Synthesis and growth mechanism of dendritic Cu 2Àx Se microstructures Emanuela Filippo ⇑ , Daniela Manno, Antonio Serra Department of Material Science, University of Salento I, 73100 Lecce, Italy article info Article history: Received 20 February 2012 Received in revised form 13 May 2012 Accepted 24 May 2012 Available online 7 June 2012 Keywords: Semiconductors Vapor deposition Scanning electron microscopy Transmission electron microscopy abstract Dendritic crystalline copper selenides Cu 2Àx Se microstructures with various dimensions have been fabri- cated in large scale through thermal treatment of CuSe powder in argon flow, without any catalyst. The CuSe powder grains were used as both reagents and substrates for the growth of the Cu 2Àx Se dendrites. The synthesized microstructures were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected area diffraction pattern and Raman spectroscopy. Each indi- vidual dendrite was mainly composed of a long central trunk with secondary lateral branches. The length of the main trunk was in the range 10–30 lm, the width of the secondary branch lay in the range 1–5 lm. The trunk was about 1–2 lm in diameter while the lateral branches were about 0.4–0.8 lm in diameter. The lateral branches grew in parallel and kept about 60° with respect to the central trunk. A possible growth mechanism has been also proposed to account the growth of these Cu 2Àx Se dendritic microstructures. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Copper selenides are well-known p-type semiconductors, which have potential applications in solar cells, gas sensors, super ionic conductors and thermoelectric converters [1]. Moreover, CuSe has been demonstrated to be a good precursor for fabricating chalcopy- rite CuInSe 2 -based nanostructures on a large scale [2]. As a kind of binary compound, copper selenide can exist in a wide range of stoi- chiometric compositions (CuSe, Cu 2 Se, CuSe 2 , Cu 3 Se 2 , Cu 5 Se 4 , Cu 7 Se 4 , etc.) and non-stoichiometric compositions (Cu 2Àx Se) [3] and it can be constructed into several crystallographic forms (monoclinic, cubic, tetragonal, hexagonal, etc.) [4]. Many recent efforts have been devoted to the synthesis of cop- per selenides micro- and nanocrystallites with various structures and morphologies by thermolysis of single-source precursor [5], ultrasonochemical techniques [6], template-directed reaction [7,8], electrochemical crystallization process [9], hot-injection method [10] and hydrothermal routes [11–13]. In particular, re- cent works report solution strategies which allow to control the shape and the structure of the synthesized Cu 2Àx Se nanocrystals by changing the precursors in the reaction [14] or the reaction parameters [12,15]. Long crystalline Cu 2Àx Se nanowire bundles [16] and nanosheets and nanoplates [17] have also been synthe- sized in a large scale by a facile water evaporation process without any directing agent and by a green method of injecting Cu(I)- complex precursor into Se-solution in paraffin liquid, respectively. To best of our knowledge there have been no reports on the synthesis of copper selenide elongated nano and micro structures by vapor phase deposition route. Nevertheless, only Li et al. [1] re- ported the synthesis of hierarchically ordered three-dimensional (3D) nanodendrites of copper selenide by a solvothermal reaction. The importance of fabricating hierarchically ordered copper sele- nide nanostructures lies in that semiconducting copper selenides can show preponderant photoelectric functions which are derived from the advanced morphology. For some examples in solar cell devices, two-dimensional or three-dimensional (2D or 3D) nano- structures or nanowebs of crystalline semiconductors can show higher efficiency of PV conversion than the simple particles and one-dimensional (1D) materials (nanorods or nanowires), since the 2D or 3D nanostructured semiconductors can effectively trans- port holes or electrons via the interconnected networks in the scaf- folds [18]. Nanodendrites, which essentially possess much more advantages than nanosheets and nanoplates in solar cell applica- tions, are indeed such network materials and their 3D dendritic nanostructures can provide both the electrical links and a high sur- face/volume ratio. In this article, we describe for the first time the successful fabrication of dendritic crystalline copper selenides Cu 2Àx Se microstructures in large scale via thermal treatment of CuSe powder in argon flow, without any catalyst. 2. Material and methods Cu 2Àx Se dendrites were synthesized in a horizontal tube furnace. CuSe powder (Sigma Aldrich, 99.5% purity) were placed in a quartz crucible, which was previ- ously ultrasonically cleaned using acetone and ethanol. The crucible was placed in the middle of a horizontal quartz furnace system. The furnace was rapidly ramped up to 500 °C and maintained for 30 min; then the furnace was increased to 1000 °C and maintained at that temperature for 120 min. Afterwards, the furnace 0925-8388/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2012.05.111 ⇑ Corresponding author. Tel.: +39 832297061; fax: +39 832297100. E-mail address: emanuela.filippo@unisalento.it (E. Filippo). Journal of Alloys and Compounds 538 (2012) 8–10 Contents lists available at SciVerse ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom