Boosting internal quantum efficiency via ultrafast triplet transfer to 2H-MoTe2 film.

Organic systems often allow to create two triplet spin states (triplet excitons) by converting an initially excited singlet spin state (a singlet exciton). An ideally designed organic/inorganic heterostructure could reach the photovoltaic energy harvest over the Shockley-Queisser (S-Q) limit because of the efficient conversion of triplet excitons into charge carriers. Here, we demonstrate the molybdenum ditelluride (MoTe2)/pentacene heterostructure to boost the carrier density via efficient triplet transfer from pentacene to MoTe2 using ultrafast transient absorption spectroscopy. We observe carrier multiplication by nearly four times by doubling carriers in MoTe2 via the inverse Auger process and subsequently doubling carriers via triplet extraction from pentacene. We also verify efficient energy conversion by doubling the photocurrent in the MoTe2/pentacene film. This puts a step forward to enhancing photovoltaic conversion efficiency beyond the S-Q limit in the organic/inorganic heterostructures.

Gate-Tunable Magnetism via Resonant Se-Vacancy Levels in WSe2.

The confined defects in 2D van der Waals (vdW)-layered semiconductors can be easily tailored using charge doping, strain, or an electric field. Nevertheless, gate-tunable magnetic order via intrinsic defects has been rarely observed to date. Herein, a gate-tunable magnetic order via resonant Se vacancies in WSe2 is demonstrated. The Se-vacancy states are probed via photocurrent measurements with gating to convert unoccupied states to partially occupied states associated with photo-excited carrier recombination. The magneto-photoresistance hysteresis is modulated by gating, which is consistent with the density functional calculations. The two energy levels associated with Se vacancies split with increasing laser power, owing to the robust Coulomb interaction and strong spin-orbit coupling. The findings offer a new approach for controlling the magnetic properties of defects in optoelectronic and spintronic devices using vdW-layered semiconductors.

One-Step Synthesis of NbSe2/Nb-Doped-WSe2 Metal/Doped-Semiconductor van der Waals Heterostructures for Doping Controlled Ohmic Contact.

van der Waals heterostructures (vdWHs) of metallic (m-) and semiconducting (s-) transition-metal dichalcogenides (TMDs) exhibit an ideal metal/semiconductor (M/S) contact in a field-effect transistor. However, in the current two-step chemical vapor deposition process, the synthesis of m-TMD on pregrown s-TMD contaminates the van der Waals (vdW) interface and hinders the doping of s-TMD. Here, NbSe2/Nb-doped-WSe2 metal-doped-semiconductor (M/d-S) vdWHs are created via a one-step synthesis approach using a niobium molar ratio-controlled solution-phase precursor. The one-step growth approach synthesizes Nb-doped WSe2 with a controllable doping concentration and metal/doped-semiconductor vdWHs. The hole carrier concentration can be precisely controlled by controlling the Nb/(W + Nb) molar ratio in the precursor solution from ∼3 × 1011/cm2 at Nb-0% to ∼1.38 × 1012/cm2 at Nb-60%; correspondingly, the contact resistance RC value decreases from 10 888.78 at Nb-0% to 70.60 kΩ.µm at Nb-60%. The Schottky barrier height measurement in the Arrhenius plots of ln(Isat/T2) versus q/KBT demonstrated an ohmic contact in the NbSe2/WxNb1-xSe2 vdWHs. Combining p-doping in WSe2 and M/d-S vdWHs, the mobility (27.24 cm2 V-1 s-1) and on/off ratio (2.2 × 107) are increased 1238 and 4400 times, respectively, compared to that using the Cr/pure-WSe2 contact (0.022 cm2 V-1 s-1 and 5 × 103, respectively). Together, the RC value using the NbSe2 contact shows 2.46 kΩ.µm, which is ∼29 times lower than that of using a metal contact. This method is expected to guide the synthesis of various M/d-S vdWHs and applications in future high-performance integrated circuits.

Escalated Photocurrent with Excitation Energy in Dual-Gated MoTe2.

Although van der Waals-layered transition metal dichalcogenides from transient absorption spectroscopy have successfully demonstrated an ideal carrier multiplication (CM) performance with an onset of nearly 2Eg, interpretation of the CM effect from the optical approach remains unresolved owing to the complexity of many-body electron-hole pairs. We demonstrate the escalated photocurrent with excitation photon energy by fabricating the dual-gate p-n junction of a MoTe2 film on a transparent substrate. Electrons and holes were efficiently extracted by eliminating the Schottky barriers in the metal contact and minimizing multiple reflections. The photocurrent was elevated proportionately to the excitation photon energy. The boosted quantum efficiency confirms the multiple electron-hole pair generation of >2Eg, consistent with CM results from an optical approach, pushing the solar cell efficiency beyond the Shockley-Queisser limit.

Decelerated Hot Carrier Cooling in Graphene via Nondissipative Carrier Injection from MoS2.

One key to improve the performance of advanced optoelectronic devices and energy harvesting in graphene is to understand the predominant carrier scattering via optical phonons. Nevertheless, low light absorbance in graphene yields a limited photoexcited carrier density, hampering the hot carrier effect, which is strongly correlated to the hot optical phonon bottleneck effect as the energy-loss channel. Here, by integrating graphene with monolayer MoS2 possessing stronger light absorbance, we demonstrate an efficient interfacial hot carrier transfer between graphene and MoS2 in their heterostructure with a prolonged relaxation time using broadband transient differential transmittance spectroscopy. We observe that the carrier relaxation time of graphene in the heterostructure is 4 times slower than that of bare graphene. This is explained by nondissipative interlayer transfer from MoS2 to graphene, which is attributed to the enhanced hot optical phonon bottleneck effect of graphene in the heterostructure by an increased photoexcited carrier population. A significant reduction of both amplitude and relaxation time in A- and B-excitons is another evidence of the interlayer transfer from MoS2 to graphene. The nondissipative interlayer charge transfer from MoS2 to graphene is confirmed by density functional calculations. This provides a different platform to further study the photoinduced hot carrier effect in graphene heterostructures for photothermoelectric detectors or hot carrier solar cells.

Efficient Gate Modulation in a Screening-Engineered MoS2/Single-Walled Carbon Nanotube Network Heterojunction Vertical Field-Effect Transistor.

In this report, a screening-engineered carbon nanotube (CNT) network/MoS2/metal heterojunction vertical field effect transistor (CNT-VFET) is fabricated for an efficient gate modulation independent of the drain voltage. The gate field in the CNT-VFET transports through the empty space of the CNT network without any screening layer and directly modulates the MoS2 semiconductor energy band, while the gate field from the Si back gate is mostly screened by the graphene layer. Consequently, the on/off ratio of CNT-VFET maintained 103 in overall drain voltages, which is 10 times and 1000 times higher than that of the graphene (Gr) VFET at Vsd = 0.1 (ratio = 81.9) and 1 V (ratio = 3), respectively. An energy band diagram simulation shows that the Schottky barrier modulation of CNT/MoS2 contact along the sweeping gate bias is independent of the drain voltage. On the other hand, the gate modulation of Gr/MoS2 is considerably reduced with increased drain voltage because more electrons are drawn into the graphene electrode and screens the gate field by applying a higher drain voltage to the graphene/MoS2/metal capacitor.

Two-Terminal Multibit Optical Memory via van der Waals Heterostructure.

2D van der Waals (vdWs) heterostructures exhibit intriguing optoelectronic properties in photodetectors, solar cells, and light-emitting diodes. In addition, these materials have the potential to be further extended to optical memories with promising broadband applications for image sensing, logic gates, and synaptic devices for neuromorphic computing. In particular, high programming voltage, high off-power consumption, and circuital complexity in integration are primary concerns in the development of three-terminal optical memory devices. This study describes a multilevel nonvolatile optical memory device with a two-terminal floating-gate field-effect transistor with a MoS2 /hexagonal boron nitride/graphene heterostructure. The device exhibits an extremely low off-current of ≈10-14 A and high optical switching on/off current ratio of over ≈106 , allowing 18 distinct current levels corresponding to more than four-bit information storage. Furthermore, it demonstrates an extended endurance of over ≈104 program-erase cycles and a long retention time exceeding 3.6 × 104 s with a low programming voltage of -10 V. This device paves the way for miniaturization and high-density integration of future optical memories with vdWs heterostructures.

Role of Hole Trap Sites in MoS2 for Inconsistency in Optical and Electrical Phenomena.

Because of strong Coulomb interaction in two-dimensional van der Waals-layered materials, the trap charges at the interface strongly influence the scattering of the majority carriers and thus often degrade their electrical properties. However, the photogenerated minority carriers can be trapped at the interface, modulate the electron-hole recombination, and eventually influence the optical properties. In this study, we report the role of the hole trap sites on the inconsistency in the electrical and optical phenomena between two systems with different interfacial trap densities, which are monolayer MoS2-based field-effect transistors (FETs) on hexagonal boron nitride (h-BN) and SiO2 substrates. Electronic transport measurements indicate that the use of h-BN as a gate insulator can induce a higher n-doping concentration of the monolayer MoS2 by suppressing the free-electron transfer from the intrinsically n-doped MoS2 to the SiO2 gate insulator. Nevertheless, optical measurements show that the electron concentration in MoS2/SiO2 is heavier than that in MoS2/h-BN, manifested by the relative red shift of the A1g Raman peak. The inconsistency in the evaluation of the electron concentration in MoS2 by electrical and optical measurements is explained by the trapping of the photogenerated holes in the spatially modulated valence band edge of the monolayer MoS2 caused by the local strain from the SiO2/Si substrate. This photoinduced electron doping in MoS2/SiO2 is further confirmed by the development of the trion component in the power-dependent photoluminescence spectra and negative shift of the threshold voltage of the FET after illumination.

Simple Chemical Treatment to n-Dope Transition-Metal Dichalcogenides and Enhance the Optical and Electrical Characteristics.

The optical and electrical properties of monolayer transition-metal dichalcogenides (1L-TMDs) are critically influenced by two dimensionally confined exciton complexes. Although extensive studies on controlling the optical properties of 1L-TMDs through external doping or defect engineering have been carried out, the effects of excess charges, defects, and the populations of exciton complexes on the light emission of 1L-TMDs are not yet fully understood. Here, we present a simple chemical treatment method for n-dope 1L-TMDs, which also enhances their optical and electrical properties. We show that dipping 1Ls of MoS2, WS2, and WSe2, whether exfoliated or grown by chemical vapor deposition, into methanol for several hours can increase the electron density and also can reduce the defects, resulting in the enhancement of their photoluminescence, light absorption, and the carrier mobility. This methanol treatment was effective for both n- and p-type 1L-TMDs, suggesting that the surface restructuring around structural defects by methanol is responsible for the enhancement of optical and electrical characteristics. Our results have revealed a simple process for external doping that can enhance both the optical and electrical properties of 1L-TMDs and help us understand how the exciton emission in 1L-TMDs can be modulated by chemical treatments.

Some remarkable on indication and conservation splencectomy results in closed abdominal injury

45 patients with spleen trauma were treated in the hospital No 19-8. Among then, 17 underwent a prevervative operation for suturing the spleen according to the state of trauma in site, the surgeon's qualification and the follow- up conditions. The preservative suture must be safe, spleen function must be preserved, any spleen edge could be partialy removed in case of injury. Early result can be altained in 94,11% and early post operative complication in 5,89% of cases.

Some consideration about clinical symptoms and patho-anatomical features of liver teratoma

A case of teratoma in a male patient aged 53 years old at the liver left lobe, hospitalized 25 November 2002 at The Hospital 198 was persented. It was a special form of mature teratoma of dermoid cyst. Macroscopically, it was a cyst of large size with thick fibroid shell, containing fat fluid, caseinous matter, hair, cartilaginous bone and even 3 molar teeth. Microscopically, it was a lining of cells of keratinoid epithelial scale tissue in the wall. Under the epithelial cover there was a conjunctive tissue inserted by sebacenous tissues, sweat gland tissues, hair alveoli and vessels with thick fibrous wall.

Surgical treatment results of simple thyroid goiter at the Hospital 198

From January 1994 to December 2003, at the Hospital 198, 697 patients (149 males, 548 females) with simple thyroid goiter, aged 16-75 years oldwere treated and operated. The age of highest incidence was 21-40 years old (79.92%). Thyroid cyst accounts for highest incidence 48.21%. According to WHO classification the incidence of surgery was mainly in the goiter of 2nd, 3rd grade. Anapathological analysis found the highest incidence 47.92% in simple colloid goiter. There were 4 cases of thyroid cancer (0.57%). General complications found in 2.44%.

Some remarks on1200 cases of surgical accidental emergency managed in the year 2003

A survey was performed at the Hospital No 108 on 1200 cases of accident emergency. Result showed a higher rate of occurrence in male than in female subjects with a ratio of 1/3.The highest incident was traffic accidents,which accounted for 65%, followed by occupational, then quotidien life accidents. Motorbike had caused 70,89% of cases of traffic accidents. In all occupational accidents, the construction works had caused 71,86%. In quotidien life criminal events had caused 39,78% of cases. Traffic accidents caused primarily traumata at lower limbs-37,30%, at skull-brain area-27,18%. In occupational works, abdomen- thoracic traumata had occurred principally -52,39%. Total mortality accounted for 0,58%.

Clinical characteristics, diagnosis and treatment of bowel obstruction due to phytobezoar

From the year 1993 to 2003, at the Hospital 19-8, 21 cases of intestinal obstruction due to food waste were treated surgery. Clinically, intestinal food waste obstruction had been moderately in progress. For diagnosis, clinics have to combine with X-ray and ultrasound. The damage was mainly seen in the intestine, but also in the stomach, and not in the colon. The operation for opening the fraction of intestine above the obstruction site for removing the food waste, then suturing immediately. This had demonstrated the effect. If the trauma was occurred late, because of the risk of rupture of the binding in the open site, the cutting-off intestine fragment was recommended.