Surface-bound Functional Groups Research Articles

Diamond surface functionalization via visible light–driven C–H activation for nanoscale quantum sensing

Nitrogen-vacancy (NV) centers in diamond are a promising platform for nanoscale NMR sensing. Despite significant progress toward using NV centers to detect and localize nuclear spins down to the single spin level, NV-based spectroscopy of individual, intact, arbitrary target molecules remains elusive. Such sensing requires that target molecules are immobilized within nanometers of NV centers with long spin coherence. The inert nature of diamond typically requires harsh functionalization techniques such as thermal annealing or plasma processing, limiting the scope of functional groups that can be attached to the surface. Solution-phase chemical methods can be readily generalized to install diverse functional groups, but they have not been widely explored for single-crystal diamond surfaces. Moreover, realizing shallow NV centers with long spin coherence times requires highly ordered single-crystal surfaces, and solution-phase functionalization has not yet been shown with such demanding conditions. In this work, we report a versatile strategy to directly functionalize C-H bonds on single-crystal diamond surfaces under ambient conditions using visible light, forming C-F, C-Cl, C-S, and C-N bonds at the surface. This method is compatible with NV centers within 10 nm of the surface with spin coherence times comparable to the state of the art. As a proof-of-principle demonstration, we use shallow ensembles of NV centers to detect nuclear spins from surface-bound functional groups. Our approach to surface functionalization opens the door to deploying NV centers as a tool for chemical sensing and single-molecule spectroscopy.

Tuning the Photoluminescence of Germanium Nanocrystals through Surface Bound Functional Groups

A room temperature, solution phase method for production of size monodisperse germanium nanocrystals (Ge NCs) terminated with different chemical functionalities (epoxy, acetate, amine, carboxylic acid, and alkyl) is reported. Ge NC photoluminescence spectra show that the emission can be tuned from the UV to the blue/green through choice of ligand. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Role of grain boundaries in tailoring electronic properties of polycrystalline graphene by chemical functionalization

Grain boundaries, inevitably present in chemical vapor deposited graphene, are expected to have considerable impact on the development of graphene-based hybrid materials with tailored material properties. We demonstrate here the critical role of polycrystallinity on the chemical functionalization of graphene comparing ozone-induced oxidation with remote plasma hydrogenation. We show that graphene oxidation and hydrogenation occur in two consecutive stages upon increasing defect density: an initial step in which surface-bound functional groups are generated, followed by the creation of vacancies. Remarkably, we find that hydrogenation yields homogeneously distributed defects while ozone-induced defects are preferentially accumulated at the grain boundaries eventually provoking local cracking of the structure. Supported by quantum simulations, our experimental findings reveal distinct electronic transport regimes depending on the density and distribution of induced defects on the polycrystalline graphene films. Our findings highlight the key role played by grain boundaries during graphene functionalization, and at the same time provide a novel perspective to tailor the properties of polycrystalline graphene.

Infrared Reflectance and Emissivity Spectra of Nanodiamonds

ABSTRACT Nanosized diamonds obtained by detonation of explosives are the subject of active studies in several scientific and technological fields. Besides their interesting peculiarities for solid-state physics studies, their presence in various circumstellar environments has been inferred from infrared (IR) spectra. Nanodiamonds are unique materials, allowing investigation of size-dependent properties of matter. We report measurements of IR properties of detonation nanodiamonds in reflectance at room temperature and in emissivity in a dedicated setup at temperatures up to 873 K. The spectra are characterized by the presence of sharp bands due to surface-bound functional groups. Thermal desorption of oxygen-containing groups leads to corresponding spectral changes. The maximal emissivity of nanodiamond powder reaches 0.985.

Grafting a homogeneous transition metal catalyst onto a silicon AFM probe: a promising strategy for chemically constructive nanolithography

We report a novel approach to chemically selective lithography using an atomic force microscope (AFM) probe with immobilized homogeneous catalyst, potentially giving access to diverse nanoscale transformations of the surface-bound functional groups. This new concept was proven for the local epoxidation of an alkene-terminated self-assembled monolayer on silicon using H2O2 as an oxidant and a catalytic silicon AFM tip charged with manganese complexes with 1,3,7-triazacyclononane type ligands.

Surface-Functionalized Polymeric Nanoparticles as Templates for Biomimetic Mineralization of Hydroxyapatite

The use of polymeric nanoparticles as templates for producing inorganic materials is an intriguing approach, as it offers the feasibility of synthesizing organic/inorganic hybrid materials for several interesting applications. Here, polymeric nanoparticles synthesized via the miniemulsion process are employed as templates for biomimetic mineralization of hydroxyapatite in the aqueous phase. The versatile miniemulsion technique allows the fabrication of surface-functionalized polymeric nanoparticles with varying amounts of surface-bound functional groups by use of different types of surfactants. Hybrid nanoparticles were formed by performing crystallization outside on the surface of the polymer nanoparticles by varying the amount of surface functional groups and were studied by high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). These hydroxyapatite/polymer hybrid nanoparticles have great potential to be used as filler or as scaffold for nucleation and growth of new bone material. They offer the feasibility of being injected directly into the damaged part in addition to being applied as coatings on implants. The use of polymeric nanoparticles coated with hydroxyapatite (HAP) for bone repair applications in addition opens new doors for realizing the potential of using the polymeric nanoparticles as carriers of drugs and growth factors to better treat bone defects and promote wound healing.

Quantitative Determination of the Chemical Composition of Silica−Poly(norbornene) Nanocomposites

Nanoparticle hybrid materials consisting of a silica core surrounded by a poly(norbornene) brush have been prepared by ring opening metathesis polymerization (ROMP). A quantitative determination of each stage of composite formation has been accomplished, including a determination of the density of surface-bound functional groups, catalyst molecules, and polymer chains. This analysis has enabled the determination of the reaction efficiency between the catalyst and the surface-bound functional groups as well as the determination of the fraction of metal-mediating species that initiate a polymer chain. Control of the chain density was demonstrated by two methods: the use of controlled reaction times between the catalyst and the surface, and the variation of the surface functional group density. Polymer chain densities resulting from composites prepared with different tether structures will also be reported. The resulting brush densities were found to span a wide range, including those previously reported for polymer layers formed by adsorption, grafting of preformed polymer chains, and surface-initiated polymerization (SIP).

Synthesis, Surface Modification, and Multilayer Construction of Mixed-Monolayer-Protected CdS Nanoparticles

Herein, we describe a study aimed at synthesizing mixed-monolayer-protected CdS nanoparticles and investigating the reactivity of surface-bound functional groups in order to facilitate the immobilization of nanoparticles on a solid substrate as well as the construction of a three-dimensional nanocomposite. CdS nanoparticles initially prepared by the reverse micelle method were used to modify nanoparticle surfaces with 1-decanethiol molecules by ligand exchange. Subsequently, 11-mercapto-1-undecanol was partially incorporated by a place exchange reaction, thereby providing stable, mixed-monolayer-protected CdS nanoparticles. The nanoparticles obtained at each step were characterized by FT-IR and UV-vis spectroscopy, transmission electron microscopy, and elemental analysis. The reactivity of surface hydroxyl groups was verified by a reaction with isocyanate-bearing molecules that provide carbamate bonds in high yields at ambient temperature. The obtained mixed-monolayer-protected nanoparticles were also successfully immobilized on a glass substrate through a carbamate-bond-forming reaction that could be further utilized for multilayer construction in a layer-by-layer fashion.

Acid−Base Properties and the Chemical Imaging of Surface-Bound Functional Groups Studied with Scanning Force Microscopy

In this paper we present a scanning force microscopy (SFM) study on electrostatic and hydrogen-bonding interactions between chemically modified SFM probes and surface functional groups. pH-dependent adhesion force measurements in aqueous media between various ionizable functional groups showed a dependency of the adhesion force on the state of ionization (acid−base properties) of these surface-bound groups. The local degree of ionization and surface pK values can be determined from the obtained “adhesion force titration curves”, which resemble conventional solution pH titration curves. In the presence of a 1:1 electrolyte, the electric double layer was probed and the measured Debye lengths were found to agree with theoretical predictions. pH-dependent lateral force imaging was found to directly map the ionization state of surface-bound functional groups.

Characterization of the chemical architecture of carbon-fiber microelectrodes. 1. Carboxylates

A new method to characterize the chemical architecture of a carbon-fiber microelectrode surface is described. Derivatization of carboxyl groups on the carbon surface with a poly(oxyalkalene)diamine (Jeffamine ED-600), followed by biotinylation of the free amine, allowed the attachment of a fluorescein isothiocyanate (FITC) conjugate of ExtrAvidin. The fluorescence observed after excitation at 488 nm was imaged with a fluorescence microscope equipped with a CCD camera, yielding a spatial map of the distribution of modified carboxyl groups on the surface of the carbon fiber with 0.5-micron resolution. Colloidal gold particles (15 nm diameter) coated with ExtrAvidin were used in place of the FITC-ExtrAvidin, and the carbon-fiber surface was imaged with scanning electron microscopy on a submicron scale. This selective information regarding surface-bound functional groups (i.e. carboxylates) has proven invaluable toward the rational design of novel sensors based on surface-modified ultramicroelectrodes.