Off-axis multilayer zone plate with 16 nm × 28 nm focus for high-resolution X-ray beam induced current imaging.

Jakob Soltau,Mikhail Lyubomirskiy,Lert Chayanun,Jesper Wallentin,Markus Osterhoff

doi:10.1107/s1600577521006159

Jakob Soltau, Mikhail Lyubomirskiy + Show 3 more

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Using multilayer zone plates (MZPs) as two-dimensional optics, focal spot sizes of less than 10 nm can be achieved, as we show here with a focus of 8.4 nm × 9.6 nm, but the need for order-sorting apertures prohibits practical working distances. To overcome this issue, here an off-axis illumination of a circular MZP is introduced to trade off between working distance and focal spot size. By this, the working distance between order-sorting aperture and sample can be more than doubled. Exploiting a 2D focus of 16 nm × 28 nm, real-space 2D mapping of local electric fields and charge carrier recombination using X-ray beam induced current in a single InP nanowire is demonstrated. Simulations show that a dedicated off-axis MZP can reach sub-10 nm focusing combined with reasonable working distances and low background, which could be used for inoperando imaging of composition, carrier collection and strain in nanostructured devices.

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For hard X-ray imaging of bulk materials and biological specimens, the development of diffractive optics such as zone plates or multilayer lenses has been transformative in recent years (Doring et al, 2013; Mohacsi et al, 2017; Bajt et al, 2018)
Using multilayer zone plates (MZPs) as two-dimensional optics, focal spot sizes of less than 10 nm can be achieved, as we show here with a focus of 8.4 nm Â 9.6 nm, but the need for order-sorting apertures prohibits practical working distances
Simulations show that a dedicated off-axis MZP can reach sub-10 nm focusing combined with reasonable working distances and low background, which could be used for in operando imaging of composition, carrier collection and strain in nanostructured devices

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Introduction

For hard X-ray imaging of bulk materials and biological specimens, the development of diffractive optics such as zone plates or multilayer lenses has been transformative in recent years (Doring et al, 2013; Mohacsi et al, 2017; Bajt et al, 2018). The most common diffractive optics for focusing X-rays are Fresnel zone plates (FZPs) which are fabricated using lithography. A smaller focal spot size can be achieved by using double-sided FZPs, for X-ray wavelengths of several nanometre and down to 1 A (Mohacsi et al, 2017). Multilayer zone plates (MZPs) are diffractive optics with smallest structure elements of down to 5 nm (Eberl et al, 2014), achieved using pulsed laser deposition (PLD). The fabrication allows the usage of MZPs at energies up to 100 keV (Osterhoff et al, 2017b)

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