[Paper Review] In-situ metallic coating of atom probe specimen for enhanced yield, performance, and increased field-of-view

Tim M. Schwarz, Eric Woods+8 more|arXiv (Cornell University)|Sep 14, 2023

Advanced Materials Characterization TechniquesEngineering3 citations

TL;DR

This paper presents an in-situ focused ion beam (FIB)-based method for depositing uniform metallic coatings (e.g., Cr) directly onto atom probe specimens immediately after preparation. The technique enhances specimen yield, improves mass resolution, increases the effective field-of-view, and enables full visualization of the original specimen surface, including native oxide layers, across diverse materials including non-metallic systems.

ABSTRACT

Atom probe tomography requires needle-shaped specimens with a diameter typically below 100 nm, making them both very fragile and reactive, and defects (notches at grain boundaries or precipitates) are known to affect the yield and data quality. The use of a conformal coating directly on the sharpened specimen has been proposed to increase yield and reduce background. However, to date, these coatings have been applied ex-situ and mostly are not uniformly. Here, we report on the controlled focused ion beam in-situ deposition of a thin metal film on specimens immediately after specimen preparation. Different metallic targets e.g. Cr were attached to a micromanipulator via a conventional lift-out method and sputtered using the Ga or Xe ions. We showcase the many advantages of coating specimens from metallic to non-metallic materials. We have identified an increase in data quality and yield, an improvement of the mass resolution, as well as an increase in the effective field-of-view enabling visualization of the entire original specimen, including the complete surface oxide layer. The ease of implementation of the approach makes it very attractive for generalizing its use across a very wide range of atom probe analyses.

Motivation & Objective

• To address low yield and poor data quality in atom probe tomography caused by specimen fragility and surface defects.
• To overcome limitations of ex-situ coating methods, which often result in non-uniform deposition and inconsistent performance.
• To develop a robust, in-situ coating technique compatible with a wide range of materials, including non-metallic and reactive specimens.
• To enhance field-of-view and data quality by enabling visualization of the entire original specimen surface, including native oxide layers.
• To streamline implementation for broad adoption across atom probe research by integrating coating into the standard FIB specimen preparation workflow.

Proposed method

• A micromanipulator is used to position a metallic target (e.g., Cr) adjacent to the atom probe specimen after FIB-based sharpening.
• Focused ion beam (FIB) sputtering with Ga or Xe ions is employed to deposit a conformal, ultra-thin metallic film directly onto the specimen surface.
• The coating is applied in-situ, immediately following specimen preparation, minimizing contamination and ensuring uniformity.
• The method is applied to both metallic and non-metallic materials, including those with reactive surfaces or complex microstructures.
• The technique is compatible with standard atom probe workflows and requires minimal modification to existing FIB-atom probe systems.
• The coating process stabilizes the specimen surface, reducing field evaporation artifacts and background noise.

Experimental results

Research questions

• RQ1 Can in-situ metallic coating significantly improve the yield of successful atom probe tomography experiments?
• RQ2 How does in-situ coating affect mass resolution and data quality in atom probe analysis?
• RQ3 To what extent does the coating increase the effective field-of-view, enabling visualization of the entire original specimen surface?
• RQ4 Can the method be effectively applied to non-metallic and reactive materials, including those with native oxide layers?
• RQ5 Is the in-situ coating process practical and scalable for routine use across diverse atom probe laboratories?

Key findings

• The in-situ metallic coating method increased specimen yield by reducing failure during field evaporation due to surface defects and reactivity.
• Mass resolution was improved, enabling better separation of closely spaced ion signals in the reconstructed 3D maps.
• The effective field-of-view was significantly expanded, allowing full visualization of the original specimen surface, including complete native oxide layers.
• The coating enabled successful analysis of previously problematic materials, including non-metallic and reactive specimens, with consistent performance.
• The technique demonstrated high reproducibility and compatibility with standard FIB-atom probe workflows, supporting broad implementation.
• The use of Cr and other metals as coating materials provided stable, conformal films that enhanced signal-to-noise ratio and reduced background.