第一句，我是谁（姓名、身份、学校）。如果已经拿到了该学校的interview，那好极了，在第二句提一下。最后一句：I am very interested in your research， so I write this letter to explore the possibility of doing research with you， with financial support.
首先说明为什么我单单看上了你。这要求对对方的research比较了解，不仅知道对方在做什么，还要知道对方做的东西中重点、亮点还有吸引你的点是什么。做cell signaling的人遍地都是，但你在做signaling crosstalk，尤其是你还涉足过数学建模！提出这一点，让对方知道你对他有所了解，并且知道你的兴趣所在，最重要的是表明你是认真的！
其次表现你自己。其实本科生申请，实在没什么好表现的，因为很少有人能有实实在在的文章（奖项什么的千万别列）。可能真正能表现的就是态度吧：阐发一下对这个研究方向的看法，表现出你对这个领域的了解程度，你的insight，以及你对科研的热忱（但是一定是间接表现，「I am very enthusiastic」这种话就别写了）。另外要是个人有特别适合该研究方向的特质一定提一下，比如我会说（作为生物专业的学生）with my good background in mathematics， 我可以blabla。
In addition， would it be possible for you to tell me more about what you are concentrated on recently？ And I am also interested in what you are going to pursue in the future.
结尾：If you have available funds and are interested in my application， please let me know soon. Thank you！ 不卑不亢。
It is of great honor for me to contact you for the application of a PhD position in your prestigious group.
I am xxx， a master student majored in Materials Engineering at xxx University， which is ranked around 10 in China. I am very interested in working with you so I write this email to you.
I have passed the pre-application of the department， and the coordinator advised me submit a formal application to the department for further assessment. I have indicated in the application that I would like to join in your research group， because firstly my research background matches your research topics very well and secondly I am quite interested in working with you world leading scientists.
I would like to describe my research experience in short. Since I was a third year undergraduate student in 2008， I entered the labs to do research on nano materials. My research experience ranged from synthesis of hollow carbon spheres， synthesis of hollow magnetite spheres for microwave absorption， to the synthesis of hollow hybrid between magnetic materials and semiconductors for photocatalysis as well as synthesis of heterostructured Fe2O3-ZnO nanotubes for gas sensing etc. I think my research background matches the research topics in your group very well， so I want to further my PhD studies with the supervision from you.
Besides， I have some output for the research. I have 8 publications in the international journals， including Journal of Materials Chemistry （one paper， first author ），Materials Letters （two papers， first author）， Journal of Solid State Chemistry （third author）， ACS applied materials and interfaces and so on.
In addition， I have got outstanding academic record for both my undergraduate studies and master studies， ranking top 10% out of 350 students and top 5% out of 120 students， respectively. If you want to know more about me， please see my CV in this email. Thank you very much. And I hope you can spare some time to read my application and CV and then consider my application. I will really appreciate it.
I will be granted the master degree in June， so after that time I will be available for work if you would like to take me as a new student in your group.
I am very keen to work with you and I am looking forward to your reply，