Plasma Sputtering for TEM Sample Preparation
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Solution Overview
Problem
Conventional methods for preparing TEM samples, such as mechanical polishing and FIB, introduce amorphous damage and surface artifacts that limit resolution in high-resolution microscopy, and existing plasma cleaning techniques often cause irreversible modifications or surface heating.
Innovation Solution
A specimen holder and mating receptacle holder arrangement that configures the sample in a plasma system to control the trajectory of low-energy ions for sputter removal at a low angle, minimizing sputter deposition and using carbon materials to prevent contamination, while actively cooling the sample to prevent heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional mechanical polishing or FIB is used to prepare TEM samples, then electron transparency is achieved, but amorphous damage and surface artifacts are introduced that limit resolution
Solution Approach 1:
The patent replaces mechanical polishing and FIB ion beam methods with a plasma-based electrostatic field system. Low-energy ions from an RF-generated plasma are accelerated through an electrostatic field to remove amorphous damage without the mechanical contact or high-energy ion beam damage associated with conventional methods
Solution Approach 2:
The patent changes the energy parameter of ions used for sample preparation from the high energies (3 keV Ar ions, 30 keV Ga ions) used in conventional methods to low energies (250 eV Ar ions), and changes the incident angle from normal to low angle (5° from surface), thereby reducing amorphous damage while maintaining material removal capability
2Object-affected harmful factors
If ion milling is used to remove amorphous damage, then surface quality improves, but an amorphous region as thick as 12 nm is created on both surfaces
Solution Approach 1:
The patent changes the ion energy from 3 keV (conventional ion milling) to 250 eV, and the incident angle from any angle to specifically 5° from the surface. These parameter changes enable removal of amorphous damage while creating less than 1 nm amorphous region, significantly improving upon conventional ion milling results
3Ease of manufacture
If FIB is used to prepare TEM samples, then sample preparation is achieved, but amorphous damage region becomes 20 nm thick or more and Ga implantation occurs
Solution Approach 1:
The patent replaces the FIB ion beam system with a plasma-based electrostatic field system. This substitution eliminates Ga ion implantation and reduces amorphous damage from 20 nm or more to less than 1 nm by using low-energy (250 eV) Ar ions accelerated through an electrostatic field rather than high-energy focused ion beam
Solution Approach 2:
The patent introduces an RF-generated plasma as an intermediary between the ion source and the sample. The plasma generates low-energy ions that are then accelerated through an electrostatic field, providing a gentler preparation method that avoids the harsh effects of direct FIB ion beam exposure
4Object-affected harmful factors
If plasma cleaning is used to remove amorphous damage, then some damage is removed, but irreversible modifications or surface heating occurs
Solution Approach 1:
The patent changes the ion energy from the higher energies used in conventional plasma cleaning to a specific low energy of 250 eV, and controls the incident angle at 5° from the surface. These parameter changes enable effective amorphous damage removal while preventing the surface heating and irreversible modifications that occur with conventional plasma cleaning methods
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively removes amorphous damage and further thins samples to achieve high-resolution imaging without surface modifications or heating, enhancing the quality of TEM and other microscopy samples.
Implementation Method 1
low energy ions from the plasma to ion sputter material from the surface and near surface region at a low angle
Implementation Method 2
ions extracted from an RF generated plasma
Implementation Method 3
the imposed electric field at the sample due to this voltage is shaped by both the geometry of the specimen and the geometry of the holder
Implementation Method 4
actively cooling the sample to prevent heating
Data Source
AI summary
A plasma system for changing a microscopy material sample comprises a microscopy material sample holder for holding a microscopy material sample in place in a desired orientation, and a receptacle holder for receiving the sample holder and an RF antenna. The microscopy sample is positioned relative to the antenna so that no point on the antenna is in direct line-of-sight contact with the microscopy sample. This feature of avoiding direct line-of-sight contact between the antenna and the sample assists in preventing, or at least minimizing, ion sputtering of system component material onto the specimen or sample 10 that is being trimmed. Moreover, portions of the system which are in direct line-of-sight contact with the sample are comprised of material having a low sputtering yield, preferably carbon. The material may comprise graphite, and may be in the form of a carbon coating or a carbon paint.