Name: studying dynamic processes of nano-sized objects in liquid using scanning transmission electron microscopy
Uploaded: 2017-02-05T14:00:00.000+00:00
Duration: 10 min 29 s
Description: Watch this Scientific Journal Video about Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy at JoVE.com

We thank E. Arzt for his support through INM. The research was in part supported by the Leibniz Competition 2014.

<ol>
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The authors have nothing to disclose.

The described protocol enables STEM of AuNPs in a liquid, including the observation of dynamic processes. The assembly of the holder is an easy-to-learn technique. However, several aspects must be considered when working with the liquid flow TEM holder. For instance, broken edges of the Si microchip or large particles on the O-rings may result in leakage of the liquid cell. On the other hand, large particles (&#62;200 nm; e.g., dust or Si debris) on the SiN membrane may result in an increased thickness of the liquid cell, leading to a low imaging contrast or to a low spatial resolution and may even cause SiN windows to break. Importantly, residues of salt or other chemicals may influence the outcome of the experiments in an undesired way. Therefore, it is crucial that the different steps of sample preparation and holder assembly are carried out carefully and in a clean and dust-free environment.
The thickness of the liquid cell determines the achievable resolution, as well as the contrast of the obtained images17. This thickness can be adjusted via spacers located on one of the two Si microchips. Depending on the dimensions of the sample, different thicknesses of the liquid cell can be realized. For the study of AuNPs, it is possible to use small spacers (200-500 nm), while whole eukaryotic cells need larger spacers of up to 5 &#181;m. The thickness of the liquid cell is further influenced by the bulging of the SiN membrane windows resulting from the pressure difference between the liquid cell and the surrounding vacuum. This effect becomes more pronounced with larger SiN membrane windows. Thus, in order to minimize the thickness of the liquid cell, it is recommended to use small SiN membrane windows. In case it is difficult to find an overlap between two small windows, they can be assembled in a crossed configuration using a different base microchip. Alternative configurations largely prevent bulging and consist of a monolithic microchip18 or membrane windows supported by pillars19, but those exhibit disadvantages regarding sample loading. One of the most challenging aspects of the current technology is the lack of precise control over the liquid thickness. Often, the liquid is much thicker than what is expected from the spacer dimensions used, as was shown here. Several groups used closed liquid chambers4,20,21,22; these systems have some advantages regarding spatial resolution, as the liquid thickness can be reduced by inducing a bubble in the liquid. Alternatively, the SiN windows can be forced to collapse, leading to a thinner liquid layer. Thirdly, the enclosure of other thinner windows exists (e.g., graphene)23, also resulting in much thinner liquids than what is possible with the system described in this protocol. However, it is impossible to flow liquid in those systems.
As for any high&#160;resolution microscopy technique, a number of experimental aspects must be considered. The most important aspect is the interaction of the electron beam with the liquid or the sample. In addition to radiation damage, which limits the achievable spatial resolution for many solid samples24, the liquid samples are also influenced by electron beam-generated radiolysis products15,25. Since these products may influence the experiment, careful data interpretation and experimental design are essential26. The microscope settings should be chosen according to the objectives of a particular study. ADF STEM is more powerful for imaging nanoparticles of a high atomic number (Z) in larger thicknesses of the liquid cell, while TEM gives better contrast on low-Z materials and is typically faster but requires thinner liquid layers3. Instead of using the ADF detector, the Bright Field (BF) detector is sometimes used to image the liquid cell, since BF STEM is advantageous for imaging low-Z materials in thick layers27. With increasing thickness of the liquid cell, more current is needed. However, this also increases the concentrations of radiolysis products and increases radiation damage. It should also be noted that an inversion of contrast is observed in the ADF detector for very thick liquids (&#62;10 &#181;m for water).
The liquid conditions were changed between our experiments by removing the holder from the microscope and exchanging both the sample and the liquid. In addition to changing the salt concentration, it is readily possible to change other properties of the liquid by flowing in different liquids (e.g., one may use buffer solutions in order to set a specific pH16 or may introduce organic solutions or other additives). It is also possible to change the liquid while the holder is still inserted in the microscope by flowing liquids through the microfluidic system. However, in this case, it is unknown at which time point the liquid at the sample changes. It is also noteworthy that microchips supporting electrodes are available, so nanoscale electrochemistry experiments can be carried out28.
The objects of study are not limited to AuNPs in water, but a wide variety of specimens can be studied using the protocol described above, including silica, titanium oxide, and polymers. If movements of the objects are too fast to capture in an image within the acquisition, the viscosity can be reduced by an order of magnitude by using a mixture of 50% glycerol and 50% water.
From the aforementioned points, a number of advantages, possibilities, and also disadvantages become apparent. When working with liquid-phase STEM, the most important disadvantages to consider are that: 1) any experiment is influenced by the dynamic interaction of the electron beam with the entire specimen (the object under observation, the liquid, and the SiN membranes); 2) sample handling is tedious, and it is often difficult to achieve a thin liquid layer because the sample or the microchips contain some micrometer-sized particles; 3) the liquid thickness usually differs largely from the intended thickness set by the spacer; and 4) spatial resolution and contrast strongly depend upon the liquid thickness and the difference between the change density of the object under observation and the liquid.
Presently, ample methods exist for the microscopy of objects in liquid with nanometer spatial resolution. Electron microscopy in amorphous ice is a powerful technique29, but the involved experimental procedures are delicate, not all experiments allow the preparation of the sample in ice, and time-resolved experiments are impossible. X-ray microscopy30,31 could in principle be used, but it has a limited spatial resolution and is not widely available in laboratories. Atomic force microscopy in liquid has been established but is a surface technique only32,33,34,35. Light microscopy does not exhibit sufficient spatial resolution. At the present, electron microscopy in liquid seems the most powerful technique for direct microscopy of nanoscale objects and processes in liquid.
Liquid-phase TEM and STEM are not yet routine analytical techniques but are still developing. The number of parameters to take into account is considerable, and it is often difficult to reproduce experimental results. Moreover, quantitative data is difficult to obtain because the effects under investigation are intertwined with processes occurring as a result of the electron beam. The protocol described here aims to standardize the experimental protocol, thereby accounting for all relevant base aspects of the experiment. We hope that this protocol will lead to better reproducibility of experimental work in this emerging field.

Conventional Scanning Transmission Electron Microscopy (STEM) is limited by the range of specimens appropriate for analysis, specifically the dry and solid samples suitable for placement in a high vacuum. However, many scientific and technological questions concern nanoscale materials and processes in liquid environment. Samples fully embedded in liquid can now be studied with STEM using a concept that involves a microfluidic chamber assembled in the specimen holder for Transmission Electron Microscopy (TEM) and STEM1. This newly developed technique has become increasingly popular, as it provides new insight into important processes of various research topics, including the growth, dissolution, and aggregation processes of nanoparticles2,3,4,5,6. Not only metals, but also biominerals7 and biological systems can be studied8,9,10,11. The sample loading and image acquisition for liquid-phase STEM is different than for STEM of dry samples and involve a protocol that requires dedicated training.
The microfluidic system consists of two silicon microchips supporting Silicon Nitride (SiN) membrane windows transparent for the electron beam at 200 keV of energy12 (see Figure 1A). Details of the dimensions and of the handling of these microchips can be found elsewhere12,13. The sample usually contains nanoscale objects. In this paper we observed gold nanoparticles (AuNPs).&#160;The AuNPs are immobilized at the top window (with respect to a downward-traveling electron beam) or float in the liquid. Nanoscale spatial resolution in STEM is obtained by scanning the electron beam over the AuNPs and collecting transmitted scattered electrons using the Annular Dark Field (ADF) detector9. The two microchips are placed in a small slot in the tip of the liquid flow TEM holder1 (the holder operates for both STEM and TEM but is referred to as the TEM holder). One of the microchips contains a spacer so that a liquid compartment is formed between the microchips. O-rings on both sides of the two microchips provide vacuum sealing of the liquid compartment13 (see Figure 1B).
The aim of this article is to demonstrate the basic steps of sample loading and data acquisition so that interested users may find easy access to this emerging new technique. A system available from a specific company is used, but the protocol is also valid for systems of other companies. The technique is more complex than conventional TEM and STEM, and a number of practical aspects must be considered when working with a liquid holder system13. Most important of all is to ensure that the liquid compartment is correctly assembled, thus providing a thin liquid layer and a vacuum seal. Therefore, it is highly important to work cleanly and to prevent the formation of dust during the preparation and assembly of the liquid flow TEM holder. In particular, the O-rings and the two silicon microchips need to be free from all contamination. Even small particles of dust on one of the microchips may severely increase the thickness of the assembled cell, which may prevent the achievement of a useful spatial resolution. A vacuum seal is important so that no contamination or damage will be left in the electron microscope after the experiment. This protocol describes the loading procedure and several necessary tests. The operation of the electron microscope is straightforward, but it requires some extra steps compared to microscopy of solid samples. With increasing liquid thicknesses, more electrons are absorbed and scattered by the liquid; a measurement of the liquid thickness is essential. Finally, the protocol explains how images are taken and how dynamic processes can be studied.
<img alt="Figure 1" src="/files/ftp_upload/54943/54943fig1.jpg" /> 
Figure 1: Liquid Flow Cell for Scanning Transmission Electron Microscopy (STEM). (A)Schematic illustration of the assembled liquid cell. Two silicon microchips with Silicon Nitride (SiN) membrane windows are positioned between two O-rings. The liquid is enclosed between the SiN membrane and is thus separated from the vacuum in the electron microscope. A focused electron beam scans over the sample. Contrast is obtained from scattered electrons. Gold nanoparticles (AuNPs) are immobilized within the liquid at the SiN membrane but can also move in the liquid. (B)Schematic side view cross section of the stack of two microchips with O-rings. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54943/54943fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table><tbody><tr><td>Binocular light microscope</td><td>Leica</td><td>M60 CMO</td><td></td></tr><tr><td>Scanning transmission electron mircoscope with spherical aberration corrector</td><td>JEOL</td><td>ARM200F</td><td></td></tr><tr><td>Liquid flow TEM specimen holder</td><td>DENS Solutions</td><td>Ocean</td><td></td></tr><tr><td>Microfluidic syringe pump</td><td>Harvard Scientific</td><td>PicoPlus</td><td></td></tr><tr><td>Plasma cleaner</td><td>Gatan</td><td>Solarus950</td><td></td></tr><tr><td>&lt;strong&gt;Chemicals&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Acetone, Rotisolv&amp;nbsp; Plus for HPLC</td><td>Sigma-Aldrich</td><td>7328.2</td><td></td></tr><tr><td>Water, chromasolv Plus for HPLC</td><td>Sigma-Aldrich</td><td>34877-2.5L</td><td></td></tr><tr><td>Ethanol, Rotisolv HPLC grade</td><td>Carl Roth</td><td>P076.2</td><td></td></tr><tr><td>Gold colloid citrate stabilized, diameter 30 nm</td><td>British-Biocell</td><td>EM.GC20</td><td></td></tr><tr><td>&lt;strong&gt;Materials&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Base silicon microchips with silicon nitride membranes of 50 nm thickness and dimensions of 20 &amp;micro;m x 0.40 mm</td><td>DENS Solutions</td><td>for Ocean system</td><td></td></tr><tr><td>Spacer silicon microchips with silicon nitride membranes of 50 nm thickness, dimensions of 20 &amp;micro;m x 0.40 mm, and spacer thickness of 200 nm</td><td>DENS Solutions</td><td>for Ocean system</td><td></td></tr><tr><td>Microfluidic peek tubing</td><td>Upchurch Scientific</td><td>1570</td><td></td></tr><tr><td>Plastic Replaceable tips Tweezers</td><td></td><td></td><td></td></tr><tr><td>(Anti-Magnetic Anti-Acid Stainless Steel body with ESD PVDF (SV) tips)</td><td>ideal-tek</td><td>2ASVR.SA</td><td></td></tr><tr><td>Teflon coated bent steel tweezers (EMS SA with &quot;PTFE&quot; Coating)</td><td>Electron Microscopy Sciences</td><td>78322-7Te</td><td></td></tr><tr><td>Teflon coated broad beak steel tweezers (EMS 2A &quot;PTFE&quot; Coating)</td><td>Electron Microscopy Sciences</td><td>78322-2ATe</td><td></td></tr><tr><td>Hamilton syringe, 1 mL, gastight (Model 1001 TLLX SYR)</td><td>Hamilton</td><td>81323</td><td></td></tr><tr><td>Clean room tissue Sontara Micropure AP (224 x 224mm)</td><td>DuPont</td><td>Sontara MicroPure</td><td></td></tr></tbody></table>

studying dynamic processes of nano-sized objects in liquid using scanning transmission electron microscopy

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a microfluidic chamber assembled in the specimen holder for Transmission Electron Microscopy (TEM) and STEM. The microfluidic system consists of two silicon microchips supporting thin Silicon Nitride (SiN) membrane windows. This article describes the basic steps of sample loading and data acquisition. Most important of all is to ensure that the liquid compartment is correctly assembled, thus providing a thin liquid layer and a vacuum seal. This protocol also includes a number of tests necessary to perform during sample loading in order to ensure correct assembly. Once the sample is loaded in the electron microscope, the liquid thickness needs to be measured. Incorrect assembly may result in a too-thick liquid, while a too-thin liquid may indicate the absence of liquid, such as when a bubble is formed. Finally, the protocol explains how images are taken and how dynamic processes can be studied. A sample containing AuNPs is imaged both in pure water and in saline.

The liquid flow TEM holder was used to study the behavior of AuNPs in liquid. AuNPs were stably immobilized on the SiN membrane in pure water and were imaged with nanoscale resolution using liquid-phase STEM (Figure 6). Excellent contrast was obtained on the strongly-scattering gold. The current density on the phosphor screen measured for a dry test sample was 20 pA/cm&#178;, while it amounted to 8 pA/cm&#178; with the liquid flow TEM holder inserted. Using Equation 1, twater = 2.4 &#177;0.5 &#181;m, much larger than what was expected based on the spacer thickness of 200 nm. Nevertheless, the thickness is not too large for the imaging of the AuNPs with nanometer spatial resolution. The liquid thickness was thicker than the 200 nm set by the spacer due to bulging of the SiN membranes, non-flatness of the microchips, and debris residing on the microchips.
For pure water, the AuNPs maintain their shape during imaging16, although reactive radiolysis products (e-aq, H&#8226;, H+, OH&#8226;) originating from the interaction of the electron beam with water may oxidize single gold atoms, leading to a change of shape of the AuNPs15. However, when the liquid flow system was used to introduce chloride ions in a second experiment, the stability of the AuNPs changed. Chloride ions are capable of stabilizing oxidized gold atoms in the form of tetrachloroaureat, AuCl4-. Figure 7 shows that the AuNPs slowly dissolved during a STEM imaging time-lapse series, similar to results reported earlier16. For the used electron dose rate, it took ~300 s to dissolve the 30 nm-sized AuNPs.
The movements of AuNPs in water were studied in a third experiment (Figure 8). Prior to the experiment, the liquid flow TEM holder was cleaned in order to remove any traces of salt. Differing from the first experiment, an alternative sample preparation approach was used to achieve a weaker attachment of the AuNPs to the SiN membrane14. In this experiment, the AuNP solution was placed on the silicon microchip and assembled in the liquid flow TEM holder without letting the solution dry out. In this way, the AuNPs easily detached from the SiN membrane upon imaging at the dose rate used. Some of the AuNPs moved away from the field of view into the bulk solutions, while the remaining AuNPs remained within the field of view in close proximity to the SiN window. Movements of these AuNPs were observed, and eventually they agglomerated. After a while, these agglomerates also detached from the SiN membrane and moved out of the field of view and into the solution.
<img alt="Figure 6" src="/files/ftp_upload/54943/54943fig6.jpg" /> 
Figure 6: Scanning Transmission Electron Microscopy (STEM) Micrograph of AuNPs 30 nm in Diameter at the Top of a Pure Water Layer. The image shown is a selected area of the original image. The image size was 1,024 x 1,024 pixels, the pixel dwell time was 19 &#181;s, the pixel size was 0.73 nm, and the magnification was 400,000X. The electron dose was thus 7.1 x 104 e-/nm&#178;. The current density measured on the phosphor screen was 8 pA/cm2, so the liquid thickness was calculated to amount to 2.4 &#181;m. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54943/54943fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" src="/files/ftp_upload/54943/54943fig7.jpg" /> 
Figure 7: Time-lapse Series of STEM Micrographs of AuNPs in Saline. (A-D) Images extracted from the time-lapse series of STEM images at 30&#160;s intervals. The AuNPs gradually dissolve in liquid as a consequence of the presence of chloride ions. The pixel dwell time was 2 &#181;s, the frame time of the time lapse series was 1.75 s, the pixel size was 0.44 nm, and the magnification was 500,000X. The electron dose per image was 1.2 x 104 e-/nm&#178;. The liquid thickness was 2.4 &#181;m. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54943/54943fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" src="/files/ftp_upload/54943/54943fig8.jpg" /> 
Figure 8: STEM Micrograph of AuNPs Moving in Pure Water. (A) SiN membrane with AuNPs, of which several are selected with arrows. (B) Motion tracks of the selected AuNPs (see A). Some AuNPs move away from the field of view during the time of imaging. The remaining AuNPs move laterally along the SiN membrane and start agglomerating. Upon reaching a critical cluster size, they dispatch from the membrane and move away from the field of view.The pixel dwell time was 1 &#181;s, the frame time was 0.52 s, the pixel size was 1.8 nm, and the magnification was 120,000X. The electron dose per image was 3.5 x 102 e-/nm&#178; and the liquid thickness was 2.4 &#181;m. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54943/54943fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy

This protocol describes the operation of a liquid flow specimen holder for scanning transmission electron microscopy of AuNPs in water, as used for the observation of nanoscale dynamic processes.

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a ...

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Nanyang Technological University

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JoVE Journal

Engineering

12.6K Views.  INM-Leibniz Institute for New Materials. This protocol describes the operation of a liquid flow specimen holder for scanning transmission electron microscopy of AuNPs in water, as used for the observation of nanoscale dynamic processes.

Video: Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy

Revealing Dynamic Processes of Materials in Liquids Using Liquid Cell Transmission Electron Microscopy

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.

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 ...

Quantitative and Qualitative Examination of Particle-particle Interactions Using Colloidal Probe Nanoscopy

Colloidal Probe Nanoscopy (CPN), the study of the nano-scale interactive forces between a specifically prepared colloidal probe and any chosen substrate using the Atomic Force Microscope (AFM), can provide key insights into physical interactions present within colloidal systems. Colloidal systems are widely existent in several applications including, pharmaceuticals, foods, paints, paper, soil and minerals, detergents, printing and much more.1-3 Furthermore, colloids can exist in many states such as emulsions, foams and suspensions. Using colloidal probe nanoscopy one can obtain key information on the adhesive properties, binding energies and even gain insight into the physical stability and coagulation kinetics of the colloids present within. Additionally, colloidal probe nanoscopy can be used with biological cells to aid in drug discovery and formulation development. In this paper we describe a method for conducting colloidal probe nanoscopy, discuss key factors that are important to consider during the measurement, and show that both quantitative and qualitative data that can be obtained from such measurements.

Colloidal probe nanoscopy can be used within a variety of fields to gain insight into the physical stability and coagulation kinetics of colloidal systems and aid in drug discovery and formulation sciences using biological systems. The method described within provides a quantitative and qualitative means to study such systems.

Colloidal Probe Nanoscopy (CPN), the study of the nano-scale interactive forces between a specifically prepared colloidal probe and any chosen substrate ...

Chemistry

In situ TEM of Biological Assemblies in Liquid

Researchers regularly use Transmission Electron Microscopes (TEMs) to examine biological entities and to assess new materials. Here, we describe an additional application for these instruments- viewing viral assemblies in a liquid environment. This exciting and novel method of visualizing biological structures utilizes a recently developed microfluidic-based specimen holder. Our video article demonstrates how to assemble and use a microfluidic holder to image liquid specimens within a TEM. In particular, we use simian rotavirus double-layered particles (DLPs) as our model system. We also describe steps to coat the surface of the liquid chamber with affinity biofilms that tether DLPs to the viewing window. This permits us to image assemblies in a manner that is suitable for 3D structure determination. Thus, we present a first glimpse of subviral particles in a native liquid environment.

In situ TEM of Biological Assemblies in Liquid

Here we describe a procedure to image viral complexes in liquid at nanometer resolution using a transmission electron microscope.

Researchers regularly use Transmission Electron Microscopes (TEMs) to examine biological entities and to assess new materials. Here, we describe an ...

Bioengineering

Sub-nanometer Resolution Imaging with Amplitude-modulation Atomic Force Microscopy in Liquid

Atomic force microscopy (AFM) has become a well-established technique for nanoscale imaging of samples in air and in liquid. Recent studies have shown that when operated in amplitude-modulation (tapping) mode, atomic or molecular-level resolution images can be achieved over a wide range of soft and hard samples in liquid. In these situations, small oscillation amplitudes (SAM-AFM) enhance the resolution by exploiting the solvated liquid at the surface of the sample. Although the technique has been successfully applied across fields as diverse as materials science, biology and biophysics and surface chemistry, obtaining high-resolution images in liquid can still remain challenging for novice users. This is partly due to the large number of variables to control and optimize such as the choice of cantilever, the sample preparation, and the correct manipulation of the imaging parameters. Here, we present a protocol for achieving high-resolution images of hard and soft samples in fluid using SAM-AFM on a commercial instrument. Our goal is to provide a step-by-step practical guide to achieving high-resolution images, including the cleaning and preparation of the apparatus and the sample, the choice of cantilever and optimization of the imaging parameters. For each step, we explain the scientific rationale behind our choices to facilitate the adaptation of the methodology to every user's specific system.

We present a method for achieving sub-nanometer resolution images with amplitude-modulation (tapping mode) atomic force microscopy in liquid. The method is demonstrated on commercial atomic force microscopes. We explain the rationale behind our choices of parameters and suggest strategies for resolution optimization.

Atomic force microscopy (AFM) has become a well-established technique for nanoscale imaging of samples in air and in liquid. Recent studies have shown ...

Liquid-cell Transmission Electron Microscopy for Tracking Self-assembly of Nanoparticles

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully understood. We have traced the trajectories of individual nanoparticles using liquid-cell transmission electron microscopy (TEM) to investigate the mechanism of the assembly process. Herein, we present the protocols used for liquid-cell TEM studies of the self-assembly mechanism. First, we introduce the detailed synthetic protocols used to produce uniformly sized platinum and lead selenide nanoparticles. Next, we present the microfabrication processes used to produce liquid cells with silicon nitride or silicon windows and then describe the loading and imaging procedures of the liquid-cell TEM technique. Several notes are included to provide helpful tips for the entire process, including how to manage the fragile cell windows. The individual motions of nanoparticles tracked by liquid-cell TEM revealed that changes in the solvent boundaries caused by evaporation affected the self-assembly process of nanoparticles. The solvent boundaries drove nanoparticles to primarily form amorphous aggregates, followed by flattening of the aggregates to produce a 2-dimensional (2D) self-assembled structure. These behaviors are also observed for different nanoparticle types and different liquid-cell compositions.

Here we introduce experimental protocols for the real-time observation of a self-assembly process using liquid-cell transmission electron microscopy.

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully ...

All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics

The miniaturization of semiconductor devices to scales where small numbers of dopants can control device properties requires the development of new techniques capable of characterizing their dynamics. Investigating single dopants requires sub-nanometer spatial resolution, which motivates the use of scanning tunneling microscopy (STM). However, conventional STM is limited to millisecond temporal resolution. Several methods have been developed to overcome this shortcoming, including all-electronic time-resolved STM, which is used in this study to examine dopant dynamics in silicon with nanosecond resolution. The methods presented here are widely accessible and allow for local measurement of a wide variety of dynamics at the atomic scale. A novel time-resolved scanning tunneling spectroscopy technique is presented and used to efficiently search for dynamics.

We demonstrate an all-electronic method to observe nanosecond-resolved charge dynamics of dopant atoms in silicon with a scanning tunneling microscope.

The miniaturization of semiconductor devices to scales where small numbers of dopants can control device properties requires the development of new ...

Using Graphene Liquid Cell Transmission Electron Microscopy to Study in Situ Nanocrystal Etching

Graphene liquid cell electron microscopy provides the ability to observe nanoscale chemical transformations and dynamics as the reactions are occurring in liquid environments. This manuscript describes the process for making graphene liquid cells through the example of graphene liquid cell transmission electron microscopy (TEM) experiments of gold nanocrystal etching. The protocol for making graphene liquid cells involves coating gold, holey-carbon TEM grids with chemical vapor deposition graphene and then using those graphene-coated grids to encapsulate liquid between two graphene surfaces. These pockets of liquid, with the nanomaterial of interest, are imaged in the electron microscope to see the dynamics of the nanoscale process, in this case the oxidative etching of gold nanorods. By controlling the electron beam dose rate, which modulates the etching species in the liquid cell, the underlying mechanisms of how atoms are removed from nanocrystals to form different facets and shapes can be better understood. Graphene liquid cell TEM has the advantages of high spatial resolution, compatibility with traditional TEM holders, and low start-up costs for research groups. Current limitations include delicate sample preparation, lack of flow capability, and reliance on electron beam-generated radiolysis products to induce reactions. With further development and control, graphene liquid cell may become a ubiquitous technique in nanomaterials and biology, and is already being used to study mechanisms governing growth, etching, and self-assembly processes of nanomaterials in liquid on the single particle level.

Using Graphene Liquid Cell Transmission Electron Microscopy to Study in Situ Nanocrystal Etching

Graphene liquid cell electron microscopy can be used to observe nanocrystal dynamics in a liquid environment with greater spatial resolution than other liquid cell electron microscopy techniques. Etching premade nanocrystals and following their shape using graphene liquid cell Transmission Electron Microscopy can yield important mechanistic information about nanoparticle transformations.

Graphene liquid cell electron microscopy provides the ability to observe nanoscale chemical transformations and dynamics as the reactions are occurring in ...

Nanoscale Characterization of Liquid-Solid Interfaces by Coupling Cryo-Focused Ion Beam Milling with Scanning Electron Microscopy and Spectroscopy

Physical and chemical processes at solid-liquid interfaces play a crucial role in many natural and technological phenomena, including catalysis, solar energy and fuel generation, and electrochemical energy storage. Nanoscale characterization of such interfaces has recently been achieved using cryogenic electron microscopy, thereby providing a new path to advancing our fundamental understanding of interface processes.
This contribution provides a practical guide to mapping the structure and chemistry of solid-liquid interfaces in materials and devices using an integrated cryogenic electron microscopy approach. In this approach, we pair cryogenic sample preparation which allows stabilization of solid-liquid interfaces with cryogenic focused ion beam (cryo-FIB) milling to create cross-sections through these complex buried structures. Cryogenic scanning electron microscopy (cryo-SEM) techniques performed in a dual-beam FIB/SEM enable direct imaging as well as chemical mapping at the nanoscale. We discuss practical challenges, strategies to overcome them, as well as protocols for obtaining optimal results. While we focus in our discussion on interfaces in energy storage devices, the methods outlined are broadly applicable to a range of fields where solid-liquid interface play a key role.

Cryogenic Focused Ion Beam (FIB) and Scanning Electron Microscopy (SEM) techniques can provide key insights into the chemistry and morphology of intact solid-liquid interfaces. Methods for preparing high quality Energy Dispersive X-ray (EDX) spectroscopic maps of such interfaces are detailed, with a focus on energy storage devices.

Physical and chemical processes at solid-liquid interfaces play a crucial role in many natural and technological phenomena, including catalysis, solar ...

Studying the Effects of Temperature on the Nucleation and Growth of Nanoparticles by Liquid-Cell Transmission Electron Microscopy

Temperature control is a recent development that provides an additional degree of freedom to study nanochemistry by liquid cell transmission electron microscopy. In this paper, we describe how to prepare an in situ heating experiment for studying the effect of temperature on the formation of gold nanoparticles driven by radiolysis in water. The protocol of the experiment is fairly simple involving a special liquid cell with uniform heating capabilities up to 100 &#176;C, a liquid-cell TEM holder with flow capabilities and an integrated interface for controlling the temperature. We show that the nucleation and growth mechanisms of gold nanoparticles are drastically impacted by the temperature in liquid cell. Using STEM imaging and nanodiffraction, the evolution of the density, size, shape and atomic structure of the growing nanoparticles are revealed in real time. Automated image processing algorithms are exploited to extract useful quantitative data from video sequences, such as the nucleation and growth rates of nanoparticles. This approach provides new inputs for understanding the complex physico-chemical processes at play during the liquid-phase synthesis of nanomaterials.

Temperature control during liquid-phase electron microscopy experiments opens up new perspectives of studying the dynamic of nanoparticles in liquid environments mimicking their formation or application media. Using recently developed heating liquid cells, we directly observed the influence of temperature on the nucleation and growth processes of gold nanoparticles in water.

Temperature control is a recent development that provides an additional degree of freedom to study nanochemistry by liquid cell transmission electron ...

Light-Induced In Situ Transmission Electron Microscopy for Observation of the Liquid-Soft Matter Interaction

The current protocol describes the modifications of the transmission electron microscope (TEM) setup for in situ light-induced observations. A glass optical fiber inserted into the electron column above the objective lens polepiece, and a laser, an adjustable light source, was used to fabricate the device. After the illuminator has been calibrated using an external measuring system, it allows one to adjust the intensity of the lighting to the needs of the observed process. This lighting system was utilized to image antimicrobial photodynamic therapy phenomena, which are currently the subject of intense research. The sample was prepared by spotting a suspension of bacteria on a carbon, graphene, or silicon nitride substrate, blotting the excess solution, spotting the photosensitizer solution, blotting the excess liquid again, and then assembling the liquid cell with a second substrate or graphene film. The process of the imaging experiment itself includes choosing the right place for observation with the use of low magnification and a minimum dose of electrons, and then cyclical activation of the light source to capture subsequent images at specified intervals with the minimum amount of electrons necessary. The electron dose of each exposure and the time and intensity of lighting used need to be carefully recorded due to the complexity of the observed phenomena as, at the same time, the process is both light- and electron-driven. After the actual experiment is performed, additional control observations must be made, in which the same doses of electrons are used but without additional light influence and smaller doses of electrons are used for higher doses of light. This makes it possible to distinguish light-induced microstructural effects from those caused by electrons in both the fields of life and materials science.

Light-Induced In Situ Transmission Electron Microscopy for Observation of the Liquid-Soft Matter Interaction

The present protocol describes transmission electron microscope (TEM) modifications with a light illumination system, the fabrication of liquid cells, and in situ TEM observations of light-induced interactions between bacterial cells and a photosensitizer. The sample preparation methods, electron beam damage, and imaging are also discussed.

The current protocol describes the modifications of the transmission electron microscope (TEM) setup for in situ light-induced observations. A glass ...

Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy

Summary

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Chapters in this video

Revealing Dynamic Processes of Materials in Liquids Using Liquid Cell Transmission Electron Microscopy

Quantitative and Qualitative Examination of Particle-particle Interactions Using Colloidal Probe Nanoscopy

In situ TEM of Biological Assemblies in Liquid

Sub-nanometer Resolution Imaging with Amplitude-modulation Atomic Force Microscopy in Liquid

Liquid-cell Transmission Electron Microscopy for Tracking Self-assembly of Nanoparticles

All-electronic Nanosecond-resolved Scanning Tunneling Microscopy: Facilitating the Investigation of Single Dopant Charge Dynamics

Using Graphene Liquid Cell Transmission Electron Microscopy to Study in Situ Nanocrystal Etching

Nanoscale Characterization of Liquid-Solid Interfaces by Coupling Cryo-Focused Ion Beam Milling with Scanning Electron Microscopy and Spectroscopy

Studying the Effects of Temperature on the Nucleation and Growth of Nanoparticles by Liquid-Cell Transmission Electron Microscopy

Light-Induced In Situ Transmission Electron Microscopy for Observation of the Liquid-Soft Matter Interaction