Advanced Materials Research Vols. 60-61

Abstract: This paper introduces a octree search Kinetic Monte Carlo(OS-KMC) that combines the topological requirements for representing an evolving multivalued surface using minimal memory and an efficient search algorithm for the realization of the KMC time evolution. In addition, the data structure for OS-KMC also provides a nature way to generate hexahedral element meshes for the integration between simulator and performance analysis tool. The density of mesh grid and the refinement of the hexahedral element can be controlled in this octree based mesh generation method. In simulating surface morphology during wet etching and micro structure formed by composite MEMS processes, the octree search KMC shows good simulation results with better calculation performance. The octree structure enables the Monte Carlo solutions for large scale problems with complex dynamic surfaces.

Abstract: Silver-doping in SnS films can improve the semiconducting properties of SnS films. Based on our previous research, SnS:Ag thin films were deposited on ITO coated glass by pulse electro-deposition in order to study their structural, optical and electrical properties. SnS:Ag thin films were characterized with X-ray diffraction (XRD) , Scanning Electron Microscope (SEM) and some other methods. The primary composition of the films is SnS, but maybe there is a little quantity of SnS2, Ag8SnS6 and other compounds. The doped films exhibit good crystallization with big grain size. They have an optical gap of 1.66~1.89eV and a high absorption coefficient (α＞5×104cm-1). Hall measurement has shown that all the samples are of p-type conduction with low resistivity of the order of 10-3Ω•cm, and the carrier concentration increases to 1019cm-3 after Ag-doping. In conclusion, the semiconducting properties of the SnS films have been improved by silver-doping. Thus, SnS:Ag thin films can be used as solar cells absorbers.

Abstract: Mg-doped (≤15at%) ZnO thin films were prepared on quartz glass substrates by sol-gel method using a spinning-techniques. The films were charactered by X-ray diffraction , UV Vis-NIR double beam spectrophotometer and a SHIMADZU fluorespectrometer. It was found that optimally crystallized when the Mg concentration is 9at% were obtained. A photoluminescence study at room temperature revealed a blue shift in the near band edge emission peak with increasing of Mg content , which is agreement with the observation from the optical transmittance measurement. The photoconductive UV detectors based on these films were investigated, and the result showed that highest response was obtained from the photodecters fabricated by films with 15at% Mg concentration.

Abstract: A kind of novel quantum dots (QDs) with poly(4-vinylpyridine) (PVPy) as shell and CdTe QDs as core was presented in this work. This core/shell ODs can conjugate DNA easily because the surface pyridyl exist on QDs, and which has potential application in DNA biosensors field. CdTe QDs were prepared in aqueous solution with 3-mercaptopropionic acid (MPA) as stabilizer. It was found that the fluorescent intensity of QDs was depended the reflux time. Following the increase of reflux time, the fluorescent intensity of QDs reached the maximum at 10 h with about 10 nm in diameters. And the fluorescent intensity of QDs was also increased. When the reflux time was 10 h, the diameter of QDs would increase to about 10 nm. After adjusted the pH of QDs solution system to 7.0, the MPA stabled QDs were purified by ultracentrifugation and freeze-drying respectively. The polymerization was performed in water when 4-vinylpyridine (VPy) used as monomer, N,N’-methylene-bisacrylamide (MBAAm) as crosslinker, potassium persulphate (PPS) as initiator and MPA stabled QDs as seeds. The surface carboxyl of MPA on QDs could promote the form of PVPy coated CdTe QDs. It was shown that the fluorescent intension of core/shell QDs was decreased following the polymerization and the diameter of QDs could increase to 20-30 nm.

Abstract: The effect of micro-hotplate (MHP) thermal deformation on the signal output of the MHP-based micro gas pressure sensor is investigated. Combining electro-thermal theoretical analysis and thermal-mechanical finite element modeling, different electro-thermal-mechanical analysis models of the sensors are built and solved at constant current condition and constant temperature condition respectively. The calculated results show that the MHP thermal deformation has little effect on the sensor signal output over the entire pressure range at constant current condition, I=0.7mA. While at constant temperature condition, Ts=400K, thermal deformation has little effect on the sensor signal output at low gas pressure, but at high pressure the effect are great. Moreover, according to the thermal-mechanical analysis, we find that optimizing thickness distribution of thin films in the MHP suspended structure can reduce thermal deformation effectively at higher temperature when the lateral dimension is same, which presents a practicable method to improve the sensor stability.

Abstract: Proliferation and migration of vascular smooth muscle cells(VSMCs) into the sub-intimal space play an important role in intimal thickening in atherosclerosis and in-stent restenosis. Arsenic compounds are natural substances that have been used in the treatment of patients with acute promyelocytic leukemia (APL).And Arsenic trioxide (As2O3) is known to be a potent inhibitor of cell proliferation.The aim of this study was to prepare arsenic trioxide (As2O3) -loaded PLGA nanoparticles(As2O3-PLGA-NP) and investigate its general properties, preservation of As2O3 bioactivity and their inhibitory effects on Rabbit Vascular Smooth Muscle Cells(RVSMCs) in vitro. With PLGA as carrier,As2O3 drug delivery nanoparticles were prepared by w /o /w double-emulsion evaporation technique，and their inhibitory effects on Rabbit Vascular Smooth Muscle Cells(VSMCs) in vitro was investigated.The results of the experiment show the self-prepared As2O3-PLGA-NP were approximately spherical,with the mean diameter of 90±25.03 nm, and the average drug loading was 1.72% .The As2O3-PLGA-NP has drug sustained-release character and can prolong the phase of the inhibitory effect of As2O3 against RVSMCs.The As2O3-PLGA-NP do not reduce the biological activity of As2O3.

Abstract: An experimental analysis of the influence of the bumps on the surface forces in micro gap plates is presented. Because of extremely small sizes of micromechanical structures in MEMS, surface forces between micromechanical components may become significant to influence behaviors of microelectromechanical devices. The bumps are important in micro structures as they change the adhesion condition of the plates, and will influence the surface forces in micro gap plates greatly. To identify relative importance of surface forces with bumps, the experimental instrument which consists of the V-shaped electrothermal microactuator, the suspended plate and the flexible beam is designed. The displacements of the suspended plate with different bumps are measured by experiments, and the surface forces are got by calculation. By analysis, it could be found that the surface force increases with the increasing drive voltage and the increasing normal voltage, and the surface force gets the minimum when the number of the bumps is 9.

Abstract: The stiffness of microstructure is an important parameter of the microsensor. It is usually obtained by FEM approach, which is difficult to give an analytical expression. This paper reports on a 2-D microaccelerometer with the complex microstructure. Its main axial stiffness is carried out by using force method as well as principle of work and strain energy. During the deduction, deformation of all beams is taken into account, so the theoretical results are in accordance with that of FEM approach very well and the error is less than one in thousand. Furthermore, we neither introduce the other assumptions nor design the special dimension. So this methodology is strict in theory, and can be extended to analysis for the displacement and stiffness of the symmetric and statically indeterminate microstructure.

Abstract: In this article, a novel kind of nanomaterials called CdTe/PAA/P-4-VP quantum dots (QDs) was studied. CdTe quantum dots were synthesized by mixing CdCl2 solution containing Mercaptopropionic Acid (MPA) stabilizer at pH 9.1 with NaHTe aqueous solution and refluxing 1 h at 96 °C. Then, CdTe solution obtained was adjusted to pH 7.5 by poly(acrylic acid) (PAA) which could provide many carboxyl groups to CdTe QDs. PAA-modified CdTe (CdTe/PAA)solution was transparent during 2 months and the fluorescence of CdTe/PAA was higher than that of CdTe at the same pH, which indicated that PAA increased the stability and fluorescence intension of CdTe QDs. Then poly(4-vinylpyridine)-coated CdTe/PAA QDs (CdTe/PAA/P-4-VP QDs) were prepared after 4-VP was polymerized on the surface of CdTe/PAA nanoparticles by using N, N'-Methylenebisacrylamide as crosslinker and potassium persulfate as initiator. The parallel experiment in which PAA was replaced by HCl was also arranged and CdTe/P-4-VP QDs was gained. Fluorescence emission spectrum (FE), transmission electron microscope (TEM), and infrared spectrum (IR) were used to characterize CdTe/PAA/P-4-VP and CdTe/P-4-VP QDs. The FE spectrum of CdTe/PAA/P-4-VP QDs had an obviously red shift compared with that of CdTe QDs while the red shift in FE spectrum of CdTe/P-4-VP QDs was not obvious, which indicated that PAA played an important role in the synthesis of P-4-VP-coated CdTe QDs. The fluorescence of CdTe/PAA/P-4-VP QDs was one times higher than that of CdTe QDs, which suggested the advantage of CdTe/PAA/P-4-VP QDs in fluorescence application. TEM photos showed that the average size of CdTe/PAA/P-4-VP QDs was 13.3nm. The IR spectrum of CdTe/PAA/P-4-VP QDs showed that characteristic absorption peak of carboxyl groups from PAA or/and MPA was wide and other absorption peaks of CdTe/PAA/P-4-VP QDs were the same with that of 4-VP which confirmed that P-4-VP coated CdTe QDs.

Abstract: : It is a test of sound transmission characteristic of PTFE Micro-aperture Membrane,through it we found that the PTFE Micro-aperture Membrane is an excellent material of sound transmission for its special structure, though the basic rule is of no difference from normal material. Something more important, from test data, it was discovered that PTFE will not affect sound transmission when aperture diameter reaches 0.22m, which is valuable for the research of sound transmission on Micro-aperture.