Epitaxial Growth of Cu[sub 2]O (111) by Electrodeposition

Abstract

Cuprous oxide (Cu 2 O)(111) crystals have been prepared at 65°C in weak acidic media (pH 4.7) by electrodeposition. The morphology was observed by scanning electron microscopy and X-ray diffraction analysis was used for investigation of the crystal phase. When a low cathodic current, -0.5 mA/cm 2 , was applied crystals formed on platinum electrode having only one phase, Cu 2 O (111), and cuprous oxide was epitaxially grown with a triangular structure of (111) phase although the electrolysis time was different. The role of a local enhancement of pH at the cathode is observed to have facilitated the deposition of Cu 2 O in weak acidic solution.Recently, various metal oxides such as AgO, 1 Tl 2 O 3 , 2 Cu 2 O, 3,4 and ZnO 5-7 have been prepared by electrochemical deposition due to the following several advantages: (i) thickness and morphology of films can be controlled precisely by adjusting electrochemical parameters, (ii) relatively uniform films can be formed on substrates of complex shapes, (iii) higher deposition rates can be easily obtained, and (iv) the equipment required is inexpensive due to the non requirement of either high vacuum or high reaction temperatures. 8 Cu 2 O is a p-type semiconductor having 2.0 eV bandgap energy and is an attractive photocatalytic material for water splitting into H 2 and O 2 under visible light irradiation. 9 Cuprous oxide is also used as a solar cell and piezoelectric and thermoelectric sensor material. 10 Cu 2 O has been manufactured by electrochemical techniques such as anodic oxidation 11-13 and cathodic deposition. 3,4 In anodic oxidation, under optimal preparation condition, passivating oxide (Cu 2 O) layers are formed on copper in alkaline media and render the metal resistant against corrosion and also show interesting semiconduction properties. Switzer et al. 3 investigated electrodeposition of Cu 2 O in alkaline copper(II) lactate solution and discussed the effect of pH and solution temperature on the film formation. They observed that Cu 2 O crystals have different orientation depending on the pH value of the solution. Cu 2 O films are deposited with (100) four-sided pyramid at pH 9, while Cu 2 O (111) has a triangular structure at pH 12. With increasing temperature, grain size of the films is reported to increase. They used the alkaline solution to make the Cu 2 O film because Cu + is stable in the alkaline solution from Pourbaix diagram. Tanaka et al. 4 investigated the effect of anions on the electrodeposition of Cu 2 O and observed the following during the formation of Cu 2 O and Cu with different cathodic potentials: (i) Cu 2 O has hexahedral, polyhedral crystals and Y-shaped particles in perchlorate, sulfate, and chlorate solutions, respectively, (ii) Cu 2 O was formed and grew larger at higher than -0.55 V (vs. saturated calomel electrode, SCE), while below -0.55 V both Cu and Cu 2 O were deposited on the surface.In this work, we report the observation that cuprous oxide can be prepared in solution with low pH. In acidic solution, Cu + is reduced to Cu metal...

Electrodeposition of Semiconductors

“…Additives such as ethylene glycol have been used with its role being speculated as being both an electrolyte modifier and a chelating agent [276]. It must be noted that in some instances no other intentionally added species other than the Cu(II) salt was present in an aqueous medium [277,278], and one of these studies [278] invokes a base electrogeneration mechanism (see above) for Cu 2 O formation.…”

“…Epitaxial growth of Cu 2 O layers has been achieved by cathodic electrosynthesis on a variety of surfaces, including Pt [278], Au [288], Si [289], and InP [289]. Copper(II) lactate solutions were used by Switzer et al [288,289] while Lee and Tak used a weak acidic solution of Cu(II) nitrate for this purpose [278].…”

“…Epitaxial growth of Cu 2 O layers has been achieved by cathodic electrosynthesis on a variety of surfaces, including Pt [278], Au [288], Si [289], and InP [289]. Copper(II) lactate solutions were used by Switzer et al [288,289] while Lee and Tak used a weak acidic solution of Cu(II) nitrate for this purpose [278]. In the case of the single-crystal Au substrate, ordered nanostructures of Cu 2 O were formed after a transition from a thermodynamically controlled orientation to a kinetically preferred orientation [288].…”

Electrochromic Mechanism of IrO[sub 2] Prepared by Pulsed Anodic Electrodeposition

“…Five different methods of preparing IrO 2 are as follows: ͑i͒ anodically electrodeposited metal oxide films like PbO 2 ; 1,10 (ii) cathodically electrodeposited metal oxide films ͑e.g., Cu 2 O, ZnO, Y 2 O 3 ); [11][12][13][14] (iii) activation of iridium metal by potential cycling to form activated iridium oxide films; 15 (iv) reactive sputtering to form sputtered iridium oxide films; 16 and (v) thermal decomposition of iridium salt solution to form thermal iridium oxide films. 17 In this work, we investigated the electrochromism mechanism of electrodeposited IrO 2 thin films via electrochemical and surface characterization using cyclic voltammetry ͑CV͒, pulsed potential method, in situ electrochemical quartz crystal microbalance ͑EQCM͒ measurement, scanning electron microscope ͑SEM͒, augerelectron spectroscopy ͑AES͒, and X-ray photoelectron spectroscopy ͑XPS͒ analysis.…”

Comparative study of applied potential differences in electrodeposition for fabricating metallic-oxide films

“…Electrodeposition of metal oxides such as Cu 2 O [7][8][9], PbO 2 [10][11], Y 2 O 3 [12], and ZnO [13][14] has the following advantages over conventional methods; (i) thickness and morphology of films can be precisely controlled by adjusting electrochemical parameters such as current or potential, (ii) relatively uniform and compact thin films can be synthesized either on substrates of complex shapes or in column shaped material, (iii) higher deposition rates can be easily obtained over conventional processing, and (iv) the equipment required is inexpensive owing to the non requirement of either high vacuum or high reaction temperature.…”