Memristive feature and mechanism induced by laser-doping in defect-free 2D semiconductor materials

Memristors as non-volatile memory devices have gained numerous attentions owing to their advantages in storage,in-memory computing, synaptic applications, etc. In recent years, two-dimensional(2D) materials with moderate defects have been discovered to exist memristive feature. However, it is very difficult to obtain moderate defect degree in 2D materials, and studied on modulation means and mechanism becomes urgent and essential. In this work, we realized memristive feature with a bipolar switching and a configurable on/off ratio in a two-terminal MoS_(2) device(on/off ratio ~100), for the first time, from absent to present using laser-modulation to few-layer defect-free MoS_(2)(about 10 layers), and its retention time in both high resistance state and low resistance state can reach 2×10^(4) s. The mechanism of the laser-induced memristive feature has been cleared by dynamic Monte Carlo simulations and first-principles calculations. Furthermore, we verified the universality of the laser-modulation by investigating other 2D materials of TMDs. Our work will open a route to modulate and optimize the performance of 2D semiconductor memristive devices.

Experimental Research on Plasma Induced by TEA CO_2 Laser Propulsion

Results in the air-breathing propulsion experiments with a parabolic light craft and a self-made UV-preionized 100 J TEA CO2 laser device are presented. Air disturbance and the spectrum of the plasma after the interaction of pulsed laser radiation with the light craft were studied. It was found that the focal length of the parabolic light craft had a significant effect on the air-disturbance. Two shock waves were detected for the longer focal length, while only one shock wave detected for the short focal length. The spectrum of the laser-induced plasma, the distribution of the characteristic lines, and the temporal behaviors of the air plasma were studied in detail. The results showed that, the evolution of the laser-induced plasma lasted 20μs, and the plasma spectrum would reach the maximum intensity at 7μs.

Three-dimensional transient simulation of CO_(2) laser tissue vaporization and experimental evaluation with a hydrogel phantom

A quantitative analysis method of CO_(2) laser treatments promotes laser treatment performance and rapid clinical application of novel treatment devices.The in silico clinical trial approach,which is based on computational simulation of light-tissue interactions using the mathematical model,can provide quantitative data.Although several simulation methods of laser tissue vaporization with CO_(2) laser treatments have been proposed,validations of the CO_(2) laser wavelength have been insuffcient.In this study,we demonstrated a tissue vaporization simulation using a CO_(2) laser and performed the experimental validation using a hydrogel phantom with constant physical parameters to evaluate the simulation accuracy of the vaporization process.The laser tissue vaporization simulation consists of the calculation of light transport,photothermal conversion,thermal diffusion,and phase change in the tissue.The vaporization width,depth,and area with CO_(2) laser irradiation to a tissue model were simulated.The simulated results differed from the actual vaporization width and depth by approximately 20%and 30%,respectively,because of the solubilization of the hydrogel phantom.Alternatively,the simulation vaporization area for all light irradiation parameters,which is related to the vaporization amount,agreed well with the actual vaporization values.These results suggest that the computational simulation can be used to evaluate the amount of tissue vaporization in the safety and effectiveness analysis of CO_(2) laser treatments.

Spectral Efficiency of Extreme Ultraviolet Emission from CO_2 Laser-Produced Tin Plasma Using a Grazing Incidence Flat-Field Spectrograph

A grazing incidence flat-field spectrograph using a concave grating was constructed to measure extreme ultraviolet （EUV） emission from a CO 2 laser-produced tin plasma throughout the wavelength region of 5 nm to 20 nm for lithography. Spectral efficiency of the EUV emission around 13.5 nm from plate, cavity, and thin foil tin targets was studied. By translating the focusing lens along the laser axis, the dependence of EUV spectra on the amount of defocus was investigated. The results showed that the spectral efficiency was higher for the cavity target in comparison to the plate or foil target, while it decreased with an increase in the defocus distance. The source＇s spectra and the EUV emission intensity normalized to the incident pulse energy at 45 from the target normal were characterized for the in-band （2% of bandwidth） region as a function of laser energy spanning from 46 mJ to 600 mJ for the pure tin plate target. The energy normalized EUV emission was found to increase with the increasing incident pulse energy. It reached the optimum value for the laser energy of around 343 mJ, after which it dropped rapidly.

Electrokinetic-mechanism of water and furfural oxidation on pulsed laser-interlaced Cu_(2)O and CoO on nickel foam

The electrocatalytic oxidation of biomass-derived furfural(FF)feedstocks into 2-furoic acid(FA)holds immense industrial potential in optics,cosmetics,polymers,and food.Herein,we fabricated Co O/Ni O/nickel foam(NF)and Cu_(2)O/Ni O/NF electrodes via in situ pulsed laser irradiation in liquids(PLIL)for the bifunctional electrocatalysis of oxygen evolution reaction(OER)and furfural oxidation reaction(FOR),respectively.Simultaneous oxidation of NF surface to NiO and deposition of CoO and/or Cu_(2)O on NF during PLIL offer distinct advantages for enhancing both the OER and FOR.CoO/NiO/NF electrocatalyst provides a consistently low overpotential of~359 m V(OER)at 10 m A/cm^(2),achieving the maximum FA yield(~16.37 m M)with 61.5%selectivity,79.5%carbon balance,and a remarkable Faradaic efficiency of~90.1%during 2 h of FOR at 1.43 V(vs.reversible hydrogen electrode).Mechanistic pathway via in situ electrochemical-Raman spectroscopy on CoO/NiO/NF reveals the involvement of phase transition intermediates(NiOOH and CoOOH)as surface-active centers during electrochemical oxidation.The carbonyl carbon in FF is attacked by hydroxyl groups to form unstable hydrates that subsequently undergo further oxidation to yield FA products.This method holds promise for large-scale applications,enabling simultaneous production of renewable building materials and fuel.

A Case of Refractory Childhood Glaucoma Secondary to Weill-Marchesani Syndrome:Management with Combined CO_(2) Laser-Assisted Sclerectomy Surgery and Trabeculectomy

A 2-year-old girl was diagnosed as Weill-Marchesani syndrome with typical systemic features of short stature,short and stubby hands and feet,language disorders and mental retardation.He developed bilateral angle closure glaucoma,ectopia lentis and suffered visual loss from the ocular features of Weill-Marchesani syndrome.The child was successfully treated by combined CO_(2) laser-assisted sclerectomy surgery and trabeculectomy.

CO_2 laser-micro plasma arc hybrid welding for galvanized steel sheets

A laser lap welding process for zinc-coated steel has a well-known unsolved problem-porosity formation. The boiling temperature of coated zinc is lower than the melting temperature of the base metal, which is steel. In the autogenous laser welding, the zinc vapor generates from the lapped surfaces expels the molten pool and the expulsion causes numerous weld defects, such as spatters and blow holes on the weld surface and porosity inside the welds. The laser-arc hybrid welding was suggested as an alternative method for the laser lap welding because the arc can preheat or post-beat the weldment according to the arrangement of the laser beam and the arc. CO2 laser-micro plasma hybrid welding was applied to the lap welding of zinc-coated steel with zero-gap. The relationships among the weld quality and process parameters of the laser-arc arrangement, and the laser-arc interspacing distance and arc current were investigated using a full-factorial experimental design. The effect of laser-arc arrangement is dominant because the leading plasma arc partially melts the upper steel sheets and vaporizes or oxidizes the coated zinc on the lapped surfaces. Compared with the result from the laser-TIG hybrid welding, the heat input from arc can be reduced by 40%.

Influence of secondary treatment with CO_2 laser irradiation for mitigation site on fused silica surface

The ablation debris and raised rim, as well as residual stress and deep crater will be formed during the mitigation of damage site with a CO2 laser irradiation on fused silica surface, which greatly affects the laser damage resistance of optics. In this study, the experimental study combined with numerical simulation is utilized to investigate the effect of the secondary treatment on a mitigated site by CO2laser irradiation. The results indicate that the ablation debris and the raised rim can be completely eliminated and the depth of crater can be reduced. Notable results show that the residual stress of the mitigation site after treatment will reduce two-thirds of the original stress. Finally, the elimination and the controlling mechanism of secondary treatment on the debris and raised rim, as well as the reasons for changing the profile and stress are analyzed. The results can provide a reference for the optimization treatment of mitigation sites by CO2laser secondary treatment.

Investigations on MoS_(2)plasma by infra-red pulsed laser irradiation in high vacuum

MoS_(2)targets were irradiated by infra-red(IR)pulsed laser in a high vacuum to determine hot plasma parameters,atomic,molecular and ion emission,and angular and charge state distributions.In this way,pulsed laser deposition(PLD)of thin films on graphene oxide substrates was also realized.An Nd:YAG laser,operating at the 1064 nm wavelength with a 5 ns pulse duration and up to a 1 J pulse energy,in a single pulse or at a 10 Hz repetition rate,was employed.Ablation yield was measured as a function of the laser fluence.Plasma was characterized using different analysis techniques,such as time-of-flight measurements,quadrupole mass spectrometry and fast CCD visible imaging.The so-produced films were characterized by composition,thickness,roughness,wetting ability,and morphology.When compared to the MoS_(2)targets,they show a slight decrease of S with respect to Mo,due to higher ablation yield,low fusion temperature and high sublimation in vacuum.The pulsed IR laser deposited Mo Sx(with 1<x<2)films are uniform,with a thickness of about 130 nm,a roughness of about 50 nm and a higher wettability than the MoS_(2)targets.Some potential applications of the pulsed IR laser-deposited Mo Sx films are also presented and discussed.

Behavior of vapor/plasma within the keyhole and above the workpiece during CO_2 laser penetration welding

In this paper, a high-speed camera and an optical emission monitor were used to study the behavior of vapor/ plasma during CO2 laser welding of SUS304 stainless steel. Results of optical emission from vapor/plasma show that two characteristic frequency bands exist, 100 -500 Hz and 1 500 -3 500 Hz. At the same time, the changing images of vapor/ plasma and bottom pool also confirm that there are two different fluctuation frequency bands. One of the frequency bands represents the characteristic of vapor/plasma within the keyhole, and it is within 167 -500 Hz. Another frequency band is within 1 500 - 3 500 Hz, and it obviously derives from the shielding gas. Some factors may cause these frequency differences between the keyhole plasma and the shielding gas plasma. One of them is that the vapor/plasma pressure within the keyhole will increase slowly.

A study on the porosity of CO_2 laser welding of titanium alloy

The CO2 laser welding of BT20 titanium alloy and Ti-23Al-17Nb titanium aluminide was conducted to investigate into the porosity in titanium alloy weld. The results show that there are two sorts of porosities observed in welds of titanium alloy laser welding based on the microscopic characteristics of the porosities. One is the metallurgical porosity with round and smooth inner wall, which results from the surface contamination. The other is the processing porosity with irregular and rough inner wall that displays the trace of the pool flowing, which results from the ruffle on the keyhole wall gathering together locally and closing down the gas in the keyhole into bubbles because of the keyhole fluctuating. The CO2 laser welding could break down easily the surface oxide film and produce little metallurgical porosity, but produces easily processing porosity when partial penetration or unstable-full penetration laser welding is conducted, which always occurs in the center of weld.

Macrostructural and microstructural features of 1000 MPa grade TRIP steel joint by CO_2 laser welding

Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.

Damage Mechanism of Al_2O_3 Ceramic Coatings Irradiated by CO_2 CW Laser

Rules and mechanism of damage in Al2O3 coatings irradiated by CO2 CW laser are studied in order to improve the ability of parts of equipment standing against the high power laser. Al2O3 coatings were sprayed by air plasma spray（APS） on the 45^# steel substrate, and then were irradiated by CO2 CW laser from 795 W/cm^2 to 31 830 W/cm^2. As the output power of the laser is increasing, its porosity is increasing and cracks are appearing and spreading quickly, And also the phase will transform from γ-Al2O3 to a-Al2O3 in the damaged areas. When the energy density is 17 507 W/cm^2, the coatings are destroyed completely. The thermal infection field on substrate is rather small. The laser energy is depleted by the phase transformation and cracks in Al2O3 coatings during the laser thermal shock.

High temperature thermoelectric properties of highly c-axis oriented Bi_2Sr_2Co_2O_y thin films fabricated by pulsed laser deposition

High-temperature thermoelectric transport property measurements have been performed on the highly c-axis oriented Bi2Sr2Co20v thin films prepared by pulsed laser deposition on LaA1Oa （001）. Both the electric resistivity p and the seebeck coefficient S of the film exhibit an increasing trend with the temperature from 300 K-1000 K and reach up to 4.8 m. cm and 202 V/K at 980 K, resulting in a power factor of 0.85 mW/mK which are comparable to those of the single crystalline samples. A small polaron hopping conduction can be responsible for the conduction mechanism of the film at high temperature. The results demonstrate that the Bi2Sr2Co2Oy thin film has potential application has high temperature thin film thermoelectric devices,

Irradiation effects of CO_2 laser parameters on surface morphology of fused silica

To understand the surface morphology evolution of fused silica induced by 10.6μm CO2 laser irradiation at different parameters, this paper reports that optical microscopy, profilometry, and hydrophilicity tests are utilized to characterize the surface structure and roughness of the laser irradiated area. The results show that three typical surface morphologies and two typical hydrophilicity test images are observed at different laser powers and pulse durations. The correlations between surface temperature and surface morphology as well as hydrophilicity behaviours are presented. The different hydrophilicity behaviours are related to surface structures of the laser-induced crater and thermal diffusion area. The thermal diffusion length monotonously increases with increasing laser power and pulse duration. The crater width is almost determined by the laser beam size. The crater depth is more sensitive to the laser power and pulse duration than the crater width.

CO_2 Laser Collective Thomson Scattering Diagnostics on the HT-7 Tokamak

A CW CO2 laser collective Thomson scattering diagnostics was developed to measure plasma density fluctuations on the HT-7 tokamak. The design and construction of CO2 laser scattering apparatus is described. The laser source is a continuous-wave CO2 laser with a cavity length of 1.9 m and a power output of about 10 W at 10.6 μm. The k-resolution of the system is △k ≈ 3.2 cm-1. The preliminary data from the diagnostic is presented.

IR Spectra Analysis of SiO_2-TiO_2-GeO_2 Gel Glass of CO_2 Laser Transmitting Hollow Waveguide

Both titanium and germanium were introduced into silicon dioxide system by sol-gel method to move its region of anomalous dispersion caused by IR resonance absorption towards the wavelength of CO 2 laser.It is indicated by IR absorption spectra that as the content of SiO 2 decreases in this glass system TiO 2 and GeO 2 tends to exist in their own phases.As for the gel glass with a composition of 40SiO 2·30TiO 2·30GeO 2,when the temperature is below 600℃,germanium atoms exist mainly in Ge-O-Ge bonds.With the temperature increasing from 800℃ to 1000℃, titanium atoms in Si-O-Ti bonds almost transform into Ti-O-Ti bonds.Furthermore,a large number of Si-O-Ti and Si-O-Ge bonds formed when the temperature approaches 800℃,which makes a notable IR absorption band round the wavelength of CO 2 laser.Therefore, sol-gel based SiO 2-TiO 2-GeO 2 gel glass is a candidate material for CO 2 laser hollow waveguide.

STUDY ON Na_2O-GeO_2-SiO_2-PbO GLASSES USED AS THE CLADDING MATERIALS OF HOLLOW WAVEGUIDES FOR TRANSMITTING CO_2 LASER

In this paper a new kind of mid - infrared fiber material is reported. The reflective coefficients (R) of glasses in the system Na2O - ZnO - GeO2-SiO2-PbO have been measured-the refractive index becomes less than unity at 1180 - 900cm-1 range because of the existence of anomalous dispersion. The optical losses of hollow waveguides were calculated,the predicted losses at 940cm-1are 0. 65 and 0. 081B/ m as the inner diameter of fiber is 0. 5 and 1. 0mm respectively. The glasses can be used as the cladding materials of hol-low waveguides for transmitting CO2 laser from the measurements of characteristic temperatures, coefficient of expansion and chemical durability.

CO_(2)LASER PLUS PHOTODYNAMIC THERAPY VERSUS CO_(2)LASER IN THE TREATMENT OF CONDYLOMA ACUMINATUM:A RANDOMIZED COMPARATIVE STUDY

To compare the efficacy and safety of CO_(2)laser plus 5-aminolevulinic acid(ALA)photodynamic therapy(PDT)with CO_(2)laser for the treatment of multiple condyloma acuminatum(CA),120 patients with multiple CA were allocated into two groups—combined group(CO_(2)laser plus ALA-PDT,n=60)and CO_(2)laser group(CO_(2)laser plus placebo-PDT,n=60).After CO_(2)laser,a 20%ALA or a placebo solution was applied to the CA area 3 h before illumination with red light(635 nm,100mW/cm^(2),80 J/cm^(2)).The treatment was repeated seven days after the first treatment if the lesions were not completely resolved.The complete response rate,recurrence rate and adverse effects in the two groups were analyzed.After two treatments,the complete response rates in the CO_(2)laser group and combined group were 100%(509/509)and 100%(507/507)in the CA(p>0:05),respectively.The recurrence rates in the CO_(2)laser group and combined group were 44.9%(229/509)and 10.6%(54/507)in the CA(p<0:05),respectively.The adverse effects in CO_(2)laser group was more than that in combined group.The combined group is a more effective treatment for multiple CA compared with CO_(2)laser group.T/S.Style the highlighted text as abstract.

Accurate method for determining vibration temperatures, and gain limitation in pulse RF-discharge CO_2 laser

An accurate method of determining gain coefficients of pulse RF-discharge CO2 laser is developed, which involves the use of both the regular 00o1 and 00o2 laser transitions as probes of CO2 laser. The results indicate that the majority of transitions in discharge have anomalous gain coefficients under RF-discharge condition. This fact has not been generally recognized and the neglect of overlapping transitions can lead to errors in determining rotational temperature.