激光燒蝕法合成一維納米線

1、A Laser Ablation Method for the Synthesis of Crystalline Semiconductor Nanowires激光燒蝕法合成結(jié)晶半導(dǎo)體納米線激光燒蝕法合成結(jié)晶半導(dǎo)體納米線論文出處：Science 279:208(1998)作者：Alfredo M. Morales Charles M. Lieber作者單位：Department of Chemistry and Chemical Biology, Harvard University, Cambridge Department of Chemistry and Chemical Biology

2、, and Division of Engineering and Applied Sciences, Harvard University, Cambridge演講者：10122800 劉旭明摘要：一種合成半導(dǎo)體納米線的方法，它利用激光燒蝕團(tuán)簇狀構(gòu)造和氣液固（VLS）模式的生長(zhǎng)，制備納米直徑催化劑團(tuán)簇。在這個(gè)過程中，激光燒蝕被用來制備納米級(jí)直徑的催化劑團(tuán)簇通過VLS增長(zhǎng)定義所產(chǎn)生的導(dǎo)線的大小。這種方法可用來制備均勻的620納米的單晶硅和3至9納米的鍺納米線，長(zhǎng)度范圍從1到30微米。根據(jù)不同的條件和催化劑材料進(jìn)行的研究證實(shí)了生長(zhǎng)機(jī)理的主要細(xì)節(jié)，并提出確定的相圖可以用來預(yù)測(cè)制備納米線索需的合理的

3、催化劑材料和生長(zhǎng)條件。主要內(nèi)容1. 1. 激光燒蝕激光燒蝕2. 2. VLSVLS生長(zhǎng)生長(zhǎng)3. 影響因素影響因素4. 4. 總結(jié)與展望總結(jié)與展望 一維納米材料(納米線)是在碳納米管的基礎(chǔ)上發(fā)展起來的，各種新穎的一維納米材料相繼被發(fā)現(xiàn)。一維納米結(jié)構(gòu)具有的許多獨(dú)特性能不僅為人們研究材料的電子、光學(xué)、輸運(yùn)性質(zhì)、機(jī)械等性能與量子尺度的關(guān)系提供了好的物質(zhì)模型，而且也為納米結(jié)構(gòu)的合成和組裝提供了新的機(jī)遇。一維納米材料的可控制備、性能研究和應(yīng)用對(duì)于促進(jìn)納米科技領(lǐng)域的發(fā)展有十分重要的作用，有助于發(fā)現(xiàn)新的效應(yīng)，發(fā)展新的器件，以至于形成新的產(chǎn)業(yè)。 激光燒蝕法是用一束高能激光輻射靶材表面,使其表面迅速加熱融化蒸發(fā),

4、隨后冷卻結(jié)晶生長(zhǎng)的一種制備材料的方法。一、激光燒蝕一、激光燒蝕圖圖1.納米線的生長(zhǎng)設(shè)備示意圖納米線的生長(zhǎng)設(shè)備示意圖A M Morales, and C M Lieber Science 1998;279:208-2111.激光脈沖輸出 2.透鏡 3目標(biāo)物體4.石英管 5冷頭 6.載氣（氬氣）一定密度的蒸發(fā)一定密度的蒸發(fā)粒子和高溫區(qū)域粒子和高溫區(qū)域,高溫區(qū)域保留一高溫區(qū)域保留一定的時(shí)間定的時(shí)間圖圖2.透射電子顯微鏡圖像透射電子顯微鏡圖像A M Morales, and C M Lieber Science 1998;279:208-211(A) A TEM image (Phillips EM4

5、20, 120-kV operating voltage) of the nanowires produced after ablation (Spectra Physics GCR-16s, 5 3 2 n m , 1 0 H z , 2 - W average power) of a Si0.9Fe0.1 target; the product was obtained from the cold finger. (B) Diffraction contrast TEM image of a Si nanowire; crystalline material (the Si core) a

6、ppears darker than amorphous material (SiOx sheath) in this imaging mode. Scale bar, 10 nm. (Inset) Convergent beam ED pattern recorded along the 211 zone axis perpendicular to the nanowire growth axis. (C) High-resolution TEM image Topcon (Topcon Technology, Tokyo, Japan) EM-002B, 200-kV operating

7、voltage of the crystalline Si core and amorphous SiOx sheath. The (111) planes (black arrows) (spacing, 0.31 nm) are oriented perpendicular to the growth direction (white arrow).二二、VLS生長(zhǎng)生長(zhǎng)v VLS生長(zhǎng)納米線（管）中存在著兩個(gè)過程：生長(zhǎng)納米線（管）中存在著兩個(gè)過程： 一是氣態(tài)原子在氣液界面不斷解離溶入液態(tài)催化劑中；一是氣態(tài)原子在氣液界面不斷解離溶入液態(tài)催化劑中； 二二是過飽和溶質(zhì)在液固界面以界面能最低的方式不

8、斷是過飽和溶質(zhì)在液固界面以界面能最低的方式不斷析出析出該過程中氣、液和固三相共存，故被稱為該過程中氣、液和固三相共存，故被稱為VLS生長(zhǎng)生長(zhǎng)。 這種制備技術(shù)具有一定的普適性，只要欲制備的材料能與其他組分形成共晶合金，則可根據(jù)相圖配制作為靶材的合金，然后按相圖中的共晶溫度調(diào)整激光蒸發(fā)和凝聚條件，就可獲得欲制備材料的納米線。液液相催化劑最小半相催化劑最小半徑為徑為0.2m數(shù)量級(jí)數(shù)量級(jí)(平衡熱力學(xué)的限制平衡熱力學(xué)的限制)激光燒蝕激光燒蝕的作用可的作用可使液相催化劑團(tuán)簇使液相催化劑團(tuán)簇尺寸達(dá)到納米級(jí)尺寸達(dá)到納米級(jí)激光燒蝕法與晶體生激光燒蝕法與晶體生長(zhǎng)的長(zhǎng)的VLS法相結(jié)合法相結(jié)合圖圖3.Si納米線生長(zhǎng)模

9、型納米線生長(zhǎng)模型A M Morales, and C M Lieber Science 1998;279:208-211Published by AAASA.氣化氣化B.液滴成核及長(zhǎng)大液滴成核及長(zhǎng)大C.硅的固化析出硅的固化析出D.硅納米線的生成硅納米線的生成圖圖4.鍺納米線的透射電子顯微鏡圖像鍺納米線的透射電子顯微鏡圖像A M Morales, and C M Lieber Science 1998;279:208-211(A)Image of the nanowire exhibiting a roughly spherical nanocluster at its end. The EDX

10、 measurements made at the white squares show that the nanocluster (upper square) has a Ge:Fe ratio of 2:1 and that the nanowire (lower square) contains only Ge. Scale bar, 9 nm. (B)Image of an isolated Ge nanowire. The nanowire diameter is 5.0 0.6 nm. Scale bar, 5 nm. (C)High-resolution TEM image of

11、 the Ge nanowire region indicated by the open black box in (B). A twin boundary oriented along the vertical direction is located at the center of this image; (111) lattice planes are visible to the left and right of the boundary. Scale bar, 1 nm. The Ge nanowires were produced by ablation (Spectra P

12、hysics GCR-16s, 532 nm, 10 Hz, 2-W average power) of a Ge0.9Fe0.1 target. The growth conditions were 820C and 300-torr Ar flowing at 50 SCCM.圖5 Ge納米線的氣液固生長(zhǎng)過程及Ge-Au二元相圖從從Ge-Au二元相圖可看二元相圖可看出出,當(dāng)溫度高于最低共熔當(dāng)溫度高于最低共熔點(diǎn)點(diǎn)(363)時(shí)，時(shí)，Ge和和Au將形成液相合金將形成液相合金()。由于液相表面的吸附系由于液相表面的吸附系數(shù)大數(shù)大,來自氣相的來自氣相的Ge將將優(yōu)先在優(yōu)先在Ge-Au的液相合的液相合金

13、表面沉積金表面沉積,當(dāng)當(dāng)Ge在在Ge-Au的液相合金中過飽和的液相合金中過飽和時(shí)時(shí),Ge納米線將在固液納米線將在固液界面處析出界面處析出(-)。v 激光強(qiáng)度激光強(qiáng)度:激發(fā)的等離子體氣焰的狀態(tài)；激發(fā)的等離子體氣焰的狀態(tài)；v 生長(zhǎng)腔壓力生長(zhǎng)腔壓力:決定內(nèi)部氣體的密度，影響熱梯度及生長(zhǎng)的速?zèng)Q定內(nèi)部氣體的密度，影響熱梯度及生長(zhǎng)的速率和方向；率和方向；v 氣流流速氣流流速:決定蒸發(fā)后等離子體的流動(dòng)速度，影響納米線在決定蒸發(fā)后等離子體的流動(dòng)速度，影響納米線在核上進(jìn)一步生長(zhǎng)的方向和速率；核上進(jìn)一步生長(zhǎng)的方向和速率；v 生長(zhǎng)時(shí)間生長(zhǎng)時(shí)間:影響納米線的生長(zhǎng)大小，過長(zhǎng)也會(huì)使副產(chǎn)品增多影響納米線的生長(zhǎng)大小，過長(zhǎng)也會(huì)

14、使副產(chǎn)品增多v 生長(zhǎng)溫度生長(zhǎng)溫度:一般高溫可以減少生成納米線時(shí)產(chǎn)生的缺陷。一般高溫可以減少生成納米線時(shí)產(chǎn)生的缺陷。三、納米三、納米線的影響因素線的影響因素四、總結(jié)與展望四、總結(jié)與展望激光燒蝕法與激光燒蝕法與VLS生長(zhǎng)機(jī)制結(jié)合起來制備出了一維納生長(zhǎng)機(jī)制結(jié)合起來制備出了一維納米材料，一維納米材料的半徑、長(zhǎng)度、形貌等受激光米材料，一維納米材料的半徑、長(zhǎng)度、形貌等受激光燒蝕法的工藝參數(shù)的控制。在該法中，燒蝕法的工藝參數(shù)的控制。在該法中， 激光燒蝕的作激光燒蝕的作用在于克服平衡狀態(tài)下團(tuán)簇的尺寸的限制，可形成比用在于克服平衡狀態(tài)下團(tuán)簇的尺寸的限制，可形成比平衡狀態(tài)下團(tuán)簇最小尺寸還要小的直徑為納米級(jí)的液平衡

15、狀態(tài)下團(tuán)簇最小尺寸還要小的直徑為納米級(jí)的液相催化劑團(tuán)簇，而該液相催化劑團(tuán)簇的尺寸大小限定相催化劑團(tuán)簇，而該液相催化劑團(tuán)簇的尺寸大小限定了后續(xù)按了后續(xù)按VLS機(jī)理生長(zhǎng)的線狀產(chǎn)物的直徑。機(jī)理生長(zhǎng)的線狀產(chǎn)物的直徑。進(jìn)一步研究納米線的生長(zhǎng)機(jī)理以及激光工藝參數(shù)與進(jìn)一步研究納米線的生長(zhǎng)機(jī)理以及激光工藝參數(shù)與制備結(jié)果的關(guān)系，在此基礎(chǔ)上找到能大量生產(chǎn)的制制備結(jié)果的關(guān)系，在此基礎(chǔ)上找到能大量生產(chǎn)的制備工藝備工藝,以便能用于工業(yè)化生產(chǎn)。以便能用于工業(yè)化生產(chǎn)?？深A(yù)見性的選擇可預(yù)見性的選擇催化劑和制備條催化劑和制備條件（普適性）件（普適性）成本高成本高有雜質(zhì)有雜質(zhì)現(xiàn)在利用該技術(shù)已成功的現(xiàn)在利用該技術(shù)已成功的制備出了制

16、備出了GaAsGaAs，SiOSiO2 2 等多等多種物質(zhì)的納米線。種物質(zhì)的納米線。LieberLieber等分別以等分別以SiSi0.90.9FeFe0.10.1，SiSi0.90.9NiNi0.10.1和和SiSi0.990.99AuAu0.010.01為靶材，為靶材，用該法制備了直徑為用該法制備了直徑為3 39 nm9 nm長(zhǎng)度為長(zhǎng)度為1 130 30 m m的單晶的單晶SiSi納納米線。同時(shí)也以米線。同時(shí)也以GeGe0.90.9FeFe0.10.1為為靶材，用該法合成了直徑為靶材，用該法合成了直徑為3 39 nm9 nm長(zhǎng)度為長(zhǎng)度為1 130 30 m m的單的單晶晶GeGe 納米線。

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