【作者】 任树洋；

【导师】 任忠鸣；

【作者基本信息】 上海大学 ， 钢铁冶金， 2011， 博士

【摘要】 当前,薄膜技术已成为新材料研制必备的、不可缺少的重要手段之一。薄膜生成过程中的沉积、结构和外延决定着薄膜的物理化学性能。磁场可以诱导磁各向异性材料沿着磁能较小的方向生长,达到控制晶体生长的目的。在薄膜制备过程中施加强磁场,可以利用磁场的磁取向作用来调节薄膜的生长过程进而改进薄膜的性能,所以,研究强磁场下薄膜的形核与生长具有很大的意义。本文采用电阻加热真空蒸发技术,在不同磁场强度、温度、基片的不同放置方式下制备了Zn、Te和Bi薄膜,利用XRD、SEM、TEM、AFM和PL谱等多种分析测试手段,研究了强磁场对薄膜的形核、取向生长、表面形貌以及表面粗糙度的影响,推导了磁场对薄膜形核的作用机理,薄膜取向生长机理及表面粗糙度改变机理。首先,在强磁场下制备了Zn薄膜,利用XRD和SEM分别研究了Zn薄膜在磁场下的取向生长和表面形貌。3T磁场以下制备的薄膜表面晶粒比无磁场下的晶粒细小,这是由于磁场对形核的促进作用以及对扩散的抑制作用引起的。不同磁场下,分别在垂直和平行磁场方向放置的基片上制备了Zn薄膜,磁场促进了垂直磁场放置基片上沉积Zn薄膜的c轴取向生长。平行磁场方向放置的基片上制备的Zn薄膜优先生长方向发生了改变,由原来的(002)生长改变成(101)生长,说明薄膜在磁场中发生了磁取向生长。初步利用磁取向理论计算,薄膜在磁场下发生磁取向生长的条件是取向能大于62J/cm~3。本文研究了Zn薄膜的取向对ZnO光电性能的影响,首先利用磁场的取向作用制备了Zn薄膜,接着在空气中通过氧化该薄膜制备了ZnO薄膜,对其进行了光电性能研究。在(101)取向的Zn薄膜氧化法制备的ZnO薄膜相对(002)取向Zn上制备的薄膜来说,前者具有更细小的晶粒。紫外可见光和荧光光谱(PL)结果显示前者具有更高的强度,原因归结于前者更细的晶粒,另外一个可能的原因是未完全氧化的Zn起到了一定的掺杂作用。为了进一步考察薄膜磁取向生长规律,本文还研究了非金属Te薄膜在磁场下的取向生长,考察了薄膜形貌与Te取向之间的关系,还考察了基片温度对Te取向的影响,最后通过Te薄膜形核初期的SEM观察发现磁场对形核的影响规律并推导了磁场对薄膜的作用机理。XRD结果表明,4T磁场下Te薄膜发生了磁取向生长,由原来的(011)变成(012)生长,而SEM扫描结果未能显示取向发生变化,FEM分析表明这是由于(011)和(012)面夹角为19°,晶粒沿生长方向倾斜较小引起的。衬底温度也可以明显的改变Te薄膜的取向生长,在4T磁场下,120℃制备的Te薄膜优先生长方向由原来的<012>变为<100>方向;温度的升高不利于磁场的取向作用。通过不同衬底制备的沉积初期Te薄膜的SEM结果可以看出,磁场对形核具有促进作用;理论分析表明磁场降低了物质临界形核半径和临界形核能,但对形核速率具有一定的一直作用。另外,在磁场下制备磁化率差异较大的Bi薄膜,并与Zn薄膜的取向规律进行了对比研究,提出了薄膜在磁场下取向生长的新判据。Bi薄膜的磁化率差异大约是Zn的十倍,和无磁场条件下相比,在磁场为6T以下强度时制备的Bi薄膜均没有发生择优取向生长,最强峰都为为(003)。这与传统的磁取向理论(?) B~2V≥kT矛盾,作者提出了磁场下薄膜取向生长的新判据,即薄膜在磁场中是否取向需满足(?)B~2V≥σ·ΔS。施加高于8T磁场,制备的Bi薄膜取向由原来的(003)变为(202)取向,验证了提出的新理论的正确性。最后,本文还利用原子力显微镜(AFM)对Bi薄膜表面形貌的粗糙度进行分析测试,研究了磁场影响Bi薄膜表面粗糙度的基本规律,并对薄膜生长的动力学过程进行了标度化研究。通过AFM结果发现施加10T磁场制备的Bi薄膜实验的均方根粗糙度Sq比未施加磁场的试样粗糙度有减小的趋势,沉积30S,60S和120S的试样均方根粗糙度Sq都有降低的趋势。进一步的分析表明,Bi薄膜隆起峰处磁感线密度的改变时粗糙度变化的原因。最后,利用动力学标度原理对Bi薄膜研究了磁场对Bi薄膜生长模式影响。结果表明,磁场未能改变Bi薄膜的生长模式,两种条件下都是随机沉积模式生长。更多还原

【Abstract】 Currently, the science and technology of film preparation has been becoming a fundamental and dispensable means for the development of new materials. The film deposition, structure and extension during the growth process determine its physical and chemical properties. Magnetic field is a novel way to control the crystal growth since it can induce the crystal to grow along the direction of lower magnetic energy because of the anisotropy of magnetic susceptibility. Appling magnetic field in the process of films can improve the film performance by orientating the crystal growth. Therefore, it has a great significance to study the effect of magnetic field on the film nucleation, growth and quality. In this paper, Zn, Te and Bi films were prepared by the method of vacuum evaporation using resistance heating technology in the magnetic field. X-ray diffraction (XRD), scanning electronic microscope (SEM), transmission electron microscope (TEM), atomic force microscope (AFM) and photoluminescence (PL) spectra were employed to study the grain orientation, surface morphology and roughness of films prepared under the different magnetic field, evaporating time, temperature, substrate type and setting direction. The results effectively explore the film nucleation and growth mechanism under the magnetic field. Thereby a new criterion for oriented growth of thin films in a magnetic field is proposed. This provides a favorable guidance for preparing film in the magnetic field in the industry.Firstly, the effect of magnetic field intensity on the grain size and orientation of Zn film were studied. The magnetic field could result in the smaller grains in the films, which is due to the nucleation promotion and the diffusion inhibition from magnetic field. The magnetic field enhances the c-axis oriented growth of Zn film prepared on the substrate which is set in the direction vertical to the magnetic field. The priority growth orientation of the samples changes from the original (002) to (101), prepared on the substrate set in the direction parallel to the magnetic field. The preliminary theoretical calculation of using magnetic orientation shows that the orientation growth of film in a magnetic field occurs when the orientation growth energy is larger than 62J/m3.Secondly, the ZnO thin films by oxidation in air were prepared under the different orientation of Zn thin films in the magnetic field. The effects of (101)-oriented and (002)-oriented Zn thin films on the grain size and optical properties of ZnO thin film were investigated. XRD and SEM results show that the former has a finer grain size. UV-Vis and photoluminescence (PL) spectroscopy results show that the former has the higher optical intensity. This is attributed to the finer grain and no full oxidization of Zn doping.Thirdly, the effects of magnetic field on the grain orientation of non-metallic bonded Te thin film were investigated. XRD results show that the grain orientation growth in Te thin films prepared in the magnetic field changes from the (011) into (012). But the SEM results show that no significant change in the surface morphology of Te films. FEM analysis shows that the reason is due to the angle of 19°between the (011) and (012) surface, which is not large to see the difference. The substrate temperature can significantly change the growth orientation from the <012> original priority growth direction into the <100> direction for Te films in the 4T magnetic field and at the temperature of 120℃. The temperature is not favorable for the orientation effect of the magnetic field. The earlier deposition of Te films on the different substrates was prepared with and without magnetic field. SEM results show that the magnetic field can promote the nucleation. The theoretical analysis shows that the magnetic field decreases the critical nucleation energy and the critical nucleation radius, but has no certain effect on the nucleation rate during the thin film growth. In addition, a new criterion ((?)B~2V≥σ·ΔS) for oriented growth of thin films in a magnetic field was proposed by investigating the Bi films which have a larger magnetic susceptibility difference among the different crystal orientation. The magnetic susceptibility difference of Bi is larger about ten times than that of Zn. The strongest peak of the Bi films prepared in less than 6T magnetic field is (003) plane, which is same as that of the samples without magnetic field (which have no preferred orientation growth). This phenomena is contradicted to the traditional theory of magnetic orientation ( (?)B~2V≥kT). Therefore, a new criterion ((?)B~2V≥σ·ΔS) for oriented growth of thin films in a magnetic field is proposed, which is evidenced by the experiment of the grain orientation from (003) to (202) of the Bi film applied larger than the 6T magnetic field.Lastly, the atomic force microscope (AFM) was introduced to study the effect of magnetic field on the surface topography of Bi films. The root mean square roughness Sq analysis shows the roughness of Bi films prepared in the 10T magnetic field tends to decrease, compared with that of the samples without magnetic field. The same orderliness is also found for the samples with the different deposition times of 30s, 60s and 120s. This may be induced by the change of the magnetic flux density at the hunch peak of Bi thin films. In the end, the research on the dynamic scaling analysis shows the magnetic field can not modify the random deposition mode of Bi thin films.更多还原