Scanning tunneling microscopy/spectroscopy on Au nanoparticles assembled using lauryl amine (LAM) and octadecane thiol (ODT)

In this report, we demonstrate scanning tunneling microscopy and spectroscopy on thin films of lauryl amine (LAM) and octadecane thiol (ODT) protected gold nanoparticles. We show that the zero current in the I-V curves (measure of Coulomb blockade (CB) of the nanoparticles) depends on the properties of the spacer molecule. In both the cases the gap voltage and the tunneling current at which the images are obtained are quite different which is further confirmed from the fitting performed based on the orthodox theory. The values for the capacitance and charging energy obtained from the fitting for ODT capped particles are comparable to the values obtained using spherical capacitor model. In contrast, values of these parameters were found to differ for LAM capped nanoparticles. While imaging, ODT capped nanoparticles were observed to drag along the scan direction leading to ordering of particles. Images of LAM capped gold nanoparticles show local ordering in self-assembly of particles although no evidence of large scale ordering in spatial Fourier transform was seen. These observations suggest that nanoparticles with larger CB would be imaged nonevasively in contrast to small CB systems for which tip induced effects will be dominant. In both the systems the current was found to rise faster than theoretical curves based on the orthodox theory suggesting that mechanism of charge transfer in this case may involve field emission rather than tunneling through a rectangular barrier. An attempt has been made to explain charge transfer based on Fowler-Nordheim (F-N) plots of the I-V curves

Scanning tunneling microscopy/spectroscopy of titanium dioxide nanoparticulate film on Au(1 1 1) surface

Scanning tunneling microscopy (STM)/scanning tunneling spectroscopy (STS) of titanium dioxide nanoparticulate film on Au(1 1 1) surface is carried out yielding topography, I-V, dI/dV versus V and normalized dI/dV versus V. Isolated nanoparticles were found to exhibit semiconducting behavior with a band gap which varies from 1 to > 3.0 eV depending on the nature of substrate/nanoparticle/tip junction formation. Increase in the particulate density resulted into change in tunneling behavior from semiconducting to metallic as characterized by decrease in non-linearity in I-V curves and increase in average tunneling conductance. The results are discussed in terms of presence of adsorbed complexes on defect structure of TiO2 surface for low coverage and availability of additional transport paths between the particles at high coverage

Self-organization of polyaniline nanorods: Towards achieving a higher conductivity

We present a scanning tunnelling microscopy and spectroscopy study of polyaniline nanostructure. Our results show the possibility of achieving a high degree of self-organization in polyaniline nanorods in the undoped as well as the doped states. The spectroscopy results clearly establish a direct correlation between the extent of ordering and the density of states at the Fermi energy of the doped samples.Small angle x-ray scattering experiment helps to understand the formation of such self-organized structures

Semiconductor–Semimetal 2D/3D MoS₂/SrRuO₃(111) TMD/TMO Heterojunction-Based ReRAM Devices

We have designed and grown MoS2/SrRuO3(111) (MoS2/SRO(111)) semiconductor (SC)/semimetal (SM) heterostructures involving transition-metal dichalcogenide (TMD) and transition-metal oxide (TMO) partners for TMD-based electronic device application. MoS2 is directly grown on a polar SrRuO3(111)/c-Al2O3 substrate by pulsed laser deposition (PLD). A comparative evaluation of few-layer (FL) versus bulk (BL) MoS2 on polar SRO(111) was performed by using several chemical and physical characterizations. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) confirm the degenerate states in strained MoS2 caused by polar SRO(111). In-plane room-temperature resistivity of 1.83 and 1.39 μΩ-cm is obtained for FL and BL MoS2/SRO, respectively. Conducting atomic force microscopy (CAFM) was used to elucidate the distribution of in-plane conductive components. The electrical current across the CAFM-tip/MoS2/SRO(111) is primarily controlled by MoS2 and its interfaces with the tip metal on one side and the oxide semimetal on the other. We find an impressive ReRAM unipolar linear I–V characteristic in the case of FL MoS2/SRO (a sharp jump by a factor of 12), while in the BL MoS2/SRO (thicker overlayer) case, only a negligible effect is noted. Studies of the work function and Schottky barrier height (SBH) modulation due to the thickness variation of the semiconductor MoS2 at the SC/SM heterojunction are performed by the electrostatic force microscopy (EFM) to unveil the mechanism of the memristor-type I–V characteristics

Self-organization of polyaniline nanorods: towards achieving a higher conductivity

We present a scanning tunnelling microscopy and spectroscopy study of polyaniline nanostructure. Our results show the possibility of achieving a high degree of self-organization in polyaniline nanorods in the undoped as well as the doped states. The spectroscopy results clearly establish a direct correlation between the extent of ordering and the density of states at the Fermi energy of the doped samples. Small angle x-ray scattering experiment helps to understand the formation of such self-organized structures

Preparation of Ni₃S₂ and Ni₃S₂–Ni Nanosheets via Solution Based Processes

An easy and convenient preparation of nanometer-thick sheets of Ni₃S₂ and Ni₃S₂–Ni from solution processed molecularly thin sheets of Ni-thiolates is described. Both the Ni₃S₂ and Ni₃S₂–Ni possessed sheet-like morphologies and displayed room temperature ferromagnetic characteristics. The ferromagnetic nature of these samples was also confirmed by MFM studies, and AFM/TEM investigations substantiated the sheet-like morphology of the samples

Growth mechanism of cadmium sulfide nanocrystals

We investigate the growth kinetics of CdS nanocrystals in the quantum confinement regime using time-resolved small-angle X-ray scattering. In contrast to earlier reports for similar systems, we establish that the growth kinetics in this case follows the Lifshitz-Slyozov-Wagner theory, for not only growth of the average diameter of the nanocrystals but also the time dependence of the size distribution and the temperature dependence of the rate constant. This is the first rigorous example of the coarsening process in the quantum confinement ( < 5 nm) regime. Ab initio studies for the reaction pathways provide a microscopic understanding of this finding