Dr Matthew Barr

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.

This work investigated the photophysical pathways for light absorption, charge generation, and charge separation in donor-acceptor nanoparticle blends of poly(3-hexylthiophene) and indene-C60-bisadduct. Optical modeling combined with steady-state and time-resolved optoelectronic characterization revealed that the nanoparticle blends experience a photocurrent limited to 60% of a bulk solution mixture. This discrepancy resulted from imperfect free charge generation inside the nanoparticles. High-resolution transmission electron microscopy and chemically resolved X-ray mapping showed that enhanced miscibility of materials did improve the donor-acceptor blending at the center of the nanoparticles; however, a residual shell of almost pure donor still restricted energy generation from these nanoparticles.

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.

Abstract Scanning transmission X-ray microscopy (STXM) compositional mapping has been used to probe the mesomorphology of nanoparticles (NPs) synthesized from two very different polymer:fullerene blends: poly(3-hexylthiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) and poly[4,8-bis(2-ethylhexyloxy)benzo(1,2-b:4,5-b')dithiophene-alt-5, 6-bis(octyloxy)-4,7-di(thiophen-2-yl)(2,1,3-benzothiadiazole)-5,5'-diyl] (PSBTBT): PCBM. The STXM data shows that both blends form core-shell NP structures with similar shell compositions, but with different polymer:fullerene ratios in the core regions. P3HT:PCBM and PSBTBT:PCBM NP organic photovoltaic (OPV) devices have been fabricated and exhibit similar device efficiencies, despite the PSBTBT being a much higher performing low band gap material. By comparing the measured NP shell and core compositions with the optimized bulk hetero-junction (BHJ) compositions, we show that the relatively higher performance of the P3HT:PCBM NP device arises from the fact that its shell composition is much closer to the optimal BHJ value than that of the PSBTBT:PCBM NP device.

Traditional artist-in-science-residency schemes have tended to focus on artists using scientific tools and technology as a medium for their art. What kind and quality of work might occur, however, between scientists working on cutting-edge solar energy research and a visual artist (a sculptor) when they are integrated in a truly collaborative environment? Is it good for the art? Is it good for the science? The authors describe a new methodology for art-science interactions whereby they have integrated arts practice within a scientific environment. A critical aspect of the methodology for the residency was the development of an interaction framework that ensured that both artist and scientist had equal voice in discussions involving the art and science of the project within an environment of mutual respect. The integration led to the development of outcomes that would not have occurred otherwise.

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.