Specific Surface Free Energy of Ruby Thin Film Grown on Sapphire Single Crystals Studied by Contact Angle of Liquid Drop
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Specific Surface Free Energy of Ruby Thin Film Grown on Sapphire Single Crystals Studied by Contact Angle of Liquid Droplet Takaomi Suzuki, Shintaro Sugane, Miki Hidaka, Katsuya Teshima, and Shuji Oishi Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano-shi, 380-8553, Japan ABSTRACT Ruby thin film was grown on sapphire substrate by evaporation method of MoO3 flux. amount of Na2CO3 was added in order to decrease the evaporation rate of flux.
Small
The contact angles
of liquids and crystal surfaces were measured for water and formamide droplets, and the specific surface free energy of each face of the crystal was calculated using Fowkes approximation and Wu’s mean equations.
The growth hillocks on the synthesized thin film were observed.
The addition of
Na2CO3 incrased the density of hillocks and the specific surface free energy was larger for the ruby thin film, which has larger number of hillocks.
INTRODUCTION Specific surface free energy (SSFE) is significant to discuss the morphology of crystals.
For
example, SSFE of equilibrium shape of single crystal is proportional to the length of normal line to the surface from the center of the crystal.
This relationship is known as Wulff’s relationship, which
was theoretically established and proposed almost hundred years ago [1].
The relationship between
the growth rate of crystal faces and their SSFE was theoretically well discussed, but experimental verification of SSFE is very few.
We first time introduced the contact angle measurement
technique for determination of the specific surface free energy of chlorapatite [2] and ruby [3] and quartz [4] single crystals.
This time, in order to familiarize our experimental technique we propose
easier way to determine the SSFE of ruby single crystal using wide face of ruby single crystals epitaxially grown on sapphire single crystal and automatic contact angle measurement apparatus.
EXPERIMENTAL MoO3 was used as flux in order to synthesize the ruby thin film.
We used a sapphire single
crystal with diameter of 25.4 mm as substrate, which has wide (0001) face.
The substrate was cut
into quarter and put into crucible with Al2O3 powder and MoO3 flux. Small amount of Na2CO3 was added into the flux in order to control the evaporation rate of the flux.
The crucible was kept at
1000 °C for 10 h for evaporation of the MoO3 flux. The details of the synthesis of the sample ruby
1
thin film crystals are described elsewhere [5].
The synthesized ruby thin films were named as
Ruby(0), Ruby(1.14), and Ruby(1.94) for the samples with the amount of added Na2CO3: none, 1.14, and 1.94 mg/g into the MoO3 flux, respectively.
The SSFE of the synthesized ruby thin film was
determined from the contact angles of water and formamide droplets dropped on the crystal surface, using an automatic contact angle analyzer (Kyowa DM500).
The surfaces of the crystals were
observed using optical microscope (Nikon E600POL).
RESULTS AND DISCUSSION The obtained contact angles of water and formamide on Ruby(
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