Gratings 1 and holograms 2 are patterned surfaces that tailor optical signals by diffraction. Despite their long history, variants with remarkable functionalities continue to be discovered 3 , 4 . Further advances could exploit Fourier optics 5 , which specifies the surface pattern that generates a desired diffracted output through its Fourier transform. To shape the optical wavefront, the ideal surface profile should contain a precise sum of sinusoidal waves, each with a well-defined amplitude, spatial frequency, and phase. However, because fabrication techniques typically yield profiles with at most a few depth levels, complex ‘wavy’ surfaces cannot be obtained, limiting the straightforward mathematical design and implementation of sophisticated diffractive optics. Here we present a simple yet powerful approach to eliminate this design–fabrication mismatch by demonstrating optical surfaces that contain an arbitrary number of specified sinusoids. We combine thermal scanning-probe lithography 6 – 8 and templating 9 to create periodic and aperiodic surface patterns with continuous depth control and subwavelength spatial resolution. Multicomponent linear gratings allow precise manipulation of electromagnetic signals through Fourier-spectrum engineering 10 . Consequently, we overcome a previous limitation in photonics by creating an ultrathin grating that simultaneously couples red, green, and blue light at the same angle of incidence. More broadly, we analytically design and accurately replicate intricate twodimensional moiré patterns 11 , 12 , quasicrystals 13 , 14 , and holograms 15 , 16 , demonstrating a variety of previously impossible diffractive surfaces. Therefore, this approach can provide benefit for optical devices (biosensors 17 , lasers 18 , 19 , metasurfaces 4 , and modulators 20 ) and emerging topics in photonics (topological structures 21 , transformation optics 22 , and valleytronics 23 ).

Plasmonic photodetectors are attracting the attention of the photonics community. Plasmonics is attractive because metallic structures have the ability to confine light by coupling an electromagnetic wave to charged carrier oscillations at the surface of the metal. The wavelength of such oscillations can be much smaller than the corresponding light wavelength in vacuum. This enables the light-matter interaction on a deep subwavelength scale, which in turn allows for more compact and potentially higher speed devices. In this review, we discuss different types of photodetectors and ways in which plasmonics can be applied to them. We elucidate several plasmonic photodetector concepts/schemes and discuss the main physical principles behind their operation. Finally, we reflect on the characteristics of an "ideal" photodetector and propose a device that might be the perfect plasmonic detector.

Phase-change materials (PCMs), which are wellestablished in optical and random-access memories, are increasingly studied for emerging topics such as brain-inspired computing and active photonics. These applications take advantage of the pronounced reflectivity and resistivity changes that accompany the structural transition in PCMs from their amorphous to crystalline state. However, PCMs are typically fabricated as thin films via sputtering, which is costly, requires advanced equipment, and limits the sample and device design. Here, we investigate a simpler and more flexible approach for applications in tunable photonics: the use of sub-10 nm colloidal PCM nanoparticles (NPs). We report the optical properties of amorphous and crystalline germanium telluride (GeTe) NP thin films from the infrared to the ultraviolet spectral range. Using spectroscopic ellipsometry with support from cross-sectional scanning electron microscopy, atomic force microscopy, and absorption spectroscopy, we extract refractive indices n, extinction coefficients k, and band gaps E g and compare these to values known for sputtered GeTe thin films. We find a decrease of n and k and an increase of E g for NP-based GeTe films, yielding insights into size-dependent property changes for nanoscale PCMs. Furthermore, our results reveal the suitability of GeTe NPs for tunable photonics in the near-infrared and visible spectral range. Thus, PCM NPs are an exciting platform that can allow material properties to be tailored depending on the target application. Finally, we studied sample reproducibility and aging of our NP films. We found that the colloidally prepared PCM thin films were stable for at least 2 months stored under nitrogen, further supporting the great promise of these materials in applications.

The fabrication of high-performance solid-state silicon quantum-devices requires high resolution patterning with minimal substrate damage. We have fabricated room temperature (RT) singleelectron transistors (SETs) based on point-contact tunnel junctions using a hybrid lithography tool capable of both high resolution thermal scanning probe lithography and high throughput direct laser writing. The best focal z-position and the offset of the tip-and the laser-writing positions were determined in situ with the scanning probe. We demonstrate <100 nm precision in the registration between the high resolution and high throughput lithographies. The SET devices were fabricated on degenerately doped n-type >10 20 /cm 3 silicon on insulator chips using a CMOS compatible geometric oxidation process. The characteristics of the three devices investigated were dominated by the presence of Si nanocrystals or phosphorous atoms embedded within the SiO 2 , forming quantum dots (QDs). The small size and strong localisation of electrons on the QDs facilitated SET operation even at RT. Temperature measurements showed that in the range 300 K>T>∼100 K, the current flow was thermally activated but at <100 K, it was dominated by tunnelling.

Atomically smooth hexagonal boron nitride (hBN) flakes have revolutionized two-dimensional (2D) optoelectronics. They provide the key substrate, encapsulant, and gate dielectric for 2D electronics while offering hyperbolic dispersion and quantum emission for photonics. The shape, thickness, and profile of these hBN flakes affect device functionality. However, researchers are restricted to simple, flat flakes, limiting next-generation devices. If arbitrary structures were possible, enhanced control over the flow of photons, electrons, and excitons could be exploited. Here, we demonstrate freeform hBN landscapes by combining thermal scanning-probe lithography and reactive-ion etching to produce previously unattainable flake structures with surprising fidelity. We fabricate photonic microelements (phase plates, grating couplers, and lenses) and show their straightforward integration, constructing a high-quality optical microcavity. We then decrease the length scale to introduce Fourier surfaces for electrons, creating sophisticated Moirépatterns for strain and bandstructure engineering. These capabilities generate opportunities for 2D polaritonics, twistronics, quantum materials, and deepultraviolet devices.