Published: December 20th, 2012
We have developed a self-contained liquid cell, which allows imaging through liquids using a transmission electron microscope. Dynamic processes of nanoparticles in liquids can be revealed in real time with sub-nanometer resolution.
The recent development for in situ transmission electron microscopy, which allows imaging through liquids with high spatial resolution, has attracted significant interests across the research fields of materials science, physics, chemistry and biology. The key enabling technology is a liquid cell. We fabricate liquid cells with thin viewing windows through a sequential microfabrication process, including silicon nitride membrane deposition, photolithographic patterning, wafer etching, cell bonding, etc. A liquid cell with the dimensions of a regular TEM grid can fit in any standard TEM sample holder. About 100 nanoliters reaction solution is loaded into the reservoirs and about 30 picoliters liquid is drawn into the viewing windows by capillary force. Subsequently, the cell is sealed and loaded into a microscope for in situ imaging. Inside the TEM, the electron beam goes through the thin liquid layer sandwiched between two silicon nitride membranes. Dynamic processes of nanoparticles in liquids, such as nucleation and growth of nanocrystals, diffusion and assembly of nanoparticles, etc., have been imaged in real time with sub-nanometer resolution. We have also applied this method to other research areas, e.g., imaging proteins in water. Liquid cell TEM is poised to play a major role in revealing dynamic processes of materials in their working environments. It may also bring high impact in the study of biological processes in their native environment.
The study of chemical reactions in liquids in real time and imaging biological materials in their native environment have been of significant interests across the research fields1-5. Due to the high spatial resolution of transmission electron microscopy (TEM), imaging through liquids using TEM has attracted a lot of attention4,5. However, it has been a great challenge to image liquid samples using TEM, since the conventional microscope is operated in a high vacuum environment. In addition, liquid samples have to be thin enough to allow the electron beam to go through. Williamson et al.6 reported that imaging of electrochemical....
1. Microfabrication of Liquid Cells
By using liquid cell TEM method, we have visualized the solution growth of Pt3Fe nanorods from nanoparticle building blocks. Figure 2 shows sequential images depicting the growth trajectory of a Pt3Fe nanorod in different solution conditions. False coloring process using Photoshop was employed to highlight the nanoparticles.
When the solvent mixture of pentadecane and oleylamine (7:3 vol/vol) was used, three distinct stages of growth can be identified (
All fabrication processes have been done in the clean room, where semiconductor devices are made.
Before the deposition of indium, O2 plasma cleaning of the chips is necessary to eliminate the organic residue on the surface. Thus, a high quality indium spacer can be achieved, which can improve the bonding of top and bottom chips and the yield of leakage free liquid cells.
The silicon nitride viewing windows with ultrathin membrane of about 13 nm thick i.......
Zheng thanks Prof. A. Paul Alivisatos and Dr. Ulrich Dahmen for helpful discussions during the early development of EM liquid cells. She is grateful to the support of DOE Office of Science Early Career Research Program.....
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