Production and Growth Mechanisms of Pd Nanoclusters

Abstract

Size-selected palladium nanoclusters have been produced by dc sputtering and inert gas condensation technique using mixtures of argon and helium gases. By controlling the source parameters, it was possible to produce Pd nanoclusters with size in the range of 2-10 nm. Transmission electron microscopy (TEM) images were used to confirm the produced sizes of nanocluster. It was found that increasing the percentage of helium to argon have two main effects: i) decreases the nanocluster size as a result of the high drift velocity of helium, and ii) decreases the number of measured nanoclusters due to the low sputtering yield of helium. Since He gas is primarily responsible for the cluster-condensation process, its partial pressure can be used to control the nanoclusters growth. The source parameters and their effects on the size and number of nanoclusters are of great importance in understanding the Pd nanoclusters growth mechanism. INTRODUCTIONMuch effort has been dedicated to investigate properties of nanoclusters which are different from those of the corresponding bulk materials. The research in this field is of strategic importance because the properties of nanoclusters can be tuned by controlling the size which create innovative materials and devices. Recently, research has been focused on palladium (Pd) nanoclusters because of their possible applications in the fields of hydrogen storage [1, 2], hydrogen detection [3], and catalysts [4][5][6]. Therefore, intensive research is required to develop nanocluster sources to produce more intensive nanocluster beam, and to provide further control of the nanocluster size distributions [7,8]. Sputtering inert gasaggregation source is a suitable standard candidate that combines both plasma sputtering and inert gas condensation without the complications of target heating [9]. In addition, plasma gas condensation is a predominant technology that can be used on large scale by industry to produce high quality metallic nanoclusters [10,11]. Nevertheless, only few systematic investigations were devoted to improve plasma gas condensation to reach an optimal large scale production of nanoclusters [9,11,12].The growth of nanoclusters may involve either or both of the following processes: i) embryo formation via three-body collision (two sputtered atoms and an inert gas atom to remove their excess kinetic energy); and ii) growth of large nanoclusters by two-body collision through nanocluster-nanocluster collision and/or by accepting atoms that have arrived to the nanocluster surface (atomic condensation) [13,14]. Hence, numbers of produced nanoclusters as well as nanoclusters' sizes are determined by the probability of the two-body and/or three-body collisions which are mainly affected by the time the nanoclusters spend within the growth region.In a previous work [13], the mean nanocluster size was controlled by changing the Ar flow rate, sputtering discharge power, and aggregation length. The produced nanocluster size was limited by the nanocluster thermodynamic stability, and the re...

Influence of carrier gas on the nucleation and growth of Nb nanoclusters formed through plasma gas condensation

“…1,2,4,5 The clusters traverse a quadrupole mass spectrometer attached to the exit of the cluster generation source. A large fraction of the nanoclusters are ionized with a negative charge.…”

“…[1][2][3][4][5][6][7][8] The ability to obtain desired nanocluster sizes and distribution is an important step in effectively utilizing these materials. These materials exhibit promising catalytic, electrical, magnetic, mechanical, and optical properties.…”

“…These materials exhibit promising catalytic, electrical, magnetic, mechanical, and optical properties. 10 Nanoclusters have been deposited onto substrates 2,5,7,8,11,12 and codeposited to form nanocomposite films using PGC processes. [1][2][3][4][5][6][7][8] The ability to obtain desired nanocluster sizes and distribution is an important step in effectively utilizing these materials.…”

“…[1][2][3][4][5][6][7][8] The ability to obtain desired nanocluster sizes and distribution is an important step in effectively utilizing these materials. [1][2][3][4][5][6]16,17 The low temperature, ferroelectric properties of niobium make Nb clusters of even greater interest. 10 Nanoclusters have been deposited onto substrates 2,5,7,8,11,12 and codeposited to form nanocomposite films using PGC processes.…”

“…[13][14][15] A wide range of possible uses makes transition metal clusters of great interest. 2,5,8,9,18 Changes in nanocluster nucleation and growth are influenced through modifying the process parameters such as Ar flow rate (f Ar ), He flow rate (f He ), sputter source ion current (SC), and aggregation length (L). 16,17 In this study, PGC is utilized to produce Nb nanoclusters using a Nanogen 50 nanoparticle source from Mantis Deposition, Ltd. (Fig.…”