Xiaohong Zhu

Enhanced dielectric properties of Ba1-xSrxTiO3 thin film grown on La1-xSrxMnO3 bottom layer

The Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} (BST)/La{sub 0.67}Sr{sub 0.33}MnO{sub 3} (LSMO) heterostructure has been fabricated by pulsed-laser deposition on (001) SrTiO{sub 3} single crystal substrate. The crystallization and surface morphology of the heterostructure have been characterized by x-ray diffraction and atomic force microscopy. The composition distribution along the depth of the heterostructure is analyzed by Auger electron spectroscopy. It is founded that the LSMO bottom layer shows a marked effect on the dielectric properties of the BST films. Comparing with BST/YBCO (YBCO-YBa{sub 2}Cu{sub 3}O{sub 7}) heterostructure grown by similar process, the dielectric loss exhibits much lower and less frequency dispersive, especially in the high frequency region. The loss tangent at 100 kHz is about 0.012 and the figure of merit factor is about 25 under the condition of 200 kV/cm. Ferroelectric hysteresis measurement shows that the remanent polarization and coercive field of the heterostructure are 3.4 {mu}C/cm{sup 2} and 39 kV/cm, respectively. These parameters are all better than BST/YBCO heterostructure. The good surface morphology and the element diffusion between BST and LSMO layers may be suggested to be responsible for the above-improved parameters of BST/LSMO heterostructure.The Ba0.7Sr0.3TiO3(BST)∕La0.67Sr0.33MnO3(LSMO) heterostructure has been fabricated by pulsed-laser deposition on (001) SrTiO3 single crystal substrate. The crystallization and surface morphology of the heterostructure have been characterized by x-ray diffraction and atomic force microscopy. The composition distribution along the depth of the heterostructure is analyzed by Auger electron spectroscopy. It is founded that the LSMO bottom layer shows a marked effect on the dielectric properties of the BST films. Comparing with BST∕YBCO (YBCO—YBa2Cu3O7) heterostructure grown by similar process, the dielectric loss exhibits much lower and less frequency dispersive, especially in the high frequency region. The loss tangent at 100kHz is about 0.012 and the figure of merit factor is about 25 under the condition of 200kV∕cm. Ferroelectric hysteresis measurement shows that the remanent polarization and coercive field of the heterostructure are 3.4μC∕cm2 and 39kV∕cm, respectively. These parameters are all better than...

Characterization of Ba0.1Sr0.9TiO3/YBa2Cu3O7-δ heterostructures on vicinal LaAlO3 substrates

Abstract Ba0.1Sr0.9TiO3/YBa2Cu3O7−δ heterostructure films have been fabricated by pulsed-laser deposition on LaAlO3 substrates. During the fabrication, a c-axis oriented YBa2Cu3O7−δ thin film with atomically smooth surfaces was epitaxially grown in the step-flow mode on a vicinal LaAlO3 substrate. The superconducting transition temperature Tc was above 88xa0K. Then a single-crystalline Ba0.1Sr0.9TiO3 layer was deposited on top of the YBa2Cu3O7−δ layer. A parallel-plate capacitor configuration was used to measure the capacitance–voltage properties of the Ba0.1Sr0.9TiO3 thin films at 300xa0K and 77xa0K, respectively. The dielectric constant and loss tangent measured at 1xa0MHz and 77xa0K are 1200 and 0.0045, respectively. A tunability of 60% has been achieved under ±30xa0V DC bias, confirming their usefulness for frequency-agile microwave devices.

Metalorganic chemical vapor deposition of GaNAs alloys using different Ga precursors

The GaNAs alloys have been grown by metalorganic chemical vapor deposition (MOCVD) using dimethylhydrazine (DMHv) as the nitrogen precursor, triethylgallium (TEGa) and trimethylgallium (TMGa) as the gallium precursors, respectively. Both symmetric (004) and asymmetric (1 1 5) high-resolution X-ray diffraction (HRXRD) were used to determine the nitrogen content in GaNAs layers. Secondary ion mass spectrometry (SIMS) was used to obtain the impurity content. T e influence of different Ga precursors on GaNAs quality has been investigated. Phase separation is observed in the direction when using TMGa as the Ga precursor but not observed when using TEGa. This phenomenon should originate from the parasitic reaction between the Ga and N precursors. Furthermore. samples grown with TEGa have better quality and less impurity contamination than those with TMGa. Nitrogen content of 5.742% has been achieved using TEGa and no phase separation observed in the sample

Nanofabrication of grid-patterned substrate by holographic lithography

The two-dimensional grid patterns on Si(001) in nanometer scale have been fabricated by holographic lithography and reactive ion etching, which can be used as a substrate for positioning Ge islands during self-assembled epitaxy to obtain an ordered Ge quantum dots matrix. By changing the configuration of the holographic lithography and the etching rate and time, we can control the grid period, the shape of the pattern cell, and the orientation of those shapes, respectively