文章来源:未知 文章作者:enread 发布时间:2014-11-19 06:09 字体: [ ]  进入论坛
A research team from Germany developed an analytical1 model to describe the structural2 dynamics3 of photoexcited thin films and verified it by ultrafast X-ray diffraction. Lattice dynamics, atomic movements in a crystal structure, can influence the physical and chemical properties of a material. The phenomenon can be directly studied using ultrafast X-ray diffraction, in which femtosecond X-ray pulses take snapshots of the atomic positions in a crystal by interacting with the structure at the core electronic level.
However, no comprehensive study has yet been carried out to characterize the photoexcited lattice dynamics of an opaque4 thin film on a semi-infinite transparent5 substrate. As a result, ultrafast X-ray diffraction data for such samples can be challenging to interpret.
Now a new study in the journal Structural Dynamics, from AIP Publishing, builds a model to help interpret such data.
To study this common scenario6, the researchers excited a thin film of metallic7 SrRuO3 deposited on a transparent SrTiO3 substrate with femtosecond near infrared8 laser pulses and subsequently probed the atomic structure with equally short hard X-ray pulses. By comparing the resulting time-resolved diffractograms for different film thicknesses and excitation conditions, they found that the lattice dynamics of the system depended on only four parameters9: the thickness of the film, its longitudinal acoustic10 sound velocity11, a scaling factor and a shape factor.
"The coherent lattice dynamics are involved in nearly any ultrafast experiment on laser-excited thin films and their time scale is mainly determined12 by the film thickness and its longitudinal sound velocity," said Daniel Schick, a researcher at the University of Potsdam. They then incorporated these factors into an analytical model that can be used to explain the observed variation in the X-ray diffraction of different thin films.
Their model allows them to describe a rather puzzling finding: although a thin film is essentially13 heated by the laser excitation and should rapidly expand, a significant part of the film is compressed for a short time of only a few picoseconds after the laser pulse hits the sample. In the ultrafast X-ray diffraction this manifests in a transient "splitting" of the thin film's Bragg peak, which provides direct information on the average atomic distances in the film. This observation can be directly linked to the spatial14 excitation profile of the thin opaque film, which is, in the simplest case, given by the optical absorption length of the laser light and is included as the shape factor in the analytical model.
After developing their model using this relatively15 simple model system, the researchers have applied16 it to study more complex ones, such as with a strong coupling of the lattice to charge or spin degrees of freedom in ferroelectric and magnetic materials.


1 analytical lLMyS     
  • I have an analytical approach to every survey.对每项调查我都采用分析方法。
  • As a result,analytical data obtained by analysts were often in disagreement.结果各个分析家所得的分析数据常常不一致。
2 structural itXw5     
  • The storm caused no structural damage.风暴没有造成建筑结构方面的破坏。
  • The North American continent is made up of three great structural entities.北美大陆是由三个构造单元组成的。
3 dynamics NuSzQq     
  • In order to succeed,you must master complicated knowledge of dynamics.要取得胜利,你必须掌握很复杂的动力学知识。
  • Dynamics is a discipline that cannot be mastered without extensive practice.动力学是一门不做大量习题就不能掌握的学科。
4 opaque jvhy1     
  • The windows are of opaque glass.这些窗户装着不透明玻璃。
  • Their intentions remained opaque.他们的意图仍然令人费解。
5 transparent Smhwx     
  • The water is so transparent that we can see the fishes swimming.水清澈透明,可以看到鱼儿游来游去。
  • The window glass is transparent.窗玻璃是透明的。
6 scenario lZoxm     
  • But the birth scenario is not completely accurate.然而分娩脚本并非完全准确的。
  • This is a totally different scenario.这是完全不同的剧本。
7 metallic LCuxO     
  • A sharp metallic note coming from the outside frightened me.外面传来尖锐铿锵的声音吓了我一跳。
  • He picked up a metallic ring last night.昨夜他捡了一个金属戒指。
8 infrared dx0yp     
  • Infrared is widely used in industry and medical science.红外线广泛应用于工业和医学科学。
  • Infrared radiation has wavelengths longer than those of visible light.红外辐射的波长比可见光的波长长。
9 parameters 166e64f6c3677d0c513901242a3e702d     
因素,特征; 界限; (限定性的)因素( parameter的名词复数 ); 参量; 参项; 决定因素
  • We have to work within the parameters of time. 我们的工作受时间所限。
  • See parameters.cpp for a compilable example. This is part of the Spirit distribution. 可编译例子见parameters.cpp.这是Spirit分发包的组成部分。
10 acoustic KJ7y8     
  • The hall has a fine acoustic.这个大厅的传音效果很好。
  • Animals use a whole rang of acoustic, visual,and chemical signals in their systems of communication.动物利用各种各样的听觉、视觉和化学信号来进行交流。
11 velocity rLYzx     
  • Einstein's theory links energy with mass and velocity of light.爱因斯坦的理论把能量同质量和光速联系起来。
  • The velocity of light is about 300000 kilometres per second.光速约为每秒300000公里。
12 determined duszmP     
  • I have determined on going to Tibet after graduation.我已决定毕业后去西藏。
  • He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。
13 essentially nntxw     
  • Really great men are essentially modest.真正的伟人大都很谦虚。
  • She is an essentially selfish person.她本质上是个自私自利的人。
14 spatial gvcww     
  • This part of brain judges the spatial relationship between objects.大脑的这部分判断物体间的空间关系。
  • They said that time is the feeling of spatial displacement.他们说时间是空间位移的感觉。
15 relatively bkqzS3     
  • The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
  • The operation was relatively painless.手术相对来说不痛。
16 applied Tz2zXA     
  • She plans to take a course in applied linguistics.她打算学习应用语言学课程。
  • This cream is best applied to the face at night.这种乳霜最好晚上擦脸用。
TAG标签: film crystal lattice