Non-equilibrium Deposition of Phase Pure Cu2O
Thin Films at Reduced Growth Temperature
Archana Subramaniyan1,2,*, John D. Perkins1, Ryan P. O’Hayre2, Stephan Lany 1,
Vladan Stevanovic1, David S. Ginley1 and Andriy Zakutayev1,*
1
2
National Renewable Energy Laboratory, Golden, CO, 80401, USA
Department of Metallurgical and Materials Engineering, Colorado School of
Mines, Golden, CO, 80401, USA
Supplemental information
Table of contents
S1. Temperature profile
S2. XRD pattern of Cu-O film with increasing temperature
S3. Cu-O film thickness
S4. Microstructural images of phase pure Cu2O thin films
S5. References
S1
S1: Temperature profile:
The temperature gradient was obtained on the 50x50 mm Eagle 2000 glass
substrate by using the setup shown in Figure 1(a) in the main manuscript. The
temperature on the surface of the glass substrate was measured in-situ using a type-K
thermocouple at heater set point temperatures 400, 500, 600 and 700 °C. The results are
shown in Figure S1.1(a).
Figure S1.1: (a) Temperature profile across the substrate surface measured in-situ via
thermocouples at heater set point temperatures of 400, 500, 600 and 700 °C. (b) The
variation of constants a, b and c in T = a+bxc as a function of the set point temperature.
The temperature profile was fitted to an empirical function T = a+bxc, where T is
the substrate temperature, x is the substrate distance, and a, b and c are constants. The
constants vary with temperature as shown in Figure S1.1 (b). From the figure, the values
of the constants a, b and c are fitted to be 0.36±0.001, 23.81±1.32 and 30 x10-5 ±
6.32x10-5 respectively. Using these constants in the fitted function, the temperature
profile can be calculated for any heater set point temperature. Figure S1.2 shows the
temperature profile for the heater set point temperature of 800 °C. At the set point
temperature of 800 °C, a temperature range of 300 – 600 °C was obtained on the surface
of the substrate.
Figure S1.2: Temperature profile across the 50x50 mm substrate at heater set point
temperature of 800 °C.
S2
S2. XRD pattern of Cu-O film with increasing temperature
With increasing temperature, either a reduced second phase forms or the x-ray
intensity of the reduced second phase increases, as shown in Figure S2.1
Figure S2.1: X-ray diffraction pattern of Cu-O library deposited at 0.025 mTorr pO2 and
20 mTorr total pressures. With increasing temperature, the x-ray intensity of Cu second
phase is increased.
S3
S3: Cu-O film thickness
The thickness range of eleven data points from the last row of the Cu-O libraries
are shown in Table S3.1. To estimate the accuracy of the thickness measured from XRF,
the thickness were also measured from cross sectional SEM images. The thickness from
XRF was found to be twice as that of SEM images as it includes both the film and the
particulates.
Table S3.1: Thickness of Cu-O libraries deposited at total chamber pressures from 3 –
100 mTorr at a constant pO2 measured via XRF.
pO2 (mTorr)
0.25
Ptot (mTorr)
3
10
20
30
60
100
Thickness (µm)
0.40 – 0.60
0.45 – 0.54
0.72 – 0.92
0.34 – 0.48
0.36 – 0.42
0.22 – 0.36
A non-monotonic trend is observed with increasing thickness. The thickness
increases with increasing total pressure up to 20 mTorr and then decreases. A similar
trend was also observed in literature1 for the deposition of Ag in Ar atmosphere, where
the decreasing thickness after a certain pressure is attributed to re-sputtering effects.
S4
S4: Microstructural images of phase pure Cu2O thin films
Secondary electron images of phase pure Cu2O deposited at 3 (and 600 C), 20
(and 308 C) and 100 mTorr (and 600 C) total pressure are shown in Figure S4.1. The
respective pure phases are highlighted in white circle in figure 3(a) in the main
manuscript. Pulsed laser deposition is notorious for generating micron sized particulates
in deposited thin films2 and we also observed Cu-O particulates in all our deposited thin
films. The grain size of the films (excluding particulates) was estimated using imagej
software and is tabulated in Table S4.1.
Figure S4.1: Secondary electron images of phase pure Cu2O synthesized at 0.25 mTorr
pO2 and (a) Ptot: 3 mTorr and T: 600 °C (b) Ptot: 20 mTorr and T: 308 °C and (c) pO2: 100
mTorr and T: 600 °C. (d) Cross sectional image of phase pure Cu2O synthesized at Ptot:
20 mTorr and T: 308 °C.
The grain size was observed to increase with increasing temperature. For
example, at 3 mTorr total pressure and 0.25 mTorr pO2, the grain size increases from 70
– 200 nm at 300 C to 350 – 640 nm at 600 C. The grain size does not change with
varying total chamber pressure, but faceted grains were observed at higher total chamber
S5
pressure (Ptot: 100 mTorr) as can be seen from Figure S4.1 (a) and (c). The cross sectional
SEM image of phase pure Cu2O shows the presence of particulates on top of the uniform
thin film.
Table S4: Estimated grain size of phase pure Cu2O deposited at three different conditions
pO2: 0.25 mTorr
Deposition
Estimated grain
condition
size
Ptot: 3 mTorr
350 – 640 nm
T: 600 C
Ptot: 20 mTorr
60 – 140 nm
T: 308 C
Ptot: 100 mTorr
280 – 660 nm
T: 600 C
S6
S5: References
1. T. Scharf, H.U. Krebs, Influence of inert gas pressure on deposition rate during pulsed
laser deposition, Applied Physics a: Materials Science & Processing, 75 (2002) 551–554.
2. D.B. Chrisey and G.K. Hubler, Pulsed Laser Deposition of Thin Films (WileyInterscience, 1994).
S7