Roman Krahne

• Dr. PhD
• Istituto Italiano di Tecnologia

Dry synthesis is a highly versatile method for the fabrication of nanoporous metal films, since it enables easy and reproducible deposition of single or multi-layers of nanostructured materials that can find intriguing applications in plasmonics, photochemistry and photocatalysis, to name a few. Here, we extend the use of this methodology to the pr...

Recent research on silver nanowires prepared on DNA templates has focused on two fundamental applications: nano-scale circuits and sensors. Despite its broad potential, the formation kinetics of DNA-templated silver nanowires remains unclear. Here, we present an experimental demonstration of the formation of silver nanowires with a diameter of 2.2+...

Tuning of dipolar polarization, piezoelectricity, and conductivity of polydimethylsiloxane (PDMS) along with thin‐film microstructuring has been simultaneously utilized here to improve its piezo‐tribo hybrid mechanical energy harvesting performance. With this intention, a morphotropic phase boundary based highly piezoelectric (Ba 0.85 Ca 0.15 )(Ti...

Dry synthesis is a highly versatile method for the fabrication of nanoporous metal films, since it enables easy and reproducible deposition of single or multi-layer(s) of nanostructured materials that can find intriguing applications in plasmonics, photochemistry and photocatalysis, to name a few. Here, we extend the use of this methodology to the...

Solid‐state nanopore gating inspired by biological ion channels is gaining increasing traction due to a large range of applications in biosensing and drug delivery. Integration of stimuli‐responsive molecules such as poly(N‐isopropylacrylamide) (PNIPAM) inside nanopores can enable temperature‐dependent gating, which so far has only been demonstrate...

With polarized and angle-resolved Raman spectroscopy studies on single two-dimensional layered perovskites (2DLP) flakes with different ammonium molecules as organic cations, in 2020 we revealed the very rich phonon spectra in the low-frequency regime. Although the phonon bands at low frequency can generally be attributed to the vibrations of the i...

Currently, there is a high interest in novel plasmonic platforms and materials able to extend their applicability into the ultraviolet (UV) region of the electromagnetic spectrum. In the UV it is possible to explore the spectral properties of biomolecules that have only a small cross-section in the visible spectral range. However, most plasmonic me...

Solid-state nanopores are a key platform for single-molecule detection and analysis, which allows property engineering by controlling size, shape, and chemical functionalization. However, approaches that rely on polymers that have limits with respect to hard- and robustness, durability, and refractive index, and nanopores made of oxides with high d...

Layered perovskites consist of stacks of inorganic semiconducting metal‐halide octahedra lattices sandwiched between organic layers with typically dielectric behavior. The in‐plane confinement of electrical carriers in such two‐dimensional metal halide perovskites drives a large range of appealing electronic properties, such as strong exciton bindi...

Solid-state nanopore gating inspired by biological ion channels is gaining increasing traction due to a large range of applications in biosensing and drug delivery. Integration of stimuli-responsive molecules such as poly(N-isopropylacrylamide) (PNIPAM) inside nanopores can enable temperature-dependent gating, which so far has only been demonstrate...

Nanopore sensing is a key technology for single-molecule detection and analysis. Solid-state nanopores have emerged as a versatile platform, since their fabrication allows to engineer their properties by controlling size, shape, and chemical functionalization. However, lithography-based fabrication approaches for non-planar nanopores-on-chip rely o...

Nanoporous metals are a class of nanostructured materials finding extensive applications in multiple fields thanks to their unique properties attributed to their high surface area and interconnected nanoscale ligaments. They can be prepared following different strategies, but the deposition of an arbitrary pure porous metal is still challenging. Re...

There is a high current interest for novel plasmonic platforms and materials able to extend their applicability into the ultraviolet (UV) region of the electromagnetic spectrum. In the UV it is possible to explore spectral properties of biomolecules with small cross section in the visible spectral range. However, most used metals in plasmonics have...

The lack of uniqueness poses a common challenge in the inverse design of nanophotonic structures. This issue arises from the presence of multiple sets of design parameters that yield identical output configurations. Several existing machine learning methods offer promising solutions for enabling flexibility in selecting sets of design variables. Ho...

Nanoporous metals are a class of nanostructured materials finding extensive applications in multiple fields thanks to their unique properties attributed to their high surface area and interconnected nanoscale ligaments. They can be prepared following different strategies, but the deposition of an arbitrary pure porous metal is still challenging. Re...

Recent advancements in the fabrication of layered halide perovskites and their subsequent modification for optoelectronic applications have ushered in a need for innovative characterisation techniques. In particular, heterostructures containing multiple phases and consequently featuring spatially defined optoelectronic properties are very challengi...

Bio‐inspired and biodegradable quantum optics scenarios constitute a pathway toward environmentally friendly front‐end technologies. Such an inspiring perspective necessitates the replacement of classic gain materials with a biological counterpart like photoluminescent bacteria. It is easy to imagine that, in this case, a planar and cell‐viable sub...

Organic-inorganic low-dimensional layered metal-halide perovskites are semiconductors in which the optoelectronic properties can be tuned by the material composition and the design of the layered architecture. While the electronic band...

One major concern toward the performance and stability of halide perovskite-based optoelectronic devices is the formation of metallic lead that promotes nonradiative recombination of charge carriers. The origin of metallic lead formation is being disputed whether it occurs during the perovskite synthesis or only after light, electron, or X-ray beam...

Ferrell and Berreman modes are absorption resonances in thin metal films and polar-dielectric media that arise from radiative bulk plasmon-polariton and phonon-polariton excitations. Compared to surface polaritons, Ferrell and Berreman modes occur due to volume charge oscillations across the medium and provide a unique pathway for light–matter inte...

Plasmonic solid‐state nanopores with tunable hole diameters can be prepared via a photocatalytic effect resulting from the enhanced electromagnetic (EM) field inside a metallic ring on top of a dielectric nanotube. Under white light illumination, the plasmon‐enhanced EM‐field induces a site‐selective metal nucleation and growth within the ring. Thi...

The strong coupling of optical resonators results in a mode splitting proportional to the coupling strength, which can be achieved with metal‐dielectric‐metal (MDM) cavities that have similar thickness and refractive index. However, an active control of the mode coupling is challenging. Here, an alternative configuration of an MDM cavity coupled wi...

We show that plasmonic solid-state nanopores with tunable hole diameter can be prepared via a photocatalytic effect resulting from the enhanced electromagnetic field inside a metallic ring prepared on top of a dielectric nanotube. Under white light illumination, the maximum field intensity in these nanorings induces a site selective metal nucleatio...

Polaritons can be generated by tuning the optical transitions of a light emitter to the resonances of a photonic cavity. We show that a dye-doped cavity generates resonant tunneling polaritons with Epsilon-Near-Zero (ENZ) effective permittivity. We studied the polariton spectral dispersion in dye-doped metal-dielectric-metal (MDM) cavities as a fun...

DNA swingarms enable the efficient and reliable translocation of multiple optical elements along a shared DNA origami track. Andreas Peil and co‐workers present in their Research Article (DOI: 10.1002/anie.202213992) that the dynamic rearrangement of AuNPs with large leaps in space can be facilitated by swinging motion, which is substantiated by di...

DNA swingarms enable the efficient and reliable translocation of multiple optical elements along a shared DNA origami track. Na Liu et al. demonstrate in their Research Article (DOI: 10.1002/ange.202213992) that the dynamic rearrangement of AuNPs with large leaps in space can be facilitated by swinging motion, which is substantiated by distinct opt...

We report a process for fabricating sub-10 nm nanopores via photocatalysis caused by electromagnetic field enhancement in plasmonic structures, which immersed in metallic salt solutions triggers hotspots for metallic deposition causing pore diameter shrinkage.

Control over multiple optical elements that can be dynamically rearranged to yield substantial three‐dimensional structural transformations is of great importance to realize reconfigurable plasmonic nanoarchitectures with sensitive and distinct optical feedback. In this work, we demonstrate a transformable plasmonic helix system, in which multiple...

Control over multiple optical elements that can be dynamically rearranged to yield substantial three‐dimensional structural transformations is of great importance to realize reconfigurable plasmonic nanoarchitectures with sensitive and distinct optical feedback. In this work, we demonstrate a transformable plasmonic helix system, in which multiple...

With the total amount of worldwide data skyrocketing, the global data storage demand is predicted to grow to 1.75×10 14 GB by 2025. Traditional storage methods have difficulties keeping pace, given that current storage media have a maximum density of 10 3 GB/mm 3. As such, the data production will far exceed the capacity of currently available stor...

Atomistically detailed computational studies of nanocrystals, such as those derived from the promising lead-halide perovskites, are challenging due to the large number of atoms and lack of symmetries to exploit. Here, focusing on methylammonium lead iodide nanocrystals, we combine a real-space tight binding model with the GW approximation to the se...

Layered metal‐halide double perovskite structures are promising lead‐free materials for optoelectronics. Their band gap, and therefore also their color, depend on the distortions of the inorganic lattice, and on the number of connected octahedra layers. In article number 2200240, Beatriz Martín‐García, Davide Spirito, Roman Krahne and co‐workers re...

With the total amount of worldwide data skyrocketing, the global data storage demand is predicted to grow to 1.75×10 14 GB by 2025. Traditional storage methods have difficulties keeping pace, given that current storage media have a maximum density of 10 3 GB/mm 3. As such, the data production will far exceed the capacity of currently available stor...

Light‐emitting diodes (LEDs) are presently not exploited at their full potential due to a multiple range of detrimental effects, such as generation of local modes, either surface plasmon‐like or optical modes, ohmic losses, or total internal reflection caused by refractive index mismatch. Herein, the authors focus on LEDs with layered architectures...

The soft hybrid organic–inorganic structure of two‐dimensional layered perovskites (2DLPs) enables broadband emission at room temperature from a single material, which makes 2DLPs promising sources for solid‐state white lighting, yet with low efficiency. The underlying photophysics involves self‐trapping of excitons favored by distortions of the in...

In article number 2101807, Roman Krahne and co‐workers introduce a simple and low‐cost fabrication method to grow metal halide perovskite microcrystals directly on functional substrates. The microcrystals feature a pyramidal cavity on their top surface that provides advantageous optoelectronic properties, since its facets lead to enhanced light emi...

Nanopore sequencing is currently a widely used technology for single-molecule DNA detection and analysis. Although the error rate is still too high to enable diagnostic applications, biological nanopores have demonstrated to be able to read the sequence of single DNA molecule, and massive efforts are now on-going to exploit the same technology for...

All‐inorganic metal halide perovskites are highly attractive materials for optoelectronics and are typically implemented as thin films, nanocrystals, and single crystals with macroscopic and millimeter‐size dimensions. Single crystals with regular shapes in the micrometer range are less explored and present an interesting alternative when a well‐de...

Layered architectures for light-emitting diodes (LEDs) are the standard approach for solution-processable materials such as metal-halide perovskites. Upon designing the composition and thicknesses of the layers forming the LED, the primary focus is typically on the optimization of charge injection and balance. However, this approach only considers...

A paper sensor was designed in order to detect the presence of nanomaterials, such as ZnO and silica nanoparticles, as well as graphene nanoplatelets (GnP), based on fluorescence changes of carbon nanodots. Paper strips were functionalized with carbon nanodots using polyvinyl alcohol (PVA) as binder. The carbon nanodots were highly fluorescent and,...

Nanopore sequencing is currently a widely used technology for single-molecule DNA detection and analysis. Although the error rate is still too high to enable diagnostic applications, biological nanopores have demonstrated to be able to read the sequence of a long DNA molecule, and massive efforts are now ongoing to exploit the same technology for d...

Cs4PbBr6 (0D) nanocrystals at room temperature have both been reported as nonemissive and green-emissive systems in conflicting reports, with no consensus regarding both the origin of the green emission and the emission quenching mechanism. Here, via ab initio molecular dynamics (AIMD) simulations and temperature-dependent photoluminescence (PL) sp...

Strong light–matter interaction is usually achieved by embedding a gain medium in a high‐quality (Q)‐factor cavity made with thick external mirrors. The high reflectivity of the mirrors poses, therefore, a trade‐off between pump radiation coupling efficiency and high Q‐factor, thus preventing the use of optical cavities in photonic contexts where t...

Layered perovskites are useful materials that contain sheets of a perovskite semiconductor enclosed by organic molecules. Crystals of layered perovskites that include sheets of a second inorganic lattice can now be grown from solution. Single crystals of a multilayered material grown from solution.

Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent c...

Alternating multilayer architectures are an ideal framework to tailor the properties of light. In photonic crystals, dielectrics with different refractive indices are periodically arranged to provide a photonic band‐gap. In this work, we show that a periodic arrangement of metal/insulator layers gives rise to an Epsilon‐Near‐Zero (ENZ) crystal with...

Mixed‐dimensional systems host interesting phenomena that involve electron and ion transport along or across the interface, with promising applications in optoelectronic and electrochemical devices. Herein, a heterosystem consisting of a graphene monolayer with a colloidal Ag2S nanocrystal film atop, in which both ions and electrons are involved in...

The field of plasmonics is capable of enabling interesting applications in the different wavelength ranges, spanning from the ultraviolet up to the infrared. The choice of plasmonic material and how the material is nanostructured have significant implications for ultimate performance of any plasmonic device. Artificially designed nanoporous metals...

The structural flexibility of 2D layered halide perovskites provides unprecedented opportunities for tuning their optical properties. For example, lattice distortions facilitate white emission that stems from self‐trapped excitons or defects, and organic cations and halides determine structural stability and emission range. Here, we investigate the...

The unique combination of organic and inorganic layers in 2D layered perovskites offers promise for the design of a variety of materials for mechatronics, flexoelectrics, energy conversion, and lighting. However, the potential tailoring of their properties through the organic building blocks is not yet well understood. Here, different classes of or...

The synergy between the organic component of two-dimensional (2D) metal halide layered perovskites and flexible polymers offers an unexplored window to tune their optical properties at low mechanical stress. Thus, there is a significant interest in exploiting their PL anisotropy by controlling their orientation and elucidating their interactions. H...

Gallium selenide (GaSe), a layered semiconductor of Group‐III monochalcogenides, has been recognized by the scientific community in recent years as an appealing material in the fields of photonics and (opto)electronics. Thanks to its pseudodirect bandgap and its thickness‐dependent (opto)electronic properties, GaSe has emerged as a promising candid...

Layered organic/inorganic double perovskite crystals emerged as Pb-free and stable materials for optoelectronics. Their phase transitions are correlated to temperature-dependent conformational changes in the organic layer and influence the distortions in the octahedral layer. Such distortions affect the band structure facilitated by the conduction...

The field of plasmonics can enable unique applications in the different wavelength ranges, from the ultraviolet up to the infrared. The choice of plasmonic material and how the material is nanostructured have significant implications for any plasmonic device's ultimate performance. Nanoporous metals (NPMs) (made of Au, Ag, Cu, Al, Mg, and Pt) have...

Halide double perovskites are an interesting alternative to Pb-containing counterparts as active materials in optoelectronic devices. Low-dimensional double perovskites are fabricated by introducing large organic cations, resulting in organic/inorganic architectures with one or more inorganic octahedra layers separated by organic cations. Here, we...

Fabricating biodegradable and insoluble nanoscale structures

Reducing plastic pollution is a critical challenge in photonics. Here, pure cellulose and derivatives from agro-waste were used to produce high-quality photonic architectures at the micro- and nanoscales. We demonstrate their use for dielectric and plasmonic colors and surface-enhanced Raman spectroscopy.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Lead-halide perovskite nanocrystals are a promising material in optical devices due to their high photoluminescence (PL) quantum yield, excellent color purity, and low stimulated emission threshold. However, one problem is the stability of the nanocrystal films under different environmental conditions, and under high temperatures. The latter is par...

Ultrafast control of light-matter interactions is fundamental in view of new technological frontiers of information processing. However, conventional optical elements are either static or feature switching speeds that are extremely low with respect to the time scales at which it is possible to control light. Here, we exploit the artificial epsilon-...

The replacement of plastic with eco-friendly and biodegradable materials is one of the most stringent environmental challenges. In this respect, cellulose outstands as a biodegradable polymer. However, a significant challenge is to obtain biodegradable materials for high-end photonics that are robust in humid environments. Here, we demonstrate the...

Metamaterials have recently established a new paradigm for enhanced light absorption in state-of-the-art photodetectors. Here, we demonstrate broadband, highly efficient, polarization-insensitive, and gate-tunable photodetection at room temperature in a novel metadevice based on gold/graphene Sierpinski carpet plasmonic fractals. We observed an unp...

Two-dimensional colloidal halide perovskite nanocrystals are promising materials for light emitting applications. In addition, they can be used as components to create a variety of materials through physical and chemical transformations. Recent studies focused on nanoplatelets that are able to self-assemble and transform on solid substrates. Yet, t...

Resistive switching memories allow electrical control of the conductivity of a material, by inducing a high resistance (OFF) or a low resistance (ON) state, using electrochemical and ion transport processes. As alternative to high temperature and vacuum-based physical sulphurization methods of silver (Ag), here we propose, as resistive switching me...

Colloidal nanocrystals are a promising fluorescent class of materials, whose spontaneous emission features can be tuned over a broad spectral range via their composition, geometry and size. However, towards embedding nanocrystals films in elaborated device geometries, one significant drawback is the sensitivity of their emission properties on furth...

The surface ligands on colloidal nanocrystals (NCs) play an important role in the performance of NCs based optoelectronic devices such as photovoltaic cells, photodetectors and light emitting diodes (LEDs). On one hand, the NC emission depends critically on the passivation of the surface to minimize trap states that can provide non-radiative recomb...

The interaction between excitons and phonons in semiconductor nanocrystals plays a crucial role in the exciton energy spectrum and dynamics, and thus in their optical properties. We investigate the exciton2 phonon coupling in giant-shell CdSe/CdS core-shell nanocrystals via resonant Raman spectroscopy. The Huang-Rhys parameter is evaluated by the i...

Metamaterials have recently established a new paradigm for enhanced light absorption in state-of-the-art photodetectors. Here, we demonstrate broadband, highly efficient, polarization-insensitive, and gate-tunable photodetection at room temperature in a novel metadevice based on gold/graphene Sierpinski carpet plasmonic fractals. We observed an unp...

Metal/Insulator/Metal nanocavities (MIMs) are highly versatile systems for nanometric light confinement and waveguiding, and their optical properties are mostly interpreted in terms of surface plasmon polaritons. Although classic electromagnetic theory accurately describes their behavior, it often lacks physical insight, letting some fundamental as...