Temperature gradient: A simple method for single crystal growth

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Temperature gradient: A simple method for single crystal growth. In this article, we provide a simple method for growth of bulk single crystalline. By the control temperature along a vertical furnace, we can easily fabricate bulk single crystals. This technique is called the temperature gradient method. To create a temperature gradient along the body of the furnace, the density of resistance wire which is coiled along the body of furnace is different.
VNU Journal of Science: Mathematics Physics, Vol. 35, No. 1 (2019) 41-46
Original article
Temperature Gradient: A Simple Method
for Single Crystal Growth
Duong Anh Tuan 1,2,*, Nguyen Thi Thanh Huong3,
Nguyen Thi Minh Hai3, Pham Anh Tuan3, Dinh Thi My Hao4, Sunglae Cho3
1Phenikaa Institute for Advanced Study, Phenikaa University, Yen Nghia, Ha Dong, Hanoi, Vietnam
2Phenikaa Research and Technology Institute, A&A Green Phoenix Group, 167 Hoang Ngan, Hanoi, Vietnam
3Department of Physics and Energy Harvest-Storage Research Center, University of Ulsan,
Ulsan 680-749, Republic of Korea
4Department of Physics, Quy Nhon University, 170 An Duong Vuong, Quy Nhon, Vietnam
Received 22 December 2018
Revised 21 January 2019; Accepted 25 January 2019
Abstract: In this article, we provide a simple method for growth of bulk single crystalline. By the
control temperature along a vertical furnace, we can easily fabricate bulk single crystals. This
technique is called the temperature gradient method. Tocreate a temperature gradient along the body
of the furnace, the density of resistance wire which is coiled along the body of furnace is different.
The density increases from the bottom to the top of the furnace. So that, at any time of the growing
process, the temperature at the bottom of furnace is the smallest. During could down process, single
crystal in the ampoule has been grown up from a seed at the bottom. Using this method, we
successfully grew layer structure single crystals such as SnSe, SnSe2, SnS, GaTe, InSe2, GaSe. X-
ray diffractionand FE-SEM measurements indicated the high qualityof single crystals. Bychanging
cooling speed, we can control the number of defects in the single crystals.
Keywords: Temperature gradient method, single crystal growth, layer structure materials.
1. Introduction
Single crystal usually gives the specific characteristics of materials comparable to polycrystalline
and amorphous. It also uses to study the fundamental properties of materials. Base on fundamental
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Corresponding author.
https//doi.org/ 10.25073/2588-1124/vnumap.4311
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D.A. Tuan et al. / VNU Journal of Science: Mathematics Physics, Vol. 35, No. 1 (2019) 41-46
properties of single crystals, we can fully understand the relationship between structure and properties
of materials. Furthermore, single crystal has been used in many regions of science and technology.
Therefore, many crystal growth techniques were developed from last centuries. Recently, single crystal
growth methods are continually improved. The Bridgman technique is the oldest method for growing
single crystals. In this technique, thecruciblewhich is containedmolten material moves alonga gradient
temperature of furnace. The crystal is solidified when the bottom of crucible moves to low-temperature
region. [1-3] Bridgman technique was developed by Stockbarger by using two separate temperature
zones. So, this method is easier for control temperature. [4-6] One of the earliest melting techniques
which is used for large single crystal is Kyropoulos method. This method is also grown from melting
material in crucible. A seed crystal on the surface of molten material is increased the size by a slowly
cooling down of the temperature. [7-9] A similar technique for growing the big size of single crystals is
czochralski method. [10-12] But in this method, the seed of crystal is rotated and moved up fromsurface
of molten material. Some other techniques such as Verneuil method and floating zone are also used for
single crystal growth. [13-15] All above techniques which are mentioned above are good for growing
big size single crystals. However, most of them are complicated. Here, we introduce a simpler technique
that is usedforgrowthsingle crystal.In thismethod, duringgrowth process, samplesdo notneed moving
and we can grow some crystals in a growth process.
2. Experiment
This study, we used homemade vertical furnaces which were designed as shown in figure 1 (a).
More detail of our furnace will be described in the discussion part. The furnaces are stable working in
the temperature range of room temperature to 1000 oC with a very stable rate of temperature. Materials
were loaded into thick wall quartz ampoules. Then, the ampoules were evacuated (<10-4 Torr) and
sealed. Another quartz tube was sealed in order to protect the sample and ampoule when the ampoule
breaks during heating due to high vapor pressure of materials and the different thermal expansion
coefficient between samples and quartz ampoule. The ampoules and the thermocouple were vertically
placed at the bottom of the furnace. In the heating up of growth process, we can select the rate from 10
to 20 oC/hour which is dependent the material.
Fig. 1. (a) Photograph of equipment in temperature gradient method. (b) Schematic of the vertical furnace used
in the temperature gradient method.
Maximum temperature is usually higher than melting point of material around 50 oC and soaked at
this temperature around 10 hours before slowly cold down to room temperature. The high purity
materials (99.999%)which were provides bySigma-Aldrich companyshould be selected forthis growth