The group has its research focus on optical and electrical properties of colloidal semiconductor nanocrystals, on metal nanostructures, graphene, and on hybrid systems that benefit from advantageous properties of those materials. Colloidal semiconductor nanocrystals can be excellent light emitters or absorbers, and the optical properties like for example the light emission wavelength, direction and polarization can be controlled via the nanocrystal size, shape and composition.This makes them very interesting as active material in light emitting, lasing, or photovoltaic devices, and we are exploring novel approaches for proof of principle prototypes.
On the other hand, metal nanostructures are very good conductors and can strongly interact with light in the visible and infrared spectral regions. Due to the presence of free electrons, light can trigger plasma oscillations named plasmons. The study of interactions between surface metal nanostructures and light opened the field of nanoplasmonics. Recently, graphene has attracted great interest as a 2D material with very appealing conductive, plasmonic, and mechanical properties.
We aim at combining the favorable properties of these materials in order to investigate complex optoelectronic systems and to pave the way for novel architectures for components in photodetectors, optical communication, photovoltaics, plasmonics, and nanoscale electronics. In collaboration with the Nanochemistry Department headed by Liberato Manna we develop novel lithography approaches for nanocrystal films that are based on the blocking of cation exchange reactions by a high-energy beam exposure.
- Optical properties of colloidal nanocrystal films and assemblies for LEDs, gain and lasing: Following our work on nanocrystal coffee-ring lasers (M. Zavelani et al., Laser&Photonics Reviews 6, 678, 2012), we have demonstrated optically pumped lasing from water-soluble core-shell CdSe/CdS nanocrystals (F. Di Stasio et al., Small 11, 1328, 2015) with further reduced threshold, and obtained substrate-free three-dimensional nanocrystal assemblies for color conversion by slow solvent evaporation on superhydrophobic substrates (A. Accardo et al., PPSC 32, 524, 2015). We developed blends of „giant-shell“ nanocrystals that show ASE over a spectral range of more that 150 nm (F. Di Stasio et al., ACS Photonics 3, 2083, 2016), which makes this material interesting for broadband lasers. Together with Iwan Moreels group we demonstrated optically pumped lasing of colloidal nanocrystals under constant power excitation (J. Grim et al., Nature Nanotechnology 9, 891, 2014). Raman spectroscopy investigation of dot-in-rod core/shell nanocrystals revealed a peculiar localization of the fundamental acoustic vibration modes near the core (M. Miscuglio et al., Nano Letters 12, 2016), which has repercussions on their ground state emission. Recently, perovskite materials such as cesium lead halide nanocrystals have become a very promising material for light emitting applications, and we have tested them for white color conversion in LEDs (F. Palazon et al., Chem. Mater. 28, 2902, 2016), and studied the impact of post synthesis treatments on films from such materials on their optical and electrical properties (F. Palazon et al., J. Mater. Chem. C 4, 9179, 2016).
- Surface enhanced Raman spectroscopy (SERS): It studies on near field enhancement of electron-beam lithography defined nanostar structures such as nanostar dimers (M. Chirumamilla et al., Adv. Mater. 26, 2353, 2014), nanostar dimers stabilized by an external ring cavity (A. Gopalakrishnan et al., ACS Nano 8, 7986, 2014), and resonance tuning (M. Chirumamilla et al., Nanotechnology 25, 235303, 2014) and hot-spot engineering (M. Chirumamilla et al., Adv. Opt. Mater. 2017) in via the nanostar size and shape have been performed in collaboration with Dr. Andrea Toma and Dr. Remo Proietti Zaccaria from the Plasmonics group at IIT.
- Photoconductive properties of nanocrystal films and assemblies: we have employed CdS nanocrystal films for oxygen sensing (L. Maserati et al., ACS Appl. Mater. Interf. 6, 9517, 2014), demonstrated the versatility of CuSe nanosheets for the fabrication of flexible conductive films (S. Vikulov et al., Adv. Funct. Mater. 26, 3670, 2016), and investigated the formation and photoconductivity of networks of CuTe nanoplatelets in a polymeric matrix (M. Arciniegas et al., Adv. Funct. Mater. 26, 4535, 2016). On the single nanostructure level we contacted individual In2Se3 nanosheets to measure their (photo)electrical properties (G. Almeida et al., JACS 139, 3005, 2017). Following up on our previous work on octapod self assembly into ordered chains and three dimensional structures, we studied octapod assembly insitu by transmission electron microscopy (E. Sutter et al., Nature Commun. 7, 11213, 2016). We also investigated DNA templates for the fabrication of suspended nanowires on micropillar arrays (E. Miele et al., Small 11, 134, 2015).
- Graphene: We developed ultrasensitive and fast photodetectors by a thin CdS nanocrystal film deposited on top of a graphene field effect transistor (D. Spirito et al., J. Phys. Chem C 119, 23859, 2015), and proposed a method for the electrical detection of propagating plasmons in graphene in collaboration with the theory group of Dr. Marco Polini (I. Torre et al., Phys. Rev. B 91, 081402R, 2015). Furtehrmore, we developed concepts for shape-control and structuring of graphene waveguides that promise a significant enhancement of graphene plasmon propagation (M. Miscuglio et al., ACS Photonics 3, 2170, 2016).
We have micromanipulator probe stations in ambient (Karl Suss) and cryogenic (Janis Research) environment that can be coupled to various light sources and lasers spanning the spectral range from UV/VIS to NIR for photoelectrical characterization. Piezo-controlled mibots (Imina) reaching nanometer control can be used for probe contacts with optical and electron microscopes. The electrical instruments such as Keithley 2612 sourcemeters, lockin amplifiers, temperature controllers etc are controlled via a Labview platform. Our group has access to the nanochemistry and optical spectroscopy labs as well as to the clean room.
- Roman Krahne (PI)
- Stefan Kudera (MSCA fellow)
- Vincenzo Caligiuri (postdoc)
- Davide Spirito (postdoc)
- Sedat Dogan (postdoc)
- Francesco De Nicola (postdoc)
- Prachi Rastogi (PhD student)
- Mario Miscuglio (PhD student)
- Milan Palei (PhD student)
- Dr. Margherita Zavelani-Rossi, Politecnico di Milano
- Prof. Pingheng Tan, Chinese Academy of Sciences, Institute of Semiconductors
- Prof. Frank Koppens, ICFO, Spain
- Prof. Christian Riekel, ESRF Grenoble, France
- Prof. Eli Sutter, University of Nebraska, USA
- Prof. Davide Comoretto, University of Genoa
- Prof. P. James Schuck, Lawrence Berkeley National Laboratory, University of California (USA)
Former Group Members
- Dr. Francesco Di Stasio; MSCA fellow at ICFO (Spain)
- Dr. Angelo Accardo, (Experienced Researcher, LAAS-CNRS & INSERM Toulouse, France)
- Dr Yang Zhang (Postdoctoral fellow University of Nebraska, Lincoln, USA)
- Dr Romain Lavieville (Postdoctoral Fellow at CEA Grenoble, France)
Roman Krahne was appointed Guest Professor at the Institute of Semiconductors, Chinese Academy of Sciences
- Roman Krahne Research gate profile
- Coffee-stain Laser video
- Physical Properties of Nanorods Book (Springer)
- Coordinator of the H2020-MSCA-RISE EU project COMPASS_691185 (2016-2020), total budget 1.2 M€
- H2020-MSCA-IF-2014 EU project 659144 - SCEL-TA (2015-2017), total budget 168k
- Fondazione CARIPLO 2013-2015, "Micro-lasers based on rod-shaped self-assembling colloidal semiconductor nanocrystals" with Politecnico di Milano, Dr. Margherita Zavelani-Rossi.
- PI for IIT in the FP7 FET Flagship "Graphene-Driven Revolutions in ICT and Beyond" (GRAPHENE), 2013-2016.
- Angelo Accardo has won the "Best Poster Award" in the
- Stefan Kudera has been awarded a Marie Sklodowska Curie Individual Fellowship
- The work on Masked Cation Exchange in Nanocrystal Films was included in the ELETTRA Highlights 2014
- The work on ENVIRONMENTAL INFLUENCE ON THE SECONDARY STRUCTURE OF AN AMYLOID BETA PEPTIDE was included in the ESRF highlights 2015.