Shot noise-mitigated secondary electron imaging with ion count-aided microscopy

Modern science is dependent on imaging on the nanoscale, often achieved through processes that detect secondary electrons created by a highly focused incident charged particle beam. Scanning electron microscopy is employed in applications such as critical-dimension metrology and inspection for semiconductor devices, materials characterization in geology, and examination of biological samples. With its applicability to non-conducting materials (not requiring sample coating before imaging), helium ion microscopy (HIM) is especially useful in the high-resolution imaging of biological samples such as animal organs, tumor cells, and viruses. However, multiple types of measurement noise limit the ultimate trade-off between image quality and the incident particle dose, which can preclude useful imaging of dose-sensitive samples. Existing methods to improve image quality do not fundamentally mitigate the noise sources. Furthermore, barriers to assigning a physically meaningful scale make these modalities qualitative. Here we introduce ion count-aided microscopy (ICAM), which is a quantitative imaging technique that uses statistically principled estimation of the secondary electron yield. With a readily implemented change in data collection, ICAM nearly eliminates the influence of source shot noise -- the random variation in the number of incident ions in a fixed time duration. In HIM, we demonstrate 3x dose reduction; based on a good match between these empirical results and theoretical performance predictions, the dose reduction factor is larger when the secondary electron yield is higher. ICAM thus facilitates imaging of fragile samples and may make imaging with heavier particles more attractive

Interfacial connections between organic perovskite/n+ silicon/catalyst that allow integration of solar cell and catalyst for hydrogen evolution from water

The rapidly increasing solar conversion efficiency (PCE) of hybrid organic-inorganic perovskite (HOIP) thin-film semiconductors has triggered interest in their use for direct solar-driven water splitting to produce hydrogen. However, application of these low-cost, electronic-structure-tunable HOIP tandem photoabsorbers has been hindered by the instability of the photovoltaic-catalyst-electrolyte (PV+E) interfaces. Here, photolytic water splitting is demonstrated using an integrated configuration consisting of an HOIP/n+silicon single junction photoabsorber and a platinum (Pt) thin film catalyst. An extended electrochemical (EC) lifetime in alkaline media is achieved using titanium nitride (TiN) on both sides of the Si support to eliminate formation of insulating silicon oxide, and as an effective diffusion barrier to allow high-temperature annealing of the catalyst/TiO2-protected-n+silicon interface necessary to retard electrolytic corrosion. Halide composition was examined in the (Cs1-xFAx)PbI3 system with a bandgap suitable for tandem operation. A fill factor (FF) of 72.5% was achieved using a Spiro-OMeTAD-hole-transport-layer (HTL)-based HOIP/n+Si solar cell, and a high photocurrent density of -15.9 mA/cm2 (at 0V vs reversible hydrogen electrode) was attained for the HOIP/n+Si/Pt photocathode in 1M NaOH under simulated one-sun illumination. While this thin-film design creates stable interfaces, the intrinsic photo- and electro-degradation of the HOIP photoabsorber remains the main obstacle for future HOIP/Si tandem PEC devices