Siwapon Srisonphan

Space charge neutralization by electron-transparent suspended graphene.

Graphene possesses many fascinating properties originating from the manifold potential for interactions at electronic, atomic, or molecular levels. Here we report measurement of electron transparency and hole charge induction response of a suspended graphene anode on top of a void channel formed in a SiO2/Si substrate. A two-dimensional (2D) electron gas induced at the oxide interface emits into air and makes a ballistic transport toward the suspended graphene. A small fraction (>~0.1%) of impinging electrons are captured at the edge of 2D hole system in graphene, demonstrating good transparency to very low energy (<3 eV) electrons. The hole charges induced in the suspended graphene anode have the effect of neutralizing the electron space charge in the void channel. This charge compensation dramatically enhances 2D electron gas emission at cathode to the level far surpassing the Child-Langmuirs space-charge-limited emission.

Rice (Oryza sativa L.) Seed Sterilization and Germination Enhancement via Atmospheric Hybrid Nonthermal Discharge Plasma

We designed a system to produce atmospheric hybrid cold-discharge plasma (HCP) based on microcorona discharge on a single dielectric barrier and applied it to inactivate microorganisms that commonly attach the rice seed husk. The cold-plasma treatment modified the surface of the rice seeds, resulting in accelerated germination and enhanced water imbibition. The treatment can operate under air-based ambient conditions without the need for a vacuum. The cold-plasma treatment completely inactivated pathogenic fungi and other microorganisms, enhancing the germination percentage and seedling quality. The final germination percentage of the treated rice seeds was ∼98%, whereas that of the nontreated seeds was ∼90%. Microcorona discharge on a single dielectric barrier provides a nonaggressive cold plasma that can be applied to organic materials without causing thermal and electrical damage. The hybrid nonthermal plasma is cost effective and consumes relatively little power, making it suitable for the surface sterilization and disinfection of organic and biological materials with large-scale compatibility.

Tuning the ballistic electron transport of spatial graphene–metal sandwich electrode on a vacuum-silicon-based device

Future high-speed electronic devices rely on the integration of hot-carrier generation and short transit time. Graphene is an attractive material because of its exceptionally high electron mobility along a 2D honeycomb lattice (in-plane transport). Here, we demonstrate the atomic and electrical interactions of graphene–metal (G–M) and metal–graphene–metal (M–G–M) sandwich electrodes on a vacuum-solid-state-based device (i.e., metal-oxide-Si (MOS) with a void channel) forming G–MOS and M–G–MOS, respectively. The combination of a graphene–metal electrode can produce an extremely high ballistic electron emission (∼106 A cm−2 at 1 V bias), traveling along the vertical direction perpendicular (out of plane) to the graphene mesh. The electron emission process is found to be very robust under low-voltage operation, even for emitters at ambient conditions. In addition, the proposed configurations exhibit electrostatic tuning of ballistic electron transport, governed either by space-charge-limited current or field-emission current, having the potential to significantly contribute to various nanoelectronic applications.

Microcorona Discharge-Mediated Nonthermal Atmospheric Plasma for Seed Surface Modification

By exploiting the physical effect of a highly nonuniform localized electric field and electron-initiated impact ionization on space charge, we generated homogeneous nonthermal plasma under ambient atmosphere. We evaluated the physical characteristics and evolution of microcorona discharge-induced nonthermal atmospheric plasma (NAP) based on a point-to-plane electrode in open air with two distinct configurations. High-voltage pulses were employed as the primary power source of corona discharge generation to reveal the fundamental mechanism, polarity effect and feasibility of using NAP for organic surface modification. Consequently, we employed NAP to modify the surface of rice (Oryza sativa L.) seeds to improve their wettability. The surface modification of the rice seeds was investigated via water apparent contact angle (ACA) and water imbibition (WI) measurements. The ACA and WI measurements revealed not only the improvement in the wetting properties but also the mutual relationships between and limitations of ACA and WI analysis. We found that the WI time reached saturation after a certain treatment time, called the threshold treatment time. Because vacuum conditions are not required, well-established NAP technology will garner interest in many fields, ranging from the life, environmental, and biomedical sciences to solid-state electronics applications.

Tuning Surface Wettability through Hot Carrier Initiated Impact Ionization in Cold Plasma

Advanced surface engineering aims to produce surfaces with well-controlled wettabilities; however, precise control over water imbibition (WI) and liquid spreading on patterned surfaces remains a challenge. Nonthermal atmospheric plasma (NAP) treatment can dramatically change wettability; however, for coated biological objects, such as seeds, plasma interaction is not entirely understood. Herein, we employed atmospheric hybrid cold plasma to elucidate how NAP fundamentally interacts with seed surfaces. We show that NAP can control WI and liquid spreading on seeds. By investigating two distinct seed surface structures and their permeabilities, we show that the modified-surface properties are primarily due to the combined effects of enhanced physical etching and chemical functionalization. We propose the tunable surface functionalization model based on electric field-assisted electron ion-initiated impact ionization enhancing the reactive species generation. Importantly, rice seeds are not damaged by plasma treatment, and 90% of treated seeds germinate upon artificial aging. The ability to control the wettability and liquid spreading of seed surfaces can help achieve seedlings of better quality, especially in difficult-to-grow regions, including those affected by drought. Well-controlled wettability and related attributes open up new avenues for the NAP treatment of a broad range of surfaces.

Polarity effect of pulsed corona discharge plasma on seed surface modification

This paper presents an experimental analysis and underlying mechanism of positive and negative pulsed corona discharge induced atmospheric non-thermal plasma. We designed a system based on point-plane configuration to produce direct corona discharge plasma (DCP) and hybrid corona discharge plasma (HCP) systems. The polarity effect of corona discharge for surface modification application on rice seeds was investigated under atmospheric dry air ambient. The reactive species under negative and positive corona discharge plasma were also studied for optimization design. The results show that only negative pulsed corona discharge is feasible for DCP system while both positive and negative pulsed corona discharge can be employed for in HCP system.

Vacuum electron-based photodiode

We have presented a detailed investigation of hybrid photodiode based on the combination of Gr/Si heterojunction and nanoscale vacuum device based on graphene-SiO2-Si (GrOS) field effect structure. We elucidate on the underlying mechanism of impact-ionization process in a two-Dimensional Electron Gas (2DEG) confined in quantum well, resulting in increasing the carrier multiplication and enabling ultrahigh speed optoelectronics.

Micro-macro bilateral in task space for delta robot by using forward and inverse kinematic

In this paper, the possibility of bilateral delta robot with micro-macro control to enhance human ability and transfer experience of operator is considered. Humans hand movement usually occur in three dimension space with high speed and small impendence from hands mass which is not capable with conventional serial robot that have slow speed and heavy moving part. As a result, parallel delta robot with properties of high speed and light moving part is chosen to suit humans hand behavioral. Micro-macro bilateral or scaling bilateral robot is a robot that scale the position or force from master robot to smaller slave robot. Convectional micro-macro in joint space or motor space bilateral system is not enough to control the task space of the delta robot due to non-linearity of delta robot kinematic. As a result, a micro-macro task space for delta robot in xyz plane by transform joint space into task space using inverse and forward kinematic of delta robot is proposed. Delta robot have rigid body properties which is necessary for detail work and can be considered appropriate micro-macro bilateral manipulator. However, direct kinematics of delta robot have around 40 solutions due to the complexity of pair of spherical joint that may present difficulty in design and manufacturing. Disturbance force is estimated by disturbance observer and scaled by conventional micro-macro method. The experiment and simulation is carry out to verify the proposed method.