Jennifer Lu

Using a ferrocenylsilane-based block copolymer as a template to produce nanotextured Ag surfaces: uniformly enhanced surface enhanced Raman scattering active substrates

We report a method of fabricating nanotextured Ag surfaces using a template of self-assembled inorganic-containing block copolymer, polystyrene-b-polyferrocenylsilane. The Ag surfaces with periodically ordered nanoscale features created by the self-organized block copolymer are capable of producing enhanced Raman signals. Using benzenethiol as a probe molecule, an enhancement factor of up to 106 has been observed. More importantly, the enhancement is very uniform; less than 10% Raman signal variation has been obtained. Furthermore, since the size and spacing of the nanostructures can be adjusted by tailoring the polymer chain length, the electromagnetic field can potentially be tuned to achieve even higher surface-enhanced Raman scattering (SERS) activity. This inorganic-containing block copolymer template approach not only provides a simple and straightforward method to fabricate SERS active substrates but also offers a means to experimentally examine the SERS mechanism.

Direct growth of carbon nanofibers to generate a 3D porous platform on a metal contact to enable an oxygen reduction reaction.

For carbon nanotube-based electronics to achieve their full performance potential, it is imperative to minimize the contact resistance between macroscale metal contacts and the carbon nanotube (CNT) nanoelectrodes. We have developed a three-dimensional electrode platform that consists of carbon nanofibers (CNFs) that are directly grown on a metal contact, such as copper (Cu). Carbon nanofiber morphology can be tailored by adjusting the annealing time of a thin electrochemically deposited nickel catalyst layer on copper. We demonstrate that increasing the annealing time increases the amount of copper infused into the nickel catalyst layer. This reduces the carbon deposition rate, and consequently a more well-defined CNF 3D architecture can be fabricated. This direct growth of CNFs on a Cu substrate yields an excellent electron transfer pathway, with contact resistance between CNFs and Cu being comparable to that of a Cu-Cu interface. Furthermore, the excellent bonding strength between CNFs and Cu can be maintained over prolonged periods of ultrasonication. The porous 3D platform affixed with intertwined CNFs allows facile surface functionalization. Using a simple solution soaking procedure, the CNF surface has been successfully functionalized with iron(II) phthalocyanine (FePc). FePc functionalized CNFs exhibit excellent oxygen reduction capability, equivalent to platinum-carbon electrodes. This result demonstrates the technological promise of this new 3D electrode platform that can be exploited in other applications that include sensing, battery, and supercapacitors.

Optothermally Responsive Nanocomposite Generating Mechanical Forces for Cells Enabled by Few-Walled Carbon Nanotubes

We have designed and fabricated a nanocomposite substrate that can deliver spatially and temporally defined mechanical forces onto cells. This nanocomposite substrate comprises a 1.5-mm-thick near-infrared (NIR) mechanoresponsive bottom layer of few-walled carbon nanotubes (FWCNTs) that are uniformly distributed and covalently connected to thermally responsive poly(N-isopropylacrylamide) and an approximately 0.15-mm-thick cell-seeding top layer of collagen-functionalized poly(acrylic acid)-co-poly(N-isopropylacrylamide) that interpenetrates into the bottom layer. Covalent coupling of all the components and uniform distribution of FWCNTs lead to a large local mechanoresponse. As an example, 50% change in strain at the point of irradiation on the order of 0.05 Hz can be produced reversibly under NIR stimulation with 0.02 wt % FWCNTs. We have further demonstrated that the mechanical strain imposed by NIR stimulation can be transmitted onto cells. Human fetal hepatocytes change shape with no sign of detrimental effect on cell viability. To the best of our knowledge, this is the first demonstration of a nanocomposite platform that can generate fast and controlled mechanical force to actuate cells. Since the amplitude, location, and timing of force can be controlled remotely with NIR, the nanocomposite substrate offers the potential to provide accurately designed force sequences for tissue engineering.

Three Dimensional Single-Walled Carbon Nanotubes

We report a simple fabrication method of creating a three-dimensional single-walled carbon nanotube (CNT) architecture in which suspended CNTs are aligned parallel to each other along the conventionally unused third dimension at lithographically defined locations. Combining top-down lithography with the bottom-up block copolymer self-assembly technique and utilizing the excellent film forming capability of polymeric materials, highly uniform catalyst nanoparticles with an average size of 2.0 nm have been deposited on sidewalls for generating CNTs with 1 nm diameter. This three-dimensional platform is useful for fundamental studies as well as technological exploration. The fabrication method described herein is applicable for the synthesis of other very small 1D nanomaterials using the catalytic vapor deposition technique.

Microwave plasma enhanced chemical vapor deposition growth of few-walled carbon nanotubes using catalyst derived from an iron-containing block copolymer precursor

The microwave plasma enhanced chemical vapor deposition (MPECVD) method is now commonly used for directional and conformal growth of carbon nanotubes (CNTs) on supporting substrates. One of the shortcomings of the current process is the lack of control of the diameter and diameter distribution of the CNTs due to difficulties in synthesizing well-dispersed catalysts. Recently, block copolymer derived catalysts have been developed which offer the potential of fine control of both the size of and the spacing between the metal clusters. In this paper we report the successful growth of CNTs with narrow diameter distribution using polystyrene-block-polyferrocenylethylmethylsilane (PS-b-PFEMS) as the catalyst precursor. The study shows that higher growth pressure leads to better CNT growth. Besides the pressure, the effects on the growth of CNTs of the growth parameters, such as temperature and precursor gas ratio, are also studied.

Controllable growth of single walled CNTs using nanotemplates from diblock copolymers

We use diblock copolymers as nanotemplates to produce various catalyst nanoclusters or catalyst-containing inorganic nanostructures with controlled size and spacing for carbon nanotube growth. We are able to generate periodically ordered catalytic nanostructures by spin coating polymer-based catalyst systems. As a result, uniformly distributed, low defect density single walled nanotubes(CNTs) have been obtained. CNTs with diameters of 1nm or less have been produced from iron-containing inorganic nanostructures using conventional chemical vapor deposition. The superior film forming ability of polymer-based catalyst systems enables selective growth of carbon nanotubes on lithographically predefined catalyst islands over a large surface area. The ability to control the density and location of CNTs offers great potential for practical applications. The initial MALDI-MS (Matrix Assisted Laser Desorption Ionization-Mass Spectrometry) results indicate that we can positively identify bovine serum albumin (BSA) at 500 attomoles using CNT surfaces produced by this method.