Activity 1. Listen and study

Unit 6. A Working Group Session.

Target Vocabulary List

1) opportunity - возможность

2) purpose - цель

3) to suggest an explanation - предложить объяснение

4) to discuss in detail - обсудить подробно

5) to obtain data - получать данные

6) to conclude - делать выводы

7) to draw conclusions - делать выводы

8) to have a look at - взглянуть на

9) relationship - взаимосвязь, взаимоотношение

10) experimental data - экспериментальные данные

11) to agree with - соответствовать

agreement - согласие, соответствие

11) to enable - давать возможность, позволять

12) to attribute to - приписывать, объяснять

13) to be brief - быть кратким

14) to keep to the point - говорить по существу

15) to identify oneself - представляться, называть себя

16) to comment on - прокомментировать

to make comments - делать комментарии

17) to be over - заканчиваться; syn. To be up

18) to wander away from the subject - уходить от предмета обсуждения

19) in view of - ввиду, по причине

20) persuasive - убедительный

Presenting a paper.

Rundle: Thank you, Mr. Chairman. I am happy to have this opportunity to present my paper at this working group session. The purpose of this study was to understand the mechanism of intersubband scattering in two-dimensional electron gas in heterostructures. It is well known that some interesting research has been done in this field in recent years. Yet. It is not clear why interband scattering rate does not increase with temperature. So the aim of this work was to find an explanation for the temperature - dependent intermodulation. We suggest an explanation in terms of oscillations in the Fermi level, which is confirmed by a model calculation. Now let me discuss in some detail the data we have obtained and the conclusions we have drawn.

I would like to start by showing some slides. (To the projectionist.) The first slide, please. Here we see the intermodulation as a function of temperature. The data have been multiplied by a factor of 2.5 to better display the low-field region. Let’s have a look at this plot. Next slide, please. This is a Dingle plot for a sample with only one subband occupied. I would like to stress that the amplitude of the resistance oscillations has been corrected for temperature. Full circles are for a temperature of 4.10 Kelvin. (To the projectionist.) Next slide, please. Could we make a picture a bit brighter? Thank you. Here we see Dingle plots for the data when two subbands are occupied. Full circles are for the low frequency, that is for the upper subband. The open circles are for the high frequency, or the lower subband. Please, note the difference between the two lines which are least-square fits to the data. I’m afraid we’ll have to skip the next two slides, because we are short of time. (To the projectionist.) Can we see the last slide, please? This slide demonstrates the relationship between the experimental data and the model calculations, and you can see a good agreement. This enabled us to make the following conclusion. When a semiclassical treatment of the amplitude of the low-field oscillations in two-dimensional systems is extended to the case of the two occupied subbands, the intercept of the Dingle plots depends on the intersubband fraction of scattering for most of the carriers. Experimental results agree with this theory and show that in the heterojunction investigated approximately one-third of the scattering is inter-subband. In contrast with the previous interpretation, we attribute the phenomenon to oscillations in the Fermi energy rather than to the acoustic phonons. Our explanation is supported by a model calculation. With this I would like to finish. If there are questions I’ll be glad to answer them. Thank you.

Activity 2. Pay attention to the presentation layout:

1. Formulating the aim:

n The aim of this study was to see...

n The aim of this work was to find...

n The purpose of this paper...

2. Pointing out the interest in a particular problem:

n There is much interest in the problem today due to the importance of...

n The problem attracts much attention today because the understanding of... is important for...

n The problem is interesting from many points of view.

3. Finishing a presentation:

n In conclusion I would like to say that the interpretation I have described is supported by experiment.

n To summarize, I would like to repeat the main points.

n Now let me repeat the main points again.

n Let me summarize the main points.

Дата добавления: 2015-05-08