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Discerning the impact of the coherent motion of the nuclei on the timing and efficiency of charge transfer at the donor-acceptor interface is essential for designing performance-enhanced optoelectronic devices. Here, we employ an experimental approach using photocurrent detection in coherent multidimensional spectroscopy to excite a donor aromatic macrocycle and collect the charge transferred to a 2D acceptor layer. For this purpose, we prepared a cobalt phthalocyanine-graphene (CoPc-Gr) interface. Unlike blends, the well-ordered architecture achieved through the physical separation of the two layers allows us to unambiguously collect the electrical signal from graphene alone and associate it with a microscopic understanding of the whole process. The CoPc-Gr interface exhibits an ultrafast electron-transfer signal, stemming from an interlayer mechanism. Remarkably, the signal presents an oscillating time evolution modulated by coherent vibrations originating from the laser-excited CoPc states. By performing Fourier analysis on the beatings and correlating it with the Raman features, along with a comprehensive first-principles characterization of the vibrational coupling in the CoPc excited states, we successfully identify both the orbitals and molecular vibrations that promote the charge transfer at the interface.

The measurement and manipulation of the coherent dynamics of excitonic states constitute a forefront research challenge in semiconductor optics and quantum-coherence-based protocols for optoelectronic technologies. Layered semiconductors have emerged as an ideal platform for the study of exciton dynamics with accessible and technologically relevant energy and time scales. Here, we investigate the subpicosecond exciton dynamics in a van der Waals semiconductor upon quasi-resonant excitation and achieve to single out an incipient coherent excitonic state. Combining broad-band transient reflectance spectroscopy and simulations based on many-body perturbation theory, we reveal a transient enhancement of the excitonic line intensity that originates from photoinduced coherent polarization that is phase-locked with the interacting electromagnetic field. This finding allows us to define the spectral signature of a coherent excitonic state and to experimentally track the dynamical crossover from coherent to incoherent exciton, unlocking the prospective optical control of an exciton population on the intrinsic quantum-coherence time scale.

Understanding the nature of the photoexcitation and ultrafast charge dynamics pathways in organic halide perovskite nanocubes and their aggregation into superlattices is key for potential applications as tunable light emitters, photon-harvesting materials, and light-amplification systems. In this work, we apply two-dimensional coherent electronic spectroscopy (2DES) to track in real time the formation of near-infrared optical excitons and their ultrafast relaxation in CH(NH2)2PbI3 nanocube superlattices. Our results unveil that the coherent ultrafast dynamics is limited by the combination of the inherent short exciton decay time (≃40 fs) and the dephasing due to the coupling with selective optical phonon modes at higher temperatures. On the picosecond time scale, we observe the progressive formation of long-lived localized trap states. The analysis of the temperature dependence of the excitonic intrinsic line width, as extracted by the antidiagonal components of the 2D spectra, unveils a dramatic change of the excitonic coherence time across the cubic to tetragonal structural transition. Our results offer a new way to control and enhance the ultrafast coherent dynamics of photocarrier generation in hybrid halide perovskite synthetic solids.

The light-mediated interaction of fermionic and bosonic excitations governs the optoelectronic properties of condensed matter systems. In photoexcited semiconductors, the coupling of electron-hole pairs (excitons) to coherent optical phonons enables a modulation of the excitonic resonance that is phase-locked to the frequency of the coupled vibrational mode. Moreover, due to the Coulombic nature of excitons, their dynamics are sensitive to transient changes in the screening by the photoexcited carriers. Interestingly, the effect of photoinduced screening on the transient optical signal originating from the exciton dynamics coupled to phonons is not yet established. By means of broadband transient reflectance spectroscopy, we disclose how exciton-phonon coupling manifests in either the presence or absence of dynamical screening in a layered semiconductor. Furthermore, we unveil the promoting role of photoinduced screening on these exciton-phonon coupled dynamics as opposed to the case in which the unscreened exciton-exciton repulsion likely dominates the nonequilibrium optical response. These findings set a protocol to look at an excitonic resonance and its fundamental many-body interactions on the ultrafast timescale and provide new perspectives on the access to nonequilibrium coupled dynamics.

Electronic noses (e-noses) have received considerable interest in the past decade as they can match the emerging needs of modern society such as environmental monitoring, health screening, and food quality tracking. For practical applications of e-noses, it is necessary to collect large amounts of data from an array of sensing devices that can detect interactions with molecules reliably and analyze them via pattern recognition. The use of graphene (Gr)-based arrays of chemiresistors in e-noses is still virtually missing, though recent reports on Gr-based chemiresistors have disclosed high sensing performances upon functionalization of the pristine layer, opening up the possibility of being implemented into e-noses. In this work, with the aim of creating a robust and chemically stable interface that combines the chemical properties of metal phthalocyanines (M-Pc, M = Fe, Co, Ni, Zn) with the superior transport properties of Gr, an array of Gr-based chemiresistor sensors functionalized with drop-cast M-Pc thin layers has been developed. The sensing capability of the array was tested towards biomarkers for breathomics application, with a focus on ammonia (NH3). Exposure to NH3 has been carried out drawing the calibration curve and estimating the detection limit for all the sensors. The discrimination capability of the array has then been tested, carrying out exposure to several gases (hydrogen sulfide, acetone, ethanol, 2-propanol, water vapour and benzene) and analysing the data through principal component analysis (PCA). The PCA pattern recognition results show that the developed e-nose is able to discriminate all the tested gases through the synergic contribution of all sensors.

Fast X-ray photoemission spectroscopy has been carried out to track the interaction of ammonia gas with hybrid materials based on ZnO nanorods and nanostructured carbon. We provide, for the first time, direct evidence of gas adsorption of ammonia on nanostructured hybrid interfaces combining photoemission with transport measurements through the resistivity change upon gas exposure. This operando methodology allowed us to reconstruct the adsorption isotherms and relate the different behavior to the sample morphology at the nanoscale. While on bare ZnO nanorods, physisorption of ammonia is detected along with photon beam assisted cracking, on the nanostructured carbon the formation of amine groups is detected, without displaying any effect induced by photon beam exposure. Our results make the present experiment an operando general methodology, with the possibility to relate the transport versus dose curves (ultimately the adsorption isotherms) to a specific investigation of the gas/surface interactions.

Managing light-matter interactions on timescales faster than the loss of electronic coherence is key for achieving full quantum control of the final products in solid-solid transformations. In this Letter, we demon-strate coherent optical control of the orbital occupation that determines the insulator-to-metal transition in the prototypical Mott insulator V2O3. Selective excitation of a specific interband transition with two phase-locked light pulses manipulates the occupation of the correlated bands in a way that depends on the coherent evolution of the photoinduced superposition of states. A comparison between experimental results and numerical solutions of the optical Bloch equations provides an electronic coherence time on the order of 5 fs. Temperature-dependent experiments suggest that the electronic coherence time is enhanced in the vicinity of the insulator-to-metal transition critical temperature, thus highlighting the role of fluctuations in determining the electronic coherence. These results open different routes to selectively switch the functionalities of quantum materials and coherently control solid-solid electronic transformations.

Electronic noses (e-noses) have received considerable interest in the past decade as they can match the emerging needs of modern society such as environmental monitoring, health screening, and food quality tracking. For practical applications of e-noses, it is necessary to collect large amounts of data from an array of sensing devices that can detect interactions with molecules reliably and analyze them via pattern recognition. The use of graphene (Gr)-based arrays of chemiresistors in e-noses is still virtually missing, though recent reports on Gr-based chemiresistors have disclosed high sensing performances upon functionalization of the pristine layer, opening up the possibility of being implemented into e-noses. In this work, with the aim of creating a robust and chemically stable interface that combines the chemical properties of metal phthalocyanines (M-Pc, M = Fe, Co, Ni, Zn) with the superior transport properties of Gr, an array of Gr-based chemiresistor sensors functionalized with drop-cast M-Pc thin layers has been developed. The sensing capability of the array was tested towards biomarkers for breathomics application, with a focus on ammonia (NH3). Exposure to NH3 has been carried out drawing the calibration curve and estimating the detection limit for all the sensors. The discrimination capability of the array has then been tested, carrying out exposure to several gases (hydrogen sulfide, acetone, ethanol, 2-propanol, water vapour and benzene) and analysing the data through principal component analysis (PCA). The PCA pattern recognition results show that the developed e-nose is able to discriminate all the tested gases through the synergic contribution of all sensors.

Sensor arrays are currently attracting the interest of researchers due to their potential of overcoming the limitations of single sensors regarding selectivity, required by specific applications. Among the materials used to develop sensor arrays, graphene has not been so far extensively exploited, despite its remarkable sensing capability. Here we present the development of a graphene-based sensor array prepared by dropcasting nanostructure and nanocomposite graphene solution on interdigitated substrates, with the aim to investigate the capability of the array to discriminate several gases related to specific applications, including environmental monitoring, food quality tracking, and breathomics. This goal is achieved in two steps: at first the sensing properties of the array have been assessed through ammonia exposures, drawing the calibration curves, estimating the limit of detection, which has been found in the ppb range for all sensors, and investigating stability and sensitivity; then, after performing exposures to acetone, ethanol, 2-propanol, sodium hypochlorite, and water vapour, chemometric tools have been exploited to investigate the discrimination capability of the array, including principal component analysis (PCA), linear discriminant analysis (LDA), and Mahalanobis distance. PCA shows that the array was able to discriminate all the tested gases with an explained variance around 95%, while with an LDA approach the array can be trained to accurately recognize unknown gas contribution, with an accuracy higher than 94%.

The possibility to increase the efficiency of photovoltaic (PV) cells based on hybrid carbon nanotube (CNT)-Si heterojunctions is related to the ability to control the chemical properties of the CNT-Si interface and of the CNT bundle layer. In spite of the encouraging performances of PV cells based on multiwall (MW) CNT, so far few efforts have been made in the study of this device compared to single wall (SW) CNT-Si interfaces. Here, surface and interface effects on the current-voltage characteristic curves of MW CNT-Si hybrid junctions are investigated through exposure to HF vapors and to 10 ppm-NO2 and compared to the effects detected in SW CNT-Si junctions. Quite similar results in terms of open circuit voltage, short circuit current density, and efficiency are found for both cells, suggesting that exposure to HF vapors mostly affects the interface chemical properties, i.e., the silicon oxidation state, that in both junctions reach an optimal state about 50 h after etching. In turn, NO2 exposure has larger effects on the SW-based cell, consistently with the larger surface-to-volume ratio of SW with respect to MW. In both cases, the efficiency value reaches a maximum after 28 min, before dropping when the NO2 molecules desorb from the surface. A combined analysis of current-voltage curves and photoemission data collected along the different phases of gas exposures allowed us to relate changes in the electrical properties to the chemistry of Si at the interface

An array of carbon nanotube (CNT)-based sensors was produced for sensing selective biomarkers and evaluating breathomics applications with the aid of clustering and classification algorithms. We assessed the sensor array performance in identifying target volatiles and we explored the combination of various classification algorithms to analyse the results obtained from a limited dataset of exhaled breath samples. The sensor array was exposed to ammonia (NH3){,} nitrogen dioxide (NO2){,} hydrogen sulphide (H2S){,} and benzene (C6H6). Among them{,} ammonia (NH3) and nitrogen dioxide (NO2) are known biomarkers of chronic obstructive pulmonary disease (COPD). Calibration curves for individual sensors in the array were obtained following exposure to the four target molecules. A remarkable response to ammonia (NH3) and nitrogen dioxide (NO2){,} according to benchmarking with available data in the literature{,} was observed. Sensor array responses were analyzed through principal component analysis (PCA){,} thus assessing the array selectivity and its capability to discriminate the four different target volatile molecules. The sensor array was then exposed to exhaled breath samples from patients affected by COPD and healthy control volunteers. A combination of PCA{,} supported vector machine (SVM){,} and linear discrimination analysis (LDA) shows that the sensor array can be trained to accurately discriminate healthy from COPD subjects{,} in spite of the limited dataset

Fast X-ray photoemission spectroscopy has been carried out to track the interaction of ammonia gas with hybrid materials based on ZnO nanorods and nanostructured carbon. We provide, for the first time, direct evidence of gas adsorption of ammonia on nanostructured hybrid interfaces combining photoemission with transport measurements through the resistivity change upon gas exposure. This operando methodology allowed us to reconstruct the adsorption isotherms and relate the different behavior to the sample morphology at the nanoscale. While on bare ZnO nanorods, physisorption of ammonia is detected along with photon beam assisted cracking, on the nanostructured carbon the formation of amine groups is detected, without displaying any effect induced by photon beam exposure. Our results make the present experiment an operando general methodology, with the possibility to relate the transport versus dose curves (ultimately the adsorption isotherms) to a specific investigation of the gas/surface interactions.

In this work, we investigate the optical properties of self-standing Si nanostructures (SiNS) as-grown, by an inductively coupled plasma torch process, and after their annealing under N2 flux at 1200 °C. We show that as-grown SiNS are embedded in a silicon oxide shell while part of the annealed SiNS transforms into silicon nitrides or oxynitrides. The analysis of the photoluminescence spectra and maps of both as-grown and annealed SiNS enabled us to confirm the occurrence of quantum confinement effects in the ultra-small SiNS and to highlight the role played by the silicon oxide, silicon nitrides, and silicon oxynitrides nanophases in the photoluminescence emission.

A sensor array based on heterojunctions between semiconducting organic layers and single walled carbon nanotube (SWCNT) films is produced to explore applications in breathomics, the molecular analysis of exhaled breath. The array is exposed to gas/volatiles relevant to specific diseases (ammonia, ethanol, acetone, 2-propanol, sodium hypochlorite, benzene, hydrogen sulfide, and nitrogen dioxide). Then, to evaluate its capability to operate with real relevant biological samples the array is exposed to human breath exhaled from healthy subjects. Finally, to provide a proof of concept of its diagnostic potential, the array is exposed to exhaled breath samples collected from subjects with chronic obstructive pulmonary disease (COPD), an airway chronic inflammatory disease not yet investigated with CNT-based sensor arrays, and breathprints are compared with those obtained from of healthy subjects. Principal component analysis shows that the sensor array is able to detect various target gas/volatiles with a clear fingerprint on a 2D subspace, is suitable for breath profiling in exhaled human breath, and is able to distinguish subjects with COPD from healthy subjects based on their breathprints. This classification ability is further improved by selecting the most responsive sensors to nitrogen dioxide, a potential biomarker of COPD.

A new paradigm for active nanophotonic structures and metadevices based on perovskites has recently emerged due to several unique features of these materials such as room-temperature exciton, tunable bandgap energy, and low-cost fabrication methods [1,2]. Progress towards future applications requiring dynamical control of the optical response will depend on our understanding of photoexcitations in these systems [3,4]. In this work, we report the first experimental observation of ultrafast all-optical modulation of Fano resonant halide perovskite nanoparticles (NP). Our measurements, corroborated by analytical and numerical models, show that the out-of-equilibrium dynamics of these systems can be thoroughly controlled by engineering the NP size.