Ablation particles parameters influences on VLS oxide nanowire growing A. Marcu a,n , C. Grigoriu a , C.P. Lungu a , T. Yanagida b , T. Kawai b a National Institute for Laser Plasma and Radiation Physics, Atomistilor 409, P.O. Box MG-36 Bucharest-Magurele, Romania b Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan article info Article history: Received 24 May 2010 Received in revised form 8 October 2010 Accepted 3 November 2010 abstract MgO nanowires were grown using vapor–liquid–solid technique by using the Pulsed Laser Ablation method in special shadow-mask system geometry. We compared the MgO nanowires morphology below and outside the shadow-mask areas obtained by using two different laser beams (193 nm—ArF excimer, and 266 Nd:YAG fourth harmonic) for target ablation. If for the first laser beam, an MgO nanowire grows outside the mask’s shadow area and the growing morphology below the mask tends to change to island growing, in the second case, the nanowire tends rather to form below the shadow-mask. Our results interpretation is based on the ablation plume particles’ flux and size. In the first case, results are interpreted based on the ablated particle flux variation in the ablation plume interaction with a plane mask. In the second case, we base our interpretation on ’big’ particles filtering by the ablation plume interaction with a plane mask. & 2010 Elsevier B.V. All rights reserved. 1. Introduction The great potential in engineering and science of the nanos- tructures [1–5] determines an extensive research activity in this field. Due to their variety of physical properties, oxides [6,7] draw attention for nanowire based functionalised devices. In particular, magnesium oxide (MgO), known as a versatile substrate for oxide thin films, becomes interesting for using in heterostructured nanowire based devices [8]. As for the synthesis of oxide materials, pulsed laser deposition (PLD) has been one of the most powerful techniques to fabricate various oxide films and recently for nanostructures as well [9]. As a Bottom–Up approach, nanostruc- ture fabrication usually starts from oxide nanowire growing. In most of the cases, the growing process is based on the vapor– liquid–solid (VLS) growing [10,11]. Since the requirements for functionalised nanostructures have increased continuously, the technique controllability requirements have increased too and necessitate a better understanding of the involved processes. Even if it is presently widely accepted that the VLS process consists of several elementary processes inside, outside and around the liquid catalyst droplets, knowledge on these absorption, desorption and deposition processes is still scarce [9,12]. The aim of this study is a better understanding of the VLS growing process and limitations. The experiments were made for the particular case of an MgO nanowire growing with the PLD method for different parameters of the ablated particles plume. While using same experimental conditions and setup, we used two different lasers, and we investigated differences between an MgO nanowire growing morphology in different substrate areas in both cases. While the VLS mechanism would basically work the same in both systems, the growing morphology differences must be related with the differences of the incoming plume parameters, due to the different laser beam–target interaction processes. 2. Experimental system MgO nanowires were grown by the VLS technique in a PLD system using an Au catalyst. Deposition temperature was about 800 1C and the ambient oxygen pressure 10 Pa. The target and the substrate were both MgO (0 0 1). The system geometry used in this experiment was an eccentric shadow-mask configuration (Fig. 1). A cooper sheet was used as a plane mask. The substrate was placed at a few centimeters from target and at several millimeters below the plane shadow-mask. Two pulsed ultraviolet laser beams were used in this experiment. One beam was from an ArF Lambda Physics excimer laser on 193 nm wavelengths and the second one from an EKSPLA Nd:YAG 4th harmonic having 266 nm wavelength. In both cases, the laser frequency was 10 Hz and deposition time 1 h. The laser power was 50 mJ in the first case and about 25 mJ in the second one. We should also mention that the lenses and windows were also different for each case. 3. Experimental results By using the Lambda Physics Laser beam in a ‘standard’ PLD geometry, the nanowire grows quasi-uniform on a 5 mm  5 mm Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physe Physica E 1386-9477/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2010.11.002 n Corresponding author. Tel./fax: + 40 21 457 4027. E-mail address: marcu@ifin.nipne.ro (A. Marcu). Please cite this article as: A. Marcu, et al., Physica E (2010), doi:10.1016/j.physe.2010.11.002 Physica E ] (]]]]) ]]]–]]]