Role of the Deposition Precursor Molecules in Defining Oxidation State of Deposited Copper in Surface Reduction Reactions on H-Terminated Si(111) Surface

Abstract

Surface-limited deposition reactions leading to the formation of copper nanoparticles on H-terminated Si(111) surface can serve as a model for understanding the role of structure of the deposition precursor molecules in determining the oxidation state of the metal deposited. This study compares three different precursor molecules: Cu(acac)2 (Cu(II) acetylacetonate), Cu(hfac)2, and Cu(hfac)VTMS (Cu(I)-(hexafluoroacetylacetonato)-vinyltrimethylsilane) as copper deposition sources in a process with a controlled oxidation state of copper. X-ray photoelectron spectroscopy suggests that single-electron reduction governs the deposition of Cu(I) from the first two precursor molecules and that the last of the precursors studied yields predominantly metallic copper. Time-of-fight secondary ion mass spectrometry (ToF-SIMS) and infrared spectroscopy are utilized to interrogate surface species produced. Atomic force microscopy is used to quantify the deposition process and to follow the size distribution of the deposited copper containing nanoparticles. A plausible explanation supported by density functional theory calculations is offered on the basis of the difference in the reaction pathways for Cu(I) and Cu(II) precursors.

Deposition of copper from Cu(i) and Cu(ii) precursors onto HOPG surface: Role of surface defects and choice of a precursor

“…Along with the satellite peaks around 940 to 945 eV, it indicates the existence of Cu(ii) on this surface. 18,51 The ratio of Cu/F is calculated to be nearly 1:1 following the reaction, suggesting that the majority of fluorine-containing species are desorbed from the surface (as this ratio is expected to be 1:12 based on the stoichiometry of the precursor). This, along with the corresponding AFM results, suggests that the reactivity of Cu(hfac) 2 towards HOPG surface is higher than that of Cu(hfac)VTMS.…”

“…Carbon peak at 284.6 eV was selected for calibration. 18,32,33 Atomic Force Microscopy (AFM) images were acquired with a J-scanner scanning probe microscope (Multimode, NanoScope V) under tapping mode. AFM probes (Budget Sensor) with a force constant of 40 N/m and a resonant frequency of 300 kHz were used.…”

“…This process has been described in detail previously. 18 Cu(hfac)VTMS was introduced into the high-vacuum chamber through a leak valve. Three cycles of freeze-pump-thaw procedure were applied before dosing.…”

“…For example, Cu(hfac)VTMS (copper(i) hexafluoroacetylacetonate vinyl trimethylsilane) and Cu(hfac) 2 (copper(ii) hexafluoroacetylacetonate) are common precursors for ALD or CVD methods and are used to produce either coppercontaining nanoparticles or continuous thin films. [18][19][20][21][22] Due to the structural differences of the two precursors, different reactivities and therefore surface morphologies of the structures produced are expected, as has been observed on surfaces such as ZnO, 22 silica, and silicon. 18,20,21 In addition, since the VTMS moiety from Cu(hfac)VTMS is expected to desorb from the substrate immediately upon adsorption, as was observed on several substrates even at room temperature, [20][21][22][23][24][25][26][27] Cu(hfac) is actually expected to be the reactive adsorbate (Figure 1(a)) that will interact with the surface for deposition based on this precursor.…”

Transmetalation Process as a Route for Preparation of Zinc-Oxide-Supported Copper Nanoparticles

“…18,19 Copper nanoparticles have been shown to form on flat substrates and on ZnO powder in a self-limiting surface process conceptually similar to ALD. 9,20,21 Common copper deposition precursors based on β -diketonate ligands were used for the deposition. The surface reactions of these precursors are limited by the delivery of the reducing agent from the underlying surface to remove β -diketonate ligands and thus the quantity of copper deposited on a surface is controlled by the surface concentration of chemical groups capable of delivering such a reducing agent.…”