Alessandro Molle

Italian National Research Council | CNR · Institute for Microelectronics and Microsystems IMM

Molybdenum disulfide (MoS2) got tremendous attention due to its atomically thin body, rich physics, and high carrier mobility. The controlled synthesis of large area and high crystalline monolayer MoS2 nanosheets on diverse substrates remains a challenge for potential practical applications. Synthesizing different structured MoS2 nanosheets with ho...

The synthesis of silicene by direct growth on silver is characterized by the formation of multiple phases and domains, posing severe constraints on the spatial charge conduction towards a technological transfer of silicene to electronic transport devices. Here we engineer the silicene/silver interface by two schemes, namely, either through decorati...

Due to their superior mechanical properties, two-dimensional (2D) materials have gained interest as active layers in flexible devices co-integrating electronic, photonic, and straintronic functions altogether. To this end, 2D bendable membranes compatible with the technological process standards and endowed with large scale uniformity are highly de...

The possibility to excite and control charges in matter on ultrafast timescales is a key requisite to overcome the current limits of information transfer and data processing. The major route towards this milestone is based on the employment of short light pulses to manipulate the electro-optical properties of a solid. Nevertheless, the elusive phys...

Silicene or the two-dimensional (2D) graphene-like silicon allotrope has recently emerged as a promising candidate for various applications in nanotechnology. However, concerns on the silicene stability still persist to date and need to be addressed aiming at the fabrication of competing and durable silicene-based devices. Here, we present an all-a...

The interest in tellurium nanostructures is on the rise due to their outstanding physical properties including high carrier mobility, anisotropic charge conduction, photoconductivity, thermoelectricity, and piezoelectricity. Applications in related technologies require tailoring the synthesis of tellurium from its preferred vertical growth toward t...

Heterostacks formed by combining two-dimensional materials show novel properties which are of great interest for new applications in electronics, photonics and even twistronics, the new emerging field born after the outstanding discoveries on twisted graphene. Here, we report the direct growth of tin nanosheets at the two-dimensional limit via mole...

Two-dimensional (2D) materials are a class of materials that can be reduced to a thickness of a few layers, exhibiting peculiar and innovative properties relative to their three-dimensional solid counterparts [...]

The epitaxy of silicene-on-Ag(111) renewed considerable interest in silicon (Si) when scaled down to the two-dimensional (2D) limit. This remains one of the most explored growth cases in the emerging 2D material fashion beyond graphene. However, out of a strict silicene framework, other allotropic forms of Si still deserve attention owing to techno...

The route towards manipulation of the optoelectronic properties of matter beyond the current limits of electronics starts from a comprehensive study of the ultrafast dynamics triggered by interaction with light. Among them, a fundamental role is played by charge photoinjection, a complex process that stems from the interplay of many different physi...

Shaping two-dimensional (2D) materials in arbitrarily complex geometries is a key to designing their unique physical properties in a controlled fashion. This is an elegant solution, taking benefit from the extreme flexibility of the 2D layers but requiring the ability to force their spatial arrangement from flat to curved geometries in a delicate b...

Among transition metal dichalcogenides, molybdenum ditelluride (MoTe2) holds significant attention due to its polymorphic nature including semiconducting, metallic, and topological semimetal phases. Considerable efforts are devoted to synthesizing MoTe2 nanosheets to make them suitable for device integration in nanotechnologies and for fundamental...

Stabilization of silicene and preservation of its structural and electronic properties are essential for its processing and future integration into devices. The stacking of silicene on stanene, creating a Xene-based heterostructure, proves to be a viable new route in this respect. Here we demonstrate the effectiveness of a stanene layer in breaking...

High-performance THz photodetection is unprecedentedly accessed by integrating a topological Dirac (Weyl) semimetal in a carefully designed antenna at deep-subwavelength scales.

Over the last decade, transition metal dichalcogenides (TMDs) have attracted immense interest because of their outstanding electrical, optical and chemical properties. Among the proposed routes to synthesize MoS2 nanosheets, chemical vapor deposition (CVD) based approach is gaining consideration because of the good balance between relatively low in...

With black phosphorus being a promising two-dimensional layered semiconductor for application to electronics and optoelectronics, an issue remains as to how heat diffusion is managed when black phosphorus is interfaced with metals, namely in a typical device heterojunction. We use Raman spectroscopy to investigate how the laser-induced heat affects...

The idea to grow the same or a different material on a substrate to create a homostructure or a heterostructure was typically grounded with multiple applications of the semiconductors technology in the electronic and photonic devices. Today, the renewed interest in this topic is mainly driven by the two-dimensional materials that can be assembled i...

The interplay between intra-band motion and inter-band transitions in photoexcited germanium is investigated by attosecond transient reflection spectroscopy. Advanced theoretical simulations interpret the sub-femtosecond optical response as charge carrier dynamics in the band structure.

Colloidal semiconductor nanoplatelets (NPLs) are a subgroup of quantum confined materials that have recently emerged as promising active materials for solution processed light-emitting diodes (LEDs) thanks to their peculiar structural and electronic properties as well as their reduced dimensionality. Nowadays, the conventional structure for NPL-bas...

The urgent quest to introduce the Xenes, a new family of graphene-like materials, into everyday technological devices further demands for a specific understanding of their reactivity to different environments. Here, the role of oxygen on the blue phosphorene fragments alloyed with Au(111) substrate, so called BlueP-Au alloy, is investigated either...

The synthesis of new Xenes and their potential applications prototypes have achieved significant milestones so far. However, to date the realization of Xene heterostructures in analogy with the well known van der Waals heterostructures remains an unresolved issue. Here, a Xene heterostructure concept based on the epitaxial combination of silicene a...

The study of MoS2/metal interfaces is crucial for engineering efficient semiconductor−metal contacts in 2D MoS2-based devices. Here we investigate a MoS2/Ag heterostructure fabricated by growing a single MoS2 layer on Ag(111) by pulsed laser deposition under ultrahigh vacuum (UHV) conditions. The surface structure is observed in situ by scanning tu...

Laser ablation in conjunction with Raman spectroscopy can be used to attain a controllable reduction of the thickness of exfoliated black phosphorus flakes and simultaneous measurement of the local temperature. However, this approach can be affected by several parameters, such as the thickness-dependent heat dissipation. Optical, thermal, and mecha...

We employed chemical vapor deposition (CVD) from powder precursors aiming at large-area growth of molybdenum ditelluride (MoTe2) thin films, with controlled allotropic 2H and 1T′ phases. This major outcome entails tuning the parametric conditions of the precursor fluxes during the deposition. Using a physical barrier, we induce a concentration grad...

Stanene is one of the most intriguing two-dimensional (2D) materials because of its nontrivial topological properties. Here, the optical properties from THz to UV of molecular beam deposited tin nanosheets on Al2O3(0001) are reported. The experimental absorption coefficient cannot be described in terms of metallic tin or tin oxides. Nonetheless, a...

Nanofabrication of flat optic silica gratings conformally layered with two-dimensional (2D) MoS2 is demonstrated over large area (cm²), achieving a strong amplification of the photon absorption in the active 2D layer. The anisotropic subwavelength silica gratings induce a highly ordered periodic modulation of the MoS2 layer, promoting the excitatio...

Flat optics nanoarrays based on few-layer MoS2 are homogeneously fabricated over large-area (cm²) transparent templates, demonstrating effective tailoring of the photon absorption in two-dimensional (2D) transition-metal dichalcogenide (TMD) layers. The subwavelength subtractive re-shaping of the few-layer MoS2 film into a one-dimensional (1D) nano...

In the realm of two-dimensional materials framework, single-element graphene-like lattices, known as Xenes, pose several issues concerning their environmental stability with implication in their use for technology transfer to a device layout. In this Discussion, we scrutinize the chemical reactivity of epitaxial silicene, taken as a case in point,...

A cost effective method to tailor the optical response of large‐area nanosheets of 2D materials is described. A reduced effective metalayer model is introduced to capture the key‐role of the out‐of‐plane component of the dielectric tensor. Such a model indicates that the optical extinction of 2D materials can be strongly altered by controlling the...

Hybrid plasmonic‐semiconductor assemblies are receiving considerable attention due to the possibility to achieve hot‐carrier‐based photodetection. In this context, 2D transition metal dichalcogenides (TMDs) coupled to metal nanostructures are very promising. However, the plasmon‐to‐TMD carrier injection process is extremely challenging to achieve a...

Synthetic two-dimensional (2D) mono-elemental crystals, namely X-enes, have recently emerged as a new frontier for atomically thin nanomaterials with on-demand properties. Among X-enes, antimonene, the β-phase allotrope of antimony, is formed by atoms arranged in buckled hexagonal rings bearing a comparatively higher environmental stability with re...

Terahertz (THz) photonics is a key-enabling technology for a wealth of urgently demanding applications and societal challenges like ultrahigh speed communication systems, medical imaging and diagnostics, industrial and food quality control, and security screening. Therefore, making novel THz materials, that are able to effectively interact and mani...

Large area molybdenum disulfide (MoS2) monolayers are typically obtained by using perylene‐3,4,9,10‐tetracarboxylic acid tetrapotassium salt (PTAS) as organic seeding promoter in chemical vapor deposition (CVD). However, the influence of the seeding promoter and the involvement of the functional groups attached to the seed molecules on the physical...

Here, two novel approaches for disassembling epitaxial silicene from the native substrate and transferring onto arbitrary target substrates are presented. From the processing perspective, the two methodologies open up a new route for handling silicene, and in general any epitaxial Xene, in view of establishing reliable process flows for the develop...

In the 2D material framework, molybdenum disulfide (MoS2) was originally studied as an archetypical transition metal dichalcogenide (TMD) material. The controlled synthesis of large-area and high-crystalline MoS2 remains a challenge for distinct practical applications from electronics to electrocatalysis. Among the proposed methods, chemical vapor...

The large foreseeable use of two-dimensional materials in nanotechnology consequently demands precise methods for their thickness measurements. Usually, having a quick and easy methodology is a key requisite for the inspection of the large number of flakes produced by exfoliation methods. An effective option in this respect relies on the measuremen...

Colloidal semiconductor nanocrystals (NCs), and recently nanoplatelets (NPLs), owing to their efficient and narrowband luminescence, are considered as frontier materials for the light-emitting diode (LED) technology. NC-LEDs typically incorporate interfacial layers as charge regulators to ensure charge balancing and high performance. In this commun...

Systems based on the combination of ferromagnetic (FM) thin films and two-dimensional (2D) transition metal dichalcogenides are currently of high interest in the context of spintronic devices. Here, we report on the fabrication of MoS2/(Fe3O4, Fe) heterojunctions by using chemical-based methods. FM thin films have been initially synthesized on top...

Xenes are two‐dimensional monoelemental materials beyond graphene ranging from silicene through borophene and to tellurene. Allessandro Molle and co‐workers (article number 1900439) review the rise of the Xenes and classify them in two generations from its early stage up to now. The attention is specifically paid to the epitaxial methodologies for...

Two-dimensional (2D) synthetic single-element materials referred to as Xenes is achieving an increasing consideration in solid-state science and technology at the extreme nanoscale. The discovery of Xenes went through two generations. The first one is limited to the elements of IV column beyond carbon in the periodic table (namely silicene, germane...

We study the optical properties of Molybdenum Disulphide nanosheets deposited by chemical vapor deposition onto a nanopatterned substrate endowed with a uniaxial corrugation. The uniaxial nanocorrugation leads to a polarization dependence in steady state and an anisotropic relaxation around the C resonance. Finite element numerical simulations allo...

Among the proposed routes to synthesize MoS 2 nanosheets, chemical vapor deposition (CVD) based approach is gaining consideration because of the good balance between relatively low installation and running costs, and the rich flexibility in terms of process parameters tuning and substrate sizing and conditioning. We grew MoS 2 nanosheets by two CVD...

The newly predicted allotropic phase of phosphorus termed blue phosphorus has been recently synthesized in its two-dimensional (2D) single layer fashion via epitaxial growth on a Au(111) substrate. The large scale epitaxy and the semiconductive character with a reported bandgap of ∼1.1 eV suggest that epitaxial phosphorene might be a suitable candi...

Two-dimensional materials are today a solid reality in condensed matter physics due to the disruptive discoveries about graphene. The class of the X-enes, namely, graphene-like single element artificial crystals, is quickly emerging driven by the high-momentum generated by silicene. Silicene, in addition to the graphene properties, shows up inciden...

Isolation of graphene is today a milestone in condensed matter physics that paved the way to a new entire class of two‐dimensional synthetic materials referred to as Xenes with no analogous bulk layered allotropes. The booming rush to discover first novel and unprecedented materials flew into two generations of Xenes, the first one strictly related...

Within the class of two-dimensional materials, transition metal dichalcogenides (TMDs), are extremely appealing for a variety of technological applications. Moreover, the manipulation of the layered morphology at the nanoscale is a knob for further tailoring their physical and chemical properties towards target applications. Here, the combination o...

The exotic electrodynamics properties of graphene come from the linearly dispersive electronic bands that host massless Dirac electrons. A similar behavior was predicted to manifest in freestanding silicene, the silicon counterpart of graphene, thereby envisaging a new route for a silicon photonics. However, the access to silicene exploitation in p...

Silicene, the ultimate scaling of a silicon atomic sheet in a buckled honeycomb lattice, represents a monoelemental class of two-dimensional (2D) materials similar to graphene but with unique potential for a host of exotic electronic properties. Nonetheless, there is a lack of experimental studies largely due to the interplay between material degra...

In the present work, we implemented an ultra-high vacuum molecular beam epitaxial growth of blue-phosphorene (hereafter termed epitaxial phosphorene) by means of P4 evaporation onto cleavable Au(111)/mica substrates. We investigated the reactivity of epitaxial phosphorene against oxygen exposure by means of XPS monitoring of the P2p photoemission l...

We study the optical properties of an anisotropic ripple-shaped two-dimensional molybdenum disulphide (MoS2) nanosheet deposited by chemical vapor deposition onto a nanopatterned silica (SiO2) substrate. We unveil a giant anisotropic optical response in the linear and nonlinear regime by a combination of optical extinction measurements, ultrafast b...

In order to enable the use of the prototypical 2D‐layered MoS2 for spintronics, its integration with ferromagnetic layers is mandatory. By employing interface‐sensitive ⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS), hard X‐ray photoelectron spectroscopy (HAXPES), and transmission electron microscopy (TEM), the chemical, structural, and mag...

Two-dimensional elemental topological insulators including silicene, germanene and stanene are currently the hottest topics in condensed matter physics. We first review the recent progress on electronic and topological properties of their monolayers from a fundamental viewpoint. Next, we describe their experimental realizations by epitaxial growth...

MoS2 and generally speaking, the wide family of transition-metal dichalcogenides represents a solid nanotechnology platform on which to engineer a wealth of new and outperforming applications involving 2D materials. An even richer flexibility can be gained by extrinsically inducing an in-plane shape anisotropy of the nanosheets. Here, the synthesis...

Besides theoretical studies, experimental investigations on silicene began with the synthesis of silicene on ceramic or metallic catalyst substrates such as ZrB2, Ir and Ag. Among various reported methods, the epitaxial growth of silicene sheet atop Ag(111) has received increasing attention and a derivative approach of using evaporated Ag(111) film...

Since the rise of graphene, the flatland of two-dimensional (2D) materials continues to expand its borders including more and more members with complementary properties. An overview of the more relevant members is proposed which accounts for the class of 2D layered transition metal dichalcogenides and elementary 2D materials. Amidst the latter ones...

Manipulating the anisotropy in 2D nanosheets is a promising way to tune or trigger functional properties at the nanoscale. Here, a novel approach is presented to introduce a one-directional anisotropy in MoS2 nanosheets via chemical vapor deposition (CVD) onto rippled patterns prepared on ion-sputtered SiO2/Si substrates. The optoelectronic propert...

The structural and electronic properties of nanoscale Si epitaxially grown on Ag(111) can be tuned from a multilayer silicene phase, where the constitutive layers incorporate a mixed sp²/sp³ bonding, to other ordinary Si phases, such as amorphous and diamond-like Si. Based on comparative scanning tunneling microscopy and Raman spectroscopy investig...

The recent integration of silicene in field-effect transistors (FET) opened new challenges in the comprehension of the chemical and physical properties of this elusive two-dimensional allotropic form of silicon. Intense efforts have been devoted to the study of the epitaxial Silicene/Ag(111) system in order to elucidate the presence of Dirac fermio...

Silicene, germanene and stanene are part of a monoelemental class of two-dimensional (2D) crystals termed 2D-Xenes (X = Si, Ge, Sn and so on) which, together with their ligand-functionalized derivatives referred to as Xanes, are comprised of group IVA atoms arranged in a honeycomb lattice — similar to graphene but with varying degrees of buckling....

Book of extended abstracts of papers presented at the international conference ACSIN 2016 held in Frascati, Rome, Italy October 9-15, 2016 Organized by the Non profit organization for scientific research Superstripes onlus, Rome International Center for Materials Science Superstripes - RICMASS. Conference chairs Antonio Bianconi - RICMASS Rome, Ita...

The structural defects in two-dimensional transition metal dichalcogenides, including point defects, dislocations and grain boundaries, are scarcely considered regarding their potential to manipulate the electrical and optical properties of this class of materials, notwithstanding the significant advances already made. Indeed, impurities and vacanc...

Supplementary Figures 1-14, Supplementary Notes 1-3 and Supplementary References