An important obstacle to long-term hydrogen sustainability is the lack of efficient and stable non-noble-metal catalysts for hydrogen generation through water electrolysis. Cobalt phosphides have emerged as earth-abundant catalysts for the hydrogen evolution reaction (HER), and its activity can be augmented by admixing synergistic elements to produce heteroatom-doped catalysts. Herein, we report an integrated computational and experimental study leading to the synthesis of Co1-xMnxP nanocrystals (NCs) displaying superior activity and stability for the alkaline HER compared to the benchmark Pt/C catalyst at higher current densities (j ≥ -35 mA/cm2). Density functional theory calculations predicted that Mn doping modulates the hydrogen adsorption energies (ΔGH) of orthorhombic CoP toward thermoneutral values. Accordingly, a series of Co1-xMnxP NCs (x = 0.038-0.169) with control over structure, morphology, and composition was produced via colloidal synthesis. Physical characterization of Co1-xMnxP NCs revealed an orthorhombic structure, pseudospherical morphology, and average diameters of ∼5.7-10.2 nm. The incorporation of Mn caused significant modulation of the electronic structure prompting a decrease in Co(2p) and P(2p) binding energies, suggesting an increase in electron density on both surface sites. Among NCs investigated, Co0.909Mn0.091P composition displayed the highest HER activity with an overpotential (η-10) of 136.29 mV at j = -10 mA/cm2, consistent with composition-dependent ΔGH studies. With a Tafel slope of 65.77 mV/dec, Co0.909Mn0.091P NCs showed similar kinetics to the Pt/C catalyst (62.31 mV/dec), indicating the Volmer-Heyrovsky HER mechanism. The highest-performing Co0.909Mn0.091P NCs showed a prominent increase in electrochemically active surface area and significantly lower charge transfer resistance compared to parent CoP NCs. The Co0.909Mn0.091P NCs showed exceptional stability in alkaline media compared to CoP NCs and commercial Pt/C catalysts. Co0.923Mn0.077P, Co0.909Mn0.091P, and Co0.831Mn0.169P compositions displayed superior HER activity and stability compared to monometallic CoP NCs suggesting that dopant-induced compositional and surface modification is an effective strategy for designing high-efficiency, durable nanostructures for numerous heterogeneous (electro)catalytic studies.

Si1-xGex alloy nanocrystals (NCs) are a class of benign semiconductors that show size and composition-tunable energy gaps and promising optical properties because of the lattice disorder. The random distribution of elements within the alloys can lead to efficient light-matter interactions, making them attractive for Si-compatible optoelectronic devices, transistors, charge storage, and memory applications. However, the fabrication of discrete, quantum-confined alloys has proved a challenging task. Herein, we report solid-state co-disproportionation of a hydrogen silsesquioxane (HSQ)/GeI2 composite precursor to produce homogeneous Si1-xGex NCs with control over the diameter (5.9 +/- 0.7-7.8 +/- 1.1 nm) and composition (x = 0-14.4%) with strong size confinement effects and visible to near IR absorption and emission properties. As-synthesized alloys show an expanded diamond cubic Si structure, a systematic red-shift of Si-Si Raman peak, and emergence of Si-Ge/Ge-Ge peaks with increasing Ge, consistent with the admixture of isovalent elements. Surface analysis of alloys reveals Si0/Ge0 core and Sin+/Gen+ surface species and efficient surface functionalization with alkyl ligands via thermal hydrosilylation and/or hydrogermylation. Alloy NCs exhibit absorption onsets (2.26-1.92 eV), indirect (1.53-1.80 eV) and direct (2.88-2.47 eV) energy gaps, and photoluminescence (PL) maxima (1.40-1.27 eV) that can be tuned by manipulating the diameter and/or composition. The experimental PL energies are consistent with those predicted by density functional theory (DFT), suggesting that the PL originates from NC core electronic transitions. The facile low-temperature solid-state synthesis and control over physical properties realized in this study will allow discrete Si1-xGex NCs to emerge as low to nontoxic, earth-abundant, and Si-compatible nanostructures for a broad range of electronic and photonic technologies.

Electrochemical water splitting represents a sustainable method for producing molecular hydrogen, a promising clean energy alternative to fossil fuels. Iron phosphides have emerged as earth-abundant catalysts for the hydrogen evolution reaction (HER), where performance can be enhanced by admixing synergetic metals to produce bimetallic catalysts. Herein, we report a theoretical and experimental study that reveals the influence of dopant-induced hexagonal to orthorhombic phase transition on the catalytic activity and stability of Fe2P nanorods (NRs) for HER. Among eight metal dopants computationally studied, Mo has been identified as the most promising dopant owing to its optimum hydrogen binding free energy (ΔG H) on the Fe2P (210) surface. Accordingly, hexagonal and orthorhombic Fe2-x Mo x P NRs (x = 0-14%) with average lengths and widths ranging from 50.9 ± 22.1 to 92.4 ± 43.8 nm and 3.8 ± 1.0 to 6.3 ± 1.8 nm, respectively, were colloidally synthesized to investigate the structure- and composition-dependent HER activity. Upon incorporation of Mo, the underlying hexagonal Fe2P phase transformed into orthorhombic Fe2-x Mo x P when x ≥ 0.11 (5.41%). The admixture of Mo caused variations in the surface chemistry, leading to a significant decrease in Feδ+ and Pδ- charges. The HER performance was observed to be both phase- and composition-dependent with mixed-phase Fe2-x Mo x P NRs (x = 0.03, 0.06, and 0.09) exhibiting superior catalytic activity and overpotentials (η-10) of 298, 267, and 222 mV, respectively at a current density (j) of -10 mA/cm2 compared to hexagonal Fe2P (η-10 = 378 mV) and orthorhombic Fe2-x Mo x P (η-10 = 331-459 mV for x = 0.12-0.28) catalysts. The highest HER performance was achieved for Fe1.91Mo0.09P NRs with a dopant composition of 4.58%, consistent with composition-dependent ΔG H calculations. Although all compositions displayed a Volmer-Heyrovsky HER mechanism, the admixture of Mo improved the HER kinetics, producing the lowest Tafel slope (167.08 mV/dec) for Fe1.91Mo0.09P NRs. The incorporation of Mo improves the charge transfer resistance and preserves the stability of hexagonal and orthorhombic NRs in alkali environments with a negligible increase in η-10 after 10 h of HER. This study advances the understanding of dopant-induced crystal structure transitions and paves the way for efficient and stable catalytic material design.

Ge1-x-y Si y Sn x quantum dots (QDs) are an attractive class of low-to-nontoxic and earth-abundant semiconductors exhibiting size and composition-tunable optical properties. Their electronic structure can be modified by varying elemental composition and quantum confinement to achieve tunable absorption and photoluminescence (PL) across the visible to near-IR spectrum. Alloying with Sn enhances oscillator strengths, whereas decreasing size and incorporating Si increase energy gaps. Herein, we report a facile colloidal route to produce Ge1-x-y Si y Sn x QDs with narrow size dispersity (4.0 ± 0.4 - 5.2 ± 0.6 nm) and variable Si (y = 0.030 - 0.252) and Sn (x = 0.044 - 0.059) compositions and investigate the influence of core/surface species on optical properties. Structural analysis reveals an expanded diamond cubic Ge lattice, a red-shifted Ge-Ge Raman peak, and the emergence of a Ge-Si peak with increasing Si composition. Successful alloying of Si and Sn into Ge host lattice is confirmed by electron microscopy, suggesting homogeneous solid solution behavior of ternary QDs. Surface analysis further indicates the presence of Ge0/Si0/Sn0 core species alongside charged Ge n+/Si n+/Sn n+ (1 ≤ n ≥ 4) surface species coordinated to passivating organic ligands. The effects of confinement and surface/core elemental composition on optical properties were revealed through composition-tunable absorption onsets (1.15 - 2.33 eV) and associated Tauc direct (1.86 - 3.03 eV) and indirect (1.01 - 1.81 eV) energy gaps achieved for QDs with x = 0.044 - 0.059 and y = 0.030 - 0.252, which are prominently blue-shifted from bulk counterparts and previously reported Ge1-x Sn x QDs. PL spectra of Ge1-x-y Si y Sn x QDs exhibit nanosecond-scale emission from 1.84 - 1.88 eV for y ≤ 0.134 and 2.32 - 2.43 eV for y ≥ 0.177 compositions, displaying similarly pronounced blueshifts from comparable Ge1-x Sn x QDs. This correlated absorption/PL tunability expands upon that demonstrated by Ge and Ge1-x Sn x counterparts widens the optical window of Group IV semiconductor nanostructures, making them attractive for visible-to-near-IR optoelectronic studies.

Dodecane-capped silicon nanocrystals (NCs) were synthesized by using a low-temperature (800-1100 degrees C) polymer variant of traditional hydrogen silsesquioxane thermal disproportionation. Highly crystalline Si NCs having tunable diameters (3.0-6.7 nm) and thus photoluminescence (PL) peaks (1.68-1.29 eV) were attained via changes in the maximum annealing temperature. Modifications in the NC band structure with diameter were explored by comparison of emission with absorption spectra obtained from diffuse reflectance spectroscopy. Large apparent energy shifts between onsets and PL were noted, being significant for smaller NCs (<=similar to 4.0 nm). This, along with comparatively "softer" onsets, is commensurate with density of states elongation around PL peaks associated with increasing confinement predicted for indirect semiconductor nanostructures. Tauc analyses of absorption additionally revealed three distinguishable optical transitions in all NCs: attributed to indirect Gamma(25 ')-Delta(1) in lower energy ranges (likely the emission progenitor), indirect Gamma(25 ')-L-1 overtaken by quasi-direct Gamma-X wave function mixing for NC diameters <=similar to 4.0 nm within the midenergy regime, and direct Gamma(25 ')-Gamma(15) transitions at energies nearing and above similar to 3 eV.

We report on quantum confined Ge 1-x-y Si y Sn x nanocrystals demonstrating both size-and composition-tunable direct visible/NIR emission (1.77 – 2.47 eV) and recombination dynamics. Temperature-dependent time-resolved photoluminescence suggests significant enhancement of oscillator strengths with Si incorporation.

Nickel phosphides are an emerging class of earth-abundant catalysts for hydrogen generation through water electrolysis. However, the hydrogen evolution reaction (HER) activity of Ni2P is lower than that of benchmark Pt group catalysts. To address this limitation, an integrated theoretical and experimental study was performed to enhance the HER activity and stability of hexagonal Ni2P through doping with synergistic transition metals. Among the nine dopants computationally studied, zinc emerged as an ideal candidate due to its ability to modulate the hydrogen binding free energy (ΔG H) closer to a thermoneutral value. Consequently, phase pure hexagonal Ni2-x Zn x P nanocrystals (NCs) with a solid spherical morphology, variable compositions (x = 0-17.14%), and size in the range of 6.8 ± 1.1-9.1 ± 1.1 nm were colloidally synthesized to investigate the HER activity and stability in alkaline electrolytes. As predicted, the HER performance was observed to be composition-dependent with Zn compositions (x) of 0.03, 0.07, and 0.15 demonstrating superior activity with overpotentials (η-10) of 188.67, 170.01, and 135.35 mV, respectively at a current density of -10 mA/cm2, in comparison to Ni2P NCs (216.2 ± 4.4 mV). Conversely, Ni2-x Zn x P NCs with x = 0.01, 0.38, 0.44, and 0.50 compositions showed a notable decrease in HER activity, with corresponding η-10 of 225.3 ± 3.2, 269.9 ± 4.3, 276.4 ± 3.7 and 263.9 ± 4.9 mV, respectively. The highest HER active catalyst was determined to be Ni1.85Zn0.15P NCs, featuring a Zn concentration of 5.24%, consistent with composition-dependent ΔG H calculations. The highest performing Ni1.85Zn0.15P NCs displayed a Heyrovsky HER mechanism, enhanced kinetics and electrochemically active surface area (ECSA), and superior corrosion tolerance with a negligible increase of η-10 after 10 h of continuous HER. This study provides critical insights into enhancing the performance of metal phosphides through doping-induced electronic structure variation, paving the way for the design of high-efficiency and durable nanostructures for heterogeneous catalytic studies.

Group IV alloy nanocrystals (NCs) are a class of direct energy gap semiconductors that show high elemental abundance, low to nontoxicity, and composition-tunable absorption and emission properties. These properties have distinguished Ge1-xSnx NCs as intriguing materials for near-infrared (IR) optical studies. Achieving a material with efficient visible emission requires a modified class of group IV alloys, and the computational studies suggest that this can be achieved with Ge1-x-ySiySnx NCs. Herein, we report a colloidal strategy for the synthesis of bulk-like (10.3 +/- 2.5-25.5 +/- 5.3 nm) and quantum-confined (3.2 +/- 0.6-4.2 +/- 1.1 nm) Ge1-x-ySiySnx alloys that show strong size confinement effects and composition-tunable visible to near IR absorption and emission properties. This synthesis produces a homogeneous alloy with a diamond cubic Ge structure and tunable Si (0.9-16.1%) and Sn (1.8-14.9%) compositions, exceeding the equilibrium solubility of Sn (<1%) in crystalline Si and Ge. Raman spectra of Ge1-x-ySiySnx alloys show a prominent red-shift of the Ge-Ge peak and the emergence of a Ge-Si peak with increasing Si/Sn, suggesting the growth of homogeneous alloys. The smaller Ge1-x-ySiySnx NCs exhibit absorption onsets from 1.21 to 1.94 eV for x = 1.8-6.8% and y = 0.9-16.1% compositions, which are blue-shifted from those reported for Ge1-x-ySiySnx bulk alloy films and Ge1-xSnx alloy NCs, indicating the influence of Si incorporation and strong size confinement effects. Solid-state photoluminescence (PL) spectra reveal core-related PL maxima from 1.77-1.97 eV in agreement with absorption onsets, consistent with the energy gaps calculated for similar to 3-4 nm alloy NCs. With a facile, low-temperature solution synthesis and direct control over physical properties, this methodology presents a noteworthy advancement in the synthesis of bulk-like and quantum-confined Ge1-x-ySiySnx alloys as versatile materials for future optical and electronic studies.

Size-confined Si nanorods (NRs) have gained notable interestbecauseof their tunable photophysical properties that make them attractivefor optoelectronic, charge storage, and sensor technologies. However,established routes for fabrication of Si NRs use well-defined substratesand/or nanoscopic seeds as promoters that cannot be easily removed,hindering the investigation of their true potential and physical properties.Herein, we report a facile, one-step route for the fabrication ofSi NRs via thermal disproportionation of hydrogen silsesquioxane (HSQ)in the presence of a molecular tin precursor (SnCl4) ata substantially lower temperature (450 degrees C) compared to thoseused in the synthesis of size-confined Si nanocrystals (>1000 degrees C).The use of these precursors allows the facile isolation of phase-pureSi NRs via HF etching and subsequent surface passivation with 1-dodecenevia hydrosilylation. The diameters (7.7-16.5 nm) of the NRscan be controlled by varying the amount of SnCl4 (0.2-3.0%)introduced during the HSQ synthesis. Physical characterization ofthe NRs suggests that the diamond cubic structure is not affectedby SnCl4, HF etching, and hydrosilylation. Surface analysisof NRs indicates the presence of Si-0 and Sin+ species, which can be attributed to core Si and surface Si speciesbonded to dodecane ligands, respectively, and a systematic variationof the Si-0:Si-C ratio with the NR diameter. TheNRs show strong size confinement effects with solid-state absorptiononsets (2.51-2.80 eV) and solution-state (Tauc) indirect energygaps (2.54-2.70 eV) that can be tuned by varying the diameter(16.5-7.7 nm). Photoluminescence (PL) and time-resolved PL(TRPL) studies reveal size-dependent emission (1.95-2.20 eV)with short, nanosecond lifetimes across the visible spectrum, whichtrend closely with absorption trends seen in solid-state absorptiondata. The facile synthesis developed for size-confined Si NRs withhigh crystallinity and tunable optical properties will promote theirapplication in optoelectronic, charge storage, and sensing studies.

Electrocatalyticwater splitting presents an exciting opportunityto produce environmentally benign hydrogen fuel to power human activities.Earth-abundant Ni5P4 has emerged as an efficientcatalyst for the hydrogen evolution reaction (HER), and its activitycan be enhanced by admixing synergistic metals to modify the surfaceaffinity and consequently the kinetics of HER. Computational studiessuggest that the HER activity of Ni5P4 can beimproved by Zn doping, causing a chemical pressure-like effect onNi(3) hollow sites. Herein, we report a facile colloidalroute to produce Ni5-x Zn x P4 nanocrystals (NCs) with control overstructure, morphology, and composition and investigate their composition-dependentHER activity in alkaline solutions. Ni5-x Zn x P4 NCs retain thehexagonal structure and solid spherical morphology of binary Ni5P4 NCs, with a notable size increase from 9.2-28.5nm for x = 0.00-1.27 compositions. Elementalmaps affirm the homogeneous ternary alloy formation with no evidenceof Zn segregation. Surface analysis of Ni5-x Zn x P4 NCs indicatessignificant modulation of the surface polarization upon Zn incorporation,resulting in a decrease in Ni & delta;+ and an increase inP(& delta;-) charges. Although all compositions followeda Volmer-Heyrovsky HER mechanism, the modulated surface polarizationenhances the reaction kinetics, producing lower Tafel slopes for Ni5-x Zn x P4 NCs (82.5-101.9 mV/dec for x = 0.10-0.84)compared to binary Ni5P4 NCs (109.9 mV/dec).Ni5-x Zn x P4 NCs showed higher HER activity with overpotentialsof 131.6-193.8 mV for x = 0.02-0.84in comparison to Ni5P4 NCs (218.1 mV) at a currentdensity of -10 mA/cm(2). Alloying with Zn increasesthe material's stability with only a & SIM;10% increase inoverpotential for Ni4.49Zn0.51P4 NCsat -50 mA/cm(2), whereas a & SIM;33% increase wasobserved for Ni5P4 NCs. At current densitiesabove -40 mA/cm(2), bimetallic NCs with x = 0.10, 0.29, and 0.51 compositions outperformed the benchmark Pt/Ccatalyst, suggesting that hexagonal alloyed Ni5-x Zn x P4 NCsare excellent candidates for practical applications that necessitatelower HER overpotentials at higher current densities.

Assembly of nanoparticles (NPs) into functional macrostructures is imperative for the development of NP-based devices. However, existing methods employ insulating organic ligands, polymers, and biomolecules as mediators for the NP assembly, which are detrimental for charge transport and interparticle coupling that impede the efficient integration of low-dimensional properties. Herein, we report a methodology for the direct self-supported assembly of Ag/Pt/Pd alloy NPs into high surface area (119.1 ± 3.9 to 140.1 ± 5.7 m2/g), mesoporous (19.7 ± 6.2 to 23.0 ± 1.6 nm), and conducting nanostructures (aerogels) that show superior electrocatalytic activity and stability in methanol (MOR) and ethanol (EOR) oxidation reactions. Ultrasmall (3.9 ± 1.3 nm) and quasi-spherical Ag/Pt/Pd alloy NPs were synthesized via stepwise galvanic replacement reaction (GRR) of glutathione (GSH)-coated Ag NPs. As-synthesized NPs were transformed into free-standing alloy hydrogels via chemical oxidation of the GSH ligands. The composition of alloy aerogels was tuned by varying the oxidant/thiolate molar ratio of the precursor NP sol that prompts Ag dealloying with in situ generated HNO3, selectively enriching the Pt and Pd catalytic sites on the aerogel surface. The highest-performing alloy aerogel (Ag0.449Pt0.480Pd0.071) demonstrates excellent mass activity for methanol (3179.5 mA/mg) and ethanol (2444.5 mA/mg) electro-oxidation reactions, which are ∼4-5 times higher than those of commercial Pt/C and Pd/C electrocatalysts. The aerogel also maintained high alcohol oxidation activity for 17 h at a constant potential of -0.3 V in an alkaline medium. The synergistic effects of noble metal alloying, high surface area and mesoporosity, and the pristine active surface of aerogels provide efficient interaction of analytes with the nanostructure surface, facilitating both MOR and EOR activity and improving tolerance for poisonous byproducts, enabling the Ag/Pt/Pd alloy aerogel a promising (electro)catalyst for a number of new technologies.

Ge1-xSnx alloy nanocrystals (NCs) are a class of semiconductors that show interesting (photo)physical properties such as composition-dependent visible to near-IR energy gaps and enhanced light- matter interactions compared to single element Ge NCs. With decreasing size and increasing Sn content, the molar absorptivity and emission efficiency increase, making these NCs attractive for optoelectronic, molecular imaging, and sensing studies. To further improve the optical stability, there is a need to passivate the Ge1-xSnx surface with a robust shell material to protect the core from oxidation and inhibit chemical exchange when exposed to extreme environments. Herein, we report a fluent synthetic method for the growth of a thin silica layer on bulk-like (14.9 +/- 1.7 nm) and quantum-confined (4.4 +/- 0.6 nm) Ge1-xSnx NCs. Physical characterization of Ge1-xSnx/SiO2 core/shell NCs suggests that the diamond cubic structure of the core is retained upon shell growth, whereas solid-state and solution-state absorption spectra confirm the composition-dependent energy gap tunability. The core-shell NCs (1.23-2.07 eV for x = 0.03-0.09) show an average energy gap increase of 0.38 eV relative to the core NCs (0.91-1.67 eV for x = 0.03-0.09) owing to minor surface etching induced by shell growth. Surface analysis of core-shell NCs suggests a notable decrease in Ge2+ species and greater dominance of Ge0 species relative to the organically passivated Ge1-xSnx core NCs, confirming the production of robust, oxidation-resistant, and optically stable Ge1-xSnx/SiO2 alloy NCs.

The ability to assemble nanoparticles (NPs) into functional nanostructures is critical for the advancement of nanoscience. However, common assembling techniques utilize organic ligands or biomolecules, which are detrimental for charge transport and interparticle coupling and impede the efficient integration of low-dimensional properties. Herein, we report a methodology for the self-supported assembly of ultrasmall (3-6 nm) Au/Ag/Pt alloy NPs into large, freestanding alloy superstructures (aerogels) that exhibit direct NP connectivity, high surface area (125 +/- 0.43 to 142 +/- 0.93 m(2)/g) and mesoporosity (21.6 +/- 2.2 nm), and superior electrocatalytic activity for the methanol oxidation reaction (MOR). Precursor Au/Ag/Pt alloy NPs and hydrogels were synthesized via a stepwise galvanic replacement reaction (GRR) of glutathione (GSH)-coated Ag NPs, followed by oxidative removal of the surfactant ligands. The composition of alloy aerogels was tuned by varying the oxidant/GSH molar ratio, which governs the extent of Ag dealloying with in situ generated HNO3 and increases the exposure of Au and Pt on the aerogel surface. The alloy aerogels exhibit superior MOR mass activity, which is 21.4 and 2.5 times higher than that of the precursor NPs and commercial Pt (40 wt %)/C electrocatalysts, respectively. The MOR surface-specific activity (MOR-SSA) of the aerogels was improved by >17% when the Pt content was increased from 22.4 to 31.2%. The aerogels exhibit improved electronic conductivity and enhanced tolerance for carbonaceous byproducts and maintained similar to 94% of the initial MOR activity at -0.3 V for 24 h in alkaline medium. The interconnected porous superstructure of the aerogel provides a facile conduit for molecules to reach the pristine active surface, whereas the presence of oxophilic Au promotes the dissociative adsorption of methanol, providing the Au/Ag/Pt alloy aerogel as a high-efficiency, durable electrocatalyst for the next generation of energy conversion studies.

Metal–semiconductor hybrid nanomaterials (HNMs) exhibit unique properties that are distinct from individual nanostructures, leading to promising applications in optical technologies. The interfacial linkage of semiconductor and metal nanoparticles (NPs) via cogelation is an effective strategy to produce HNMs that show strong plasmon‐exciton coupling and improved physical properties. However, optical properties of these hybrids show little to no tunability. Herein, CdSe/Ag hybrid aerogels that show tunable absorption and photoluminescence (PL) are produced by cogelation of CdSe nanorods (NRs) or NPs with Ag hollow NPs. Hybrid electronic states are created by overlapping the excitonic absorption of CdSe NRs or NPs with the plasmonic absorption of Ag NPs. Physical characterization of the hybrids reveals an interconnected network of hexagonal CdSe and cubic Ag NPs, linked by Ag + and Se 2− surface species, without intervening ligands. PL spectra exhibit maxima at 640 and 720 nm for the CdSe NPs/Ag and CdSe NRs/Ag hybrids, respectively, corresponding to new radiative decay mechanisms. Time‐resolved PL data support the emergence of new radiative pathways, kinetically and energetically distinct from the excitonic and plasmonic properties of primary NPs. This new approach of metal–semiconductor hybrid formation through cogelation is intriguing for the design of high‐efficiency HNMs without detrimental PL quenching.

Ge1-xSnx nanocrystals (NCs) are a class of direct-gap semiconductors that show size- and composition-tunable energy gaps and enhanced absorption and emission properties compared to single-element Ge NCs. With decreasing size and increasing Sn content, optical transition oscillator strength and absorption increases, making these NCs attractive for optoelectronic devices, field effect transistors, and charge storage applications. Herein, we report the synthesis of Ge1-xSnx NCs with varying sizes (ranging from 4.7 +/- 0.6 to 8.6 +/- 1.9 nm) and varying Sn compositions (x = 0.01-0.08), followed by successful exchange of insulating surfactant ligands with molecular metal chalcogenides (MCCs), to produce solution-processed conductive NC thin films. Structural and surface analysis of pre- and post-exchanged NCs indicates a diamond cubic structure and replacement of amine surface ligands with the MCC. Electron micrographs of alloy NCs show a notable decrease in size upon ligand exchange, which is consistent with the etching induced by chalcogenide ligands. The size confinement effects have resulted in energy gaps that are significantly blue-shifted from bulk Ge for the Ge1-xSnx alloy quantum dots with composition-tunable solution-state (1.68-1.26 eV for x = 0.01-0.08) energy gaps and solid-state (1.54-1.20 eV for x = 0.01-0.08) absorption onsets. Electrical characterization of the uniform NC films (thickness = 197 +/- 5 nm) reveals that the films are insulating prior to ligand exchange and show >3 orders of magnitude increase in conductivity (3.5 x 10(-6) S/cm for Ge0.92Sn0.08 NCs) upon functionalization with MCC. The electrical conductivity of the films increases with the increasing Sn composition (1.2 x 10(-6)-3.5 x 10(-6) S/cm for x = 0.01-0.08), which is consistent with the increased spin-orbital coupling and reduction in energy gaps realized through homogeneous alloying of cubic Ge and alpha-Sn.

Although germanium (Ge) is a semiconductor frequently used in many facets of materials science, its optical applications are limited because of an indirect band structure, which significantly diminishes absorption and emission efficiency. However, sufficiently high levels of tin (Sn) alloying enable an indirect-to-direct band structure crossover, resulting in improved optical properties. Moreover, the bandgap of GeSn alloys can be tuned by simply varying the alloy composition; therefore, the material can be modified for compatibility with silicon (Si) based electronics. While lattice mismatch makes the solubility of Sn in Ge extremely low in bulk alloys (<1%), metastable nanoalloys produced under nonequilibrium conditions show minimum to no lattice strain, allowing the synthesis of GeSn nanoalloys with wider tunability of Sn (up to 95%). Furthermore, the size-tunable confinement energy characteristic of GeSn nanoalloys has been shown to greatly increase the energy gaps, resulting in tunable visible to near-IR optical properties. Herein, the authors summarize recent advances in the synthesis of 0D and 1D GeSn alloy nanostructures and their emerging physical properties in light of their potential applications in advanced electronic and photonic technologies.

Electrochemical water splitting represents a sustainable method to produce molecular hydrogen, a foreseeable clean energy alternative to exhaustible fossil fuels. Transition-metal phosphides (TMPs) are emerging as earth-abundant catalysts for water splitting, and their activity can be further improved by incorporation of synergetic metals to produce bimetallic TMP catalysts. Herein, two distinct colloidal chemistry methods were developed to produce discrete nickel molybdenum phosphide (Ni-Mo-P) nanoparticles (NPs) that show varying crystal structures, morphologies, and compositions as alkaline hydrogen evolution reaction (HER) catalysts. The one-pot route produced smaller homogeneous NPs, ranging from 4 to 11 nm, with a nearspherical morphology. The two-pot synthesis resulted in larger heterogeneous NPs, ranging from similar to 50 to 80 nm, with a polygonal morphology. Both nanostructures show either a hexagonal Ni2P or tetragonal Ni12P5 crystal structure and a shift in X-ray diffraction patterns to lower 2 theta angles, consistent with the formation of bimetallic TMPs. The X-ray photoelectron spectra indicate the presence of partially charged core species (Ni delta+, Mo delta+, and P delta-) as well as minor higher valent (Nin+, Mon+, and PO43-, n >= 2) surface species, presumably bound to surfactant ligands and/or oxides. Among heterogeneous and homogeneous NPs investigated, the hexagonal Ni2-xMoxP NPs show lower overpotentials (i.e., high HER activity) in comparison to tetragonal Ni12-xMoxP5 NPs. The HER activity of both nanostructures follows a mixed Volmer-Heyrovsky reaction mechanism consistent with Tafel slopes of 49.5-100.6 mV/dec. The homogeneous and heterogeneous Ni1.87Mo0.13P NPs showed the lowest overpotentials of 101 and 96 mV, respectively, and outperformed both hexagonal Ni2P (156 mV) and tetragonal Ni12-xMoxP (198 mV) NPs at a current density of -10 mA/cm(2). This work provides insights into the design and synthesis of high-efficiency TMP nanostructures for alkaline HER studies.