nanodevices

Why Xidex Decided to Build a Nanomanipulator

 

 A few years ago we decided that Xidex’s engineering team needed a nanomanipulator to do mechanical probing and electrical testing of carbon nanotube based nanodevices in our own SEM lab. This work required ultra-low drift and ultra-low electrical noise plus a combination of long-range travel and smooth fine-range motion with nanometer-scale resolution. We checked out commercially available nanomanipulators and sought advice from our friends in universities and other nanotechnology companies who were doing similar work.

We found to our dismay that:

  • When they were being used, the nanomanipulators our colleagues had bought were taking hours to accomplish tasks that should be done in a few minutes.

  • Another leading nanomanipulator promised to do it all, but ended up not doing anything very well, and took up precious lab space with multiple control boxes, cables, and hardware modules.

  • Finally, our nanoscientist friends told us how they had already put a lot of valuable time into fine tuning their experimental methods, so they wanted a tool that did what they wanted the way they wanted it done.Instead, nanomanipulators on the market were pretty much designed to do things one way. Customizing the available hardware & software would be a prohibitive task for Xidex

 

So, we decided to build our own nanomanipulaton system!

The Right Hardware - We knew that the nanopositioning harware would be the heart of the system, and we had to get it right on the first try. Our product designers rejected the idea of manipulator arms swinging in arcs and moving radially to reach points in 3D space, because that architecture requires complex coupled motion just to move in a straight line - this is always a potential source of positioning errors.  Arc motion also has different ranges, resolutions and speeds in different directions, making experiments harder to plan and carry out. We also did not like the idea of stacking a tube piezo on top of a separate inertial drive unit as a way to combine continuous, high resolution piezo motion with the long-range motion an inertial drive can produce. This intuition was confirmed by users of the leading nanomanipulation system optimized for electrical probing, which is based on this architecture.  They told us that their electrical probing unit was taking as much as 30 minutes to stabilize the inherent thermal-mechanical drift before measurements could be made. We knew from experience that this kind of excessive drift and instability can be associated with tube piezos and complicated stacked-up hardware. In the end, we opted for a nanopositioner design consisting of three orthogonal stages, each having a stacked piezo integrated directly with an inertial drive bearing. This simple, robust architecture provides the same range of motion, positioning resolution and speed in all three orthogonal directions. We selected stacked piezos that would produce up to ± 3.5 µm of continuous motion with sub nanometer resolution, necessary for many nanoscience applications, in addition to generating the cyclic motion needed for inertial drive. We made the range of the inertial drive units large, 15 mm in all three directions, which lets the nanomanipulator reach all points of interest in most nanoscience applications without making other cumbersome adjustments.

Our designers insisted on flexible mounting options for the nanopositioner. They were aware of the fact that the leading nanomanipulator used for electrical probing could only be mounted on an annular ring attached to the SEM stage, yet they did not want to impose such a restriction on the system we were developing. Our design team wanted to be able to install the system onto the stage door assembly, freeing up the additional degrees of freedom provided by the SEM stage. However, we also liked the flexibility of being able to mount the system on the SEM stage or even the chamber wall if desired. The system we designed met all of these requirements.

Finally, we designed the inertial drive units to have high static stiffness, with around 106 N/m of mechanical impedance, and to have high load capacity that supports dynamic loads up to 2 N and static loads greater than 2 N. The resulting nanopositioner hardware has very low drift of < 1 nm/min, which is critical in many nanoscience applications, for which a unit needs to stay put when parked. The high stiffness, high load capacity, low drift and simple, open architecture have the added benefit of letting the nanopositioner support a variety of different end effectors and other payloads that could not be carried by other nanopositioning systems (i.e., without causing excessive static and dynamic loads or requiring complex attachment systems). Achieving this high level of adaptability to future needs was important to our design team. We needed a hardware platform that could support different applications, many of which were not yet identified, without having to develop a variety of different nanopositioners.

The Right Software If the nanopositioner is the “heart” of the system, then the software is its “brain.” We had already made extensive use of LabVIEW™ at Xidex because of the ease with which new applications can be developed and the availability of a wide variety of hardware interface modules. This made LabVIEW the natural choice for software to drive our new nanomanipulator. We started out by building a library of LabVIEW applications to drive the nanopositioner in different modes, electrically characterize nanodevices and do other specialized tasks like trimming nanotubes to a desired length. We started calling these applications “Actions” and the name stuck.

In contrast to the easy user programmability provided by LabVIEW, existing nanomanipulators on the market either offered an inflexible Windows-based interface or were limited to separate, fixed firmware modules containing data structures that internally control various devices. Although some application-specific software, off-line parameter setups and even LabVIEW DLLs (dynamic link libraries) were available with other systems, our design team insisted on much more. As with the hardware side of the system, we were committed to building a system that could be programmed, virtually “on the fly” as our needs changed. In keeping with this design philosophy, our software developers created a “Toolbox” which is basically a scripting environment that lets a user of the system call any of the LabVIEW Actions that have already been written and combine them in new ways to accomplish new tasks. With both the Actions library and the Toolbox in place, we were finally satisfied that the “brain” of our new nanomanipulation system would be just as powerful and adaptable as the hardware at its “heart.”

The Right Interface – One of the nanomanipulators on the market uses PlayStation style levers, with one lever per axis and a separate “joystick” for each nanopositioner. We have found that these levers can be very difficult to operate when trying to complete delicate, high precision tasks. Another existing system uses an XYZ joystick to switch between coarse and fine modes of operation, and drives multiple nanopositioners. We liked the idea of one joystick driving multiple nanopositioners. However, the speed of this existing nanomanipulator joystick, which functions on the basis of “proportional control”, yields an end-result where the necessary delicate manual positioning of the joystick, with respect to a reference joystick position, is not good for fine control.

Our design team went with the idea of using one USB joystick to control and switch between multiple nanopositioners. However, we made the speed of our nanopositioner selectable with a hat switch on the joystick instead of letting it vary with the user’s hand motion. We made the joystick capable of generating all of the commands needed to control the system. These include controlling the XYZ directions of the selected nanopositioner with 7 motion speeds and 3 modes of operation (Multi-Step, Single Step and Fine Motion). Speeds and the modes for XY and Z axes are controlled separately, which is especially well-suited for fine control in an SEM instrument where the depth of focus is an issue. We used one of the joystick buttons to select from the available menu of LabVIEW Actions, and gave the system voice feedback so the user can know which Action is currently selected without turning away from the live SEM image to look at the computer screen. We use the joystick trigger to start and stop the selected Action. Voice feedback also confirms the selected speeds and modes of operation. We provided a user friendly on-screen interface which is also capable of controlling the system. However, found that building all of the same functionality into the joystick, and adding voice feedback, made the system exceptionally easy to use. Visitors to our lab who tried driving the system found it highly intuitive, quick to learn and fun to use.

The Right Controller – As with other major system components, we took note of what was already available on the nanomanipulator market and made changes resulting in an innovative alternative. The controller that came with one of the existing nanomanipulators was a large floor-mounted unit. Another system had a reasonably compact table top controller, but upgrades required additional control boxes. Still another system forced users to deal a separate control box for each nanopositioner and each application-specific end-effector. Furthermore, we found that the cabling architecture limited the number of different end-effectors that can be used. None of the existing nanomanipulator systems could be expanded to multiple nanopositioners without introducing a proportionally large number of cables.

We made our controller fit into a compact desktop unit that saves valuable lab space. To keep down the number of cables, our control architecture incorporates a multi-device network that lets the controller communicate simultaneously with multiple end effectors over a common set of cables. This also has the advantage of enabling multiple different end effectors without having to add a proportional number of dedicated cables.

The NanoBot® System 

We originally set out to build out the right nanomanipulator for doing nanoscience in our own lab, and we succeeded! The system greatly increased the productivity of our R&D team, allowing us to easily manipulate and test nanodevices, quickly build new LabVIEW Actions as needed and focus on our nananodevice research.

Then it happened. Colleagues who visited our lab were so intrigued with the innovative, easy-to-use system we had created, that they started asking us to build one they could take back to their own lab. A more systematic assessment of the marketplace confirmed that there was indeed a very large unmet demand for a commercial nanomanipulation system with the unique combination of features and benefits that our system already had.

We made the business decision to productize the prototype, revisiting some of our earlier choices with design-for-manufacturability in mind, and conducting extensive performance testing to assure high reliability for future customers. We registered the NanoBot® trademark, giving the product its own unique identity. The first commercial NanoBot units started selling in 2009 to nanoscientists in industry and academia. Customers who own a NanoBot system appreciate the fact that they can configure it with specialized end effectors that meet their immediate needs and augment it later with additional plug-and-play nanopositioners and end effectors that will continue to enhance R&D productivity as their needs grow and diversify.

Because of its simple, robust design, we are able to minimize manufacturing costs and pass the savings on to our customers. Cost is always important, but in these challenging times it can often make the difference as to whether or not a much-needed system can even be acquired. Still, the work must go on, and sooner or later most nanoscientists experience the need to manipulate and measure the devices and materials they are observing in in their SEMs. We are extremely pleased to be able to offer the NanoBot system to the nanoscience community as an affordable system that boosts their R&D productivity. Please visit the Products section of the web site for more detailed information on the NanoBot system, and the Application Notes section for descriptions to the NanoBot system in action. And, give us a call! You really need to get your hands on one of these.

The Parallel Multi-Precursor Gas Delivery System 

As noted above, a nanomanipulator lets the nanosientist manipulate and measure nanomaterials and devices in addition to just observing them in an SEM. But what about fabricating new nanodevices? And what if nanodevices need to be cut to smaller sizes or cleaned of unwanted materials? Operations of this kind are often called nanomaterial “editing,” a term which encompasses both material deposition and material removal.

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. We looked for a gas delivery system that would let us do EBID and EBIE in our SEM. However, as in our earlier experience when looking for a nanomanipultor, we were disappointed by the gas delivery choices available in the commercial marketplace.

We recognized the opportunity to offer nanoscientists an innovative gas delivery system in which the nozzle assembly would be carried as an end-effector on the NanoBot nanomanipulator. Xidex introduced the first commercial versions of our multi-precursor gas delivery system to the nanoscience community in 2010. We called it the Parallel Multi-Precursor Gas Delivery (MPGD) system to emphasize the fact that the precursors travel through separate delivery tubes, not through the same tube one after another. Naturally, the Parallel MPGD system benefits from the same tradition of LabVIEW based control and user interface that makes the NanoBot so user friendly. The LabVIEW™ based applications library provided with the system enables basic deposition and etching operations, including selection of process gasses, programming of process gas flow rates and management of reservoir temperature. Parallel-MGPD operations can be seamlessly integrated with XYZ navigation and positioning and other NanoBot applications. In addition, the user has the option of creating custom applications using the applications Toolbox which can then be added to the applications library.

The power of combining superior nanomanipulation capability with gas delivery is already paying off. Experiments using water vapor to etch carbon nanotubes conducted at Xidex and The University of Tennessee have shown that improved etching correlates with use of a small, precisely controlled distance between the nozzle and the sample. We found that the small distance between the nozzle and the sample results in an increase of the localized gas pressure which in turn is responsible for the improved etching of carbon nanotubes. The Products section of the web site has more detailed information and the Application Notes page has links to to several case studies describing the Parallel MPGD system in action.

Looking to the Future 

Now that the NanoBot and Parallel-MGPD systems have proven themselves as valuable tools for the nanoscientist, we are busy adding other new capabilities like gripping, force sensing and specialized electrical and mechanical probes. The Products section of the site has detailed descriptions of the available gripper and force sensor modules. There is no end in sight to what this robust nanopositioning platform can do when combined with specialized end effectors. Combining the open hardware architecture of the NanoBot system with the open software environment provided by LabVIEW has already put a lot of power in the hands of the nanoscience community. We wish our customers well as they continue to find exciting new uses for Xidex’s NanoBot system. Please give us a call. We would enjoy answering your questions and arranging for a demonstration.