A series of polymer semiconductors incorporating 2,1,3-benzothiadiazole-5,6-dicarboxylicimide (BTZI) as strong electron-withdrawing unit and an alkoxy-functionalized head-to-head linkage containing bithiophene or bithiazole as highly electron-rich co-unit are designed and synthesized. Because of the strong intramolecular charge transfer characteristics, all three polymers BTZI-TRTOR (P1), BTZI-BTOR (P2), and BTZI-BTzOR (P3) exhibit narrow bandgaps of 1.13, 1.05, and 0.92 eV, respectively, resulting in a very broad absorption ranging from 350 to 1400 nm. The highly electron-deficient 2,1,3-benzothiadiazole-5,6-dicarboxylicimide and alkoxy-functionalized bithiophene (or thiazole) lead to polymers with low-lying lowest unoccupied molecular orbitals (-3.96 to -4.28 eV) and high-lying highest occupied molecular orbitals (-5.01 to -5.20 eV). Hence, P1 and P3 show substantial and balanced ambipolar transport with electron mobilities/hole mobilities of up to 0.86/0.51 and 0.95/0.50 cm V s, respectively, and polymer P2 containing the strongest donor unit exhibited unipolar p-type performance with an average hole mobility of 0.40 cm V s in top-gate/bottom-contact thin-film transistors with gold as the source and drain electrodes. When incorporated into bulk heterojunction polymer solar cells, the narrow bandgap (1.13 eV) polymer P1 shows an encouraging power conversion efficiency of 4.15% with a relatively large open-circuit voltage of 0.69 V, which corresponds to a remarkably small energy loss of 0.44 eV. The power conversion efficiency of P1 is among the highest reported to date with such a small energy loss in polymer:fullerene solar cells.

The availability of intense soft x-ray beams with tunable energy and polarization has pushed the development of highly sensitive, element-specific, and noninvasive microscopy techniques to investigate condensed matter with high spatial and temporal resolution. The short wavelengths of soft x-rays promise to reach spatial resolutions in the deep single-digit nanometer regime, providing unprecedented access to magnetic phenomena at fundamental length scales. Despite considerable efforts in soft x-ray microscopy techniques, a two-dimensional resolution of 10 nm has not yet been surpassed in direct imaging. Here, we report on a significant step beyond this long-standing limit by combining newly developed soft x-ray Fresnel zone plate lenses with advanced precision in scanning control and careful optical design. With this approach, we achieve an image resolution of 7 nm. By combining this highly precise microscopy technique with the x-ray magnetic circular dichroism effect, we reveal dimensionality effects in an ensemble of interacting magnetic nanoparticles. Such effects are topical in current nanomagnetism research and highlight the opportunities of highresolution soft x-ray microscopy in magnetism research and beyond.

Moving towards significantly smaller nanostructures, direct structuring techniques such as electron beam lithography approach fundamental limitations in feature size and aspect ratios. Application of nanostructures like diffractive X-ray lenses require feature sizes of below 10 nm to enter a new regime in high resolution X-ray microscopy. As such dimensions are difficult to obtain using conventional electron beam lithography, we pursue a line-doubling approach. We demonstrate that this method yields structure sizes as small as 6.4 nm. X-ray lenses fabricated in this way are tested for their efficiency and microscopic resolution. In addition, the line-doubling technique is successfully extended to a six-fold scheme, where each line in a template structure written by electron beam lithography evolves into six metal lines.

* Benedikt Rösner, benedikt.roesner@psi.ch X-ray microscopy and spectroscopy are powerful tools to gain valuable insight into many exciting, scientifically relevant samples. Development in microscopic methods has always aimed for achieving spatial resolutions as high as possible. Although highly confined X-ray beams with spot sizes well below 10 nm have been characterized in recent years using mirrors [1], Fresnel zone plate (FZP) lenses [2,3] or multilayer Laue lenses [4,5], X-ray imaging with single-digit nanometer resolution remains an extreme challenge.We report on unprecedented spatial resolution down to 7 nm achieved at two soft X-ray microscopes using photon energies between 700 eV and 850 eV. The experiments were performed at the scanning transmission X-ray microscopes (STXM) at the PolLux beamline at the Swiss Light Source [6] and the Hermes beamline at Synchrotron Soleil [7]. The scientific applications of these two instruments lie in the combination of microscopy and spectroscopy, where high spatial resolution provides a major benefit for scientific research.The key element in a STXM for achieving small spot sizes and thus high resolution is the Fresnel zone plate (FZP) commonly used as X-ray lens. An elegant method to fabricate high-resolution FZPs has been introduced by doubling the line density obtained from the lithography step utilizing atomic layer deposition [8,9]. This method has been applied to fabricate FZPs with zone widths down to 12 nm [8][9][10]. By further optimization of the nanofabrication process, we have fabricated FZPs with outermost zone widths well below 10 nm and heights between 60 nm and 80 nm [11]. The specifications for the lenses were chosen according to the illumination at the PolLux and Hermes beamlines [6,7], ensuring that the zone plate dimensions match the coherence length and energy bandwidth of each beamline. To achieve the highest possible spatial resolution, the experimental geometry and mechanical stability of the STXM endstations had to be optimized. Special attention has to be paid to the extremely short focal length, and to the mechanical stability of the sample stage. While the former challenge can be addressed by using a thin order-sorting aperture, the latter one has to be addressed by carefully optimizing the position control and feedback system. In this way, the maximum amplitude of sample displacement with respect to the zone plate has been brought to ± 3 nm perpendicular to the beam axis.In order to characterize the spatial resolution of our FZPs, we recorded images of high-resolution test patterns. The test patterns consist of a periodic repetitions of an iridium line, an HSQ line, a second iridium line, and a gap. The lateral dimensions of each line or gap of the investigated test samples are 10 nm, 9 nm, 8 nm, and 7 nm (Figure 1). We scanned the test objects in point-by-point mode with steps