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Organic-inorganic hybrid perovskites have electronic and optoelectronic properties that make them appealing in many device applications.sup.1-4. Although many approaches focus on polycrystalline materials.sup.5-7, single-crystal hybrid perovskites show improved carrier transport and enhanced stability over their polycrystalline counterparts, due to their orientation-dependent transport behaviour.sup.8-10 and lower defect concentrations.sup.11,12. However, the fabrication of single-crystal hybrid perovskites, and controlling their morphology and composition, are challenging.sup.12. Here we report a solution-based lithography-assisted epitaxial-growth-and-transfer method for fabricating single-crystal hybrid perovskites on arbitrary substrates, with precise control of their thickness (from about 600 nanometres to about 100 micrometres), area (continuous thin films up to about 5.5 centimetres by 5.5 centimetres), and composition gradient in the thickness direction (for example, from methylammonium lead iodide, MAPbI.sub.3, to MAPb.sub.0.5Sn.sub.0.5I.sub.3). The transferred single-crystal hybrid perovskites are of comparable quality to those directly grown on epitaxial substrates, and are mechanically flexible depending on the thickness. Lead-tin gradient alloying allows the formation of a graded electronic bandgap, which increases the carrier mobility and impedes carrier recombination. Devices based on these single-crystal hybrid perovskites show not only high stability against various degradation factors but also good performance (for example, solar cells based on lead-tin-gradient structures with an average efficiency of 18.77 per cent). A solution-based lithography-assisted epitaxial-growth-and-transfer method is used to fabricate single-crystal hybrid perovskites on any surface, with precise control of the thickness, area and chemical composition gradient., Author(s): Yusheng Lei [sup.1] , Yimu Chen [sup.1] , Ruiqi Zhang [sup.1] , Yuheng Li [sup.1] , Qizhang Yan [sup.1] , Seunghyun Lee [sup.2] , Yugang Yu [sup.3] , Hsinhan [...]

Strain engineering is a powerful tool with which to enhance semiconductor device performance.sup.1,2. Halide perovskites have shown great promise in device applications owing to their remarkable electronic and optoelectronic properties.sup.3-5. Although applying strain to halide perovskites has been frequently attempted, including using hydrostatic pressurization.sup.6-8, electrostriction.sup.9, annealing.sup.10-12, van der Waals force.sup.13, thermal expansion mismatch.sup.14, and heat-induced substrate phase transition.sup.15, the controllable and device-compatible strain engineering of halide perovskites by chemical epitaxy remains a challenge, owing to the absence of suitable lattice-mismatched epitaxial substrates. Here we report the strained epitaxial growth of halide perovskite single-crystal thin films on lattice-mismatched halide perovskite substrates. We investigated strain engineering of [alpha]-formamidinium lead iodide ([alpha]-FAPbI.sub.3) using both experimental techniques and theoretical calculations. By tailoring the substrate composition--and therefore its lattice parameter--a compressive strain as high as 2.4 per cent is applied to the epitaxial [alpha]-FAPbI.sub.3 thin film. We demonstrate that this strain effectively changes the crystal structure, reduces the bandgap and increases the hole mobility of [alpha]-FAPbI.sub.3. Strained epitaxy is also shown to have a substantial stabilization effect on the [alpha]-FAPbI.sub.3 phase owing to the synergistic effects of epitaxial stabilization and strain neutralization. As an example, strain engineering is applied to enhance the performance of an [alpha]-FAPbI.sub.3-based photodetector. A method of deposition of mixed-cation hybrid perovskite films as lattice-mismatched substrates for an [alpha]-FAPbI.sub.3 film is described, giving strains of up to 2.4 per cent while also stabilizing the metastable [alpha]-FAPbI.sub.3 phase for several hundred days., Author(s): Yimu Chen [sup.1] , Yusheng Lei [sup.1] , Yuheng Li [sup.1] , Yugang Yu [sup.2] , Jinze Cai [sup.2] , Ming-Hui Chiu [sup.3] , Rahul Rao [sup.4] , Yue [...]

Abstract. Warehouses occupy much space and land, which has become increasingly scarce in many parts of Europe, Asia, and the United States, particularly close to areas where demand is generated, [...]

Abstract. We sequence storage and retrieval jobs to minimize total travel time of a storage/retrieval (S/R) machine in a two-depot automated storage/retrieval system. These systems include storage systems with aisle-captive [...]

Annually, millions of containers enter and exit the stacking area of a terminal. If the stacking operations are not efficient, long ship, train, and truck delays will result. To improve [...]

Compact, multi-deep three-dimensional (3D), Automated Storage and Retrieval Systems (AS/RS) are becoming more common, due to new technologies, lower investment costs, time efficiency and compact size. Decision-making research on these systems is still in its infancy. This paper studies a particular compact system with rotating conveyors for the depth movement and a Storage/Retrieval (S/R) machine for the horizontal and vertical movement of unit loads. The optimal storage zone boundaries are determined for this system with two product c1asses: high-and low-turnover, by minimizing the expected S/R machine travel time. We formulate a mixed-integer non-linear programming model to determine the zone boundaries. A decomposition algorithm and a one-dimensional search scheme are developed to solve the model. The algorithm is complex, but the results are appealing since most of them are in c1osed-form and easy to apply to optimally layout the 3D AS/RS rack. The results show that the S/R machine travel time is significantly influenced by the zone dimensions, zone sizes and ABC curve skewness (presenting turnover patterns of different products). The presented results are compared with those under random storage and it is shown that significant reductions of the machine travel time are obtainable by using c1ass-based storage. [Supplementary materials are available for this artic1e. Go to the publisher's online edition of IIE Transactions for the following free supplemental resource: Appendix] Keywords: Order picking, storage rack design, AS/RS, travel time model, c1ass-based storage, 1. Introduction Approaches to improve order picking efficiency and reduce storage space often also shorten customer response times in supply chains, decrease costs and improve associated customer service. It is [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ejor.2007.10.016 Byline: Yugang Yu (a)(b), Feng Chu (c), Haoxun Chen (c) Keywords: Supply chain inventory; Stackelberg game; Lot-sizing; Pricing; Raw materials Abstract: Vendor managed inventory (VMI) is an inventory management strategy to let a vendor manage his retailers' inventories, which makes the vendor have the opportunity to obtain some inventory and market-related information of his retailers. This paper discusses how the vendor can take advantage of this information for increasing his own profit by using a Stackelberg game in a VMI system. The vendor here is a manufacturer who procures raw materials to produce a finished product and supplies it at the same wholesale price to multiple retailers. The retailers then sell the product in independent markets at retail prices. Solution procedures are developed to find the Stackelberg game equilibrium that each enterprise is not willing to deviate from for maximizing his own profit. The equilibrium makes the manufacturer benefited, and the retailers' profits maximized. The equilibrium can then be improved for further benefiting the manufacturer and his retailers if the retailers are willing to cooperate with the manufacturer by using a cooperative contract. Finally, a numerical example and the corresponding sensitivity analysis are given to illustrate that: (1) the manufacturer can benefit from his leadership, and monopolize the added profit of the VMI system in some cases; (2) The manufacturer can further improve his own profit, and then the retailers' profits by the cooperative contract, as compared to the Stackelberg equilibrium; (3) market and raw material related parameters have significant influence on every enterprise's net profit. Author Affiliation: (a) RSM (Rotterdam School of Management), Erasmus University, The Netherlands (b) Business School, University of Science and Technology of China, Hefei, Anhui 230026, China (c) FRE CNRS 2848 ICD-LOSI, University of Technology of Troyes, 10010 Troyes, France Article History: Received 4 March 2005; Accepted 11 October 2007

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ejor.2005.09.045 Byline: Yugang Yu, Feng Chu, Haoxun Chen Keywords: Inventory; Routing; Transportation; Pumping Abstract: We give a counterexample to illustrate that a key theorem in the paper entitled 'Coordination of production and distribution planning' (European Journal of Operational Research 72, 503-517) is not correct, and then analyze where an error occurs in the proof of the theorem. Author Affiliation: FRE CNRS 2732 ISTIT-OSI, University of Technology of Troyes, 12, rue Marie Curie BP 2060, 10010 Troyes, France Article History: Received 4 March 2005; Accepted 11 September 2005