Thin oxide films were grown anodically on polycrystalline copper and single crystals Cu(100), Cu(110)
and Cu(111). Semiconductor properties of copper oxides were obtained by photocurrent measurements. The
morphology of the anodic oxides was monitored by SEM. A p-type conductivity was established for Cu2O
and СuO formed on Cu during the anodic polarization. The main semiconductor properties do not depend
on the crystal face; the band gap in thin Cu2O is equal to 2.2 eV.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3499

Eliseev, D.S.

Ganzha, S.V.

Grushevskaya, S.N.

Vvedenskii, A.V.

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 1 No 3, 03TF01 (4pp) (2012) 
 
 
2304-1862/2012/1(3)03TF01(4) 03TF01-1  2012 Sumy State University 
Thin Oxide Films on Copper Single Crystals: Anodic Formation  
and Photoelectrochemical Properties 
 
A.V. Vvedenskii, S.N. Grushevskaya*, S.V. Ganzha, D.S. Eliseev 
 
Voronezh State University, 1, Universitetskaya Sq., 394006 Voronezh, Russia 
 
(Received 01 February 2012; published online18 July 2012) 
 
Thin oxide films were grown anodically on polycrystalline copper and single crystals Cu(100), Cu(110) 
and Cu(111). Semiconductor properties of copper oxides were obtained by photocurrent measurements. The 
morphology of the anodic oxides was monitored by SEM. A p-type conductivity was established for Cu2O 
and СuO formed on Cu during the anodic polarization. The main semiconductor properties do not depend 
on the crystal face; the band gap in thin Cu2O is equal to 2.2 eV. 
 
Keywords: Copper, Single crystals, Anodic oxide formation, Photocurrent, Spectroscopy. 
 
  PACS number: 82.45. – h 
 
 
______________ 
* sg@chem.vsu.ru 
1. INTRODUCTION 
 
Metal oxides are widely used in photolytic hydrogen 
evolution, electrocatalysis as well as in the production 
of current-generating devices, UV- and IR-sensors. 
Cu(I) oxide is considered as a perspective material  due 
to the optimal combination of the number of 
parameters such as non-toxicity, low cost, simple 
production and the bandgap, providing the adsorption 
of most spectrum. Cu(II) oxide films can be grown much 
thicker than Cu(I) oxide, being using in barrier devices. 
The properties of thin oxide films and the kinetics of 
their formation depend on the electrode potential and 
solution composition as well as the crystal structure 
and chemical composition of the electrode surface. The 
latter is revealed for nanosized films of Ag(I) oxide on 
Ag and Ag-Au alloys [1, 2]. 
The aim was to establish the role of crystal 
structure of copper surface in the kinetics of anodic 
growth and properties of nanosized films of 
semiconductor  Cu(I) and Cu(II) oxides. 
 
2. EXPERIMENTAL 
 
The investigation were carried out on polycrystal-
line copper (0.9999) and single crystals Cu(100), 
Cu(110) and Cu(111) (0.99999) in deaerated 0.1 M KOH 
prepared from double-distilled water and reagent-grade 
chemicals. Single crystals were prepared by “Materials 
Technology & Crystals for Research, Development and 
Production” with accuracy ≤ 2 . 
The kinetics of anodic formation and the properties 
of Cu(I) and Cu(II) oxides were examined by cyclic volt-
ammetry and chronoammetry with synchronous regis-
tration of photocurrent. The polarization of static elec-
trodes during the preparation and the film growth was 
carried out using the computerized potentiostatic com-
plex IPC-Compact (Institute of Physical Chemistry and 
Electrochemistry of Russian Academy of Science). The 
potentials are given in s.h.e. scale. 
The super-bright light emitting diodes “LIGITEK” 
were used as a source of quasi-monochromatic UV-
irradiation (   385-875 nm) in the photoelectrochemi-
cal measurements. The density of photon flux was con-
stant and equal to 3.04 1015 photon cm – 2 s – 1. The dura-
tion and frequency of light pulses were 50 ms and 5 Hz. 
The morphology and the chemical composition of 
the electrode surface were monitored by scanning elec-
tron microscopy (JEOL JSM 6380LV) and energy dis-
persion X-ray analysis (INCAx – sight 250). 
 
3. ANODIC FORMATION OF THIN OXIDE 
FILMS 
 
The voltammograms of copper in a wide potential 
range show the two main peaks A1 and A2, correspond-
ing to Cu(I) and Cu(II) formation (Fig. 1a). The peak 
potential A2 ennobles and the peak current decreases: 
Cu(poly) > Cu(110) > Cu(111) > Cu(100). 
The potential and current of A1 peak on Cu(111) 
and polycrystalline copper are identical. On Cu(110) 
and Cu(100) the peak potential A1 is more negative 
and the peak current is lower as compared with poly-
crystalline copper (Fig. 1b); the difference in the ca-
thodic peaks C1 and C2 is less significant. 
The processing of the voltammograms in the criteri-
al coordinates shows that the anodic formation and 
cathodic reduction of Cu(I) oxide on polycrystalline 
copper and single crystals proceeds with a noticeable 
diffusion limitation in solid phase. The charge transfer 
is not equilibrium. 
In the potential range more negative than the equi-
librium potential of Cu(I) oxide formation we managed 
to reveal the weak anodic and cathodic peaks (Fig. 2a), 
corresponding to the adsorption of hydroxyl-ion with 
charge transfer [3, 4] and subsequent desorption of hy-
droxyl-radical: 
 
 Cu(hkl) + OH– = Cu(hkl) – OHads + e–.  
 
The integer of anodic currents gives the values of qa, 
corresponding to the charging of pseudo-capacity of the 
adsorption and the extent of surface filling by oxygen 
(Fig. 2b). In general the values of surface filling are 
low; Cu(111) shows the maximal surface filling. At  
E < – 0.7 V the chemisorption of OH- on copper does not 
occur. 
 
 A.V. VVEDENSKII, S.N. GRUSHEVSKAYA, S.V. GANZHA, D.S. ELISEEV  PROC. NAP 1, 03TF01 (2012) 
 
 
03TF01-2 
 
 
Fig. 1 – Cyclic voltammograms of polycrystalline copper and 
single crystals in 0.1 M KOH 
 
The values of current efficiency of oxide formation on 
different single crystals are similar and hardly differ 
from the current efficiency obtained for polycrystalline 
copper (Table 1). The film thickness sharply increases 
and the current efficiency noticeably decreases at tran-
sition to positive potentials where the formation of 
Cu(II) oxide is possible. 
 
 
 
Fig. 2 – Cyclic voltammograms (а) and the dynamics of oxygen 
adsorption (b) on single crystals of copper in 0.1 M KOH 
 
 
Table 1 –  Anodic charge of Cu(I) and Cu(II) oxide formation Qa, cathodic charge of reduction Qc, current efficiency  and the 
average thickness of oxide film L 
 
Substrate Oxide Е / V Qa / mC Qc / mC  / % L / nm 
Cu(111) 
Cu2O -0.16 0.29 0.26 90 1.6 
CuO 0.10 15.2 7.9 52 52 
Cu(110) 
Cu2O -0.16 0.78 0.77 99 4.7 
CuO 0.10 21.0 12.8 61 84 
Cu(100) 
Cu2O -0.16 0.43 0.37 85 2.3 
CuO 0.10 15.3 10.4 68 68 
Cu(poly) 
Cu2O -0.17 1.00 0.99 99 1.9 
CuO 0.10 10.0 6.3 63 6.5 
 
 
4. PHOTOELECTROCHEMICAL PARAMETERS 
OF CU(I) AND CU(II) OXIDE FILMS 
 
The negative photocurrent appears 10-30 minutes 
after the start of the anodic potentiostatic polarization 
of Cu(111) and Cu(100), proving the formation of p-type 
oxide film. The amplitude of the photocurrent increases 
with film thickness and then stabilizes (Fig. 3). The 
theory of thin semiconducting films [1, 2] makes it pos-
sible to obtain the parameters of oxide phase (Table 2). 
The values of optical density , space charge region W 
and concentration of acceptor defects NA do not vary 
with the crystal face of the substrate. Besides, they are 
close to similar parameters of the oxide formed on poly-
crystalline copper. However, the values of maximal pho-
tocurrent maxphi  and of complex parameter f(1 – 
out
refR ) on 
Cu(100) exceed the values obtained on Cu(111) and 
polycrystalline copper. One can assume that the oxide 
formed on Cu(100) has a high effectiveness  of light 
adsorption and of subsequent assimilation f of electrons 
in the electrochemical reaction. On the other hand, the 
different values of maxphi  and f(1 – 
out
refR ) can be caused 
by the different coefficients out
refR  of light reflection form 
the oxide/solution interface, since the morphology of 
oxide film on Cu(poly) and Cu(111) sharply differ from 
the oxide film on Cu(100). 
Spectral dependence of photocurrent in Cu2O films 
on Cu(110) and Cu(100) has two peaks in short-wave 
range (Fig. 4). Cu2O oxide formed on Cu(111) generates  
 
 
 
Fig. 3 –  Photocurrent dependence on the thickness of Cu(I) 
oxide film at E  – 0.20 V 
 THIN OXIDE FILMS ON COPPER SINGLE CRYSTALS… PROC. NAP 1, 03TF01 (2012) 
 
 
03TF01-3 
Table 2 – The structural and optical characteristics of Cu2O at E  – 0.20 V, = 400 nm and 0 = 3.04 1015 photon cm-2 s-1 
 
Substrate 
max
phi / А cm
-2 f(1 – out
refR ) 10
4 10-5 / cm-1 W / nm NA 10-17 / cm-3 
Cu(111) 0.35 7.2 19.2 21.5 2.04 
Cu(100) 11.9 240.3 11.1 28.9 1.13 
Cu(poly) 2.20 45.2 7.6 40.7 0.48 
 
 
 
Fig. 4 –  Spectral dependence of photocurrent in Cu(I) (а) and Cu(II) (b) oxides on single crystals of copper at E = -0.17 V 
 
the negative photocurrent only at = 400 nm. The reliable 
linearization in coordinates criterial for non-direct transi-
tions occurs for Cu(100). The band gap is equal to 2.2 eV 
as it was obtained for Cu2O on polycrystalline copper. 
At the potentials of CuO formation an additional 
peak appears in the spectral dependence at low energy 
(   600 nm). The linearization is not possible, however a 
red boundary of the additional peak is close to CuO band 
gap (1.5 eV). The position of two main peaks remains the 
same as it was during Cu2O formation. Hence, the film 
consists of both Cu(I) and Cu(II) oxides. Cu2O makes the 
main contribution in the photocurrent amplitude. In 
general, band structure of anodic oxides Cu(I) and Cu(II) 
is invariant to the crystal state of the electrode. 
 
5. THE MORPHOLOGY OF OXIDE FILMS 
 
The more relief Cu2O film formed on Cu(100) (Fig. 
5b) is similar to the film formed on polycrystalline cop-
per (Fig. 5a). High and comparative photocurrents are 
typical for these two cases. Since oxide films formed on 
Cu(110) and Cu(111) look like “smooth” and do not 
show clear structural elements (Figs. 5c and 5d), they  
 
 
 
Fig. 5 – SEM-images of Cu(I) oxide film (20 nm) formed on 
polycrystalline copper (a), Cu(100) (b), Cu(110) (c) and Cu(111) 
(d) at Е = – 0.19 V (60 min) 
generate low photocurrent. Most probably, the anodic 
growth of Cu2O is realized in two different ways, i) the 
formation and overlapping of 3D-nuclea on Cu(100) and  
Cu(poly), ii) the formation of 2D-layers on Cu(110) and 
Cu(111). A noticeable difference in the electrochemical 
behavior, morphology and photocurrent amplitude for 
the oxides on different substrates proves the direct 
electrochemical way of oxide formation, not the mecha-
nism of dissolution/precipitation. 
In the potential range of Cu(II) oxide growth the 
amplitude of photocurrent is nearly constant for differ-
ent single crystals and three times higher than it was 
for polycrystalline copper. 
The results of SEM confirm the lack of noticeable 
difference in the structure and shape of crystals of ox-
ide phase (Fig. 6). One can see large needle-shaped 
objects apparently corresponding to CuO with mono-
clinic crystal system. Besides large CuO crystals, the 
particles with smaller size present, probably Cu2O un-
delayer. In general, the influence of crystal structure of 
the substrate to the photoelectrochemical, structural 
and morphological properties of oxide is negligible. 
 
 
 
Fig. 6 – SEM-images of Cu(II) oxide film (60 nm) formed on 
polycrystalline copper (a), Cu(111) (b), Cu(110) (c) and Cu(100) 
(d) at Е = 0.10 V (20 min) 
 A.V. VVEDENSKII, S.N. GRUSHEVSKAYA, S.V. GANZHA, D.S. ELISEEV  PROC. NAP 1, 03TF01 (2012) 
 
 
03TF01-4 
6. CONCLUSION 
 
The anodic oxidation of single crystals of copper in 
0.1 M KOH proceeds with a noticeable diffusion limita-
tion in solid phase. The oxide formation is preceded by 
chemisorption of OH-ions above -0.7 V. The extent of 
surface filling by oxygen does not exceeds 0.12 in the 
potential range up to -0.4 V and it is maximal for 
Cu(111). The current efficiency of the Cu(I) oxide for-
mation  is about 90 ÷ 100 %, the current efficiency of 
Cu(II) oxide formation is about 50 ÷ 60 %. At the poten-
tials of Cu(II) formation both Cu2O and CuO are incorpo-
rated into the oxide film. The negative photocurrent 
proves the p-type of Cu(I) and Cu(II) oxides. The oxide 
parameters slightly change with the crystal structure 
of the substrate. The morphology of the oxide phase 
plays an important role. 
 
AKNOWLEDGEMENTS 
 
Authors are grateful for financial supporting to 
RFBR (project 09-03-00554-а). 
 
REFERENCES 
 
1. A. Vvedenskii, S. Grushevskaya, D. Kudryashov, 
S. Ganzha, J. Solid State Electrochem.  14, 1401 (2010). 
2. D.A. Kudryashov, S.N. Grushevskaya, S.V. Ganzha, 
A.V. Vvedenskii, Prot. Metals Phys. Chem. Surf. 45, 501 
(2009). 
3. J. Kunze, V. Maurice, L.H. Klein, H.-H. Strehblow, 
P. Marcus, J. Electroanal. Chem. 554, 113 (2003). 
4. V.D. Jovich, B.M. Jovich, J. Serb. Chem. Soc. 67, 531 (2002). 
5. S.V. Ganzha, S.N. Maksimova, S.N. Grushevskaya, 
A.V. Vvedenskii, Prot. Metals Phys. Chem. Surf. 47, 191 
(2011). 
 
 


English

Thin Oxide Films on Copper Single Crystals: Anodic Formation and Photoelectrochemical Properties

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 1 No 3, 03TF01 (4pp) (2012)   2304-1862/2012/1(3)03TF01(4) 03TF01-1  2012 Sumy State University Thin Oxide Films on Copper Single Crystals: Anodic Formation  and Photoelectrochemical Properties  A.V. Vvedenskii, S.N. Grushevskaya*, S.V. Ganzha, D.S. Eliseev  Voronezh State University, 1, Universitetskaya Sq., 394006 Voronezh, Russia  (Received 01 February 2012; published online18 July 2012)  Thin oxide films were grown anodically on polycrystalline copper and single crystals Cu(100), Cu(110) and Cu(111). Semiconductor properties of copper oxides were obtained by photocurrent measurements. The morphology of the anodic oxides was monitored by SEM. A p-type conductivity was established for Cu2O and СuO formed on Cu during the anodic polarization. The main semiconductor properties do not depend on the crystal face; the band gap in thin Cu2O is equal to 2.2 eV.  Keywords: Copper, Single crystals, Anodic oxide formation, Photocurrent, Spectroscopy.    PACS number: 82.45. – h   ______________ * sg@chem.vsu.ru 1. INTRODUCTION  Metal oxides are widely used in photolytic hydrogen evolution, electrocatalysis as well as in the production of current-generating devices, UV- and IR-sensors. Cu(I) oxide is considered as a perspective material  due to the optimal combination of the number of parameters such as non-toxicity, low cost, simple production and the bandgap, providing the adsorption of most spectrum. Cu(II) oxide films can be grown much thicker than Cu(I) oxide, being using in barrier devices. The properties of thin oxide films and the kinetics of their formation depend on the electrode potential and solution composition as well as the crystal structure and chemical composition of the electrode surface. The latter is revealed for nanosized films of Ag(I) oxide on Ag and Ag-Au alloys [1, 2]. The aim was to establish the role of crystal structure of copper surface in the kinetics of anodic growth and properties of nanosized films of semiconductor  Cu(I) and Cu(II) oxides.  2. EXPERIMENTAL  The investigation were carried out on polycrystal-line copper (0.9999) and single crystals Cu(100), Cu(110) and Cu(111) (0.99999) in deaerated 0.1 M KOH prepared from double-distilled water and reagent-grade chemicals. Single crystals were prepared by “Materials Technology & Crystals for Research, Development and Production” with accuracy ≤ 2 . The kinetics of anodic formation and the properties of Cu(I) and Cu(II) oxides were examined by cyclic volt-ammetry and chronoammetry with synchronous regis-tration of photocurrent. The polarization of static elec-trodes during the preparation and the film growth was carried out using the computerized potentiostatic com-plex IPC-Compact (Institute of Physical Chemistry and Electrochemistry of Russian Academy of Science). The potentials are given in s.h.e. scale. The super-bright light emitting diodes “LIGITEK” were used as a source of quasi-monochromatic UV-irradiation (   385-875 nm) in the photoelectrochemi-cal measurements. The density of photon flux was con-stant and equal to 3.04 1015 photon cm – 2 s – 1. The dura-tion and frequency of light pulses were 50 ms and 5 Hz. The morphology and the chemical composition of the electrode surface were monitored by scanning elec-tron microscopy (JEOL JSM 6380LV) and energy dis-persion X-ray analysis (INCAx – sight 250).  3. ANODIC FORMATION OF THIN OXIDE FILMS  The voltammograms of copper in a wide potential range show the two main peaks A1 and A2, correspond-ing to Cu(I) and Cu(II) formation (Fig. 1a). The peak potential A2 ennobles and the peak current decreases: Cu(poly) > Cu(110) > Cu(111) > Cu(100). The potential and current of A1 peak on Cu(111) and polycrystalline copper are identical. On Cu(110) and Cu(100) the peak potential A1 is more negative and the peak current is lower as compared with poly-crystalline copper (Fig. 1b); the difference in the ca-thodic peaks C1 and C2 is less significant. The processing of the voltammograms in the criteri-al coordinates shows that the anodic formation and cathodic reduction of Cu(I) oxide on polycrystalline copper and single crystals proceeds with a noticeable diffusion limitation in solid phase. The charge transfer is not equilibrium. In the potential range more negative than the equi-librium potential of Cu(I) oxide formation we managed to reveal the weak anodic and cathodic peaks (Fig. 2a), corresponding to the adsorption of hydroxyl-ion with charge transfer [3, 4] and subsequent desorption of hy-droxyl-radical:   Cu(hkl) + OH– = Cu(hkl) – OHads + e–.   The integer of anodic currents gives the values of qa, corresponding to the charging of pseudo-capacity of the adsorption and the extent of surface filling by oxygen (Fig. 2b). In general the values of surface filling are low; Cu(111) shows the maximal surface filling. At  E < – 0.7 V the chemisorption of OH- on copper does not occur.   A.V. VVEDENSKII, S.N. GRUSHEVSKAYA, S.V. GANZHA, D.S. ELISEEV  PROC. NAP 1, 03TF01 (2012)   03TF01-2   Fig. 1 – Cyclic voltammograms of polycrystalline copper and single crystals in 0.1 M KOH  The values of current efficiency of oxide formation on different single crystals are similar and hardly differ from the current efficiency obtained for polycrystalline copper (Table 1). The film thickness sharply increases and the current efficiency noticeably decreases at tran-sition to positive potentials where the formation of Cu(II) oxide is possible.    Fig. 2 – Cyclic voltammograms (а) and the dynamics of oxygen adsorption (b) on single crystals of copper in 0.1 M KOH   Table 1 –  Anodic charge of Cu(I) and Cu(II) oxide formation Qa, cathodic charge of reduction Qc, current efficiency  and the average thickness of oxide film L  Substrate Oxide Е / V Qa / mC Qc / mC  / % L / nm Cu(111) Cu2O -0.16 0.29 0.26 90 1.6 CuO 0.10 15.2 7.9 52 52 Cu(110) Cu2O -0.16 0.78 0.77 99 4.7 CuO 0.10 21.0 12.8 61 84 Cu(100) Cu2O -0.16 0.43 0.37 85 2.3 CuO 0.10 15.3 10.4 68 68 Cu(poly) Cu2O -0.17 1.00 0.99 99 1.9 CuO 0.10 10.0 6.3 63 6.5   4. PHOTOELECTROCHEMICAL PARAMETERS OF CU(I) AND CU(II) OXIDE FILMS  The negative photocurrent appears 10-30 minutes after the start of the anodic potentiostatic polarization of Cu(111) and Cu(100), proving the formation of p-type oxide film. The amplitude of the photocurrent increases with film thickness and then stabilizes (Fig. 3). The theory of thin semiconducting films [1, 2] makes it pos-sible to obtain the parameters of oxide phase (Table 2). The values of optical density , space charge region W and concentration of acceptor defects NA do not vary with the crystal face of the substrate. Besides, they are close to similar parameters of the oxide formed on poly-crystalline copper. However, the values of maximal pho-tocurrent maxphi  and of complex parameter f(1 – outrefR ) on Cu(100) exceed the values obtained on Cu(111) and polycrystalline copper. One can assume that the oxide formed on Cu(100) has a high effectiveness  of light adsorption and of subsequent assimilation f of electrons in the electrochemical reaction. On the other hand, the different values of maxphi  and f(1 – outrefR ) can be caused by the different coefficients outrefR  of light reflection form the oxide/solution interface, since the morphology of oxide film on Cu(poly) and Cu(111) sharply differ from the oxide film on Cu(100). Spectral dependence of photocurrent in Cu2O films on Cu(110) and Cu(100) has two peaks in short-wave range (Fig. 4). Cu2O oxide formed on Cu(111) generates     Fig. 3 –  Photocurrent dependence on the thickness of Cu(I) oxide film at E  – 0.20 V  THIN OXIDE FILMS ON COPPER SINGLE CRYSTALS… PROC. NAP 1, 03TF01 (2012)   03TF01-3 Table 2 – The structural and optical characteristics of Cu2O at E  – 0.20 V, = 400 nm and 0 = 3.04 1015 photon cm-2 s-1  Substrate maxphi / А cm-2 f(1 – outrefR ) 104 10-5 / cm-1 W / nm NA 10-17 / cm-3 Cu(111) 0.35 7.2 19.2 21.5 2.04 Cu(100) 11.9 240.3 11.1 28.9 1.13 Cu(poly) 2.20 45.2 7.6 40.7 0.48    Fig. 4 –  Spectral dependence of photocurrent in Cu(I) (а) and Cu(II) (b) oxides on single crystals of copper at E = -0.17 V  the negative photocurrent only at = 400 nm. The reliable linearization in coordinates criterial for non-direct transi-tions occurs for Cu(100). The band gap is equal to 2.2 eV as it was obtained for Cu2O on polycrystalline copper. At the potentials of CuO formation an additional peak appears in the spectral dependence at low energy (   600 nm). The linearization is not possible, however a red boundary of the additional peak is close to CuO band gap (1.5 eV). The position of two main peaks remains the same as it was during Cu2O formation. Hence, the film consists of both Cu(I) and Cu(II) oxides. Cu2O makes the main contribution in the photocurrent amplitude. In general, band structure of anodic oxides Cu(I) and Cu(II) is invariant to the crystal state of the electrode.  5. THE MORPHOLOGY OF OXIDE FILMS  The more relief Cu2O film formed on Cu(100) (Fig. 5b) is similar to the film formed on polycrystalline cop-per (Fig. 5a). High and comparative photocurrents are typical for these two cases. Since oxide films formed on Cu(110) and Cu(111) look like “smooth” and do not show clear structural elements (Figs. 5c and 5d), they     Fig. 5 – SEM-images of Cu(I) oxide film (20 nm) formed on polycrystalline copper (a), Cu(100) (b), Cu(110) (c) and Cu(111) (d) at Е = – 0.19 V (60 min) generate low photocurrent. Most probably, the anodic growth of Cu2O is realized in two different ways, i) the formation and overlapping of 3D-nuclea on Cu(100) and  Cu(poly), ii) the formation of 2D-layers on Cu(110) and Cu(111). A noticeable difference in the electrochemical behavior, morphology and photocurrent amplitude for the oxides on different substrates proves the direct electrochemical way of oxide formation, not the mecha-nism of dissolution/precipitation. In the potential range of Cu(II) oxide growth the amplitude of photocurrent is nearly constant for differ-ent single crystals and three times higher than it was for polycrystalline copper. The results of SEM confirm the lack of noticeable difference in the structure and shape of crystals of ox-ide phase (Fig. 6). One can see large needle-shaped objects apparently corresponding to CuO with mono-clinic crystal system. Besides large CuO crystals, the particles with smaller size present, probably Cu2O un-delayer. In general, the influence of crystal structure of the substrate to the photoelectrochemical, structural and morphological properties of oxide is negligible.    Fig. 6 – SEM-images of Cu(II) oxide film (60 nm) formed on polycrystalline copper (a), Cu(111) (b), Cu(110) (c) and Cu(100) (d) at Е = 0.10 V (20 min)  A.V. VVEDENSKII, S.N. GRUSHEVSKAYA, S.V. GANZHA, D.S. ELISEEV  PROC. NAP 1, 03TF01 (2012)   03TF01-4 6. CONCLUSION  The anodic oxidation of single crystals of copper in 0.1 M KOH proceeds with a noticeable diffusion limita-tion in solid phase. The oxide formation is preceded by chemisorption of OH-ions above -0.7 V. The extent of surface filling by oxygen does not exceeds 0.12 in the potential range up to -0.4 V and it is maximal for Cu(111). The current efficiency of the Cu(I) oxide for-mation  is about 90 ÷ 100 %, the current efficiency of Cu(II) oxide formation is about 50 ÷ 60 %. At the poten-tials of Cu(II) formation both Cu2O and CuO are incorpo-rated into the oxide film. The negative photocurrent proves the p-type of Cu(I) and Cu(II) oxides. The oxide parameters slightly change with the crystal structure of the substrate. The morphology of the oxide phase plays an important role.  AKNOWLEDGEMENTS  Authors are grateful for financial supporting to RFBR (project 09-03-00554-а).  REFERENCES  1. A. Vvedenskii, S. Grushevskaya, D. Kudryashov, S. Ganzha, J. Solid State Electrochem.  14, 1401 (2010). 2. D.A. Kudryashov, S.N. Grushevskaya, S.V. Ganzha, A.V. Vvedenskii, Prot. Metals Phys. Chem. Surf. 45, 501 (2009). 3. J. Kunze, V. Maurice, L.H. Klein, H.-H. Strehblow, P. Marcus, J. Electroanal. Chem. 554, 113 (2003). 4. V.D. Jovich, B.M. Jovich, J. Serb. Chem. Soc. 67, 531 (2002). 5. S.V. Ganzha, S.N. Maksimova, S.N. Grushevskaya, A.V. Vvedenskii, Prot. Metals Phys. Chem. Surf. 47, 191 (2011).   

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Thin Oxide Films on Copper Single Crystals: Anodic Formation and Photoelectrochemical Properties

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