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.

玻璃在自然界和技术中都存在，从固化的熔岩到我们的窗户或pyrex炊具，再到我们智能手机上的大猩猩玻璃或DVD的可重写层。然而，它仍然是物理学的尚未解决的问题之一。或更准确地说，我们不确定其进化的原子机制。眼镜可以在某种程度上将其描述为被捕的液体。与原子或分子以明确定义的几何顺序定位的晶体相反，玻璃中的原子和分子倾向于随机定位，就像液体中的原子和分子一样，但几乎是固体，如固体，与液体相反。问题来自其中的“几乎”部分。在熔点，TM，原子或分子的近距离接近，但与其他原子一起拖动时，粘度很小，因此玻璃鼓风机必须小心，不要丢下玻璃鼓风机，不要放下他在吹管末端握住的玻璃。随着玻璃的冷却，原子的移动要求越来越多的其他原子同时移动，因此随着粘度的增加，直到玻璃块达到温度，称为玻璃过渡TG，一切似乎都停止了。还是我们认为确实发生的事情。实际上，即使在TG以下，事情仍然在移动，至少如果将玻璃以无限缓慢的速度带到TG。这称为放松。在TG附近和下方发生的过程是什么以及它们的空间范围保持不明。该研究计划的目的是通过以下方式识别它们。通过轰击形成非常沉重的原子玻璃的材料以低能加速，我们将生产很小的玻璃区域。离子撞击将在一层材料上形成一个玻璃区域，或者会转变为受影响的纳米颗粒，我们先前将其沉积在表面上。这将在纳米氧计的表面上完成，纳米层仪的表面是由薄层膜制成的设备，该膜在上面运行金属条，既可以用作加热器和温度计。因此，随着松弛过程的进行，该设备将用于测量纳米颗粒释放的热量。由于它们的尺寸很小（遍布几纳米），因此放松过程不能涉及那么多原子。此外，它们足够小，可以对完整粒子进行原子模拟。通过将测量的热量与模拟中能量的演变进行比较，我们应该能够找到材料中的松弛机制。将要研究的材料将是Geo2，是Sio2的更容易测量的兄弟，这是大多数窗户和岩石所制成的，而GE2SB2TE5是基于重写DVD的玻璃，其行为与Geo2和Sio2的行为非常不同。