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Alkali metal doping and grain boundaries (GB) have been at the center of attention within the Cu(In,Ga)(S,Se)2 photovoltaics community for years. This study provides the first experimental evidence that the GB of sodium‐doped CuInSe2 thin films may undertake reversible oxidation even at room temperature, whereas undoped films may not. The findings are corroborated by cathodoluminescence imaging, secondary ion mass spectrometry, and Kelvin probe force microscopy on air‐exposed films subsequently subject to vacuum. A thermochemical assessment identifies the likely solid–gas equilibria involved. These reactions open new research questions with respect to the beneficial role played by alkali metal dopants in chalcopyrite solar cells and may steer the community toward new breakthroughs. [ABSTRACT FROM AUTHOR]

Cost-effective, active, and durable electrodes are required for the development of the efficient alkaline water electrolysis towards green hydrogen production. Here, we report successful fabrication of such electrodes by means of robust radio frequency magnetron sputtering that produces uniform, crystalline, and phase pure catalytic iridium thin films over nickel foam current collectors. The effect of working pressure of argon gas during sputtering on the physicochemical and electrochemical properties of the as-fabricated electrodes has been investigated. Specifically, it has been established that the employment of working pressure of 3 Pa afforded the electrodes with the lowest mass loading of precious iridium metal (≈0.32%), but exhibiting the best alkaline water electrolysis performance. The electrodes demonstrated favourable overpotentials of 14 mV and 318 mV at current densities of ±10 mA/cm2 toward hydrogen (HER) and oxygen (OER) evolution reactions, respectively. Furthermore, as a cathode and an anode for overall water splitting (OWS) in alkaline electrolyte, the electrode exhibited the cell voltage of 1.57 V at 10 mA/cm2 and stably performed electrolysis at different applied current densities. The electrochemical performance of the electrodes has been corroborated by work function measurements using Kelvin probe force microscopy. • Phase pure Ir thin films on nickel foam were fabricated by RF magnetron sputtering. • The effect of the working gas pressure on HER and OER performance was observed. • Bifunctional NiF@Ir-3 electrode can stably sustain OWS at several current densities. • Work function measurements prove to be a useful tool to validate electrochemical results. [ABSTRACT FROM AUTHOR]

Abstract: We have studied the electronic properties at the interface of a PTCDA molecular film on Au(111) by means of scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS) and angle resolved ultraviolet photoelectron spectroscopy (ARUPS). Measurements were performed for the clean Au(111) surface as well as for 1ML and multilayer coverage of PTCDA. STS curves recorded for 1ML PTCDA film show a feature at the density of states inside the PTCDA gap and a metallic behavior, in contrast to higher coverage, where a semiconductor behavior is observed. By relating this information to the band dispersion of the electronic states close to the Fermi edge, we can assign this electronic feature to the Au(111) Shockley surface state. By comparison of intramolecularly resolved STM images with first-principles calculations of the free molecule we show that the electronic molecular states at the interface are not altered by the gold surface. All these facts indicate a weak interaction of the PTCDA molecules with the Au surface and we conclude that the observed metallicity of the interface is provided by the gold substrate rather than by the organic layer. [Copyright &y& Elsevier]

• Xenon deposition on graphene gives rise to well-ordered islands in the submonolayer regime. • Force spectroscopy can clearly distinguish xenon islands from graphene regions. • Individual xenon atoms can be extracted from the islands. • Functionalization of atomic force microscopy (AFM) tips has been revealed as a powerful tool to. Functionalization of atomic force microscopy (AFM) tips has been revealed as a powerful tool to achieve an enhanced resolution allowing to resolve intramolecular features. Such functionalization can be performed by placing different species at the apex, as Xe adatoms. Functionalized tips could be useful to investigate molecules adsorbed on graphene (Gr) surfaces, where the molecule-graphene interaction is expected to be low. In particular, the Gr/Pt(111) interface has been shown to present a low molecule–substrate interaction that keeps the properties of the adsorbed molecule close to the free-molecule state. In this work, we have investigated the adsorption of Xe on graphene on Pt(111) surfaces, a necessary previous step to the in-situ functionalization of tips with Xe on these surfaces. For this purpose, we have employed a home-made cantilever-based non-contact atomic force microscope (ncAFM) operated under ultrahigh vacuum conditions at 5 K. Our results show the growth of well-ordered Xe islands in the submonolayer regime. Then, we show that force spectroscopy can be used to distinguish these islands from the bare graphene areas without the need of atomic resolution. Finally, the extraction of single Xe adatoms from the surface and the corresponding tip functionalization have been explored. [ABSTRACT FROM AUTHOR]

The application of scanning tunneling microscopy and spectroscopy (STM/STS) to the study of structural and electronic properties of organic/inorganic systems is presented here. The investigation of PTCDA (3,4,9,10, perylene tetracarboxylic dianhydride, C24O6H8) on semiconductor or metal surfaces by means of STM/STS shows a wide diversity of results indicating a complex behavior of the PTCDA molecules. It has been found that the surface reactivity highly influences the PTCDA adsorption and growth properties. The degree of molecule–surface interaction can lead to randomly chemisorbed molecules on highly reactive substrates, to one‐dimensional row formation on moderately reactive surfaces and well‐ordered overlayers in the case of physisorbed PTCDA molecules on weakly reactive surfaces. Scanning tunneling microscopy (STM) is a widely used technique for characterizing molecular layers. This article reviews some representative examples of PTCDA molecular layers grown and measured under ultrahigh vacuum conditions with STM. Results of PTCDA growth on several different substrates, including metals, semiconductors, and two‐dimensional materials, are shown, emphasizing their similarities and differences arising from the variability of the molecule–substrate interaction. [ABSTRACT FROM AUTHOR]

2D materials are considered the future of electronics and photonics, stimulated by their remarkable performance. Among the 2D materials family, β‐In2Se3 shows good mobility, excellent photoresponsivity, and exotic ferroelectricity, making it suitable for a wide variety of applications. To date, most reported devices from 2D materials in general, and β‐In2Se3 in specific, rely on cumbersome fabrication methods using mechanical exfoliation and transfer of layers onto other substrates. However, for a successful adoption of 2D materials in industry, reliable and reproducible large‐area growth of 2D materials is required. Here, the wafer‐scale epitaxial growth of 2D β‐In2Se3 on c‐sapphire using molecular beam epitaxy is demonstrated. Excellent materials quality of thick (90 nm) and very thin films, down to two quintuple layers (2 nm) is confirmed. Furthermore, the fabrication of hundreds of photodetector devices on a 2 in. wafer, using five quintuple layers of β‐In2Se3, is demonstrated. They are sensitive to near‐infrared light up to 898 nm wavelength and show a response time of ≈7 ms, which is faster than any result previously reported for β‐In2Se3 photodetectors. The devices are produced using photolithography and other standard semiconductor processing methods, which allows easy integration into the current Si technology. [ABSTRACT FROM AUTHOR]

The fabrication of Sb2Se3 thin-film solar cells deposited by a pulsed hybrid reactive magnetron sputtering (PHRMS) was proposed and examined for different growth conditions. The influence of growth temperature and Se pulse period were studied in terms of morphology, crystal structure, and composition. The Sb2Se3 growth showed to be dependent on the growth temperature, with a larger crystal size for growth at 270 °C. By controlling the Se pulse period, the crystal structure and crystal size could be modified as a function of the supplied Se amount. The solar cell performance for Sb2Se3 absorbers deposited at various temperatures, Se pulse periods and thicknesses were assessed through current-voltage characteristics. A power conversion efficiency (PCE) of 3.7% was achieved for a Sb2Se3 solar cell with 900 nm thickness, Sb2Se3 deposited at 270 °C and Se pulses with 0.1 s duration and period of 0.5 s. Finally, annealing the complete solar cell at 100 °C led to a further improvement of the Voc, leading to a PCE of 3.8%, slightly higher than the best reported Sb2Se3 solar cell prepared by sputtering without post-selenization. [ABSTRACT FROM AUTHOR]

The effect of selenium‐free annealing on cesium fluoride (CsF)‐treated Cu(In,Ga)Se2 (CIGS) thin films is investigated and their solar cell performance is evaluated. Annealing of CsF‐treated CIGS thin films changes the surface morphology and the chemical composition, and reduces the Urbach energy. However, the full benefit of the reduced Urbach energies of the annealed samples is not obtained, because of an increased buffer/CIGS interface recombination as a consequence of re‐evaporation of the alkali‐containing layer from the surface region upon annealing. On the other hand, CsF‐treated CIGS thin films without any annealing after the post‐deposition treatment (PDT) preserve the alkali‐containing layer at the surface, thereby leading to an improved buffer/CIGS interface. Consequently, the open‐circuit voltage (VOC) and fill factor improve significantly in these devices. The Urbach energies of both annealed and nonannealed solar cells are calculated from external quantum efficiency measurement to understand their impact on VOC and VOC deficit. No correlation between the VOC deficit and the Urbach energies is observed. [ABSTRACT FROM AUTHOR]

• Study of the self-assembly of chloroaluminum phthalocyanine on graphene on Pt(111) • Squared-shaped molecular lattices orientated following the graphene lattice directions. • No influence of moiré patterns in the molecular ordering is observed. • HOMO and LUMO orbitals characterized by Scanning Tunneling Spectroscopy and images. Phthalocyanines are promising molecules for the development of organic electronic devices, for instance, molecular heterojunctions in organic solar cells or organic field-effect transistors. For an optimum performance of these devices, the molecular ordering on the substrate and the molecular electronic level alignment have been shown as crucial factors. In this work, the self-assembled structure and the electronic structure of chloroaluminum phthalocyanines (ClAlPc) on graphene grown on Pt(111) surfaces have been studied by scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) and low-temperature conditions. Graphene grown on Pt(111) exhibits multiple moiré patterns with different periodicities, offering a benchmark to investigate the influence of the graphene and the moiré patterns in the ClAlPc ordering. This surface allows to extend previous works performed on graphite and graphene on Cu(100), where no moiré patterns are found. Well-ordered molecular islands exhibiting rotational domains have been observed in the submonolayer regime. The orientation of individual ClAlPc molecules within the structure unit cell has been characterized pointing out to a Cl-Up configuration adopted by the molecules. Our measurements show a correlation between the molecular lattice orientation and the graphene directions, whereas no influence of the underlying moiré patterns has been found. Finally, the ClAlPc electronic structure has been characterized indicating a weak graphene-molecule interaction. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanotips for Atomic Force Microscopy by manipulation of metallic nanoclusters. • Cluster nanotips minimize long range van der Waals interactions. • Nanoclusters on graphene are used to functionalize Atomic Force Microscopy tips. • The same built-up nanotip is robust enough to be used with different samples. • The built-up AFM nanotips show a greatly enhance spatial resolution. The ability to probe tip-sample interactions by Atomic Force Microscopy (AFM) has recently boosted our understanding of the matter at the atomic scale, enabling the study of properties of surfaces and adsorbates which were previously inaccessible. Nevertheless, this sensitivity to forces presents some drawbacks, as the requirement of a sharp tip apex to prevent the loss of spatial resolution due to the existence of long-range interactions. In this work, we have overcome this long-standing challenge by investigating the controlled extraction of single metallic nanoclusters, selectively grown on graphene. Our results show that the successive extraction of cluster allows to grow nanotips, which minimize the long-range tip-sample interactions and greatly enhance the topographic resolution. We have demonstrated that the created nanotips are very stable, which enables exchanging the sample and using the same nanotip to explore different surfaces without loss of resolution. Since metallic clusters of very different materials and sizes can be grown and selectively extracted by AFM, ours work paves also the way to the specific functionalization of AFM-tips to sense a large variety of interactions. [ABSTRACT FROM AUTHOR]

Chalcopyrite solar cells achieve efficiencies above 23%. The latest improvements are due to post‐deposition treatments (PDT) with heavy alkalis. This study provides a comprehensive description of the effect of PDT on the chemical and electronic structure of surface and bulk of Cu(In,Ga)Se2. Chemical changes at the surface appear similar, independent of absorber or alkali. However, the effect on the surface electronic structure differs with absorber or type of treatment, although the improvement of the solar cell efficiency is the same. Thus, changes at the surface cannot be the only effect of the PDT treatment. The main effect of PDT with heavy alkalis concerns bulk recombination. The reduction in bulk recombination goes along with a reduced density of electronic tail states. Improvements in open‐circuit voltage appear together with reduced band bending at grain boundaries. Heavy alkalis accumulate at grain boundaries and are not detected in the grains. This behavior is understood by the energetics of the formation of single‐phase Cu‐alkali compounds. Thus, the efficiency improvement with heavy alkali PDT can be attributed to reduced band bending at grain boundaries, which reduces tail states and nonradiative recombination and is caused by accumulation of heavy alkalis at grain boundaries. [ABSTRACT FROM AUTHOR]

Rhenium-based 2D transition metal dichalcogenides such as ReSe2 are suitable candidates as photoactive materials for optoelectronic devices. Here, photodetectors based on mechanically exfoliated ReSe2 crystals were fabricated using chemical vapor deposited (CVD) graphene single-crystal (GSC) as lateral contacts. A "pick & place" method was adopted to transfer the desired crystals to the intended position, easing the device fabrication while reducing potential contaminations. A similar device with Au was fabricated to compare contacts' performance. Lastly, a CVD hexagonal boron nitride (hBN) substrate passivation layer was designed and introduced in the device architecture. Raman spectroscopy was carried out to evaluate the device materials' structural and electronic properties. Kelvin probe force measurements were done to calculate the materials' work function, measuring a minimal Schottky barrier height for the GSC/ReSe2 contact (0.06 eV). Regarding the electrical performance, I-V curves showed sizable currents in the GSC/ReSe2 devices in the dark and under illumination. The devices presented high photocurrent and responsivity, along with an external quantum efficiency greatly exceeding 100%, confirming the non-blocking nature of the GSC contacts at high bias voltage (above 2 V). When introducing the hBN passivation layer, the device under white light reached a photo-to-dark current ratio up to 106. [ABSTRACT FROM AUTHOR]