Ballistic PbTe Nanowire Devices

Disorder is the primary obstacle in current Majorana nanowire experiments. Reducing disorder or achieving ballistic transport is thus of paramount importance. In clean and ballistic nanowire devices, quantized conductance is expected with plateau quality serving as a benchmark for disorder assessment. Here, we introduce ballistic PbTe nanowire devices grown using the selective-area-growth (SAG) technique. Quantized conductance plateaus in units of $2e^2/h$ are observed at zero magnetic field. This observation represents an advancement in diminishing disorder within SAG nanowires, as none of the previously studied SAG nanowires (InSb or InAs) exhibit zero-field ballistic transport. Notably, the plateau values indicate that the ubiquitous valley degeneracy in PbTe is lifted in nanowire devices. This degeneracy lifting addresses an additional concern in the pursuit of Majorana realization. Moreover, these ballistic PbTe nanowires may enable the search for clean signatures of the spin-orbit helical gap in future devices

Observation of plateau regions for zero bias peaks within 5% of the quantized conductance value 2e2/h2e^2/h

Probing an isolated Majorana zero mode is predicted to reveal a tunneling conductance quantized at $2e^2/h$ at zero temperature. Experimentally, a zero-bias peak (ZBP) is expected and its height should remain robust against relevant parameter tuning, forming a quantized plateau. Here, we report the observation of large ZBPs in a thin InAs-Al hybrid nanowire device. The ZBP height can stick close to $2e^2/h$, mostly within 5% tolerance, by sweeping gate voltages and magnetic field. We further map out the phase diagram and identify two plateau regions in the phase space. Our result constitutes a step forward towards establishing Majorana zero modes.Comment: Raw data and processing codes within this paper are available at https://doi.org/10.5281/zenodo.654697

Combination effects of graphene and layered double hydroxides on intumescent flame-retardant poly(methyl methacrylate) nanocomposites

A novel intumescent flame-retardant poly(methyl methacrylate) (PMMA) nanocomposite has been prepared via in situ polymerization by incorporating intumescent flame retardants (IFRs), graphene and layered double hydroxides (LDHs). Results from X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that a fine dispersion of IFR particles, intercalated LDHs and exfoliated graphene is achieved in the PMMA matrix. Thermal and flammability properties of PMMA nanocomposite were investigated using thermogravimetry, cone calorimetry, limiting oxygen index (LOI) and vertical burning (UL-94). The use of IFRs in combination with graphene and LDHs in the PMMA matrix improves greatly the thermal stability and flame retardant properties of the nanocomposites. The PMMA/IFR/RGO/LDH nanocomposites, filled with 10. wt.% IFRs, 1. wt.% graphene and 5. wt.% LDHs, achieve the LOI value of 28.2% and UL-94 V1 grade. Compared with neat PMMA, the PHRR of PMMA/IFRs/RGO/LDHs is reduced by about 45%, while the mechanical properties of PMMA/IFR/RGO/LDH nanocomposites exhibit almost no deterioration. The results from scanning electronic microscopy (SEM) confirm that the compact and dense intumescent char enhanced with LDHs and graphene nanosheets is formed for the PMMA/IFR/RGO/LDH nanocomposites during combustion, which inhibits the transmission of heat and mass when exposed to flame or heat source, and thus improves the flame retardant properties of the nanocomposites

Ultrafast growth of single-crystal graphene assisted by a continuous oxygen supply

Graphene has a range of unique physical properties(1,2) and could be of use in the development of a variety of electronic, photonic and photovoltaic devices(3-5). For most applications, large-area high-quality graphene films are required and chemical vapour deposition (CVD) synthesis of graphene on copper surfaces has been of particular interest due to its simplicity and cost effectiveness(6-15). However, the rates of growth for graphene by CVD on copper are less than 0.4 mu m s(-1), and therefore the synthesis of large, single-crystal graphene domains takes at least a few hours. Here, we show that single-crystal graphene can be grown on copper foils with a growth rate of 60 mu m s(-1). Our high growth rate is achieved by placing the copper foil above an oxide substrate with a gap of similar to 15 mu m between them. The oxide substrate provides a continuous supply of oxygen to the surface of the copper catalyst during the CVD growth, which significantly lowers the energy barrier to the decomposition of the carbon feedstock and increases the growth rate. With this approach, we are able to grow single-crystal graphene domains with a lateral size of 0.3 mm in just 5 s.ope