Yonatan Calahorra

Localized electromechanical interactions in ferroelectric P(VDF-TrFE) nanowires investigated by scanning probe microscopy

S.K.-N. and Y.C. are grateful for financial support from the European Research Council through an ERC Starting Grant (Grant No. ERC-2014-STG-639526, NANOGEN). R.A.W. thanks the EPSRC Cambridge NanoDTC, EP/G037221/1, for studentship funding. Q.J. is grateful for financial support through a Marie Sklodowska Curie Fellowship, H2020-MSCA-IF-2015-702868.

Direct observation of shear piezoelectricity in poly-l-lactic acid nanowires

Piezoelectric polymers are capable of interconverting mechanical and electrical energy, and are therefore candidate materials for biomedical applications such as sensors, actuators, and energy harvesters. In particular, nanowires of these materials are attractive as they can be unclamped, flexible and sensitive to small vibrations. Poly-l-lactic acid (PLLA) nanowires have been investigated for their use in biological applications, but their piezoelectric properties have never been fully characterised, even though macroscopic films and fibres have been shown to exhibit shear piezoelectricity. This piezoelectric mode is particularly interesting for in vivo applications where shear forces are especially relevant, and is similar to what has been observed in natural materials such as bone and DNA. Here, using piezo-response force microscopy (PFM), we report the first direct observation of shear piezoelectricity in highly crystalline and oriented PLLA nanowires grown by a novel template-wetting method. Our resu...

Surface depletion effects in semiconducting nanowires having a non-uniform radial doping profile

Doping profile has a significant effect on nanowire (NW) electrostatics, an effect that is expected to influence NW contact and transport properties. Herein, the electrostatic potential of nanowires (NWs) of non-uniform radial doping is calculated by two means: depletion approximation and a numerical calculation. Two profiles are considered: linear and exponential, corresponding to shallow and abrupt distributions; the results are compared to planar systems with similar doping profiles, and to uniformly doped NW systems. For a given average doping distribution, a non-uniform doping profile results in significantly lower carrier concentrations, an effect which intensifies with doping non-uniformity. Furthermore, in some cases, band diagrams obtained for the exponential doping profile vary greatly from any uniform doping, indicating that unique properties are expected for such NWs.

Catalyst shape engineering for anisotropic cross-sectioned nanowire growth.

The ability to engineer material properties at the nanoscale is a crucial prerequisite for nanotechnology. Hereunder, we suggest and demonstrate a novel approach to realize non-hemispherically shaped nanowire catalysts, subsequently used to grow InP nanowires with a cross section anisotropy ratio of up to 1:1.8. Gold was deposited inside high aspect ratio nanotrenches in a 5 nm thick SiNx selective area mask; inside the growth chamber, upon heating to 455 °C, the thin gold stripes agglomerated, resulting in an ellipsoidal dome (hemiellipsoid). The initial shape of the catalyst was preserved during growth to realize asymmetrically cross-sectioned nanowires. Moreover, the crystalline nature of the nanowire side facets was found to depend on the nano-trench orientation atop the substrate, resulting in hexagonal or octagonal cross-sections when the nano-trenches are aligned or misaligned with the [1̄10] orientation atop a [111]B substrate. These results establish the role of catalyst shape as a unique tool to engineer nanowire growth, potentially allowing further control over its physical properties.

Reduction of nanowire diameter beyond lithography limits by controlled catalyst dewetting

Catalyst assisted vapour-liquid–solid is the most common method to realize bottom-up nanowire growth; establishing a parallel process for obtaining nanoscale catalysts at pre-defined locations is paramount for further advancement towards commercial nanowire applications. Herein, the effect of a selective area mask on the dewetting of metallic nanowire catalysts, deposited within lithography-defined mask pinholes, is reported. It was found that thin disc-like catalysts, with diameters of 120–450 nm, were transformed through dewetting into hemisphere-like catalysts, having diameters 2–3 fold smaller; the process was optimized to about 95% yield in preventing catalyst splitting, as would otherwise be expected due to their thickness-to-diameter ratio, which was as low as 1/60. The catalysts subsequently facilitated InP and InAs nanowire growth. We suggest that the mask edges prevent surface migration mediated spreading of the dewetted metal, and therefore induce its agglomeration into a single particle. This result presents a general strategy to diminish lithography-set dimensions for NW growth, and may answer a fundamental challenge faced by bottom-up nanowire technology.

Research data supporting [Mapping piezoelectric response in nanomaterials using a dedicated non destructive scanning probe technique]

These files contain the raw data used to extract ND-PFM signals in Figure 2,3,4 of the manuscript. The MATALB code used to perform virtual lock-in operation is present.

Research data supporting [The effect of crystal structure on the electromechanical properties of piezoelectric Nylon-11 nanowires]

Research data supporting_Nylon NW SPM.zip file contains original SEM images and experimental data in the main text of the manuscript and supporting information. The original SEM images contain original scales and beam conditions at which SEM images were taken. raw-data.xlsx contains data files for the graphs, such as XRD, QNM, and PFM characterization, discussed in the main text of the manuscript and the supporting information.

Direct observation of shear piezoelectricity in poly-

S.K.-N., Y.C., and M.S. are grateful for financial support from the European Research Council through an ERC Starting Grant (Grant No. ERC-2014-STG-639526, NANOGEN). M.S. gratefully acknowledges studentship funding from the Cambridge Commonwealth, European and International Trust. Q.J. is grateful for financial support through a Marie Sklodowska Curie Fellowship, No. H2020-MSCAIF-2015-702868. This work was partially funded by the Cambridge Synthetic Biology Strategic Research Initiative through a SynBio Fund.

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Figures.zip file contains original SEM images and graphical images included in the main text and the supporting information of the manuscript. The original SEM images contain original scales and beam conditions at which SEM images were taken. SEM images in the manuscript and supporting information may have been taken as a whole or a part of the original images wherever apply. Likewise the scale in the manuscript images have been re‐drawn in order to enhance the clarity of the images, but depict true scale as they were in original. Data Files.zip contains data files for the graphs discussed in the main text and supporting information of the manuscript. Theoretical data. zip contains data file for the XRD plots and DFT theory for figure 5c and figure S1 asap

-lactic acid nanowires

Experimental data from investigation into shear piezoelectricity in PLLA nanowires. Results from characterisation using XRD, DSC and PFM are included, as are results from computational modelling.