Search

The advent of halide perovskites in recent years has opened an avenue for redeveloping perovskite materials as semiconductors. In the quest for semiconducting perovskites, chalcogenides, which exhibit higher stability than their halide siblings and often direct band gaps for optoelectronics, have attracted more and more attention. So far, functional chalcogenide perovskites have been exclusively sulfides. Here, employing first-principles calculations and the criterion of phase stability in addition to the commonly used thermodynamic and dynamical criteria, we precisely predict the existence of LaScSe3as a thermodynamically stable selenide perovskite, which is validated by our experimental synthesis. Combining hybrid functional and many-body quasi-particle (G0W0and Bethe–Salpeter equation) calculations, we predict that LaScSe3is a direct-gap semiconductor having the band gap in the green-to-blue region and capable of p- and n-type bipolar doping, potentially for optoelectronic applications.

• Three typical layers of oxidation products tend to form on the surface, namely, the dense oxide layer (DOL) composed of (Zr,Hf)O 2 and CoSb, the alternate oxide layer (AOL) composed of repeated (Zr,Hf)O 2 and CoSb 2 O 6 /Co 3 O 4 , and the CoSb layer between the DOL and AOL. • The mass gain during oxidation is mainly caused by the rapid growth of the AOL, which is controlled by the outward diffusion of Zr/Hf and inward diffusion of oxygen. • The formation of continuous CoSb layer and DOL can block the outward diffusion of Zr and Hf. • A simple approach is proposed to improve the oxidation resistance by pre-oxidizing the sample in low oxygen pressure to form the dense (Zr,Hf)O 2 and CoSb layers as oxidation protecting and/or diffusion blocking layers. ZrCoSb-based half-Heusler (HH) compounds are among the most promising thermoelectric (TE) materials for high-temperature power generation. Oxidation resistance is one of the key issues for realizing the practical application of TE materials for long-term service in the ambient working environment. In this work, the oxidation behavior of Zr 0.5 Hf 0.5 CoSb 0.8 Sn 0.2 (ZHCSS) half-Heusler is systematically studied in the service temperature range from 873 to 1073 K. It is revealed that three typical layers of oxidation products tend to form on the surface of HH sample, namely, the dense oxide layer (DOL) composed of (Zr,Hf)O 2 and CoSb, the alternate oxide layer (AOL) composed of repeated (Zr,Hf)O 2 and CoSb 2 O 6 /Co 3 O 4 , and the CoSb layer between the DOL and AOL. The mass gain during oxidation is mainly caused by the rapid growth of AOL, which is controlled by the outward diffusion of Zr/Hf and the inward diffusion of oxygen. The formation of a continuous CoSb layer and DOL is found beneficial to block the outward diffusion of Zr/Hf. Based on the analysis of the dominant factors on the outward and inward diffusions as well as the reaction activation energy, a simple approach is proposed to improve the oxidation resistance of Zr 0.5 Hf 0.5 CoSb 0.8 Sn 0.2 by pre-oxidizing the sample in low oxygen pressure to form the dense (Zr,Hf)O 2 and CoSb layers as oxidation protecting and/or diffusion blocking layers. The oxidation test shows the effectiveness of such pre-oxidation on the formation and growth of the AOL and therefore on improving the service stability of Zr 0.5 Hf 0.5 CoSb 0.8 Sn 0.2 at high temperatures in the air. [ABSTRACT FROM AUTHOR]

Single-crystal lutetium yttrium oxyorthosilicate doped by cerium (LYSO:Ce) has been widely adopted as a scintillator material for radiation detection. The demands from nuclear medical imaging, as well as high-energy physics, are calling for ever-increasing scintillation properties. Here, Al3+codoping of LYSO:Ce is realized for the first time, and a series of LYSO:Ce,xAl (x= 0, 0.3, 0.6, and 1.0 atom %) crystals are successfully grown by a micro-pulling down (μ-PD) method. It is found that at x= 0.6 atom %, the overall scintillation properties are simultaneously improved. In particular, the slow component of rise time and the afterglow level are drastically reduced by 350% (from 304 to 86 ps) and an order of magnitude (from 0.2 to 0.02%), respectively. The energy resolution is also enhanced from 16.1 to 10.9%. These results are attributed to the fact that Al3+codoping significantly reduces the concentration of traps, accelerates the excited state lifetime of Ce3+ions and introduces a faster scintillating luminescence center, Ce4+ions. Our LYSO:Ce,0.6 atom % Al crystal offers a gain in the image signal-to-noise ratio of 1.4 over the non-codoped crystal, which will significantly benefit the next-generation time-of-flight positron emission tomography and enable more precise diagnosis of diseases.

Pyroelectricity describes the generation of electricity by temporal temperature change in polar materials1–3. When free-standing pyroelectric materials approach the 2D crystalline limit, how pyroelectricity behaves remained largely unknown. Here, using three model pyroelectric materials whose bonding characters along the out-of-plane direction vary from van der Waals (In2Se3), quasi-van der Waals (CsBiNb2O7) to ionic/covalent (ZnO), we experimentally show the dimensionality effect on pyroelectricity and the relation between lattice dynamics and pyroelectricity. We find that, for all three materials, when the thickness of free-standing sheets becomes small, their pyroelectric coefficients increase rapidly. We show that the material with chemical bonds along the out-of-plane direction exhibits the greatest dimensionality effect. Experimental observations evidence the possible influence of changed phonon dynamics in crystals with reduced thickness on their pyroelectricity. Our findings should stimulate fundamental study on pyroelectricity in ultra-thin materials and inspire technological development for potential pyroelectric applications in thermal imaging and energy harvesting.

Low-dimensional organic–metal halides are regarded as an emerging class of X-ray scintillation materials, but most of the discovered compounds are confronted with challenges of toxicity and instability. To address these challenges, we herein report two lead-free zero-dimensional (0D) hybrid halides, (Bmpip)2Cu2Br4and PPh4CuBr2single crystals, grown by the low-cost solution-processing method. By single-crystal X-ray diffraction refinement, the crystal structures of (Bmpip)2Cu2Br4and PPh4CuBr2were determined to be orthorhombic and monoclinic crystal systems, respectively. (Bmpip)2Cu2Br4and PPh4CuBr2show broadband orange and yellow emissions peaking at 620 and 538 nm, respectively. Different from the emission nature of the recent reported Cu-based halide hybrids, both (Bmpip)2Cu2Br4and PPh4CuBr2emit from excitons bound to defects featuring spin-allowed transition, enabling them to possess fast scintillation decay time of tens of nanoseconds, respectively. In particular, the (Bmpip)2Cu2Br4single crystal has a high photoluminescence quantum yield of 48.2%, a high scintillation yield of 16,000 photons/MeV, and a low detection limit of 710 nGyair/s. Due to the combination of nontoxicity, long-term stability, and decent detection performance, (Bmpip)2Cu2Br4could be regarded as a promising X-ray scintillator.

Spintronic devices, by harnessing the spin degree of freedom, are expected to outperform charge-based devices in terms of energy efficiency and speed of operation. The use of an electric field to control spin at room temperature has been pursued for decades. A major hurdle that has contributed to the slow progress in this regard is the dilemma between effective control and strong spin relaxation. For example, in a Rashba/Dresselhaus material with strong spin–orbit coupling, although the internal magnetic field could be substantial enough to effectively control spin precession, often, the spin-relaxation time becomes extremely short as a consequence of Dyakonov–Perel scattering. To address this, a persistent spin helix has been proposed in systems with SU(2) symmetry. Here we show the discovery of the persistent spin helix in an organic–inorganic hybrid ferroelectric halide perovskite whose layered nature makes it intrinsically like a quantum well. We demonstrate that the spin-polarized band structure is switchable at room temperature via an intrinsic ferroelectric field. We reveal valley–spin coupling through a circular photogalvanic effect in single-crystalline bulk crystals. The favoured short spin helix wavelength (three orders of magnitude shorter than in III–V materials), room-temperature operation and non-volatility make the hybrid perovskite an ideal platform for understanding symmetry-tuned spin dynamics, towards designing practical spintronic materials and devices that can resolve the control-relaxation dilemma.

Chalcogenide perovskites (CPs) exhibiting lower band gaps than oxide perovskites and higher stability than halide perovskites are promising materials for photovoltaic and optoelectronic applications. For such applications, the absence of deep defect levels serving as recombination centers (dubbed defect tolerance) is a highly desirable property. Here, using density functional theory (DFT) calculations, we study the intrinsic defects in BaZrS3, a representative CP material. We compare Hubbard-Uand hybrid functional methods, both of which have been widely used in addressing the band gap problem of semi-local functionals in DFT. We find that tuning the Uvalue to obtain experimental bulk band gap and then using the obtained Uvalue for defect calculations may result in over-localization of defect states. In the hybrid functional calculation, the band gap of BaZrS3can be accurately obtained. We observe the formation of small S-atom clusters in both methods, which tend to self-passivate the defects from forming mid-gap levels. Even though in the hybrid functional calculations several relatively deep defects are observed, all of them exhibit too high formation energy to play a significant role if the materials are prepared under thermal equilibrium. BaZrS3is thus expected to exhibit sufficient defect tolerance promising for photovoltaic and optoelectronic applications.

Ceria (CeO2) on Pt(111) has been widely studied in model catalysis due to the strong interfacial interaction between CeO2and platinum (Pt). Although extensive studies have been conducted on monolayered CeO2islands on the Pt(111) surface, the atomic and electronic structures of the island edge are still elusive. Herein, density functional theory calculations are employed to simulate the CeO2(111) surface, the CeO2monolayer on Pt(111), and their edges. It is found that unlike the outmost O–Ce–O layer of CeO2(111), the CeO2layer on Pt(111) is negatively charged and has non-zero magnetic moments. For the CeO2(111) surface, the stoichiometric-type edge is the most stable, and the atomic orders of two edges from outside in are Os2––Ce4+–Oi2–and Oi2––Ce4+–Os2–. For the CeO2/Pt(111) surface, however, only at high temperature and under ultra-high vacuum conditions, the most stable edge is the same as that of CeO2(111). Otherwise, an oxygen-rich edge will be formed, where the atomic orders of two edges from outside in are Oi2––Os2––Ce4+and Oi2––Ce4+–Os2–. Furthermore, the adsorption energy of the K ion on the Oi2––Os2––Ce4+-type edge is lower than that on the Oi2––Ce4+–Os2–-type edge, indicating a stronger adsorbability of the Oi2––Os2––Ce4+-type edge toward positively-charged ions. The edge structures proposed here and the corresponding electronic properties provide an insight into the interaction between CeO2and the Pt surface, which helps to understand the catalytic mechanism on the CeO2/Pt(111) surface.

Organic–inorganic hybrids may offer material properties not available from their inorganic components. However, they are typically less stable and disordered. Long-term stability study of the hybrid materials, over the anticipated lifespan of a real-world electronic device, is practically nonexistent. Disordering, prevalent in most nanostructure assemblies, is a prominent adversary to quantum coherence. A family of perfectly ordered II–VI-based hybrid nanostructures has been shown to possess many unusual properties and potential applications. Here, using a prototype structure β-ZnTe(en)0.5—a hybrid superlattice—and applying an array of optical, structural, surface, thermal, and electrical characterization techniques, in conjunction with density-functional theory calculations, we have performed a comprehensive and correlative study of the crystalline quality, structural degradation, electronic, optical, and transport properties on samples from over 15 years old to the recently synthesized. The findings show that not only do they exhibit an exceptionally high level of crystallinity in both macroscopic and microscopic scale, comparable to high-quality binary semiconductors; and greatly enhanced material properties, compared to those of the inorganic constituents; but also, some of them over 15 years old remain as good in structure and property as freshly made ones. This study reveals (1) what level of structural perfectness is achievable in a complex organic–inorganic hybrid structure or a man-made superlattice, suggesting a nontraditional strategy to make periodically stacked heterostructures with abrupt interfaces; and (2) how the stability of a hybrid material is affected differently by its intrinsic attributes, primarily formation energy, and extrinsic factors, such as surface and defects. By correlating the rarely found long-term stability with the calculated relatively large formation energy of β-ZnTe(en)0.5and contrasting with the case of hybrid perovskite, this work illustrates that formation energy can serve as an effective screening parameter for the long-term stability potential of hybrid materials. The results of the prototype II–VI hybrid structures will, on one hand, inspire directions for future exploration of the hybrid materials, and, on the other hand, provide metrics for assessing the structural perfectness and long-term stability of the hybrid materials.

ZnO-based catalysts have been widely used in industrial reactions involving syngas conversions. Hydrogen dynamics on the surface of the catalyst is an essential process for understanding the mechanisms of such reactions. As a polar material, however, the role of ZnO surface polarity on hydrogen dynamics has not been studied under operando conditions. Here, we investigate the behavior of polar (0001) and (0001̅) surfaces of single-crystal ZnO under different H2pressures using near-ambient-pressure X-ray photoelectron spectroscopy. We found that the (0001̅) surface shows a monotonic and irreversible band bending with increasing H2pressure. In contrast, the (0001) surface shows two opposite responses depending on H2pressure, which are reversible in pressure cycles. This polarity- and pressure-dependent hydrogen dynamics is clearly understood with the assistance from first-principles calculations. In particular, the amphoteric behavior of atomic H is identified to play a key role.

In this work, we demonstrate an ultrasensitive, visible-blind ultraviolet (UV) photodetector based on perovskite–polymer hybrid structure. A novel wide-band-gap vacancy-ordered lead-free inorganic perovskite Cs2SnCl6with Nd3+doping is employed in the active layer of this hybrid photodetector. Remarkably, with interfacial charge-controlled hole-injection operating mechanism, our device achieves a maximum detectivity of 6.3 × 1015Jones at 372 nm, fast photoresponse speed with rise time and fall time in the order of milliseconds, and a large linear dynamic range of 118 dB. The performance is significantly better than most of the existing organic and inorganic semiconductor UV photodetectors reported so far, and its detectivity is close to 1 order of magnitude higher than that of the photomultiplication tube (PMT) in the UV region. In addition, the photodetector demonstrated excellent environmental stability, which is critical for commercial deployment of perovskite-based optoelectronic devices. The results presented in this work open a new route toward development of high-performance optoelectronic devices using perovskite-based hybrid nanomaterial systems.

With the influx of flexible electronics as well as the emergence or prediction of unique phenomena in two-dimensional forms of materials, epitaxy at weakly coupled interfaces is gaining momentum as a feasible technique to develop nanostructured and two-dimensional materials. The weak substrate–film chemical interaction expected in this method of epitaxy has been believed to be crucial in enabling not only the formation of sharp heterostructures but also the mechanical exfoliation of the epilayer. In this report, we unravel an unconventional understanding of epitaxy at weakly coupled interfaces, entailing ions of the van der Waals substrate being scavenged by the growing film, resulting in the formation of a distinct and uniform unit-cell-thick interfacial layer. Using a layered Dion–Jacobson perovskite as the substrate and VO2as the growing epilayer, we show that VO2scavenges ions from the substrate and forms an epitaxial vanadate compound. Additionally, the crystal anisotropy of the substrate significantly modifies the energy landscape for diffusion of ions and leads to the creation of a unit-cell-thick epitaxial Aurivillius phase at the interface, predicted to exhibit the ferroelectric Rashba–Dresselhaus effect. The scavenging effect, interfaced with an anisotropic low-dimensional substrate, opens a new window to develop two-dimensional flexible components for future electronics.

β-FeSi2has long been investigated as a promising thermoelectric (TE) material working at high temperatures due to its combining features of environmental friendliness, good thermal stability, and strong oxidation resistance. However, the real application of β-FeSi2is still limited by its low TE figure of merit (zT). In this study, nearly doubled zTin p-type β-FeSi2has been achieved via synergistically optimizing electrical and thermal transports. Based on the first-principles calculations, Al with shallow acceptor transition level and high carrier donation efficiency is chosen to dope β-FeSi2. Significantly improved electrical transport, particularly in the low temperature range, has been obtained in the Al-doped β-FeSi2system. The power factor for FeSi1.96Al0.04at 300 K is even higher than that of p-type β-FeSi2-based compounds reported previously at high temperatures. By alloying β-FeSi2with Os at the Fe sites, we further lower the lattice thermal conductivity. Fe0.80Os0.20Si1.96Al0.04possesses the lowest lattice thermal conductivity among the β-FeSi2compounds prepared by the equilibrium method. Finally, a record-high zTvalue of 0.35 is obtained for p-type Fe0.80Os0.20Si1.96Al0.04. This study is expected to accelerate the application of β-FeSi2.

Octahedron rotation (OR) is a unique structural feature in most perovskite materials. During dimensional reduction from bulk to two-dimensional (2D) perovskites, how the OR pattern evolves is still an open question. Here, we employ an adapted Glazer's notation from bulk perovskites to systematically study the structural evolution of 2D perovskites by fully considering the possible OR patterns. Applying this approach to the 2D Ba–Zr–S system, we establish the relationship between the OR pattern and slab thickness. It is found that as the thickness decreases, the OR pattern undergoes a transition by suppressing out-of-plane rotations. The OR in 2D chalcogenide perovskites could result in an anti-confinement effect, i.e., reducing the band gap to even below that of the bulk by countering the quantum confinement effect. In addition, we show that the Ba–Zr–S 2D perovskites exhibit reasonable electron mobility of ∼150 cm2V−1s−1and large exciton binding energy of ∼0.9 eV. Combining the slab thickness and strain as effective knobs for widely tuning the electronic structure, we suggest the 2D chalcogenide perovskites as promising optoelectronic materials.

Controlling superconducting phase transition on a two-dimensional (2D) material is of great fundamental and technological interest from the viewpoint of making 2D resistance-free electronic circuits. Here, we demonstrate that a 1T-to-2Hphase transition can be induced on the topmost monolayer of bulk (<100 nm thick) 1T-TaS2by thermal annealing. The monolayer 2H-TaS2on bulk 1T-TaS2exhibits a superconducting transition temperature (Tc) of 2.1 K, which is significantly enhanced compared to that of bulk 2H-TaS2. Scanning tunneling microscopy measurements reveal a 3 × 3 charge density wave (CDW) in the phase-switched monolayer at 4.5 K. The enhanced Tcis explained by the suppressed 3 × 3 CDW and a charge-transfer doping from the 1Tsubstrate. We further show that the monolayer 2H-TaS2could be switched back to 1Tphase by applying a voltage pulse. The observed surface-limited superconducting phase transition offers a convenient way to prepare robust 2D superconductivity on bulk 1T-TaS2crystal, thereby bypassing the need to exfoliate monolayer samples.

Advances in perovskite solar cells require development of means to control and eliminate the nonradiative charge recombination pathway. Using ab initiononadiabatic molecular dynamics, we demonstrate that charge recombination in perovskites is extremely sensitive to the charge state of the halogen vacancy. A missing iodine anion in MAPbI3has almost no effect on charge losses. However, when the vacancy is reduced, the recombination is accelerated by up to 2 orders of magnitude. The acceleration occurs due to formation of a deep hole trap in the singly reduced vacancy, and both deep and shallow hole traps for the doubly reduced vacancy. The shallow hole involves a significant rearrangement of the Pb–I lattice, leading to a new chemical species: a Pb–Pb dimer bound by the vacancy charge, and under-coordinated iodine bonds. Hole trapping by the singly reduced iodide vacancy operates parallel to recombination of free electron and hole, accelerating charge losses by a factor of 5. The doubly reduced vacancy acts by a sequential mechanism-free hole, to shallow trap, to deep trap, to free electron, and accelerates the recombination by a factor of 50. The study demonstrates that iodine anion vacancy can be beneficial to the performance, because it causes minor changes to the charge carrier lifetime, while increasing charge carrier concentration. However, the neutral iodine and iodine cation vacancies should be strongly avoided. The detailed insights into the charge carrier trapping and relaxation mechanisms provided by the simulation are essential for development of efficient photocatalytic, photovoltaic, optoelectronic and related devices.

Abstract

Electronic applications require the ability to dope a material with a controllable amount of impurities. However, current understanding of the doping mechanism in colloidal–synthesized quantum dots (QDs) is still limited. This is in contrast with bulk semiconductors for which first-principles-based theories have been well established. Using prototype CdSe as an example, here we propose an atomistic theory for the doping of colloidal-synthesized QDs. The key in our theory is the evaluation of atomic chemical potential inside the solution, whose range can deviate considerably from the bulk value due to the presence of solvent. This theory, coupled to first-principles calculations and ab initio molecular dynamics, is able to explain the difference of doping limit in Mn (or Co)-doped CdSe QDs and their bulk counterparts. It also explains the doping behavior of a number of other 3d transition-metal impurities in CdSe QDs in contrast with the solid case.

We report the synthesis and characterization of a novel class of ionic semiconductor materials – inorganic chalcogenide perovskites. Several different compounds including BaZrS3, CaZrS3, SrTiS3and SrZrS3were synthesized by high temperature sulfurization of their oxide counterparts. Their crystal structures were identified by XRD and composition by EDX. UV–vis and photoluminescence measurements confirmed that they are direct gap semiconductors with band gap values consistent with theoretical predictions. By adopting an anion alloying approach, we demonstrate widely tunable band gap from 1.73eV to 2.87eV. These strongly ionic semiconductors provide a new avenue for engineering the semiconducting properties for applications such as energy harvesting, solid state lighting and sensing.

Organometallic nanomaterials hold the promise for molecular hydrogen (H2) storage by providing nearly ideal binding strength to H2for room-temperature applications. Synthesizing such materials, however, faces severe setbacks due to the problem of metal clustering. Inspired by a recent experimental breakthrough (J. Am. Chem. Soc.2008, 130, 6992), which demonstrates enhanced H2binding in Ti-grafted mesoporous silica, we propose combining the graphene oxide (GO) technique with Ti anchoring to overcome the current synthesis bottleneck for practical storage materials. Similar to silica, GO contains ample hydroxyl groups, which are the active sites for anchoring Ti atoms. GO can be routinely synthesized and is much lighter than silica. Hence, higher gravimetric storage capacity can be readily achieved. Our first-principles computations suggest that GO is primarily made of low-energy oxygen-containing structural motifs on the graphene sheet. The Ti atoms bind strongly to the oxygen sites with binding energies as high as 450 kJ/mol. This is comparable to that of silica and is indeed enough to prevent the Ti atoms from clustering. Each Ti can bind multiple H2with the desired binding energies (14−41 kJ/mol-H2). The estimated theoretical gravimetric and volumetric densities are 4.9 wt % and 64 g/L, respectively.

The kagome lattice has attracted intense interest with the promise of realizing topological phases built from strongly interacting electrons. However, fabricating two-dimensional (2D) kagome materials with nontrivial topology is still a key challenge. Here, we report the growth of single-layer iron germanide kagome nanoflakes by molecular beam epitaxy. Using scanning tunneling microscopy/spectroscopy, we unravel the real-space electronic localization of the kagome flat bands. First-principles calculations demonstrate the topological band inversion, suggesting the topological nature of the experimentally observed edge mode. Apart from the intrinsic topological states that potentially host chiral edge modes, the realization of kagome materials in the 2D limit also holds promise for future studies of geometric frustration.

Owing to its superior visible light absorption and high chemical stability, chalcogenide perovskite barium zirconium sulfide (BaZrS3) has attracted significant attention in the past few years as a potential alternative to hybrid halide perovskites for optoelectronics. However, the high processing temperatures of BaZrS3thin films at above 1000 ℃ severely limits their potential for device applications. Herein, we report the synthesis of BaZrS3thin films at temperatures as low as 500 ℃, by changing the chemical reaction pathway. The single phase BaZrS3thin film was confirmed by X-ray diffraction and Raman spectroscopy. Atomic force microscopy and scanning electron microscopy show that crystalline size and surface roughness were consistently reduced with decreasing annealing temperature. The lower temperatures further eliminate sulfur vacancies and carbon contaminations associated with high temperature processing. The ability to synthesize chalcogenide perovskite thin films at lower temperatures removes a major hurdle for their device fabrication. The photodetectors demonstrate fast response and an on/off ratio of 80. The fabricated field effect transistors show an ambipolar behavior with electron and hole mobilities of 16.8 cm2/Vs and 2.6 cm2/Vs, respectively.

Hard carbons (HCs) as an anode material in sodium ion batteries present enhanced electrochemical performances in ether-based electrolytes, giving them potential for use in practical applications. However, the underlying mechanism behind the excellent performances is still in question. Here, ex situ nuclear magnetic resonance, gas chromatography–mass spectrometry, and high-resolution transmission electron microscopy were used to clarify the insightful chemistry of ether- and ester-based electrolytes in terms of the solid–electrolyte interphase (SEI) on hard carbons. The results confirm the marked electrolyte decomposition and the formation of a SEI film in EC/DEC but no SEI film in the case of diglyme. In situ electrochemical quartz crystal microbalance and molecular dynamics support that ether molecules have likely been co-intercalated into hard carbons. To our knowledge, these results are reported for the first time. It might be very useful for the rational design of advanced electrode materials based on HCs in the future.

The electronic properties of halogens on the surface of metals have attracted substantial attention due to their promotion effects on surface molecular dehydrogenation reactions. Herein, the electronic properties of the submonolayer Br on Cu(111) were studied by combining scanning tunneling microscopy and density functional theory (DFT) calculations. The local work function of Br islands is found to range from 5.1 to 5.8 eV, which is higher than that of the Cu substrate (∼4.3 eV). Intriguingly, the Br atoms at the edge of islands possess a lower work function than the internal atoms, which originates from a larger local dipole induced by the stronger interfacial charge transfer between internal Br atoms and Cu, as supported by the DFT calculations. This phenomenon is in sharp contrast to the common intuition that the edge atoms tend to receive more charges from the substrate due to the contact with more neutral substrate atoms. Such a counterintuitive observation can be attributed to the stabilization of charged internal Br by neighboring atoms. These findings provide a deep insight of the interactions between halogen adsorbates and the metal surface, which leads to a comprehensive understanding of the microscopic mechanism of halogen-promoted reactions.

BaZrS3is a prototypical chalcogenide perovskite, an emerging class of unconventional semiconductor. Recent results on powder samples reveal that it is a material with a direct band gap of 1.7–1.8 eV, a very strong light-matter interaction, and a high chemical stability. Due to the lack of quality thin films, however, many fundamental properties of chalcogenide perovskites remain unknown, hindering their applications in optoelectronics. Here we report the fabrication of BaZrS3thin films, by sulfurization of oxide films deposited by pulsed laser deposition. We show that these films are n-type with carrier densities in the range of 1019-1020 cm−3. Depending on the processing temperature, the Hall mobility ranges from 2.1 to 13.7 cm2/Vs. The absorption coefficient is > 105 cm−1 at photon energy >1.97 eV. Temperature dependent conductivity measurements suggest shallow donor levels. By assuring that BaZrS3is a promising candidate, these results potentially unleash the family of chalcogenide perovskites for optoelectronics such as photodetectors, photovoltaics, and light emitting diodes.

We present a comparison based on first-principles calculations of the electronic structure of nonalkylated and alkylated dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene: DNTT and DNTT-C10. The calculations show that the addition of alkyl chains decreases intermolecular distances, in agreement with experiments. Calculations indicate that effective masses are reduced by the addition of alkyl chains, and within a simple deformation potential model, this translates into higher mobility for DNTT-C10. The shorter intermolecular distances found in DNTT-C10are attributed to van der Waals interactions between alkyl chains.