Showing papers by "Yang Yang published in 1998"

Polymer electroluminescent devices processed by inkjet printing: I. Polymer light-emitting logo

Abstract: Inkjet printing (IJP) technology is a popular technology for desktop publishing. Since some of the conducting (or conjugated) polymers are solution processable, IJP technology becomes an ideal method for printing polymer light-emitting diodes with high resolution. Unfortunately, the polymer film printed from an inkjet printer usually consists of pin-holes, and this intrinsic character makes it unsuitable for fabricating high quality polymer electronic devices, particularly for devices in the sandwich structure. In this letter, we submit a hybrid structure, which consists of an inkjet printed layer in conjunction with another uniform spin coated polymer layer, as an alternative to the regular inkjet printed structure. The uniform layer serves as a buffer layer to seal the pin-holes and the IJP layer is the layer consisting of the desired pattern, for example the red–green–blue dots for a multicolor display. To demonstrate, we applied this hybrid technology to fabricate efficient and large area polymer ligh...

Dual-color polymer light-emitting pixels processed by hybrid inkjet printing

Abstract: A hybrid inkjet printing (HIJP) technology, which combines a pin-hole free polymer buffer layer and an inkjet printed polymer layer, allows the patterning of high quality polymer light-emitting devices. In this letter, we present a successful demonstration of controllable patterning of dual-color polymer light-emitting pixels using this HIJP technique. In this demonstration, the polymer buffer layer is a wide band gap, blue emitting semiconducting polymer prepared by the spin-casting technique. The inkjet printed layer is a red-orange semiconducting polymer which was printed onto the buffer layer. When a proper solvent was selected, the printed polymer diffused into the buffer layer and efficient energy transfer took place generating a red-orange photoluminescence and electroluminescence from the inkjet printed sites. Based on this principle, blue and orange-red dual-color polymer light-emitting pixels were fabricated on the same substrate. The use of this concept represents an entirely new technology for...

Polymer/metal interfaces and the performance of polymer light-emitting diodes

Abstract: Conjugated polymers are often treated as semiconductors with low doping concentrations. Unlike the traditional semiconductors which have a high density of surface states (mainly due to the dangling bonds), the nature of the metal/polymer interface, including barrier height and charge injection efficiency, is quite sensitive to the work function of the contact metal. In this article, we present evidence to show that the pinning of the surface Fermi level effect commonly observed at the silicon/metal interface can also be observed at the metal/polymer interface. It is achieved by controlling the doping level at the metal/polymer [poly(2-methoxy-5(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) or MEH-PPV] interface. ITO/MEH-PPV/Al devices doped with 2 A of calcium on the cathode side of the interfacial layer have the same device performance as the ITO/MEH-PPV/Ca devices. The heavily n-doped region pins the surface energy level, hence the polymer interface at the cathode side is no longer sensitive to the work function of the overcoated metal. It is believed that either the midgap bipolaron energy states created by the dopants or the sharp band bending at the interface is responsible for facilitating the electron injection. On the other hand, a p-doped region at the anode side, obtained by using a thin layer of an acid at the interface, pins the surface energy level and makes the contact insensitive to the work function of the anode. Therefore, an efficient polymer light-emitting diode with the p-i-n structure has been demonstrated without the matching of the work function of the metal electrodes.

Structural and electrical properties of chemical vapor deposition tungsten overgrowth on physical vapor deposited and metalorganic chemical vapor deposited TiN adhesion layers

Abstract: The structure and electrical properties of chemical vapor deposited W (CVD-W) films on various physical vapor deposited or metalorganic chemical vapor deposited TiN films have been investigated. The growth orientations of the TiN adhesion layers were controlled by deposition method and film thickness. The growth orientations of CVD-W films were found to depend strongly on the microstructures of TiN. The grain sizes and electrical resistivity of CVD-W were found to increase and decrease, respectively, with the grain sizes of underlying TiN layers.

Polymer light-emitting logos processed by ink-jet printing technology

Abstract: Ink-jet printing (IJP) technology is a popular technology for desktop publishing. Since some of the conducting polymers are solution processable, IJP technology becomes an ideal method for printing polymer light-emitting diodes with high resolution. In this manuscript, we present the first successful demonstration of patterning the polymer electroluminescent devices using the IJP technology. Unfortunately due to the dot form printing by the IJP, the polymer film printed from an ink-jet printer consists of pin-holes. This makes it unsuitable for fabricating high quality polymer electronic devices, particularly for devices in the sandwich structure. In this paper, we submit a hybrid structure, which consists of an ink-jet printed layer in conjunction with another uniform spin coated polymer layer, as an alternative to the regular ink-jet printed structure. The uniform spin coated polymer layer, as an alternative to the regular ink-jet printed structure. The uniform layer serves as a buffer layer to seal the pin hoe.s and the IJP layer is the layer consisting of the desired pattern, for example the red-green-blue dots for a multicolor display. To demonstrate, we applied this hybrid technology to fabricate efficient and large area polymer light-emitting logos. The use of this concept represents a whole new technology of fabricating polymer electronic device with lateral patterning capability.

Dual-color polymer light-emitting pixels processed by hybrid inkjet printing

Abstract: We present a successful demonstration of controllable patterning of dual-color polymer light-emitting pixels using a hybrid inkjet printing technique. In this demonstration, the polymer buffer layer is a wide bandgap, blue emitting semiconducting polymer, poly[2,5-bis[2-(N,N,N-triethylammonium) ethoxy]-1,4-phenylene-alt-1,4-phenylene] dibromide (PPP-NEt 3 + ), prepared by the spin-casting technique. The inkjet printed layer is a red-orange semiconductor polymer, poly(5-methoxy-2-propanoxysulfonide-1,4-phenylene vinylene) (MPS-PPV) which was printed onto the buffer layer. When a proper solvent was selected, MPS-PPV diffused into the buffer layer and efficient energy transfer took place from the PPP-NEt 3 + to the MPS-PPV generating a red-orange photoluminescence and electroluminescence from the inkjet printed sites. Based on this principle, blue and orange-red dual-color polymer light-emitting pixels were fabricated on the same substrate. The use of this concept represents an entirely new technology for fabricating polymer multicolor displays with high-resolution, lateral patterning capability.

Study of hydration of OPC/PFA blend with various activators using microwave technique

Abstract: The early hydration of ordinary Portland cement (OPC) pulverized fly ash (PFA) blends with various PFA proportions was investigated using microwave technique and conduction calorimeter. It is found that PFA acts as almost inert filler in the OPC/PFA blends during the first 40 h of hydration, thus it retards the early hydration of the blends. To accelerate the pozzolanic hydration of the PFA, three different additives were studied. It is found that both Ca(OH)2 and Na2SO4 can accelerate the early hydration of the OPC/PFA blends, but Na2SO4 is more effective than Ca(OH)2, whereas NaOH is not suitable for the acceleration of the early hydration of the OPC/PFA blend. © 1998 Kluwer Academic Publishers

[Study on health status of 3,333 old people in Chengdu City, Sichuan Province]

Abstract: In order to study the health status of 3,333 old people (over 60) in Chengdu city, a survey was carried out from May 1996 to Nov. 1996. Results revealed that 79.4% of old people had a history of chronic diseases. The first ten common chronic diseases were stated as follows: rheumatic arthritis, hypertension, benign prostatic hypertrophy, chronic bronchitis, cataract, chronic gastritis, osteoarthrosis, asthma and diabetes mellitus. There were significant differences of body weight index, vision and auditus disorder among old people according to their age (P < 0.01). As ageing grows, old people's physical condition and daily-life-capacity decline. In order to improve the quality of life among the aged, following aspects as popularizing health education on self care, strengthening programs on prevention and care of chronic diseases, expanding the medical and nursing services in community and easier access to hospitalization etc should be promoted.