Showing papers by "Joshua E. Goldberger published in 2016"
TL;DR: A selfassembling biomaterial system in which peptide amphiphiles present a peptide derived from tenascin-C that promotes neurite outgrowth is described, which has significant potential in neuroregenerative medicine.
63 citations
TL;DR: In this paper, the role of ligand size and electronegativity on functionalization density, framework structure, and electronic structure was established through the synthesis of numerous ligand-functionalized germanane crystals.
Abstract: The covalent functionalization of 2D crystals is an emerging route for tailoring the electronic structure and generating novel phenomena. Understanding the influence of ligand chemistry will enable the rational tailoring of their properties. Through the synthesis of numerous ligand-functionalized germanane crystals, we establish the role of ligand size and electronegativity on functionalization density, framework structure, and electronic structure. Nearly uniform termination only occurs with small ligands. Ligands that are too sterically bulky will lead to partial hydrogen termination of the framework. With a homogeneous distribution of different ligands, the band gaps and Raman shifts are dictated by their relative stoichiometry in a pseudolinear fashion similar to Vegard’s law. Larger and more electronegative ligands expand the germanane framework, thereby lowering the band gap and Raman shift. Simply by changing the identity of the organic ligand, the band gap can be tuned by ∼15%, highlighting the po...
62 citations
TL;DR: This work shows that NaSn2As2 is a highly conducting 2D semimetal, with resistivities on the order of 10-6 Ω·m, and expands the family of exfoliatable 2D materials to layered van der Waals Zintl phases, opening up opportunities in electronics and spintronics.
Abstract: The discovery of new families of exfoliatable 2D crystals that have diverse sets of electronic, optical, and spin–orbit coupling properties enables the realization of unique physical phenomena in these few-atom-thick building blocks and in proximity to other materials. Herein, using NaSn2As2 as a model system, we demonstrate that layered Zintl phases having the stoichiometry ATt2Pn2 (A = group 1 or 2 element, Tt = group 14 tetrel element, and Pn = group 15 pnictogen element) and feature networks separated by van der Waals gaps can be readily exfoliated with both mechanical and liquid-phase methods. We identified the symmetries of the Raman-active modes of the bulk crystals via polarized Raman spectroscopy. The bulk and mechanically exfoliated NaSn2As2 samples are resistant toward oxidation, with only the top surface oxidizing in ambient conditions over a couple of days, while the liquid-exfoliated samples oxidize much more quickly in ambient conditions. Employing angle-resolved photoemission spectroscopy,...
45 citations
TL;DR: In this article, the effectiveness of different topochemical methods to maximize methyl-termination in GeCH3 was compared, and it was shown that a previously developed CH3I/H2O phase transfer route produces a small percentage of partially oxidized germanane.
Abstract: The topotactic transformation of Zintl phases such as CaGe2 into organic-terminated germanium graphane analogues using haloalkanes is a powerful route for generating new 2D optoelectronic and spintronic building blocks. However, uniform ligand coverage is necessary for optimizing the properties and stability of these single-atom-thick frameworks. Here, we compare the effectiveness of different topochemical methods to maximize methyl-termination in GeCH3. We show that a previously developed CH3I/H2O phase transfer route produces a small percentage of partially oxidized germanane. The partially oxidized termination is readily removed upon HCl treatment, which leads to Ge–Cl termination, but rapidly reoxidizes after exposure to the ambient atmosphere. We then show that a one-pot route with CH3I in distilled CH3CN solvent and at least six equivalents of H2O results in no oxidation. The GeCH3 prepared from this one-pot route also has an increased −CH3/–H ratio of termination from ∼90:10 to ∼95:5, is air-stable...
36 citations
TL;DR: This work demonstrates that GeH can be electronically doped by incorporating stoichiometric equivalents of phosphorus dopant atoms into the CaGe2 precursor, and predicts that the current distribution in top-contacted crystals is restricted to only the topmost, water activated crystal layers.
Abstract: The synthesis of germanane (GeH) has opened the door for covalently functionalizable 2D materials in electronics. Herein, we demonstrate that GeH can be electronically doped by incorporating stoichiometric equivalents of phosphorus dopant atoms into the CaGe2 precursor. The electronic properties of these doped materials show significant atmospheric sensitivity, and we observe a reduction in resistance by up to three orders of magnitude when doped samples are measured in water-containing atmospheres. This variation in resistance is a result of water activation of the phosphorus dopants. Transport measurements in different contact geometries show a significant anisotropy between in-plane and out-of-plane resistances, with a much larger out-of-plane resistance. These measurements along with finite element modeling results predict that the current distribution in top-contacted crystals is restricted to only the topmost, water activated crystal layers. Taken together, these results pave the way for future electronic and optoelectronic applications utilizing group IV graphane analogues.
29 citations
TL;DR: In this paper, the authors employed a four-probe thermal transport measurement method to obtain the basal-plane thermal conductivity of thin exfoliated GeH flakes and correlated the measurement results with the crystal structure.
Abstract: Germanane (GeH), a hydrogen-terminated layered germanium structure, has recently been synthesized. Here, we employed a four-probe thermal transport measurement method to obtain the basal-plane thermal conductivity of thin exfoliated GeH flakes and correlated the measurement results with the crystal structure. The obtained thermal conductivity increases with increasing temperature, suggesting that extrinsic grain boundary and defect scattering dominate over intrinsic phonon-phonon scattering. Annealing a polycrystalline GeH sample at 195 °C caused it to become amorphous, reducing the room-temperature thermal conductivity from 0.53 ± 0.09 W m−1 K−1, which is close to the value calculated for 16 nm grain size, to 0.29 ± 0.05 W m−1 K−1, which approaches the calculated amorphous limit in the basal plane thermal conductivity.
12 citations
TL;DR: The first early transition metal dicubane cluster was reported in this article, where electron paramagnetic resonance and magnetic susceptibility measurements showed that the cluster has one unpaired electron localized on a single V4+, which according to DFT simulations is the central bridging vanadium.
Abstract: The discovery of novel transition metal cubane clusters with different electron counts and topologies is of considerable importance due to the prevalence of this structure type in catalytic proteins. Here, we report the solvothermal synthesis and full characterization of [V7S8Cl2(en)8]Cl4 (en = ethylenediamine), the first early transition metal dicubane cluster. Electron paramagnetic resonance and magnetic susceptibility measurements show that the cluster has one unpaired electron localized on a single V4+, which according to DFT simulations is the central bridging vanadium. The remaining V3+ atoms feature significant metal–metal bonding.
4 citations
TL;DR: Cl4 is solvothermally synthesized from mixtures of VCl4, thiourea, and en (autoclave, 160 °C, 5 d; 61% yield) as mentioned in this paper.
Abstract: [V7S8Cl2(en)8]Cl4 is solvothermally synthesized from mixtures of VCl4, thiourea, and en (autoclave, 160 °C, 5 d; 61% yield).