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For the design and optimization of near-infrared photothermal nanohybrids, tailoring the energy gap of nanohybrids plays a crucial role in attaining a satisfactory photothermal therapeutic efficacy for cancer and remains a challenge. Herein, we report an electron donor-acceptor effect-induced organic/inorganic nanohybrid with a low energy gap (denoted as ICG/Ag/LDH) by the in situ deposition of Ag nanoparticles onto the CoAl-LDH surface, followed by the coupling of ICG. A combination study verifies that the supported Ag nanoparticles as the electron donor (D) push electrons into the conjugated system of ICG by the electronic interaction between ICG and Ag, while OH groups of LDHs as the electron acceptor (A) pull electrons from the conjugated system of ICG by hydrogen bonding (N···H-O). This induces the formation of the D-A conjugated π-system and has a strong influence on the π-conjugated system of ICG, thus leading to a prominent decrease toward the energy gap and correspondingly an ultra-long redshift (∼115 nm). The resulting ICG/Ag/LDHs show an enhanced photothermal conversion efficiency (∼45.5%) at 808 nm laser exposure, which is ∼1.6 times larger than that of ICG (∼28.4%). Such a high photothermal performance is attributed to the fact that ICG/Ag/LDHs possess a D-π-A hybrid structure and a resulting lower energy gap, thus effectively promoting nonradiative transitions and leading to enhancement of the photothermal effect. Both in vitro and in vivo results confirm the good biocompatible properties and capability of the ICG/Ag/LDHs for NIR-triggered cancer treatment. This research demonstrates a successful paradigm for the rational design and preparation of new nanohybrids through the modulation of electron donor-acceptor effect, which offers a new avenue to achieve efficient phototherapeutic agent for improving the cancer therapeutic outcomes.

In this work, we have prepared antimonene oxide quantum dots and their hybrid ormosil gel glasses by using liquid-phase antimony exfoliation and sol–gel methods, respectively. Due to their having hydroxyl groups and due to the small size of the nanodots, the antimonene oxide quantum dots showed good compatibility and high dispersibility in liquid and solid media. These gel glasses showed high transparency and uniformity, and concentrations of dopant quantum dots as high as 2.00 wt% were achieved. These quantum dots and their hybrid gel glasses exhibited outstanding optical limiting performance in the visible, mid-wave, and near-infrared regions (532–1570 nm). The mechanism of optical limiting includes nonlinear absorption, nonlinear refraction, and nonlinear scattering, and these results might find numerous promising applications in many fields such as laser protection and laser shaping.

Photoacoustics is a promising technique for in-depth imaging of biological tissues. However, the lateral resolution of photoacoustic imaging is limited by size of the optical excitation spot, and therefore by light diffraction and scattering. Several super-resolution approaches, among which methods based on localization of labels and particles, have been suggested, presenting promising but limited solutions. This work demonstrates a novel concept for extended-resolution imaging based on separation and localization of multiple sub-pixel absorbers, each characterized by a distinct acoustic response. Sparse autoencoder algorithm is used to blindly decompose the acoustic signal into its various sources and resolve sub-pixel features. This method can be used independently or as a combination with other super-resolution techniques to gain further resolution enhancement and may also be extended to other imaging schemes. In this paper, the general idea is presented in details and experimentally demonstrated.

1T phase of transition metal dichalcogenides (TMDCs) formed by group 10 transition metals (e.g. Pt, Pd) have attracted increasing interests due to their novel properties and potential device applications. Synthesis of large scale thin films with controlled phase is critical especially considering that these materials have relatively strong interlayer interaction and are difficult to exfoliate. Here we report the growth of centimeter-scale PtTe, 1T-PtTe2 and 1T-PtSe2 films via direct deposition of Pt metals followed by tellurization or selenization. We find that by controlling the Te flux, a hitherto-unexplored PtTe phase can also be obtained, which can be further tuned into PtTe2 by high temperature annealing under Te flux. These films with different thickness can be grown on a wide range of substrates, including NaCl which can be further dissolved to obtain free-standing PtTe2 or PtSe2 films. Moreover, a systematic thickness dependent resistivity and Hall conductivity measurements show that distinguished from the semiconducting PtSe2 with hole carriers, PtTe2 and PtTe films are metallic. Our work opens new opportunities for investigating the physical properties and potential applications of group 10 TMDC films and the new monochalcogenide PtTe film.

Quantum limit is quite easy to achieve once the band crossing exists exactly at the Fermi level ($E_F$) in topological semimetals. In multilayered Dirac fermion system, the density of Dirac fermions on the zeroth Landau levels (LLs) increases in proportion to the magnetic field, resulting in intriguing angle- and field-dependent interlayer tunneling conductivity near the quantum limit. BaGa$_2$ is an example of multilayered Dirac semimetal with anisotropic Dirac cone close to $E_F$, providing a good platform to study its interlayer transport properties. In this paper, we report the negative interlayer magnetoresistance (NIMR, I//c and B//c) induced by the tunneling of Dirac fermions on the zeroth LLs of neighbouring Ga layers in BaGa$_2$. When the field deviates from the c-axis, the interlayer resistivity $\rho_{zz}(\theta)$ increases and finally results in a peak with the field perpendicular to the c-axis. These unusual interlayer transport properties (NIMR and resistivity peak with B$\perp$c) are observed together for the first time in Dirac semimetal under ambient pressure and are well explained by the model of tunneling between Dirac fermions in the quantum limit., Comment: 12 pages, 8 figures, with supplementary materials

For effective treatment of ischemic cerebral thrombosis, it is of great significance to find a facile way in assessing the early damage of blood-brain barrier (BBB) after ischemic stroke during thrombolysis by integrating thrombolytic agents with fluorescent materials. Herein, a novel type of protein-carbon dot nanohybrids is reported by the incorporation of carbon dots on thrombolytic agents through covalent linkage. Both in vitro and ex vivo fluorescence imaging measurements have demonstrated remarkable imaging effects in the brain of transient middle cerebral artery occlusion mice. Besides, the outstanding thrombolytic capacity of the nanohybrids was determined by in vitro thrombolysis tests. As one of the few reports of the construction of thrombolytic agents and fluorescent nanomaterials, the nanohybrids retain thrombolysis ability and fluorescent traceability simultaneously. It may provide a promising indicator for early BBB damage and thrombolytic agent distribution to estimate the possibility of symptomatic intracranial hemorrhage after thrombolysis and supply tissue window evidence for clinical thrombolytic agent application.

Organic nonlinear optical (NLO) materials have attracted immense scientific interest in various fields. Broadband NLO response extending to near-infrared (NIR) region is extremely important and remains challenging. Herein, two diketopyrrolopyrrole (DPP)-based donor-acceptor (D-A)-type π-conjugated copolymers with and without Pt(II) incorporation are rationally designed and synthesized toward broadband NLO response materials. The broad intramolecular charge transfer (ICT) absorption reaching 1000 nm due to the strong D-A interaction is well demonstrated by photophysical characterizations. The NLO properties of copolymers are studied using Z-scan technology. Owing to their extended π-conjugated D-A systems and near-infrared ICT absorption properties, both copolymers exhibit laser-induced NLO response to nanosecond as well as picosecond laser pulses upon the wavelengths of 532 and 1064 nm. Interestingly, introducing Pt(II) into the copolymer backbone can evidently improve the NLO property or unexpectedly switch the NLO response from saturable absorption to reverse saturable absorption. Meanwhile, both copolymers are successfully employed as optical limiting materials and exhibit broadband optical limiting abilities. Therefore, we present an efficient strategy toward broadband NLO materials, which may significantly facilitate the understanding of organic molecular structure-property relationship and promote their practical application.

In recent years, single-atom catalysts (SACs) have attracted enormous attention due their effectiveness in promoting a variety of catalytic reactions. However, the ability of SACs to enhance cancer phototherapies has received little attention to date. Herein, we synthesized a metal organic framework (MOF) rich in porphyrin-like single atom Fe(III) centers (denoted herein as porphyrin-MOF or P-MOF) and then evaluated the performance of the P-MOF for cancer treatment by photodynamic therapy (PDT) and photothermal therapy (PTT) under NIR (808 nm) irradiation, as well as photoacoustic imaging (PAI) of tumors. On acccount of the abundance of single atom Fe(III) centers, the P-MOF material demonstrated excellent performance for modulation of the hypoxic tumor microenvironment of Hela cell tumors in mice, while also demonstrating good properties as a photoacoustic imaging (PAI) agent. Density functional theory (DFT) calculations were used to elucidate the superior performance of P-MOF in these applications relative to Fe2O3 (a Fe(III) reference compound). The calculations revealed that the narrow band gap energy of P-MOF (1.31 eV) enabled strong absorption of NIR photons, thereby inducing nonradiative transitions that converted incident light into heat to promote PTT. Further, a facile change of the spin state of the single atom Fe(III) centers in P-MOF under NIR irradiation transformed coordinated triplet oxygen (3O2) to singlet oxygen (1O2), benefiting PDT. This work demonstrates the great future potential of both SACs and MOFs as multifunctional agents for cancer treatment and tumor imaging.

Recently, tremendous attention has been evoked in the discovery of defect-engineered nanomaterials for near-infrared second window (NIR-II)-driven cancer therapy. Herein, we have constructed a novel type of carbon defects enriched in boron carbide nanomaterial (denoted as B4C@C) through reacting B4C and glucose by a hydrothermal method. The carbon defect concentration in B4C@C has been significantly increased after coating with glucose; thus, B4C@C exhibited a distinct photothermal response under the NIR-II window and the efficiency of photothermal conversion is determined to reach 45.4%, which is higher than the carbon-based nanomaterials in the NIR-II region. Both Raman spectra and X-ray photoelectron spectroscopy (XPS) spectra reveal that B4C@C has rich sp2-hybridized carbon defects and effectively increases the NIR-II window light absorption capacity, thus enhancing the nonradiative recombination rate and improving the NIR-II photothermal effect. Furthermore, the B4C@C nanosheets allows for tumor phototherapy and simultaneous photoacoustic imaging. This work indicates the huge potential of B4C@C as a novel photothermal agent, which might arise much attention in exploring boron-based nanomaterials for the advantage of cancer therapy.

Currently, two-dimensional materials are being actively pursued in catalysis and other fields due their abundance of defects, which results in enhanced performance relative to their bulk defect-free counterparts. To date, the exploitation of defects in two-dimensional materials to enhance photothermal therapies has received little attention, motivating a detailed investigation. Herein, we successfully fabricated a series of novel CoFe-based photothermal agents (CoFe-x) by heating CoFe-layered double hydroxide (CoFe-LDH) nanosheets at different temperatures (x) between 200-800 °C under a Ar atmosphere. The CoFe-x products differed in their particle size, cobalt defect concentration, and electronic structure, with the CoFe-500 product containing the highest concentration of Co2+ defects and most efficient photothermal performance under near-infrared (NIR, 808 nm) irradiation. Experiments and density functional theory (DFT) calculations revealed that Co2+ defects modify the electronic structure of CoFe-x, narrowing the band gap and thus increasing the nonradiative recombination rate, thereby improving the NIR-driven photothermal properties. In vitro and in vivo results demonstrated that CoFe-500 was an efficient agent for photothermal cancer treatment and also near-infrared (NIR) thermal imaging, magnetic resonance (MR) imaging, and photoacoustic (PA) imaging. This work provides valuable new insights about the role of defects in the rational design of nanoagents with optimized structures for improved cancer therapy.

In medical applications, two-dimensional nanomaterials have been widely studied on account of their intriguing properties such as good biocompatibility, stability, and multifunctionality. Herein, an ultrathin MnO2 nanosheet has been fabricated by a simplistic hydrothermal process. The high photothermal conversion performance (62.4%) can be attributed to the vacancy in the ultrathin MnO2 nanosheet, as confirmed by the extended X-ray absorption fine structure results and the density functional theory calculation, benefiting photoacoustic imaging-guided cancer therapy. This highly efficient vacancy-induced photothermal therapy has been reported for the first time. As a result, this work demonstrates that this ultrathin MnO2 nanosheet has a potential to construct a nanosystem for imaging-guided cancer therapy.

Biaxial deformation of suspended membranes widely exists and is used in nanoindentation to probe elastic properties of structurally isotropic two-dimensional (2D) materials. However, the elastic properties and, in particular, the fracture behaviors of anisotropic 2D materials remain largely unclarified in the case of biaxial deformation. MoTe2 is a polymorphic 2D material with both isotropic (2H) and anisotropic (1T′ and Td) phases and, therefore, an ideal system of single-stoichiometric materials with which to study these critical issues. Here, we report the elastic properties and fracture behaviors of biaxially deformed, polymorphic MoTe2 by combining temperature-variant nanoindentation and first-principles calculations. It is found that due to similar atomic bonding, the effective moduli of the three phases deviate by less than 15%. However, the breaking strengths of distorted 1T′ and Td phases are only half the value of 2H phase due to their uneven distribution of bonding strengths. Fractures of both ...

Okara is a by-product of tofu manufacturing and is usually used as a feedstuff. Herein, we developed a methodology of using okara as a carbon source for the preparation of photothermal nano-materials. It's interesting to find that just after calcination, the carbonized okara forms sphere-shaped hollow particles (denoted as HCNS) with an average diameter of 200 nm. Owning to the existence of a cavity, the HCNS was found to exhibit not only a good photothermal conversion efficiency, but also an ideal photoacoustic imaging property, which makes it a promising agent for imaging-guided photothermal therapy (PTT). The high photothermal conversion efficiency can result from the high carbon content and its hollow morphology. The in vitro and in vivo results both demonstrated the biocompatibility and capacity of the plant source carbon spheres for NIR-triggered cancer treatment. Therefore, the current work suggests a new method to gain a safe and low-cost photothermal platform which could be further exploited in biomedical fields.

A series of silver nanoparticle (Ag NP) Ormosil glasses were fabricated with a sol–gel method. Ag NPs disperse uniformly in sol–gel matrices, proven by scanning electron microscopy and mapping analysis. The as-prepared glasses have high transmittance in the visible and near infrared region. Ag NP Ormosil glasses exhibit excellent optical limiting (OL) properties with a broad band (532–1064 nm), low OL FON (32 mJ cm−2@532 nm and 101 mJ cm−2@1064 nm) and high damage thresholds (over 10 J cm−2@532 nm and 30 J cm−2@1064 nm) through Z-scan and nonlinear transmission methods. Z-scan measurements show that the OL property comes from nonlinear absorption and nonlinear scattering. The good nonlinear optical performance has thus endowed the Ag NP Ormosil glasses with a potential application in OL devices.

In this work, we synthesized a hypoxia responsive upconversion nanosensor by the conjugation of oxygen insensitive upconversion carbon dots (CDs) with an oxygen sensitive ruthenium(ii) complex (Rud2b). The CD-Rud2b conjugate was then PEGylated to mediate the formation of nano-sized assemblies of the resultant polymer probe (CD-Ru-mPEG) in aqueous solution. The strategy allows the oxygen sensitive probe (Rud2b) to be excited by NIR irradiation and achieve upconverted emission through the Forster resonance energy transfer process from the CDs. The oxygen sensitivity of the ruthenium moiety was well-preserved in the polymeric aggregates because the PEG chains could prohibit the occurrence of self-quenching that may occur due to the close packing of the probes. Such an upconversion photoluminescence property makes the CD-Ru-mPEG nanosensor work as a biocompatible imaging system to monitor the oxygen level in cells and the hypoxic condition in vivo.

The rapid, complete, targeted and safe treatment for tumors remains a key issue in cancer therapy. A novel treatment of solid tumors by supramolecular photocatalyst Nano-SA-TCPP with the irradiation of 600–700 nm wavelength is established. Solid tumors (100 mm3) can be eliminated within 10 min. The 50-day mouse survival rate was increased from 0% to 100% after the photocatalytic therapy. The breakthrough was owing to the cell membrane rupture and the cytoplasmic loss caused by photogenerated holes inside cancer cells. The porphyrin-based photocatalysts can be internalized in a targeted manner by cancer cells due to the size selection effect, without entering the normal cells. The therapy has no toxicity or side effects for normal cells and organisms. Moreover, the photocatalytic therapy is effective for a variety of cancer cell lines. Because of its high efficiency, safety and universality, the photocatalytic therapy provides us with a new lancet to conquer the tumor., The solid tumor (about 100 mm3) can be eliminated rapidly via the novel photocatalytic therapy induced by photogenerated holes of the supramolecular porphyrin photocatalyst.

Black phosphorus is reported to be a bipolar pseudospin semiconductor, exhibiting a net pseudospin polarization with opposite polarization directions for the conduction and valence bands. These properties make it a promising candidate for application in pseudospintronics.

Transition-metal dichalcogenides exhibit strong quantum confinement effects, and their electronic structure is strongly dependent on the number of layers. Resolving the thickness-dependent electronic structure is important. While the electronic structure of atomically thin 2H-MoSe2 or 2H-MoS2 have been explored, information on the experimental electronic structure of 2H-MoTe2 is still missing. Here, by using nanospot angle-resolved photoemission spectroscopy (nanoARPES), we reveal the experimental electronic structure of exfoliated 2H-MoTe2 thin flakes with different thickness (three, five, and seven monolayers). Well-separated quantum-well states are clearly observed in thin 2H-MoTe2 flakes at deep valence bands at energies between −3 to −5 eV, while those at the top of the valence band between −1 and −2 eV are much more closely spaced compared with those from 2H-MoSe2 and 2H-MoS2. First-principles calculation shows that the main difference is attributed to the weaker hybridization and smaller energy dif...

A class of graphene oxide (GO) Ormosil glasses with excellent nonlinear optical properties were made with sol-gel method. The as-prepared GO Ormosil glasses were highly transparent in visible and near-infrared region, due to the uniform dispersion of modified GO in the matrix. These Ormosil glasses have a broadband optical limiting effect from 532 to 1570 nm, with lower optical limiting onset energy density (FON). The nonlinear absorption coefficients of the Ormosil glass could reach 210.62, 647.96, and 43.10 cm GW−1 at 532, 1064, and 1570 nm. The optical limiting properties of the Ormosil glasses come from nonlinear absorption proved by Z-scan measurements. Therefore, the Ormosil glasses have potential applications in nonlinear optical areas.

Advanced biocompatible and robust platforms equipped with diverse properties are highly required in biomedical imaging applications for the early detection of atherosclerotic vascular disease and cancers. Designing nanohybrids composed of noble metals and fluorescent materials is a new way to perform multimodal imaging to overcome the limitations of single-modality counterparts. Herein, we propose the novel design of a multimodal contrast agent; namely, an enhanced nanohybrid comprising gold nanorods (GNRs) and carbon dots (CDs) with silica (SiO2) as a bridge. The nanohybrid (GNR@SiO2@CD) construction is based on covalent bonding between SiO2 and the silane-functionalized CDs, which links the GNRs with the CDs to form typical core–shell units. The novel structure not only retains and even highly improves the optical properties of the GNRs and CDs, but also possesses superior imaging performance in both diffusion reflection (DR) and fluorescence lifetime imaging microscopy (FLIM) measurements compared with bare GNRs or fluorescence dyes and CDs. The superior bioimaging properties of the GNR@SiO2@CD nanohybrids were successfully exploited for in vitro DR and FLIM measurements of macrophages within tissue-like phantoms, paving the way toward a theranostic contrast agent for atherosclerosis and cancer.

Recently, carbon dots have emerged as novel luminous materials due to their excellent luminous performance. However, it is still challenging to obtain high quantum yields of red emission in carbon dots. Herein, we synthesized a new type of high efficiency red emission-carbon dots from 1,4-phenylene diisocyanate by a solvothermal method. Furthermore, the carbon dots were used to fabricate trichromatic white LEDs that possess a high luminous efficacy and color rendering index. In this study, we propose an approach for achieving high carbon dots with quantum yields by introducing more conjugated nitrogen groups in a graphitic layered structure. Moreover, the high efficiency red emission carbon dots can greatly promote carbon dots’ application in white LEDs, demonstrating that the as-prepared carbon dots are promising materials in LEDs, displays and even in other light applications.

Carbon dots (CDs) are hotspot materials in the lighting and display fields due to their low toxicity, high photostability and ease of functionalization. However, the development of white LEDs (WLEDs) is seriously restricted by the limited CDs with high photoluminescence quantum yield in the blue band and the absence of red-emitting CDs (R-CDs) with excellent photoluminescence intensity. In this work, we prepared alkali-induced R-CDs with quantum yields as high as 80%. The optical properties of the R-CDs are modulated by the alkali-induced surface electronic states. The R-CDs were doped into amino silane to realize highly efficient solid-state red luminescence. The R-CDs were combined with N-(2-aminoethyl)-3-aminopropyltrimethoxysilane-functionalized green-emitting CDs (G-SiCDs) with a quantum yield of 49% to fabricate G-SiCDs/R-CDs gel-glasses with tunable color gamut. The G-SiCDs/R-CDs nanohybrids showed excellent transmittance and thermal stability for use in WLEDs. A trichromatic warm WLED was built as a demonstration and displayed a luminous efficiency of 68.58 lm W−1 and a CRI of 90.2. These characteristics satisfy the requirements for indoor lighting.

Gold nanoparticle (AuNP)–gel glass composites were prepared on a carboxyl organosilicon oligomer by an in situ method using hydrosilane as a reductant. The organosilicon oligomer stabilized AuNPs, and hydrosilane directly bonded to the oligomer after the reducing reaction. The reaction and samples were characterized by FT-IR spectroscopy, UV-vis absorption spectrometry, UV-vis-NIR transmission spectrometry, TEM, EDS, XPS and SEM. Meanwhile, the nonlinear optical limiting properties of the AuNP–gel glass composites were investigated using the Z-scan technique and optical limiting measurements, and these composites exhibited broadband nonlinear optical limiting properties (532 nm and 1064 nm). This new reductant is a promising candidate for in situ preparation without the need for extra stabilizing agents or removal of residue byproducts, and the generated particles exhibited uniform size and distribution, providing a new insight into the preparation of metal–polymer nanocomposites.

The C3v-symmetric hetera buckybowl trichalcogenasumanenes have attracted recent interest due to their unique features in chemical and optoelectronic aspects. To gain a nonlinear optical (NLO) response, the electron-withdrawing unit pyrazine was introduced onto tricalcogenasumanenes to give the pyrazine-fused trithiasumanene (1) and triselenasumanene (2) as reported herein. Compounds 1 and 2 exhibit typical NLO properties which are verified using open-aperture Z-scan technology under a 532 nm nanosecond laser pulse. It is found that the NLO performance of these two molecules is much better than the state-of-the-art NLO material C60. The time-resolved transient absorption clearly verified that the NLO properties of 1 and 2 originate from the reverse saturable absorption (RSA) of the triplet excited-state. Owing to their remarkable NLO performance, 1 and 2 are further employed as optical power limiting (OPL) materials. Compounds 1 and 2 exhibit OPL behavior with a limiting threshold of 1.78 J cm−2 and 2.43 J cm−2, respectively; this performance is better than that of C60 (12.85 J cm−2). This work indicates that the sumanene derivatives are promising candidates for NLO and OPL materials.

To accomplish broadband optical limiting with high visible-light region (ca. 400–700 nm) transmittance, as well as to satisfy the requirement of practical applications, a novel molecule, TTF-Pt(bzimb), has been rationally designed and synthesized by connecting an excellent electron donating tetrathiafulvalene and a Pt(II)-incorporated electron withdrawing Pt(bzimb) with a C–C triple bond. Chlorine substituted Cl-Pt(bzimb) was presented for comparison. As expected, the theoretical calculation results clearly demonstrate that TTF-Pt(bzimb) exhibits a twisted conformation with a dihedral angle of 50° at the C–C triple bond. The intramolecular charge transfer existing between the donor and the acceptor is well evidenced by a series of experimental results such as UV-vis spectra, fluorescence spectra, and CV. Benefiting from a unique conformation, TTF-Pt(bzimb) and its doped Ormosil gel glasses in a methyltriethoxysilane matrix exhibit broadband (532 and 1064 nm) optical limiting behaviour with high visible-light transmittance. Furthermore, TTF-Pt(bzimb) shows more remarkable optical limiting behaviour than the state-of-the-art optical limiting material, C60, under 532 nm. Thus, our results disclose a rational molecular design strategy for the accomplishment of remarkable optical limiting. TTF-Pt(bzimb) and its gel glasses can be considered as promising candidates for the applications of optical limiting and for use in nonlinear optical devices.

Large scale epitaxial growth and transfer of monolayer MoS2 has attracted great attention in recent years. Here, we report the wafer-scale epitaxial growth of highly oriented continuous and uniform monolayer MoS2 films on single-crystalline sapphire wafers by chemical vapor deposition (CVD) method. The epitaxial film is of high quality and stitched by many 0°, 60° domains and 60°-domain boundaries. Moreover, such wafer-scale monolayer MoS2 films can be transferred and stacked by a simple stamp-transfer process, and the substrate is reusable for subsequent growth. Our progress would facilitate the scalable fabrication of various electronic, valleytronic, and optoelectronic devices for practical applications.

Topological semimetals have recently attracted extensive research interests as host materials to condensed matter physics counterparts of Dirac and Weyl fermions originally proposed in high energy physics. These fermions with linear dispersions near the Dirac or Weyl points obey Lorentz invariance, and the chiral anomaly leads to novel quantum phenomena such as negative magnetoresistance. The Lorentz invariance is, however, not necessarily respected in condensed matter physics, and thus Lorentz-violating type-II Dirac fermions with strongly tilted cones can be realized in topological semimetals. Here, we report the first experimental evidence of type-II Dirac fermions in bulk stoichiometric PtTe$_2$ single crystal. Angle-resolved photoemission spectroscopy (ARPES) measurements and first-principles calculations reveal a pair of strongly tilted Dirac cones along the $\Gamma$-A direction under the symmetry protection, confirming PtTe$_2$ as a type-II Dirac semimetal. The realization of type-II Dirac fermions opens a new door for exotic physical properties distinguished from type-I Dirac fermions in condensed matter materials., Comment: 12 pages, 4 figures

Transition metal dichalcogenides (TMDs) are van der Waals layered materials with sizable and tunable bandgaps, offering promising platforms for two-dimensional electronics and optoelectronics. To this end, the bottleneck is how to acquire high-quality single crystals in a facile and efficient manner. As one of the most widely employed method of single-crystal growth, conventional chemical vapor transport (CVT) generally encountered problems including the excess nucleation that leads to small crystal clusters and slow growth rate. To address these issues, a seed crystal is introduced to suppress the nucleation and an inner tube is adopted as both a separator and a flow restrictor, favoring the growth of large-size and high-quality TMD single crystals successfully. Three examples are presented, the effective growth of millimeter-sized MoSe2 and MoTe2 single crystals, and the greatly shortened growth period for PtSe2 single crystal, all of which are synthesized in high quality according to detailed characterizations. The mechanism of seeded CVT is discussed. Furthermore, a phototransistor based on exfoliated multi-layered MoSe2 displays excellent photoresponse in ambient conditions, and considerably rapid rise and fall time of 110 and 125 us are obtained. This work paves the way for developing a facile and versatile method to synthesize high-quality TMD single crystals in laboratory, which could serve as favorable functional materials for potential low-dimensional optoelectronics.

Weyl semimetals have been classified into type-I and type-II with respect to the geometry of their Fermi surfaces at the Weyl points. Here, we propose a new class of Weyl semimetal, whose unique Fermi surface contains two electron or two hole pockets touching at a multi-Weyl point, dubbed as type-III Weyl semimetal. Based on first-principles calculations, we first show that quasi-one-dimensional compound (TaSe4)2I is a type-III Weyl semimetal with larger chiral charges. (TaSe4)2I can support four-fold helicoidal surface states with remarkably long Fermi arcs on the (001) surface. Angle-resolved photoemission spectroscopy measurements are in agreement with the gapless nature of (TaSe4)2I at room temperature and reveal its characteristic dispersion. In addition, our calculations show that external strain could induce topological phase transitions in (TaSe4)2I among the type-III, type-II, and type-I Weyl semimetals, accompanied with the Lifshitz transitions of the Fermi surfaces. Therefore, our work first experimentally indicates (TaSe4)2I as a type-III Weyl semimetal and provides a promising platform to further investigate the novel physics of type-III Weyl fermions., 5 figures

Currently, there is tremendous interest in the discovery of new and improved photothermal agents for near-infrared (NIR)-driven cancer therapy. Herein, a series of novel photothermal agents, comprising copper nanoparticles supported on defective porous carbon polyhedra are successfully prepared by heating a Cu-BTC metal-organic framework (MOF) precursor at different temperatures (t) in the range 400-900 °C under an argon atmosphere. The copper nanoparticle size and carbon defect concentration in the obtained products (denoted herein as Cu@CPP-t) increase with synthesis temperature, thus imparting the Cu@CPP-t samples with distinct NIR absorption properties and photothermal heating responses. The Cu@CPP-800 sample shows a remarkable photothermal conversion efficiency of 48.5% under 808 nm laser irradiation, representing one of the highest photothermal efficiencies yet reported for a carbon-based photothermal agent. In vivo experiments conducted with tumor bearing nude Balb/c mice confirm the efficacy of Cu@CPP-800 as a very promising NIR-driven phototherapy agent for cancer treatment. Results encourage the wider use of MOFs as low cost precursors for the synthesis of carbon-supported metal nanoparticle composites for photothermal therapy.

Luminescent materials with high efficiency, narrow emission bandwidth and long emission wavelength have attracted extensive attention in recent years. However, for novel luminescent carbon dots, it is still a major challenge to obtain these properties simultaneously. Here, this type of carbon dot was proposed using 1,4-diaminonaphthalene as the initial source. The carbon dots demonstrate strong orange emission with the highest quantum yield of 82% and an extremely narrow emission bandwidth of 30 nm. It is found that the orange emission of carbon dots is attributed to the high defect amounts including nitrogen and oxygen doping. The high carboxyl group content leads to a high efficiency and the uniform size distribution results in a narrow bandwidth. The carbon dots are used as the gain medium of a whispering gallery mode microcavity laser. A low excitation threshold of 12 kW cm−2 and a high quality factor of ∼3600 can be obtained from the microcavity lasers. This work has provided a didactic example to develop high-quality long emission-wavelength carbon dots with strong emission and an ultra-narrow emission bandwidth, which makes it possible to expand the application of original and high-performance lasers or other optical devices.

In this work, silane-functionalized carbon dots with green and red emission (G-SiCDs and R-SiCDs) were prepared via a one-step solvothermal method. Red LEDs were fabricated using a combination of R-SiCDs and blue LED chips since there have been few reports on red LEDs that have carbon dots as a converter. Also, different ratios of G-SiCDs to R-SiCDs were adjusted so they could serve as optical converters in trichromatic WLEDs. Compared to G-SiCD-based dichromatic WLEDs, the color rendering index (CRI), which represents the true color of irradiated objects, of R-SiCD- and G-SiCD-based trichromatic WLEDs was found to be significantly improved from 58 to 88. The CIE coordinates of the G-SiCD- and R-SiCD-based trichromatic WLEDs were very close to and were even the same as pure white light (0.33, 0.33). G-SiCDs and R-SiCDs have a similar functional alkoxysilane group, thus they will show good compatibility and can co-condense with each other to form a 3D cross-linking structure. What's more, environmental SiCDs have the potential to be luminescent and encapsulation layers simultaneously in trichromatic WLEDs. This strategy will help to avoid traditional compatibility problems between luminescent and encapsulation materials in WLEDs. The as-prepared polymerizable SiCDs could provide a new opportunity to simplify the preparation process and improve the optical performances of WLEDs.

In this work, aminopropylmethylpolysiloxane (AMS) functionalized luminescent carbon dots (AMS-CDs) were prepared via a one-step solvothermal method. AMS-CDs could be self- or co-cross-linking with AMS to form 3D flexible transparent silicone rubbers (SRs) where CDs acted as cross-linking points, so the loading fraction of AMS-CDs could be adjusted from 10 to 100 wt %, thus modulating fluorescence properties and flexibility of silicone rubbers. Because of the self-curing property and high thermal stability, AMS-CDs were also studied in white LEDs (WLEDs), serving as a color conversion and encapsulation layer of GaN based blue LEDs simultaneously that would avoid the traditional problem of poor compatibility between emitting and packaging materials. And the color coordinate of AMS-CDs based WLEDs (0.33, 0.28) was very close to the pure white light. In addition, the obtained CDs cross-linked SRs had good transparency (T80%) at 510-1400 nm and high refractive indexes (1.33-1.54) that could meet the need of commercial packaging materials and optical application. AMS-CDs were also promising to be used in the UV LEDs based WLEDs according to their wide wavelength emission and flexible optoelectronic device.

During the storage of agricultural products, the oxygen concentration in the packages represents the level of food respiration and hence indicates its freshness. Herein, self-referenced photoluminescent oxygen sensitive fibrous membranes were prepared, with the inclusion of an oxygen-sensitive probe, i.e. tris (4,7-diphenyl-1,10-phenanthroline) ruthenium (II) dichloride (RuDPP), with an oxygen-insensitive luminophore, i.e. silane-functionalized carbon dots (SiCDs). Silicone was selected as the matrix, obtained via sol-gel process, and was electrospun to get nanofibers containing mesoporous microstructure and with high oxygen permeability. The as-prepared RuDPP@SiCDs/SiO2 fibrous membranes possessed hydrophobicity and exhibited ideal oxygen sensitivity, which realized a remote evaluation of the freshness of packaged fruits, through ratiometric photoluminescence imaging on the concentration change of environmental oxygen. The results indicate that such kind of oxygen-sensitive fiber membranes are capable as an optical oxygen sensor for agricultural applications.

We report experimental evidence of charge density wave (CDW) transition in monolayer 1T-VTe$_2$ film. 4$\times$4 reconstruction peaks are observed by low energy electron diffraction below the transition temperature $T_{CDW}$ = 186 K. Angle-resolved photoemission spectroscopy measurements reveal arc-like pockets with anisotropic CDW gaps up to 50 meV. The anisotropic CDW gap is attributed to the imperfect nesting of the CDW wave vector, and first-principles calculations reveal phonon softening at the same vector, suggesting the important roles of Fermi surface nesting and electron-phonon interaction in the CDW mechanism.

Both p-type and n-type MoTe2 transistors are needed to fabricate complementary electronic and optoelectronic devices. In this study, we fabricate air-stable p-type multi-layered MoTe2 transistors using Au as electrode and achieve the conversion of p-type transistor to n-type by annealing it in vacuum. Temperature-dependent in situ measurements assisted by the results given by first-principle simulations indicate that n-type conductance is an intrinsic property, which is attributed to tellurium vacancies in MoTe2, while the device in air experiences a charge transfer which is caused by oxygen/water redox couple and is converted to air-stable p-type transistor. Based on p-type and n-type multi-layered MoTe2 transistors, we demonstrate a complementary inverter with gain values as high as 9 at V DD = 5 V.

Emphasis using phototheranostics has been placed on the construction of multifunctional nanoplatforms for simultaneous tumor diagnosis and therapy. Herein, we put forth a novel nanosized luminescent material using the incorporation of red emissive carbon dots on gold nanorods through polyethylene glycol as a covalent linkage for dual-modal imaging and photothermal therapy. The novel nanohybrids, not only retain the optical properties of the gold nanorod and carbon dots, but also possess superior imaging performance in both confocal laser scanning microscopy and fluorescence lifetime imaging microscopy. The nanohybrids also exhibit excellent photothermal performance as phototheranostic nanohybrid probes for in vitro assays. This study promises a new multifunctional nanoplatform for cancer diagnostics and therapeutics.

We report the electronic structure of CuTe with a high charge density wave (CDW) transition temperature T_{c}=335 K by angle-resolved photoemission spectroscopy. An anisotropic charge density wave gap with a maximum value of 190meV is observed in the quasi-one-dimensional band formed by Te p_{x} orbitals. The CDW gap can be filled by increasing the temperature or electron doping through insitu potassium deposition. Combining the experimental results with calculated electron scattering susceptibility and phonon dispersion, we suggest that both Fermi surface nesting and electron-phonon coupling play important roles in the emergence of the CDW.

It is a great challenge to develop multifunctional nanocarriers for cancer diagnosis and therapy. Herein, versatile CDs/ICG-uLDHs nanovehicles for triple-modal fluorescence/photoacoustic/two-photon bioimaging and effective photothermal therapy were prepared via a facile self-assembly of red emission carbon dots (CDs), indocyanine green (ICG) with the ultrathin layered double hydroxides (uLDHs). Due to the J-aggregates of ICG constructed in the self-assembly process, CDs/ICG-uLDHs was able to stabilize the photothermal agent ICG and enhanced its photothermal efficiency. Furthermore, the unique confinement effect of uLDHs has extended the fluorescence lifetime of CDs in favor of bioimaging. Considering the excellent in vitro and in vivo phototherapeutics and multimodal imaging effects, this work provides a promising platform for the construction of multifunctional theranostic nanocarrier system for the cancer treatment.

The interlayer coupling can be used to engineer the electronic structure of van der Waals heterostructures (superlattices) to obtain properties that are not possible in a single material. So far research in heterostructures has been focused on commensurate superlattices with a long-ranged Moir\'e period. Incommensurate heterostructures with rotational symmetry but not translational symmetry (in analogy to quasicrystals) are not only rare in nature, but also the interlayer interaction has often been assumed to be negligible due to the lack of phase coherence. Here we report the successful growth of quasicrystalline 30{\deg} twisted bilayer graphene (30{\deg}-tBLG) which is stabilized by the Pt(111) substrate, and reveal its electronic structure. The 30{\deg}-tBLG is confirmed by low energy electron diffraction and the intervalley double-resonance Raman mode at 1383 cm$^{-1}$. Moreover, the emergence of mirrored Dirac cones inside the Brillouin zone of each graphene layer and a gap opening at the zone boundary suggest that these two graphene layers are coupled via a generalized Umklapp scattering mechanism, i.e. scattering of Dirac cone in one graphene layer by the reciprocal lattice vector of the other graphene layer. Our work highlights the important role of interlayer coupling in incommensurate quasicrystalline superlattices, thereby extending band structure engineering to incommensurate superstructures., Comment: Evidences of quasicrystalline 30{\deg}-tBLG from LEED, Raman and ARPES (combined with regular and nano-size beam spot), submitted on December 1, 2017, has been accepted by PNAS

SnSe, a group IV-VI monochalcogenide with layered crystal structure similar to black phosphorus, has recently attracted extensive interests due to its excellent thermoelectric properties and potential device applications. Experimental electronic structure of both the valence and conduction bands is critical for understanding the effects of hole versus electron doping on the thermoelectric properties, and to further reveal possible change of the band gap upon doping. Here, we report the multivalley valence bands with a large effective mass on semiconducting SnSe crystals and reveal single-valley conduction bands through electron doping to provide a complete picture of the thermoelectric physics. Moreover, by electron doping through potassium deposition, the band gap of SnSe can be widely tuned from 1.2 eV to 0.4 eV, providing new opportunities for tunable electronic and optoelectronic devices.

Carbon dots (CDs) have potentials to be utilized in optoelectronic devices, bioimaging, and photocatalysis. The majority of the current CDs with high quantum yield to date were limited in the blue light emission region. Herein, on the basis of surface electron-state engineering, we report a kind of CDs with reversible switching ability between green and red photoluminescence with a quantum yield (QY) of both up to 80%. Highly efficient green and red solid-state luminescence is realized by doping CDs into a highly transparent matrix of methyltriethoxysilane and 3-triethoxysilylpropylamine to form CDs/gel glasses composites with QYs of 80 and 78%. The CDs/gel glasses show better transmittance in visible light bands and excellent thermal stability. A blue-pumped CDs/gel glasses phosphor-based trichromatic white light-emitting diode (WLED) is realized, whose color rendering index is 92.9. The WLED gets the highest luminous efficiency of 71.75 lm W–1 in CDs-based trichromatic WLEDs. This work opens a door for ...

Hydrophilic hydroxylated hexagonal boron nitride nanosheets (BNNSs), also called 'white graphene', exhibit high water solubility, compatibility, dispersity with physical and/or chemical effects on the gel matrix, and unexpected but outstanding near-infrared adsorption and nonlinear optical limiting properties. These properties mean that hydroxylated BNNSs are suitable for practical applications in solidification and devices. Hydroxylated BNNSs are doped into an organically modified silicate matrix through a facile sol-gel process. The resulting BNNS-organically modified silicate glass hybrids demonstrate various solid structures (glass, coating, and film), good uniformity, thermostability, toughness, and high linear transmittance in the visible and near-infrared regions. Hybrid glasses showed large optical limiting effects and high doping concentrations without the addition of a compatibiliser, and their limiting thresholds and concentration exceed those of the corresponding suspensions by factors of 1.3-2 and 20-130, respectively. The optical limiting performance of BNNSs is almost equal to or may exceed those of graphene oxide and graphene in solutions and doped glasses. The combined mechanisms of nonlinear absorption, refraction, and scattering are deduced. A solid organically modified silicate hybrid transparent system doped with BNNSs is a promising candidate material for optical limiters and nonlinear optical devices. This system could be an efficient solid-state optical limiter in the visible and long-wavelength near-infrared regions (532-2000 nm).

By controllable synthesis of a carbon precursor and with a suitable preparation routine, a series of single-layer and single-crystalline graphene quantum dots (GQDs) with uniform size distribution were prepared from C96H30. It was found that the absorption, photoluminescence (PL) and two-photon photoluminescence (TPPL) show a high size-dependent effect with a redshift that occurs as the size grows. Two-photon absorption (TPA) properties of GQDs were measured at 800 nm under a femtosecond pulse laser. Two-photon bioimaging of HeLa cells was carried out to determine TPA properties. Most significantly, the as-prepared GQDs showed potential in a practical application in two-photon cell bioimaging due to their high contrast TPPL. In addition, the superior nonlinear absorption, stable TPPL and excellent solubility were beneficial to the optical limiting (OL) properties.

In this paper, in situ bifunctionalized carbon dots (B-N-CDs) with boronic acid and amino groups were prepared by a simple hydrothermal method using 3-aminophenylboronic acid as the sole precursor. The high quantum yield of B-N-CDs is as high as 67%, leading to fluorescence emission observed even under daylight excitation. The B-N-CDs exhibited obvious fluorescence enhancement to trace dopamine in the range of 1 pM to 1 μM with a detection limit of 0.1 pM (S/N = 3), which is two orders of magnitude more sensitive than that of present fluorescent sensors. The excellent sensing performance is based on the interaction of two functional groups with DA. This dopamine probe owned advantages of high sensitivity, superior selectivity, good reproducibility and simplicity. Moreover, the analytical reliability of this dopamine sensor was demonstrated in human serum samples.

We report the first observation of the non-magnetic Barkhausen effect in van der Waals layered crystals, specifically, during transitions between the T d and 1T' phases in type-II Weyl semimetal MoTe2. Thinning down the MoTe2 crystal from bulk material to about 25 nm results in a drastic strengthening of the hysteresis in the phase transition, with the difference in critical temperature increasing from ~40 K to more than 300 K. The Barkhausen effect appears for thin samples and the temperature range of the Barkhausen zone grows approximately linearly with reducing sample thickness, pointing to a surface origin of the phase pinning effects. The distribution of the Barkhausen jumps shows a power law behavior, with its critical exponent α = 1.27, in good agreement with existing scaling theory. Temperature-dependent Raman spectroscopy on MoTe2 crystals of various thicknesses shows results consistent with our transport measurements.

In this study, we fabricate air-stable p-type multi-layered MoTe2 phototransistor using Au as electrodes, which shows pronounced photovoltaic response in off-state with asymmetric contact form. By analyzing the spatially resolved photoresponse using scanning photocurrent microscopy, we found that the potential steps are formed in the vicinity of the electrodes/MoTe2 interface due to the doping of the MoTe2 by the metal contacts. The potential step dominates the separation of photoexcited electron-hole pairs in short-circuit condition or with small V sd biased. Based on these findings, we infer that the asymmetric contact cross-section between MoTe2-source and MoTe2-drain electrodes is the reason to form non-zero net current and photovoltaic response. Furthermore, MoTe2 phototransistor shows a faster response in short-circuit condition than that with higher biased V sd within sub-millisecond, and its spectral range can be extended to the infrared end of 1550 nm. Electronic supplementary material The online version of this article (10.1186/s11671-017-2373-5) contains supplementary material, which is available to authorized users.

While a monolayer ${\mathrm{PtSe}}_{2}$ film is a semiconductor with interesting spin structure, bulk ${\mathrm{PtSe}}_{2}$ crystal has been predicted to be a topological Dirac semimetal that can host a new type of Lorentz-violating Dirac fermions. Despite the intriguing predictions, experimental progress on the electronic structure of bulk ${\mathrm{PtSe}}_{2}$ has been hindered due to the lack of large, high-quality single-crystal samples. Here we report the growth and characterization of high-quality ${\mathrm{PtSe}}_{2}$ single crystals and reveal the electronic structure to provide direct evidence for the existence of three-dimensional type-II Dirac fermions. A comparison of the crystal, vibrational, and electronic structure to a related compound, ${\mathrm{PtTe}}_{2}$, is also discussed. Our work provides an important platform for exploring the novel quantum phenomena associated with type-II Dirac fermions in the $1T\ensuremath{-}{\mathrm{PtSe}}_{2}$ class of transition-metal dichalcogenides.

A supramolecular nanovehicle, denoted as ICG-DOX/Gd-LDH, was synthesized by the co-intercalation of indocyanine green (ICG) and doxorubicin hydrochloride (DOX) into a gallery of Gd3+-doped-layered double hydroxide (Gd-LDH) such that to achieve a chemo-photothermal synergistic therapeutic agent. The unique structure of Gd-LDH can not only stabilize the photothermal agent ICG to enhance the photothermal efficiency, but also hamper the recombination between electron and holes, leading to the generation of more reactive oxygen species (ROS) under irradiation in the NIR range. Together with the loading capacity of DOX, ICG-DOX/Gd-LDH exhibited excellent combinatorial effects on tumor growth inhibition in both in vitro studies on HeLa cell line and in vivo tests over tumor-bearing mouse models. Moreover, it showed ideal ability for long-term tracing of the carrier distribution via either MRI or fluorescence imaging. Thus, this study indicates that Gd-LDH is a promising platform for the construction of multifunctional formulations, especially theranostic nano-systems for cancer treatment.