以時間解析熱光反射技術測量鑽石薄膜熱傳現象

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2015

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結晶性的鑽石有獨特的性質,如高硬度、高熱傳導率以及低摩擦係數;然而,鑽石薄膜的性質與結晶性的鑽石略有不同,鑽石薄膜的性質決定於長晶技術以及參數,因而可以藉由長晶技術的不同而有不一樣的應用。鑽石薄膜可以在氬氣與甲烷的系統中通入氫氣的微波電漿輔助化學氣相沉積法 (microwave plasma enhanced chemical vapor deposition) 系統製成奈米尺度的大小,不同的百分比的氫氣會影響鑽石薄膜的顆粒結構,以至於影響其熱傳導性質。我們藉由以時間解析熱光反射 (time domain thermoreflectance) 技術測量不同長晶條件下鑽石薄膜的熱傳導性質,此技術必須將鑽石薄膜表面鍍一層鋁膜作為吸收層。當光學脈衝雷射照射在鋁膜,鋁膜吸收脈衝光後產生熱後,可以顯示鋁膜表面溫度在幾個奈秒時間的變化,再藉由理論模型去擬合實驗曲線並求得鑽石薄膜的熱傳導性質。此外,鑽石薄膜的厚度可藉由掃描式電子顯微鏡 (scanning electron microscope) 測得。
Crystalline diamond possesses several fascinating properties such as high mechanical hardness, high thermal conductivity and low friction coefficient. However, diamond thin films do not always possess the same properties of crystalline diamond. It was demonstrated that the properties of diamond thin films vary a lot depending on the growth techniques and parameters. It is thus possible to optimize the properties of diamond thin films for particular applications. Diamond thin films were engineered at nanoscale by introducing H2 in the commonly used Ar/CH4 deposition plasma in a microwave plasma enhanced chemical vapor deposition (MPECVD) system. The presence of H2 influenced the granular structure of diamond films, resulting in different thermal properties. We utilized time domain thermoreflectance (TDTR) techniques to measure the thermal conductivities of diamond thin films deposited with different growth conditions. For TDTR measurement, all of diamond thin films were coated with an Al thin film as a transducer. After the optical pump pulses generated heat in the Al thin film, we monitored the time evolution of temperature near the surface of the Al film up to a few nanoseconds.We used a heat flow model to fit the TDTR traces and obtained the thermal conductivities of diamond thin films with different granular structures. The thicknesses of the diamond thin films were measured by scanning electron microscope (SEM).

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鑽石薄膜, 以時間解析熱光反射技術, 熱傳導係數, 熱傳導率, diamond thin film, time domain thermoreflectance, thermal conductivity, thermal conductance

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