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Table-Top Lasers for Resonant Infrared Deposition of Polymer Films

用于聚合物薄膜共振红外沉积的台式激光器

基本信息

批准号：
EP/I02798X/1
负责人：
David Patrick Shepherd
金额：
$ 65.21万
依托单位：
University of Southampton
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2012
资助国家：
英国
起止时间：
2012 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FI02798X%2F1
关键词：
Table Top Lasers Resonant Infrared

项目摘要

Thin films of organic molecules and polymers play a critical role in a huge number of electronic, photonic, mechanical, and medical technologies that are crucial to modern life. Significant examples include antistiction coatings for micro-mechanical systems such as computer magnetic disk drives, multi-layer films for light-emitting devices and flexible displays, thin film transistors for computer and TV displays, and biodegradable coatings for time-release drug delivery. Current industrial technologies for deposition of such films have some significant drawbacks. For example, thin films of conjugated polymers, used in organic light-emitting diodes and photovoltaic solar cells, have been fabricated by a variety of methods based on solution casting processes, but this leads to solvent induced conformational defects that adversely influence the optoelectronic behaviour. As a solution-free alternative, thermal evaporation is viable for short chain oligomers and small organic molecules, but is very challenging for long-chain conjugated polymers. As another example, thin films of PTFE are desirable for a large number of applications due to its biocompatibility, low frictional resistance, chemical inertness, and low dielectric constant, and again many techniques have been developed for its deposition but each has certain drawbacks. For example, spin coating is problematic due to a lack of suitable solvents and a need for post-annealing that can be undesirable for microelectronic structures, while plasma polymerisation of fluorocarbon monomers and sputtering techniques produce fluorine deficient PTFE films. It is for these reasons that laser-based deposition of polymer films has become important. UV lasers may be used for pulsed laser deposition of polymers but it is difficult to grow a film with the same chemical structure as the starting material. Typically, the polymer is converted to monomers and small oligomeric fragments in the plume and repolymerisation occurs upon deposition. However, if repolymerisation is incomplete or if there are missing groups due to direct scission photoreactions then the film will be chemically modified. Matrix-assisted pulsed-laser evaporation aims to resolve this issue by dissolving the polymer in a volatile solvent, which is then frozen to create a solid target. Ideally the polymer would be transparent to the incident light and the host highly absorbent, thereby limiting direct interaction between the laser and the polymer. However, this ideal situation is not easily accomplished using UV lasers.These problems have led to the development of resonant infrared pulsed laser deposition (RIR-PLD) where excitation of vibrational resonances can lead to the breaking of relatively weak intermolecular bonds and deposition of polymer films with unmodified chemical structure. This technique can be applied directly to the polymer or in a matrix-assisted format. However, the relevant vibrational modes lie within the molecular fingerprint region of the IR spectrum (2-10um) where there is an unfortunate dearth of appropriate laser sources. Consequently, the vast majority of RIR-PLD experiments to date have been performed using a free-electron laser. While this source is ideal for demonstration purposes it is certainly not suitable for a commercial processing facility.We therefore propose to build a novel, compact and efficient source of high-energy picosecond pulses with broad tunability in the mid-IR. The source is based on an synchronously pumped optical parametric oscillator with a fibre feedback arm to conveniently allow long cavity lengths, relatively low repetition rates, and hence high pulse energies. It will be pumped by a simple gain switched diode laser, scaled to high average powers by an Yb-doped fibre amplifier. This table-top replacement for the FEL will revolutionise thin-film polymer deposition and consequently impact strongly upon a number of important applications.

有机分子和聚合物薄膜在对现代生活至关重要的大量电子、光子、机械和医疗技术中发挥着关键作用。重要的例子包括用于微型机械系统的防粘涂层，如计算机磁盘驱动器，用于发光设备和柔性显示器的多层薄膜，用于计算机和电视显示器的薄膜晶体管，以及用于时间释放药物输送的可生物降解涂层。目前用于沉积这类薄膜的工业技术具有一些明显的缺陷。例如，用于有机发光二极管和光伏太阳能电池的共轭聚合物薄膜，已经通过基于溶液浇注工艺的各种方法制备，但这会导致溶剂诱导的构象缺陷，从而对光电行为产生不利影响。作为一种无溶液的替代方法，热蒸发对于短链齐聚物和有机小分子是可行的，但对于长链共轭聚合物是非常具有挑战性的。作为另一个例子，聚四氟乙烯薄膜由于其生物相容性、低摩擦阻力、化学惰性和低介电常数而被大量应用，同样地，已经开发了许多沉积技术，但每一种技术都有一定的缺点。例如，旋涂是有问题的，因为缺乏合适的溶剂，并且需要对微电子结构进行后退火，而氟碳单体的等离子体聚合和溅射技术则生产缺乏氟的聚四氟乙烯薄膜。正是由于这些原因，基于激光的聚合物薄膜沉积变得重要起来。紫外光激光可以用于脉冲激光沉积聚合物，但很难生长出与起始材料具有相同化学结构的薄膜。通常，聚合物在羽毛中转化为单体和小的低聚片段，并在沉积时进行重新聚合。然而，如果重新聚合不完全，或者如果由于直接裂解光反应而缺少基团，那么薄膜将进行化学修饰。基质辅助脉冲激光蒸发旨在通过将聚合物溶解在挥发性溶剂中来解决这个问题，然后将其冻结以产生固体靶标。理想情况下，聚合物对入射光是透明的，并且主体具有高吸水性，从而限制了激光和聚合物之间的直接相互作用。这些问题导致了共振红外脉冲激光沉积(RIR-PLD)技术的发展。在共振红外脉冲激光沉积(RIR-PLD)中，振动共振的激发可以导致相对较弱的分子间键断裂，并沉积出化学结构不变的聚合物薄膜。该技术可直接应用于聚合物或以基质辅助形式应用。然而，相关的振动模式位于红外光谱的分子指纹区域(2-10微米)，不幸的是缺乏合适的激光光源。因此，到目前为止，绝大多数RIR-PLD实验都是使用自由电子激光进行的。虽然这种光源是理想的演示用途，但它肯定不适合商业处理设备。因此，我们建议在中红外波段建立一种新颖、紧凑、高效的高能量可调谐皮秒脉冲光源。该光源基于带有光纤反馈臂的同步泵浦光学参量振荡器，以方便地允许较长的腔长、相对较低的重复率以及较高的脉冲能量。它将由一个简单的增益开关半导体激光器泵浦，并通过掺Yb光纤放大器放大到高平均功率。这种台式自由电子激光的替代品将使薄膜聚合物沉积发生革命性变化，从而对许多重要应用产生重大影响。