Roman Krahne

Roman Krahne
Istituto Italiano di Tecnologia | IIT · Department of Nanostructures

Dr. PhD

About

230
Publications
46,115
Reads
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7,184
Citations
Citations since 2017
113 Research Items
4558 Citations
201720182019202020212022202302004006008001,000
201720182019202020212022202302004006008001,000
201720182019202020212022202302004006008001,000
201720182019202020212022202302004006008001,000
Additional affiliations
June 2009 - present
Istituto Italiano di Tecnologia
Description
  • Group Leader
December 2003 - June 2009
CNR/INFM
Position
  • Researcher
Description
  • Electrical and optical properties of nanostructures
January 1997 - November 2000
University of Hamburg
Description
  • PhD thesis on FIR spectroscopy on low-dimensional electron systems

Publications

Publications (230)
Article
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...
Article
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...
Article
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...
Article
Full-text available
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...
Preprint
Here, we show that plasmonic solid-state nanopores can be prepared via a photocatalytic effect resulting from the enhanced E-field inside a metallic ring prepared on top of a dielectric pillar. The area of maximum plasmonic field in nanorings ordered over large arrays induce a site selectivity for metal nucleation and growth. We used this approach...
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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...
Preprint
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...
Cover Page
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...
Preprint
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...
Article
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...
Cover Page
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...
Article
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...
Article
Full-text available
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...
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Full-text available
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...
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Full-text available
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...
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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,...
Preprint
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...
Article
Full-text available
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...
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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...
Article
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.
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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...
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Full-text available
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...
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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...
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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...
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Full-text available
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...
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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...
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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...
Article
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...
Cover Page
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...
Preprint
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...
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Full-text available
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...
Cover Page
Full-text available
Fabricating biodegradable and insoluble nanoscale structures
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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.
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Full-text available
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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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...
Article
Full-text available
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-...
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Full-text available
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...
Preprint
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...
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Full-text available
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...
Preprint
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...
Preprint
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...
Preprint
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...
Preprint
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...
Article
Full-text available
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...
Preprint
Full-text available
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...
Preprint
Directing and polarizing the emission of a fluorophore is of fundamental importance in the perspective of novel photonic sources based on emerging nano-emitter technologies. These two tasks are usually accomplished by a sophisticated and demanding structuring of the optical environment in which the emitter is immersed, or by non-trivial chemical en...
Preprint
The coupling between multiple nanocavities in close vicinity leads to hybridization of their modes. Stacked Metal/Insulator/Metal (MIM) nanocavities constitute a highly versatile and very interesting model system to study and engineer such mode coupling, since they can be realized by lithography-free fabrication methods with fine control on the opt...
Preprint
Plasmonic metasurfaces have spawned the field of flat optics using nanostructured planar metallic or dielectric surfaces that can replace bulky optical elements and enhance the capabilities of traditional far-field optics. Furthermore, the potential of flat optics can go far beyond far-field modulation, and can be exploited for functionality in the...
Preprint
Colloidal core/shell nanocrystals are key materials for optoelectronics, enabling control over essential properties via precise engineering of the shape, thickness, and crystal lattice structure of their shell. Here, we apply the growth protocol for CdS branched nanocrystals on CdSe nanoplatelet seeds and obtain bone-shaped heterostructures with a...
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Full-text available
We demonstrate patterning of metal surfaces based on lift-off of perovskite nanocrystals that enables the fabrication of nanometer-size features without the use of resist-based nanolithography. The perovskite nanocrystals act as templates for defining the shape of the apertures in metal layers, and we exploit the variety of sizes and shapes that ca...
Preprint
Full-text available
The photoluminescence (PL), color purity, and stability of lead halide perovskite nanocrystals depend critically on the surface passivation. We present a study on the temperature dependent PL and PL decay dynamics of lead bromide perovskite nanocrystals characterized by different types of A cations, surface ligands, and nanocrystal sizes. Throughou...
Preprint
Full-text available
The vibrational modes in organic/inorganic layered perovskites are of fundamental importance for their optoelectronic properties. The hierarchical architecture of the Ruddlesden-Popper phase of these materials allows for distinct directionality of the vibrational modes withrespect to the main axes of the pseudocubic lattice in the octahedral plane....
Preprint
Among the large family of transition metal dichalcogenides (TMDCs), recently ReS2 has stood out due to its nearly layer-independent optoelectronic and physicochemical properties. These are related to its 1T distorted octahedral structure, which leads to strong in-plane anisotropy and the presence of active sites at its surface, which makes ReS2 int...
Article
Full-text available
The vibrational modes in organic/inorganic layered perovskites are of fundamental importance for their optoelectronic properties. The hierarchical architecture of the Ruddlesden-Popper phase of these materials allows for distinct directionality of the vibrational modes with respect to the main axes of the pseudocubic lattice in the octahedral plane...
Article
Full-text available
Layered semiconductors of the IIIA–VIA group have attracted considerable attention in (opto)electronic applications thanks to their atomically thin structures and their thickness‐dependent optical and electronic properties, which promise ultrafast response and high sensitivity. In particular, 2D indium selenide (InSe) has emerged as a promising can...
Article
Full-text available
Partial Hg2+-->Cd2+ cation exchange (CE) reactions were exploited to transform colloidal CdTe nanocrystals (NCs, 4-6 nm in size) into [email protected] [email protected] nanostructures. This was achieved by working under a slow CE rate, which limited the exchange to the surface of the CdTe NCs. In such nanostructures, when annealed at mild temperat...
Preprint
Full-text available
Ultrafast control of light-matter interactions constitutes a crucial feature 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 timescales at which it is possible to control light. Here, we exploit high-qual...
Article
Full-text available
The photoluminescence (PL), color purity, and stability of lead halide perovskite nanocrystals depend critically on the surface passivation. We present a study on the temperature dependent PL and PL decay dynamics of lead bromide perovskite nanocrystals characterized by different types of A cations, surface ligands, and nanocrystal sizes. Throughou...