has boosted the field of large-area flexible and printed electronics. These advances have enabled... more has boosted the field of large-area flexible and printed electronics. These advances have enabled a plethora of applications such as organic light-emitting diodes, [1,2] organic photovoltaics, [3,4] organic thermoelectrics, [5,6] organic field-effect transistors (OFETs), [7-10] organic (bio)sensors, [11-13] and neuromorphic devices. [14,15] In this context, organic field-effect transistors (OFETs) are not only relevant for their direct technological application, but they also represent an ideal test-bed to investigate thin-film electrical properties. Organic semiconductors are typically classified in two main families, namely conjugated polymers and small molecules. The former, polymers, are particularly appealing as a result of their solution processability, and OFETs with charge mobility above the standard for hydrogenated amorphous silicon (0.5-1 cm 2 V −1 s −1) have been extensively reported. [16] The latter, small molecules, are prone to arrange in ordered molecular crystals, and through several years of chemical tailoring and fine tuning of the films processing, small-molecule OFETs with field-effect mobility >10 cm 2 V −1 s −1 have been achieved. [17-19] The chemical root of the π-conjugation of these materials is associated with the sp 2-hybridization of carbon atoms in their backbone. This peculiar trait is also common to Solution-processed, large-area, and flexible electronics largely relies on the excellent electronic properties of sp 2-hybridized carbon molecules, either in the form of π-conjugated small molecules and polymers or graphene and carbon nanotubes. Carbon with sp-hybridization, the foundation of the elusive allotrope carbyne, offers vast opportunities for functionalized molecules in the form of linear carbon atomic wires (CAWs), with intriguing and even superior predicted electronic properties. While CAWs represent a vibrant field of research, to date, they have only been applied sparingly to molecular devices. The recent observation of the field-effect in microcrystalline cumulenes suggests their potential applications in solution-processed thin-film transistors but concerns surrounding the stability and electronic performance have precluded developments in this direction. In the present study, ideal field-effect characteristics are demonstrated for solution-processed thin films of tetraphenyl[3]cumulene, the shortest semiconducting CAW. Films are deposited through a scalable, large-area, meniscus-coating technique, providing transistors with hole mobilities in excess of 0.1 cm 2 V −1 s −1 , as well as promising operational stability under dark conditions. These results offer a solid foundation for the exploitation of a vast class of molecular semiconductors for organic electronics based on sp-hybridized carbon systems and create a previously unexplored paradigm.
γ-graphdiyne is a 2D carbon structure beyond graphene: it is formed by sp and sp 2 carbon atoms o... more γ-graphdiyne is a 2D carbon structure beyond graphene: it is formed by sp and sp 2 carbon atoms organized as hexagonal rings connected by linear links, and it is predicted to be a semiconductor. The lateral confinement of γ-graphdiyne nanoribbons can affect the electronic and vibrational properties, even in complex ways. By means of periodic Density Functional Theory (DFT) calculations we investigate here the electronic band structure, the Raman and IR spectra of the γ-graphdiyne 2D crystal and related nanoribbons. We discuss the effect of the functional and basis set on the evaluation of the band gap, highlighting the reliability of hybrid functionals. By joining DFT calculations with a symmetry analysis, we assign in detail the IR and Raman spectra of γ-graphdiyne. On this basis we show the modulation of the gap in nanoribbons of increasing width and different edges (armchair, zigzag). We assess how confinement affects the Raman and IR spectra of such nanoribbons by comparing their vibrational modes with the phonons of the parent 2D crystal. Our symmetry-based classification allows identifying the marker bands sensitive to the edge structure and lateral confinement of nanoribbons of increasing width. These results show the effectiveness of vibrational spectroscopy for the characterization of such nanostructures.
Polyynes are linear carbon chains characterized by alternated single and triple bonds and termina... more Polyynes are linear carbon chains characterized by alternated single and triple bonds and terminated by hydrogen or other terminal substituents. They can be synthesized by pulsed laser ablation in liquid (PLAL) as a scalable, cost-effective, and fast physical technique. Water can be employed as a solvent for PLAL to avoid toxicity problems and to reduce costs compared to organic solvents. However, in in this case, the production yield of polyynes reached is extremely low and prevents further characterization and implementation in new functional materials. In this work, we synthesized polyynes by pulsed laser ablation in water and we optimized the process parameters to improve the yield of polyynes by PLAL. Then, we developed a procedure entirely based on reversed-phase high-performance liquid chromatography (RP-HPLC) which effectively enables the concentration, separation and collection of polyynes according to their length. Since the polyynes sample is an aqueous solution, we could inject it directly into the RP-HPLC column without the dilution step required in the case of a sample in an organic solvent. Thanks to our single RP-HPLC procedure, it is possible to highly increase the concentration and separately characterize different size-selected polyynes for further use in functional materials.
As renewable energy is becoming a crucial energy source to meet the global demand, electrochemica... more As renewable energy is becoming a crucial energy source to meet the global demand, electrochemical energy storage devices become indispensable for efficient energy storage and reliable supply. The electrode material is the key factor determining the energy storage capacity and the power delivery of the devices. Carbon-based materials, specifically graphite, activated carbons etc, are extensively used as electrodes, yet their low energy densities impede the development of advanced energy storage materials. Decoration by nanoparticles of metals, metal oxides, nitrides, carbides, phosphides, chalcogenides and bimetallic components is one of the most promising and easy-to-implement strategies to significantly enhance the structural and electronic properties, pore refinement, charge storage and charge-transfer kinetics of both pristine and doped carbon structures, thereby making their performance promising for next-generation energy storage devices. Structuring the materials at nanoscale...
Stable polyyne chains terminated with biphenyl end groups (a,u-biphenylpolyynes) were synthesized... more Stable polyyne chains terminated with biphenyl end groups (a,u-biphenylpolyynes) were synthesized in a single step through a simple procedure by using the Cadiot-Chodkiewicz reaction conditions. The a,ubiphenylpolyynes were separated through HPLC analysis and identified by means of their electronic absorption spectra. The a,u-biphenylpolyynes were studied by FT-IR and Raman spectroscopy and the spectral interpretation was supported with DFT calculations. A peculiarly low reactivity of a,u-biphenylpolyynes with ozone was observed.
Polyynes are linear sp-carbon chains of finite length consisting in a sequence of alternated sing... more Polyynes are linear sp-carbon chains of finite length consisting in a sequence of alternated single and triple bonds and displaying appealing optical and electronic properties. A simple, low cost and scalable production technique for polyynes is the submerged arc discharge (SAD) in liquid, which so far, has been mainly exploited in organic solvents. In this work, we investigated in detail SAD in water as a cheap and non-toxic solvent for the production of polyynes. The role of process parameters such as current (10-25 A) and voltage (20-25 V) in the production yield have been investigated, as well as polyynes stability. Polyynes terminated by hydrogen (CnH2: n=6-16) were identified by High-Performance Liquid Chromatography (HPLC) coupled with UV-Visible absorption spectroscopy and with the support of density functional theory (DFT) calculations. Size-selected polyynes separated by HPLC were analyzed by surface enhanced Raman spectroscopy (SERS). The formation process was monitored b...
sp-Hybridized carbon atomic wires are appealing systems with large property tunability. In partic... more sp-Hybridized carbon atomic wires are appealing systems with large property tunability. In particular, their electronic properties are intimately related to length, structure, and type of functional end-groups as well as to other effects such as the intermolecular charge transfer with metal nanoparticles. Here, by a combined Raman, Surface Enhanced Raman Scattering (SERS) investigation and first principles calculations of different N,N-dimethylanilino-terminated polyynes, we suggest that, upon charge transfer interaction with silver nanoparticles, the function of sp-carbon atomic wire can change from electron donor to electron acceptor by increasing the wire length. In addition, the insertion into the wire of a strong electrophilic group (1,1,4,4-tetracyanobuta-1,3-diene-2,3-diyl) changes the electronaccepting molecular regions involved in this intermolecular charge transfer. our results indicate that carbon atomic wires could display a tunable charge transfer between the sp-wire and the metal, and hold promise as active materials in organic optoelectronics and photovoltaics. Carbon atoms with sp-hybridization arrange in linear structures, constituting the ideal infinite 1D carbon wire (i.e. the carbyne) 1,2. Carbyne attracts interest as a new carbon allotrope 3-6 and for its predicted fascinating properties, such as exceptional mechanical stiffness, electron mobility, thermal conduction, as well as peculiar strain induced metal-to-insulator transition, ballistic transport, and nonlinear optical properties, as recently pointed out by a number of works 7-16. Most of these properties are a direct consequence of the π-electron conjugation resulting from the linear configuration and the hybridization state. In finite carbon-atom wires (CAWs), the properties can be modulated by adjusting the length of the sp-carbon chain and the type of the end-group 17. Such opportunity fits with experimentally available systems whose length ranges typically from two carbon atoms to a few tens 18 , with the record length of 44 atoms reached by R. Tykwinski 19. As a recent example of the potential exploitation of such tunability, optical supermultiplexing and barcoding have been successfully demonstrated with a set of finite polyynes with engineered length and termination 20. In addition to the property modulation, the end-group can be used to control the structural and electronic configuration inducing either the polyyne-like structure 21 (i.e. alternating triple and single bonds in a dimerized geometry) or the cumulene-like structure 22-25 (i.e. sequence of double bonds in equalized geometry). Recently, rational chemical synthesis successfully provided many stable systems with controlled size and type of termination 17-19,22-24,26. The proper choice of terminating groups showed to be a promising strategy to improve stability against cross-linking reactions. Typical terminations include sp 2 aromatic groups able to ensure steric hindrance and long-term stability in ambient conditions opening new possibilities for understanding structure-property relationship through a detailed investigation of these systems. Vibrational spectroscopy has shown all its potential for detecting and investigating structural and electronic properties of sp-carbon systems 27. Raman spectroscopy can provide unambiguous insights on the structure and properties of sp-carbon molecules and thin films due to its extreme sensitivity to carbon hybridization, π-conjugation, and local order 1,27-29. In addition, Surface Enhanced Raman Scattering (SERS) gives access to the study of the interaction with metal nanoparticles and charge transfer processes 17,30-32. SERS exploits the local enhancement of the electric field upon excitation of surface plasmons by incident photons (i.e. electromagnetic SERS effect) or due to a charge transfer and the formation of a complex between the investigated molecule and the metal nanoparticle (i.e. chemical SERS effect). In the case of H-terminated polyynes, we showed an enhancement factor of 10 6 with respect to normal Raman 30,31. The chemical SERS
Besides graphite and diamond, the solid allotropes of carbon in sp 2 and sp 3 hybridization, the ... more Besides graphite and diamond, the solid allotropes of carbon in sp 2 and sp 3 hybridization, the possible existence of a third allotrope based on the sp-carbon linear chain, the Carbyne, has stimulated researchers for a long time. The advent of fullerenes, nanotubes and graphene has opened new opportunities and nurtured the interest in novel carbon allotropes including linear structures. The efforts made in this direction produced a number of interesting sp-hybridized carbon molecules and nanostructures in the form of carbon-atom wires. We here discuss some of the new perspectives opened by the recent advancements in the research on sp-carbon systems.
Novel bis(biphenyl)-capped polyynes have been synthesized to investigate the modulation of the el... more Novel bis(biphenyl)-capped polyynes have been synthesized to investigate the modulation of the electronic and optical properties of sp-hybridized carbon-atom wires (CAWs) capped with π-conjugated sp 2 endgroups. Raman and Surface Enhanced Raman spectroscopy (SERS) investigation of these systems and Density Functional Theory (DFT) calculations reveal structural changes from polyyne-like with alternating single-triple bonds towards cumulene-like with more equalized bonds as a consequence of the charge transfer occurring when wires interact with metallic nanoparticles. While polyynes have semiconducting electronic properties, a more equalized system tends to a cumulene-like structure characterized by a nearly metallic behavior. The possibility to drive a semiconductor-to-metal transition has been investigated by systematic DFT calculations on a series of CAWs capped with different conjugated endgroups revealing that the modulation of the structural, electronic and vibrational properties of the sp-carbon chain towards the metallic wire cannot be simply obtained by using extended π-conjugated sp 2 carbon endgroups, but require a suitable chemical design of the endgroup and control of charge transfer. These results provide useful guidelines for the design of novel sp-sp 2 hybrid carbon nanosystems with tunable properties, where graphene-like and polyyne-like domains are closely interconnected. The capability to tune the final electronic or optical response of the material makes these hybrid sp-sp 2 systems appealing for a future all-carbon-based science and technology.
Graphene, nanotubes and other carbon nanostructures have shown potential as candidates for advanc... more Graphene, nanotubes and other carbon nanostructures have shown potential as candidates for advanced technological applications due to the different coordination of carbon atoms and to the possibility of π-conjugation. In this context, atomic-scale wires comprised of sp-hybridized carbon atoms represent ideal 1D systems to potentially downscale devices to the atomic level. Carbon-atom wires (CAWs) can be arranged in two possible structures: a sequence of double bonds (cumulenes), resulting in a 1D metal, or an alternating sequence of single–triple bonds (polyynes), expected to show semiconducting properties. The electronic and optical properties of CAWs can be finely tuned by controlling the wire length (i.e., the number of carbon atoms) and the type of termination (e.g., atom, molecular group or nanostructure). Although linear, sp-hybridized carbon systems are still considered elusive and unstable materials, a number of nanostructures consisting of sp-carbon wires have been produced...
Thin films synthesized by assembling clusters present interesting chemical and physical propertie... more Thin films synthesized by assembling clusters present interesting chemical and physical properties and a large specific surface, and are appealing for functional applications (e.g. sensing and catalysis). Also, clusters supported on surfaces are interesting both for nanocatalysis applications and for fundamental research. By means of pulsed laser deposition (PLD) in a background atmosphere we can induce cluster aggregation in the ablation plume and control the deposition kinetic energy of the clusters. These phenomena depend on the plume expansion dynamics and their influence on the properties of the deposited films has been investigated as a function of the background gas mass and pressure. The control of these parameters permits variation of the film surface morphology, from a compact structure with a very smooth surface, to a film with a controlled roughness at the nanoscale, to an open, low density meso- and nanostructure characterized by a high fraction of voids and by a large specific area. Thin films of WOx, TiOx, Pd/PdO, and Ag were deposited and characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman spectroscopy. Post-deposition annealing permits control of the crystalline degree of the films, which in the case of tungsten and titanium oxide is found to depend on the original nanostructure, while a different degree of oxidation can be induced by controlling the amount of oxygen in the deposition chamber. In-situ scanning tunneling microscopy (STM) was employed to study the first stages of growth of W films on different substrates. This opens the possibility to tailor the material properties through the control of the building nano-units.
Tungsten oxide thin films are interesting for their electrochromic and gas sensing properties. Fo... more Tungsten oxide thin films are interesting for their electrochromic and gas sensing properties. For technological applications, the control of morphology (effective surface, porosity) and structure (crystallinity, stoichiometry) at the nanoscale is of paramount interest to deliver distinctive properties. Nanostructured tungsten and tungsten oxide films have been synthesized by nanosecond pulsed laser deposition (PLD) starting from a W metallic target. Both inert and reactive buffer gases (He, Ar, dry air) have been exploited to induce cluster ...
In this work we report on the preparation by Pulsed Laser Deposition (PLD) of tungsten oxide laye... more In this work we report on the preparation by Pulsed Laser Deposition (PLD) of tungsten oxide layers featuring different morphologies, dominated by either nanoparticles or nanorods, with the aim to investigate the different gas-sensing properties of these nanostructures. A detailed structural analysis is reported showing morphological stability of the films under thermal annealing and phase transition. Emphasis is also given to the characterization of networking connections of the prepared layers, determinant for the electrical properties of the chemiresistor devices. Results show that samples with nanorod morphology exhibit an increased specific sensitivity to ammonia. The higher sensitivity of nanoparticles to other compounds such as ethanol or acetone suggests that these complementary sensitivities can be exploited to obtain selective gas detection in electronic nose systems.
Protein misfolding and aggregation in intracellular and extracellular spaces is regarded as a mai... more Protein misfolding and aggregation in intracellular and extracellular spaces is regarded as a main marker of the presence of degenerative disorders such as amyloidoses. To elucidate the mechanisms of protein misfolding, the interaction of proteins with inorganic surfaces is of particular relevance, since surfaces displaying different wettability properties may represent model systems of the cell membrane. Here, we unveil the role of surface hydrophobicity/hydrophilicity in the misfolding of the Josephin domain (JD), a globular-shaped domain of ataxin-3, the protein responsible for the spinocerebellar ataxia type 3. By means of a combined experimental and theoretical approach based on atomic force microscopy, Fourier transform infrared spectroscopy and molecular dynamics simulations, we reveal changes in JD morphology and secondary structure elicited by the interaction with the hydrophobic gold substrate, but not by the hydrophilic mica. Our results demonstrate that the interaction with the gold surface triggers misfolding of the JD when it is in native-like configuration, while no structural modification is observed after the protein has undergone oligomerization. This raises the possibility that biological membranes would be unable to affect amyloid oligomeric structures and toxicity.
A novel form of amorphous carbon with sp-sp 2 hybridization has been recently produced by superso... more A novel form of amorphous carbon with sp-sp 2 hybridization has been recently produced by supersonic cluster beam deposition showing the presence in the film of both polyynic and cumulenic species [L. Ravagnan et al. Phys. Rev. Lett. 98, 216103 (2007)]. Here we present a in situ Raman characterization of the low frequency vibrational region (400-800 cm-1) of sp-sp 2 films at different temperatures. We report the presence of two peaks at 450 cm-1 and 720 cm-1. The lower frequency peak shows an evolution with the variation of the sp content and it can be attributed, with the support of density functional theory (DFT) simulations, to bending modes of sp linear structures. The peak at 720 cm-1 does not vary with the sp content and it can be attributed to a feature in the vibrational density of states activated by the disorder of the sp 2 phase.
We report on DNA arrays produced by Dip Pen Nanolithography (DPN) on a novel Au-Ag micro patterne... more We report on DNA arrays produced by Dip Pen Nanolithography (DPN) on a novel Au-Ag micro patterned template stripped surface. DNA arrays have been investigated by atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) showing that the patterned template stripped substrate enables easy retrieval of the DPN-functionalized zone with a standard optical microscope permitting a multi-instrument and multi-technique local detection and analysis. Moreover the smooth surface of the Au squares (~ 5-10 Ǻ roughness) allows to be sensitive to the hybridization of the oligonucleotide array with label-free target DNA. Our Au-Ag substrates, combining the retrieving capabilities of the patterned surface with the smoothness of the template stripped technique, are candidates for the investigation of DPN nanostructures and for the development of label free detection methods for DNA nanoarrays based on the use of scanning probes.
A series of α, ω-diphenylpolyynes were synthesized through the Cadiot Chodkiewicz reaction starti... more A series of α, ω-diphenylpolyynes were synthesized through the Cadiot Chodkiewicz reaction starting from Cu (I)-phenylacetylide and diiodoacetylene. The complete series of diphenylpolyynes Φ-(C [tbnd] C) n-Φ with n= 2, 3, 4 and 5 was obtained and analyzed by ...
has boosted the field of large-area flexible and printed electronics. These advances have enabled... more has boosted the field of large-area flexible and printed electronics. These advances have enabled a plethora of applications such as organic light-emitting diodes, [1,2] organic photovoltaics, [3,4] organic thermoelectrics, [5,6] organic field-effect transistors (OFETs), [7-10] organic (bio)sensors, [11-13] and neuromorphic devices. [14,15] In this context, organic field-effect transistors (OFETs) are not only relevant for their direct technological application, but they also represent an ideal test-bed to investigate thin-film electrical properties. Organic semiconductors are typically classified in two main families, namely conjugated polymers and small molecules. The former, polymers, are particularly appealing as a result of their solution processability, and OFETs with charge mobility above the standard for hydrogenated amorphous silicon (0.5-1 cm 2 V −1 s −1) have been extensively reported. [16] The latter, small molecules, are prone to arrange in ordered molecular crystals, and through several years of chemical tailoring and fine tuning of the films processing, small-molecule OFETs with field-effect mobility >10 cm 2 V −1 s −1 have been achieved. [17-19] The chemical root of the π-conjugation of these materials is associated with the sp 2-hybridization of carbon atoms in their backbone. This peculiar trait is also common to Solution-processed, large-area, and flexible electronics largely relies on the excellent electronic properties of sp 2-hybridized carbon molecules, either in the form of π-conjugated small molecules and polymers or graphene and carbon nanotubes. Carbon with sp-hybridization, the foundation of the elusive allotrope carbyne, offers vast opportunities for functionalized molecules in the form of linear carbon atomic wires (CAWs), with intriguing and even superior predicted electronic properties. While CAWs represent a vibrant field of research, to date, they have only been applied sparingly to molecular devices. The recent observation of the field-effect in microcrystalline cumulenes suggests their potential applications in solution-processed thin-film transistors but concerns surrounding the stability and electronic performance have precluded developments in this direction. In the present study, ideal field-effect characteristics are demonstrated for solution-processed thin films of tetraphenyl[3]cumulene, the shortest semiconducting CAW. Films are deposited through a scalable, large-area, meniscus-coating technique, providing transistors with hole mobilities in excess of 0.1 cm 2 V −1 s −1 , as well as promising operational stability under dark conditions. These results offer a solid foundation for the exploitation of a vast class of molecular semiconductors for organic electronics based on sp-hybridized carbon systems and create a previously unexplored paradigm.
γ-graphdiyne is a 2D carbon structure beyond graphene: it is formed by sp and sp 2 carbon atoms o... more γ-graphdiyne is a 2D carbon structure beyond graphene: it is formed by sp and sp 2 carbon atoms organized as hexagonal rings connected by linear links, and it is predicted to be a semiconductor. The lateral confinement of γ-graphdiyne nanoribbons can affect the electronic and vibrational properties, even in complex ways. By means of periodic Density Functional Theory (DFT) calculations we investigate here the electronic band structure, the Raman and IR spectra of the γ-graphdiyne 2D crystal and related nanoribbons. We discuss the effect of the functional and basis set on the evaluation of the band gap, highlighting the reliability of hybrid functionals. By joining DFT calculations with a symmetry analysis, we assign in detail the IR and Raman spectra of γ-graphdiyne. On this basis we show the modulation of the gap in nanoribbons of increasing width and different edges (armchair, zigzag). We assess how confinement affects the Raman and IR spectra of such nanoribbons by comparing their vibrational modes with the phonons of the parent 2D crystal. Our symmetry-based classification allows identifying the marker bands sensitive to the edge structure and lateral confinement of nanoribbons of increasing width. These results show the effectiveness of vibrational spectroscopy for the characterization of such nanostructures.
Polyynes are linear carbon chains characterized by alternated single and triple bonds and termina... more Polyynes are linear carbon chains characterized by alternated single and triple bonds and terminated by hydrogen or other terminal substituents. They can be synthesized by pulsed laser ablation in liquid (PLAL) as a scalable, cost-effective, and fast physical technique. Water can be employed as a solvent for PLAL to avoid toxicity problems and to reduce costs compared to organic solvents. However, in in this case, the production yield of polyynes reached is extremely low and prevents further characterization and implementation in new functional materials. In this work, we synthesized polyynes by pulsed laser ablation in water and we optimized the process parameters to improve the yield of polyynes by PLAL. Then, we developed a procedure entirely based on reversed-phase high-performance liquid chromatography (RP-HPLC) which effectively enables the concentration, separation and collection of polyynes according to their length. Since the polyynes sample is an aqueous solution, we could inject it directly into the RP-HPLC column without the dilution step required in the case of a sample in an organic solvent. Thanks to our single RP-HPLC procedure, it is possible to highly increase the concentration and separately characterize different size-selected polyynes for further use in functional materials.
As renewable energy is becoming a crucial energy source to meet the global demand, electrochemica... more As renewable energy is becoming a crucial energy source to meet the global demand, electrochemical energy storage devices become indispensable for efficient energy storage and reliable supply. The electrode material is the key factor determining the energy storage capacity and the power delivery of the devices. Carbon-based materials, specifically graphite, activated carbons etc, are extensively used as electrodes, yet their low energy densities impede the development of advanced energy storage materials. Decoration by nanoparticles of metals, metal oxides, nitrides, carbides, phosphides, chalcogenides and bimetallic components is one of the most promising and easy-to-implement strategies to significantly enhance the structural and electronic properties, pore refinement, charge storage and charge-transfer kinetics of both pristine and doped carbon structures, thereby making their performance promising for next-generation energy storage devices. Structuring the materials at nanoscale...
Stable polyyne chains terminated with biphenyl end groups (a,u-biphenylpolyynes) were synthesized... more Stable polyyne chains terminated with biphenyl end groups (a,u-biphenylpolyynes) were synthesized in a single step through a simple procedure by using the Cadiot-Chodkiewicz reaction conditions. The a,ubiphenylpolyynes were separated through HPLC analysis and identified by means of their electronic absorption spectra. The a,u-biphenylpolyynes were studied by FT-IR and Raman spectroscopy and the spectral interpretation was supported with DFT calculations. A peculiarly low reactivity of a,u-biphenylpolyynes with ozone was observed.
Polyynes are linear sp-carbon chains of finite length consisting in a sequence of alternated sing... more Polyynes are linear sp-carbon chains of finite length consisting in a sequence of alternated single and triple bonds and displaying appealing optical and electronic properties. A simple, low cost and scalable production technique for polyynes is the submerged arc discharge (SAD) in liquid, which so far, has been mainly exploited in organic solvents. In this work, we investigated in detail SAD in water as a cheap and non-toxic solvent for the production of polyynes. The role of process parameters such as current (10-25 A) and voltage (20-25 V) in the production yield have been investigated, as well as polyynes stability. Polyynes terminated by hydrogen (CnH2: n=6-16) were identified by High-Performance Liquid Chromatography (HPLC) coupled with UV-Visible absorption spectroscopy and with the support of density functional theory (DFT) calculations. Size-selected polyynes separated by HPLC were analyzed by surface enhanced Raman spectroscopy (SERS). The formation process was monitored b...
sp-Hybridized carbon atomic wires are appealing systems with large property tunability. In partic... more sp-Hybridized carbon atomic wires are appealing systems with large property tunability. In particular, their electronic properties are intimately related to length, structure, and type of functional end-groups as well as to other effects such as the intermolecular charge transfer with metal nanoparticles. Here, by a combined Raman, Surface Enhanced Raman Scattering (SERS) investigation and first principles calculations of different N,N-dimethylanilino-terminated polyynes, we suggest that, upon charge transfer interaction with silver nanoparticles, the function of sp-carbon atomic wire can change from electron donor to electron acceptor by increasing the wire length. In addition, the insertion into the wire of a strong electrophilic group (1,1,4,4-tetracyanobuta-1,3-diene-2,3-diyl) changes the electronaccepting molecular regions involved in this intermolecular charge transfer. our results indicate that carbon atomic wires could display a tunable charge transfer between the sp-wire and the metal, and hold promise as active materials in organic optoelectronics and photovoltaics. Carbon atoms with sp-hybridization arrange in linear structures, constituting the ideal infinite 1D carbon wire (i.e. the carbyne) 1,2. Carbyne attracts interest as a new carbon allotrope 3-6 and for its predicted fascinating properties, such as exceptional mechanical stiffness, electron mobility, thermal conduction, as well as peculiar strain induced metal-to-insulator transition, ballistic transport, and nonlinear optical properties, as recently pointed out by a number of works 7-16. Most of these properties are a direct consequence of the π-electron conjugation resulting from the linear configuration and the hybridization state. In finite carbon-atom wires (CAWs), the properties can be modulated by adjusting the length of the sp-carbon chain and the type of the end-group 17. Such opportunity fits with experimentally available systems whose length ranges typically from two carbon atoms to a few tens 18 , with the record length of 44 atoms reached by R. Tykwinski 19. As a recent example of the potential exploitation of such tunability, optical supermultiplexing and barcoding have been successfully demonstrated with a set of finite polyynes with engineered length and termination 20. In addition to the property modulation, the end-group can be used to control the structural and electronic configuration inducing either the polyyne-like structure 21 (i.e. alternating triple and single bonds in a dimerized geometry) or the cumulene-like structure 22-25 (i.e. sequence of double bonds in equalized geometry). Recently, rational chemical synthesis successfully provided many stable systems with controlled size and type of termination 17-19,22-24,26. The proper choice of terminating groups showed to be a promising strategy to improve stability against cross-linking reactions. Typical terminations include sp 2 aromatic groups able to ensure steric hindrance and long-term stability in ambient conditions opening new possibilities for understanding structure-property relationship through a detailed investigation of these systems. Vibrational spectroscopy has shown all its potential for detecting and investigating structural and electronic properties of sp-carbon systems 27. Raman spectroscopy can provide unambiguous insights on the structure and properties of sp-carbon molecules and thin films due to its extreme sensitivity to carbon hybridization, π-conjugation, and local order 1,27-29. In addition, Surface Enhanced Raman Scattering (SERS) gives access to the study of the interaction with metal nanoparticles and charge transfer processes 17,30-32. SERS exploits the local enhancement of the electric field upon excitation of surface plasmons by incident photons (i.e. electromagnetic SERS effect) or due to a charge transfer and the formation of a complex between the investigated molecule and the metal nanoparticle (i.e. chemical SERS effect). In the case of H-terminated polyynes, we showed an enhancement factor of 10 6 with respect to normal Raman 30,31. The chemical SERS
Besides graphite and diamond, the solid allotropes of carbon in sp 2 and sp 3 hybridization, the ... more Besides graphite and diamond, the solid allotropes of carbon in sp 2 and sp 3 hybridization, the possible existence of a third allotrope based on the sp-carbon linear chain, the Carbyne, has stimulated researchers for a long time. The advent of fullerenes, nanotubes and graphene has opened new opportunities and nurtured the interest in novel carbon allotropes including linear structures. The efforts made in this direction produced a number of interesting sp-hybridized carbon molecules and nanostructures in the form of carbon-atom wires. We here discuss some of the new perspectives opened by the recent advancements in the research on sp-carbon systems.
Novel bis(biphenyl)-capped polyynes have been synthesized to investigate the modulation of the el... more Novel bis(biphenyl)-capped polyynes have been synthesized to investigate the modulation of the electronic and optical properties of sp-hybridized carbon-atom wires (CAWs) capped with π-conjugated sp 2 endgroups. Raman and Surface Enhanced Raman spectroscopy (SERS) investigation of these systems and Density Functional Theory (DFT) calculations reveal structural changes from polyyne-like with alternating single-triple bonds towards cumulene-like with more equalized bonds as a consequence of the charge transfer occurring when wires interact with metallic nanoparticles. While polyynes have semiconducting electronic properties, a more equalized system tends to a cumulene-like structure characterized by a nearly metallic behavior. The possibility to drive a semiconductor-to-metal transition has been investigated by systematic DFT calculations on a series of CAWs capped with different conjugated endgroups revealing that the modulation of the structural, electronic and vibrational properties of the sp-carbon chain towards the metallic wire cannot be simply obtained by using extended π-conjugated sp 2 carbon endgroups, but require a suitable chemical design of the endgroup and control of charge transfer. These results provide useful guidelines for the design of novel sp-sp 2 hybrid carbon nanosystems with tunable properties, where graphene-like and polyyne-like domains are closely interconnected. The capability to tune the final electronic or optical response of the material makes these hybrid sp-sp 2 systems appealing for a future all-carbon-based science and technology.
Graphene, nanotubes and other carbon nanostructures have shown potential as candidates for advanc... more Graphene, nanotubes and other carbon nanostructures have shown potential as candidates for advanced technological applications due to the different coordination of carbon atoms and to the possibility of π-conjugation. In this context, atomic-scale wires comprised of sp-hybridized carbon atoms represent ideal 1D systems to potentially downscale devices to the atomic level. Carbon-atom wires (CAWs) can be arranged in two possible structures: a sequence of double bonds (cumulenes), resulting in a 1D metal, or an alternating sequence of single–triple bonds (polyynes), expected to show semiconducting properties. The electronic and optical properties of CAWs can be finely tuned by controlling the wire length (i.e., the number of carbon atoms) and the type of termination (e.g., atom, molecular group or nanostructure). Although linear, sp-hybridized carbon systems are still considered elusive and unstable materials, a number of nanostructures consisting of sp-carbon wires have been produced...
Thin films synthesized by assembling clusters present interesting chemical and physical propertie... more Thin films synthesized by assembling clusters present interesting chemical and physical properties and a large specific surface, and are appealing for functional applications (e.g. sensing and catalysis). Also, clusters supported on surfaces are interesting both for nanocatalysis applications and for fundamental research. By means of pulsed laser deposition (PLD) in a background atmosphere we can induce cluster aggregation in the ablation plume and control the deposition kinetic energy of the clusters. These phenomena depend on the plume expansion dynamics and their influence on the properties of the deposited films has been investigated as a function of the background gas mass and pressure. The control of these parameters permits variation of the film surface morphology, from a compact structure with a very smooth surface, to a film with a controlled roughness at the nanoscale, to an open, low density meso- and nanostructure characterized by a high fraction of voids and by a large specific area. Thin films of WOx, TiOx, Pd/PdO, and Ag were deposited and characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman spectroscopy. Post-deposition annealing permits control of the crystalline degree of the films, which in the case of tungsten and titanium oxide is found to depend on the original nanostructure, while a different degree of oxidation can be induced by controlling the amount of oxygen in the deposition chamber. In-situ scanning tunneling microscopy (STM) was employed to study the first stages of growth of W films on different substrates. This opens the possibility to tailor the material properties through the control of the building nano-units.
Tungsten oxide thin films are interesting for their electrochromic and gas sensing properties. Fo... more Tungsten oxide thin films are interesting for their electrochromic and gas sensing properties. For technological applications, the control of morphology (effective surface, porosity) and structure (crystallinity, stoichiometry) at the nanoscale is of paramount interest to deliver distinctive properties. Nanostructured tungsten and tungsten oxide films have been synthesized by nanosecond pulsed laser deposition (PLD) starting from a W metallic target. Both inert and reactive buffer gases (He, Ar, dry air) have been exploited to induce cluster ...
In this work we report on the preparation by Pulsed Laser Deposition (PLD) of tungsten oxide laye... more In this work we report on the preparation by Pulsed Laser Deposition (PLD) of tungsten oxide layers featuring different morphologies, dominated by either nanoparticles or nanorods, with the aim to investigate the different gas-sensing properties of these nanostructures. A detailed structural analysis is reported showing morphological stability of the films under thermal annealing and phase transition. Emphasis is also given to the characterization of networking connections of the prepared layers, determinant for the electrical properties of the chemiresistor devices. Results show that samples with nanorod morphology exhibit an increased specific sensitivity to ammonia. The higher sensitivity of nanoparticles to other compounds such as ethanol or acetone suggests that these complementary sensitivities can be exploited to obtain selective gas detection in electronic nose systems.
Protein misfolding and aggregation in intracellular and extracellular spaces is regarded as a mai... more Protein misfolding and aggregation in intracellular and extracellular spaces is regarded as a main marker of the presence of degenerative disorders such as amyloidoses. To elucidate the mechanisms of protein misfolding, the interaction of proteins with inorganic surfaces is of particular relevance, since surfaces displaying different wettability properties may represent model systems of the cell membrane. Here, we unveil the role of surface hydrophobicity/hydrophilicity in the misfolding of the Josephin domain (JD), a globular-shaped domain of ataxin-3, the protein responsible for the spinocerebellar ataxia type 3. By means of a combined experimental and theoretical approach based on atomic force microscopy, Fourier transform infrared spectroscopy and molecular dynamics simulations, we reveal changes in JD morphology and secondary structure elicited by the interaction with the hydrophobic gold substrate, but not by the hydrophilic mica. Our results demonstrate that the interaction with the gold surface triggers misfolding of the JD when it is in native-like configuration, while no structural modification is observed after the protein has undergone oligomerization. This raises the possibility that biological membranes would be unable to affect amyloid oligomeric structures and toxicity.
A novel form of amorphous carbon with sp-sp 2 hybridization has been recently produced by superso... more A novel form of amorphous carbon with sp-sp 2 hybridization has been recently produced by supersonic cluster beam deposition showing the presence in the film of both polyynic and cumulenic species [L. Ravagnan et al. Phys. Rev. Lett. 98, 216103 (2007)]. Here we present a in situ Raman characterization of the low frequency vibrational region (400-800 cm-1) of sp-sp 2 films at different temperatures. We report the presence of two peaks at 450 cm-1 and 720 cm-1. The lower frequency peak shows an evolution with the variation of the sp content and it can be attributed, with the support of density functional theory (DFT) simulations, to bending modes of sp linear structures. The peak at 720 cm-1 does not vary with the sp content and it can be attributed to a feature in the vibrational density of states activated by the disorder of the sp 2 phase.
We report on DNA arrays produced by Dip Pen Nanolithography (DPN) on a novel Au-Ag micro patterne... more We report on DNA arrays produced by Dip Pen Nanolithography (DPN) on a novel Au-Ag micro patterned template stripped surface. DNA arrays have been investigated by atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) showing that the patterned template stripped substrate enables easy retrieval of the DPN-functionalized zone with a standard optical microscope permitting a multi-instrument and multi-technique local detection and analysis. Moreover the smooth surface of the Au squares (~ 5-10 Ǻ roughness) allows to be sensitive to the hybridization of the oligonucleotide array with label-free target DNA. Our Au-Ag substrates, combining the retrieving capabilities of the patterned surface with the smoothness of the template stripped technique, are candidates for the investigation of DPN nanostructures and for the development of label free detection methods for DNA nanoarrays based on the use of scanning probes.
A series of α, ω-diphenylpolyynes were synthesized through the Cadiot Chodkiewicz reaction starti... more A series of α, ω-diphenylpolyynes were synthesized through the Cadiot Chodkiewicz reaction starting from Cu (I)-phenylacetylide and diiodoacetylene. The complete series of diphenylpolyynes Φ-(C [tbnd] C) n-Φ with n= 2, 3, 4 and 5 was obtained and analyzed by ...
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Papers by Carlo S Casari