Tuning the Copper Cluster´s Size By Electrodeposition from Perchlorate Aqueous Solutions. a Morphological Study through Current Density Transients and Atomic Force Microscopy
Authors: Mendoza Huizar Luis Humberto , García-Rodríguez Diana Elizabeth , Sausedo-Solorio José Manuel 
Published: February 2020

Introduction
Copper nanoparticles (CuN) are widely used as cooling fluids for electronic systems [1], conductive inks [2], biosensors [3], electrochemical sensors [4], antimicrobial agents [5], among others. Also, CuN exhibit great catalytic activities, and nonlinear optical properties, which could result in many applications in optical devices and nonlinear optical materials, such as optical switches or photochromic glasses [5]. Currently the main methods to synthesize them include chemical reduction [6], in situ chemical synthetic route [7], and electrodeposition [8], among others. Specifically, electrodeposition is commonly used to synthesize nanoparticles because it is relatively simple and low cost procedure in comparison with other techniques [8]. However, it is important to remind that physical and chemical properties exhibited by CuN are highly dependent on their size and morphology by which, one of the main difficulty during their synthesis is tailoring and fine-tune the cluster’s size and the properties of these for a given application [9]. Thus, in the present work we analyze the possibility to get different cluster size maintaining constant the plating bath and modifying exclusively the applied potential on the electrode surface. Also, we carry out the morphological characterization of the CuN employing Atomic Force Microscopy (AFM) and its simulation through the current density transients.
Methodology
The copper electrodeposition onto HOPG electrode was carried out from a plating bath containing 0.01 M CuClO4 + 1 M NaClO4 at pH=5. All plating baths were prepared using analytic grade reagents and ultra pure water (Millipore-Q system) and they were deoxygenated by bubbling N2 for 15 minutes before each experiment. For these experiments, freshly cleaved HOPG surfaces were employed in each experiment. In all cases a graphite bar was used as counter electrode while an Ag/AgCl electrode (in saturated KCl), with a Luggin capillary was used as reference electrode. All experiments were carried out at 25 oC in unstirred solutions. The electrochemical experiments were carried out in an EPSILON potentiostat with the BASi-EpsilonEC software. Cyclic voltammetry was carried out in the 0.600 V to -0.800 V potential range. The characterization of CuN was performed with an Atomic Force Microscopy (AFM) a JEOL JSPM 4210 microscope in the lift mode.
Results and discussion
We analyzed the morphology of the copper deposits obtained when a potential step value in the range of [-0.075 - -0.175] V was applied during 5 seconds on the electrode surface. In Figure 1 is shown the experimental current density transient when a potential value of -0.075 V was applied. Also, note that under these conditions is possible to get the formation of homogeneous copper nanoclusters. In same Figure is reported the simulated density current transient and the morphology related to this transient. Observe that the simulated transient is similar to the experimental one, Moreover, the morphology predicted through this transient is similar to the experimental AFM image.
Conclusions
In the present work, it was tuned the copper cluster´s size by electrodeposition from perchlorate aqueous solutions applying different potential values on the electrode surface. The AFM study revealed the presence of copper clusters of nanometric dimensions. The simulation of the experimental transients, allow us to predict the morphology of the deposits through the simulated transients.

Acknowledgements: LHMH gratefully acknowledges financial support from CONACYT (project CB2015-257823) and to the Universidad Autónoma del Estado de Hidalgo.
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Figure 1