研究目的
To develop and demonstrate a device that combines nanofluidics and cryogenic transmission electron microscopy (cryo-TEM) for inspecting water-soluble samples under near-native conditions, enabling high-resolution imaging with reduced sample-environment interaction and compatibility with rapid freezing for vitreous water formation.
研究成果
The study successfully developed a microfabrication process for nanofluidic devices compatible with cryo-TEM, enabling high-resolution imaging of liquid samples under near-native conditions. The devices feature self-aligned, thin silicon nitride windows and are capable of withstanding plunge freezing to form vitreous water, avoiding crystalline ice formation. Demonstrated with colloidal Au particles, the technology shows promise for applications in life and materials sciences where sample preservation and radiation damage mitigation are critical. Future work should focus on improving window smoothness, reducing charging effects, and extending the platform to other microscopy techniques like soft X-ray imaging.
研究不足
The devices are fragile at cryogenic temperatures due to large silicon nitride membranes, requiring careful handling. Charging effects occur during electron imaging due to non-conductive membranes, which can be partially mitigated by pre-exposure but remain a common issue. Surface roughness of sacrificial layers affects window uniformity, and process variability can lead to non-uniform observation windows and crystallinity in membranes. The thickness of samples may vary due to uncertainties in sacrificial layer deposition. Future optimizations could include using graphene to reduce charging and improve window quality.
1：Experimental Design and Method Selection:
The study involved designing and fabricating nanofluidic devices with electron-transparent silicon nitride windows for cryo-TEM applications. The fabrication process utilized semiconductor and micro-electro-mechanical systems technology, including low-pressure chemical vapor deposition (LPCVD) for silicon nitride layers, plasma-enhanced chemical vapor deposition (PECVD) for sacrificial silicon oxide layers, deep reactive ion etching (DRIE) for membrane release, and electron beam lithography for patterning windows. The methodology aimed to create monolithic devices on a single wafer to avoid alignment issues and enhance thermal stress resistance.
2：Sample Selection and Data Sources:
Samples included 10 nm colloidal Au suspension in distilled water for cryo-TEM imaging tests. Data were acquired through cryo-TEM imaging using an FEI F30 Polara microscope.
3：List of Experimental Equipment and Materials:
Equipment included a Vistec EBPG 5000plusES electron beam writer, SVCS furnace for LPCVD, DRIE reactor, reactive ion etching (RIE) system, scanning electron microscope (SEM), focused ion beam for cross-sectioning, FEI F30 Polara TEM, Gatan K2 Summit direct electron detector, and Quantum energy filter. Materials included silicon wafers, silicon nitride (SiNx), silicon oxide (SiO2), polymethylmethacrylate (PMMA) photoresist, negative resist (e.g., AZ nLOF 2035), buffered HF solution, and ethane-propane mixture for plunge freezing.
4：Experimental Procedures and Operational Workflow:
The fabrication process involved depositing and patterning sacrificial SiO2 and LPCVD SiNx layers on silicon wafers, releasing membranes via DRIE, patterning windows using through-membrane electron beam lithography, etching windows with RIE, coating with thin LPCVD SiNx for ultra-thin windows, etching inlets/outlets, releasing the flow channel by dissolving sacrificial oxide, and plugging release holes with negative resist. For cryo-TEM experiments, chips were loaded with Au suspension, plunge-frozen in ethane-propane, transferred to the TEM, and imaged at cryogenic temperatures with dose-fractionated movies collected and aligned.
5：Data Analysis Methods:
TEM images were digitized using a Gatan K2 Summit detector, and frames were aligned and integrated using MotionCor2 software. Analysis included assessing ice vitrification, sample thickness estimation from electron scattering, and resolution evaluation of imaged particles.
独家科研数据包，助您复现前沿成果，加速创新突破
获取完整内容
