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High-entropy alloys and compounds have emerged as an attractive research area in part because of their distinctive solid-solution structure and multi-element compositions that provide near-limitless tailorability. A diverse array of reports describing high-entropy compounds, including carbides, nitrides, sulfides, oxides, fluorides, silicides, and borides, has resulted. Strikingly, exploration of high-entropy germanides (HEGs) has remained relatively limited. In this study, we present a detailed investigation into the synthesis of HEGs, specifically AuAgCuPdPtGe and FeCoNiCrVGe, viaa rapid thermal annealing. The structural, compositional, and morphological characteristics of the synthesized HEGs were assessed using laboratory X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Complementing these post-synthesis analyses, we interrogated the formation and growth mechanisms using in situheating XRD and TEM and determined that HEG formation involved initial decomposition of germanane (GeNSs) during the annealing, followed by gradual grain growth viaatom diffusion at temperatures below 600 °C, and finally a rapid grain growth process at elevated temperatures.

Crystalline silicon particles sustaining Mie resonances are readily obtained from the thermal processing of hydrogen silsesquioxane (HSQ). Here, the mechanisms involved in silicon particle formation and growth from HSQ are investigated through real-time in situanalysis using an environmental transmission electron microscope and X-ray diffractometer. The nucleation of Si nanodomains is observed starting around 1000 °C. For the first time, a highly mobile intermediate phase is experimentally observed, thus demonstrating a previously unknown growth mechanism. At least two growth processes occur simultaneously: the coalescence of small particles into larger particles and growth mode by particle displacement through the matrix toward the HSQ grain surface. Postsynthetic characterization by scanning electron microscopy further supports the latter growth mechanism. The gaseous environment employed during synthesis impacts particle formation and growth under both in situand ex situconditions, impacting the particle yield and structural homogeneity. Understanding the formation mechanisms of particles provides promising pathways for reducing the energy cost of this synthetic route.

The unique solid-solution structure and multi-element compositions of high-entropy alloy nanoparticles (HEA NPs) have garnered substantial attention. Various methods have been developed to prepare a diverse array of HEA NPs using different substrates for support and stabilization. In this study, we present a facile surface-mediated reduction method to prepare HEA NPs (AuAgCuPdPt) decorated germanane (HEA NPs@GeNSs), and employ X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) to characterize their structure, composition, and morphology. Subsequently, we demonstrate that the HEA NPs can be liberated from the surfaces of GeNSs as freestanding systems viastraightforward exposure to UV light. We also explore germanium nanoparticles (GeNPs) as an alternative substrate for HEA NP formation/production, given their similarity to germanane and their Ge–H surface. Finally, we extend our investigation to bulk Ge wafers and demonstrate successful deposition of HEA NPs.

Silicon on silica materials are ubiquitous in 21st century technology. From nanoparticles to integrated circuits, these systems are integral for modern semiconductor fabrication. While the Si–SiO2interface is often (incorrectly) presumed to be stable, the direct reduction of silica by silicon is possible at high temperatures, resulting in the evolution of silicon monoxide (SiO) gas. Under appropriate conditions, this somewhat unexpected reaction can complicate solid state nanomaterial syntheses by etching away the desired products. This report describes an investigation into the SiO evolution reaction by interrogation of powdered Si–SiO2mixtures before and after thermal treatment. The impacts of processing temperature, time, and sample composition are examined and discussed. Of particular importance, this investigation reveals the underappreciated role of silica crystallinity (cristobalite) in this solid-state reaction under comparatively low temperature conditions (ca.1200 °C). With an improved understanding of SiO evolution, we hope to inspire new creative pathways for Si–SiO2interface manipulation.

Sensitizing crystalline silicon (c-Si) with an infrared-sensitive material, such as lead sulfide (PbS) colloidal quantum dots (CQDs), provides a straightforward strategy for enhancing the infrared-light sensitivity of a Si-based photodetector. However, it remains challenging to construct a high-efficiency photodetector based upon a Si:CQD heterojunction. Herein, we demonstrate that Si surface passivation is crucial for building a high-performance Si:CQD heterojunction photodetector. We have studied one-step methyl iodine (CH3I) and two-step chlorination/methylation processes for Si surface passivation. Transient photocurrent (TPC) and transient photovoltage (TPV) decay measurements reveal that the two-step passivated Si:CQD interface exhibits fewer trap states and decreased recombination rates. These passivated substrates were incorporated into prototype Si:CQD infrared photodiodes, and the best performance photodiode based upon the two-step passivation shows an external quantum efficiency (EQE) of 31% at 1280 nm, which represents a near 2-fold increase over the standard device based upon the one-step CH3I passivated Si.

Polygermanes are germanium-based analogues of polyolefins and possess polymer backbones made up catenated Ge atoms. In the present contribution we report the preparation of a germanium polyethylene analogue, polydihydrogermane (GeH2)n, via two straightforward approaches that involve topotactic deintercalation of Ca ions from the CaGe Zintl phase. The resulting (GeH2)npossesses morphologically dependent chemical and electronic properties and thermally decomposes to yield amorphous hydrogenated Ge. We also show that the resulting (GeH2)nprovides a platform from which functionalized polygermanes can be prepared via thermally induced hydrogermylation-mediated pendant group substitution.

Luminescent silicon nanoparticles have been widely recognized as an alternative for metal-based quantum dots (QDs) for optoelectronics partly because of the high abundance and biocompatibility of silicon. To date, the broad photoluminescence line width (often >100 nm) of silicon QDs has been a hurdle to achieving competitive spectral purity and incorporating them into light-emitting devices. Herein we report fabrication and testing of straightforward configuration of Fabry–Pérot resonators that incorporates a thin layer of SiQD–polymer hybrid/blend between two reflective silver mirrors; remarkably these devices exhibit up-to-14-fold narrowing of SiQD emission and achieve a spectral bandwidth as narrow as ca. 9 nm. Our polymer-based, SiQD-containing Fabry–Pérot resonators also provide convenient spectral tunability, can be prepared using a variety of polymer hosts and substrates, and enable rigid as well as flexible devices.

Quantum dots (QDs) are semiconductor nanoparticles that exhibit photoluminescent properties useful for applications in the field of diagnostics and medicine. Successful implementation of these QDs for bio-imaging and bio/chemical sensing typically involves conjugation to biologically active molecules for recognition and signal generation. Unfortunately, traditional and widely studied QDs are based upon heavy metals and other toxic elements (e.g., Cd- and Pb-based QDs), which precludes their safe use in actual biological systems. Silicon quantum dots (SiQDs) offer the same advantages as these heavy-metal-based QDs with the added benefits of nontoxicity and abundance. The preparation of functional bio-inorganic hybrids from SiQDs and biomolecules has lagged significantly compared to their traditional toxic counterparts because of the challenges associated with the synthesis of water-soluble SiQDs and their relative instability in aqueous environments. Advances in SiQD synthesis and surface functionalization, however, have made possible the preparation of functional bio-inorganic hybrids from SiQDs and biological molecules through different bioconjugation reactions. In this contribution, we review the various bioconjugate reactions by which SiQDs have been linked to biomolecules and implemented as platforms for bio-imaging and bio/chemical sensing. We also highlight the challenges that need to be addressed and overcome for these materials to reach their full potential. Lastly, we give prospective applications where this unique class of nontoxic and biocompatible materials can be of great utility in the future.

Nanostructured Ge is considered a highly promising material for Li-ion battery applications as Ge offers high specific capacity and Li-ion diffusivity, while inherent mesoporous nanostructures can contribute resistance against capacity fading as typically induced by high volume expansion in bulk Ge films. Mesoporous GeOx/Ge/C films are synthesized using K4Ge9Zintl clusters as a Ge precursor and the amphiphilic diblock copolymer polystyrene-block-polyethylene oxide as a templating tool. As compared to a reference sample without post-treatment, enhanced surface-to-volume ratios are achieved through post-treatment with a poor-good azeotrope solvent mixture. High capacities of over 2000 mA h g–1are obtained with good stability over 300 cycles. Information from morphological and compositional characterization for both reference and post-treated sample suggests that the good electrochemical performance originates from reversible GeO2conversion reactions.

“Two quantum dots, both alike in composition, but differing in structure, where we lay our scene, From broader classes, to bring deeper understanding, to the crystalline core that drives the quantum dot’s sheen.” In this contribution we examine two families of silicon quantum dots (SiQDs) that bring to mind the Capulets and the Montagues in Shakespeare’s Romeo and Juliet because of their stark similarities and differences. SiQDs are highly luminescent, heavy-metal-free, and based upon earth-abundant elements. As such, they have attracted attention for far-reaching applications ranging from biological imaging to luminescent solar concentrators to light-emitting diodes that rely on their size-dependent optical response. Unfortunately, correlating SiQDs “size” to their photoluminescence (PL) maximum is often challenging. Herein, we provide essential structural insight into the correlation between the dimensions and PL maximum of SiQDs through a direct comparison of samples that exhibit statistically identical physical dimensions (dTEM) and chemical compositions but different crystallite size (dXRD) and PL maxima. We then expand the scope of this investigation and systematically compare groupings of SiQDs: one in which the dXRDand dTEMagree and one where dXRD< dTEM. This latter comparison clearly shows that dXRDbetter predicts SiQD optical response when using the well-established effective mass approximation.

Covalently bonded organic monolayers play important roles in defining the solution processability, ambient stability, and electronic properties of two-dimensional (2D) materials such as germanium nanosheets (GeNSs); they also hold promise of providing avenues for the fabrication of future generation electronic and optical devices. Functionalization of GeNSs normally involves surface moieties linked through covalent Ge–C bonds. In the present contribution we extend the scope of surface linkages to include Si–Ge bonding and present the first demonstration of heteronuclear dehydrocoupling of organosilanes to hydride-terminated GeNSs obtained from the deintercalation and exfoliation of CaGe2. We further exploit this new surface reactivity and demonstrate the preparation of directly bonded silicon quantum dot–Ge nanosheet hybrids.

Nanoparticles (NPs) continue to be developed as labels for bioanalysis and imaging due to their small size and, in many cases, emergent properties such as photoluminescence (PL) and superparamagnetism. Some applications stand to benefit from amplification of the advantageous properties of a NP, but this amplification is not a simple matter of scaling for size-dependent properties. One promising approach to amplification is, therefore, to assemble many copies of a NP into a larger but still nanoscale and colloidal entity. Here, we use multiple types of hydrophobic nanocrystal to show that amphiphilic dextran is a versatile material for the preparation and surface functionalization of such super-NP assemblies: CdSe/CdS/ZnS quantum dots (QDs), InP/ZnS QDs, and Si QDs; iron oxide magnetic NPs (MNPs); composites of QDs and MNPs; and composites of QDs and MNPs with fluorene-based and phenylenevinylene-based conjugated polymers. The amphiphilic dextran was also useful for the preparation of conjugated polymer NPs (CPNs) without the inclusion of inorganic nanocrystals. The prepared super-NPs and CPNs were characterized, physically and photophysically, at both the ensemble and the single-particle levels. Per colloidal entity, the super-QDs were orders of magnitude brighter than the individual QDs. This enhancement enabled assemblies of nominally more benign InP/ZnS and Si QDs to be competitive alternative materials to CdSe/CdS/ZnS QDs, which are normally much brighter when compared as individual nanocrystals. The dextran functionalization imparted low nonspecific binding and enabled the use of tetrameric antibody complexes (TACs) for simple and selective immunolabeling of cells with all of the prepared super-NP, CPN, and composite materials. Labeling with the super-QDs provided significantly enhanced PL signals, the super-MNPs enabled magnetic pull-down of cells, and both capabilities were concurrently available with composite assemblies. Overall, this study demonstrates that the preparatory method and functional benefits of amphiphilic dextran extend to a range of hydrophobic materials and combinations thereof. There is strong potential for assembling a diverse set of property-amplified designer labels that are ready-made for in vitroapplications in bioanalysis and imaging.

Despite the widespread use of hydrofluoric acid (HF) in the preparation of silicon surfaces, the true nature of fluorinated surface species remains unclear. Here, we employ an array of characterization techniques led by solid-state nuclear magnetic resonance spectroscopy to uncover the nature of fluorinated moieties on the surface of hydride-terminated silicon nanoparticles (H-SiNPs). A structural model that explains the observed trends in 19F and 29Si magnetic shielding is proposed and further supported by quantum chemical computations. Fluorine is incorporated into local oxidation domains on the surface and clustered at the interface of the oxide and surrounding hydride-terminated surface. Silicon sites capped by a single fluorine are also identified by their distinct 19F and 29Si chemical shifts, providing insight into how fluorine termination influences the electronic structure. The extent of fluorine passivation and the effects of fluorine on the optical properties of SiNPs are also discussed. Finally, challenges associated with Teflon contamination are highlighted that future explorations of nanomaterials may have to contend with.

Ratiometric photoluminescent detection of the toxicologically potent organophosphate ester nerve agents paraoxon (PX) and parathion (PT) using the complementary optical and chemical properties of the long Stokes shift green fluorescent protein variant, mAmetrine1.2 (mAm), and red-emitting silicon-based quantum dots (SiQDs) is reported. PX and PT selectively quench SiQD photoluminescence (PL) through a dynamic quenching mechanism, thereby, facilitating the development of a ratiometric sensor platform that shows micromolar limits of detection for PX and PT and that is unaffected by the presence of common inorganic and organic interferents. As a part of the present study, we also demonstrate that the paper-based sensors derived from mAm and SiQDs detect PX and PT at concentrations as low as 5 μM using a readily available commercial color analysis smartphone “app”. The ratiometric sensor reported herein can potentially be used for the convenient and rapid on-site detection and quantification of PX and PT in real-world samples.

Silicon nanoparticles (SiNPs) are biologically compatible, metal-free quantum dots that exhibit size and surface tailorable photoluminescence. The nanostructure of these materials influences their optical, chemical, and material properties and hence plays an important role in their future-generation applications in sensors, battery electrodes, optical materials, and contrast agents, among others. In this work, we employ a complement of methods including X-ray photoelectron spectroscopy (XPS), bright-field transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy to interrogate the bulk structure of hydride-terminated SiNPs (H-SiNPs) ranging from 3 to 64 nm in diameter and effectively probe their surface. By applying these methods, we have demonstrated that H-SiNPs consist of a size dependent layered structure made up of surface, subsurface, and core silicon regimes. The surface silicon species are manifested by a broad underlying feature in the corresponding 29Si NMR spectra between −80 to −120 ppm for small nanoparticles (NPs), whereas the sharp resonance at higher frequency (ca. −80.9 ppm, 1 ppm full-width at half-maximum) present in large NPs is attributed to a well-ordered crystalline silicon core. A critical size junction has been identified for 9 nm H-SiNPs, where XPS and NMR show features arising from surface, subsurface, and core silicon species features arising from surface, subsurface, and core silicon species. This structural insight provides essential understanding and potential advancement in the development of SiNP-based applications in photovoltaics, battery anodes, and sensors.

Amphiphilic nanoparticles (AP-NPs) are attractive for many far-reaching applications in diverse sectors. Amphiphilic silicon nanocrystals (AP-SiNCs) are particularly promising for luminescence-based bioimaging, biosensing, and drug delivery because of their size- and surface chemistry-dependent photoluminescence (PL), high PL quantum yield, long-term photostability, and robustness to bioconjugation. Numerous studies demonstrated the synthesis of high-quality SiNCs that are compatible with organic solvents. However, preparing water-soluble SiNCs while maintaining their attractive PL properties is very challenging, and to date, only one report of blue-emitting AP-SiNCs has appeared. This report outlines a straightforward one-step thermal hydrosilylation approach that affords AP-SiNCs soluble in aqueous media in high concentrations (i.e., 14.4 mg/mL silicon core-based), exhibit bright long-lived PL in the red/near-infrared spectral region, are biocompatible, and present bioconjugable surface groups.

Silicon is recognized as a promising anode material for high-performance lithium ion batteries due to its high theoretical specific capacity and elemental abundance. Challenges related to the low electrical conductivity of Si and large volume changes during the lithiation/delithiation cycles, as well as the low rate of lithium diffusion in silicon anodes, hinder practical applications. To provide fundamental insights into these issues, silicon nanocrystal/graphene aerogel nanocomposites were synthesized by combining undecanoic acid-functionalized silicon nanocrystals of various sizes (SiX-COOH, where Xrepresents the nanocrystal diameter of 3, 5, 8, and 15 nm) with conductive mesoporous graphene aerogels (GAs). The silicon nanocrystals are evenly dispersed throughout the graphene aerogel as shown by energy-dispersive X-ray (EDX) mapping. In terms of electrochemical performance, SiX-COOH/GA nanocomposites demonstrated a clear dependence on the size of the embedded silicon nanocrystals, with the composites comprising the larger silicon nanocrystals showing a higher initial capacity but accompanied by rapid decay of capacity retention over 100 cycles. To study the effect of thermal processing on the electrochemical performance, SiX-COOH/GA nanocomposites were annealed at 600 °C to yield annealed SiX/GA nanocomposites. The annealed nanocomposite composed of the smallest silicon nanocrystals, Si3/GA, exhibits a stable specific capacity of ∼1100 mAh/g and capacity retention of over 90% after 500 cycles when tested at a current density of 400 mA/g.

We introduce a straightforward and cost-effective water-assisted approach to transfer patterns of nanomaterials onto diverse substrates. The transfer method relies on the hydrophobic effect and utilizes a water-soluble polymer film as a carrier to transfer hydrophobic nanomaterials from a patterned source substrate onto a target substrate. Using this approach, nanomaterials are transferred readily from solutions onto surfaces of various shapes and compositions with high fidelity for feature sizes approaching 10 microns.

Germanium nanocrystals (GeNCs) hold great promise as active materials in many applications including solar cells, biological imaging, Bragg reflectors, light-emitting diodes, and nonvolatile memory devices. However, because of the size-, shape-, and composition-dependent nature of their properties, it is essential that methods affording high-purity, well-defined GeNCs be developed. Herein, we report a systematic investigation of a series of “Ge(OH)2” precursors using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and solid-state 73Ge NMR and correlate their properties with the GeNCs obtained from their thermal processing. This study provides important insights into the role of the Ge(OH)2internal structure and will allow for future rational design and practical application of GeNCs.

Thiol–ene polymer/Si nanocrystal bulk hybrids were synthesized from alkyl-passivated Si nanocrystal (Si NC) toluene solutions. Radicals in the polymer provided a copassivation of “dark” Si NCs, making them optically active and leading to a substantial ensemble quantum yield increase. Optical stability over several months was confirmed. The presented materials exhibit the highest photoluminescence quantum yield (∼65%) of any solid-state Si NC hybrid reported to date. The broad tunability of thiol–ene polymer reactivity provides facile glass integration, as demonstrated by a laminated structure. This, together with extremely fast polymerization, makes the demonstrated hybrid material a promising candidate for light converting applications.

Environmental contextThe fate of nanomaterials in the environment is related to their colloidal stability. Although numerous studies have examined their homoagglomeration, their low concentration and the presence of high concentrations of natural particles implies that heteroagglomeration rather than homoagglomeration is likely to occur under natural conditions. In this paper, two state-of-the art analytical techniques were used to identify the conditions under which nanosilver was most likely to form heteroagglomerates in natural waters. AbstractThe environmental risk of nanomaterials will depend on their persistence, mobility, toxicity and bioaccumulation. Each of these parameters is related to their fate (especially dissolution, agglomeration). The goal of this paper was to understand the heteroagglomeration of silver nanoparticles in natural waters. Two small silver nanoparticles (nAg, ~3nm; polyacrylic acid- and citrate-stabilised) were covalently labelled with a fluorescent dye and then mixed with colloidal silicon oxides (SiO2, ~18.5nm) or clays (~550nm SWy-2 montmorillonite). Homo- and heteroagglomeration of the nAg were first studied in controlled synthetic waters that were representative of natural fresh waters (50μg Ag L-1; pH 7.0; ionic strength 10-7 to 10-1 M Ca) by following the sizes of the nAg by fluorescence correlation spectroscopy. The polyacrylic acid-coated nanosilver was extremely stable under all conditions, including in the presence of other colloids and at high ionic strengths. However, the citrate-coated nanosilver formed heteroaggregates in presence of both colloidal SiO2 and clay particles. Nanoparticle surface properties appeared to play a key role in controlling the physicochemical stability of the nAg. For example, the polyacrylic acid stabilized nAg-remained extremely stable in the water column, even under conditions for which surrounding colloidal particles were agglomerating. Finally, enhanced dark-field microscopy was then used to further characterise the heteroagglomeration of a citrate-coated nAg with suspensions of colloidal clay, colloidal SiO2 or natural (river) water.

Surface-engineered amphiphilic polymer-coated silicon nanoparticles (SiNPs) were employed as photocatalysts to capture and degrade a model organic contaminant (methanol) in water. This study represents the first time SiNPs have been employed in the initiation of advanced oxidation processes that are commonly used to degrade organic constituents in industrial wastewaters. The quantum yield of photocatalytic methanol oxidation and the corresponding yield factor for the generation of active OH radicals are reported. The size and surface defect dependent photocatalytic activity of SiNPs was investigated. The yield factors (η) decreased with increasing particle size and reached impressive values that exceeded that of equivalent TiO2nanoparticle systems by 3–4 times and are comparable to the robust UV/Cl2and UV/H2O2systems. The higher photocatalytic efficiency of SiNPs is attributed to the combined effects of quantum confinement, effective band gap, and surface states, among which surface states play a dominant role. SiNPs provide a potentially tunable, biologically inert, and robust nanoparticle system for photocatalytic oxidation of wastewater contaminants.

Spectrally resolved photoluminescence (PL) decays were measured for samples of colloidal, ligand-passivated silicon nanocrystals. These samples have PL emission energies with peak positions in the range ∼1.4–1.8 eV and quantum yields of ∼30–70%. Their ensemble PL decays are characterized by a stretched-exponential decay with a dispersion factor of ∼0.8, which changes to an almost monoexponential character at fixed detection energies. The dispersion factors and decay rates for various detection energies were extracted from spectrally resolved curves using a mathematical approach that excluded the effect of homogeneous line width broadening. Since nonradiative recombination would introduce a random lifetime variation, leading to a stretched-exponential decay for an ensemble, we conclude that the observed monoexponential decay in size-selected ensembles signifies negligible nonradiative transitions of a similar strength to the radiative one. This conjecture is further supported as extracted decay rates agree with radiative rates reported in the literature, suggesting 100% internal quantum efficiency over a broad range of emission wavelengths. The apparent differences in the quantum yields can then be explained by a varying fraction of “dark” or blinking nanocrystals.

The syntheses of colloidal silicon nanocrystals (Si-NCs) with dimensions in the 3–4 nm size regime as well as effective methodologies for their functionalization with alkyl, amine, phosphine, and acetal functional groups are reported. Through rational variation in the surface moieties we demonstrate that the photoluminescence of Si-NCs can be effectively tuned across the entire visible spectral region without changing particle size. The surface-state dependent emission exhibited short-lived excited-states and higher relative photoluminescence quantum yields compared to Si-NCs of equivalent size exhibiting emission originating from the band gap transition. The Si-NCs were exhaustively characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transformed infrared spectroscopy (FTIR), and their optical properties were thoroughly investigated using fluorescence spectroscopy, excited-state lifetime measurements, photobleaching experiments, and solvatochromism studies.

Silicon nanocrystals (Si NCs) are attractive functional materials. They are compatible with standard electronics and communications platforms and are biocompatible. Numerous methods have been developed to realize size-controlled Si NC synthesis. While these procedures produce Si NCs that appear identical, their optical responses can differ dramatically. Si NCs prepared using high-temperature methods routinely exhibit photoluminescence agreeing with the effective mass approximation (EMA), while those prepared viasolution methods exhibit blue emission that is somewhat independent of particle size. Despite many proposals, a definitive explanation for this difference has been elusive for no less than a decade. This apparent dichotomy brings into question our understanding of Si NC properties and potentially limits the scope of their application. The present contribution takes a substantial step forward toward identifying the origin of the blue emission that is not expected based upon EMA predictions. It describes a detailed comparison of Si NCs obtained from three of the most widely cited procedures as well as the conversion of red-emitting Si NCs to blue emitters upon exposure to nitrogen-containing reagents. Analysis of the evidence is consistent with the hypothesis that the presence of trace nitrogen and oxygen even at the parts per million level in Si NCs gives rise to the blue emission.

Environmental context The mobility and bioavailability of both contaminants and nutrients in the environment depends, to a large extent, on their diffusion. Because the majority of microorganisms in the environment are embedded in biofilms, it is essential to quantify diffusion in biofilms in order to evaluate the risk of emerging contaminants, including nanomaterials and charged solutes. This study quantifies diffusion, in a model environmental biofilm, for a number of model contaminants of variable size and charge. Abstract The effect of solute and biofilm charge on self-diffusion (Brownian motion) in biofilms is examined. Diffusion coefficients (D) of several model (fluorescent) solutes (rhodamine B; tetramethylrhodamine, methyl ester; Oregon Green 488 carboxylic acid, succinimidyl ester and Oregon Green 488 carboxylic acid) and nanoparticles (functionalised silicon, gold and titanium) were determined using fluorescence correlation spectroscopy (FCS). Somewhat surprisingly, little effect due to charge was observed on the diffusion measurements in the biofilms. Furthermore, the ratio of the diffusion coefficient in the biofilm with respect to that in water (Db/Dw) remained virtually constant across a wide range of ionic strengths (0.1–100mM) for both negatively and positively charged probes. In contrast, the self-diffusion coefficients of nanoparticles with sizes >10nm greatly decreased in the biofilms with respect to those in water. Furthermore, much larger nanoparticles (>66nm) appeared to be completely excluded from the biofilms. The results indicated that for many oligotrophic biofilms in the environment, the diffusion of solutes and nanoparticles will be primarily controlled by obstruction rather than electrostatic interactions. The results also imply that most nanomaterials will become significantly less mobile and less bioavailable (to non-planktonic organisms) as they increase in size beyond ~10nm.

We present an X-ray absorption spectroscopic study of the optical and electronic properties of freestanding, alkyl-functionalized silicon nanocrystals (Si-NCs). These materials were derived from thermal processing of hydrogen silsesquioxane, subsequently etched with hydrofluoric acid and functionalized via photochemical hydrosilylation with alkenes. These materials are of interest for their size-dependent photoluminescence (PL), that spans the visible and near-IR regions. Using near-edge X-ray absorption fine structure spectroscopy and X-ray excited optical luminescence, we have investigated the impact of quantum confinement effects and surface species on the Si-NC PL. These materials exhibit PL found to be consistent with the quantum confinement model; however, ambient oxidation was proposed to strongly influence the results.

We present a study of the photochemical hydrosilylation of freestanding silicon nanocrystals (Si-NCs) using a near-UV source. The impact of reaction with alkenes and alkynes was studied using in situphotoluminescence (PL) spectroscopy, allowing measurement of both changes in intensity and PL maxima during the reaction. Understanding this behavior is important for the utilization of these materials in a number of applications where hydrosilylation is a leading method to functionalize Si-NCs. Changes in the PL were studied and shown arise from the influence of oxidation as well as the Si−C bond formation. Hydrosilylation with a range of conjugated alkynyl species was studied to understand how the introduction of these species to the NC surface can quench the PL from Si-NCs. These results were explained in context of the free-radical and exciton-mediated mechanisms for photochemical hydrosilylation proposed for Si-NCs. Materials in this study were characterized by Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), selected electron area diffraction (SAED), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA) and dynamic light scattering (DLS).

Freestanding silicon nanoparticles (FS-nc-Si) have intriguing chemical and optical properties. The present contribution outlines known synthetic methodologies and protocols for surface functionalization. Recent advancements in tailoring the photoluminescence properties of FS-nc-Si and future research directions will be briefly discussed.

The photoluminescent properties of allylamine terminated silicon nanocrystals (Si‐NCs) are investigated. Chloride surface terminated Si‐NCs of different sizes react with allylamine yielding NCs that exhibit size independent blue luminescent NCs. NCs were characterized using X‐ray diffraction, Fourier transformed infrared spectroscopy, photoluminescence spectroscopy, and dynamic light scattering.

Silicon nanocrystals exhibit optoelectronic properties that are favorable for applications such as sensing and biological imaging. Synthesizing a stimuli responsive material with controlled hydrophilicity can benefit these applications. One of the most promising surface species for inducing reversible control of hydrophilicity contains amidine functional groups; unfortunately, this functionality will also bind to the nanocrystal surface and influence the photoluminescence of the material. To combat these limitations, a Lewis acid protection method has been developed to prevent the nitrogen atoms from attaching to the silicon surface for the functionalization of amidine terminated silicon nanocrystals. Silicon nanocrystals (Si‐NCs) have interesting optoelectronic propertiesand amidines are known to switch from hydrophobic to hydrophilic in the presence of CO2due to acid‐base chemistry. By coupling these materials, a phase transferable luminescent material was created that has potential as a removable sensor or in tissue targeting for biological imaging applications.

A new, thermally initiated hydrogermylation-based method for the synthesis and surface functionalization of air- and moisture-stable germanium quantum dots is reported.

Surface chemistry can play an important role in determining the optical properties of silicon nanocrystals. On this page, referring to the article by Mita Dasog and Jonathan G. C. Veinot(pp. 1844–1846) it is shown that by changing the surface of silicon nanocrystals, their emission color can be tuned. Hydride surface terminated silicon nanocrystals emit red/orange whereas, when surface groups attached through nitrogen atoms are present they emit blue. Chloride atoms quench the photoluminescence. The photoluminescence properties are shown as a background together with a transmission electron micrograph image of silicon nanocrystals.

Review: 140 refs.

Iron/iron oxide core shell nanoparticles are a versatile support for immobilizing catalytic metals.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

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