電流輔助熱處理對電沉積於聚苯乙烯球模板3-D碲化鉍熱電性質之影響

Influence of Current-Assisted Annealing on Thermoelectric Properties of 3-Dimension Bismuth Telluride Electrodeposited on Polystyrene Sphere Template

賴韋成(Lai, Weicheng)

指導教授 ： 林昭任

國立中正大學/工學院/化學工程學系/碩士(2012年)

摘要

本實驗為利用聚苯乙烯微球(polystyrene sphere)進行電泳法製作三維結構基板，並於基板常壓電鍍碲化鉍熱電材料，探討不同熱處理方式對熱電性質(載子濃度、遷移率、電阻率)與結構之影響。實驗操作因子分別為改變沉積電位(-80mV~-140mV)來找出符合Bi2Te3組成之條件、聚苯乙烯微球移除率對熱電材料性質影響、不同熱處理方式對熱電性質之改善、分析聚苯乙烯微球粒徑對熱電性質的影響。實驗結果顯示，當沉積電位為-0.12Ｖ時，電沉積之碲化鉍才符合Bi2Te3之化學計量數比例。聚苯乙烯球若移除不完全，當熱處理溫度過高時，會破壞碲化鉍3D結構，造成Seebeck係數與Power factor驟降之現象。為了增進熱電優值，故希望藉由熱處理來消除晶格缺陷，使得碲化鉍結構更加完整，進而促使Seebeck係數提升。從實驗結果發現，電流輔助退火可以有效的消除晶格缺陷，使得結晶性上升，且效果優於一般傳統退火方式。實驗結果指出，以300nmPS球為模板電沉積之Bi2Te3膜經過305℃、外加電流150 mA之電流輔助退火處理持續5分鐘，其Power factor值由未經退火之97.86μV/mK2上升至最大值233.37μV/mK2。

關鍵字

熱電材料 ； 碲化鉍 ； 電流輔助退火

並列摘要

This study was to investigate the preparation of a three-dimensional (3-D) thermoelectric material of bismuth telluride (BixTey) by electrodepositing bismuth telluride in a 3-D polystyrene (PS) template. The 3-D PS template was made of electrophoretic depositing PS sphere on the ITO glass substrate. The 3-D structure morphology was observed and several thermoelectric properties were measured including Seebeck coefficient (S), carrier concentration (n), resistivity (ρ), and mobility (μ) to investigate the influence of different thermal treatments on the thermoelectric material. Three methods have been employed to enhance the power factor (S2/ρ)： (1) changing the depositing potentials (-80mV~ -140mV) to adjust the stoichiometry close Bi2Te3, (2) investigating the influence on the thermoelectric properties whether the PS sphere template was removed or not, (3) applying two types of thermal treatments to improve the thermoelectric properties, (4) analyzing the effect of pore size of the 3-D PS template on the thermoelectric properties. It was found that when -0.12V was set as the depositing potential, the stoichiometry of the Bismuth Telluride films met Bi2Te3. Besides, if the PS sphere template was not entirely removed, as the annealing temperature reaching high enough the 3-D structure would be destroyed causing the plunge of the Seebeck coefficient and power factor. In order to enhance the figure of merit, the thermal treatments were employed to reduce the structural imperfection. The analysis of XRD presented the current-assisted annealing could eliminate crystal lattice defects more effectively than the conventional thermal annealing and enhance the crystallinity. The results showed that the power factor of the 3-D Bi2Te3 films with 300nm pore size treated with current-assisted annealing at a current of 150 mA and 305℃ for 5 minutes increased from 97.86μV/mK2 to 233.37μV/mK2.

參考文獻

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