Respondence of Sample Temperature during Straight-Line Ion Implantation

Transcription

1 Respondence of Sample Temperature during Straight-Line Ion Implantation XU Liyun JIN Fanya SHI Zhongbing LIU Huaying WANG Ke SHEN Liru TONG Honghui Key ward Ion implantation Respondence of temperature Simulation There are many advantages of material surface modification by ion beam, such as the ions are selected freely and the temperature of specimens is unconfined during the process of implantation. Due to the conduction of energy provided by the implanted ions, it will bring about the respondence of sample temperature which promotes the compound to form, integrate and diffuse efficiently [1-3]. It plays special role in the treatment of materials for intensification. However, sometimes exceeding high temperature caused by continual collisions will induce the phenomenon which lead the specimens losing mechanism and hardness decreasing, especially for bearing steel or alloy of aluminum [4]. From the aspects of which electric energy changed into thermal energy, respondence of sample temperature is connected with many aspects such as the current of ion beam, the energy of ion and the surface area of ion implantation. As for the theory calculation, it was very complicated when considered conduction of heat. So a theoretic model for calculation of the sample temperature during straight-line ion was established based on the results of experiment which taked the pure aluminum as the samples at first, and then in comparison with the values measured in the experiment. Through the continual amendments, some applications of the results of simulation could be provided to control the temperature. 1 Experiment method Taking pure aluminum 50mm 5mm as the samples with the stylets of thermocouple buried in. Preparation of the specimens for implantation were done by mechanical grinding and polishing, and then ultrasonically cleaned in acetone and alcohol. Experiments were prepared by using DLZ-100 deposition equipment which belonged to southwestern institute of physics, as shown in Fig.1. The base pressure was lower than Pa and the working pressure was approximately Pa. During the process of the implantation, the temperature of samples

2 was detected by the stylet of thermocouple, then conveyed to the recording apparatus. The substrates were cooled during implantation by water cooling system. Fig.1 Sketch of the device for testing the temperature of samples 2 Results of the experiment and simulation During the process of straight-line ion implantation, the respondence of temperature is determined by many aspects such as the current of ion beam, the energy of ion, the radiation and conduction of heat etc [5]. The correspondence relation can be described in the following form : UI t = Slc T + ( S +So ) ( T 4 T 4 D ) t + KS ( T - TD)/l (1) where U, the voltage of implantation, I, the average current density of ion beam, t, the time of implantation,, the coefficient for amendment;,c, K and the density( kg/m 3 ) is the specific heat ( KJ/( kg K),273K), the rate of conduction of heat and the rate of radiation of heat (as showed in table 1 [5] ) of the pure aluminum respectively; S,So and l is the bottom area, the side area and thickness of the specimen respectively;,the coefficient of Stefen-Boltzman ( WP(m 2 K 4 ) ), the rate of contact conduction between solid interfaces (with the varied kinds of materials and difference of the contact area between the specimens and the sample holder, the values of are different); T,T D and T is the temperature of the specimens, the temperature of environment inside the vacuum chamber (293 K) and the added temperature respectively. Before calculating the ascending temperature,, the rate of contact conduction between solid interfaces was established the third power of T (the temperature of the specimens) based on the experiment results during the process of temperature decreasing. The basic equation was as

3 follows: Slc T = ( S + So ) ( T 4 T 4 D ) t + KS ( T - TD)/l (2) meanwhile, the rate of conduction of heat (K) and the rate of radiation of heat ( ) was also established the third power of T (the temperature of the specimens) according of the values provided with the table 1 [6]. Of course, the quadric electrons produced by the ion implantation into the surface of specimens have more effects on the calculation values, so the coefficient for amendment ( ) should be drawn on during the theoretic model. Table 1 the rate of conduction of heat and the rate of radiation of heat of the specimen under different temperature T/ K/W (m K) When implantations occurred at a high power density (W=UI) in continual ways, the temperature of specimens attained by calculation arised rapidly in the beginning, the trend of curves as well. And compared with the values measured in the experiment, it was easy to achieve the balance temperature. Perhaps this could be explained by follows: during the process of the increase of temperature, on account of the stylet of thermocouple emerging in the bottom of the specimens, moreover, the energy of the specimens couldn t achieve the balance by radiation and conduction of heat in short time, so that there were somewhat errors between the values attained by experiment and calculation. With the continuance of implantation, the errors were decreased because the increase of temperature was small in unit time, and then the system achieved the balance of heat gradually. The curves of respondence of temperature are attained by experiment and calculation at the condition of low electric current, the values were in good agreement with each other. When implantations occurred in interval ways (implantation time: 7min; interval time: 5min) on the condition of 60kV accelerated voltage, 5.4mA electric current and 1.8mA electric current,

4 the values of temperature are attained by experiment and calculation. Compared with continual implantation, interval implantation was the same in the physics mechanism of respondence of temperature, however, the balance temperature was lower when implantation occurred at the same power density. The decrease temperature was also determined by the radiation and conduction of heat during the interval process. The curves of simulating temperature were in good agreement with the curves measured in the experiment. 3 Application of the simulation Because of the annealing temperature of some materials (such as bearing steel) was very low, it was very necessary to control the temperature of specimens during the process of treatment for intensification by ion implantation. Of course, the requirement for applying this technology could be met by decreasing the power density of implanted ions or prolonging the interval time. However, in our experiments especially for some industrial applications, how to achieve the most efficient? By calculation and simulation, can we choose the optimal technology parameters just illustrated as follows: The simulation curves of respondence temperature caused by varied kinds of ion implantation which occurred on the condition of 60kV accelerated voltage, 1.74mA electric current were shown.from that, We could conclude that the ultimate balance temperature of specimens would be attained with different implantation time and different interval time. It was the two kinds of simulation curves of respondence temperature caused by different ion implantation ways on the condition of 60kV accelerated voltage, 1.74mA electric current which controlled the temperature of specimens under 300. Through compiling programs, ion implantation was carried out for16 minutes continually in the beginning, then taken by circular ways. Fortunately all these could be operated by computer. 4 Conclusion From the above discussion, the important results were summarized as follows: (1)Respondence of sample temperature was connected with many aspects such as the current of ion beam, the energy of ion and the surface area of ion implantation. From the aspects of which electric energy changed into thermal energy, the calculated values of the temperature were in good agreement with the values measured in the experiment. (2)According of the results of simulation and the requirements of specimens themselves, we could choose varied kinds of ways of ion implantation and the optimal technology parameters operated by computer. REFERENCES 1 Zhang tonghe,wu yuguang, et al. Properties of Corrosion Resistance in C + +W + Dual Implanted Steel with Nanometer Phases. Surface and Coatings Technology, 2000, ( ) :181 2 Zeng yiwei, Ji chengzhou. Study on High Dose Ion Implantation in Aluminum Foil. Surface and Coatings Technology,2000, ( ): Zeng Z M,.Zhang T, Tian X B,et al. Surface Modification of 9cr18 Bearing Steels by a Metal and Carbon Co-Plasma Immersion Ion Implantation. Surface and Coatings Technology, 2000, ( ) :236 4 Jin Fanya, Tong Honghui, et al. Improvement of Mechanical Properties of W9Cr4V2Mo Bearing Steel Using

5 Compound Ion Implantation. Heat Treatment of Metals (in Chinese), 2003,28 (10):5 5 Zhang Tonghe, Chen Jun. Surface Modification Technology by Ion Implantation (in Chinese), Beijing: Metallurgy Industry Press, Zhan Zaiji, Ma Xinxin, et al. Prediction of Sample Temperature during Plasma-based Ion Implantation. Journal of Harbin Institute of Technology (in Chinese), 2000,32 (1):15