Anisotropic Synthesis of Armchair Graphene Nanoribbon Arrays from Sub-5 nm Seeds at Variable Pitches on Germanium.

At widths below 10 nm, armchair graphene nanoribbons become semiconductors. One promising route to synthesize nanoribbons is chemical vapor deposition (CVD) of hydrocarbons on Ge(001), and synthesis from seeds reduces nanoribbon polydispersity. In this contribution, we advance the seed-initiated synthesis of nanoribbons and explore the impact of seed size and nanoribbon spacing on growth kinetics. Periodic arrays of graphene seeds are lithographically patterned and etched to reduce their diameter. The viability of initiating synthesis from sub-5 nm seeds is demonstrated, and the pitch between nanoribbons is reduced from 500 to 50 nm to show that crowding effects do not perturb nanoribbon growth kinetics. The invariance of kinetics with pitch in combination with density functional theory (DFT) calculations indicate that (1) the growth species for synthesis has a diffusion length of ≪50 nm and/or (2) the kinetics are strongly attachment-limited. These results demonstrate that seed-initiated synthesis on Ge(001) is a promising route for creating dense arrays of armchair graphene nanoribbons for semiconductor electronics applications.

Alignment of semiconducting graphene nanoribbons on vicinal Ge(001).

Chemical vapor deposition of CH4 on Ge(001) can enable anisotropic growth of narrow, semiconducting graphene nanoribbons with predominately smooth armchair edges and high-performance charge transport properties. However, such nanoribbons are not aligned in one direction but instead grow perpendicularly, which is not optimal for integration into high-performance electronics. Here, it is demonstrated that vicinal Ge(001) substrates can be used to synthesize armchair nanoribbons, of which ∼90% are aligned within ±1.5° perpendicular to the miscut. When the growth rate is slow, graphene crystals evolve as nanoribbons. However, as the growth rate increases, the uphill and downhill crystal edges evolve asymmetrically. This asymmetry is consistent with stronger binding between the downhill edge and the Ge surface, for example due to different edge termination as shown by density functional theory calculations. By tailoring growth rate and time, nanoribbons with sub-10 nm widths that exhibit excellent charge transport characteristics, including simultaneous high on-state conductance of 8.0 µS and a high on/off conductance ratio of 570 in field-effect transistors, are achieved. Large-area alignment of semiconducting ribbons with promising charge transport properties is an important step towards understanding the anisotropic nanoribbon growth and integrating these materials into scalable, future semiconductor technologies.

Controlled delivery of antibodies from injectable hydrogels.

Therapeutic antibodies are currently used for the treatment of various diseases, but large doses delivered systemically are typically required. Localized controlled delivery techniques would afford major benefits such as decreasing side effects and required doses. Injectable biopolymer systems are an attractive solution due to their minimally invasive potential for controlled release in a localized area. Here, alginate-chitosan hydrogels are demonstrated to provide controlled delivery of IgG model antibodies and also of Fab antibody fragments. Also, an alternate delivery system comprised of poly(lactic-co-glycolic acid) (PLGA) microspheres loaded with antibodies and encapsulated in alginate was shown to successfully provide another level of control over release. These biopolymer systems that offer controlled delivery for antibodies and antibody fragments will be promising for many applications in drug delivery and regenerative medicine.