HfO2 Thin Films Prepared by
Hydrothermal Synthesis
Shen Jun, Wang Shengzhao, Wang Xiaodong, Zhang Zhihua, Zhou Bin, Wu Guangming
(Tongji Univer sity, Shan ghai 200092, China)
Abstract: Hf O2 sols were prepared by hydrothermal synthesis from HfOCl2·8H2O (precur sor). Hf O2 thin films were f urther prepared via a sp in coatin g method. TEM an d p article size an alyzer were ud to characterize the micro str ucture and particle size distribution of the Hf O2 so ls. It is foun d that the particle size in HfO2 sols can be controlled from abo ut 3 nm to 100 nm via chan ging reaction param eters. The HfO2 an d HfO2-P VP thin films were characterized by ellip someter, atomic for ce microscope (AFM), and Four ier-transform infr ared spectroscopy (FTIR) respectively. The roughn ess of Hf O2-P VP films is less than 0.5 nm and the refractive index is abo ut 1.75. The results sho w that the lar damage threshold of HfO2 f ilm s is higher than 15 J/cm3 (1064 nm, 1 ns), while the lar damage thresho ld for Hf O2-P VP coatin gs can be as high as 20 J/cm3 (1064 nm,
1 ns). The mechanism of the lar damage process of HfO2-PVP coatin gs was also discusd.
Key words: HfO2 films; hy drothermal synthesis; h igh refractive index; HfO2-P VP thin films
CLC number: O484.1 Document code: A Article ID: 1002-185X(2010)S2-052-05
It is well known that optical coatings are generally prepared by the physical vapor deposition (PVD) technology[1]. Recently sol-gel techno logy has become an effective and competitive alternative. Colloidal-bad HfO2 coatings have unique properties such as nanoscale pores and crystallite s izes. And this wet chemical coating technique is normally a room temperature process with less expensive equipment. Moreover, it is easy for industrial scale up. Sol gel-derived HfO2 coatings are of great technological interest in the fields of corrosion protection, nsor films, as well as catalytic films[2-4]. Moreover, with high dielectric constant and high refractive index[5], HfO2 thin films are expected to have important applications in the field of electronics and optics[6-9]. In the prent paper, HfO2 colloidal suspension was synthesized via a hydrothermal process and the features of HfO2 and HfO2-PVP coatings were investigated. solution in order to adsorb and remove the acids. At the end of reaction the pH value of the solution was 4.0. The clear solution was held at 150-250 °C for 1-2 h in a stainless steel autoclave coated with Teflon linear. Then it was quenched in an ice-bath to a regular temperature. Finally the water was replaced by 2-methoxyethano l (b.p. 124 °C) by distillation. The clear and stable ethano l sol containing 5wt% HfO2
with the particle size of about 12 nm was obtained.
HfO2-PVP sol was obtained by adding different PVP solid content into HfO2 sol. Subquently, HfO2 and HfO2-PVP thin films were deposited on silicon-wafers, K9 glass or quartz glass us ing a spin coating method with the speed in the range of 2000-3000 r/min. The films were heated by a heating plate with the tempe-rature controlled from 80 to 500 °C for 0.5-2 h in air.
2
2.1
Results and Discussions
Effect of hydrothermal s ynthesis temperature
on the particles size of HfO2 sols
The autoclave was filled to 70 percent of its volume.
1Experimental
HfO2 colloidal suspension was synthesized via hydrothermal process. A solution of hafnium oxychloride
octahydrate (HfOCl2·8H2O) was first dissolved in water (0.4 mol·dm-3). The pH value of the resultant solution was less than 1.0. Anion exchange res in was added in the The following parameters were t for the hydrothermal synthesis: the precursor concentration of 0.35 mol/L, pH value of 3.5 and time of 42 min. Experiments reveal that
Received date: 2010-04-21
Foundation item: Supported by Chine National Foundation of High Technology (2008AA8041606); Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology (07DZ22302); Shanghai Educational Development Foundation (2007CG26); Program for Young Excellent Talents in Tongji University (2006KJ052)
Corresponding author: Shen Jun, Ph. D., Professor, Pohl Institute of Solid State Physics, Tongji University, Shanghai 200092, P. R. China, Tel/Fax:0086-21-65896071,E-mail:****************
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Shen Jun et al: HfO2 Thin Films Prepared by Hydrothermal Synthesis
饮料可以带上高铁吗the hydrothermal synthesis temperature has an significant effect on the particle size of HfO2 sols (Fig.1).
When the temperature of water was 165 °C, the particle of HfO2 sols was s mall with size around 3 nm. At this time, hydrothermal synthesis was not full y carried out. With increas ing of the hydrothermal synthesis temperature, HfO2 sols particle size incread continually. When the temperature of water reached 180 °C, HfO2 particles mainly distributed in a narrow range around 7 nm. When the temperature of water reached 195 °C, particle distribution curve of HfO2 sols manifest that the particles grew rapidly and distributed in a wider scope. There are two peaks in the HfO2 particle distribution curve. The peaks prent that the particles mainly distributed in 15 and 75 nm around (Fig.1). mol/L and pH value of about 0.50, hydrothermal synthesis reaction would not fully proceed. Therefore, small particles with an average size of 3 nm in the solution were obrved. With lowered concentration of the precursor and higher pH value of the solution, the particle size incread in the hydrothermal reaction of the HfO2 sols. The precursor with concentration of 0.35 mol/L made sols with s maller particles mainly distri-bute in a narrow range around 7 nm. While the pre-cursor with concentration of 0.20 mol/L generated the HfO2 so
l of incread particle s ize with a very narrow distribution at around 9 nm, which can be en from the particle size distribution curve.
2.3Effect of hydrothermal synthesis time on the
particle size of HfO2 sol
电脑显示桌面Hydrothermal synthesis time was changed in order to
行军九日2.2 Influence of precursor concentration on
reaction of the hydrothermal process the
investigate the effect of the time on HfO2 particle size and
distribution of the sol. Other reaction parameters were
controlled as the precursor concentration of 0.35 mol/L,
the pH value of about 3.5, hydrothermal synthesis
temperature of 180 °C, and 70% of the autoclave filled.
Under longer hydrothermal synthesis time, HfO2 sols’ particle size grew larger, and the particle distribution
became wider (Fig.3). Hydrothermal synthesis process
included an initial generation of the nuclear particles and
a subquent growth in particle s ize. When the
hydrothermal synthesis time was short, the nucleus had
not yet formed or the number of nuclei wasn’t enough.
Conquently, the reaction couldn’t proceed completely
without the precipitation from the HfO2 nucleation.
W hen the reactio n time was 40 min, HfO2 s ol particles were mainly distributed around 3 nm. When the
respon time reached 42 min, for mation of a large鲨鱼怎么做好吃
number of nuclei in the solution led to a rapid increa in
the concentration till saturation of the HfO2 sols. Con-
quently, the sols had s mall particle s ize and narrow
particle dis tribution. The analys is showed a s ma ller
HfOCl2·8H2O with different concentrations, 0.20, 0.35, and 0.50 mol/L, were prepared respectively, with the autoclave filled in 70%, hydrothermal temperature of 180 °C and reaction time of 42 min. Subquently, the effect of the precursor concentration on HfO2 particle size distribution was investigated.
W hen other conditions were s et, the precu rsor concentration has great influence on the s ize of particles in the sol (Fig.2). With precursor concentration of 0.50
Particle Size/nm
Fig.1 Particles size distribution of HfO2 sols at different
hydrothermal synthesis temperatures
particle distribution in HfO sol with the major particle
2
5
5
4
4
3
3
2
2
1
1
P article Size/n m
Particle Size/nm
90 100
Fig.2 Particle size distribution of HfO2 sol with differ ent
precursor concentration
Fig.3 Particle size distribution of HfO2 sol for different
hydrothermal synthesis time V
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稀有金属材料与工程 第 39 卷
size at around 7 nm. larger HfO 2 particle Meanwh ile, the reaction showed size and incread number of 2.4 Effect of pH value on the hydrothermal synthesis
time of ideal HfO 2 sol
The quality ratio of ion exchange resin to particles. The main reason was that HfO 2 particles grew up and clustered gradually due to high temperature and high pressure. This reason lead to increa in the particle size and the clustering process of particles.
The particle continuously incread in size and its distribution range became wider with the extension of hydrothermal synthesis time. When the respon time reached 45 min, the sol particle distribution curve had two distribution peaks: around 9 and 20 nm. Hydro- thermal synthesis time of 50 min also resulted in particle size distribution curve with two peaks at about 15 and 70 nm. HfO 2 sol particles were mainly distributed in about 40 nm with wider size distribution at reaction time of 55 min.
TEM images in Fig.4 prents a gradual growth in sol particles in increasing hydrothermal synthesis time. At the same time, the particles clustered and the cluster size incread as the reaction time incread. Finally, some large s ize hard clusters could be formed. The hard clusters would influence the sol properties, even
leading to the sols no longer uful for coating.
precursors quality was changed to adjust the solution pH value. W ith 70% of the autoclave filled, the precursor concentration of 0.35 mol/L, and the hydrothermal temperature of 180 °C, the influence of pH value on the hydrothermal synthesis process was also investigated (Table 1).
The hydrothermal synthesis time of the ideal sols incread as a result of a decrea in the pH value. Due to the existence of H +, the induced time was extended and the efficiency was reduced for the hydrothermal synthesis. Eventually, we could u the previous ly mentioned parameters to optimize the preparation conditions for the targeted HfO 2 sols.
2.5 Influence of coating technology on the refractive
index Effect of different coating speed on the film refractive index and the thickness was investigated. HfO 2 thin films were coated on different substrates with different speeds and the resultant films were annealed in the same heating treatment process. The refractive index and the thickness of the thin films were examined by ellipsometer.
The speed of the spin coating machine had impact on the refractive index and the thickness of HfO 2 thin film. A higher speed led to a dry film before reaching the desired speed. Conquently, further higher speed had no significant influence on the thickness of HfO 2 thin film (Fig.5). We assumed th
at there was no simple linear relationship between the thickness of the films and the rotational speed of the spin coater.
2.6 Influence of the accession of PVP on the HfO 2
films refractive index
Table 2 displays the effect of PVP content on the film refractive index and the thickness. With the increa of the PVP content in the sol, refractive index of films became too higher.
When the PVP/HfO 2 (mass ratio) reached to 10%, the refractive index of HfO 2-PVP film was 1.75, much higher than that of HfO 2 thin film (1.630). However, with further increa of PVP, the refractive index of
a
Table 1 E ffect of pH value on the hydrothermal time
1:2 2:3 1:1 2:1 1:0
HfOCl 2·8H 2O ：
Anion-exchan ge resin
2.33 2.03 1.80 1.60 0.76 pH value of HfOCl 2
aqueo us solution Hydrothermal Fig.4 TEM images of Hf O 2 sols with differ ent hydrother-
mal synthesis time: (a) 40 min, (b) 50 min, and (c) 55 min
26
28
30
32
42
synthesis time/min
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Shen Jun et al : HfO 2 Thin Films Prepared by Hydrothermal Synthesis
temperature should not exceed 300 °C when the organic binder PVP was ud in the HfO 2 film. 2.8 HfO 2-PVP film morphology
The surface toughness R a of HfO 2-PVP thin films were different (Fig.7) at various temperatures. The organic ingred ients in the pores of HfO 2-PVP thin film burned gradually at that increas ing temperature. When the temperature reached 450 °C, some HfO 2 particles in the thin film grew larger and crystallized. This is the reason why the R a values of HfO 2-PVP thin film incread to 0.798 nm at 450 °C.
2.9 Effect of the accession PVP on the lar damage threshold of HfO 2-PVP film
In the HfO 2-PVP film, PVP wrapped the HfO 2
particles. Therefore, in the lar irradiation, PVP functioned to protect HfO 2 particles. Becau of its flexibility, PVP could easily reduce the lar impact on 1.640
70
Thickness o f H fO 2 thin fil m Refractive index o f H fO 2 thin fil m
1.635 65 1.630
60 1.625 55 1.620 50 1.615
45
1.610
2 3 4
Speed of Spin-Coatin g/×103 r·min -1
Fig.5 Effect of the rotational speed on the film thickness
and refractive in dex
T able 2 Influence of the PVP/ HfO 2 mass ratio on
HfO 2-PVP thin films thickness and refrac- tive index
西游记第一回读书笔记
Mass r atio of PVP/ HfO 2 Refractive index Thickness/nm
the HfO films and thermal stress inside the film. The 2 100/0
5/100 10/100 15/100
20/100
1.590
1.736 1.750 1.743 1.730
45.12 76.34 81.18 73.26 74.61
experiments showed that the lar damage threshold of the HfO 2-PVP film was 20 J/cm 2 (1064 n
m, 1ns, with 150 °C heating treatment), higher than the as-prepared HfO 2 thin film of 15 J/cm 2 (1064 nm, 1ns).
脚手架施工方案HfO 2-PVP film dropped slightly. This is becau PVP had relatively low refractive index contrast with HfO 2 skeleton.
2.7 FTIR of HfO 2-PVP film
The infrared spectra of HfO 2-PVP thin film with different temperature of heat treatment manifes ted different pecks (Fig.6). As shown in the infrared spectra, when the heating temperature incread, some infrared absorption peaks (between 1292 and 1662 cm -1) corre- sponding to various organic groups were weakened. This could be explained by the gradual burn ing out of organic ingredients in the film at high-temperature. When the temperature reached 450 °C, the absorptio n peaks a
R a =0.410 nm
b
cm -1 between 1292 and 1662 disappeared. The main reason was that organic solvents and PVP in the film burned out at a high temperature. Clearly, the treating
R a =0.653 nm
c
450 °C
300 °C 150 °C
3000
665
3400
1292
R a =0.798 nm
1600
500
1500 2500
3500
4500
Fig.7 AFM photos of HfO 2-PVP thin films after different
heating treatment at different temperatures: (a) 150 °C, (b) 300°C, and (c) 450 °C
Waven um ber/cm -1
Fig.6 FTIR spectra of HfO 2-P VP thin films
T r a n s m i t t a n c e /a .u
T h i c k n e s s /n m
R e f r a c t i v e I n d e x
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3Conclusions
Ideal HfO2 sol
286(1-2): 127
[3] Mehner A, Klumper-Westkamp H, Hoffmann F et al. Thin
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Chemica l[J], 1995, 25(1-3): 705
[5] Luo Aiy un, Shen Jun, Yan g Fan et al. High Power La r and
Particle Beams[J], 2006, 18(9): 1486
[6] Xu Xian g, Zhou Bin, Liu Ch unze et al. Journal of Inorganic
Materia ls[J], 2006, 21(3): 753
[7] Rainer F, De Marco F P, Staggs M C et al. Proc SPIE[J], 1994,
2114(9): 9
[8] Floch H G, Bellev ille P F. Proc SPIE[J], 1996, 2714(521): 521
[9] Thomas I M. Proc SPIE[J], 1994, 2288(50): 50
[10] Wang Shen gzh ao(王生钊), Sh en Jun(沈军) et al. Jou rnal of
Tongji University(Natu ral Scien ce)(同济大学学报)[J], 2007,
35(12): 1666
was obtained via hydrothermal
with the optimum reaction para-
synthesis technology
meters concluded in the paper. Colloid-bad HfO2 and
HfO2-PVP high refractive index coatings[10] were prepared
on glass substrates by spin-coating techno logy. The
features of HfO2-PVP coatings by different temperature
treatments were investigated for a desired R a of around
0.4 nm. Lar damage threshold of 20 J/cm2 for
HfO2-PVP coatings was achieved using high power lar
屠乃奔倚其下at the wavelength of 1064 nm and puls width of 1 ns.
References
[1] Sh en Jun, Zhan g Qinyuan, Wan g Jue et al. Jou rnal of Sol-Gel
Science and Technology[J], 2000, 19(1-3): 271
[2] Di Maggio R, Rossi S, Scar di P. Thin Solid Film s[J], 1996,
水热合成法制备HfO2 薄膜
沈军，王生钊，王晓栋，张志华，周斌，吴广明
(同济大学，上海200092)
摘要：以HfOCl2·8H2O 为前驱体采用水热合成法制备了HfO2 溶胶，采用旋涂法制备了HfO2-P VP 薄膜。利用透射电镜和粒度分析仪观察和表征Hf O2 溶胶的微观结构和粒度分布。实验发现，通过调整不同的水热合成温度、反应物前驱体浓度、溶液的pH 值和水热合成时间等制备条件，可以在3~100 nm 范围内对Hf O2 溶胶颗粒的大小进行控制。分别采用椭偏仪，原子力显微镜，傅里叶红外变换光谱对Hf O2–PVP 薄膜的形貌和结构进行了表征和测量。结果表明，旋涂法制备的Hf O2-P VP 薄膜的粗糙度小于0.5 nm，折射率达1.75 左右。实验还发现，HfO2 薄膜的激光损伤阈值达到15 J/cm3（1064 nm，1 ns），Hf O2-P VP 薄膜的激光损伤阈值可高达20 J/cm3 (1064 nm，1 ns)。还对HfO2-P VP 薄膜中有机粘结剂PVP 在激光诱导损伤过程中的作用机理进行了初步探讨。关键词：Hf O2 薄膜；水热合成；高折射率；HfO2-P VP 薄膜
作者简介：沈军，男，1967 年生，博士，教授，博士生导师，同济大学波耳固体物理研究所，上海200092，电话/传真：************，E-mail: sh enjj@on
