This disclosure relates generally to specimen mounts for use with transmission electron microscopes, and more particularly to specimen mounts for in-operando electrical measurements.
Understanding the relationship between the properties and the structures of materials is the basis for development of new and better materials for next generation energy technologies. Transmission electron microscopy (TEM) has been indispensable for this development by providing detailed structural motifs down to the atomic scale of the materials. However, great details of atomic structure obtained by state-of-the-art electron microscopy may not always be the property-dictating atomic structures. In those cases the atomic structures are not enough to predict or understand emergent behaviors and properties in advanced materials systems. In order to directly probe the property-dictating structural motifs, it may be necessary to directly correlate electron microscopy data with local properties measured from TEM samples under external stimuli, such as, for example, electric/magnetic fields, photo excitation, temperature, or mechanical strain. In order to observe atomic structures in response to an electric bias, holder chips that provide an electrical bias to the samples have been developed.
Because the current specimen mounts locate the samples approximately at the center of the chip. The conventional specimen mounts require multiple preparation steps which can result in damage and contamination of the sample. Furthermore, the location of the sample on the specimen mount may make it difficult to manipulate or clean the sample after mounting it onto the chip.
Embodiments of the invention provide for an electron microscope sample holder, which includes a membrane, a support frame partially surrounding a perimeter or a circumference of the membrane, a mounting area for mounting a sample to the membrane, where the mounting area abuts a perimeter or a circumference of the membrane not surrounded by the support frame, at least two of conducting contact pads mounted on a the support frame, and at least one electrode lead mounted on the membrane and in electric contact with at least one conducting contact pad.
The embodiments provide for the ability to perform FIB sample cleaning after mounting the sample on the sample holder and after connecting sample and chip electrodes. There is no need to detach the sample from the holder for additional cleaning steps if TEM experiments indicate it is required.
The embodiments are compatible with post-FIB, low energy ion cleaning processes (e.g., using a NanoMill system).
The embodiments allow for the mounting of a thick sample on the chip, prior to thinning it down to electron transparency thickness, thus reducing considerably the chance of damaging the sample.
The embodiments reduce number of steps required to mount TEM-ready samples on electrical biasing chips, thus minimizing the chances of sample damage.
The embodiments allow cleaning the sample after electrode definition via electron or ion assisted deposition of platinum (or other metal) compound, thus allowing the removal of contamination originated by this process.
Because the sample is only attached at one edge to the embodied holders, capacitance and leakage current effects are reduced.
FIB cleaning of mounted samples does not affect the mechanical stability of the chip's dielectric membrane, nor interferes with the physical integrity of the electrical contacts between sample and chip.
The sample 140 is placed and secured adjacent to the membrane 125 in a mounting area 128. The mounting area 128 abuts the second partial membrane perimeter or circumference 127. Distributed across the frame 115 are contact pads 120 (only one is labeled for simplicity). When the holder chips 100, 200, and 300 are placed on a sample probe in the TEM, the contact pads 120 connect electrically with electric contacts on the sample probe. At least one electrode lead 130 is situated on the membrane 125 (only two electrode leads shown, and only one is labeled for simplicity). The electrode lead 130 connects the contact 120 electrically with the mounting area 128. Although only two electrode leads 130 are shown in
After the sample 140 is placed and secured adjacent to the membrane 125 in the mounting area 128, interconnects 150 may deposited from the electrode leads 130 to sample electrodes 142 and 144. The interconnects may be deposited using, for example, ion bean assisted deposition of a metal compound (usually platinum).
In
The membrane 125 may be made out of any suitable material and which is well-known in the art. In one embodiment the membrane material is silicon nitride (Si3N4). The frame 115 may be made out of any suitable material and which is well-known in the art. In one embodiment the frame material is silicon (Si).
The embodiments disclosed herein avoids a drawback of conventional TEM chips which is that, once mounted, samples cannot be further thinned or cleaned. It is common to mount a sample on a chip, perform a TEM study and find out that the quality of the experiment is hindered due to sample contamination, damage, or excessive sample thickness issues. These problems may remediated if there existed a simple way to perform further cleaning on the sample. The impracticality of cleaning mounted samples on conventional chips is due to the fact that samples are placed parallel to the chip surface and at a large distance away from the edges of the chip (
Furthermore, the embodiments disclosed herein avoids the need for multiple sample preparation steps. The placement of focused ion beam (FIB) technique lift-out samples on conventional chips involves multiple steps which increase the chances of losing or damaging the sample. These steps are:
Furthermore, the embodiments disclosed herein may help avoid the risk of damaging samples when transferring them onto a chip. In conventional chips, samples need to be pre-thinned to thicknesses of about 50 nm before being placed on the chip. Hence, there is considerable risk of damaging the delicate samples during this procedure. The embodiments disclosed herein also reduce the risk of contaminating samples during electrode definition. After a successful placement of a sample on an aperture on the chip, the operator connects sample electrodes to predefined electrodes on the chip. This procedure uses electron or ion beam assisted deposition of a metal compound, which involves the possibility of contaminating the region of interest on the sample.
Additionally the embodiments disclosed herein may reduce limited electrical performance due to stray capacitance and current leakage problems. Conventional TEM sample holders place samples against a thin insulating dielectric membrane, which may add a considerable and unwanted capacitance to the system under study (sample). In addition, leakage current increases in this configuration, limiting the available range of voltage or electric field that can be applied on the sample.
The embodiments disclosed herein include chips fabricated with predefined electrodes, on which an operator can mount thick FIB lift-out samples in a flag-style fashion. This leaves both sides of the sample available for FIB thinning. Using the chips disclosed herein may involve the following simple sample fabrication steps:
The chips embodied herein require just one step of sample transfer, from lift-out to the TEM chip, compared to the three transfer steps required in conventional chips (from lift-out to thinning grid, from thinning grid to manipulator probe, and from probe to chip). As used herein with respect to the present sample holder, “thick” corresponds to thicknesses on the order of a few microns (1 μm-5 μm, μm=micrometer). Whereas, “thin” as used herein corresponds to thicknesses that are transparent to an electron beam which is about 100 nm (nm=nanometer) or less. Reducing the amount of transfer steps is beneficial as each of these transfer steps involves some chance of destroying the sample.
Furthermore, the embodied chips allow for further processing of the sample after being mounted. If a TEM experiments indicate the need of additional sample cleaning, an operator can just load the chip in a FIB system and proceed with the cleaning without the need to remove the sample from the chip. In contrast, performing additional sample cleaning in conventional chips involves five steps, namely: a) unmount sample from chip, b) mount sample on thinning grid, c) clean the sample, d) remount sample on chip, and e) reconnect sample and chip electrodes. The delicate, electron-transparent sample has a high chance of breaking during this multi-step procedure.
Embodiments of the present electron microscope sample holder described herein may include a support frame, a membrane that has a perimeter partially surrounded by the support frame and a perimeter partially not surrounded by the support frame, a plurality of sample mounting areas with at least one of the sample mounting areas abutting the perimeter partially not surrounded by the support frame, a plurality of conducting contact pads mounted on a the support frame, and at least one electrode lead mounted on the membrane and in electric contact with at least one conducting contact pad.
The present electron microscope sample holder may also include the perimeter partially not surrounded comprising an indentation. And, the sample mounting area may be situated in the indentation. Further, the perimeter of the present electron microscope sample holder may be a circumference.
In one embodiment the sample holder may have a perimeter, and the membrane of the electron microscope sample holder may have a plurality of edges that are partially surrounded by the support frame, and at least one edge that is partially not surrounded by the support frame. The perimeter partially not surrounded by the support frame may comprise an indentation. And the sample mounting area may be situated in the indentation. Further the indentation may be curved or may have a plurality of edges.
In another embodiment, the sample holder may have a membrane with four edges. The four edges may form the perimeter where three of the four edges are partially surrounded by the support frame, and one of the four edges is partially not surrounded by the support frame. The one edge that is partially not surrounded by the support frame may have an indentation. And the sample mounting area may be situated in the indentation.
It will be appreciated by persons skilled in the art that the embodiments of the present sample holder are not limited to what has been particularly shown and described in the specification. Rather, the scope of the present sample holder is defined by the claims which follow. It should further be understood that the above description is only representative of illustrative examples of embodiments. For the reader's convenience, the above description has focused on a representative sample of possible embodiments, a sample that teaches the principles of the present invention. Other embodiments may result from a different combination of portions of different embodiments.
The specification has not attempted to exhaustively enumerate all possible variations. That alternate embodiments may not have been presented for a specific portion of the invention, and may result from a different combination of described portions, or that other undescribed alternate embodiments may be available for a portion, is not to be considered a disclaimer of those alternate embodiments. It will be appreciated that many of those undescribed embodiments are within the literal scope of the following claims, and others are equivalent. Furthermore, all references, publications, U.S. Patents, and U.S. Patent Application Publications cited throughout this specification are hereby incorporated by reference in their entireties as if fully set forth in this specification.
This application claims the benefit of U.S. Provisional Application No. 62/622,347, filed on Jan. 26, 2018, which is hereby incorporated by reference in its entirety.
This invention was made with Government support under contract number DE-SC0012704 awarded by the U.S. Department of Energy. The Government has certain rights in the invention.
Number | Date | Country | |
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62622347 | Jan 2018 | US |