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The chemistry of carbon surfaces has regained traction in recent years in view of its applicability towards covalent modification of a variety of (2D) materials. A general requisite is the formation of a dense and well-defined monolayer of aryl groups covalently bound to the surface. Given the use of reactive chemistries however, it is often not easy to achieve precise control over the monolayer growth while maintaining high grafting densities. Here we present a straightforward experimental protocol for the fabrication of well-defined covalent monolayers onto the surface of graphite. Using a combination of surface analytical tools, we demonstrate that the ascorbic acid mediated dediazoniation of aryldiazonium salts leads to self-limiting growth of monolayers with high grafting densities. The aryl radicals preferentially attach to the basal plane of the substrate and once the surface is covered with a covalent monolayer, the surface reaction does not proceed further to an appreciable extent. The layer thickness of the covalent films was measured using atomic force microscopy whereas the grafting efficiencies were assessed using Raman spectroscopy. The chemical composition of the grafted films was studied using X-ray photoelectron spectroscopy whereas scanning tunneling microscopy provided nanometer scale insight into the structure of the covalent films. Mechanistic aspects of the process are also discussed. The self-terminating chemistry described here is a new addition to the synthetic armory for covalent modification of materials and sets a strong foundation for achieving precise nanoscale control over the covalent functionalization process. ispartof: NANOSCALE vol:12 issue:36 pages:18782-18789 ispartof: location:England status: published

The integration of graphene, and more broadly two-dimensional materials, into devices and hybrid materials often requires the deposition of thin films on their usually inert surface. As a result, strategies for the introduction of surface reactive sites have been developed but currently pose a dilemma between robustness and preservation of the graphene properties. A method is reported here for covalently modifying graphitic surfaces, introducing functional groups that act as reactive sites for the growth of high quality dielectric layers. Aryl diazonium species containing tri-methoxy groups are covalently bonded (grafted) to highly oriented pyrolytic graphite (HOPG) and graphene, acting as seeding species for atomic layer deposition (ALD) of Al2O3, a high-κ dielectric material. A smooth and uniform dielectric film growth is confirmed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrical measurements. Raman spectroscopy showed that the aryl groups gradually detach from the graphitic surface during the Al2O3 ALD process at 150 °C, with the surface reverting back to the original sp2-hybridized state and without damaging the dielectric layer. Thus, the grafted aryl groups can act as a sacrificial seeding layer after healing the defects of the graphitic surface with annealing treatment.

Plenty of strategies focused on covalent interaction have been developed to functionalize graphene's surface in order to employ it in a wide range of applications. Among them, the use of radical species including nitrene, carbene and aryl diazonium salts is regarded as a promising strategy to establish the covalent functionalization of graphene. In this work, we highlight the effect of diazonium chemistry on the electronic properties of graphene on SiC. On the basis of X-ray and synchrotron-based photoemission experiments, we were able to prove that 3,4,5-trimethoxybenzenediazonium (TMeOD) units, reduced and chemisorbed onto graphene using electrochemistry, preserve the electronic structure of the Dirac cone, through inducing a slightly additional n-type doping of graphene, as revealed by a downshift of the Dirac cone probed by angle-resolved photoemission experiments. ispartof: NANOSCALE vol:12 issue:16 pages:9032-9037 ispartof: location:England status: published

Controlled covalent functionalization of graphitic surfaces with molecular scale precision is crucial for tailored modulation of the chemical and physical properties of carbon materials. We herein present that porous self-assembled molecular networks (SAMNs) act as nanometer scale template for the covalent electrochemical functionalization of graphite using an aryldiazonium salt. Hexagonally aligned achiral grafted species with lateral periodicity of 2.3, 2.7, and 3.0 nm were achieved utilizing SAMNs having different pore-to-pore distances. The unit cell vectors of the grafted pattern match those of the SAMN. After the covalent grafting, the template SAMNs can be removed by simple washing with a common organic solvent. We briefly discuss the mechanism of the observed pattern transfer. The unit cell vectors of the grafted pattern align along nonsymmetry axes of graphite, leading to mirror image grafted domains, in accordance with the domain-specific chirality of the template. In the case in which a homochiral building block is used for SAMN formation, one of the 2D mirror image grafted patterns is canceled. This is the first example of a nearly crystalline one-sided or supratopic covalent chemical functionalization. In addition, the positional control imposed by the SAMN renders the functionalized surface (homo)chiral reaching a novel level of control for the functionalization of carbon surfaces, including surface-supported graphene. ispartof: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY vol:142 issue:16 pages:7699-7708 ispartof: location:United States status: published

Chemical reaction with diazonium molecules has revealed to be a powerful method for the surface chemical modification of graphite, carbon nanotubes and recently also of graphene. Graphene electronic structure modification using diazonium molecules is strongly influenced by graphene growth and by the supporting materials. Here, carrying on a detailed study of core levels and valence band photoemission measurements, we are able to reconstruct the interface chemistry of trimethoxybenzenediazonium-based molecules electrochemically grafted on graphene on copper. The band energy alignment at the molecule-graphene interface has been traced revealing the energy position of the HOMO band with respect to the Fermi level. ispartof: SCIENTIFIC REPORTS vol:10 issue:1 ispartof: location:England status: published

Grafting of aryl radicals generated by electrochemical reduction of aryldiazonium salts has been extensively studied on various surfaces. However, there exists two unclear aspects; the first one is the generality of the blocking ability of simple functional groups toward multilayer growth, and the second one is the electronic impact of substituent groups of aryl radicals on grafting efficiency. To address these aspects, we have studied the electrochemical functionalization of graphite using aryldiazonium salts having electron-donating or electron-withdrawing groups at the 3,4,5-positions. Atomic force microscopy investigation of the functionalized surfaces revealed the formation of monolayers for all aryldiazonium salts, and thus, nitro, carboxy, ester, methyl, and methoxy groups at the 3,4,5-positions of the benzene ring suppress polyaryl growth. The degree of grafting estimated by scanning tunneling microscopy imaging and Raman spectroscopy of the functionalized surfaces depends on the electronic state of the aryl radicals, in which the radicals with electron-donating groups show a high degree of functionalization, whereas those with electron-withdrawing groups exhibit a low degree of functionalization. We discuss several possibilities that affect grafting density. Though there are several factors, we hypothesize that one factor to explain the observed reactivity trend is the electronic property of the aryl radicals, namely, the relative position of the singly occupied molecular orbital energy levels of the aryl radicals with respect to the graphite Fermi energy level. ispartof: LANGMUIR vol:35 issue:6 pages:2089-2098 ispartof: location:United States status: published

An approach for nanoscale covalent functionalization of graphite surfaces employing self-assembled molecular monolayers of n-alkanes as templating masks is presented. Linearly aligned aryl groups with a lateral periodicity of 5 or 7 nm are demonstrated utilizing molecular templates of different lengths. The key feature of this approach is the use of a phase separated solution double layer consisting of a thin organic layer containing template molecules topped by an aqueous layer containing aryldiazonium molecules capable of electrochemical reduction to generate aryl radicals which bring about surface grafting. Upon sweeping of the potential, lateral displacement dynamics at the n-alkane terminal edges acts in conjunction with electrochemical diffusion to result in templated covalent bond formation in a linear fashion. This protocol was demonstrated to be applicable to linear grafting of graphene. The present processing described herein is useful for the realization of rationally designed nanoscale materials. ispartof: ACS NANO vol:12 issue:11 pages:11520-11528 ispartof: location:United States status: published

Chemisorption on electrode surfaces by means of electrochemical “grafting” of diazonium based compounds has demonstrated the ability to introduce robust functional character to electrode surfaces, i.e., selective binding and recognition. Unfortunately, chemical decomposition of the active diazonium compounds frequently plagues the extent of surface functionalization. Impacts of diazonium degradation on the grafting process can be limited by activation (diazotization) from stable aniline precursors moments before the electrochemical treatment. In this work, we investigate how kinetic control of this diazotization activation reaction impacts the resultant electrochemical grafting on highly oriented pyrolytic graphite (HOPG) electrode surfaces. Using simple aniline precursors, diazotization reactions are carried out with four different protocols: ex situ activation, ex situ activation & stirring, in situ activation, and in situ activation & stirring. The resultant HOPG electrode surfaces are analyzed using scanning tunneling microscopy and Raman spectroscopy, to reveal hindered surface functionalization from in situ activation methods. Increases in the already high grafting densities achieved from ex situ diazotization can be enhanced by stirring the solution while applying the electrochemical potential. Stirring is shown to replenish the depletion layer that arises after the electrochemical potential is applied. Overall, this work highlights the role of diffusion, depletion, and electric double layers involved in diazonium based electrochemical grafting processes.

Structural fabrics in a late Archean/early Proterozoic granite batholith at Lac du Bonnet, Manitoba, Canada, have been used to develop the temporal sequence of paleostress axis orientations. Orientations of the in situ stress field have been measured, both at surface and below surface at Atomic Energy of Canada Ltd.'s Underground Research Laboratory, through the techniques of borehole hydraulic fracturing, overcoring, and shaft wall convergence, and through quarry data and surface pop-ups. The fabric, interpreted paleostress and in situ stress directions are compared with each other and with regional stress orientations suggested by other authors for the western Superior Province. North, and NNE to NE trends for in situ maximum compressive stresses measured above the 250-m depth, possibly contain a large component of remanent stress. In situ stresses with SE to SSE trends are common near NE-striking thrust faults below the 250-m depth. This could be a Proterozoic remanent stress recovery, or it could be fabric-controlled. Neither NE- nor SE-trending in situ measurements wholly represent that of the present-day plate-induced active tectonic stress.

Different numerical methods used to distinguish between organic soil types are evaluated. The research was initiated by the suggestion that acid leaching from mining wastes could be prevented by capping the tailings with a self-renewing methane-producing muskeg bog, in order to prevent the penetration of oxygen to the wastes. Thirty organic soils from bogs in the mining districts of Elliot Lake, Sudbury, and Timmins, Ontario, and Noranda, Quebec, were sampled and 28 soil characteristics were measured. These characteristics, whose values are normally or lognormally distributed, were analyzed by several different statistical methods. Some characteristics indicate the existence of two populations, and others are bivariantly correlated. Canonical discriminant analysis was more successful than cluster analysis in separating the bogs into well-defined geographical groups. However, principal component analysis proved best at grouping the organic soils according to their organic and inorganic components, and we suggest that this is a suitable method for the general discrimination of organic soil types. Methane was present in all the 17 bogs tested for it, and in two very wet bogs more than 2 mmol of methane per liter were extracted. Key words: Muskeg bog, organic soils, soil characterization, principal component analysis

An approximate net slip for the No. 3 Vein fault at Opemiska Copper Mines (Que.) Ltd. property, in northwestern Quebec, has been obtained by comparing ore widths with the potential dilation from several possible fault movements. A reference plane of 096 °strike, 71 °north dip, has been chosen as a compromise between the two common attitudes of the vein. The ore stays close to the footwall of the fault, so that footwall topography has been used to calculate dilation. The zero dilation contours for 10 rectilinear movements and one rotation have been constructed, and their correspondence with the boundary between ore and waste used to choose a net slip of 41 m (135 ft) downward for the footwall, along a line pitching 50° in the reference plane, as the best solution. A close match between ore widths and more detailed dilation contours confirms this choice.

A technique is described for measuring recoverable strain in situ using bridged photoelastic bar gages and a simple reflecting polariscope. Rosettes of 0.2 × 0.4 × 4-cm bars are bonded to the rock for 0.6 cm at each end. Change in strain is measured following overcoring with a 10-cm bit. Correction for strains in the order of 30 · 10 −6 /°C, due to differential thermal expansion between rock and gage, are made by monitoring dummy gages mounted on free blocks. Bar gages have been satisfactorily tested against foil resistance gages. Rosettes mounted closely adjacent on a free granite block showed a reasonable homogeneity of response.