Daoli Zhang

Preparation and characteristic of the thermistor materials in the thick-film integrated temperature–humidity sensor

Abstract The designing, preparation, and characteristic of the thermistor materials in a thick-film integrated temperature–humidity sensor were investigated in detail. This article presented the relationship between resistance–temperature characteristics and the composition of the negative temperature coefficient thermistor materials, which matched with humidity sensitive material in the integrated sensor. The effects of the fabrication processing on the R–T characteristic and the material granularity, granularity uniformity were presented. Finally this article provided some experimental data of the thermistor materials and the characteristic curves of the thick-film integrated temperature–humidity sensor prepared from the material.

Quantum dot PbS0.9Se0.1/TiO2 heterojunction solar cells

We report on photovoltaic cells based on ternary PbS(0.9)Se(0.1) quantum dots utilizing a heterojunction type device configuration. The best device shows an AM 1.5 power conversion efficiency of 4.25%. Furthermore, this ternary PbS(x)Se(1-x) quantum dot heterojunction device has a peak external quantum efficiency above 100% at 2.76 eV, approximately 2.7× the bandgap energy. The ternary quantum dots combine the higher short circuit currents of the binary PbSe system with the higher open circuit voltages of the binary PbS system.

Air stability of TiO2/PbS colloidal nanoparticle solar cells and its impact on power efficiency

The short-term (less than 1 hour) exposure of TiO2/PbS quantum dot photovoltaics to air increases the open circuit voltage (Voc) and fill factor (FF) while slightly decreasing the short circuit current density (Jsc), leading to a power conversion efficiency above 4% and a peak external quantum efficiency over 80% for 1.1 eV PbS. The resulting Jsc, Voc, and FF under 100 mW/cm2 AM1.5 are 18.6 mA/cm2, 0.517 V, and 42% for 1.1 eV PbS and 8.03 mA/cm2, 0.655 V, and 35% for 1.7 eV PbS, respectively. Long-term air exposures result in much lower conductivities. Furthermore, short-term air exposure effects are fully reversible upon removal from air, and longer-term effects are mostly reversible through soaking in 1,2-ethanedithiol.

One-pot synthesis of hydrophilic CuInS2 and CuInS2–ZnS colloidal quantum dots

A green method for the one-pot direct synthesis of hydrophilic CuInS2 and CuInS2–ZnS colloidal quantum dots was developed employing N,N-dimethylformamide (DMF) as a solvent. Highly reactive H2S gas, in situ generated from the reaction between FeS and H2SO4, was utilized as the sulphur source for the synthesis of hydrophilic CuInS2 quantum dots. Short chain thiols were applied as ligands, reactivity controllers and sulphur sources for the growth of the ZnS shell. The growth of CuInS2 quantum dots experiences a typical Ostwald ripening process, and it should be controlled in 45 min due to the pyrolysis of the ligands. The reaction temperature should not exceed 130 °C. The ZnS shell was grown on CuInS2 quantum dots in a very simple and one-pot approach. Both the luminescence and optical stability were improved substantially after the formation of the ZnS shell. The versatility of this synthetic strategy was demonstrated by extending it to the synthesis of other metal sulphide quantum dots, for instance, CdS and ZnS quantum dots.

Negative differential resistance behavior in phosphorus-doped armchair graphene nanoribbon junctions

In this present work, we investigate the electronic transport properties of phosphorus-doped armchair graphene nanoribbon (AGNR) junctions by employing nonequilibrium Greens functions in combination with the density-function theory. Two phosphorus (P) atoms are considered to substitute the central carbon atom with the different width of AGNRs. The results indicate that the electronic transport behaviors are strongly dependent on the width of the P-doped graphene nanoribbons. The current-voltage characteristics of the doped AGNR junctions reveal an interesting negative differential resistance (NDR) and exhibit three distinct family (3 n, 3 n + 1, 3 n + 2) behaviors. These results display that P doping is a very good way to achieve NDR of the graphene nanoribbon devices.

The electronic transport behavior of hybridized zigzag graphene and boron nitride nanoribbons

In this present work, we have investigated the electronic transport properties of the hybridized structure constructed by the zigzag graphene and boron-nitride (BN) nanoribbons (Z-BnNmCp, n + m + p = 16) through employing nonequilibrium Greens functions in combination with the density-functional theory. The results demonstrate that the electronic transport properties of the hybridized Z-BnNmCp nanoribbons are strongly dependent on the width of boron-nitride or graphene nanoribbons. When the numbers of n and m are not equal, the negative differential resistance behavior is observed, which can be modulated by varying the width of BN nanoribbons. The conductance of the hybridized Z-BnNmCp nanoribbons with odd numbers of zigzag carbon chains also increases by the width of BN nanoribbons.

Phosphorus-doping-induced rectifying behavior in armchair graphene nanoribbons devices

Based on nonequilibrium Greens functions in combination with density-functions theory, the transport properties of armchair graphene nanoribbon (AGNR) devices were investigated, in which one lead is undoped armchair graphene nanoribbons, and the other is phosphorus (P)-doped armchair graphene nanoribbons. The results manifest that there is the rectification behavior with large rectifying ratio in the AGNR devices and the rectification characteristics can be modulated by changing the width of the graphene nanoribbons. On the contrary, for the same width of the graphene nanoribbons, the position of P dopant has little or no effect on changing I-V characteristics.

Analysis on the aging characteristics of PTCR of donor-doped barium titanate

The resistance versus time curves of room temperature unload ageing, high temperature unload ageing and high temperature continuous load test ageing of PTC thermistors are measured. At the initial aging stage under both high temperature unload ageing and high temperature continuous load test ageing, the resistance decreases first, and then increases, which are different from that of the room temperature aging. Such abnormal phenomena exist in the initial ageing stage and are attributed to buffering of the unstable mechanical stress and desorption of the absorbed oxygen molecules under the thermal action. R � /T characteristic curves of aged sample are different from that of oxidized and reduced samples. A new mechanism is proposed to interpret the aging characteristics of the donor-doped BaTiO3 PTC thermistor. # 2002 Elsevier Science B.V. All rights reserved.

Synthesis and growth kinetics of high quality InAs nanocrystals using in situ generated AsH3 as the arsenic source

High quality InAs nanocrystals were synthesized using in situ generated AsH3 as arsenic precursor. The growth process was studied by monitoring the absorption spectra. An injection of additional solvent was adopted to control the nucleation. The growth of InAs nanocrystals should be controlled in 20–30 min, an extension of growth would lead to dissolution of the nanocrystals due to the instability of the monomers formed from AsH3. Addition of zinc stearate along with an indium source improved the photoluminescence without leading to doping of InAs nanocrystals.

A new method for microwave dielectric measurement of low loss ceramics

Abstract In this paper a novel resonant method was proposed for the determination of dielectric constant and loss tangent of low loss ceramic materials used for dielectric resonators at microwave frequencies. The details of the design and fabrication of the cavity, the input and output coupling transmission lines and the substrate were discussed. The radial mode matching (RMM) technique was used to determine the exact frequencies of this resonant configuration as a function of the permittivity of the sample. And the relation between the loss tangent of the sample and the unloaded quality factor ( Q l ) of this structure was obtained on the basis of the electromagnetic field distribution. Some numerical results for the direct and inverse problems were presented to validate these relationships. The absolute uncertainties of the measurement were presented. Lastly the procedure of measurement was discussed.