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Colloidal InSb quantum dots (QDs) are a potential alternative to toxic Pb‐ and Hg‐chalcogenide QDs for covering the technologically important near‐infrared/shortwave infrared (NIR/SWIR) spectral range. However, appropriate Sb precursors are scarce and obtaining narrow size distributions is challenging. Tris(dimethylamido)antimony (Sb(NMe2)3) is an appealing choice due to its commercial availability and non‐pyrophoric character but implies the reduction of antimony from the +3 to the required –3 state. In reported works, strong reducing agents such as lithium triethylborohydride are used, which lead to the fast co‐reduction of both Sb3+ and In3+. The downsides of this approach are reproducibility issues and the risk of forming metal nanoparticles due to the different reduction kinetics of Sb3+ and In3+. Here, indium(I) halides are explored as simultaneous indium source and mild reducing agent for the antimony precursor. The wavelength of the excitonic absorption peak of the phase‐pure InSb QDs obtained with this approach can be tuned from 630 to 1890 nm, which corresponds to a size range of ≈2–7 nm. The synthesis can also be conducted in a heat‐up manner, which facilitates the scale‐up and paves the way for the use of InSb QDs in applications such as NIR/SWIR photodetectors, cameras, biological imaging, and telecommunications. [ABSTRACT FROM AUTHOR]

Among colloidal nanocrystals, 2D nanoplatelets offer a unique set of properties with exceptionally narrow luminescence and low lasing thresholds. Furthermore, their anisotropic shape expands the playground for the complex design of heterostructures where spectra but also scattering rates can be engineered. A challenge that still remains is to combine shell growth which makes NPLs stable, with spectral tunability. Indeed, most reported shelled nanoplatelets end up being red emitters due to a loss of quantum confinement. Here, the combination of both lateral and in‐plane confinements within a single heterostructure is explored. A CdS/CdSe/CdS/CdZnS core–crown–crown shell structure that enables yellow emission is grown and that is responsive to a large range of excitation including visible photons, X‐ray photons, electron beams, and electrical excitations. k.p simulations predict that emission tunability of up to several 100 s of meV can be obtained in ideal structures. This material also displays stimulated emission resulting from bi‐exciton emission with a low threshold. Once integrated into an LED stack, this material is compatible with sub‐bandgap excitation and exhibits high luminance. Scaling of the electroluminescence properties by downsizing the pixel size is also investigated. [ABSTRACT FROM AUTHOR]

Due to the increase of energy consumption and the resulting ecological challenge, a collective awareness leads to the development of renewable energies and more efficient materials to increase the green energy production. Development of efficient photovoltaic materials is very closely related to their chemical and electronic properties. A better knowledge of these imbricated properties is needed, in addition to a better comprehension of their interplay with charge transport mechanisms. Exciton creation and recombination processes, charge transfer and charge collection processes take place at the surface and interface of the photoactive materials. Photoemission spectroscopy as chemical specific and surface sensitive spectroscopic technique is a method of choice on the study of physical phenomena at the origin of photoconversion efficiency. Time resolved photoemission spectroscopy has been recently renewed interest covering time scale from fs to more than seconds. It permits to probe the dynamics of relaxation of photoexcited charges and determine their lifetime. It finds application in various materials used in solar photovoltaics. In this paper, we define the physical and chemical properties determined by the combination of high resolution and time resolved photoemission spectroscopy. We show examples dealing with the development of renewable energy and energy consumption reduction in agreement with the current ecological trend for a better future.

Magneto-dynamics and its interfacial modulation have attracted much attention in energy-efficient and nonvolatile spintronic devices. In particular, the antiferromagnetic coupling at the interface plays a crucial role in spin dynamic behaviors. In this work, we utilize rare-earth holmium (Ho) to interface with transition-metal alloy Ni80Fe20(Py) and achieve a naturally formed antiferromagnetic coupling between Py and interfacial Ho via the magnetic proximity effect, as confirmed by element-specific synchrotron radiation x-ray magnetic circular dichroism hysteresis loops. Importantly, the antiferromagnetic coupled interface is preserved even at a low temperature of 4.2 K, which is below the Curie temperature of Ho. Using ferromagnetic resonance analysis, we reveal that the Gilbert damping and the interfacial spin mixing conductance of the Py/Ho bilayers are much larger than those of the Py/Pt and Py/Pd, suggesting a superior spin transparent efficiency on such an interface with an antiferromagnetic coupling. More importantly, upon the insertion of 2-nm-thick Cu, the antiferromagnetic coupling disappears, associated with the evident suppression of Gilbert damping. This strengthens the critical role of the antiferromagnetic coupled interface in the magneto-dynamics of the transition-metal/rare-earth bilayers and provides a promising way of magneto-dynamics modulation in antiferromagnet-based devices. [ABSTRACT FROM AUTHOR]

HgTe nanocrystals offer a unique spectral tunability with both absorption and emission covering the near and mid‐infrared as well as the THz window. Nevertheless, a very limited amount of work is dedicated to electroluminescence from this material. An efficient diode not only requires designing a structure that achieves a high electrical efficiency (i.e., efficient electron and hole injections), but also finding a way to efficiently extract the emitted photons. The shift from visible to infrared certainly demands revisiting the strategies proposed for shorter wavelengths (microlens arrays). Here, a metallic grating is used to enhance the photoluminscence signal up to a factor of 4 while enabling directionality in the emission, which is driven by the grating period. [ABSTRACT FROM AUTHOR]

The design of infrared nanocrystals‐based (NCs) photodiodes faces a major challenge related to the identification of barriers with a well‐suited band alignment or strategy to finely control the carrier density. Here, this study explores a general complementary approach where the carrier density control is achieved by coupling an NC layer to a ferroelectric material. The up‐and‐down change in ferroelectric polarization directly impacts the NC electronic structure, resulting in the formation of a lateral pn junction. This effect is uncovered directly using nano X‐ray photoemission spectroscopy, which shows a relative energy shift of 115 meV of the NC photoemission signal over the two different up‐ and down‐polarized ferroelectric regions, a shift as large as the open circuit value obtained in the diode stack. The performance of this pn junction reveals enhanced responsivity and reduced noise that lead to a factor 40 increase in the detectivity value. [ABSTRACT FROM AUTHOR]

Environmentally friendly catalytic composites based on cobalt and a natural clay as catalytically active phase and support, respectively, are herein reported for the valorization of fatty acids and esters, in particular for wastes coming from agri-food industry, by selective hydrogenation processes. The as-prepared innovative materials are constituted of zero-valent cobalt nanoparticles immobilized on both pristine halloysite and an ammonium-functionalized clay, with the former support exhibiting better particle distribution on the support as only Co agglomerates could be obtained for ammonium-functionalized halloysite. Under optimized conditions (5 mol % Co, 120 °C, 40 bar), high conversions and remarkable chemoselectivity were observed, leading to the exclusive formation of saturated fatty acids or esters, as well as the formation of tristearin used as a food additive. [ABSTRACT FROM AUTHOR]

From the first initiatives [[1]] to the most recent developments of synchrotron-based techniques for the study of cultural and natural heritage materials, many synchrotron facilities have developed their own scientific programs in this field [[2]]. Ender to hard X-rays 3-23 keVMacro: 250 × 200 µm Micro: 5 to 10 µmXRF, XRD, DANES, DAFS, EXAFS, XANES imaging or punctual measurementsU X-ray tomography Synchrotron X-ray micro- and nanotomography allow the study of the detailed 3D morphology of bulk samples, with a spatial resolution that can go down to the sub-micrometer range for "standard" parallel-beam projection microtomography setups, and down to less than 50 nm in nano-tomography methods using more recent and more complex schemes, such as hard X-ray transmission X-ray microscopy (TXM). D micro spectral imaging with XRF, XANES, and XRD 3D computed tomography with absorption and phase contrast (in the future)T. [Extracted from the article]

The adsorption of phthalocyanine (H2Pc) on the 6H-SiC(0001)-(3 × 3) surface is investigated using X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS), and density functional theory (DFT) calculations. Spectral features are tracked from the submonolayer to the multilayer growth regime, observing a significant modification of spectroscopic signals at low coverage with respect to the multilayer films, where molecules are weakly interacting. Molecules stay nearly flat on the surface at the mono and submonolayers. Previously proposed adsorption models, where the molecule binds by two N atoms to corresponding Si adatoms, do not reproduce the experimental spectra at the submonolayer coverage. We find instead that another adsorption model where the molecule replaces the two central H atoms by a Si adatom, effectively forming Si-phthalocyanine (SiPc), is both energetically more stable and yields in combination a better agreement between the experimental and simulated spectra. This suggests that the 6H-SiC(0001)-(3 × 3) surface may be a candidate substrate for the on-surface synthesis of SiPc molecules. [ABSTRACT FROM AUTHOR]

Thanks to their narrow band gap nature and fairly high carrier mobility, HgTe nanocrystals (NCs) are of utmost interest for optoelectronics beyond the telecom window (λ > 1.55 μm). In particular, they offer an interesting cost-effective alternative to the well-developed InGaAs technology. However, in contrast to PbS, far less work has been dedicated to the integration of this material in photodiodes. In the short-wave infrared region, HgTe NCs have a more p-type character than in the mid-wave infrared region, thus promoting the development of new electron transport layers with an optimized band alignment. As for perovskites, HgTe NCs present a fairly deep band gap with respect to vacuum. Thus, we were motivated by the strategy developed for perovskite solar cells, for which SnO2 has led to the best performing devices. Here, we explore the following stack made of SnO2/HgTe/Ag2Te, in which the SnO2 and Ag2Te layers behave as electron and hole extractors, respectively. Using X-ray photoemission, we show that SnO2 presents a nearly optimal band alignment with HgTe to efficiently filter the hole dark current while letting the photoelectrons flow. The obtained I–V curve exhibits an increased rectifying behavior, and the diode stack presents a high internal efficiency for the diode (above 60%) and an external quantum efficiency that is mostly limited by the absorption magnitude. Furthermore, we tackle a crucial challenge for the transfer of such a diode onto readout circuits, which prevents back-side illumination. We also demonstrate that the diode stack is reversible with a partially transparent conducting electrode on the top, while preserving the device's responsivity. Finally, we show that such a SnO2 layer is also beneficial for electron injection and leads to an enhanced electroluminescence signal as the diode is operated under forward bias. This work is an essential step toward the design of a focal plane array with a HgTe NC-based photodiode. [ABSTRACT FROM AUTHOR]

We have monitored the temporal evolution of the band bending at controlled silicon surfaces after a fs laser pump excitation. Time-resolved surface photo-voltage (SPV) experiments were performed using time resolved photoemission spectroscopy with time resolution of about 30 ns. To disentangle the influence of doping and surface termination on SPV dynamics, we compare the results obtained on two surface terminations: the water saturated (H,OH)–Si(001) surface and the thermally oxidized Si(001) one. The SPV dynamics were explored as a function of laser fluence and as a function of time for the two surface terminations at given doping levels. The return to equilibrium involves a characteristic time in the 0.1 μs to 10 μs range, depending on the surface termination and bulk doping. Exploring several laser fluences, different SPV regimes were found for the two surface terminations at given doping levels. For low laser fluence the SPV dynamic follows the commonly accepted thermionic model. At higher fluence, the SPV signal reaches a saturation value, and if the fluence is further increased, the decay time of the SPV increases and can no longer be explained by a thermionic model alone. [ABSTRACT FROM AUTHOR]

Recently, electron correlation has been shown to play an important role in unconventional plasmon generation in highly correlated electron systems. Electrons in topological insulators, on the other hand, are massless and insensitive to nonmagnetic scattering due to their protection by time-reversal symmetry, which makes these materials appealing platforms for hosting exotic plasmonic excitations. Here, using a combination of angle-dependent spectroscopic ellipsometry and angle-resolved photoemission spectroscopy as a function of temperature supported by first-principles calculations, we reveal a new pair of correlated plasmonic excitations at 1.04 and 1.52 eV and a significant Fermi level shift of 0.12 eV accompanied by spectral weight transfer in the topological insulator bismuth selenide (Bi2Se3). Interestingly, such a spectral weight transfer over a broad energy range causes a drastic change in the charge carrier density whereby the contribution of charge carriers in the bulk starts to rival those in the surface states and Bi2Se3 becomes more uniformly conducting. Our results show the importance of electronic correlations in determining the electronic structure and appearance of correlated plasmons in topological insulators and their potential applications in plasmonics. Condensed-matter physics: mapping temperature changes The temperature dependence of plasmons, exotic particles of light and matter, in topological insulators has been mapped by researchers in Singapore, France and the US. Topological insulators can conduct an electrical current on their surface even though they are insulators on the inside. This gives rise to unusual properties, such as effectively massless electrons. Andrivo Rusydi and Thomas Whitcher from the National University of Singapore and co-workers have investigated how the long-range interactions between these electrons change with temperature. They used numerous state-of-the-art experimental techniques to map the possible energy levels of the electrons in the topological insulator bismuth selenide. The results, supported by numerical calculations, provided evidence of the existence of plasmons: particles created when electrons strongly couple to light. Long-range plasmon interactions could be useful in plasmonics, a form of information processing. Using a combination of angle-dependent spectroscopic ellipsometry and angle-resolved photoemission spectroscopy as a function of temperature and supported by first-principles calculations, we reveal a new pair of correlated plasmonic excitations at 1.04 and 1.52 eV and a significant Fermi level shift of 0.12 eV, accompanied by spectral weight transfer in the topological insulator, Bismuth Selenide (Bi2Se3). Interestingly, such a spectral weight transfer over a broad energy range causes a drastic change in the charge-carrier density whereby the contribution of charge-carriers in the bulk starts to rival those in the surface states and Bi2Se3 becomes more uniformly conducting. [ABSTRACT FROM AUTHOR]

While 1T′ phase-pure MX2 (M = Mo, W; X = Se, Te) have recently been reported to be superconductors, Weyl semimetals, or quantum spin Hall insulators, the electronic properties of phase-pure 1T′-WS2 samples are still lacking thorough investigation. Here, we report the study of single-layer 1T′-WS2 nanosheets prepared from lithium exfoliation of WS2. We confirmed the composition and structure of single layer 1T′-WS2 flakes using X-ray photoelectron spectroscopy, Raman spectroscopy, and aberration corrected transmission electron microscopy (STEM). The distorted octahedral structure related to the 1T′ phase with a 2a × 2a superstructure is evidenced using STEM. Photoemission and electronic measurements uncover the presence of a narrow bandgap (>120 meV) in the 1T′-WS2 nanosheets, which is completely different from semiconducting bulk or single-layer 1H-WS2. The material is found to be ambipolar with a p-type nature. At low temperatures, a slow photoresponse is also observed. [ABSTRACT FROM AUTHOR]

The self-assembly of star-shaped 1,3,5-tris(3,5-dibromophenyl)benzene molecules on Au(111)-(UGRAPHIC DISPLAY="INLINE" ID="UGT3" SRC="UGT3"/) in a vacuum is investigated using scanning tunneling microscopy and core-level spectroscopy. Scanning tunneling microscopy shows that the molecules self-assemble into a hexagonal porous halogen-bonded nanoarchitecture. This structure is stabilized by X3-A synthons composed of three type-II halogen-interactions (halogen-bonds). The molecules are oriented along the same direction in this arrangement. Domain boundaries are observed in the hcp region of the herringbone gold surface reconstruction. Molecules of the neighboring domains are rotated by 180°. The domain boundaries are stabilized by the formation of X3-B synthons composed of two type-II and one type-I halogen-interactions between molecules of the neighboring domains. Core-level spectroscopy confirms the existence of two types of halogen-interactions in the organic layer. These observations show that the gold surface reconstructions can be exploited to modify the long-range supramolecular halogen-bonded self-assemblies. [ABSTRACT FROM AUTHOR]

Colloidal nanocrystals are playing an increasing role for the development of low cost optoelectronics. Among these materials, 2D nanoplatelets (NPL) offer particularly well-controlled optical features and their integration into device such as transistor and photoconductor is here discussed. We present recent results obtained on the optoelectronic properties of CdSe/CdS and HgTe 2D nanoplatelets (NPL). The manuscript is organized along three main sections. The first part is an introduction to 2D NPLs and their structural and optical properties. The second part gets focused on CdSe/CdS NPL and their photoconductive properties. We in particular highlight the key role plays by the 2D geometries on the charge dissociation. Finally the last part of the paper discusses about the recent report of HgTe and HgSe NPL with optical features in the near infrared. Here we discuss how the surface chemistry can be used to tune the majority carrier and the photoconductive properties of the material. [ABSTRACT FROM AUTHOR]

The SOLEIL synchrotron radiation source is regularly operated in special filling modes dedicated to pump-probe experiments. Among others, the low-α mode operation is characterized by shorter pulse duration and represents the natural bridge between 50 ps synchrotron pulses and femtosecond experiments. Here, the capabilities in low-α mode of the experimental set-ups developed at the TEMPO beamline to perform pump-probe experiments with soft X-rays based on photoelectron or photon detection are presented. A 282 kHz repetition-rate femtosecond laser is synchronized with the synchrotron radiation time structure to induce fast electronic and/or magnetic excitations. Detection is performed using a two-dimensional space resolution plus time resolution detector based on microchannel plates equipped with a delay line. Results of time-resolved photoelectron spectroscopy, circular dichroism and magnetic scattering experiments are reported, and their respective advantages and limitations in the framework of high-time-resolution pump-probe experiments compared and discussed. [ABSTRACT FROM AUTHOR]

Among colloidal nanocrystals, 2D nanoplatelets (NPLs) made of cadmium chalcogenides have led to especially well controlled optical features. However, the growth of core shell heterostructures has so far been mostly focused on CdS shells, while more confined materials will be more promising to decouple the emitting quantum states of the core from their external environment. Using k.p simulation, we demonstrate that a ZnS shell reduces by a factor 10 the leakage of the wavefunction into the surrounding medium. Using X-ray photoemission (XPS), we confirm that the CdSe active layer is indeed unoxidized. Finally, we build an effective electronic spectrum for these CdSe/ZnS NPLs on an absolute energy scale which is a critical set of parameters for the future integration of this material into optoelectronic devices. We determine the work function (WF) to be 4.47 eV while the material is behaving as an n-type semiconductor. [ABSTRACT FROM AUTHOR]