利用化學氣相沈積法製備矽空缺鑽石之特性研究

Study on synthesis and characterization of silicon-vacancy centers in diamond via chemical vapor deposition process

蘇尼(Srinivasu Kunuku)

指導教授 ： 林諭男 ； 柳克強

國立清華大學/原子科學院/工程與系統科學系/博士(2017年)

摘要

鑽石中的矽空缺(SiV)擁有極佳光譜性質其包含在736 nm ~ 746 nm明顯的零聲子峰值(zero phonon line, ZPL)且極窄的發光峰值半高寬。因此矽空缺作為單光子源於量子運算或是生物標定應用皆是優良的選擇。含有矽空缺之奈米鑽石如鑽石奈米線、鑽石奈米島以及鑽石顆粒皆顯示出高零聲子峰值(ZPL) 發光強度和極窄的零聲子峰值半高寬。因此本研究主要目的於製備以及研究含有矽空缺之超奈米晶鑽石中(大小約10 nm)以及其中矽空缺光譜特性。傳統上利用化學氣象法製程製備出含有矽空缺之鑽石，當在鑽石製程時高微波功率與高成長溫度環境使矽雜質會參入鑽石中。本研究中利用以下兩種方式製備出含有矽空缺之超奈米晶鑽石，(i)利用電漿輔助化學氣象沉積法(Microwave enhanced chemical vapor deposition , MPECVD)製程進行低成長溫度矽參雜；(ii)將CVD製備之超奈米晶鑽石和單晶鑽石進行矽離子佈值.
在第一種方式中，於低製程溫度(<550 oC)下於利用矽基板成長之不同微結構矽參雜鑽石薄膜。不同微結構鑽石薄膜分別為微米晶鑽石薄膜(microcrystalline diamond, MCD)、奈米晶鑽石(nanocrystalline diamond, NCD)、超奈米晶鑽石(ultrananocrystalline diamond, UNCD)和氮氣電漿超奈米晶鑽石(nitrogen incorporated UNCD, N-UNCD)。並開發一簡易結構化製程於上述鑽石薄膜，利用自組金奈米顆粒為遮罩進行O2/CF4電漿離子蝕刻(RIE)製程。電子掃描式顯微鏡可發現微結構之鑽石薄膜經離子蝕刻製程後皆呈現高密度垂直結構化奈米鑽石。紫外拉曼光譜(UV-Raman spectroscopy)顯示經離子蝕刻製程後鑽石薄膜品質未降低，光致發光光譜(photoluminescence, PL)則發現結構化微米晶鑽石錐及奈米鑽石針尖擁有高氮空缺放射，但超奈米晶鑽石柱之氮空缺發射則被抑制。
在第二種方式中，嘗試利用不同二氧化矽(SiO2)基板進行微米晶鑽石薄膜、奈米晶鑽石、超奈米晶鑽石和氮氣電漿超奈米晶鑽石矽參雜製程，如二氧化矽(SiO2)、鈉鈣玻璃(soda-lime glass)以及鈉鈣玻璃纖維。此部分樣品光致發光光譜中可發現有波長位於738 nm~740 nm矽空缺放射，而在超奈米晶鑽石中之矽空缺發射亮度高並清晰。鈉鈣玻璃上之超奈米晶鑽石呈現顆粒狀而非薄膜狀，這些超奈米晶鑽石顆粒擁有清晰之矽空缺發射且能抑制氮空缺發射。穿透式電子顯微鏡(Transmission electron microscopy, TEM)通常使用於研究鑽石微結構變化對於矽空缺光譜性質的影響，於穿透式電子顯微鏡中可發現超奈米晶鑽石薄膜有較大鑽石團簇產生，其可能為造成超奈米晶鑽石薄膜有氮空缺之因素。在此開發出一簡易製程於製備出高發射強度含矽空缺之超奈米晶鑽石顆粒，將成長於鈉鈣玻璃纖維上之含矽空缺的超奈米晶鑽石顆粒經超音波震洗機剝落懸浮於去離子水中，再將含有超奈米晶鑽石顆粒的懸浮液塗佈在已有倒金字塔圖形化之矽基板上。於時間解析光致發光光譜(Time- resolved PL spectroscopy)中發現含矽空缺的超奈米晶鑽石顆粒有較低之衰變時間τ ~ 0.20 ns(矽空缺衰變時間約1~2 ns)，矽空缺有較低之衰變時間因是由於超奈米晶鑽石品質較差，含有大量缺陷以及非鑽碳。由於以上樣品發現有較高矽空缺密度，故進行以下兩種實驗方式改善矽空缺量即將含矽空缺的超奈米晶鑽石結構化成柱狀或是針尖狀。結構化後之含矽空缺的超奈米晶鑽石有明亮且較窄發射半高寬約7 nm~10.5 nm，且有較短衰變時間τ ~ 0.20 ns。
接著為增強超奈米晶鑽石中矽空缺衰變時間，利用MPECVD製程將超奈米晶鑽石成長於鍍鈦藍寶石基板，並進行矽離子佈值(佈值能量：125 keV，佈值劑量：1013 ions/cm2)。此樣品呈現明亮矽空缺發射以及零聲子峰值半高寬約為7.0 nm，並增加衰變時間至τ= 0.43 ns。接著為比較含矽空缺高品質單晶鑽石樣品與含矽空缺的超奈米晶鑽石之光譜特性差異，將Ia和IIa單晶鑽石基板進行矽離子佈值(佈值能量：350 keV，佈值劑量：1010 ions/cm2)。含有矽空缺之IIa單晶鑽石樣品其有明亮的發射及較窄零聲子峰值半高寬約6 nm，並將衰變時間改善τ= 1.3 ns。
從以上之研究可發現，奈米結構化含矽空缺超奈米晶鑽石以及含矽空缺超奈米晶鑽石顆粒有強矽空缺發射，極具生物標定應用之潛力。另一方面利用高品質單晶鑽石基板進行矽離子佈值則可作為單光子源材料。

關鍵字

鑽石彩色中心 ； 單光子源 ； 化學氣相沉積 ； 零聲子線 ； 光致發光

並列摘要

Silicon-vacancy (SiV) centers in diamonds present exceptional spectral properties, including bright zero phonon line (ZPL) at wavelengths of 736 nm 746 nm and a narrow emission linewidth. As a single photon source, SiV center is a promising candidate for quantum computing as well as biomarking applications. The SiV centers in nanodiamonds, including diamond nanowires, diamond nanoislands, and diamond particles, present high-intensity of ZPL emissions over a narrow linewidth. In this study, we investigated the fabrication of ultrananocrystalline diamond (UNCD) nanostructures (UNCD size ~ 10 nm) and the spectral characteristics of the SiV centers contained within. SiV centers are typically created via chemical vapor deposition (CVD). In this process, Si impurities are incorporated within the diamond during the growth process, at elevated temperatures under high microwave powers. In this study, we created SiV centers in UNCD using two methods: (i) in-situ Si-doping during microwave plasma-enhanced chemical vapor deposition (MPECVD) at low growth temperatures; (ii) Si-ion implantation in UNCD and single crystalline diamond (SCD).
The first method begins with in-situ Si-doping of diamond films with various granular structures grown on a Si-substrate at low temperature (< 550 oC). The films include microcrystalline diamond (MCD), nanocrystalline diamond (NCD), UNCD, and nitrogen-incorporated UNCD (N-UNCD) films. We devised a simple process for the fabrication of diamond nanostructures within these films using a self-assembled mask of Au nanodots followed by reactive ion etching (RIE) under O2/CF4 plasma. Field emission scanning electron microscopic images of the diamond nanostructures revealed the formation of vertical nanostructures with high density. UV-Raman spectroscopy confirmed that RIE did not degrade the quality of the diamond nanostructures. Photoluminescence (PL) spectroscopy revealed strong NV emissions from MCD nanocones and NCD nanotips as well as the quenching of NV emissions from UNCD nanopillars.
The second process involves the in-situ Si-doping of diamond using various silicon oxide (SiO2) substrates, including SiO2, soda-lime glass, and soda-lime glass fibers, for the growth of MCD, NCD, and UNCD films. The PL spectra of the resulting UNCD diamond films revealed SiV centers with bright and clear emission at 738 nm - 740 nm and suppressed NV emissions. The UNCD formed as particulates rather than as a film on soda-lime glass fibers. Transmission electron microscopy (TEM) was used to study the influence of microstructure on the spectral characteristics of SiV centers. The TEM micrographs of UNCD films reveal the presence of large aggregate, which might be the cause of the NV emission from the UNCD films. We developed a simple process for the synthesis of SiV-UNCD particulates with bright emissions, wherein SiV-UNCD nanoclusters/soda-lime glass fibers were ultrasonicated in DI water, and then the water was spread over Si inverted pyramids. Time-resolved PL spectroscopy measurements of SiV-UNCD particulates revealed that the SiV centers have a short decay time of  ~ 0.20 ns (SiV decay time ~ 1-2 ns). This can be attributed to the low quality of the UNCD, which includes a large number of defects and non-diamond carbon phases. We also developed two approaches to the fabrication of bright SiV-UNCD nanostructures; i.e., top-down approach for fabrication of SiV-UNCD nano-rods and bottom-up approach for fabrication of SiV-UNCD nano-tips. The resulting SiV-UNCD nanostructures exhibit bright emission over a narrow linewidth of ~ 7 nm  10.5 nm with shorter decay time of  ~ 0.2 ns.
To enhance the decay time of SiV centers, UNCD has grown on a Ti/Sapphire substrate using MPECVD, followed by Si-ion implantation under the following parameters: E = 125 keV and dose = 1013 ions/cm2. The resulting SiV-UNCD nanoclusters present bright SiV emission with ZPL width of ~ 7.0 nm and  = 0.43 ns. Si-ion implantation was also performed on SCD (type Ia & type IIa) with E = 350 keV and dose = 1010 ions/cm2 to facilitate a comparison of the spectral characteristics of SiV-UNCD in high-quality diamond with SiV centers. The SiV centers in type IIa SCD present bright emission, narrow ZPL width of ~ 6 nm and enhanced decay time of  = 1.30 ns. The SiV-UNCD nanostructures and SiV-UNCD particulates developed in this study have considerable potential in biomarking applications, due to their strong SiV emissions. Furthermore, the Si-ion implanted type IIa SCD samples are applicable as a single photon emitter in quantum information processing and quantum computation applications.

並列關鍵字

Diamond color center ； Single photon source ； Chemical vapor deposition ； Zero phonon line ； Photoluminescence

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