Ruonan Ma

Synthesis of high quality n-type CdS nanobelts and their applications in nanodevices

High quality n-type CdS nanobelts (NBs) were synthesized via an in situ indium doping chemical vapor deposition method and fabricated into field effect transistors (FETs). The electron concentrations and mobilities of these CdS NBs are around (1.0x10(16)-3.0x10(17))/cm(3) and 100-350 cm(2)/V s, respectively. An on-off ratio greater than 10(8) and a subthreshold swing as small as 65 mV/decade are obtained at room temperature, which give the best performance of CdS nanowire/nanobelt FETs reported so far. n-type CdS NB/p(+)-Si heterojunction light emitting diodes were fabricated. Their electroluminescence spectra are dominated by an intense sharp band-edge emission and free from deep-level defect emissions. (c) 2006 American Institute of Physics.

Non-thermal plasma-activated water inactivation of food-borne pathogen on fresh produce.

Non-thermal plasma has been widely considered to be an effective method for decontamination of foods. Recently, numerous studies report that plasma-activated water (PAW) also has outstanding antibacterial ability. This study presents the first report on the potential of PAW for the inactivation of Staphylococcus aureus (S. aureus) inoculated on strawberries. PAW treatments achieved a reduction of S. aureus ranging from 1.6 to 2.3 log at day-0 storage, while 1.7 to 3.4 log at day-4 storage. The inactivation efficiency depended on the plasma-activated time for PAW generation and PAW-treated time of strawberries inoculated with S. aureus. LIVE/DEAD staining and scanning electron microscopy results confirm that PAW could damage the bacterial cell wall. Moreover, optical emission spectra and oxidation reduction potential results demonstrate the inactivation is mainly attributed to oxidative stress induced by reactive oxygen species in PAW. In addition, no significant change was found in color, firmness and pH of the PAW treated strawberries. Thus, PAW can be a promising alternative to traditional sanitizers applied in the fresh produce industry.

A study of oxidative stress induced by non-thermal plasma-activated water for bacterial damage

Ar/O2 (2%) cold plasma microjet was used to create plasma-activated water (PAW). The disinfection efficacy of PAW against Staphylococcus aureus showed that PAW can effectively disinfect bacteria. Optical emission spectra and oxidation reduction potential results demonstrated the inactivation is attributed to oxidative stress induced by reactive oxygen species in PAW. Moreover, the results of X-ray photoelectron spectroscopy, atomic absorption spectrometry, and transmission electron microscopy suggested that the chemical state of cell surface, the integrity of cell membrane, as well as the cell internal components and structure were damaged by the oxidative stress.

Electrical properties of Cu doped p-ZnTe nanowires

Single crystalline zincblende p-ZnTe nanowires (NWs) were synthesized via the vapour phase transport method. Based on either as-grown or Cu doped ZnTe NWs, single NW field effect transistors were fabricated and they were used to study the electrical properties of ZnTe NWs. Electrical transport measurements show that the as-grown ZnTe NWs are of p-type and very high resistivity. After 30 min immersion in Cu(NO3)2 solution, their conductivity can be increased by about three orders of magnitude. The hole concentrations of the p-type ZnTe nanowires could be controlled in a range from 7.0 × 1017 to 3.5 × 1018 cm−3 by changing the immersion duration. The doped p-type ZnTe NWs may have potential applications in nanoscale electronic and optoelectronic devices.

Schottky junction photovoltaic devices based on CdS single nanobelts

Schottky junction photovoltaic (PV) devices were fabricated on single CdS nanobelts (NBs). Au was used as the Schottky contact, and In/Au was used as the ohmic contact to CdS NB. Typically, the Schottky junction exhibits a well-defined rectifying behavior in the dark with a rectification ratio greater than 10(3) at +/- 0.3 V; and the PV device exhibits a clear PV behavior with an open circuit photovoltage of about 0.16 V, a short circuit current of about 23.8 pA, a maximum output power of about 1.6 pW, and a fill factor of 42%. Moreover, the output power can be multiplied by connecting two or more of the Schottky junction PV devices, made on a single CdS NB, in parallel or in series. This study demonstrates that the 1D Schottky junction PV devices, which have the merits of low cost, easy fabrication and material universality, can be an important candidate for power sources in nano-optoelectronic systems.

Enhancement-mode metal-semiconductor field-effect transistors based on single n-CdS nanowires

Enhancement-mode (E-mode) metal-semiconductor field-effect transistors (MESFETs) based on single nanowires (NWs) were reported. The single NW used is n-CdS NW. Source-drain channel of the nano-MESFET is pinched off by the top surrounding Schottky gate at zero bias. When Schottky gate voltage (VG) changes from 0to0.25V, the source-drain current increases exponentially with VG, and an on/off current ratio of 5×103 is obtained. The maximum transconductance is 14.6nA∕V, and the gate leakage current is lower than source-drain current by more than two orders of magnitude. Their results suggest a way of fabricating E-mode nano-field-effect transistors.

Effect of plasma activated water on the postharvest quality of button mushrooms, Agaricus bisporus.

Non-thermal plasma is a new approach to improving microbiological safety while maintaining the sensory attributes of the treated foods. Recent research has reported that plasma activated water (PAW) can also efficiently inactivate a wide variety of microorganisms. This study invested the effects of plasma-activated water soaking on the postharvest preservation of button mushrooms (Agaricus bisporus) over seven days of storage at 20°C. Plasma activated water reduced the microbial counts by 1.5 log and 0.5 log for bacteria and fungi during storage, respectively. Furthermore, the corresponding physicochemical and biological properties were assessed between plasma activated water soaking groups and control groups. The results for firmness, respiration rate and relative electrical conductivity suggested that plasma activated water soaking can delay mushroom softening. Meanwhile, no significant change was observed in the color, pH, or antioxidant properties of A. bisporus treated with plasma activated water. Thus, plasma activated water soaking is a promising method for postharvest fresh-keeping of A. bisporus.

Bactericidal Effects against S. aureus and Physicochemical Properties of Plasma Activated Water stored at different temperatures.

Water activated by non-thermal plasma creates an acidified solution containing reactive oxygen and nitrogen species, known as plasma-activated water (PAW). The objective of this study was to investigate the effects of different storage temperatures (25 °C, 4 °C, −20 °C, −80 °C) on bactericidal activities against S. aureus and physicochemical properties of PAW up to 30 days. Interestingly, PAW stored at −80 °C yielded the best antibacterial activity against Staphylococcus aureus, 3~4 log reduction over a 30-day period after PAW generation; meanwhile, PAW stored at 25 °C, 4 °C, and −20 °C, respectively, yielded 0.2~2 log decrease in cell viability after the same exposure and storage time. These results were verified by scanning electron microscope (SEM). The physicochemical properties of PAW stored at different temperatures were evaluated, including pH, oxidation reduction potential (ORP), and hydrogen peroxide, nitrate, nitrite anion and NO radical levels. These findings suggested that bacterial activity of PAW stored at 25 °C, 4 °C, −20 °C decreased over time, and depended on three germicidal factors, specifically ORP, H2O2, and NO3−. Moreover, PAW stored at −80 °C retained bactericidal activity, with NO2− contributing to bactericidal ability in association with H2O2. Our findings provide a basis for PAW storage and practical applications in disinfection and food preservation.

High-performance nanowire complementary metal-semiconductor inverters

We demonstrated the construction of complementary metal-semiconductor (CMES) inverters with single n- and p-type nanowires (NWs) on the same chip. A single p-type NW was assembled by the side of an n-type NW via the electric field assembly method. n- and p-channel metal-semiconductor field-effect transistors were fabricated with n- and p-type NWs, respectively. Based on this, high-performance NW CMES NOT logic gate (inverter) was built. The NW CMES inverters have low operating voltage (≤2 V), high voltage gain (≥7), and low static power dissipation (≤0.3 nW).

An evaluation of anti-oxidative protection for cells against atmospheric pressure cold plasma treatment

With the development of plasma medicine, safety issues are emerging as a serious concern. In this study, both intracellular (genetic engineering) and extracellular (scavengers) measures were tested in an effort to determine the best protection for cells against plasma-induced oxidative stress. All results of immediate reactive species detection, short term survival and long term proliferation, suggest that intracellular pathways are superior in reducing oxidative stress and cell death. This work provides a potential mechanism to enhance safety and identifies precautionary measures that should be taken in future clinical applications of plasmas.