激光烧蚀法合成一维纳米线

1、A Laser Ablation Method for the Synthesis of Crystalline Semiconductor Nanowires激光烧蚀法合成结晶半导体纳米线激光烧蚀法合成结晶半导体纳米线论文出处：Science 279:208(1998)作者：Alfredo M. Morales Charles M. Lieber作者单位：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演讲者：10122800 刘旭明摘要：一种合成半导体纳米线的方法，它利用激光烧蚀团簇状构造和气液固（VLS）模式的生长，制备纳米直径催化剂团簇。在这个过程中，激光烧蚀被用来制备纳米级直径的催化剂团簇通过VLS增长定义所产生的导线的大小。这种方法可用来制备均匀的620纳米的单晶硅和3至9纳米的锗纳米线，长度范围从1到30微米。根据不同的条件和催化剂材料进行的研究证实了生长机理的主要细节，并提出确定的相图可以用来预测制备纳米线索需的合理的

3、催化剂材料和生长条件。主要内容1. 1. 激光烧蚀激光烧蚀2. 2. VLSVLS生长生长3. 影响因素影响因素4. 4. 总结与展望总结与展望 一维纳米材料(纳米线)是在碳纳米管的基础上发展起来的，各种新颖的一维纳米材料相继被发现。一维纳米结构具有的许多独特性能不仅为人们研究材料的电子、光学、输运性质、机械等性能与量子尺度的关系提供了好的物质模型，而且也为纳米结构的合成和组装提供了新的机遇。一维纳米材料的可控制备、性能研究和应用对于促进纳米科技领域的发展有十分重要的作用，有助于发现新的效应，发展新的器件，以至于形成新的产业。 激光烧蚀法是用一束高能激光辐射靶材表面,使其表面迅速加热融化蒸发,

4、随后冷却结晶生长的一种制备材料的方法。一、激光烧蚀一、激光烧蚀图图1.纳米线的生长设备示意图纳米线的生长设备示意图A M Morales, and C M Lieber Science 1998;279:208-2111.激光脉冲输出 2.透镜 3目标物体4.石英管 5冷头 6.载气（氩气）一定密度的蒸发一定密度的蒸发粒子和高温区域粒子和高温区域,高温区域保留一高温区域保留一定的时间定的时间图图2.透射电子显微镜图像透射电子显微镜图像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生长生长v VLS生长纳米线（管）中存在着两个过程：生长纳米线（管）中存在着两个过程： 一是气态原子在气液界面不断解离溶入液态催化剂中；一是气态原子在气液界面不断解离溶入液态催化剂中； 二二是过饱和溶质在液固界面以界面能最低的方式不

8、断是过饱和溶质在液固界面以界面能最低的方式不断析出析出该过程中气、液和固三相共存，故被称为该过程中气、液和固三相共存，故被称为VLS生长生长。 这种制备技术具有一定的普适性，只要欲制备的材料能与其他组分形成共晶合金，则可根据相图配制作为靶材的合金，然后按相图中的共晶温度调整激光蒸发和凝聚条件，就可获得欲制备材料的纳米线。液液相催化剂最小半相催化剂最小半径为径为0.2m数量级数量级(平衡热力学的限制平衡热力学的限制)激光烧蚀激光烧蚀的作用可的作用可使液相催化剂团簇使液相催化剂团簇尺寸达到纳米级尺寸达到纳米级激光烧蚀法与晶体生激光烧蚀法与晶体生长的长的VLS法相结合法相结合图图3.Si纳米线生长模

9、型纳米线生长模型A M Morales, and C M Lieber Science 1998;279:208-211Published by AAASA.气化气化B.液滴成核及长大液滴成核及长大C.硅的固化析出硅的固化析出D.硅纳米线的生成硅纳米线的生成图图4.锗纳米线的透射电子显微镜图像锗纳米线的透射电子显微镜图像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.图5 Ge纳米线的气液固生长过程及Ge-Au二元相图从从Ge-Au二元相图可看二元相图可看出出,当温度高于最低共熔当温度高于最低共熔点点(363)时，时，Ge和和Au将形成液相合金将形成液相合金()。由于液相表面的吸附系由于液相表面的吸附系数大数大,来自气相的来自气相的Ge将将优先在优先在Ge-Au的液相合的液相合金

13、表面沉积金表面沉积,当当Ge在在Ge-Au的液相合金中过饱和的液相合金中过饱和时时,Ge纳米线将在固液纳米线将在固液界面处析出界面处析出(-)。v 激光强度激光强度:激发的等离子体气焰的状态；激发的等离子体气焰的状态；v 生长腔压力生长腔压力:决定内部气体的密度，影响热梯度及生长的速决定内部气体的密度，影响热梯度及生长的速率和方向；率和方向；v 气流流速气流流速:决定蒸发后等离子体的流动速度，影响纳米线在决定蒸发后等离子体的流动速度，影响纳米线在核上进一步生长的方向和速率；核上进一步生长的方向和速率；v 生长时间生长时间:影响纳米线的生长大小，过长也会使副产品增多影响纳米线的生长大小，过长也会

14、使副产品增多v 生长温度生长温度:一般高温可以减少生成纳米线时产生的缺陷。一般高温可以减少生成纳米线时产生的缺陷。三、纳米三、纳米线的影响因素线的影响因素四、总结与展望四、总结与展望激光烧蚀法与激光烧蚀法与VLS生长机制结合起来制备出了一维纳生长机制结合起来制备出了一维纳米材料，一维纳米材料的半径、长度、形貌等受激光米材料，一维纳米材料的半径、长度、形貌等受激光烧蚀法的工艺参数的控制。在该法中，烧蚀法的工艺参数的控制。在该法中， 激光烧蚀的作激光烧蚀的作用在于克服平衡状态下团簇的尺寸的限制，可形成比用在于克服平衡状态下团簇的尺寸的限制，可形成比平衡状态下团簇最小尺寸还要小的直径为纳米级的液平衡

15、状态下团簇最小尺寸还要小的直径为纳米级的液相催化剂团簇，而该液相催化剂团簇的尺寸大小限定相催化剂团簇，而该液相催化剂团簇的尺寸大小限定了后续按了后续按VLS机理生长的线状产物的直径。机理生长的线状产物的直径。进一步研究纳米线的生长机理以及激光工艺参数与进一步研究纳米线的生长机理以及激光工艺参数与制备结果的关系，在此基础上找到能大量生产的制制备结果的关系，在此基础上找到能大量生产的制备工艺备工艺,以便能用于工业化生产。以便能用于工业化生产。可预见性的选择可预见性的选择催化剂和制备条催化剂和制备条件（普适性）件（普适性）成本高成本高有杂质有杂质现在利用该技术已成功的现在利用该技术已成功的制备出了制

16、备出了GaAsGaAs，SiOSiO2 2 等多等多种物质的纳米线。种物质的纳米线。LieberLieber等分别以等分别以SiSi0.90.9FeFe0.10.1，SiSi0.90.9NiNi0.10.1和和SiSi0.990.99AuAu0.010.01为靶材，为靶材，用该法制备了直径为用该法制备了直径为3 39 nm9 nm长度为长度为1 130 30 m m的单晶的单晶SiSi纳纳米线。同时也以米线。同时也以GeGe0.90.9FeFe0.10.1为为靶材，用该法合成了直径为靶材，用该法合成了直径为3 39 nm9 nm长度为长度为1 130 30 m m的单的单晶晶GeGe 纳米线。

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