, enabling high adsorption capacity (264 mg/g) of MB. The abundance of hydroxyl, carboxyl, and siloxane groups enabled cationic dye sorption through ionic interaction. The removal efficiency of MB was ~99% under a wide solution pH range from 10 mg/L of MB, in which the adsorbent dose was 2 g/L. Both Langmuir (R2 = 0.99; p < 0.001) and Freundlich (R2 = 0.99; p < 0.001) isotherm models fitted well, whereas trends of kinetics model fitting are pseudo-second-order (R2 = 0.99) > intraparticle diffusion (R2 = 0.93) > pseudo-first-order (R2 = 0.87). Energy-dispersive X-ray spectroscopy (EDS) elemental mapping demonstrated that MB has a co-distribution with silicon, aluminium, and alginate carbon phase but is limited with iron and nickel, indicating HNTs and alginate polymer performed as sorption sites, whereas NiZnFe4O4 performed as a catalyst. The presence (post-sorption) and absence (pre-sorption) of inorganic, total carbon or total organic carbon content at different solution pH, contact time, and initial concentration of MB demonstrated that the adsorbent act as a catalyst as well for degradation of MB. NiZnFe4O4-HNT@alg triggers efficient removal of MB with the assist of adsorption and catalytic degradation at broad solution pH. A comparison in removal of MB by various adsorbents including, biochars, clays, activated carbon, nanoparticles, polymers, nano composites, graphene oxides, carbon nanotubes, and polymer beads with the result of this study were performed, illustrating competitive sorption capacity of NiZnFe4O4-HNT@alg.

Understanding doping in polymer semiconductors has important implications for the development of organic electronic devices. This study reports a detailed investigation of the doping of the poly(3-hexylthiophene) (P3HT)/Nafion bilayer interfaces commonly used in organic biosensors. A combination of UV-visible spectroscopy, dynamic secondary ion mass spectrometry (d-SIMS), dynamic mechanical thermal analysis, and electrical device characterization reveals that the doping of P3HT increases with annealing temperature, and this increase is associated with thermally activated interdiffusion of the P3HT and Nafion. First-principles modeling of d-SIMS depth profiling data demonstrates that the diffusivity coefficient is a strong function of the molar concentration, resulting in a discrete intermixed region at the P3HT/Nafion interface that grows with increasing annealing temperature. Correlating the electrical conductance measurements with the diffusion model provides a detailed model for the temperature-modulated doping that occurs in P3HT/Nafion bilayers. Point-of-care testing has created a market for low-cost sensor technology, with printed organic electronic sensors well positioned to meet this demand, and this article constitutes a detailed study of the doping mechanism underlying such future platforms for the development of sensing technologies based on organic semiconductors.

Here we report the application of a conjugated copolymer based on thiophene and quinoxaline units, namely poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1), to nanoparticle organic photovoltaics (NP-OPVs). TQ1 exhibits more desirable material properties for NP-OPV fabrication and operation, particularly a high glass transition temperature (Tg) and amorphous nature, compared to the commonly applied semicrystalline polymer poly(3-hexylthiophene) (P3HT). This study reports the optimisation of TQ1:PC71BM (phenyl C71 butyric acid methyl ester) NP-OPV device performance by the application of mild thermal annealing treatments in the range of the Tg (sub-Tg and post-Tg), both in the active layer drying stage and post-cathode deposition annealing stage of device fabrication, and an in-depth study of the effect of these treatments on nanoparticle film morphology. In addition, we report a type of morphological evolution in nanoparticle films for OPV active layers that has not previously been observed, that of PC71BM nano-pathway formation between dispersed PC71BM-rich nanoparticle cores, which have the benefit of making the bulk film more conducive to charge percolation and extraction.

Delicate structures (such as biological samples, organic films for polymer electronics and adsorbate layers) suffer degradation under the energetic probes of traditional microscopies. Furthermore, the charged nature of these probes presents difficulties when imaging with electric or magnetic fields, or for insulating materials where the addition of a conductive coating is not desirable. Scanning helium microscopy is able to image such structures completely non-destructively by taking advantage of a neutral helium beam as a chemically, electrically and magnetically inert probe of the sample surface. Here we present scanning helium micrographs demonstrating image contrast arising from a range of mechanisms including, for the first time, chemical contrast observed from a series of metal-semiconductor interfaces. The ability of scanning helium microscopy to distinguish between materials without the risk of damage makes it ideal for investigating a wide range of systems.

We investigate the suitability of four different inorganic materials (chromium oxide (CrOX), titanium oxide (TiOX), aluminium doped zinc oxide (AZO) and zinc oxide (ZnO)) as electrode transport layers in fully roll-to-roll (R2R) fabricated P3HT:ICxA organic solar cells. CrOX and TiOX were found to be unsuitable, as the CrOX devices did not exhibit rectifying behaviour while the TiOX devices did not withstand the annealing conditions. Of the last two ETLs, ZnO showed by far the most promise with devices demonstrating an average efficiency of 2.2%, which is the highest reported value for R2R devices in normal geometry, and a significantly extended lifetime compared with AZO devices under ISOS-L-2 conditions.

We present a scanning helium microscope equipped to make use of the unique contrast mechanisms, surface sensitivity, and zero damage imaging the technique affords. The new design delivers an order of magnitude increase in the available helium signal, yielding a higher contrast and signal-to-noise ratio. These improvements allow the microscope to produce high quality, intuitive images of samples using topological contrast, while setting the stage for investigations into further contrast mechanisms.