Direct and scalable synthesis of monodisperse gold nanoclusters is highly desired but remains a great challenge due to the complexity of chemical reactions. In this regard, a suitable precursor is important as it can simplify the synthesis processes and offer controllability in tuning the product. In this study, we found that Au(PPh3)2Cl could be used as an effective precursor for the direct synthesis of atomically monodisperse [Au8(PPh3)7]2+ nanoclusters without the need of tedious post-synthetic purification steps. The Au(PPh3)2Cl precursor could be directly reduced by NaBH4 (0.25 molar equivalent) in a dichloromethane solution; this produced Au8 clusters with a 35% reaction yield. Time-dependent mass spectrometry and in situ UV-vis absorption spectroscopy reveal that the synthesis process is initiated by the rapid formation of the Au6–Au8 mixture, followed by a slow spontaneous self-focusing process that converges the mixture into atomically monodisperse Au8. The success of this direct synthesis has been hypothesized to arise from the relatively stronger Au(I)⋯Au(I) aurophilic attraction between Au(I)-PPh3 complexes that facilitates the aggregation of Au(I)-PPh3 on Au(0) cores.

Luminescent gold nanoclusters have recently emerged as an important class of sensing and imaging materials in optical applications. Here we report a red-emitting gold nanocluster with a precise molecular formula of Au7(DHLA)2Cl2, synthesized via the size-focusing strategy using a bidentate ligand of dihydrolipoic acid (DHLA). This Au nanocluster is water-soluble and emits fluorescence at 683 nm with a quantum yield of 3.6% in water. The intense fluorescence of Au7(DHLA)2Cl2 originates from the aggregation of Au(I)–DHLA/Cl motifs on the Au(0) core in a rigid core/shell-like structure. Moreover, we find that trace levels of Fe2+ ions can quench selectively and sensitively the fluorescence of the Au7(DHLA)2Cl2 nanocluster, making it a potential fluorescent sensor for Fe2+ with a limit of detection of 3.8 μM (0.2 ppm). A dissociation-induced fluorescence quenching mechanism is also proposed to describe the fluorescence response of the nanocluster to Fe2+ ions.

•Luminescent [Au15(SR)14-16]+ complex is synthesized by dodecanethiol reducing HAuCl4 in toluene.•Non-luminescent [Au7(SR)6]+ complex is yielded by the same synthesis in ethanol.•The relationship between the luminescence intensity and solvent polarity is studied.•Luminescence of Au(I)-SR complexes originates from aggregation of the bilayer supramolecular structures.•Aggregation increases as solvent polarity decreases.This work presents a study on the correlation between luminescence property of Au(I)-SR (SR: thiolate) complexes and solvent polarity. Luminescent [Au15(SR)14–16]+ complexes were synthesized in the weakly polar solvent of toluene, while the non-luminescent [Au7(SR)6]+ species were obtained by the same synthesis method in the polar solvent of ethanol. The dependence of luminescence intensity on the mixed solvent with various toluene/ethanol ratios was also explored. It is proposed that the luminescence of Au(I)-SR complexes originates from the aggregation of the bilayer supramolecular structures induced by the weakly polar solvent. This aggregation strengthens the intra and intercomplex aurophilic Au(I)···Au(I) interactions and subsequently enhances the luminescence intensity of the complexes.

•Thiol-etching reaction of diphosphine-protected Au nanoclusters is reported.•Combined spectroscopic techniques are employed to identify the reaction product.•The etching reaction yields a gold(I)-thiolate complex Au2L5(RS).•Etching products of diphosphine- and PPh3- protected Au nanoclusters are different.Thiol-etching triphenylphosphine (PPh3)-protected Au nanoclusters has been widely used to synthesize thiolated Au nanoclusters, while few studies have been reported on the thiol-etching reaction starting from diphosphine-protected Au clusters. Here the thiol-etching reaction in chloroform (CHCl3) for 1,5-Bis(diphenylphosphino) pentane (L5) protected Au11 nanoclusters is presented, and synchrotron radiation X-ray absorption fine structure, UV–vis absorption and mass spectra are combined to identify the reaction products. It is revealed that a gold(I)-thiolate complex Au2L5(RS) is produced, contrary to the case of thiol-etching PPh3-protected Au clusters where formation of thermodynamically stable Au25 or Au11 clusters is achieved.

Outstanding magnetic properties are highly desired for two-dimensional ultrathin semiconductor nanosheets. Here, we propose a phase incorporation strategy to induce robust room-temperature ferromagnetism in a nonmagnetic MoS2 semiconductor. A two-step hydrothermal method was used to intentionally introduce sulfur vacancies in a 2H-MoS2 ultrathin nanosheet host, which prompts the transformation of the surrounding 2H-MoS2 local lattice into a trigonal (1T-MoS2) phase. 25% 1T-MoS2 phase incorporation in 2H-MoS2 nanosheets can enhance the electron carrier concentration by an order, introduce a Mo4+ 4d energy state within the bandgap, and create a robust intrinsic ferromagnetic response of 0.25 μB/Mo by the exchange interactions between sulfur vacancy and the Mo4+ 4d bandgap state at room temperature. This design opens up new possibility for effective manipulation of exchange interactions in two-dimensional nanostructures.

Knowledge of the molecular formation mechanism of metal nanoclusters is essential for developing chemistry for accurate control over their synthesis. Herein, the “top-down” synthetic process of monodisperse Au13 nanoclusters via HCl etching of polydisperse Aun clusters (15 ≤ n ≤ 65) is traced by a combination of in situ X-ray/UV-vis absorption spectroscopy and time-dependent mass spectrometry. It is revealed experimentally that the HCl-induced synthesis of Au13 is achieved by accurately controlling the etching process with two distinctive steps, in sharp contrast to the traditional thiol-etching mechanism through release of the Au(I) complex. The first step involves the direct fragmentation of the initial larger Aun clusters into metastable intermediate Au8–Au13 smaller clusters. This is a critical step, which allows for the secondary size-growth step of the intermediates toward the atomically monodisperse Au13 clusters via incorporating the reactive Au(I)–Cl species in the solution. Such a secondary-growth pathway is further confirmed by the successful growth of Au13 through reaction of isolated Au11 clusters with AuClPPh3 in the HCl environment. This work addresses the importance of reaction intermediates in guiding the way towards controllable synthesis of metal nanoclusters.

Solvent has a key role in the controllable synthesis of nanocrystals (NCs). Here, using X-ray absorption spectroscopy, we demonstrate that solvent can significantly influence the adsorption of thiols on Au NCs, and thereby affects their growth. It is shown that increasing the solvent polarities leads to the higher thiol coverage on the NC surface. The high coverage of thiols then retards the growth of particles, and as a result, the NCs’ sizes decrease with the increase in the solvents’ polarities. The underlying reason for the solvent dependence is proposed to be the synergistic effects of different hydrogen bond and hydrophobic interactions between the sulfhydryl and alkyl groups of thiols with the solvents molecules. This work addresses the important role of the solvent environments in the size-controlled synthesis of NCs.

Manipulating the ferromagnetic interactions in diluted magnetic semiconductor quantum dots (DMSQDs) is a central theme to the development of next-generation spin-based information technologies, but this remains a great challenge because of the intrinsic antiferromagnetic coupling between impurity ions therein. Here, we propose an effective approach capable of activating ferromagnetic exchange in ZnO-based DMSQDs, by virtue of a core/shell structure that engineers the energy level of the magnetic impurity 3d levels relative to the band edge. This idea has been successfully applied to Zn0.96Co0.04O DMSQDs covered by a shell of ZnS or Ag2S. First-principles calculations further indicate that covering a ZnS shell around the Co-doped ZnO core drives a transition of antiferromagnetic-to-ferromagnetic interaction, which occurs within an effective depth of 1.2 nm underneath the surface in the core. This design opens up new possibility for effective manipulation of exchange interactions in doped oxide nanostructures for future spintronics applications.

Understanding the kinetic mechanism during ligand adsorption on gold nanocrystals is important for designing and fine-tuning their properties and implications. Here, we report a kinetic study on the adsorption process of dodecanethiol ligands on Au nanocrystals of 3.3 nm by an in situ time-resolved X-ray absorption fine structure technique. A two-step process of dodecanethiol adsorption on Au NC surfaces is proposed based on the obtained ligand coverage, which shows a quick increase from 0 to 0.40 within the first 20 min, followed by a much slower increase to the limiting value of 0.94. In-depth analysis suggests that the first stage involves the quick adsorption of dodecanethiol to the corner and edge sites of Au NCs surfaces, leading to remarkable surface Au–Au bond length relaxation (from 2.79 to 2.81 Å) and pronounced gold-to-ligand charge transfer. The second step that corresponds to the much slower adsorption process to the surface facets could be described by the Langmuir kinetics equation with an adsorption rate constant of 0.0132 min−1 and an initial coverage of 0.41, in good agreement with the initially preferable adsorption of thiols to the most favorable sites.

Elemental codoping has been an effective way to modify the structural and electronic properties of semiconductors. By use of X-ray diffraction and X-ray absorption fine structure spectroscopy, we show that the spatial occupations of Co and Cu codopants in ZnO thin films could be regulated by the crystal orientation of the matrix prepared by pulsed laser deposition at different temperatures. At deposition temperatures lower than 300 °C, the ZnO matrix was grown along the [201] preferential orientation, with the substitutional incorporation of Co dopants and formation of metallic Cu nanoclusters. Increasing the growth temperature to 300 °C or higher drives a transform of the ZnO film to the c-axial [002] preferred orientation. Consequently, the Cu atoms aggregate into larger fcc-structured Cu nanocrystals that attract part of the Co dopants to precipitate out as metallic clusters. The relation between the growth orientation of ZnO thin films and the occupation positions of Co/Cu codopants is discussed in terms of the temperature-dependent mobility and formation energy of the doping atoms.

Whether and how nanoclusters possessing a rich diversity of possible geometric configurations can transform from one structural type to another are critical issues in cluster science. Here we demonstrate an icosahedral-to-cuboctahedral structural transformation of Au nanoclusters driven by changing the chemical environment. For icosahedral Au13 clusters protected by a mixture of dodecanethiol and triphenylphosphine ligands, solvent exchange of ethanol by hexane leads to quick selective desorption of the thiolate layers from the cluster surface. The surviving Au cores then undergo a much slower energy-minimization process via structural rearrangement, stabilized in the cuboctahedral structure and protected by triphenylphosphine in the hexane environment. In response to the dramatically changed atomic structure, the character of the electronic structure of the Au clusters is converted from semiconducting to metallic. This work addresses the structure–property correlation and its strong dependence on the chemical environment for metal nanoclusters.

Synthesis of monodisperse small Au nanoparticles in a controllable manner is of great importance for fundamental science and technical applications. Here, we report a “precursor continuous-supply” strategy for controllable synthesis of 0.9–3.3 nm Au nanoparticles with a narrow size distribution of 0.1–0.2 nm, using a weak reductant to slow-down the reducing rate of AuClPPh3 precursor in ethanol. Time-dependent X-ray absorption and UV-Vis absorption measurements revealed that owing to the joint use of AuClPPh3 and ethanol, the remnant AuClPPh3 was self-supplied and the precursor concentration was maintained at a level near to its equilibrium solubility (ca. 1.65 mmol L−1) in ethanol. Hence the nucleation duration was extended that focused the initial size distribution of the Au clusters. With reaction going on for 58 min, most of AuClPPh3 with a nominal Au concentration of 17.86 mmol L−1 was converted to ethanol-soluble Au clusters with a size of about 1.0 nm, resulting in a high-yield synthesis.

Synthesis of monodisperse small Au nanoparticles in a controllable manner is of great importance for fundamental science and technical applications. Here, we report a “precursor continuous-supply” strategy for controllable synthesis of 0.9–3.3 nm Au nanoparticles with a narrow size distribution of 0.1–0.2 nm, using a weak reductant to slow-down the reducing rate of AuClPPh3 precursor in ethanol. Time-dependent X-ray absorption and UV-Vis absorption measurements revealed that owing to the joint use of AuClPPh3 and ethanol, the remnant AuClPPh3 was self-supplied and the precursor concentration was maintained at a level near to its equilibrium solubility (ca. 1.65 mmol L−1) in ethanol. Hence the nucleation duration was extended that focused the initial size distribution of the Au clusters. With reaction going on for 58 min, most of AuClPPh3 with a nominal Au concentration of 17.86 mmol L−1 was converted to ethanol-soluble Au clusters with a size of about 1.0 nm, resulting in a high-yield synthesis.

Luminescent gold nanoclusters have recently emerged as an important class of sensing and imaging materials in optical applications. Here we report a red-emitting gold nanocluster with a precise molecular formula of Au7(DHLA)2Cl2, synthesized via the size-focusing strategy using a bidentate ligand of dihydrolipoic acid (DHLA). This Au nanocluster is water-soluble and emits fluorescence at 683 nm with a quantum yield of 3.6% in water. The intense fluorescence of Au7(DHLA)2Cl2 originates from the aggregation of Au(I)–DHLA/Cl motifs on the Au(0) core in a rigid core/shell-like structure. Moreover, we find that trace levels of Fe2+ ions can quench selectively and sensitively the fluorescence of the Au7(DHLA)2Cl2 nanocluster, making it a potential fluorescent sensor for Fe2+ with a limit of detection of 3.8 μM (0.2 ppm). A dissociation-induced fluorescence quenching mechanism is also proposed to describe the fluorescence response of the nanocluster to Fe2+ ions.