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In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/nanoscale Page 1 of 7 Nanoscale Journal Name RSC Publishing ARTICLE The functionalization of nanodiamonds (diamondoids ) as key parameter of their easily controlled self- Cite this: DOI: 10.1039/x0xx00000x assembly in micro- and nanocrystals from vapor phase Received 00th January 2012, a,b a c c c Accepted 00th January 2012 Maria A. Gunawan, Didier Poinsot, Bruno Domenichini, Céline Dirand, Sébastien Chevalier, Andrey A. Fokin, b,d Peter R. Schreiner *b and Jean-Cyrille Hierso *a,e DOI: 10.1039/x0xx00000x www.rsc.org/ We detail herein readily accessible processes to control previously unobserved robust self- assemblies of nanodiamonds (diamondoids ) in micro- and nanocrystals from their mild vapor deposition. The chemical functionalization of uniform and discernible nanodiamonds was found a key parameter, and depending on the type of functional group (hydroxy, fluorine, etc.) and its position on the diamondoid, the structure of the discrete deposits can vary dramatically. Thus, well-defined anisotropic structures such as rods, needles, triangles or truncated octahedra Manuscript shapes can be obtained, and self-assembled edifices of sizes ranging from 20 nm to several hundred micrometers formed with conservation of a similar structure for a given diamondoid. Key thermodynamic data including sublimation enthalpy of diamondoid derivatives are reported, and SEM of the self-assemblies coupled with EDX analyses and XRD attest for the nature and purity of nanodiamonds crystals deposits. This attractive method is simple and outperforms in terms of deposit quality dip-coating methods we used. This vapor phase deposition approach is expected to allow for an easy formation of diamondoid nanoobjects on different types of substrates. Accepted Introduction followed by growth may also pave the way to access continuous diamond thin films of better defined structure and Diamondoids are cage hydrocarbon molecules that can be surface.14 Diamondoids may serve also as precursors in described as fully hydrogen-terminated nanometer-sized “bottom-up” strategies to build organohybrids, 15 and to devise diamonds. 1,2 Adamantane ( 1) and diamantane ( 2) are the diamond structures under conditions that are possibly milder smallest diamondoids and their selective functionalization can than the chemical vapor deposition (CVD) conditions currently be achieved with high efficiency at various positions of the used for diamond growth. 16 Methods have been reported akin to hydrocarbon cage (Fig. 1). 1 Ultra-disperse detonation CVD that yielded higher diamondoids (more than four carbon 3-6 7 17 nanodiamond, and diamondoids (also called nanodiamonds ) fused-cages) and even diamond from diamondoid seeds. have shown impressive success in the utilization of diamond OH F Nanoscale properties in various areas that span the fields of nanomedicine, 8-10 nanodevices for energy, 11a and molecular OH machines. 12,13 For instance, large area self-assembled monolayers of thiolated diamondoids on gold surfaces exhibit 1 2 3 4 5 intense monochromatic photoemission with energy distribution adamantane diamantane 1-hydroxydiamantane 4-hydroxydiamantane 4-fluorodiamantane width < 0.5 eV, which is related to the negative electron affinity (C H ) 10 16 (C14H20) (C14H20O) (C H O) (C H F) of the surface-attached nanodiamonds. 11 14 20 14 19 Fig. 1 Fully hydrogenated hydrocarbon cages adamantane 1 and diamantane 2, Another attractive and hitherto unmet challenge in this field and functionalized diamantane analogues 3–5. is the construction of organic materials and organohybrids based on nano- and microcrystals of functionalized diamondoids. Based on such edifices, carbon nucleation This journal is © The Royal Society of Chemistry 2013 J. Name ., 2013, 00 , 1-3 | 1 Nanoscale Page 2 of 7 ARTICLE Journal Name However, for applications of nanodiamonds-based materials Table 1 . Thermodynamic data for sublimation of 1–5 a built “bottom-up” there is still a need for better fundamental Clausius-Clapeyron equations ∆H0 (kJ mol –1) r2 understanding and mastering of the conditions of nucleation, 1 ln P = –7212.4/T + 26.869 60.0 ± 5 0.9991 18 growth and self-assembly of diamondoids units. Additionally, 2 ln P = –11073/T + 37.172 92.1 ± 5 0.9992 general interest in dispersed micro- and nanocrystals stems 3 ln P = –12282/T + 39.589 102.1 ± 5 0.9960 from the fact that their properties dramatically change with 4 ln P = –13087/T + 42.196 108.8 ± 5 0.9983 5 ln P = –11597/T + 38.335 96.4 ± 5 0.9965 their size and shape, 19 and many applications from optical a (plasmon absorption) to medical (transportation through pressure in Pa, T in K (see SI for measurement full details). biological barriers) illustrate this point. We thus report on The enthalpies of sublimation obtained from these equations are readily accessible processes for the mild vapor deposition of ∆H0 = 60.0 kJ mol –1 for 1, 92.1 kJ mol –1 for 2, 102.1 kJ mol –1 functionalized diamondoids that provide robust self-assembly for 3, 108.8 kJ mol –1 for 4, and 96.4 kJ mol –1 for 5, indicating of nanodiamonds micro- and nanocrystals. Key thermodynamic the highest volatility for adamantane, and the lowest for data including sublimation enthalpy of several diamondoid hydroxydiamantane derivatives. The enthalpy of sublimation derivatives are reported from a new measurement protocol at obtained for adamantane 1 following equilibrium state pressure solid-vapor thermodynamic equilibrium state. Easily accessible measurements, ∆H0 = 60.0 kJ mol –1 (14.3 kcal mol –1), is processes for self-assembled edifices of sizes ranging from 20 consistent with the values previously reported (14.2±0.3 kcal nm to several hundred micrometers are reported with mol –1). 21a This was also the case for diamantane 2 remarkable conservation of the general geometry for a given measurements ( ∆H0 = 92.1 kJ mol –1), with the values obtained diamondoid, chemical analysis with microscopy ascertaining using calorimetry bomb combustion, 21a and gas-saturation the full preservation of the nature of nanodiamonds. temperature scanning (95.9 kJ mol –1). 23 As expected, the 0 Results and Discussions fluorodiamantane 5 was found fairly volatile with a ∆H = 96.4 kJ mol –1 approaching the one we found for pristine diamantane. Due to the volatility of adamantane ( 1) and diamantane ( 2) Due to a noticeable hygroscopic behaviour of the (Fig. 1), we envisioned that vapor deposition of functionalized hydroxydiamantanes a good reproducibility required cautiously Manuscript diamondoids might be a general and convenient access to dried finely divided pure hydroxydiamantane powders to nanocrystals, microcrystals, and thin films of carbon-based exclude water traces. It was determined that 4- materials. The control of a given vapor deposition process hydroxydiamantane 4 is significantly less volatile, ∆H0 = 108.8 entails knowledge of the partial pressure of the source under the kJ mol –1, than 1-hydroxydiamantane 3, ∆H0 = 102.1 kJ mol –1.24 experimental conditions. Accordingly, enthalpies of The vapor deposition of 1–5 was then conducted, under sublimation are critical thermodynamic properties of the tuneable conditions of pressure and temperature, on silicon and condensed phase in relation with vapor pressure. Therefore, our mica substrates using a simple sublimation apparatus (see SI). vapor deposition studies were first devoted to measuring The deposition experiments were conducted first under air or sublimation enthalpies of pristine adamantane and diamantane argon atmosphere 1.0 bar (10 5 Pa), and then either under static Accepted for which different values have been reported. 20,21 Conversely, vacuum (initial pressure 5.3 mbar), or dynamic vacuum (5.3 fundamental studies of the vapor pressure of functionalized mbar). Temperature conditions ranging between 50 and 110 °C diamondoids remain very limited. 21b We found significant were investigated. Higher sublimation temperatures favour a differences in the reported values for the enthalpies of higher vapor supersaturation regime, which in turn favours sublimation (see SI, Table 1S), depending on the measurement effective nucleation in comparison to crystals growth. A good and calculation methods. Mainly destructive calorimetric nucleation rate, in comparison to growth rate, then will quickly measurements had been conducted using total combustion of generate numerous small crystals of critical size that will no the diamondoids in a bomb calorimeter. 22 This prompted us to longer disappear to serve as “nutrients”