Parallel Gas Injection System FAQ

What does the Parallel MPGD system do?

The Parallel MPGD system makes it possible to fabricate new nanodevices and nanostructures inside the SEM or FIB. It can also be used to cut Nano devices to smaller sizes or selectively clean unwanted materials from surfaces. Operations of this kind are often called nanomaterial “editing,” a term which encompasses both material deposition and material removal.

Where can the Parallel MPGD system be mounted?

The precursor canister module can generally be mounted on either the door assembly or the chamber wall. The nanopositioner carrying the nozzle assembly can be mounted on either the SEM/FIB stage, the door assembly or the chamber wall.

What precursors can be used with the Parallel MPGD system?

The Parallel MPGD system can deliver up to four different gas precursors to the surface of a sample mounted inside the SEM or FIB. Examples of precursors that can be delivered include platinum, tungsten, gold, TEOS, oxygen, and water vapor.

How does nanomaterial “editing” work in an electron microscope?

Electron beam deposition (EBID) and electron beam etching (EBIE) represent attractive methods for nanomaterial editing and can be performed in electron microscopes. Both EBID and EBIE require delivery of selected precursors to a substrate. With EBID, the electron beam dissociates the precursor gas, leaving behind condensed material. With EBIE, dissociated species react with substrate material, forming volatile species which desorb from the substrate surface.

What comes with the Parallel MPGD system?

The Parallel MPGD system includes a precursor canister module that can accommodate up to four different precursors, a separate flexible delivery tube and set of valves for precursor, a nozzle assembly that mounts as an end effector on a NanoBot XYZ nanopositioner, a compact desk top control module, a vacuum feedthrough, a mounting bracket for the precursor canister adjustable to fit the particular model of SEM or FIB, and a library of LabVIEW™ based applications for gas deposition and etching. The Parallel MPGD system uses the same laptop computer or PC and joystick that are used to run the NanoBot nanomanipulator.

Can the Parallel MPGD system be used together with other NanoBot systems?

Yes. For example, one or more additional NanoBot XYZ nanopositioners can be used to bring a mechanical or electrical probe, force sensor, gripper, or other end effector into close proximity or contact with the same sample that is being used with the Parallel MPGD system.

How long does it take to purge the system before another gas can be used?

The Parallel MPGD system is designed to virtually eliminate purge time, typically reducing it to a few seconds. This is made possible by use of valves mounted on the nozzle assembly itself, which enable fast on-off control of the gas flow within each individual nozzle.

Can multiple precursors be used at the same time?

Yes. The Parallel MPGD system can be used to deliver up to four precursors at the same time, although the applications of which we are aware use at most two precursors at the same time.

What applications would use multiple precursors at the same time?

One example is to simultaneously deliver different precursor gasses which have been selected so as to achieve competitive etching and deposition in a controlled manner. With the capability of delivering two gasses at the same time, it becomes possible to use a stable organometallic precursor for electron beam induced deposition (EBID) while, at the same time, using a different precursor selected to volatilize unwanted organic contamination using electron beam induced etching (EBIE). The same rationale can be extended to beam induced deposition of a dielectric material, such as tetraethyl orthosilicate (TEOS). In this case, the addition of a second gas, such as water vapor or oxygen, will result in a deposited material that is expected to be more dielectric then if the TEOS were deposited by itself.

Do different precursors ever mix?

Each precursor travels through a separate tube and nozzle, so it never mixes with other precursors anywhere within the Parallel MPGD system. In cases where multiple precursors are used at the same time, the multi-nozzle fixture mounted on the nanopositioner enables mixing of multiple gasses at the sample surface, but not within the Parallel MPGD system.

What nozzle-to-sample distance should be used?

In general, the nozzle-to-sample distance should be as small as possible consistent with the coverage area required by the particular application. We have shown, for example, that for the case of electron beam induced etching (EBIE) the etching time and rate both improve by minimizing the separation distance between the sample surface and the gas nozzle. It has also been observed that, for a smaller sample-nozzle gap, the probe current decreases. This decrease in probe current is due to ionization and competitive positive current flow, which increases with decreased spacing because of enhanced local pressure. The end-result is that the higher local pressure is responsible for an increased and optimal etching rate. These results demonstrate that a smaller nozzle gap leads to a faster etch rate and a lower sample current. (For details, see the Xidex Application Note., Vapor Phase Editing of Carbon Nanotube Based Nanodevices: Using the NanoBot® System with Gas Delivery.)