Atmospheric pressure-spatial atomic layer deposition (AP-SALD) is a promising open-air deposition technique for high-throughput manufacturing of nanoscale films, yet the nucleation and property evolution in these films has not been studied in detail. In this work, in situ reflectance spectroscopy was implemented in an AP-SALD system to measure the properties of Zinc oxide (ZnO) and Aluminum oxide (Al 2 O 3 ) films during their deposition. For the first time, this revealed a substrate nucleation period for this technique, where the length of the nucleation time was sensitive to the deposition parameters. The in situ characterization of thickness showed that varying the deposition parameters can achieve a wide range of growth rates (0.1-3 nm/cycle), and the evolution of optical properties throughout film growth was observed. For ZnO, the initial bandgap increased when deposited at lower temperatures and subsequently decreased as the film thickness increased. Similarly, for Al 2 O 3 the refractive index was lower for films deposited at a lower temperature and subsequently increased as the film thickness increased. Notably, where other implementations of reflectance spectroscopy require previous knowledge of the film's optical properties to fit the spectra to optical dispersion models, the approach developed here utilizes a large range of initial guesses that are inputted into a Levenberg-Marquardt fitting algorithm in parallel to accurately determine both the film thickness and complex refractive index.

standard von Neumann architecture. [1][2][3][4][5] Among the different materials that have been developed, the study of synaptic devices based on 1D semiconductor nanomaterials is still very limited, with notable reports on carbon nanotubes, [6] Bi 1−x Sb x nanowires, [7] TiO 2 nanowires, [8] organic P 3 HT-polyethylene oxide coresheath nanowires, [9] etc. These studies form a solid foundation to the integration and assembly of 1D nanomaterials for large-scale neuromorphic computing application. However, due to their high surface-to-volume ratio, the electrical performance of semiconductor nanowire devices is strongly influenced by the nature of their surface. [10,11] Surface states of semiconductor nanowires, which are closely related to the morphology and sizes of nanowires, naturally exist due to dangling bonds or surface reconstruction of nanowires. Some surface defects or adsorbates can also lead to surface states on the nanowires. These surface states can produce randomly localized charges, which significantly affect the charge transport behavior, potentially causing band-bending between an electrode and the semiconductor nanowire or even pinning of the Fermi level. [10,12] These surface defects can cause variations of the contact behavior (i.e., Ohmic or Schottky), even for the same type of nanowire-electrode configuration. As a typical example, ZnO nanowires, which have been widely used in field effect transistors, [10,13,14] sensors, [15,16] photodetectors, [17,18] mersistors, [19][20][21] etc., have demonstrated contradictory contact behaviors on Au [22][23][24][25] and Ti [26,27] electrodes. Eliminating the effect of surface defects on semiconductor nanowire devices, especially the contact between electrodes and the nanowire is a major obstacle to achieving improved performance in these devices.In this research, we propose the introduction of an ultrathin metal oxide interfacial layer between Au electrodes and ZnO nanowires to minimize the electrical effect of surface defects on ZnO nanowires. An improved and symmetrical volatile threshold memristive behavior [28] is obtained which was further used to mimic some basic shortterm synaptic functionalities such as excitatory current response, paired-pulse facilitation and depression, and short-term plasticity, promising for neuromorphic computing applications. [29][30][31][32][33] One-dimensional semiconductor nanowires have been widely used as important building blocks in a number of devices. However, the performance of these devices is seriously hindered by the surface states/defects on the nanowires, which is a great obstacle to the realization of controllable and predictable characteristics. The introduction of an ultrathin metal oxide layer between Au electrodes and a ZnO nanowire is used to eliminate the surface effects of the nanowires, leading to improved volatile threshold switching performance. Study of the conduction mechanism demonstrates that the TiO x interfacial layer functions as a barrier between the electrodes and the nanowire, wherein th...

Atmospheric-pressure spatial atomic layer deposition (AP-SALD) and atmospheric-pressure spatial chemical vapor deposition (AP-SCVD) are rapid, open-air techniques for the deposition of conformal, pinhole-free films over large areas. In this work, a precursor nebulizer and an ozone generator are incorporated into an AP-SALD system to enable the deposition of tungsten oxide (WO3) films by AP-SCVD. The precursors bis(t-butylimido) bis(dimethylamino) tungsten(VI) and ozone are used with a film deposition temperature of 350 °C to achieve a growth per cycle of 1.2 Å/cycle. A bandgap of 3.26 eV and a refractive index of 2.36 were obtained, consistent with the previous reports for WO3 films. The pinhole-free films were found to be a mixture of hexagonal and monoclinic WO3, with an increasing monoclinic nature after annealing. Additionally, the as-deposited film was substoichiometric with an O/W ratio of 2.3, which increased to 2.36 after annealing at 450 °C. The successful open-air deposition of tungsten oxide via the incorporation of a precursor nebulizer and ozone generator paves the way for large-area deposition of tungsten oxide for commercial applications.

No abstract

No abstract