看测量热迁移Measuring Thermal MigrationSeptember 15, 2023??Physics?16, 157T
he slow drift of microscale features on a surface reveals the for
ce driving atoms from the hot to the cold side of the material.In
cell phones and other devices, a large temperature difference ac
ross a microcircuit can cause atoms to migrate, eventually result
ing in faulty electrical connections. This so-called thermomigrat
ion has now been tracked at the microscale, revealing a diffusion
-related force that drives the motion [https://physics.aps.org/ar
ticles/v16/157?utm_campaign=weekly&utm_medium=email&utm_source=em
ailalert1]. The researchers studied shallow depressions, or “basi
ns,” on the surface of a square silicon wafer that was heated on
one edge and cooled on the opposite edge. They observed the motio
n of the basins as atoms migrated in response to the temperature
difference. The inferred force and the general characterization o
f the process could help other researchers develop new ways to co
ntrol the growth of nanostructures.The rate of thermomigration fr
om one place to another is proportional to the temperature differ
ence (gradient) between the two locations. “Engineers work a lot
on design to avoid thermal gradients,” says Frédéric Leroy from t
he Aix-Marseille University in France. But he says that a deeper
understanding of basic principles behind the motion has been lack
ing. “We propose a way to measure the migration quantitatively in
order to have a very precise value of the force driving the moti
on.”To capture the atomic motion, Leroy and his colleagues starte
d with a 9-mm-wide silicon wafer, which had a very flat, uniform
surface. They applied a heat source to one edge and a heat sink t
o the other, creating a temperature difference of roughly 100° C.
Under this gradient, the team expected that silicon atoms on the
surface would migrate from hotter to colder regions. But actuall
y seeing this movement would be difficult. “We do not measure the
atomic motion directly because atoms are moving much too fast,”
Leroy says.Adapted from F. Leroy?et al. [https://physics.aps.org/
articles/v16/157?utm_campaign=weekly&utm_medium=email&utm_source=
emailalert1]Organized retreat.?On the surface of a silicon wafer,
the observed advance of a basin is explained as the diffusion of
atoms from the hotter front wall to the cooler back wall.Instead
, the researchers used an electron microscope to observe one-atom
-deep depressions on the wafer surface. By taking a series of ima
ges, the team detected movement of these several-micrometer-wide
features toward the hot edge of the wafer at a speed of about 0.2
nanometers per second (nm/s).The researchers explain the basin m
otion as the result of silicon atom diffusion. Atoms detach from
the hotter wall of a basin and begin moving randomly along the ba
sin floor, as in a 2D gas. When one of these diffusing atoms reac
hes the colder wall of the basin, it can reattach. The net effect
is an advance of the basin walls in the direction of the heat so
urce. Using this diffusion model, the team was able to calculate
a thermomigration force of roughly 10?8?eV/nm, which is millions
of times smaller than the forces responsible for chemical bonding
. Leroy says that the thermomigration force should be stronger wi
thin microcircuits, where the thermal gradients are larger. But d
etermining how much stronger the force would be will require more
experiments with other types of materials. These tests could ind
icate whether the diffusion mechanism that the team observes is a
general feature of thermomigration.Surface scientist Hiroki Hibi
no from Kwansei Gakuin University in Japan was surprised that the
motion of the basins was so clear in the data, given that the at
omic motion is very complicated and the temperature difference ac
ross basins was small (around 0.04° C). “The authors’ successful
extraction of the thermomigration effect from the complicated pro
cesses is due to the well-designed experiments,” Hibino says.Cond
ensed-matter theorist Olivier Pierre-Louis from the University of
Lyon 1 in France agrees, commenting that the work demonstrates “
beautiful technical prowess” and that “the experimental measureme
nts are impressive.” However, he believes that further work is ne
eded to develop the theoretical model. Better understanding of th
ermomigration, he says, could lead to new nanostructure fabricati
on techniques in which thermal gradients shuffle atoms over a sur
face (see?https://physics.aps.org/articles/v15/s83Synopsis: Rearr
anging Nanoclusters Using Randomness). “Thanks to their paper, we
now have numbers to say what is possible and what is not,” Pierr
e-Louis says.测量热迁移2023年9月15日?物理16,157微尺度特征在表面上的缓慢漂移揭示了驱动原子从材料的热侧到
冷侧的力。在手机和其他设备中，微电路上的巨大温差会导致原子迁移，最终导致电气连接故障。这种所谓的热迁移现在已经在微观尺度上进行了追
踪，揭示了驱动运动的扩散相关力[1]。研究人员研究了一块方形硅片表面的浅凹陷或“盆地”，硅片的一边加热，另一边冷却。他们观察到原子
随着温差的变化而迁移时盆地的运动。推断出的力和过程的一般特征可以帮助其他研究人员开发控制纳米结构生长的新方法。从一个地方到另一个地
方的温度迁移速率与两个地点之间的温差(梯度)成正比。“工程师们在设计上做了很多工作，以避免热梯度，”法国艾克斯-马赛大学的frac
imdsamric Leroy说。但他表示，对该动议背后的基本原理缺乏更深入的理解。“我们提出了一种定量测量移动的方法，以便对驱动
运动的力有一个非常精确的值。”为了捕捉原子运动，Leroy和他的同事们从一块9毫米宽的硅片开始，它的表面非常平坦，均匀。他们在一面
施加热源，另一面施加散热器，产生了大约100摄氏度的温差。在这个梯度下，研究小组预计表面上的硅原子会从较热的区域迁移到较冷的区域。
但实际上很难看到这种变化。“我们不能直接测量原子的运动，因为原子运动得太快了，”Leroy说。组织撤退。在硅片表面，观察到的盆的推
进被解释为原子从较热的前壁扩散到较冷的后壁。相反，研究人员使用电子显微镜观察晶圆表面的单原子深度凹陷。通过拍摄一系列图像，研究小组
检测到这些几微米宽的特征以每秒0.2纳米(nm/s)的速度向晶圆热边缘移动。研究人员将盆地运动解释为硅原子扩散的结果。原子从盆地较
热的壁上分离出来，开始沿着盆地底部随机移动，就像在二维气体中一样。当其中一个扩散的原子到达盆地较冷的壁时，它可以重新附着。净效应是
盆地壁在热源方向上的推进。利用这种扩散模型，研究小组能够计算出大约10?8 eV/nm的热迁移力，这比化学键的力小数百万倍。Ler
oy说，在热梯度较大的微电路中，热迁移力应该更强。但要确定这种力的强度，还需要对其他类型的材料进行更多的实验。这些测试可以表明，研
究小组观察到的扩散机制是否是热迁移的一般特征。日本关西学院大学的地表科学家Hiroki Hibino对数据中盆地的运动如此清晰感到惊讶，因为原子运动非常复杂，盆地之间的温差很小(约0.04°C)。Hibino说:“作者成功地从复杂的过程中提取了热迁移效应，这要归功于精心设计的实验。”法国里昂大学的凝聚态物质理论家Olivier Pierre-Louis对此表示赞同，他评论说，这项工作展示了“美丽的技术实力”，“实验测量结果令人印象深刻”。然而，他认为需要进一步的工作来发展理论模型。他说，更好地理解热迁移可能会导致新的纳米结构制造技术，在这种技术中，热梯度会在表面上打乱原子的排列(见摘要:利用随机性重新排列纳米团簇)。“多亏了他们的论文，我们现在有了数字来说明什么是可能的，什么是不可能的，”皮埃尔-路易斯说。以上翻译结果来自有道神经网络翻译（YNMT）· 通用场景看了文章：热量流动也是双向的，大家有什么想法呢？ |
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