Formation of sub-micron size carbon structures by plasma jets emitted from a pulsed capillary discharge H. Bhuyan a, *, M. Favre a , E. Valderrama a , G. Avaria a , E. Wyndham a , H. Chuaqui a , J. Baier a , H. Kelly b , D. Grondona b , A. Marquez b a Pontificia Universidad Catolica de Chile, Departamento de Fisica, Casilla 306, Santiago 22, Chile b Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Instituto de Fisica del Plasma (CONICET), Universidad de Buenos Aires, Ciudad Universitaria, Pabellon 1, 1428 Buenos Aires, Argentina 1. Introduction Pulsed capillary discharges (PCD) have been mainly investi- gated as efficient radiation sources emitting in the extreme ultraviolet (EUV) to the soft X-ray region[1–6]. Further work in PCD has also been reported in the context of laser pulse transport through plasma guides [7]. Generically, the PCD is a member of the z-pinch family, a low pressure transient discharge where a cylindrical plasma column is compressed and heated by an axial current flowing through the plasma. Two different mechanism are used for plasma initiation inside the capillary. In the first case, a sliding discharge along the inner capillary wall results in a capillary plasma which is dominated by wall ablated material [8]. In the second case, on axis initiation results in a capillary plasma where the plasma content is defined by the filling gas. In an open cathode configuration on-axis initial plasma formation is achieved by electron beams, which are produced naturally due to the hollow cathode effect [9]. The transient behavior and characteristic geometry of a PCD, a narrow open ends tube with a large aspect ratio, establishes natural conditions for the generation of energetic plasma jets [10–12]. An efficient power coupling into the capillary plasma is required in order to produce a high energy density transient capillary plasma, which can lead to the emission of fast plasma jets. In our case this is achieved by using a discharge geometry consisting of a small capillary coupled to a coaxial capacitive energy storage system to reduce circuit inductance. The capillary tube can be of different materials (alumina, boron nitride, polyethylene, etc.) and dimensions (centimeters length and up to a few millimeters diameter). One end of the capillary, the anode, is kept at lower pressure, whereas the hollow cathode end is at higher pressure, in order to favor electron beam emission [13] and also, to keep a fast gas flow through the capillary in repetitive operation. The capillary can be operated in a wide range of gas pressures. The resulting supersonic plasma jet emitted from the open end of the capillary propagates in the low pressure background gas [11]. The interaction of the plasma jet with the low pressure background gas results in the formation of a transient volume plasma with features similar to those produced by the penetration of a laser ablation plume in a low pressure neutral background gas [14]. Although laser ablation plasmas have been used in surface science investigations for more than ten years [15], until now very few studies have been carried out to investigate the Applied Surface Science 255 (2009) 3558–3562 ARTICLE INFO Article history: Received 3 July 2008 Received in revised form 26 September 2008 Accepted 30 September 2008 Available online 14 October 2008 PACS: 52.80.Tn 52.77.-j Keywords: Plasma jets Carbon coatings Capillary discharge ABSTRACT We have performed an experimental investigation of the potential use of intense plasma jets produced in a repetitive pulsed capillary discharge (PCD) operating in methane gas, to irradiate Si (1 0 0) substrates. The surface modifications induced by the plasma jet using two different material inserts at the capillary end, graphite and titanium, are characterized using standard surface science diagnostic tools, such as scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis and Raman spectroscopy (RS). It has been found that the application of methane plasma jet results in the formation of sub-micron size carbon structures. It is observed that the resulting plasma irradiated surface morphologies are different, depending on the different material inserts used at the capillary end, at otherwise identical operational conditions. To investigate the species responsible for the observed surface changes in different material inserts to the capillary, optical-emission spectroscopy (OES) was recorded using a 300– 1000 nm spectrometer. The OES results show the presence of H, CH and C 2 Swan band in the discharge plasma, which play a significant role in the formation of the carbon structures. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. E-mail address: hbhuyan@fis.puc.cl (H. Bhuyan). Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.09.086