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ME Channels / Micro / Nano

Tech Front: New Process Allows Nanofibers to Grow at Room Temperature

Researchers at North Carolina State University (Raleigh, NC) have devised a safer method of growing vertically aligned carbon nanofibers (VACNF) with ambient air, rather than using toxic chemicals like ammonia at very high temperatures in a vacuum chamber.

VACNFs, which hold promise for gene-delivery tools, sensors, batteries and other technologies, are typically manufactured by placing a substrate coated with nickel nanoparticles in a vacuum chamber heated to 700°C (1292°F). The chamber is filled with ammonia gas and either acetylene or acetone gas, which contain carbon, and a voltage is applied to the substrate and an anode in the chamber to ionize the gas, creating plasma that directs the nanofiber growth.

“This discovery makes VACNF manufacture safer and cheaper, because you don’t need to account for the risks and costs associated with ammonia gas,” said Anatoli Melechko, an adjunct associate professor of materials science and engineering at NC State and senior author of a paper on the work. “This also raises the possibility of growing VACNF on a much larger scale.”
Researchers demonstrated that they can grow vertically-aligned carbon nanofibers using ambient air, rather than ammonia gas.
Ammonia has been used in the process to keep carbon from forming a crust on the nanoparticles, which would prevent the formation of VACNF. “We didn’t think we could grow VACNFs without ammonia or a hydrogen gas,” Melechko said. The team tried the conventional vacuum technique, using acetone gas. When they replaced the ammonia gas with ambient air, it worked. The size, shape and alignment of the nanofibers also were consistent with the fibers produced using conventional techniques.

“We did this using the vacuum technique without ammonia,” Melechko said. “But it creates the theoretical possibility of growing VACNF without a vacuum chamber. If that can be done, you would be able to create VACNF on a much larger scale.” Melechko also credited the role of two high school students involved in the work, A. Kodumagulla and V. Varanasi, who are lead authors of the paper. “This discovery would not have happened if not for their approach to the problem, which was free from any preconceptions,” Melechko said. “I think they’re future materials engineers.”

The paper, “Aerosynthesis: Growth of Vertically-aligned Carbon Nanofibres with Air DC Plasma,” is published online in the journal Nanomaterials and Nanotechnology. Co-authors include former NC State doctoral student R.C. Pearce; NC State doctoral student W.C. Wu; Dr. Joseph Tracy, an associate professor of materials science and engineering at NC State; and D.K. Hensley and T.E. McKnight of Oak Ridge National Laboratory. The work was partially supported by a National Science Foundation grant.

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Non-Destructive Testing Software

A new software solution for non-destructive testing (NDT) will allow inspection analysts to create and share inspection procedures with field inspectors around the world. Developed by DolphiTech AS (Raufoss, Norway), the DolphiCam TeamCenter software solution integrates with the DolphiCam Ultrasound Camera system and enables true scalable and team-based NDT.

With the increased use of carbon fiber reinforced plastic (CFRP), the need for NDT is rising, but NDT equipment is expensive and requires time-consuming, costly training. “Today’s NDT solutions simply do not scale,” said Jan Olav Endrerud, vice president, product and marketing at DolphiTech. With DolphiCam TeamCenter, an NDT expert can generate inspection procedures containing instructions, photos and sample ultrasound images, as well as embedded camera and material settings.

Field inspectors simply hook up their DolphiCam and perform inspections according to the procedure. Reports are automatically created upon completion, which can then be sent back to the NDT expert, insurance companies or other interested parties. The system uses matrix transducer technology and is extremely portable, user-friendly, offering 2D and 3D images of internal structures in modern, lightweight materials. For more information, visit www.dolphitech.comME

New Arbitrary Spindle-Speed Override Option

FANUC America Corp. (Rochester Hills, MI) is now offering the arbitrary speed threading option on its 0i-TD and 0i Mate-TD CNCs for new turning machines. Arbitrary speed threading enables adjusting the spindle speed during thread cutting to control chatter, and it also provides the functionality to quickly rethread or repair existing threads.
The FANUC arbitrary speed threading option allows operators to adjust spindle speed during thread cutting to control chatter.
Ideally suited for oil & gas industry pipe and fitting thread maintenance, the new speed threading option allows adjustment of the spindle speed during a threading cycle to eliminate vibration and chatter. This feature is valuable for thread repair as chatter is more likely to occur with the small amounts of material typically being removed. Without arbitrary speed threading, the spindle speed override is inhibited during threading in order to prevent damaging the part, as a change in thread lead would occur. The arbitrary speed threading function ensures that the cutting tool remains coordinated with the spindle speed at all times during threading to produce the programmed lead.

Repairing existing threads is fast and easy for operators using the FANUC Manual Guide I conversational programming, which enables CNC operators without G-code knowledge to use the graphical systems to help answer simple questions to generate a suitable thread repair program. The arbitrary speed threading can be used with constant lead threading, threading cycle and multiple threading cycle. In addition to repetitive machining, the same thread shape can be machined even if the spindle speed is changed between roughing and finishing passes.

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Micro/Nano Knowledge and Breakthroughs

A number of SME Technical Papers delve into advanced micro and nanomanufacturing applications and research. Relevant underlying search terms range from micromilling and micromolding to nanostructures and nanolithography. Many of the papers have been presented at SME’s Micro/Nano conferences and expositions over the last decade and at the annual North American Manufacturing Research Conference (NAMRC). 

A proposed technology for additive layer-by-layer fabrication of arbitrarily shaped 3D silicon micro and nanostructures (SME Technical Paper TP13PUB58) could change and greatly simplify the fabrication of many MEMS (microelectromechanical system), NEMS (nanoelectromechanical system) and silicon photonic devices without requiring a fully equipped semiconductor cleanroom. The method is in principle also viable for the implementation of 3D structures in semiconductors other than silicon.

Scanning probe lithography is a low-cost, low-effort technique in fabricating polymeric or metallic nanostructures in the sub-50 nm realm and has potential for producing complex 3D nanostructures. A nanolithography method using atomic force microscopy (AFM) assisted by ultrasonic vibration (TP12PUB77) successfully enabled a high-speed, tunable nanomachining approach on polymethylmethacrylate (PMMA) film. A lithography speed of 100 µm/sec was achieved—significantly better than other known mechanical modification methods, and the machined patterns were transferred to silicon through reactive ion etching.

SEM images (post-release etch) show a 3D-printed Si structure consisting of two layers. The enlarged view of two cantilever beams shows that the narrow beam is free-etched while the wide beam is still supported. Lateral feature sizes down to 500 nm were demonstrated.

An earlier paper (TP06PUB98) on electromachining of nanoscale features using AFM showed the feasibility of complex-featured nano-groove machining in a dielectric medium. Nano-conical cavities with different sizes were machined on copper samples when deionized water/electrolytes were used as the medium between the conductive tip and the sample after the application of ultra-short voltage pulses. Traditional macroscale touch-off error-reduction methods cannot be used for micromilling, and some proposed microscale methods (acoustic emissions, optical, force monitoring) require extensive instrumentation and can be expensive. In TP09PUB98, the precision of an inexpensive conductivity-based touch-off method for micromilling is investigated. Touch-off accuracy within 1 µm was achieved, provided that process variables, such as feedrate, voltage, tool size and, notably, spindle condition, were properly set. Breakthroughs in the manufacturing and assembly of microsystems from precise metal, ceramic and plastic parts are described in TP07PUB17. MEMS-scale metal microcomponents, including springs, gears and latches, are affordably fabricated with consistent, predictable material properties and with finer, better-shaped features than stamping or EDM. ME

Tech Front is edited by Senior Editors Patrick Waurzyniak,, and Ellen Kehoe,


This article was first published in the June 2014 edition of Manufacturing Engineering magazine. Click here for PDF.  

Published Date : 6/1/2014

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