Nathan R. Franklin

Molecular photodesorption from single-walled carbon nanotubes

Probing the photoelectrical properties of single-walled carbon nanotubes (SWNTs) led to the discovery of photoinduced molecular desorption phenomena in nanotube molecular wires. These phenomena were found to be generic to various molecule–nanotube systems. Photodesorption strongly depends on the wavelength of light, the details of which lead to a fundamental understanding of how light stimulates molecular desorption from nanotubes. The results have important implications to nanotube-based molecular electronics, miniature chemical sensors, and optoelectronic devices.

Integration of suspended carbon nanotube arrays into electronic devices and electromechanical systems

A synthetic strategy is devised for reliable integration of long suspended single-walled carbon nanotubes into electrically addressable devices. The method involves patterned growth of nanotubes to bridge predefined molybdenum electrodes, and is versatile in yielding various microstructures comprised of suspended nanotubes that are electrically wired up. The approach affords single-walled nanotube devices without any postgrowth processing, and will find applications in scalable nanotube transistors (mobility up to 10 000 cm2/V s) and nanoelectromechanical systems based on nanowires.

Exploiting the properties of carbon nanotubes for nanolithography

Carbon nanotube tips are explored in fabricating oxide nanostructures on silicon surfaces with an atomic force microscope. Nanotubes can write nanostructures at speeds up to 0.5 mm/s over large surface areas, and present a solution to the long-standing tip-wear problem. Experimental and theoretical work find that nanotube tips are impervious to high compressive and lateral forces and breakdown in high electric fields. A “cleaving” method is developed to reproducibly obtain dome-closed multi-walled nanotube tips with suitable length. Nanotube materials could become key elements for future miniaturization applications.

Patterned growth of single-walled carbon nanotubes on full 4-inch wafers

Patterned growth of single-walled carbon nanotubes (SWNTs) is achieved on full 4-in. SiO2/Si wafers. Catalytic islands with high uniformity over the entire wafer are obtained by a deep ultraviolet photolithography technique. Growth by chemical vapor deposition of methane is found to be very sensitive to the amount of H2 co-flow. Understanding of the chemistry enables the growth of high quality SWNTs from massive arrays (107–108) of well-defined surface sites. The scale up in patterned nanotube growth shall pave the way to large-scale molecular wire devices.

Carbon nanotube arrays on silicon substrates and their possible application

Abstract A method to grow regular arrays of oriented carbon nanotubes on silicon substrates is presented. It has been found that porous silicon is an ideal substrate for growing self-oriented carbon nanotubes on large surfaces. The growth mechanism of nanotube arrays has been discussed. The potential applications of carbon nanotube arrays in flat panel display and in synthesizing of other semiconducting nanorods on silicon substrates through the carbon nanotube-confined reaction have also been studied.

Extreme Short-Channel Effect on RTS and Inverse Scaling Behavior: Source–Drain Implantation Effect in 25-nm nand Flash Memory

In 25-nm NAND Flash memory, source-drain implantation conditions significantly affect random telegraph signal (RTS). In this extremely short gate length regime, RTS is proportional to the effective gate length (Leff) which exhibits an “inverse scaling effect.” Process simulation reveals that the laterally straggled and diffused As atoms from source/drain are sufficient to change the effective boron concentration even in the center of the channel which changes macroscale potential profile for the short-channel effect but also changes RTS by modulating random discrete dopant (RDD) effect. This result continues up to 10 000 program/erase cycles which indicates that the defect generation rate for RTS is not changed under the relevant doping conditions. Modeling of the source-drain dopant distribution must include atomistic simulation for accurate prediction of the RDD effect in NAND Flash memory below 30 nm.

Fully inverted single-digit nanometer domains in ferroelectric films

Achieving stable single-digit nanometer inverted domains in ferroelectric thin films is a fundamental issue that has remained a bottleneck for the development of ultrahigh density (>1 Tbit/in.^2) probe-based memory devices using ferroelectric media. Here, we demonstrate that such domains remain stable only if they are fully inverted through the entire ferroelectric film thickness, which is dependent on a critical ratio of electrode size to the film thickness. This understanding enables the formation of stable domains as small as 4 nm in diameter, corresponding to 10 unit cells in size. Such domain size corresponds to 40 Tbit/in.^2 data storage densities

Tuning the Built-in Electric Field in Ferroelectric Pb(Zr0.2Ti0.8)O3 Films for Long-Term Stability of Single-Digit Nanometer Inverted Domains

The emergence of new technologies, such as whole genome sequencing systems, which generate a large amount of data, is requiring ultrahigh storage capacities. Due to their compactness and low power consumption, probe-based memory devices using Pb(Zr(0.2)Ti(0.8))O(3) (PZT) ferroelectric films are the ideal candidate for such applications where portability is desired. To achieve ultrahigh (>1 Tbit/in(2)) storage densities, sub-10 nm inverted domains are required. However, such domains remain unstable and can invert back to their original polarization due to the effects of an antiparallel built-in electric field in the PZT film, domain-wall, and depolarization energies. Here, we show that the built-in electric-field can be tuned and suppressed by repetitive hydrogen and oxygen plasma treatments. Such treatments trigger reversible Pb reduction/oxidation activity, which alters the electrochemistry of the Pb overlayer and compensates for charges induced by the Pb vacancies. This tuning mechanism is used to demonstrate the writing of stable and equal size sub-4 nm domains in both up- and down-polarized PZT films, corresponding to eight inverted unit-cells. The bit sizes recorded here are the smallest ever achieved, which correspond to potential 60 Tbit/in(2) data storage densities.