[en] A review on the mechanisms and characterization methods of electronic transport through self-assembled monolayers (SAMs) is presented. Using SAMs of alkanethiols in a nanometre scale device structure, tunnelling is unambiguously demonstrated as the main intrinsic conduction mechanism for defect-free large bandgap SAMs, exhibiting well-known temperature and length dependences. Inelastic electron tunnelling spectroscopy exhibits clear vibrational modes of the molecules in the device, presenting direct evidence of the presence of molecules in the device

[en] Inelastic electron tunneling spectroscopy (IETS) has become a premier analytical tool in the investigation of nano scale and molecular junctions. The IETS spectrum provides invaluable information about the structure, bonding, and orientation of component molecules in the junctions. One of the major advantages of IETS is its sensitivity and resolution at the level of single molecules. This review discusses how IETS is used to study molecular transport junctions and presents an overview of recent experimental studies.

[en] We investigated the effects of the structural defects intentionally created by electron-beam irradiation with an energy of 30 keV on the electrical properties of monolayer MoS2 field effect transistors (FETs). We observed that the created defects by electron beam irradiation on the MoS2 surface working as trap sites deteriorated the carrier mobility and carrier concentration with increasing the subthreshold swing value and shifting the threshold voltage in MoS2 FETs. The electrical properties of electron-beam irradiated MoS2 FETs were slightly improved by treating the devices with thiol-terminated molecules which presumably passivated the structural defects of MoS2. The results of this study may enhance the understanding of the electrical properties of MoS2 FETs in terms of creating and passivating defect sites.

[en] We studied organic resistive memory devices with interfacial oxide layers, the thickness of which depended on O₂ plasma treatment time. The different interfacial oxide thicknesses sequentially changed the ON and OFF states of the final memory devices. We found that the memory devices that had undergone additional plasma treatment showed higher ON/OFF ratios than devices without the treatment, which was due to the relatively large OFF resistance values. However, a long oxidation process widened the threshold voltage distribution and degraded the switching reproducibility. This indicates that the oxidation process should be carefully optimized to provide practical high-performance organic memory.

[en] We have investigated the effect of excimer laser annealing on the chemical bonding, electrical, and optical properties of ZnO nanowires. We demonstrate that after laser annealing on the ZnO nanowire field effect transistors, the on-current increases and the threshold voltage shifts in the negative gate bias direction. These electrical results are attributed to the increase of oxygen vacancies as n-type dopants after laser annealing, consistent with the shifts towards higher binding energies of Zn 2p and O 1s in the x-ray photoelectron spectroscopy analysis of as-grown nanowires and laser-annealed ZnO nanowires.

[en] We fabricated and characterized MoS_2 field effect transistors. First, we measured the electrical properties of MoS_2 field effect transistors (FETs) that were made with mechanically exfoliated MoS_2 flakes. Then, we deposited Au nanoparticles on the MoS_2 channel and measured the electrical properties. We observed whether the source-drain current increased or decreased after the Au particles were deposited. The deposited Au particles either formed an extra current path and increased the current or behaved as charge-withdrawing sites and decreased the current. Next, we deposited alkanethiol molecules on the Au particles to reduce the work function of the Au. Alkanethiol molecules are known to form a self-assembled monolayer on the Au surface, and the electric dipole moment of the molecules causes the work function of the Au to decrease. Au particles can capture electrons from the MoS_2 channel due to their high work function. However, the decreased work function of the Au particles subjected to alkanethiol treatment could cause captured electrons to be released from the Au particles to MoS_2. Therefore, the current increased after alkanethiol treatment. This study may provide useful methods to utilize surface treatments with particles and molecules to tailor the electrical properties of MoS_2-based FETs. (paper)

[en] We investigated the effects of passivation on the electrical characteristics of molybdenum disulfide (MoS₂) field effect transistors (FETs) under nitrogen, vacuum, and oxygen environments. When the MoS₂ FETs were exposed to oxygen, the on-current decreased and the threshold voltage shifted in the positive gate bias direction as a result of electrons being trapped by the adsorbed oxygen at the MoS₂ surface. In contrast, the electrical properties of the MoS₂ FETs changed only slightly in the different environments when a passivation layer was created using polymethyl methacrylate (PMMA). Specifically, the carrier concentration of unpassivated devices was reduced to 6.5 × 10¹⁵ cm⁻² in oxygen from 16.3 × 10¹⁵ cm⁻² in nitrogen environment. However, in PMMA-passivated devices, the carrier concentration remained nearly unchanged in the range of 1–3 × 10¹⁵ cm⁻² regardless of the environment. Our study suggests that surface passivation is important for MoS₂-based electronic devices. (paper)

[en] We fabricated 8 × 8 arrays of non-volatile resistive memory devices on commercially available Scotch^® Magic^™ tape as a flexible substrate. The memory devices consist of double active layers of Al₂O₃ with a structure of Au/Al₂O₃/Au/Al₂O₃/Al (50 nm/20 nm/20 nm/20 nm/50 nm) on attachable tape substrates. Because the memory devices were fabricated using only dry and low temperature processes, the tape substrate did not suffer from any physical or chemical damage during the fabrication. The fabricated memory devices were turned to the low resistance state at ∼3.5 V and turned to the high resistance state at ∼10 V with a negative differential resistance region after ∼5 V, showing typical unipolar non-volatile resistive memory behavior. The memory devices on the tape substrates exhibited reasonable electrical performances including a high ON/OFF ratio of 10⁴, endurance over 200 cycles of reading/writing processes, and retention times of over 10⁴ s in both the flat and bent configurations. (paper)

[en] We investigated the photoconductive characteristics of molybdenum disulfide (MoS₂) field-effect transistors (FETs) that were fabricated with mechanically exfoliated multi-layer MoS₂ flakes. Upon exposure to UV light, we observed an increase in the MoS₂ FET current because of electron–hole pair generation. The MoS₂ FET current decayed after the UV light was turned off. The current decay processes were fitted using exponential functions with different decay characteristics. Specifically, a fast decay was used at the early stages immediately after turning off the light to account for the exciton relaxation, and a slow decay was used at later stages long after turning off the light due to charge trapping at the oxygen-related defect sites on the MoS₂ surface. This photocurrent decay phenomenon of the MoS₂ FET was influenced by the measurement environment (i.e., vacuum or oxygen environment) and the electrical gate-bias stress conditions (positive or negative gate biases). The results of this study will enhance the understanding of the influence of environmental and measurement conditions on the optical and electrical properties of MoS₂ FETs. (paper)

[en] Due to the significant advantages of the molecule, such as small size, chemical synthesis, and compatibility with biological tissues, single-molecule devices have attracted widespread attention, and have become a complementary development direction of silicon-based electronic devices. This work provided a simplified method based on electrochemical corrosion to obtain a pair of nano-electrodes that can match the molecular size by controlling the voltage applied on the cathode/the anode and monitoring the current through the circuit in real-time. Because the thermal expansion coefficient of the gold electrodes is much larger than the substrate which supports the electrodes, the distance between the electrodes can be modulated by controlling the ambient temperature, that is to say, the connection and separation of the gold electrodes can be repeatedly operated by changing the ambient temperature. Furthermore, the modulation of the gap size between the electrodes via light illumination was successfully realized. The measured quantized conductance values indicate that the separation/reconnection of the individual metal atoms can be achieved via controlling the light intensity. The experimental results show that the gap size between electrodes can be precisely controlled via temperature/light modulation without the assist of high-precision instruments. Its two-dimensional configuration with planar substrate provides a new method to assist the integration of on-chip molecular devices. (authors)