Direct imaging of self-assembled magnetic nanoparticle arrays: Phase stability and magnetic effects on morphology
Direct imaging of self-assembled magnetic nanoparticle arrays: Phase stability and magnetic effects on morphology
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自组装磁性纳米颗粒阵列的直接成像：相稳定性和磁对形态的影响
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
S. Majetich
中科院分区：
文献类型：
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作者：
S. Yamamuro;D. Farrell;S. Majetich
化学稳定的7.0 nm Fe和3.9 nm FePt纳米颗粒自组装成薄阵列，并通过透射电子显微镜成像。通过光场成像和投影势像模拟相结合的方法，对阵列的局部填充结构和堆叠序列进行了唯一识别。7.0 nm的FePt纳米颗粒表现为六方密排（hcp）和面心立方（fcc）结构，3.9 nm的FePt纳米颗粒表现为松散的体心立方（bcc）结构，fcc和hcp也表现为松散的体心立方结构。bcc结构的形成是由颗粒的大振动熵和表面活性剂分子构象的竞争焓和熵效应引起的软颗粒间排斥驱动的。唯一的异常是铁纳米粒子倾向于形成奇数层的hcp阵列。这归因于超铁磁有序阵列层之间的厚度和层径相关的磁耦合。
Chemically stabilized 7.0 nm Fe and 3.9 nm FePt nanoparticles have been self-assembled into thin arrays, and imaged by transmission electron microscopy. The local packing structures and stacking sequences of the arrays were uniquely identified by a combination of bright-field imaging and projected potential image simulations. Close-packed structures, hexagonal close-packed (hcp) and face-centered cubic (fcc), were observed for 7.0 nm Fe nanoparticles, while a loosely packed body-centered cubic (bcc) structure was detected for 3.9 nm FePt nanoparticles as well as fcc and hcp. The bcc structure formation is driven by the large vibrational entropy of particles and the soft interparticle repulsions originating from competing enthalpic and entropic effects on surfactant molecule conformation. The sole anomaly noted is a preference for forming hcp arrays with odd numbers of layers observed for Fe nanoparticles. This is attributed to the thickness- and layer-diameter-dependent magnetic coupling between superferromagnetically ordered array layers.