7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Deposition and Modification of Semiconductor Thin Films ThroughAtmospheric Pressure PlasmaYu Xu1, Cheng-Ran Du1*, Sergey Kharapak3, Ke Ding1, Mierk Schwabe3, Ying Guo1, Jian-Jun Shi1,and Jing Zhang2†
1
College of Science, Donghua University，2Institut für Materialphysik im Weltraum, DeutschesZentrum für Luft- und Raumfahrt (DLR),Electronic address: chengran.du@dhu.edu.cn; jingzh@dhu.edu.cn
Nanoparticles grown in a plasma are used to visualize
the process of film deposition in a pulsed
radio-frequency (rf) atmospheric pressure glow discharge.
Modulating the plasma makes it possible to successfully
prepare porous TiO2 films[1]. We study the trapping of theparticles in the sheath during the plasma-on phase andcompare it with numerical simulations. During theplasma-off phase, the particles are driven to the substrateby the electric field generated by residual ions, leading to
the formation of porous TiO2 film. Using video
microscopy, the collective dynamics of particles in thewhole process is revealed at the most fundamental"kinetic" level.
Using pulse-modulated atmospheric pressure radio
frequency (RF) plasma, dense anatase TiO2 thin films
were successfully deposited on a temperature-sensitive
substrate (polyethylene terephthalate)[2]. Transmission
electron microscopy (TEM) results revealed that TiO2
nanoparticles grown and turn to anatase through plasmain just about 70 ms. Laser light scattering analysis
indicated that the TiO2 particles were trapped above thesubstrate at a height of approximately 0.27 mm during
the plasma process, which is consistent with thesimulated plasma sheath thickness of 0.26 mm. A

pulse-modulated atmospheric pressure RF plasma
deposition has been proposed.
To enhance the visible light response of TiO2 films,
atmospheric pressure He/H2 plasma treatment wasapplied. The originally white TiO2 thin film turned
completely black after plasma modification. The
modified thin film exhibited a significant enhancementin visible light absorption and reduction in bandgap,
which are advantageous for improving the utilization
efficiency of solar radiation. X-ray photoelectron
spectroscopy (XPS) results showed that a portion of Ti4+
had been reduced to Ti3+, resulting in self-doping andchanges in the band structure. I-V tests indicated that theresistance of the treated samples was reduced by a factorof 107 times compared to the original sample. Hydrogenions gain high kinetic energy as they are accelerated by
the plasma sheath, which is believed to play a crucialrole in plasma modification.

Figure 1. Dust dynamics in plasma, (a) dust distribution
from font side view at plasma on time in 50% duty cycle
plasma discharge, and (b) dust particles dynamics in theduty cycle discharge, and (c) plasma discharge intensity
at the corresponding time to the particles dynamics, and(d) substrate intensity at the corresponding time.
possible mechanism for explaining the behavior ofFigure 2. Planar and cross-sectional SEM micrographsof anatase TiO2 thin films deposited with the duty cycle(a), (b) 90%; (c), (d) 70%, and (e), (f) 50% at 305oC,
266 oC, and 216 oC, respectively.

References[1] Y. Xu et al, arXiv e-prints. 2019, arXiv:1903.09379.
[2] Y. Xu et al, Plasma Process. Polym.18(10) 2100050 (2021).