Substrate effects on glass formation in simple monatomic supercooled liquids Vo Van Hoang a,⇑ , Dao Kim Thoa b , Takashi Odagaki c , Le Ngoc Qui b a Comp. Physics Lab, Institute of Technology, Vietnam National University – HochiMinh City, 268 Ly Thuong Kiet Street, District 10, HochiMinh City, Viet Nam b Dept. of Physics, School of Natural Sciences, Can Tho University, Can Tho City, Viet Nam c Department of Physics, Tokyo Denki University, Hatoyama Hikigun, Saitama 350-0394, Japan article info Article history: Received 10 July 2014 In final form 24 November 2014 Available online 3 December 2014 Keywords: Glass thin films Glass transition Substrate effects on glass formation abstract Glass formation in simple monatomic supercooled liquids on substrate is studied via molecular dynamics simulations. We find that glass formation in thin films on substrate exhibits a ‘heterogeneous’ behavior, i.e. solidlike atoms initiate/enhance simultaneously in the near substrate region and in the interior of the system, then solidlike domain grows outward to the free surface. Substrate causes strong layering of the near substrate region of liquid and glass. Layering is enhanced with decreasing temperature and layering region exhibits a glassy behavior instead of crystalline one. We find that structure and dynamics of liquid and glass in the near substrate region is different from those of the remaining part of thin films. This means that thin films formed on substrate can be divided into three distinct parts: near substrate region, interior and free surface region. We find a significant amount of liquidlike atoms even at T < T g which may perform local motion like Johari–Goldstein process. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Atomic mechanism of glass formation in thin films has attracted a great interest and has been under intensive investigations by both experiments and computer simulations. So far our under- standing of a glass formation in thin films is still poor including effects of substrate on the phenomenon and it remains an active research area (see [1–15] and references therein). Some important substrate effects can be listed as given below: i. Substrate should induce layering of particles of liquids adja- cent to the substrate–liquid interface (see [2–4] and refer- ences therein) and it can modify structure of the near substrate region of liquids and glasses [1]. ii. Depending on the behavior of substrate (rough or smooth), substrate can increase or decrease relaxation time of parti- cles near the substrate–liquid interfaces (see [10–15] and references therein). Similarly, it can increase or decrease glass transition temperature depending on the behavior of the substrate–liquid interaction [5]. iii. Substrate can reduce or accelerate mobility of particles near the substrate–liquid interface compared to that in the inte- rior of the system depending on the behavior of substrate (see [10–15] and references therein). Note that in the present work we focus attention on the sup- ported thin films (i.e. thin films formed on a crystal substrate), although in some cases effects of crystal substrate on structure and properties of thin films are similar to the effects of hard wall on thin films confined between two hard walls. Therefore, we do not pay attention on the review of hard wall effects. That is, it is found by computer simulations that in the first few liquid layers adjacent to the structured substrate, icosahedral packing of atoms is suppressed while the magnitude of a local icosahedral order in the next layers depends on details of the particle–substrate inter- action [1]. It is found that strong particle–substrate attraction leads to the enhancement of a local icosahedral order in these layers compared to that of the bulk liquid [1]. On the other hand, layering of liquids and glasses at the interface with a substrate is another interesting problem. Layering of liquids in contact with substrate has been previously predicted theoretically and evidenced by experiments (see [2–4,16–18] and references therein). That is, high-resolution transmission electron microscopy images of the room-temperature fluid xenon in small faceted cavities in aluminum show the presence of three-well-defined layers within the fluid at each facet [2]. Similarly, ordered liquid aluminum at http://dx.doi.org/10.1016/j.chemphys.2014.11.017 0301-0104/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: vvhoang2002@yahoo.com (V.V. Hoang). Chemical Physics 447 (2015) 1–9 Contents lists available at ScienceDirect Chemical Physics journal homepage: www.elsevier.com/locate/chemphys