Self-Assembled Pillar-like Structures in Nanodiamond Layers by Pulsed Spray Technique Grazia Cicala,* ,† Alessandro Massaro, † Luciano Velardi, † Giorgio S. Senesi, † and Antonio Valentini ‡ † CNR-IMIP, Via Amendola 122/D, 70126 Bari, Italy ‡ Department of Physics, University of Bari, Via Orabona 4, 70126 Bari, Italy * S Supporting Information ABSTRACT: Pillar-like structures of nanodiamonds on a silicon substrate are self-assembled for the first time by a pulsed spray technique. This technique allows us to deposit nanodiamond layers by using high quality nanocrystals of 250 nm dispersed in 1,2-dichloroethane (DCE) solvent. The analysis of 2D/3D confocal and atomic force microscopy images evidences the presence of self-assembled pillar-like structures distributed in an irregular way. The proposed method is simple, easy and cheap, and does not require complex growth processes or structured materials, ideal for upscaling toward industrial biochip implementation and photonic applications. The suggested formation mechanisms of self-assembly are based on the so-called coffee stain effect, i.e., on the time evolution of DCE evaporation. KEYWORDS: diamond, nanoparticles, self-assembly, spray technique, pillar-like structures ■ INTRODUCTION The fabrication of nanostructures, structured and aligned nanoparticles and nanodevices represents an important and hot topic in the nanotechnology field. Usually, the top-down and bottom-up approaches are followed to form and engineer the nanosystems mentioned above. The top-down technology is widely employed in the micro- and nanoelectronic industry, and uses e-beam lithography and reactive ion etching methods to go down to small sizes. Diamond nanowires 1 and nanopillars 2 for photonic devices are recent examples of a top-down nanofabrication starting from single-crystalline diamond. Contrarily, the bottom-up approach, very commonly used in the growth of aligned carbon nanotubes (CNTs) 3 and in natural biological systems, consists in the self-assembly of larger and complex systems starting from single units (atom, molecule, particle) by using various (grafting and spraying) methods. The formation of self-assembled structures depends critically on the physical and chemical environmental conditions employed. Recently, the self-assembly of octapod- shaped colloidal nanocrystals has been reported 4 and has been explained to be due to the solvent evaporation from poly(methyl methacrylate). Typical examples of self-assembled structures are the architectures of ZnO nanowires on organized CNT able to generate photocurrent under UV irradiation, 5 and single spherical gold nanoparticles used as electromagnetic radiators. 6 Diamond powders/nanoparticles of various sizes ranging from a few nanometers to tens of micrometers have been and are still used to treat the nondiamond substrates in order to enhance the nucleation process before the growth of thin diamond films by chemical vapor deposition (CVD) techniques such as microwave CVD 7 or hot filament CVD. 8 More recently, nondiamond substrates such as Si, AlN and sapphire, have been highly seeded using monodispersed nanodiamond (ND) particles. Specifically, the modification of nanodiamond surface makes them negatively or positively charged if annealed in oxygen or hydrogen, respectively, and allows to strongly affect the ND-substrate electrostatic interaction from repulsive to attractive. 9 In particular, a native silicon oxide layer (with negative ζ-potential values) is omnipresent on the silicon wafer, thus the Si substrate presents a negative surface charge. 9 Moreover, in the last years, ND particles have become widely available at low costs for a variety of synthesis techniques. They are ideal candidates for a wide range of applications as fillers for nanocomposites to improve the mechanical properties, in tribology, in mechanics because the ND particles are used as polishing material for the surface finish of watch sapphires, hard disks, etc., and in the biomedical field. 10 The large surface area of NDs is suitable for adsorbing biomolecules. Many different functional groups can be attached to a ND surface, allowing quite sophisticated surface functionalizations 11 without compromising the properties of the diamond core. The presence of surface groups open many chances for the surface modification of ND. For example, further functionalization of amino groups permits us to graft DNA pieces on the coated ND particles. 10 Received: September 2, 2014 Accepted: November 17, 2014 Published: November 17, 2014 Research Article www.acsami.org © 2014 American Chemical Society 21101 dx.doi.org/10.1021/am505974d | ACS Appl. Mater. Interfaces 2014, 6, 21101-21109