ZnCdSe量子点的激子行为研究

用金属有机化学气相沉积(MOCVD)的方法在晶格失配较小的情况下制备了ZnCdSe量子点。并用原子力显微镜(AFM)和极低温度下的发光光谱确认了量子点的形成。原子力显微镜观测的形貌变化发现。随着生长后时间的增加,量子点的尺寸逐渐增大。而密度减小,这是由于熟化过程作用的结果。随着量子点生长完毕与加盖层之间间隔时间的增加,量子点的发光峰位明显红移,且由变温光谱得到的激子束缚能逐渐变小。这可以解释为随着间隔时间的增加,量子点的熟化过程导致量子点的尺寸增大,量子限域效应减弱所致。     

Surface diffusion of copper on tantalum substrates by Ostwald ripening

In this work, we report on the determination of surface diffusion coefficient of copper on tantalum substrates by Ostwald ripening. It is shown that impurities, such as oxygen, strongly influence the kinetics of dewetting of copper films on tantalum substrates. Two technologically important interfaces with copper were investigated: Cu/β-Ta and Cu/α-Ta. For copper surface diffusion on β-Ta surface, a surface diffusion coefficient of was measured at 550 °C. The temperature dependence of surface diffusion was investigated between 400 °C and 550 °C. Using an Arrhenius relationship, an activation energy of 0.83 ± 0.1 eV and a pre-exponential factor of were calculated. For copper surface diffusion on α-Ta surface, a diffusion coefficient of was measured at 550 °C. We discuss the diffusion mechanism involved during the cluster growth and the origin of the faster surface diffusion of copper on the β-Ta substrate as compared to the α-Ta phase.     

Estimate of the attenuation coefficient using a clinical array transducer for the detection of cervical ripening in human pregnancy

Premature delivery is the leading cause of infant mortality in the United States. Currently, premature delivery cannot be prevented and new treatments are difficult to develop due to the inability to diagnose symptoms prior to uterine contractions. Cervical ripening is a long period that precedes the active phase of uterine contractions and cervical dilation. The changes in the microstructure of the cervix during cervical ripening suggest that the ultrasonic attenuation should decrease. The objective of this study is to use the reference phantom algorithm to estimate the ultrasonic attenuation in the cervix of pregnant human patients. Prior to applying the algorithm to in vivo human data, two homogeneous phantoms with known attenuation coefficients were used to validate the algorithm and to find the length and the width of the region of interest (ROI) that achieves the smallest error in the attenuation coefficient estimates. In the phantom data, we found that the errors in the attenuation coefficients estimates are less than 12% for ROIs that contain 40 wavelengths or more axially and 30 echo lines or more laterally. The reference phantom algorithm was then used to obtain attenuation maps of the echoes from two human pregnant cervices at different gestational ages. It was observed that the mean of the attenuation coefficient estimates in the cervix of the patient at a more advanced gestational age is smaller than the mean of the attenuation coefficient estimates in the cervix of the patient at an earlier gestational age which suggests that ultrasonic attenuation decreases with increasing gestational age. We also observed a large variance between the attenuation coefficient estimates in the different regions of the cervix due to the natural variation in tissue micro-structures across the cervix. The preliminary results indicate that the algorithm could potentially provide an important diagnostic tool for diagnosing the risk of premature delivery.     

Ostwald‐Ripening‐Induced Growth of Parallel Face‐Exposed Ag Nanoplates on Micro‐Hemispheres for High SERS Activity

Ag nanoplates, as two‐dimensional plasmonic nanostructures, have attracted intensive attention due to their strong shape‐dependent optical properties and related applications. Here parallel face‐exposed Ag nanoplates vertically grown on micro‐hemisphere surfaces have been achieved by firstly electrodepositing the micro‐hemispheres assembled by Ag nanoplates, whose planar surfaces are stuck together, on indium tin oxide substrates, and then Ostwald ripening the as‐electrodeposited micro‐hemispheres in water. The sizes of the nanoplates and the gaps between the neighboring nanoplates have been tailored by tuning the Ostwald‐ripening duration, so that the SERS activity of the micro‐hemispheres has been remarkably improved. The improved SERS activity can be well explained by our systematic finite‐element simulation. Therefore, Ostwald ripening offers a route to the synthesis of Ag nanoplates, and the optimization of plasmon coupling and SERS activity of nanostructure‐assembled systems.     

One‐Pot Template‐Free Synthesis of NaYF4 Upconversion Hollow Nanospheres for Bioimaging and Drug Delivery

Hollow‐structured nanomaterials with fluorescent properties are extremely attractive for image‐guided cancer therapy. In this paper, sub‐100 nm and hydrophilic NaYF₄ upconversion (UC) hollow nanospheres (HNSs) with multicolor UC luminescence and drug‐delivery properties were successfully prepared by a facile one‐pot template‐free hydrothermal route using polyetherimide (PEI) polymer as the stabilizing agent. XRD, SEM, TEM, and N₂‐adsorption/desorption were used to characterize the as‐obtained products. The growth mechanism of the HNSs has been systematically investigated on the basis of the Ostwald ripening. Under 980 nm excitation, UC emissions of HNSs can be tuned by a simple change of the concentration or combination of various upconverters. As a result, the PEI‐coated HNSs could be used as efficient probes for in vitro upconversion luminescence (UCL) cell imaging. Furthermore, a doxorubicin storage/release behavior and cancer‐cell‐killing ability investigation reveal that the product has the potential to be a drug carrier for cancer therapy.     

Self‐template hydrothermal synthesis ZnS microspheres

Zinc sulfide (ZnS) microspheres were synthesized by a self‐template hydrothermal route using thiourea as sulphur source. The formation of these hollow spheres was mainly attributed to the oriented aggregation of ZnS nanocystals around the gas‐liquid interface between gas (H₂S, NH₃, or CO₂) and water followed by an Ostwald ripening process. The gas bubbles of H₂S, NH₃, or CO₂ produced during the reaction might play a soft‐template to form ZnS hollow microspheres. The products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), electron diffraction (ED), and photoluminescence (PL). The crystal structure of prepared ZnS microspheres is hexagonal phase polycrystalline. The average microspheres diameter is 1.5 ‐ 6 µm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

锰的硅化物薄膜在Si(100)-2×1表面生长的STM研究

锰的硅化物在微电子器件、自旋电子学器件等领域具有良好的应用前景, 了解锰的硅化物薄膜在硅表面的生长规律是其走向实际应用的关键步骤之一. 本文采用分子束外延方法在Si(100)-2× 1表面沉积了约4个原子层的锰薄膜, 并利用超高真空扫描隧道显微镜研究了该薄膜与硅衬底之间在250-750℃范围内的固相反应情况. 室温下沉积在硅衬底表面的锰原子与衬底不发生反应, 薄膜由无序的锰团簇构成; 当退火温度高于290℃时, 锰原子与衬底开始发生反应, 生成外形不规则的枝晶状锰硅化物和富锰的三维小岛; 325℃时, 衬