Dendrite engineering on xenon crystals.
Dendrite engineering on xenon crystals.
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氙晶体上的枝晶工程。
DOI：
10.1103/physreve.75.061603
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
J. Bilgram
中科院分区：
文献类型：
--
作者：
M. Fell;J. Bilgram
实验工作主要集中在氙树枝的瞬时生长、形态转变和控制。枝晶自由生长受到两种不同机制的干扰：摇动和加热到熔化温度。自发的和亚稳态的多尖端组态稳定，粗化减少，导致更密集的侧枝生长，在抖动过程中发现了周期性的尖端分裂。另一方面，加热导致受控的侧向分支和尖端形状的特征转变。除了随机噪声驱动的增长外，还发现了一个确定性的行为。研究结果支持了极限环的存在。这两种扰动机制一起实现了“树枝晶工程”--即在晶体生长过程中对晶体形状进行可重复的控制。发现枝晶自由生长的尖端分裂不是将尖端一分为二，而是改变了主尖和翅片各自的生长速度。然后，后者超过主技巧并发展成新的技巧。用这种机制解释了三尖端和四尖端组态的产生。对生长容器内热流和对流的有限元计算表明，必须摒弃单一轴对称环向对流滚流横跨整个生长容器的想法。在地球重力作用下，对流的主要作用是压缩向下生长尖端周围的扩散温度场。基于晶体形状和晶体中热流的相互作用，发展了一个解释树枝状晶体(如雪晶)对称性的模型。
The experimental work presented focuses on transient growth, morphological transitions, and control of xenon dendrites. Dendritic free growth is perturbed by two different mechanisms: Shaking and heating up to the melting temperature. Spontaneous and metastable multitip configurations are stabilized, coarsening is reduced, leading to a denser sidebranch growth, and a periodic tip splitting is found during perturbation by shaking. On the other hand, heating leads to controlled sidebranching and characteristic transitions of the tip shape. A deterministic behavior is found besides the random-noise-driven growth. The existence of a limit cycle is supported by the findings. Together the two perturbation mechanisms allow a "dendrite engineering"--i.e., a reproducible controlling of the crystal shape during its growth. The tip splitting for dendritic free growth is found not to be a splitting of the tip in two; rather, the respective growth velocities of the main tip and the fins change. The latter then surpass the main tip and develop into new tips. The occurrence of three- and four-tip configurations is explained with this mechanism. Finite-element calculations of the heat flow and the convective flow in the growth vessel show that the idea of a single axisymmetric toroidal convection roll across the whole growth vessel has to be dropped. The main effect of convection under Earth's gravity is the compression of the diffusive temperature field around the downward-growing tip. A model to explain the symmetry of dendritic crystals--e.g., snow crystals--is developed, based on the interaction of crystal shape and heat flow in the crystal.
影响因子：
2.9
作者：
KOO, KK;ANANTH, R;GILL, WN
通讯作者：
GILL, WN