1,720,963 research outputs found
Advanced CVD technology for 2D materials: graphene and transition metal di-chalcogenides
No full textGraphene, one of the most important two dimensional (2D) materials, has been attracting increasing interest and new applications in nano-scale electronic and photonic applications through the unprecedented electronic and optical properties it offers. However, the zero bandgap of graphene has restricted its use in some optoelectronic applications. Recently, transition metal dichalcogenides (TMDCs), two-dimensional layered materials, such as MoS2, MoSe2, WS2 and WSe2 have become a noteworthy complimentary material to graphene sharing many of its properties. They may however offer properties that are unattainable in graphene since TMDCs offer tuneability allowing a bandgap transition from indirect to direct with the single layer. This has led to use of TMDCs in applications such as transistors, photodetectors and electroluminescent devices. Chemical vapour deposition (CVD) technology has the advantage of offering conformal, scalable, and controllable thin film growth on a variety of different substrates. In this talk we describe our recent development in 2D materials, in particularly graphene and TMDCs, by the CVD technology and discuss their potential applications
Fabrication of thin film solar cell materials by APCVD
No full textThin film solar cells are currently being implemented commercially as they reduce the amount of semiconductor material required for each cell when compared to silicon wafers, thereby lowering the cost of production. Currently two direct band gap chalcogenide thin-film technologies, CdTe and CuInGa(S,Se)2 (CIGS), yield the highest reported power conversion efficiencies of 16.5% and 20.3%, respectively. In addition, Cu2ZnSnS4 (CZTS) is one of the most promising chalcogenide thin film photovoltaic absorber materials; with an optimal band gap of about 1.5 eV. More importantly, CZTS consists of abundant and non-toxic elements, so research on CZTS thin-film solar cells has been increasing significantly in recent years. Moreover, Sb2S3 based chalcogenide thin films have been proposed for use in photovoltaic applications. The preparation of chalcogenide thin films solar cells commonly use physical vapour deposition methods including thermal/e-beam evaporation, sputtering, and pulsed laser deposition, electrochemical deposition, spray pyrolysis, solution-based synthesis, followed by the sulfurization or selenization annealing process. In this paper, we report a non-vacuum process, using atmospheric pressure chemical vapour deposition (APCVD), to fabricate chalcogenide thin film solar cell materials as well as transparent conductive oxide (TCO) thin films. The optical, electrical, and structural properties of these materials were characterized by UV-VIS-NIR, four-point probes, SEM, EDX, XRD, Micro-Raman
Fabrication of chalcogenide and emerging materials by novel CVD technology
No full textChemical vapour deposition (CVD) technology is a widely used method in the optoelectronics and semiconductor industries, producing high purity thin films, in crystalline, amorphous and epitaxial phases. A variety of materials can be produced in this way although for the most part use of the technique has focussed on poly-silicon, silicon dioxide, silicon nitride and metallic materials. The advantages of CVD processing, which offers offer superior quality compared to conventional methods such as sputtering or co-evaporation, include conformality, coverage, and stoichiometry control. The process should also be more economical and scalable to large substrates as it can take place at atmospheric pressure rather than under vacuum conditions.The ORC has a long history of exploiting CVD for optoelectronic applications, initially depositing high purity silica for the achievement of some the worlds’ lowest loss optical fibres. Since 2001, we have been extending our CVD technology to the chalcogenides and are now routinely depositing germanium and antimony based sulphides on a variety of substrates including glass, silicon and flexible metallic and polyimide materials for optical applications and now we are in the process to fabricate these chalcogenide glasses in the fibre preform.In addition, our CVD technology has also been applied to fabricate chalcogenide materials for phase change memory applications, grapheme and molybdenum disulphide thin films for nano-electronic applications, and transparent conductive oxides, copper indium gallium sulphide, and copper zinc tin sulphide thin films for photovoltaic applications
Nanoscale MoS<sub>2</sub> thin films fabricated by atmospheric pressure chemical vapour deposition at ambient temperature
No full textWe report on the fabrication of scalable MoS2 thin films by atmospheric pressure chemical vapour deposition (APCVD) through the reaction of a MoCl5 precursor and the reactive gas H2S at ambient temperature. As the deposition is taking place at room temperature, these MoS2 thin films can be easily processed with conventional lithography and pre-patterned substrates to create a desired structure. We have deposited and characterized such films on SiO2/Si, silica, and sapphire substrates. As-deposited Mo-S thin films contain MoS2, MoS3, and some unreacted Cl atoms, however pure crystalline MoS2 thin films can be obtained through further reaction with H2 and H2S mixture gases in a two-step annealing process. The as-deposited films are robust and this further annealing can take place after photoresist removal. We have characterized fully annealed MoS2 thin films with SEM, EDX, micro-Raman, UV-VIS-NIR spectrometry, and Hall Effect measurement techniques. The annealed MoS2 thin films show the two characteristic MoS2 Raman peaks, E12g at ~382 cm-1 and A1g at ~405 cm-1, and a band gap of ~1.81eV, has been measured by UV-VIS-NIR spectrometry. The electrical characteristics of these APCVD grown MoS2 films, show they are n-type semiconductor with sheet resistance of 193.5 ± 0.6 Ohms/square, mobility of 33.8 ± 2.4 cm2.V-1.s-1, and carrier density of 1.23 ± 0.09e+21 cm-3. We believe this process and resulting MoS2 films show great promise for nanoelectronic and optoelectronic applications
Recent advances in the application of Chalcogenide Thin Films
No full textAmorphous chalcogenide films have now established themselves as an important optoelectronic material, with proven commercial and technological value demonstrated in part through their use as phase change media in past and future solid state memory technology. For the past decade, we have maintained a research program in the synthesis, characterization and application of chalcogenide thin films, now encompassing a range of metallic sulphides and application areas. In this talk we describe recent work on chalcogenide thin films deposited by both physical vapour deposition and atmospheric pressure chemical vapour deposition and discuss their application in phase change memory, solar cell, optical waveguide devices and as functional component in active metamaterials
Ultra low power consuming thermally stable sulphide materials for resistive and phase change memristive application
No full textThe use of conventional chalcogenide alloys in rewritable optical disks and the latest generation of electronic memories (phase change and nano-ionic memories) has provided clear commercial and technological advances for the field of data storage, by virtue of the many well-known attributes, in particular scaling, cycling endurance and speed, that these chalcogenide materials offer. While the switching power and current consumption of established germanium antimony telluride based phase change memory cells are a major factor in chip design in real world applications, the thermal stability and high on-state power consumption of these device can be a major obstacle in the path to full commercialization. In this work we describe our research in material discovery and prototype device fabrication and characterization, which through high throughput screening has demonstrated thermally stable, low current consuming chalcogenides for applications in PCRAM and oxygen doped chalcogenides for RRAM which significantly outperform the current contenders
Crystallisation study of the Cu<sub>2</sub>ZnSnS<sub>4</sub> chalcogenide material for solar applications
No full textSecond generation thin-film chalcogenide materials, in particular CuInGa(S,Se)2 (CIGS) and CdTe, have been among the most promising and quickly became commercial candidates for large-scale PV manufacturing. These materials offer stable and efficient (above 10%) photovoltaic modules fabricated by scalable thin-film technologies and cell efficiencies above 20 % (CIGS). Indium-free kesterite-related materials such as Cu2ZnSnS4 have attracted significant research interest due to their similar properties to CIGS. In these materials, indium is replaced with earth-abundant zinc and tin metals. The quaternary semiconductor Cu2ZnSnS4(CZTS) is a relatively new photovoltaic material and is expected to be interesting for environmentally amenable solar cells, as its constituents are nontoxic and abundant in the Earth's crust. The CZTS thin films show p-type conductivity, a band gap of 1.44–1.51 eV that is ideal to achieve the highest solar-cell conversion efficiency, and relatively high optical absorption in the visible light range
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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