In Situ Characterization of Boehmite Particles in Water Using Liquid SEM

Summary

We present a procedure for real-time imaging and elemental composition analysis of boehmite particles in deionized water by in situ liquid Scanning Electron Microscopy.

Abstract

In situ imaging and elemental analysis of boehmite (AlOOH) particles in water is realized using the System for Analysis at the Liquid Vacuum Interface (SALVI) and Scanning Electron Microscopy (SEM). This paper describes the method and key steps in integrating the vacuum compatible SAVLI to SEM and obtaining secondary electron (SE) images of particles in liquid in high vacuum. Energy dispersive x-ray spectroscopy (EDX) is used to obtain elemental analysis of particles in liquid and control samples including deionized (DI) water only and an empty channel as well. Synthesized boehmite (AlOOH) particles suspended in liquid are used as a model in the liquid SEM illustration. The results demonstrate that the particles can be imaged in the SE mode with good resolution (i.e., 400 nm). The AlOOH EDX spectrum shows significant signal from the aluminum (Al) when compared with the DI water and the empty channel control. In situ liquid SEM is a powerful technique to study particles in liquid with many exciting applications. This procedure aims to provide technical know-how in order to conduct liquid SEM imaging and EDX analysis using SALVI and to reduce potential pitfalls when using this approach.

Introduction

Scanning Electron Microscope (SEM) has been widely applied to investigate a variety of specimens by producing high resolution imaging¹. The energy dispersive x-ray spectroscopy (EDX) associated with the SEM enables the determination of elemental composition¹. Traditionally, SEM is applied for imaging only dry and solid samples. In the last 30 years, Environmental SEM (ESEM) was developed for analyzing the partial hydrated samples in a vapor environment^2,3,4,5. However, ESEM is unable to image t....

Protocol

1. Prepare AlOOH Liquid Sample

NOTE: Do not touch the specimen or anything inside the SEM chamber with bare hands. Powder free gloves should be worn at all times when handling the SALVI device and mounting it onto the SEM stage in order to avoid potential contamination during surface analysis.

1. Make an AlOOH stock solution (1 mg/mL)
   1. Dissolve 10 mg of AlOOH powder in 10 mL DI water to make the 1 mg/mL AlOOH stock solution.
   2. Ultrasonicate the stock solution for 5 min.
      NOTE: The pH of the stock solution is approximately 4.6 measured by a pH meter. The solution of pH is not adjusted and ....

Results

The representative results are presented to show how the particles are imaged and analyzed using in situ liquid SEM imaging coupled with EDX. The results include SE images and EDX spectra. The SE images were obtained at 100,000X and 200,000X magnification levels in Figure 1. Figure 1a depicts the SE image of the AlOOH, Figure 1b DI water, and Figure 1c the hole .......

Discussion

SEM is a powerful technique in surface characterization of organic and inorganic materials on a nanoscale (nm) level with high resolution¹. For example, it is widely used for analyzing the solid and dry samples such as geological materials²⁶ and semiconductor²⁷. However, it has limitations in characterizing the wet and liquid samples due to the incompatibility of liquid within the highly vacuumed environment required for electron microscopy

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Carbon Coater	Cressington	208 Carbon	It is accompanied with thickness monitor MTM-10.
SEM	FEI	Quanta 3D FEG	It provides highly resolved scanning electron microscopy and elemental analysis.
System for Analysis at the Liquid Vacuum Interface (SALVI)	Pacific Northwest National Laboratory	N/A	SALVI is a unique, vacuum compatible microfluidic cell that enables the characterization of the liquid sample using vacuu- based scientific instrument.
PEEK Union	Valco	ZU1TPK	The polyether ether ketone union is used for connecting the inlet and outlet of SALVI
Syringe	BD	309659	1 mL
Pipette	Thermo Fisher Scientific	21-377-821	Range: 100 to 1,000 mL
Pipette Tip 1	Neptune	2112.96.BS	1,000 µL
Pipette Tip 2	Rainin	17001865	20 µL
Syringe Pump	Harvard Apparatus	70-2213	It is used to inject the liquid sample into the SALVI device.
pH meter	Fisher Scientific/accumet	13-636-AP72	It is used for measuring the pH of AlOOH in DI water.
Barnstead Ultrapure Water System, UV/UF	Thermo Scientific Barnstead	Nanopure diamond D11931	It is used for producing DI water.
Centrifuge tubes	Fisher scientific/Falcon	15-527-90	15 mL
Bransonic ultrasonic cleaner	Sigma-Aldrich	2510	It is used to ultrasonicate the AlOOH liquid sample.
Balance	Mettler Toledo	11106015	XS64
AlOOH	Pacific Northwest National Laboratory	N/A	It is synthesized by scientists at Pacific Northwest National Laboratory.
xT microscope Control	FEI	Quanta 3D FEG	Default microscope control software of SEM Quanta 3D FEG
EDAX Genesis software	EDAX	N/A	The software is used for collecting the EDX elemental information of the samples.
Teflon tubing	SUPELCO	58697-U	It is used for introducing the sample into the microchannel and holding adequate volume of liquid.