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: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=708321
• 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领域无处不在，从凝固的熔岩到我们的窗户或耐热玻璃炊具，再到智能手机上的大猩猩玻璃或dvd的可重写层。然而，它仍然是物理学中未解决的问题之一。或者更准确地说，我们并不确切地知道它们进化背后的原子机制。在某种程度上，玻璃可以被描述为一种滞留的液体。晶体中原子或分子的位置是按照明确的几何顺序排列的，而玻璃中的原子和分子往往是随机排列的，就像液体中的原子和分子一样，但几乎是不动的，就像固体中的原子和分子一样，而液体则相反。问题来自于“几乎”的部分。在熔点Tm附近但刚好低于熔点Tm时，原子或分子可以在小范围内移动，同时拖动其他原子，所以粘度很小，吹玻璃的人必须小心，不要把吹管末端的玻璃弄掉。当玻璃冷却时，一个原子的运动需要越来越多的其他原子同时运动，因此随着粘度的增加，直到玻璃片达到一个温度，称为玻璃转变Tg，在那里一切似乎都停止了。还是我们认为会发生的事。事实上，即使低于Tg，物体仍然在运动，至少如果玻璃以不是无限慢的速度被带到Tg。这叫做松弛。在Tg附近和以下发生的过程以及它们的空间范围仍未确定。本研究计划的目标是通过以下方式识别它们。通过用很重的原子在低能量下加速轰击形成玻璃的材料，我们将产生非常小的玻璃区域。离子的撞击会在一层材料上形成一个玻璃区，或者将我们之前沉积在表面上的受撞击的纳米颗粒转化为玻璃。这将在纳米热量计的表面完成，纳米热量计是一种由薄层薄膜制成的装置，上面有一条金属条，既是加热器又是温度计。因此，该装置将用于测量纳米颗粒在松弛过程中释放的热量。由于它们的尺寸很小（直径只有几纳米），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。通过将测量的热量与模拟中的能量演变进行比较，我们应该能够找到材料中的松弛机制。将被研究的材料将是GeO2和Ge2Sb2Te5，前者是SiO2的兄弟，更容易测量，大多数窗户和岩石都是由SiO2制成的，后者是可重写dvd的基础玻璃，其性能与GeO2和SiO2非常不同。