Reconsideration of Nanowire Growth Theory at Low Temperatures

We present a growth model that describes the nanowire length and radius versus time in the absence of evaporation or scattering of semiconductor atoms (group III atoms in the case of III-V NWs) from the substrate, nanowire sidewalls or catalyst nanoparticle. The model applies equally well to low-temperature metal-catalyzed or selective area growth of elemental or III-V nanowires on patterned substrates. Surface diffusion transport and radial growth on the nanowire sidewalls are carefully considered under the constraint of the total material balance, yielding some new effects. The nanowire growth process is shown to proceed in two steps. In the first step, the nanowire length increases linearly with time and is inversely proportional to the nanowire radius squared and the nanowire surface density, without radial growth. In the second step, the nanowire length obeys the Chini equation, resulting in a non-linear increase in length with time and radial growth. The nanowire radii converge to a stationary value in the large time limit, showing a kind of size-narrowing effect. The model fits the data on the growth kinetics of a single self-catalyzed GaAs nanowire on a Si substrate well.

Hybrid ZnO/MoS2 Core/Sheath Heterostructures for Photoelectrochemical Water Splitting

The rational synthesis of semiconducting materials with enhanced photoelectrocatalytic efficiency under visible light illumination is a long-standing issue. ZnO has been systematically explored in this field, as it offers the feasibility to grow a wide range of nanocrystal morphology; however, its wide band gap precludes visible light absorption. We report on a novel method for the controlled growth of semiconductor heterostructures and, in particular, core/sheath ZnO/MoS2 nanowire arrays and the evaluation of their photoelectrochemical efficiency in oxygen evolution reaction. ZnO nanowire arrays, with a narrow distribution of nanowire diameters, were grown on FTO substrates by chemical bath deposition. Layers of Mo metal at various thicknesses were sputtered on the nanowire surface, and the Mo layers were sulfurized at low temperature, providing in a controlled way few layers of MoS2, in the range from one to three monolayers. The heterostructures were characterized by electron microscopy (SEM, TEM) and spectroscopy (XPS, Raman, PL). The photoelectrochemical properties of the heterostructures were found to depend on the thickness of the pre-deposited Mo film, exhibiting maximum efficiency for moderate values of Mo film thickness. Long-term stability, in relation to similar heterostructures in the literature, has been observed.

REARRANGEMENT OF THE CONFORMATIONAL STRUCTURE OF POLYAMPHOLYTES ON THE SURFACE OF A METAL NANOWIRE IN A TRANSVERSE MICROWAVE ELECTRIC FIELD

Molecular dynamics has been employed to study the rearrangement of the conformational structure of polyampholytes adsorbed on the surface of a gold nanowire with a periodic change in time of its polarity in the transverse direction at an ultrahigh frequency. The radial distributions of the atomic density of the polypeptide and its angular distributions on the nanowire surface have been calculated. At high temperatures, temporary fluctuations in the conformational structure of the adsorbed polyampholyte polypeptide were observed. In this case, for half the period of the nanowire polarity change, the macrochain conformation changed from dense enveloping of the nanowire to an elongated conformational structure along the dipole moment of the nanowire. At low temperature and the nanowire dipole moment, the swelling of the fringe of the adsorbed polyampholyte was observed with a displacement of most of its links to one side with respect to the plane perpendicular to the direction of the nanowire dipole moment and passing through its axis. At low temperature and high values of the nanowire dipole moment, the polyampholyte polypeptide was desorbed from the nanowire surface. An analytical model of conformational rearrangements of a polyampholyte Gaussian chain in the form of an external field perturbation theory is presented.

Indication of the Coronavirus Model Using a Nanowire Biosensor

The presented results indicate virus-like particles of the coronavirus (CVP) using a nanowire (NW) biosensor based on silicon-on-insulator technology. In the experiment, we used suspensions of CVP and of specific antibodies to the virus. Measurements of the current value of the field-effect transistor before and after the introduction of the CVP on the surface of the nanowire were performed. Results showed antibody + CVP complexes on the phase section with the surface of the nanowire modulate the current of the field-effect transistor; CVP has an electrically positive charge on the phase section “nanowire surface-viral suspension»; antibody + CVP complexes have an electrically negative charge on the phase section “nanowire surface-viral suspension”; the sensitivity of the biosensor is made up of 10−18 M; the time display was 200–300 s.

Highly Efficient Silicon Nanowire Surface Passivation by Bismuth Nano-Coating for Multifunctional Bi@SiNWs Heterostructures

A key requirement for the development of highly efficient silicon nanowires (SiNWs) for use in various kinds of cutting-edge applications is the outstanding passivation of their surfaces. In this vein, we report on a superior passivation of a SiNWs surface by bismuth nano-coating (BiNC) for the first time. A metal-assisted chemical etching technique was used to produce the SiNW arrays, while the BiNCs were anchored on the NWs through thermal evaporation. The systematic studies by Scanning Electron Microscopy (SEM), energy dispersive X-ray spectra (EDX), and Fourier Transform Infra-Red (FTIR) spectroscopies highlight the successful decoration of SiNWs by BiNC. The photoluminescence (PL) emission properties of the samples were studied in the visible and near-infrared (NIR) spectral range. Interestingly, nine-fold visible PL enhancement and NIR broadband emission were recorded for the Bi-modified SiNWs. To our best knowledge, this is the first observation of NIR luminescence from Bi-coated SiNWs (Bi@SiNWs), and thus sheds light on a new family of Bi-doped materials operating in the NIR and covering the important telecommunication wavelengths. Excellent anti-reflectance abilities of ~10% and 8% are observed for pure SiNWs and Bi@SiNWs, respectively, as compared to the Si wafer (50–90%). A large decrease in the recombination activities is also obtained from Bi@SiNWs heterostructures. The reasons behind the superior improvement of the Bi@SiNWs performance are discussed in detail. The findings demonstrate the effectiveness of Bi as a novel surface passivation coating, where Bi@SiNWs heterostructures are very promising and multifunctional for photovoltaics, optoelectronics, and telecommunications.

Molecular Cu(I)-Cu(II) Photosensitizer-Catalyst Photoelectrode for Water Oxidation

Photochemical splitting of H₂O to H₂ and O₂ is one approach to generate "solar fuels." Cu(II)-based electrocatalysts for water oxidation in aqueous solution have been studied previously, but photodriving these systems still remains a challenge. Light harvesting units can be employed for this purpose, that upon photoexcitation generate a high energy excited state and give rise to a charge separated state. In this work, a bis-diimine Cu(I)-based donor-chromophore-acceptor (D-C-A) system is synthesized, characterized, and applied as the light harvesting component of a photoanode. Here, this molecular assembly was integrated onto a zinc oxide (ZnO) nanowire surface on a fluorine-doped tin oxide (FTO) glass slide. Upon photoexcitation, chronoamperometric studies reveal that the integrated triad can inject electrons directly into the conduction band of zinc oxide generating oxidizing equivalents that are then transferred to a Cu(II) water oxidation catalyst in aqueous solution yielding O₂ from H₂O with a Faradaic efficiency of 76%. <br>

Molecular Cu(I)-Cu(II) Photosensitizer-Catalyst Photoelectrode for Water Oxidation

Photochemical splitting of H₂O to H₂ and O₂ is one approach to generate "solar fuels." Cu(II)-based electrocatalysts for water oxidation in aqueous solution have been studied previously, but photodriving these systems still remains a challenge. Light harvesting units can be employed for this purpose, that upon photoexcitation generate a high energy excited state and give rise to a charge separated state. In this work, a bis-diimine Cu(I)-based donor-chromophore-acceptor (D-C-A) system is synthesized, characterized, and applied as the light harvesting component of a photoanode. Here, this molecular assembly was integrated onto a zinc oxide (ZnO) nanowire surface on a fluorine-doped tin oxide (FTO) glass slide. Upon photoexcitation, chronoamperometric studies reveal that the integrated triad can inject electrons directly into the conduction band of zinc oxide generating oxidizing equivalents that are then transferred to a Cu(II) water oxidation catalyst in aqueous solution yielding O₂ from H₂O with a Faradaic efficiency of 76%. <br>