Evolution of nanoscale glasses

纳米级玻璃的演变

• 批准号: RGPIN-2014-06458
• 负责人: Schiettekatte, François
• 金额: $ 3.5万
• 依托单位: Université de Montréal
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=689681
• 关键词: Evolution; nanoscale; glasses

Glass exists everywhere in nature and in technology, from solidified lava to our windows or Pyrex cookware, to Gorilla glass on our smartphones or in the rewritable layer of DVDs. And yet, it remains one of the unsolved problems of physics. Or more accurately, we do not know precisely the atomic mechanisms underlying their evolution. Glasses can be described to some extent as an arrested liquid. Contrarily to crystals where the atoms or molecules are positioned in a well-defined geometrical order, the atoms and molecules in a glass tend to be positioned randomly, like those in a liquid, but almost immobile, as in solids and contrarily to liquids. The problem comes from the "almost" part of it. Near but just below the melting point, Tm, the atoms or molecules can move around on a small scale while dragging with them the other atoms, so viscosity is small, and the glass blower has to be careful not to drop the gather of glass he holds at the end of his blowpipe. As the glass cools off, the movement of an atom requires that an increasing number of other atoms move at the same time, therefore with increasing viscosity, until the piece of glass reaches a temperature, called the glass transition Tg, where everything seems to stop. Or is it what we think does happens. In fact, even below Tg, things still move, at least if the glass is brought to Tg at a rate that is not infinitely slow. This is called relaxation. What are the processes occurring near and below Tg remain unidentified, as well as their spatial extent. The goal of this research program is to identify them in the following way. By bombarding materials that form glass with very heavy atoms accelerated at a low energy, we will produce very small regions of glass. The ions impact will each form a zone of glass on a layer of material, or will transform into glass the impacted nanoparticles, which we will have previously deposited on the surface. This will be done at the surface of a nanocalorimeter, a device made of a thin layer membrane on which runs a metallic strip, which serves both as a heater and thermometer. Hence, the device will be used to measure the heat released by the nanoparticles as the relaxation process goes on. Because of their small size (few nanometers across), the relaxation process cannot involve so many atoms. Furthermore, they are small enough that an atomistic simulation of the complete particle can be carried out. By comparing the heat measured to the evolution of the energy in the simulation, we should be able to find what are the relaxation mechanisms in the material. The material that will be investigated will be the GeO2, the more easily measurable brother of SiO2, which is what most windows and rocks are made of, and Ge2Sb2Te5, a glass at the basis of rewritable DVDs and that behaves very differently than GeO2 and SiO2.

玻璃在自然界和科技中无处不在，从凝固的熔岩到我们的窗户或Pyrex炊具，再到我们智能手机上的Gorilla玻璃或DVD的夹层。然而，它仍然是物理学未解决的问题之一。或者更准确地说，我们不知道它们进化背后的原子机制。玻璃在某种程度上可以被描述为一种被捕获的液体。与原子或分子以明确定义的几何顺序排列的晶体不同，玻璃中的原子和分子倾向于随机排列，就像液体中的原子和分子一样，但几乎不动，就像固体中的原子和分子一样，而液体则相反。问题出在“几乎”的部分，即接近熔点Tm但刚好低于熔点Tm时，原子或分子可以在小范围内移动，同时拖动其他原子，因此粘度很小，玻璃吹制工必须小心，不要让他在吹管末端拿着的玻璃碎片掉落。当玻璃冷却时，原子的运动需要越来越多的其他原子同时运动，因此粘度增加，直到玻璃片达到称为玻璃化转变Tg的温度，在那里一切似乎都停止了。或者是我们认为发生的事情。事实上，即使低于Tg，物体仍然会移动，至少如果玻璃以不是无限慢的速度达到Tg的话。这就是所谓的放松。在Tg附近和以下发生的过程以及它们的空间范围仍然没有确定。本研究计划的目标是通过以下方式识别它们。通过用低能加速的重原子轰击形成玻璃的材料，我们将产生非常小的玻璃区域。离子撞击将各自在材料层上形成玻璃区，或者将撞击的纳米颗粒转化为玻璃，这些纳米颗粒之前将沉积在表面上。这将在纳米热量计的表面完成，纳米热量计是一种由薄层膜制成的装置，其上运行着金属条，既用作加热器又用作温度计。因此，该装置将用于测量纳米粒子在弛豫过程中释放的热量。由于纳米粒子的尺寸很小（只有几纳米宽），弛豫过程不可能涉及这么多原子。此外，它们足够小，可以进行完整粒子的原子模拟。通过比较测量到的热量与模拟中的能量演化，我们应该能够找到材料中的弛豫机制。将被研究的材料将是GeO2，SiO2的更容易测量的兄弟，这是大多数窗户和岩石的组成，以及Ge2Sb2Te5，一种基于DVD的玻璃，其行为与GeO2和SiO2非常不同。