In vivo neuronal and astrocytic activation in somatosensory cortex by acupuncture stimuli.

Acupuncture is a medical treatment that has been widely practiced in China for over 3000 years, yet the neural mechanisms of acupuncture are not fully understood. We hypothesized that neurons and astrocytes act independently and synergistically under acupuncture stimulation. To investigate this, we used two-photon in vivo calcium recording to observe the effects of acupuncture stimulation at ST36 (Zusanli) in mice. Acupuncture stimulation in peripheral acupoints potentiated calcium signals of pyramidal neurons and astrocytes in the somatosensory cortex and resulted in late-onset calcium transients in astrocytes. Chemogenetic inhibition of neurons augmented the astrocytic activity. These findings suggest that acupuncture activates neuronal and astrocytic activity in the somatosensory cortex and provide evidence for the involvement of both neurons and astrocytes in acupuncture treatment.

Low-Temperature-Processed High-Performance Pentacene OTFTs with Optimal Nd-Ti Oxynitride Mixture as Gate Dielectric.

When processed at a low temperature of 200 °C, organic thin-film transistors (OTFTs) with pentacene channel adopting high-k Neodymium-Titanium oxynitride mixtures (NdTiON) with various Ti contents as gate dielectrics are fabricated. The Ti content in the NdTiON is varied by co-sputtering a Ti target at 0 W, 10 W, 20 W and 30 W, respectively, while fixing the sputtering power of an Nd target at 45 W. High-performance OTFT is obtained for the 20 W-sputtered Ti, including a small threshold voltage of -0.71 V and high carrier mobility of 1.70 cm2/V·s. The mobility improvement for the optimal Ti content can be attributed to smoother dielectric surface and resultant larger overlying pentacene grains as reflected by Atomic Force Microscopy measurements. Moreover, this sample with the optimal Ti content shows much higher mobility than its counterpart processed at a higher temperature of 400 °C (0.8 cm2/V·s) because it has a thinner gate-dielectric/gate-electrode interlayer for stronger screening on the remote phonon scattering by the gate electrode. In addition, a high dielectric constant of around 10 is obtained for the NdTiON gate dielectric that contributes to a threshold voltage smaller than 1 V for the pentacene OTFT, implying the high potential of the Nd-Ti oxynitride in future high-performance organic devices.

Improved subthreshold swing of MoS2 negative-capacitance transistor by fluorine-plasma treatment on ferroelectric Hf0.5Zr0.5O2 gate dielectric.

In this work, the ferroelectricity of hafnium zirconium oxide (Hf0.5Zr0.5O2, HZO) is enhanced by fluorine (F)-plasma treatment, which is used to fabricate MoS2 negative-capacitance field-effect transistor. Measurements show that the subthreshold swing of the transistor is significantly reduced to 17.8 mV dec-1 over almost four orders of output current, as compared to its counterpart without the F-plasma treatment (37.4 mV dec-1). The involved mechanism is that during the F-plasma treatment, F atoms can be incorporated into the HZO bulk to passive its oxygen vacancies and interface traps, thus forming robust Zr-F and Hf-F bonds. Therefore, the F-plasma-treated HZO film exhibits much less oxygen vacancies than the untreated HZO film, which is beneficial to enhancing the amplification effect on the surface potential of the MoS2 channel during the NC operation.

Optimizing Al-doped ZrO2 as the gate dielectric for MoS2 field-effect transistors.

In this work, we investigate the effects on the electrical properties of few-layered MoS2 field-effect transistors (FETs) following Al incorporation into ZrO2 as the gate dielectrics of the devices. A large improvement in device performance is achieved with the Al-doped ZrO2 gate dielectric when Zr:Al = 1:1. The relevant MoS2 transistor exhibits the best electrical characteristics: high carrier mobility of 40.6 cm2 V-1 s-1 (41% higher than that of the control sample, and an intrinsic mobility of 68.0 cm2 V-1 s-1), a small subthreshold swing of 143 mV dec-1, high on/off current ratio of 6 × 106 and small threshold voltage of 0.71 V. These are attributed to the facts that (i) Al incorporation into ZrO2 can decrease its oxygen vacancies; densify the dielectric film; and smooth the gate dielectric surface, thus reducing the traps at/near the Zr0.5Al0.5O y /MoS2 interface and the gate leakage current; (ii) adjusting the dielectric constant of the gate dielectric to an appropriate value, which achieves a reasonable trade-off between the gate screening effect on the Coulomb-impurity scattering and the surface optical phonon scattering. These results demonstrate that optimized Zr0.5Al0.5Oy is a potential gate dielectric material for MoS2 FET applications.

Damage-free mica/MoS2 interface for high-performance multilayer MoS2 field-effect transistors.

For top-gated MoS2 field-effect transistors, damaging the MoS2 surface to the MoS2 channel are inevitable due to chemical bonding and/or high-energy metal atoms during the vacuum deposition of gate dielectric, thus leading to degradations of field-effect mobility (µ FE) and subthreshold swing (SS). A top-gated MoS2 transistor is fabricated by directly transferring a 9 nm mica flake (as gate dielectric) onto the MoS2 surface without any chemical bonding, and exhibits excellent electrical properties with an on-off ratio of ∼108, a low threshold voltage of ∼0.2 V, a record µ FE of 134 cm2 V-1 s-1, a small SS of 72 mV dec-1 and a low interface-state density of 8.8 × 1011 cm-2 eV-1, without relying on electrode-contact engineered and/or phase-engineered MoS2. Although the equivalent oxide thickness of the mica dielectric is in the sub-5 nm regime, enhanced stability characterized by normalized threshold voltage shift (1.2 × 10-2 V MV-1 cm-1) has also been demonstrated for the transistor after a gate-bias stressing at 4.4 MV cm-1 for 103 s. All these improvements should be ascribed to a damage-free MoS2 channel achieved by a dry transfer of gate dielectric and a clean and smooth surface of the mica flake, which greatly decreases the charged-impurity and interface-roughness scatterings. The proposed transistor with low threshold voltage and high stability is highly desirable for low-power electronic applications.

Effects of HfO2 encapsulation on electrical performances of few-layered MoS2 transistor with ALD HfO2 as back-gate dielectric.

The carrier mobility of MoS2 transistors can be greatly improved by the screening role of high-k gate dielectric. In this work, atomic-layer deposited (ALD) HfO2 annealed in NH3 is used to replace SiO2 as the gate dielectric to fabricate back-gated few-layered MoS2 transistors, and good electrical properties are achieved with field-effect mobility (µ) of 19.1 cm2 V-1 s-1, subthreshold swing (SS) of 123.6 mV dec-1 and on/off ratio of 3.76 × 105. Furthermore, enhanced device performance is obtained when the surface of the MoS2 channel is coated by an ALD HfO2 layer with different thicknesses (10, 15 and 20 nm), where the transistor with a 15 nm HfO2 encapsulation layer exhibits the best overall electrical properties: µ = 42.1 cm2 V-1 s-1, SS = 87.9 mV dec-1 and on/off ratio of 2.72 × 106. These improvements should be associated with the enhanced screening effect on charged-impurity scattering and protection from absorption of environmental gas molecules by the high-k encapsulation. The capacitance equivalent thickness of the back-gate dielectric (HfO2) is only 6.58 nm, which is conducive to scaling of the MoS2 transistors.

Design of superparamagnetic nanoparticles for magnetic particle imaging (MPI).

Magnetic particle imaging (MPI) is a promising medical imaging technique producing quantitative images of the distribution of tracer materials (superparamagnetic nanoparticles) without interference from the anatomical background of the imaging objects (either phantoms or lab animals). Theoretically, the MPI platform can image with relatively high temporal and spatial resolution and sensitivity. In practice, the quality of the MPI images hinges on both the applied magnetic field and the properties of the tracer nanoparticles. Langevin theory can model the performance of superparamagnetic nanoparticles and predict the crucial influence of nanoparticle core size on the MPI signal. In addition, the core size distribution, anisotropy of the magnetic core and surface modification of the superparamagnetic nanoparticles also determine the spatial resolution and sensitivity of the MPI images. As a result, through rational design of superparamagnetic nanoparticles, the performance of MPI could be effectively optimized. In this review, the performance of superparamagnetic nanoparticles in MPI is investigated. Rational synthesis and modification of superparamagnetic nanoparticles are discussed and summarized. The potential medical application areas for MPI, including cardiovascular system, oncology, stem cell tracking and immune related imaging are also analyzed and forecasted.