---
title: In Situ Liquid Phase TEM
url: https://www.emergentmind.com/topics/in-situ-liquid-phase-transmission-electron-microscopy
type: topic
---

# In Situ Liquid Phase TEM

In situ liquid phase transmission electron microscopy (LP-TEM) is a suite of methodologies enabling real-time, nanometer-to-atomic scale imaging and spectroscopy of dynamic processes occurring in liquids. By confining a thin layer of liquid within the electron-beam path—using either hermetically sealed microfluidic cells, windowless open-cell geometries in environmental TEM (ETEM), or, in some cases, native sample wetting—LP-TEM overcomes the vacuum incompatibility of liquids in conventional TEM. This facilitates operando investigations of phenomena such as colloidal self-assembly, nanocrystal growth, phase transitions, electrochemical reactions, and interfacial dynamics, under precisely controlled chemical and physical stimuli.

## 1. Architectures and Instrumentation for In Situ Liquid Phase TEM

Three principal approaches to LP-TEM have emerged:

- **Closed-Cell Liquid Flow Holders:** The canonical platform consists of two electron-transparent windows (Si₃N₄, graphene) separated by spacers defining a narrow liquid gap (typically 50–800 nm) [1010.3286, 1212.1501]. The cell is hermetically sealed (polymer, epoxy, o-rings) and integrates fluidic ports for solution exchange, as well as optional electrodes.
- **Open-Cell Environmental TEM (ETEM):** In open-cell ETEM, a standard TEM grid is exposed to a controlled water-vapor atmosphere. Hygroscopic salt particles (e.g., NaCl) nucleate and sustain stable liquid droplets on the grid, provided temperature and partial pressure of water vapor are tightly regulated (T = 1–10 °C, pH₂O ≤ 18 Torr) [2308.09832]. No confining windows are used, offering unrestricted geometry.
- **2D Heterostructure Liquid Cells:** Recent advances utilize stacks of 2D materials (graphene, hBN) to form ultrathin liquid enclosures (~70 nm total, including a monolayer MoS₂) with high mechanical stability and minimal scattering [2203.04906]. This enables true atomic resolution.

Auxiliary functions—such as in situ electrical biasing (three-electrode configuration for electrochemistry [1311.6490]), on-chip microheating/cooling [2101.02935], or integrated illumination for photochemical studies—are implemented through MEMS structures or custom holder designs.

Key setup attributes:

| Parameter             | Closed-cell           | Open-cell ETEM         | 2D heterostructure    |
|-----------------------|----------------------|------------------------|----------------------|
| Window material       | Si₃N₄, graphene      | None                   | Graphene, hBN        |
| Liquid thickness      | 50–800 nm            | 1–6 μm droplets        | ~70 nm               |
| Pressure control      | <atm (sealed)        | pH₂O ≲ 18 Torr         | Hermetic (ambient)   |
| Sample load           | Wet or dry           | Dry (hydrated in situ) | Dry stack            |

## 2. Imaging Modalities and Experimental Protocols

LP-TEM is compatible with both conventional TEM and scanning TEM (STEM) modes. Bright-field, dark-field, and high-angle annular dark-field (HAADF) detectors are routinely used. Energy-dispersive X-ray spectroscopy (EDS) and, crucially, electron energy loss spectroscopy (EELS) provide complementary chemical sensitivity [1212.1501, 1311.6490].

- **Spatial resolution:** Closed-cell geometries (liquid thickness ≲ 500 nm) routinely achieve ≲ 1 nm resolution in STEM [1010.3286], with true atomic resolution (~0.1–0.2 nm) attainable in ultrathin 2D heterostructure cells [2203.04906]. Open-cell ETEM achieves ≲ 1 nm in the best-case regions but is limited by thicker pathlengths [2308.09832].
- **Temporal resolution:** Frame rates ~0.5–2 Hz are typical for video capture (limited by readout and SNR), with sub-0.5 s/frame routine for dynamic events [1110.3273].
- **Beam dose management:** Dose rates are minimized to suppress radiolysis, typically ≲10³–10⁴ e⁻ nm⁻² s⁻¹, using low accelerating voltages (20–300 kV) and short dwell times. For sensitive soft matter, lower dose rates (∼0.25–2.7 e⁻ nm⁻² s⁻¹) are favored [2512.23588].

**Example closed-cell protocol:** Assemble liquid cell, fill with aqueous nanoparticle suspension, seal; mount in TEM, evacuate; apply desired electrical or thermal stimuli, capture images or spectra over time.

**Open-cell protocol:** Deposit salt and specimen dry on standard grid, mount in cooled holder, insert into ETEM, raise water-vapor pressure to induce droplet formation, then image [2308.09832].

## 3. Quantitative Capabilities and Chemical Mapping

LP-TEM allows the extraction of quantitative kinetic, structural, and chemical information from dynamic, solvated systems:

- **Particle dynamics:** Brownian motion, aggregation rates, and trajectory statistics are captured at nanometer resolution. Mean-squared displacement (MSD) analysis yields diffusion coefficients (e.g., for Pt adatoms on MoS₂: D_liquid ≳ 0.25 nm²·s⁻¹ [2203.04906]).
- **Colloidal self-assembly:** In situ visualization of diffusion-limited aggregation (DLA), with real-time fractal dimension analysis matching bulk scattering data [1010.3286].
- **Electrochemical processes:** LP-TEM liquid-flow holders with integrated electrodes enable operando monitoring of ion transfer in batteries. Valence EELS fingerprinting discriminates lithiated/delithiated phases (E_PEAK ≈ 5 eV for FePO₄; E_PEAK ≈ 6.2 eV for solvated LiSO₄) and maps spatial concentration of charge carriers [1311.6490].
- **Phase transitions in soft matter:** Beam-induced and thermally driven mesophase transitions in nanoconfined liquid crystals can be temporally resolved and linked quantitatively to thermal modeling (ΔT ≈ 8–15 K in 30–40 s at D ≈ 1 e⁻ nm⁻² s⁻¹ for 8CB LC) [2512.23588].

### EELS in Liquids

- **Thickness measurement:** Log-ratio method $t = \lambda \ln(I_t/I_0)$ relates the inelastic mean free path (λ) to zero-loss and total counts.
- **Optical gap and plasmon peaks:** Valence-loss (< 50 eV) spectra remain interpretable up to t/λ ≈ 7.
- **Chemical mapping:** For LiFePO₄: EFTEM at 5 eV images FePO₄ domains, at 6.2 eV images solvated Li⁺ [1311.6490].

## 4. Beam–Sample Interactions and Artifacts

Beam–liquid interactions are central to LP-TEM experimental design:

- **Radiolysis:** Electron impact on water generates hydrated electrons, H·, ·OH, leading to byproducts (H₂, H₂O₂) and bubble formation. Bubble nucleation rate $J \sim \exp(-\Delta G^*/k_BT)$ depends on H₂ supersaturation [1210.3380].
- **Thermal effects:** For soft matter (e.g., liquid crystals), beam heating, not radiolysis, typically dominates phase transition kinetics; the temperature rise is quantitatively modeled by $\frac{\partial T}{\partial t} = \alpha \frac{\partial^2 T}{\partial x^2} + Q(x,t)/(\rho C_p)$ [2512.23588].
- **Spatial artifacts:** Closed cell windows (Si₃N₄, graphene) can bulge, affecting sample thickness and resolution [1212.1501]. Open cell avoids window-induced artifacts.
- **Dose mitigation:** Pulsed/blanked beam, radical scavengers, and ultrathin liquid layers (< 200 nm) suppress bubble nucleation and minimize artifacts [1210.3380].

## 5. Applications and Case Studies

LP-TEM offers access to a wide spectrum of dynamic in-liquid phenomena across diverse domains:

- **Colloid and nanomaterial physics:** Real-time imaging of gold particle aggregation and nanorod capillarity-induced alignment [1010.3286, 1110.3273].
- **Battery science:** Nanoscale mapping of lithiation/delithiation and ion distributions in operando electrode/electrolyte systems [1311.6490].
- **Catalysis:** Single-atom dynamics on 2D supports in liquid environments, providing direct evidence for solvation-modified diffusion and binding [2203.04906].
- **Materials phase transitions:** Observation of melting/solidification and spheroidization in alloy systems using MEMS-based heating [2101.02935]. Dynamic beam-induced phase transitions and defect dynamics within nanoconfined liquid crystals [2512.23588].
- **Biological and soft matter systems:** Studies of protein aggregation, gelation, and membrane interactions at nanometer resolution under true solution conditions (prospective).

## 6. Comparative Analysis of LP-TEM Geometries

| Attribute           | Open-Cell ETEM [2308.09832] | Closed-Cell [1010.3286,1212.1501] | 2D Heterostructure [2203.04906]        |
|---------------------|-----------------------------|------------------------------------|----------------------------------------|
| Sample loading      | Dry, standard grid          | Wet or dry, device assembly        | 2D transfer, dry stack                 |
| Liquid thickness    | μm-scale (droplets)         | 100–800 nm (fixed)                 | ~70 nm (total, incl. windows)          |
| Imaging artifacts   | No windows                  | Window bulging, finite t           | Minimal, atomic-scale                  |
| Spatial freedom     | Unconstrained               | Fixed cell geometry                | 2D/planar confinement                  |
| Max resolution      | ≲1 nm (best-case)           | ≲1 nm (optimal), ≳10 nm (t ≳ 1 μm) | Atomic (sub-Å) for single atoms        |
| Environmental control | T: 1–10 °C, pH₂O limited | T: wide (−196 °C to >100 °C), P: multi-atm | Ambient, no P control             |
| Major advantages    | Flexible geometry           | Robust, high throughput            | True atomic imaging in liquid          |
| Major limitations   | Temp. stability, droplet size| Windows, liquid thickness          | Fabrication complexity                 |

## 7. Limitations, Challenges, and Future Developments

Challenges in LP-TEM are centered on:

- **Beam-induced chemistry:** Even at low doses, radiolysis and thermal effects can dominate observed behavior in sensitive materials or induce non-equilibrium states.
- **Thickness/resolution trade-off:** Achieving atomic to nanometer resolution requires total sample thicknesses ≲ 100 nm. Advanced windowless or graphene-window geometries minimize scattering but are not yet widely available.
- **Sample environment flexibility:** Open-cell ETEM affords unique geometry for external stimuli (illumination, magnetic fields), but requires precise humidity/temperature regulation [2308.09832].
- **Quantitative chemical mapping:** EELS-based chemical fingerprinting in thick liquid requires signal optimization (selecting sub-gap and sub-plasmon energy-loss windows). Multiple scattering and window artifacts limit conventional EELS for t/λ > 3 [1212.1501].
- **Soft matter and biological systems:** Precise control of dose and temperature is critical to capture reversible, intrinsic phase dynamics without beam-induced artifacts (e.g., for nanoconfined LCs [2512.23588]).
- **Future directions:** Integration of in situ illumination, improved thermal management, advanced direct-electron detection, microfluidic mixing, and atomic layer encapsulation (graphene, hBN) are priorities to expand the scope and accuracy of LP-TEM for complex, multidimensional in-liquid phenomena.

Research continues to improve liquid-cell architectures, spectroscopic sensitivity, and methods for artifact mitigation, with the aim of enabling robust, artifact-free operando imaging and spectroscopy of dynamic processes in real liquids at atomic spatial and sub-second temporal resolution.

Source: https://www.emergentmind.com/topics/in-situ-liquid-phase-transmission-electron-microscopy