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1.
    
There is great interest in self‐assembled oxide vertical nanocomposite films consisting of epitaxial spinel pillars in a single crystal perovskite matrix, due to their tunable electronic, magnetic, and multiferroic properties. Varying the composition or geometry of the pillars in the out‐of‐plane direction has not been previously reported but can provide new routes to tailoring their properties in three dimensions. In this work, ferrimagnetic epitaxial CoFe2O4, MgFe2O4, or NiFe2O4 spinel nanopillars with an out‐of‐plane modulation in their composition and shape are grown in a BiFeO3 matrix on a (001) SrTiO3 substrate using pulsed laser deposition. Changing the pillar composition during growth produces a homogeneous pillar composition due to cation interdiffusion, but this can be suppressed using a sufficiently thick blocking layer of BiFeO3 to produce bi‐pillar films containing for example a layer of magnetically hard CoFe2O4 pillars and a layer of magnetically soft MgFe2O4 pillars, which form in different locations. A thinner blocking layer enables contact between the top of the CoFe2O4 and the bottom of the MgFe2O4 which leads to correlated growth of the MgFe2O4 pillars directly above the CoFe2O4 pillars and provides a path for interdiffusion. The magnetic hysteresis of the nanocomposites is related to the pillar structure.  相似文献   

2.
    
Perovskite‐spinel epitaxial nanocomposite thin films are commonly grown on single crystal perovskite substrates, but integration onto a Si substrate can greatly increase their usefulness in devices. Epitaxial BiFeO3–CoFe2O4 nanocomposites consisting of CoFe2O4 pillars in a BiFeO3 matrix are grown on (001) Si with two types of buffer layers: molecular beam epitaxy (MBE)‐grown SrTiO3‐coated Si and pulsed‐laser‐deposited (PLD) Sr(Ti0.65Fe0.35)O3/CeO2/yttria‐stabilized ZrO2/Si. The nanocomposite grows with the same crystallographic orientation and morphology as that observed on single crystal SrTiO3 when the buffered Si substrates are smooth, but roughness of the Sr(Ti0.65Fe0.35)O3 promoted additional CoFe2O4 pillar orientations with 45° rotation. The nanocomposites on MBE‐buffered Si show very high magnetic anisotropy resulting from magnetoelastic effects, whereas the hysteresis of nanocomposites on PLD‐buffered Si can be understood as a combination of the hysteresis of the Sr(Ti0.65Fe0.35)O3 film and the CoFe2O4 pillars.  相似文献   

3.
    
A strain‐driven BiFeO3 (BFO) tetragonal to rhombohedral phase transition is demonstrated in self‐assembled BiFeO3‐CoFe2O4 (BFO‐CFO) nanocomposites on LaAlO3 (110)‐oriented substrates with varying thickness. The CFO forms parallel nanoscale fin‐shaped structures within a BFO matrix. Out‐of‐plane lattice strain from the BFO/CFO interfaces stabilizes the BFO rhombohedral‐like phase. The BFO exhibits a range of ferroelectric textures including stripe domains and centered domain arrangements, and the magnetic anisotropy of CFO shows a thickness‐dependent reorientation.  相似文献   

4.
    
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5.
    
Spontaneous self‐assembly of a multication nanophase in another multication matrix phase is a promising bottom‐up approach to fabricate novel, nanocomposite structures for a range of applications. In an effort to understand the mechanisms for such self‐assembly, complimentary experimental and theoretical studies are reported to first understand and then control or guide the self‐assembly of insulating BaZrO3 (BZO) nanodots within REBa2Cu3O7–δ (RE = rare earth elements including Y, REBCO) superconducting films. The strain field developed around BZO nanodots embedded in the REBCO matrix is a key driving force dictating the self‐assembly of BZO nanodots along REBCO c‐axis. The size selection and spatial ordering of BZO self‐assembly are simulated using thermodynamic and kinetic models. The BZO self‐assembly is controllable by tuning the interphase strain field. REBCO superconducting films with BZO defect arrays self‐assembled to align in both vertical (REBCO c‐axis) and horizontal (REBCO ab‐planes) directions result in the maximized pinning and Jc performance for all field angles with smaller angular Jc anisotropy. The work has broad implications for the fabrication of controlled self‐assembled nanostructures for a range of applications via strain‐tuning.  相似文献   

6.
    
Dielectric surface modifications (DSMs) can improve the performance of organic thin‐film transistors (OTFTs) significantly. In order to gain a deeper understanding of this performance enhancement and to facilitate high‐mobility transistors, perylene based devices utilizing novel dielectric surface modifications have been produced. Novel DSMs, based on derivates of tridecyltrichlorosilane (TTS) with different functional end‐groups as well as polymeric dielectrics have been applied to tailor the adhesion energy of perylene. The resulting samples were characterized by electronic transport measurements, scanning probe microscopy, and X‐ray diffraction (XRD). Measurements of the surface free energy of the modified dielectric enabled the calculation of the adhesion energy of perylene upon these novel DSMs by the equation‐of‐state approach. These calculations demonstrate the successful tailoring of the adhesion energy. With these novel DSMs, perylene thin‐films with a superior film quality were produced, which enabled high‐performance perylene‐based OTFTs with high charge‐carrier mobility.  相似文献   

7.
本文较系统地介绍了高温超导薄膜的制备方法与生长机理,讨论了生长工艺与薄膜超导性能之间的关系,并对高温超导薄膜的异质外延、多层膜结构及超晶格制备等一些最新进展作了介绍。  相似文献   

8.
    
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9.
    
Achieving self‐assembling/self‐organizing systems is the holy grail of nanotechnology. Spontaneous organization is not unique to the physical sciences since nature has been producing such systems for millions of years. In biological systems global patterns emerge from numerous interactions among lower‐level components of the system. The same is true for physical systems. In this review, the self‐assembly mechanisms of oxide nanocomposite films, as well as the advantageous functionalities that arise from such ordered structures, are explored.  相似文献   

10.
    
Mechanical buckling usually means catastrophic failure in structural mechanics systems. However, controlled buckling of thin films on compliant substrates has been used to advantage in diverse fields such as micro‐/nanofabrication, optics, bioengineering, and metrology as well as fundamental mechanics studies. In this Feature Article, a mechanical buckling model is presented, which sprang, in part, from the buckling study of high‐quality, single‐crystalline nanomaterials. To check the mechanical‐buckling phenomenon down to the nano‐/molecular scale, well‐aligned single‐walled carbon nanotube arrays and cross linked carbon‐based monolayers are transferred from growth substrate onto elastomeric substrate and then they are buckled into well‐defined shapes that are amenable to quantitative analysis. From this nano‐ or molecular‐scale buckling, it is shown that the mechanical moduli of nanoscale materials can easily be determined, even using a model based on continuum mechanics. In addition, buckling phenomena can be utilized for the determination of mechanical moduli of organic functional materials such as poly(3‐hexylthiophene) (P3HT) and P3HT/6,6‐phenyl‐C61‐butyric acid methyl ester (PCBM) composite, which are widely used for organic transistors and organic photovoltaics. The results provide useful information for the realization of flexible and/or stretchable organic electronics. Finally, the fabrication and applications of “wavy, stretchable” single‐crystal Si electronics on elastomeric substrates are demonstrated.  相似文献   

11.
    
Thickness‐dependent structure–property relationships in strained SrRuO3 thin films on GdScO3 (GSO) substrates are reported. The film is found to have epitaxially stabilized crystal structures that vary with the film thickness. Below 16 nm, the √2apc × √2apc × 2apc monoclinic structure is stabilized while above 16 nm the film has the apc × 2apc × apc tetragonal structure. The thickness‐dependent structural changes are ascribed to the substrate‐induced modification in the RuO6 octahedral rotation pattern, which highlights the significance of the octahedral rotations for the epitaxial strain accommodation in the coherently‐grown films. Close relationships between the structural and physical properties of the films are also found. The monoclinic film has the uniaxial magnetic easy axis 45° away from the [110]GSO direction while the tetragonal film has the one that lies along the in‐plane [1–10]GSO direction. The results demonstrate that the octahedral rotations in the strained perovskite oxide thin films are a key factor for determining their structure phases and physical properties.  相似文献   

12.
Owing to its excellent electrical property,YBCO thin film is much better than metal in the application for microwave devices. It makes the devices smaller, lighter, and with higher quality factor and lower insertion loss. YBCO thin film has attracted attentions for many years. Aiming at the uniformity and property of 3-inch double-sided YBCO thin film, the following aspects is considered in this dissertation:  相似文献   

13.
    
Tunable and enhanced low‐field magnetoresistance (LFMR) is observed in epitaxial (La0.7Sr0.3MnO3)0.5:(ZnO)0.5 (LSMO:ZnO) self‐assembled vertically aligned nanocomposite (VAN) thin films, which have been grown on SrTiO3 (001) substrates by pulsed laser deposition (PLD). The enhanced LFMR properties of the VAN films reach values as high as 17.5% at 40 K and 30% at 154 K. They can be attributed to the spin‐polarized tunneling across the artificial vertical grain boundaries (GBs) introduced by the secondary ZnO nanocolumns and the enhancement of spin fluctuation depression at the spin‐disordered phase boundary regions. More interestingly, the vertical residual strain and the LFMR peak position of the VAN films can be systematically tuned by changing the deposition frequency. The tunability of the physical properties is associated with the vertical phase boundaries that change as a function of the deposition frequency. The results suggest that the tunable artificial vertical GB and spin‐disordered phase boundary in the unique VAN system with vertical ferromagnetic‐insulating‐ferromagnetic (FM‐I‐FM) structure provides a viable route to manipulate the low‐field magnetotransport properties in VAN films with favorable epitaxial quality.  相似文献   

14.
    
Here, a new approach to the layer‐by‐layer solution‐processed fabrication of organic/inorganic hybrid self‐assembled nanodielectrics (SANDs) is reported and it is demonstrated that these ultrathin gate dielectric films can be printed. The organic SAND component, named P‐PAE, consists of polarizable π‐electron phosphonic acid‐based units bound to a polymeric backbone. Thus, the new polymeric SAND (PSAND) can be fabricated either by spin‐coating or blade‐coating in air, by alternating P‐PAE, a capping reagent layer, and an ultrathin ZrOx layer. The new PSANDs thickness vary from 6 to 15 nm depending on the number of organic‐ZrOx bilayers, exhibit tunable film thickness, well‐defined nanostructures, large electrical capacitance (up to 558 nF cm?2), and good insulating properties (leakage current densities as low as 10?6 A cm?2). Organic thin‐film transistors that are fabricated with representative p‐/n‐type organic molecular/polymeric semiconducting materials, function well at low voltages (<3.0 V). Furthermore, flexible TFTs fabricated with PSAND exhibit excellent mechanical flexibility and good stress stability, offering a promising route to low operating voltage flexible electronics. Finally, printable PSANDs are also demonstrated and afford TFTs with electrical properties comparable to those achieved with the spin‐coated PSAND‐based devices.  相似文献   

15.
    
Directed self‐assembled nanomaterials with biological applications have attracted great interest. Here, arrowhead gold nanorod (NR) dimers with side‐by‐side and end‐to‐end motifs (known as AHSBS and AHETE dimers, respectively) presented based on selective modification of arrowhead NRs with DNA and polyethylene glycol, possessing intense surface enhanced Raman scattering (SERS) signals, are assembled for in situ intracellular microRNA detection. The arrowhead NR dimers are capable of recognizing target microRNA in a sequence‐specific manner as Raman signals significantly enhanced within dimers with both motifs. Following recognition, the dimers gradually disassemble, resulting in decreased SERS signals to achieve effective in situ Raman imaging and quantify the detection of target microRNA. The SERS intensity shows a linear relationship with intracellular target microRNA and a limit of detection of 0.011 amol ngRNA?1 for the AHETE dimer and 0.023 amol ngRNA?1 for the AHSBS dimer, respectively. The sensitivity for AHETE dimers is ≈2.1 times higher than that for AHSBS dimers, which is attributed to the small quantity of recognized molecules and stronger electrical enhancement, which causes greater SERS signals in the AHETE dimers. This approach opens up a new avenue for directed nanomaterials assembly and biological detection in living cells.  相似文献   

16.
    
Materials and technology development for designing innovative and efficient X‐ray radiation detectors is of utmost importance for a wide range of applications ranging from security to medical imaging. Here, highly sensitive direct X‐ray detectors based on novel cesium (Cs)‐based triple cation mixed halide perovskite thin films are reported. Despite being in a thin film form, the devices exhibit a remarkably high X‐ray sensitivity of (3.7 ± 0.1) µC Gy?1 cm?2 under short‐circuit conditions. At a small reverse bias of 0.4 V, the sensitivity further increases by orders of magnitude reaching a record value of (97 ± 1) µC Gy?1 cm?2 which surpasses state‐of‐the‐art inorganic large‐area detectors (a‐Se and poly‐CZT). Based on detailed structural, electrical, and spectroscopic investigations, the exceptional sensitivity of the triple cation Cs perovskite is attributed to its high ambipolar mobility‐lifetime product as well as to the formation of a pure stable perovskite phase with a low degree of energetic disorder, due to an efficient solution‐based alloying of individual n‐ and p‐type perovskite semiconductors.  相似文献   

17.
    
Multiferroic materials have driven significant research interest due to their promising technological potential. Developing new room‐temperature multiferroics and understanding their fundamental properties are important to reveal unanticipated physical phenomena and potential applications. Here, a new room temperature multiferroic nanocomposite comprised of an ordered ferrimagnetic spinel α‐LiFe5O8 (LFO) and a ferroelectric perovskite BiFeO3 (BFO) is presented. It is observed that lithium (Li)‐doping in BFO favors the formation of LFO spinel as a secondary phase during the synthesis of LixBi1?xFeO3 ceramics. Multimodal functional and chemical imaging methods are used to map the relationship between doping‐induced phase separation and local ferroic properties in both the BFO‐LFO composite ceramics and self‐assembled nanocomposite thin films. The energetics of phase separation in Li doped BFO and the formation of BFO‐LFO composites are supported by first principles calculations. These findings shed light on Li's role in the formation of a functionally important room temperature multiferroic and open a new approach in the synthesis of light element doped nanocomposites for future energy, sensing, and memory applications.  相似文献   

18.
    
Self‐assembled nanocomposite films and coatings have huge potential for many functional and structural applications. However, control and manipulation of the nanostructures is still at very early stage. Here, guidelines are established for manipulating the types of composite structures that can be achieved. In order to do this, a well studied (YBa2Cu3O7‐δ)1‐x:(BaZrO3)x ‘model’ system is used. A switch from BaZrO3 nanorods in YBa2Cu3O7‐δ matrix to planar, horizontal layered plates is found with increasing x, with a transitional cross‐ply structure forming between these states at x = 0.4. The switch is related to a release in strain energy which builds up in the YBa2Cu3O7‐δ with increasing x. At x = 0.5, an unusually low strain state is observed in the planar composite structure, which is postulated to arise from a pseudo‐spinodal mechanism.  相似文献   

19.
ZnO薄膜紫外受激发射研究的最新进展   总被引：3，自引：0，他引：3  
ZnO是一种新型的Ⅱ-Ⅵ族半导体材料,具有优良的晶格、光学和电学性能,其显著优点是在紫外波段存在着受激发射.光泵浦紫外受激发射的获得和自形成谐振腔的发现,使ZnO薄膜成为一种备受青睐的新型光电材料,在紫外探测器,LED,LD等领域有着广阔的应用前景.文章详细阐述了ZnO薄膜的紫外受激发射研究的最新进展.  相似文献   

20.
    
This paper examines the microstructure evolution of 3,4,9,10‐perylene‐tetracarboxylic bis‐benzimidazole (PTCBI) thin films resulting from conditions imposed during film deposition. Modification of the silicon dioxide interface with a hydrophobic monolayer (octadecyltrichlorosilane (OTS‐18)) alters the PTCBI growth habit by changing the unit cell contact plane. PTCBI films deposited on oxide surface have an orientation of (011), while films atop OTS‐treated oxide surface have a preferred orientation of (001). The quality of the self assembled monolayer does not appear to influence the PTCBI growth preference significantly yet it enhances the carrier mobility, suggesting that charge traps are adequately passivated due to uniform monolayer coverage. High‐quality monolayers result in n‐type carrier mobility values of 0.05 cm2V–1s–1 Increasing the substrate temperature during PTCBI film deposition correlates with an increase in mobility that is most significant for films deposited on OTS‐treated surface.  相似文献   

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