英文原文：
CHAPTER 1
Pulsed Laser Deposition of Complex Materials: Progress Towards
Applications
DAVID P. NORTON
University of Florida, Department of Materials Science and Engineering, Gainesville, Florida
1.1 INTRODUCTION
In experimental science, it is a rare thing for a newly discovered (or rediscovered) synthesis technique to immediately deliver both enhanced performance and simplicity in use in a field of accelerating interest. Nevertheless, such was the case with the rediscovery of pulsed laser deposition(PLD) in the late 1980s. The use of a pulsed laser as a directed energy source for evaporative film growth has been explored since the discovery of lasers [Hass and Ramsey, 1969; Smith and Turner, 1965]. Initial activities were limited in scope and involved both continuous-wave (cw) and pulsed lasers. The first experiments in pulsed laser deposition were carried out in the 1960s; limited efforts continued into the 1970s and 1980s. Then, in the late 1980s, pulsed laser deposition was popularized as a fast and reproducible oxide film growth technique through its success in growing in situ epitaxial high-temperature superconducting films [Inam et al., 1988]. The challenges for in situ growth of high-temperature superconducting oxide thin films were obvious. The compounds required multiple cations with diverse evaporative properties that had to be delivered in the correct stoichiometry in order to realize a superconducting film. Simultaneously, the material was an oxide, requiring an oxidizing ambient during growth. Pulsed laser deposition had several characteristics that made it remarkably competitive in the complex oxide thin-film research arena as compared to other film growth techniques. These principle attractive features were stoichiometric transfer, excited oxidizing species, and simplicity in initial setup and in the investigation of arbitratry oxide compounds. One could rapidly investigate thin-film deposition of nearly any oxide compound regardless of the complexity of the crystal chemistry. Significant development of pulsed laser deposition has continued and over the past 15 years, PLD has evolved from an academic curiousity into a broadly applicable technique for thin-film deposition research [Saenger, 1993; Kaczmarek, 1997; Willmott and Huber, 2000; Dubowski, 1988; Dieleman et al., 1992]. Today, PLD is used in the deposition of insulators, semiconductors, metals, polymers, and even biological materials. Few material synthesis techniques have enjoyed such rapid and widespread penetration into research and application venues.
Pulsed Laser Deposition of Thin Films: Applications-Led Growth of Functional Materials
Edited by Robert Eason Copyright # 2007 John Wiley & Sons, Inc.
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4 PULSED LASER DEPOSITION OF COMPLEX MATERIALS
1.2 WHAT IS PLD?
The applicability and acceptance of pulsed laser deposition in thin-film research rests largely in its simplicity in implementation. Pulsed laser deposition is a physical vapor deposition process, carried out in a vacuum system,that shares some process characteristics common with molecular beam epitaxy and some with sputter deposition. In PLD, shown schematically in Figure 1.1, a pulsed laser is focused onto a target of the material to be deposited. For sufficiently high laser energy density, each laser pulse vaporizes or ablates a small amount of the material creating a plasma plume. The ablated material is ejected from the target in a highly forward-directed plume. The ablation plume provides the material flux for film growth. For multicomponent inorganics, PLD has proven remarkably effective at yielding epitaxial films. In this case, ablation conditions are chosen such that the ablation plume consists primarily of atomic, diatomic, and other low-mass species. This is typically achieved by selecting an ultraviolet (UV) laser wavelength and nanosecond pulse width that is strongly absorbed by a small volume of the target material. Laser absorption by the ejected material creates a plasma. For the deposition of macromolecular organic materials, conditions can be chosen whereby absorption is over a larger volume with little laser absorption in the plume. This permits a large fraction of the molecular material to be ablated intact. For polymeric materials,transfer of intact polymer chains has been demonstrated. For even ‘‘softer’’materials in which the direct absorption by the laser would be destructive to molecular functionality, the formation of composite ablation targets consisting of the soft component embedded in an optically absorbing matrix has been investigated (see, e.g., Chapter 3).
Several features make PLD particularly attractive for complex material film growth. These include stoichiometric transfer of material from the target, generation of energetic species,hyperthermal reaction between the ablated cations and the background gas in the ablation plasma,and compatibility with background pressures ranging from ultrahigh vacuum (UHV) to 1 Torr. Multication films can be deposited with PLD using single, stoichiometric targets of the material of interest, or with multiple targets for each element. With PLD, the thickness distribution from a
Figure 1.1 Schematic of the PLD process.
WHAT IS PLD? 55 stationary plume is quite nonuniform due to the highly forward-directed nature of the ablation plume. To first order, the distribution of material deposited from the ablation plume is symmetric with respect to the target surface normal and can be described in terms of a cos neyT distribution,where n can vary from ～4–30. However, raster scanning of the ablation beam over the target and/or rotating the substrate can produce uniform film coverage over large areas, and this topic is covered in Chapter 9.
One of the most important and enabling characteristics in PLD is the ability to realize stoichiometric transfer of ablated material from multication targets for many materials. This arises from the nonequilibrium nature of the ablation process itself due to absorption of high laser energy density by a small volume of material. For low laser fluence and/or low absorption at the laser wavelength, the laser pulse would simply heat the target, with ejected flux due to thermal evaporation of target species. In this case, the evaporative flux from a multicomponent target would be determined by the vapor pressures of the constituents. As the laser fluence is increased, an ablation threshold is reached where laser energy absorption is higher than that needed for evaporation. The ablation threshold is dependent on the absorption coefficient of the material and is thus wavelength dependent.At still higher fluences, absorption by the ablated species occurs, resulting in the formation of a plasma at the target surface. With appropriate choice of ablation wavelength and absorbing target material, high-energy densities are absorbed by a small volume of material, resulting in vaporization that is not dependent on the vapor pressures of the constituent cations.
In pulsed-laser deposition, a background gas is often introduced that serves two purposes. First, the formation of multication thin-film materials often requires a reactive species (e.g., molecular oxygen for oxides) as a component of the flux. The amount of reactant gas required for phase formation will depend on the thermodynamic stability of the desired phase. Interaction of ablated species with the background gas often produces molecular species in the ablation plume. These species facilitate multication phase formation. In addition to actively participating in the chemistry of film growth, the background gas can also be used to reduce the kinetic energies of the ablated species. Time-resolved spectroscopy studies of ablation plume expansion have shown that kinetic energies on the order of several hundred electron volts can be observed [Chen et al., 1996]. A background gas can moderate the plume energies to much less than 1 eV. The vapor formed by laser ablation compresses the surrounding background gas resulting in the formation of a shock wave.Interaction with the ambient gas slows the ablation plume expansion.
For the deposition of multication materials, target selection can have significant impact on film growth properties, including particulate density, epitaxy, phase formation, and deposition rate. As a minimum requirement, ablation requires a target material possessing a high optical absorption coefficient at the selected laser wavelength. In general, the phase of the target does not need to be the same as that of the desired film. Only the cation stoichiometry need be identical to that of the films, assuming stoichiometric transfer and negligible evaporation from the film surface. For ceramic targets, one prefers target materials that are highly dense, as this will reduce particulate formation during the ablation process. As an alternative to polycrystalline ceramics, the use of single crystals as ablation targets has been investigated and shown to be effective in further reduction of droplet densities [Li et al., 1998]. The exception to this is wide bandgap insulators, such as Al2O3, where insufficient optical absorption makes single crystals unattractive as ablation targets. For soft materials, including biological materials, the target might be the material of interest or the material embedded in a matrix of an optically absorbing substance that does not deposit but yields an efficient ablation process.
An alternative to ceramic or single-crystal targets is reactive PLD where the targets consist of the constituent cations, while the anion is supplied by the background gas. In general, the ablation process is less efficient for metal cations due to higher reflectivity and thermal conductivity. In addition, films deposited via ablation of metal targets can exhibit high particulate densities due to the ejection of molten droplets: for some systems, this problem can be addressed by using liquid metal targets. For some specific multication systems, metal targets have useful advantages. For the growth of multication films in which cation purity is an important issue, metals are often available with the
6 PULSED LASER DEPOSITION OF COMPLEX MATERIALS
highest purity. In addition, for insulators that possess particularly wide optical bandgaps, such as MgO, the ablation efficiency from ceramic or single-crystal targets is low for commercially available pulsed laser wavelengths.
One also needs to consider the laser wavelength used for ablation. Efficient ablation of the target material requires the nonequilibrium excitation of the ablated volume to temperatures well above that required for evaporation. This generally requires the laser pulse to be short in duration, high in energy density, and highly absorbed by the target material. For ceramic targets, this is most easily achieved via the use of short wavelength lasers operating in the ultraviolet. High-energy ultraviolet laser pulses can be readily provided via excimer lasers or frequency-tripled or quadrupled Nd : YAG solid-state lasers. In some cases, a more efficient source is an infrared laser whose energy corresponds to a vibrational mode of the ablation target material [Bubb et al., 2002].
In laser ablation, each ablation pulse will typically provide material sufficient for the deposition of only a submonolayer of the desired phase. The amount of film growth per laser pulse will depend on multiple factors, including target –substrate separation, background gas pressure and laser spot size, and laser energy density. Under typical conditions, the deposition rate per laser pulse can range from 0.001 to 1 A
? per pulse. As such, PLD enables laser shot-to-shot control of the deposition process that is ideal for multilayer and interface formation where submonolayer control is needed. This degree of control can be seen from the in situ surface studies using reflection high-energy electron diffraction (RHEED), as discussed in detail in Chapter 8
[Bozovic and Eckstein, 1995; Foxon, 1991]. RHEED provides a means of determining the crystallinity and smoothness of a surface, and oscillations in the intensity of diffraction spots during film growth correlate to the atomic layer-by-layer growth of the material. Figure
1.2 shows the specular intensity of RHEED data for an epitaxial oxide film being deposited by PLD [Rijnders et al., 2000]. Two types of time-
0 350 Time (s)
0 40 Time (s) Figure 1.2 The specular RHEED intensity during PLD at 1 Hz (T ? 750o C, p O 2 ? 3 Pa). The insets give enlarged intensity after one laser pulse at 0.9 and 0.95 unit-cell layer coverage y. Also shown is (a) intensity variations of the specular reflection during PLD at 1 Hz and (b) interval deposition using the (b) t=0.45 s t=0.25 s
(a)
I n t e n s i t y (a r b i t r a r y u n i t s )
WHAT IS PLD? 75 laser repetition rate
of 10 Hz (T ? 800o C, p O2 ? 10 Pa) [Rijnders et al., 2000].
8 PULSED LASER DEPOSITION OF COMPLEX MATERIALS
dependent structure can be observed in the RHEED intensity plot. First, the oscillations observed in the intensity in Figure 1.2a represent the deposition of single unit cells of the oxide film. Specular RHEED intensity is dependent on the spatial coherence of the surface atoms. As layer-by-layer growth cycles through submonolayer coverage of the surface, RHEED intensity decreases, while for completed layers, the intensity is high. The oscillations seen in Figure 1.2a indicate that unit cell by unit cell growth on an atomically flat surface is occurring. The superimposed time-dependent substructure in the RHEED intensity seen in Figure 1.2b corresponds to surface redistribution of ablation plume species that have condensed on the surface from an individual ablation pulse. The time dependence of this structure yields insight into the nucleation and growth of the film at the submonolayer level for the arrival of each ablation plume.
For multicomponent film growth, most of the limitations identified early in the development of PLD have been allieviated. A key development for the utilization of pulsed laser deposition for applications in industry has been the realization of schemes by which large area substrates can be effectively coated. The dynamics of the laser ablation process result in a highly focused plume of material ejected from the target. While this leads to a deposition efficiency on the order of 70%, it also results in a significant variation in deposition rate over distances on the order of a few centimeters. For uniform film thickness over large areas, manipulation of the plume –substrate positioning is required. Several approaches have been implemented to overcome this limitation, the most straightforward being to combine substrate rotation with rastering of the ablation beam over a large ablation target. This will, to first order, provide a means for covering large area substrates. However, one must take into account the decrease in plume energies and change in plume stoichiometry as one moves to the edge of the plume region.
In pulsed laser deposition, the kinetic energies of ions and neutral species in the ablation plume can range from a few tenths to as high as several hundred electron volts. These energies are sufficient to modify the stress state of films through defect formation as has been documented for ion-beam- assisted approaches. The most common consequence of allowing deposition from an unabated energetic plume is the introduction of compressive stress. The origin of compressive stress due to energetic bombardment is associated with subsurface damage from the impinging energetic species, as schematically illustrated in Figure 1.3, leading to interstitial defects [Norton et al., 1999]. In this
500
Energetic atoms from ablation plume impinge on surface
400
300
200
100
660 nm CeO 2 on 110 μm Si Curvature due to plume- induced compressive stress Collisions induce subsurface implantation to interstitials 00 200 400 600 800 1000 Scan distance (μm)
Interstitials induce compressive
stress in growing film
Figure 1.3 Schematic of plume-induced stress in PLD-deposited films.
Z (n m )
WHAT IS PLD? 95 case, the energetic depositing atoms displace underlying atoms in the film, resulting in atoms displaced to interstitial sites. Stress on the order of gigapascals has been observed. For thin substrates, this compressive stress can be sufficient to induce bowing of the structure as indicated in Figure 1.3 for CeO2 on a thin Si wafer. The kinetic energy necessary for the onset of recoil implantation of surface atoms into the film interior through bombardment is material dependent but is often observed for ion bombarding energies of a few electron volts or greater [Muller, 1989]. For oxides, the energetic bombarding cations can also preferentially sputter oxygen atoms from the surface, resulting in films that are oxygen deficient. The kinetic energy of ablated species is largely dependent on laser energy and gas-phase collisions. Fortunately, the use of a background gas to thermalize the plume is usually effective in eliminating this problem.
Another potential issue with PLD is the ejection of micron-size particles in the ablation process. This is often observed when the penetration depth of the laser pulse into the target material is large.If these particles are deposited onto the substrate, they present obvious problems in the formation of multilayer device structures. The use of highly dense ablation targets and ablation wavelengths that are strongly absorbed by the target tends to reduce or eliminate particle formation. Mechanical techniques have been developed to reduce particle density in the event that target density and/or laser wavelength optimization fails to eliminate particulates. These include velocity filters [Pechen et al.,1995], off-axis laser deposition [Holzapfel et al., 1992], and line-of-sight shadow masks [Trajanovic et al., 1997]. Cross-beam techniques have also been considered as described in Chapter 6.
In addition to particles ejected from the ablation targets, one can also observe nanoparticles that form in the gas phase when the background pressure is sufficiently high for heterogeneous particle nucleation. These particles can become embedded in a depositing film. Figure 1.4 shows a cross- section transmission electron microscopy image of a CeO2 film with the initial growth occurring at high pressure while the remaining film was grown at low pressure. CeO2 nanoparticles are clearly evident in the epitaxial CeO2 thin-film matrix [Norton et al., 1998]. In particular, the nanoparticles,with diameters ranging from 10 to 40 nm, are seen in the layer formed by ablating a CeO2 target in a hydrogen–argon background gas at a pressure of 200 mTorr. In contrast, the upper part of the CeO2
film is devoid of nanoparticles and was deposited in a background pressure of 10-5 Torr where gas-phase collisions are minimal. While the formation of nanoparticles is generally undesirable for thin-film growth, this heterogeneous gas-phase nucleation has been intentionally exploited in the synthesis and study of nanomaterials, including oxides and semiconductors.
While stoichiometric transfer of target composition is readily achieved for nearly every material,this does not ensure stoichiometric film growth at elevated temperature if any of the cation species possess high vapor pressures. Specific cations for which the sticking coefficient is an issue include K, Li, Na, Tl, Mg, Pb, Cd, and Zn. We consider as an example ZnGa2O4 [Lee et al., 1999], which is a wide bandgap semiconducting spinel that is of interest as a phosphor material. Films deposited using a stoichiometric single ZnGa2O4 target will show significant Zn deficiency for elevated deposition temperatures due to the higher vapor pressure of Zn relative to that of Ga. Figure 1.5 shows the
Figure 1.4 Cross-section TEM image of a CeO2 film grown at high and low pressure, with CeO2 nanoparticles forming at the high background pressure.
10 PULSED LASER DEPOSITION OF COMPLEX MATERIALS
Target PO2 P tot(mTorr)
Single Mosaic Target
400 450 500 550 600 650 700 750
Substrate temperature (C)
Figure 1.5 Plot of the Zn/Ga ratio for ZnGa2O4 films deposited using mosaic ablation targets.
Zn/Ga ratio for films deposited at several different background pressures. Note that stoichiometric ZnGa2O4 corresponds to a Zn/Ga ratio of 0.5. Using a stoichiometric target, a Zn/Ga ratio as low as0.12 is observed for films deposited at 500o C. The optimal growth temperature, on the order of 600 –700o C, yields even greater deficiency in Zn content. One means of compensating for the loss of the volatile species in the films is to use a mosaic target consisting of the desired material and an additional region rich in the volatile component. Figure 1.5 compares the results for ZnGa2O4 films deposited with a single ZnGa2O4 target versus mosaic ZnGa2O4/ZnO targets. Stoichiometric ZnGa2O4 films required a target mosaic of 50% ZnGa2O4, 50% ZnO. The additional ZnO flux provides a means of overcoming the disparity in cation vapor pressure. Note that the stoichiometry also depended on oxygen partial pressure, which likely reflects the difference in vapor pressure for Zn as compared to ZnO.
1.3 WHERE IS PULSED LASER DEPOSITION BEING APPLIED?
Given the attractive characteristics of pulsed laser deposition in the synthesis of multicomponent thin-film materials, a number of applications are being actively pursued using this technique. In some cases, the application focuses on the synthesis of a thin-film material or structure. In other cases, the research has targeted the development of specific devices. It is interesting to consider specific structures, devices, and applications for which PLD has been successfully applied. Many of these topics are discussed in more detail in later chapters in Parts 3 and 4.
1.3.1 Complex Oxide Film Growth
In the growth of crystalline oxides, PLD has proven to be most effective. The growth of complex oxides requires the delivery of a growth flux with the correct stoichiometry in an oxidizing ambient that is favorable for the desired phase formation. The utility of pulsed laser deposition in reproducing target stoichiometry has been demonstrated for a number of multication oxides. Early success in realizing stoichiometric YBa2Cu3O7 clearly delineated this advantage for pulsed laser deposition. In recent years, even more complex crystal structures have been successfully grown using this approach. Consider, for example, the growth of the Y-type magnetoplumbite Ba2Co2Fe12O22compound. This material is a ferromagnetic oxide of potential interest in thin-film magnetic device applications [Sudakar et al., 2003]. The epitaxial growth of Ba2Co2Fe12O22 is challenging as it possesses a remarkably complex crystal structure as illustrated in Figure 1.6a. The unit cell possesses a huge lattice parameter of 43.5 A?. Despite the complexity of the crystal structure, the epitaxial growth of Ba2Co2Fe12O22 has been realized via pulsed laser deposition [Ohkubo et al., 2003]. Figure 1.6b and 1.6c show the X-ray diffraction data for an epitaxial film, along with the
I II
ZnGa2O4
ZnO
Z
n
/
G
a
Single 24 60
Mosaic I 24 60
Mosaic II 24 60
Mosaic II 45 60
Mosaic II 60 60
Mosaic II 75 100
WHERE IS PULSED LASER DEPOSITION BEING APPLIED?9
Figure 1.6 Crystal structure, X-ray diffraction data, and TEM image of a Ba2Co2Fe12O22 film grown by PLD [Ohkubo et al., 2003].
cross-sectional transmission electron microscopy (TEM) image. It should be noted that this result was obtained using a combinatorial synthesis approach in which multiple process parameters(composition, temperature) are explored in parallel through the use of combinatorial arrays or compositional spread techniques. Pulsed laser deposition has proven to be easily adaptable to combinatorial techniques for thin-film research. The ability to grow epitaxial, multication complex inorganic thin films has been, and continues to be, one of the enabling strengths of PLD.
1.3.2 Epitaxial Interface and Superlattice Formation
Developments in oxide PLD film growth have provided remarkable opportunities in the synthesis of epitaxial heterostructures and superlattices [Yilmaz et al., 1991; Fernandez et al., 1998; Chang et al., 1999; Smolenskii et al., 1984; Xu et al., 2000]. Superlattices of oxides, such as the (001) KNbO3/KTaO3 perovskite structure shown in Figure 1.7, have been realized for a number of material systems, with individual layers as thin as a single unit cell [Christen et al., 1996, 1998; Specht et al.,1998]. Excellent film flatness and crystallinity are evidenced in these films, and the interfaces can be
Figure 1.7 Cross-section Z-contrast STEM image of a KTaO3/KNbO3 superlattice structure grown by pulsed laser deposition.
10 PULSED LASER DEPOSITION OF COMPLEX MATERIALS
Figure 1.8 Cross-section Z-contract STEM image of a CeO2/Ge epitaxial interface fabricated using PLD. compositionally sharp on an atomic scale as seen in Figure 1.7. In the formation of atomically abrupt interfaces and superlattice structures, PLD is competitive with other film growth techniques,including molecular orbital chemical vapor deposition (MOCVD) and molecular beam epitaxy(MBE). The formation of epitaxial oxide superlattices has been used to investigate the effects of reduced dimensionality on a number of phenomena. Superconductivity in single unit cell YBa2Cu3O7 layers was first demonstrated using PLD. Low dimensionality behavior has been investigated for ferroelectric and magnetic oxides.
Pulsed laser deposition also yields the opportunity to create atomically abrupt interfaces between materials that are chemically dissimilar, including epitaxial metal–oxide and semiconductor–oxide structures. A key factor in the formation of atomically abrupt interfaces between oxide films and nonoxide surfaces is to identify conditions where undesirable interfacial reactions are minimal yet compatible with oxide epitaxy. Laser ablation film growth is particularly well suited for nucleation in a reactive environment since it is compatible with a large range of background pressures. For example, a hydrogen-assisted nucleation approach has been used to grow atomically abrupt,epitaxial CeO2/Ge interfaces [Norton et al., 2000]. During the initial nucleation of CeO2 on Ge, the hydrogen partial pressure and substrate temperature are chosen such that the native oxide, GeO2, is thermodynamically unstable, and under these conditions, the epitaxial growth of an oxide can be achieved on the Ge surface without interference from native oxides. The deposited oxide material must itself be thermodynamically stable under the conditions used during nucleation, and epitaxy will be determined by the chemistry and structure of the two materials. For CeO2 nucleated on (001) Ge in hydrogen gas using pulsed laser deposition, the film can be epitaxial with an interface that is atomically abrupt as is evident in the cross-section Z-contrast scanning transmission electron microscopy image shown in Figure 1.8. A similar approach has been used to form epitaxial interfaces between various oxides and metals (e.g., Ni and Ni alloys), as well as compound semiconductors, including InP. The latter is of interest as it provides a means of integrating electronic oxides with photonic and microwave electronics.
龙源期刊网 https://www.doczj.com/doc/d214729080.html, 浅谈激光烧蚀技术的应用及研究进展 作者：宫琳琳李爽 来源：《科技资讯》2014年第04期 摘要：随着激光技术的发展，当今社会激光烧蚀技术越来越受到了人们的关注。本文主 要介绍了几种激光烧蚀技术的不同应用，以及对激光烧蚀技术的进展做了简单的研究。 关键词：烧蚀等离子体聚合物 中图分类号：O657.3 文献标识码：A 文章编号：1672-3791（2014）02（a）-0019-01 激光烧蚀技术是通过飞秒-纳秒量级的脉冲激光来将材料表面烧蚀，已经被广泛应用于微加工、外科手术、X射线激光、生物分子质谱以及一些艺术品修复/清洁等领域；对激光烧蚀 产生的等离子体的光学/光谱诊断是研究等离子体动力学的主要方法之一。 1 激光烧蚀技术的应用 1.1 激光烧蚀光谱（LAS、LIBS）技术的应用 近年来光谱领域发展迅速，其中激光烧蚀光谱技术是其中一种比较崭新的分析手段。该技术主要是通过聚焦强激光束激发样品靶面，产生高温等离子体，通过测定等离子体冷却过程中发射光谱的波长与强度来进行定量分析、元素定性。激光烧蚀光谱技术虽然对于痕量元素的分析能力不足，但是该技术并不需要对样品进行繁琐的化学处理，具有破坏性小，具有快速、实时、可远程监测等特点，被广泛应用于地质、冶金、核工业、材料、燃料能源、生物医药等领域；电感耦合等离子体质谱（ICP2MS） 分析技术是一种公认的高灵敏度、强有力的、多元素及同位素分析技术。 1.2 激光烧蚀技术在微纳米材料制备中的应用 激光与靶材相互作用后，周围的物理空间便可粗略的分为高温高压等离子体聚集区、液相区和固相区三个区域，如图1所示。等离子体聚集区是由离子、电子以及未电离的中性粒子集合组成，整体呈现电中性，该区域对激光能量的传输障碍比较小。液相区是靠近等离子聚集区的熔融层，材料处于液态或固-液共存态。靠近液相区的是固相区，该区域虽然也吸收了激光能量，能使温度升高，但是能量强度不足以使该层进行熔化。基于激光烧蚀技术制备的各类材料的生长过程，如一维纳米线和零维纳米颗粒、二维薄膜等，几乎都是通过应用高温高压等离子体的成核、生长所完成。因此，激光烧蚀产生的高温高压等离子体在激光烧蚀技术制备微纳米材料中起着重要的作用。
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安全信息 在使用该产品之前，请先阅读和了解这份用户手册并熟悉我们为您提供的信息。 这份用户手册提供了重要的产品操作，安全以及其他信息给您以及所有将来的用户作参考。为了确保操作安全和产品的最佳性能，请遵循以下注意和警告事项以及该手册的其他信息去操作。 ●锐科公司脉冲光纤激光器是IV级的激光产品。在打开24VDC电源前，要确保连 接是正确的24VDC的电源并确认正负极，错误连接电源，将会损坏激光器。 ●该激光器在1064nm波长范围内发出超过5W、10W、15W、20W、25W、30W（根 据不同激光器型号）的激光辐射。避免眼睛和皮肤接触到光输出端直接发出或散射出来的辐射。 ●不要打开机器，因为没有可供用户使用的产品零件或配件。所有保养或维修只能在 锐科公司内进行。 ●不要直接观看输出头，在操作该机器时要确保长期配戴激光安全眼镜。 安全标识及位置 上面二个安全标识符号表示有激光辐射，我们把这符号标在产品光纤盒体盖顶上。
目录 1．产品描述 (1) 1.1 产品描述 (1) 1.2实际配置清单 (1) 1.3使用环境要求及注意事项 (1) 1.4技术参数 (2) 2．安装 (3) 2.1 安装尺寸图 (3) 2.2 安装方法 (4) 3．控制接口 (5) 4．操作程序 (6) 4.1 前期检查工作 (6) 4.2 操作步骤 (6) 4.3打标过程中应注意的事项 (6) 5．质保及返修、退货流程 (7) 5.1一般保修 (7) 5.2保修的限定性 (7) 5.3服务和维修 (7)
1．产品描述 1.1 产品描述 锐科脉冲激光器是是为高速和高效的激光打标系统而专门发展的。为工业激光打标机和其它应用提供了一款理想的高功率激光能量源。 脉冲激光器相对于传统的激光器，能够对每瓦的泵浦光转换效率提高10倍以上，低能量消耗的自动设计，适合实验室或室外操作。精巧，可独立放置，可随时使用，能够直接嵌入用户的设备上。 激光器可发出1064nm波长的脉冲激光，通过工业激光器标准接口来控制，激光器需要使用24V直流供电。 1.2实际配置清单 请根据图表1参考所包括的清单。 表1 1.3使用环境要求及注意事项 脉冲激光器需使用24VDC±1V直流电。 1)注意：使用激光器时要将接地线可靠接地。 2)没有内置可供使用的零件，所有维修应由合格的锐科人员来进行，为了防止电击， 请不要损坏标签和揭开盖子，否则产品的任何损坏将不被保修。 3)激光器的输出头是与光缆相连接的,使用时请小心处理输出头，防止灰尘或其它污 染，清洁输出端透镜时请使用专用的镜头纸。激光器没有安装在系统设备上且不 出光的时候，请将光隔离器保护罩盖好以免灰尘污染。
脉冲激光沉积PZT/LSMO薄膜结构及输运特性的研究 摘要 锆钛酸铅（Pb(Zr x Ti1-x)O3，简称PZT）材料因其具有优良的铁电、压电、热释电、电光和非线性光学等特性而备受关注。同时，PZT作为一类典型的铁电材料，其显著的反常光生伏打效应，为新型太阳能电池材料的研究创造条件。本文利用脉冲准分子激光在STO单晶基片上淀积了LSMO和P ZT的.并通过高频溅射将Pt蒸镀在PZT薄膜上作为上电极;用X射线衍射表征了PZT铁电薄膜和该多层膜的晶相结构，测量了PZT的铁电性能和介电特性。讨论了PZT/薄膜的制备工艺。以及工艺条件对晶相结构和薄膜性能的影响。在密封的液氮杜瓦瓶里用四探针法对薄膜的输运特性进行了测试，. 关键词：PZT薄膜激光脉冲淀积电滞回线，漏电流
Study on structure and Transport Characteristic of PZT/LSMO Thin Film By Pulsed-Laser Deposition Abstract
绪论. PZT具有一系列优异的性能，如压电、铁电、热释电、介电、光电等，利用这些性质可以成 性能优良的器件。与其他铁电材料相比，PZT具有很多优点，例如：较高的居里点（200℃以上）且可以通过改变锆钛含量比实现对居里温度的控制；它的热释电系数较大，同时介电常数和介电 损耗较小，而且可以通过对PZT掺杂入Mn、Bi等其他元素或单纯改变PZT的锆钛含量比的方 式来改善其性能；在准同型相界附近具有优异的压电性能。因此PZT是一种优异的压电、铁电 和热释电材料，已在众多领域被广泛的应用 1.PTZ铁电薄膜 随着铁电薄膜和微电子技术相结合而发展起来的集成铁电学的出现，铁电薄膜的制备、结构、性能及其应用已成为国际上新材料研究十分活跃领域，其中钙钛矿结构的锆钛酸铅(PZT)铁电薄膜由于具有优越铁电、介电、压电、热释电以及能够与半导体技术兼容等特点，使之在微机电系统(MEMS)等领域具有广泛的应用前景。由于基于PZT的器件具有工作带宽广、反应速度快和灵敏性高等优点，因此PZT薄膜可以用于MEMS领域的各个方面，例如压电激励器、焦热红外探测器、随机存储器和超声器件。为了满足不断提高的微纳米机械器件的要求和与硅基器件的兼容，在硅衬底上生长高质量的PZT薄膜就变得越来越重要. 1.1 铁电薄膜材料的研究现状,7]。 目前，铁电薄膜的研究主要集中在以下几个方面：新的合成技术与沉积技术，薄膜的检测与表征技术，结构与性能的关系以及工艺与微结构关系，界面特性（包括金属-铁电薄膜界面和铁电薄膜与半导体兼容），新薄膜材料的研究等方向。应用研究则主要集中在：光电子学（电光应用、光学相位调制、光折变、集成光学等），压电应用（SAW器件、微控制器、微马达、微机械阀等），热释电学（单元探测器和线性阵列探测器）和铁电随机存储器[8]。 1.2 铁电材料的自发极化和电滞回线 自发极化是指在没有外电场时，铁电体内正、负电荷中心不重合，形成有一定规则排列的电偶极矩而产生的极化。电滞回线是指自发极化强度P滞后于外加电场强度E的变化轨迹，如图1.1所示。图中O点是指外加电场为0时的状态，电偶极矩呈杂乱分布，总电矩为0，所以通常情况下铁电体不显电性。当场强较弱时，极化强度随场强近似呈线性变化，如OA段。当场强逐渐变大，P随场强呈非线性变化并迅速达到饱和，如ABC，做BC的反向延长线与纵轴的交点E称为饱和极化强度P s，B点处电偶极矩受外加电场的影响基本趋于同一方向。当场强逐渐减小时，曲线不按照原轨迹返回，呈BD段，当外界场强减小到0时，存在剩余极化强度P r，反方向增加场强，极化强度下降，当场强达到E c时，极化强度变为0，E c称为矫顽场强，此时总的电偶极矩为0。场强继续增大，极化强度反向增加，直至达到饱和，如FG所示。如电场再次减小而后反向增加，曲线呈GHC变化，最后形成一条封闭的曲线。P r和E c是反映铁电性能的重要指标，回线矩形度越好表明铁电性能越强，所以电滞回线是检测铁电性的一个重要标志[9]。
一种脉冲激光功率采集和控制系统的设计 0 引言 近几年来光纤激光器在激光打标和激光加工方面取得了迅速的发展，而用于激光打标和加工方面的激光器一般采用峰值功率较高的脉冲光纤激光器。激光功率是激光器最主要的参量，激光输出功率严重的影响着激光加工的质量。在激光加工过程中，如何能实时监控激光功率的变化，提高激光功率的稳定性和控制精度，对产品的精密加工有着极其重要的作用。此类型激光器其功率值在不同的加工设计中其平均功率是变化的，这就给光功率的实时采集和控制带来的麻烦。本文通过对脉冲光信号的研究，设计出了基于峰值保持电路的小信号处理电路，和基于PID算法的单片机控制系统。通过硬件电路和软件系统的设计解决了光纤激光器中脉冲激光的采集和光功率稳恒的问题。 系统的硬件电路框图如图1所示，PIN管对激光器中的脉冲光进行采集，把脉冲式的光信号转换成脉冲式的电信号。采集到的脉冲光信号经放大电路进行放大，本设计采用了两级放大，将小信号放大到能够进行处理的信号。然后经峰值保持电路采集峰值电压(此峰值电压与光信号的功率成线性关系)。在经过A／D 转换电路将峰值电压信号转换成数字信号在单片机中进行处理。在单片机中主要运用了PID算法对功率进行控制，将调节后的值送给LD驱动电路进行功率调节。最终使功率稳定地输出。 2 系统的硬件电路设计 2．1 光电转换部分 本论文的光电采集部分主要用了PIN光电二极管，PIN管能很好地将光信号转换成电信号。PIN二极管对低频信号具有整流作用，而对高频信号则具有阻抗作用。PIN光电二极管具有以下优点：响应速度快；线性好、频带宽、信号失真小；噪声低，器件本身对信号影响小；体积小、寿命长、可靠性高、工作电压低。其采集到的脉冲峰值电压与光功率成线性关系。所以可以通过采集峰值电压的信号来对光功率进行采集处理。 2．2 小信号处理电路 小信号处理电路主要包括小信号放大电路和峰值保持电路。
周期量级激光脉冲相干控制及其算法的研究 【摘要】：超强超短激光与物质的相互作用的研究是国际重要的前沿研究领域。超强超短激光与物质的相互作用产生若干奇特的物理现象。在理论研究方面随着激光强度的不断提高，非线性效应不断增强，使得传统的微扰理论束手无策，新的非微扰理论应运而生；在技术方面，随着超短激光脉冲技术的不断发展，已经能够产生高强度的少周期和亚周期超短脉冲，这种周期量级超短激光脉冲失去了波动所特有的周期性特征，从而导致一系列全新的物理现象与规律，开创了极端非线性相互作用的最前沿，受到了广泛的关注。在少周期和亚周期的尺度下，现有的近似方法存在缺陷，因此研究高精度、无数值色散、高效率、数值稳定的数值计算方法就显得非常重要且必要，本文重点探索建立适用的数值计算方法，并在数值模拟的基础上，研究空心波导中高次谐波、软X-射线及单阿秒脉冲产生，多能级介质中少周期激光脉冲的传输特性，亚周期脉冲与二能级系统的相互作用的动力学过程，以及多能级量子系统的相干控制和选态激发等问题。取得的主要创新成果有：1．研究了Maxwell-Schr(?)nger耦合方程组的数值解法，首次模拟较高压强下不同的惰性气体在周期性波导中高次谐波的产生，得到了效率增强、级次延伸的高次谐波谱，同时谐波的转换效率也提高了至少两个量级；并讨论不同调制周期对谐波的影响。在此基础上我们研究了线性啁啾调制波导中单阿秒脉冲的产生，并找到了有利于产生单阿秒软X-射线脉冲的方法。结果表明线性啁啾光纤改
善了频率截止区域高次谐波的相位匹配状况，截止频率附近的谐波得到了不同程度的相位匹配，并且聚合成一个很宽的连续带，实现了单阿秒脉冲，并使脉冲的能量提高了100倍以上。我们分别在He气和Ar气中得到了波长短至4.66nm和8.69nm、脉宽仅为255as和279as 的单阿秒脉冲。可见合理选择啁啾参数，完全有可能产生脉宽更短的波长可至“水窗”波段的单阿秒脉冲。2．利用移动窗口技术构造了一套求解Maxwell-Bloch耦合方程组的高阶时域有限差分(FDTD)方法，该方法适用于模拟周期、亚周期量级激光脉冲在各种介质中的传输过程，具有无数值色散、数值稳定、精度高、效率高等特点。并且在此基础上模拟了开放二能级介质中周期量级椭圆偏振激光脉冲的传输，发现了一些新的物理现象和效应，脉冲在传输过程中发生分裂的规律以及电离效应对脉冲传输的影响等。3．研究了亚周期脉冲与二能级系统相互作用的动力学特性。我们发现，亚周期脉冲的载波频率会发生蓝移，蓝移的程度随脉冲包络所包含的周期数呈反向变化，当包含的周期数超过二时，频率的蓝移现象基本上消失，对于四分之一周期脉冲，其载波频率翻了一倍。其次，模拟结果表明，载波相位在亚周期脉冲与二能级系统相互作用的过程中扮演重要角色。我们还分别用解析方法和数值模拟证明了旋波近似在这样的尺度下是完全失效的。4．改进了遗传算法，提高了处理多变量优化问题的收敛速度。首次利用改进的遗传算法实现了多能级量子系统中完全布居转移和选态激发，分别研究了脉冲强度、延迟时间、啁啾率和失谐量等因素与完全布居转移和选态激发的关系，并发现了一些实现完全布居转移和选
液相激光烧蚀法制备纳米材料 ?引言 液相激光烧蚀（Laser Ablation in Liquid，LAL）是一种简单、绿色的纳米材料制备技术，通常只需在水中或有机液相条件下进行。近年来，LAL已被用于制备一系列具有特殊形貌、微观结构的纳米材料，以及在探索新兴的，在光学、显示、探测、生物等领域的性能和应用中，实现了功能化纳米材料的一步制备。 与传统的纳米材料制备方法相比，液相激光烧蚀法有以下的优势：（1）它是一种“简单且干净”的合成手段，由于减少了副产物的生成。并且简化了反应的前驱物的使用，确保了最终产物很高的纯度，而且具有较高的表面活性；（2）液相激光烧蚀法在温和的条件下能够制备出高温高压的亚稳相；（3）更重要的是这种制备方法几乎对所有纳米材料都有普适性，由于用液相激光烧蚀法制备新的纳米材料需要用到液体和固体靶材，研究者可以根据材料的属性来选择所需的靶材和液体来合成纳米颗粒和结构；（4）纳米结构的相、尺寸和形状可以通过改变激光参数和外部条件来合成，而且很多反应一步就能实现，避免了繁杂的后处理。液相激光烧蚀法能够制备多种亚稳相的纳米材料，得到的纳米颗粒胶体的纯度接近100%，并且适用于几乎所有材料体系，因此，已经成为一种普适的，并且有效的制备纳米材料的手段。 ?实验目的 (1)了解液相激光烧蚀法的基本原理、应用领域与发展前景； (2)以纳秒激光器为例，了解液相激光烧蚀过程的物理化学变化，观察液相激光烧蚀过程； (3)学习利用液相激光烧蚀法制备纳米材料。 ?实验原理 等离子体主导着纳秒激光的反应过程，其中包括了等离子体的产生，转化与淬灭。具体的反应过程如下：当激光作用于浸没在液体下的靶材时，激光脉冲以一定深度击穿靶材表面，产生的强电场使电子在1ns激光脉冲下，从被轰击体中迁移出来。电子在电磁场中产生自由电子振荡，并且与块体靶材中的原子发生碰撞，将一定的能量传递给晶格，材料随之被加热并蒸发，在高能量的激光下转变成等离子体。等离子体中通常包含多种活性物质，包括原子、分子、电子、离子、团簇、微粒和熔融球体等。最初形成的等离子体直接形成于激光与靶材的相互作用，因而被称为激光诱导等离子体。 接着，该激光诱导等离子体的扩散强烈地被其周围的液相介质束缚，从而继续吸收激光的后半部分能量，并且得到靶材离化材料的补充，等离子体迅速绝热膨胀，伴随着膨胀，在等离子膨胀方向的前端产生冲击波，在液体的束缚下，冲击波的反作用力导致等离子内部额外的压力。该额外的压力被称为等离子体诱导压力。并且，该压力会导致等离子的温度上升。因此，
脉冲激光沉积技术 所谓“脉冲激光沉积技术”是将脉冲准分子激光所产生的高功率脉冲激光束 聚焦作用于真空室内的靶材表面，使靶在极短的时间内加热熔化、气化直至使靶材表面产生高温高压等离子体，形成一个看起来像羽毛状的发光团—羽辉；等离子体羽辉垂直于靶材表面定向局域膨胀发射从而在衬底上沉积形成薄膜。 脉冲激光沉积（PLD）是一种新型的制膜技术，PLD制备薄膜大体可分为三个过程：激光与靶材相互作用产生等离子体；等离子体在空间的输运；等离子体在基片上沉积形成薄膜。与其它制膜技术相比，PLD具有以下特点和优势： 一、所沉积形成的薄膜可以和靶材成分保持一致。由于等离子体的瞬间爆炸性发射，不存在成分择优蒸发效应以及等离子体发射的沿靶轴向的空间约束效应，因此膜与靶材的成分保持一致。由于同样的原理，PLD可以制备出含有易挥发元素的多元化合物薄膜。 二、可在较低温度下原位生长织构膜或外延单晶膜。由于等离子体中原子的能量比通常蒸发法产生的离子能量要大得多，原子沿表面的迁移扩散更剧烈，故在较低温度下也能实现外延生长，而低的脉冲重复频率也使原子在两次脉冲发射之间有足够的时间扩散到平衡的位置，有利于薄膜的外延生长。PLD的这一特点使之适用于制备高质量的高温超导、铁电、压电、电光等多种功能薄膜。 三、能够获得连续的极细薄膜，制备出高质量纳米薄膜。由于高的离子动能具有显著增强二维生长和抑制三维生长的作用，故PLD促进薄膜的生长沿二维展开，并且可以避免分离核岛的出现。 四、生长速率较快，效率高。比如，在典型的制备氧化物薄膜的条件下，1小时即可获得1微米左右的膜厚。 五、生长过程中可原位引入多种气体，包括活性和惰性气体，甚至它们的化合物。气氛气体的压强可变范围较大，其上限可达1torr.甚至更高，这点是其它技术难以比拟的。气氛气体的引入，可在反应气氛中制膜，使环境气体电离并参与薄膜沉积反应，对于提高薄膜质量具有重要意义。 六、由于换靶位置灵活，便于实现多层膜及超晶格薄膜的生长，这种原位沉积所形成的多层膜具有原子级清洁的界面。 七、成膜污染小。由于激光是一种十分干净的能源，加热靶时不会带进杂质，这就避免了使用柑祸等加热镀膜原材料时对所沉积的薄膜造成污染的问题。 正因为脉冲激光沉积技术具有上述突出优点，再加上该技术设备较简单，操作易控制，可采用操作简便的多靶台，灵活性大，故适用范围广，并为多元化合物薄膜、多层膜及超晶格膜的制备提供了方便。目前，该技术已被广泛运用于各种功能性薄膜的制备和研究，包括高温超导、铁电、压电、半导体及超晶格等薄膜，甚至可用于制备生物活性薄膜，显示出广泛的应用前景。
《表面科学与技术》课程作业 关于脉冲激光沉积（PLD）薄膜技术的探讨 摘要：薄膜材料广泛应用在半导体材料、超导材料、生物材料、微电子元件等方面。为了得到高质量的薄膜材料，科学家一直在寻找和探讨各种新的技术，脉冲激光沉积（Pulsed Laser Diposition PLD）薄膜技术是近年来快速发展起来的使用范围最广，最有前途的制膜技术之一。本文介绍了脉冲激光沉积(PLD)薄膜技术的原理及特点，并与其他薄膜技术进行对比，探讨衬底温度、靶材与基底的距离、退火温度、靶材的致密度、激光能量、激光频率等参数对薄膜质量的影响。分析了脉冲激光沉积技术在功能薄膜材料中的应用和研究现状，并展望了该技术的应用前景。 关键字：脉冲激光沉积（PLD）等离子体薄膜技术 前言 上世纪60年代第一台红宝石激光器的问世，开启了激光与物质相互作用的全新领域。科学家们发现当用激光照射固体材料时，有电子、离子和中性原子从固体表面逃逸出来，这些跑出来的粒子在材料附近形成一个发光的等离子区，其温度估计在几千到一万度之间，随后有人想到，若能使这些粒子在衬底上凝结，就可得到薄膜，这就是最初激光镀膜的概念。最初有人尝试用激光制备光学薄膜，这种方法经分析类似于电子束打靶蒸发镀膜，没有体现出其优势来，因此这项技术一直不被人们重视。直到1987年，美国Bell实验室首次成功地利用短波长脉冲准分子激光制备了高质量的钇钡铜氧超导薄膜，这一创举使得脉冲激光沉积(Pulsed Laser Deposition，简称PLD)技术受到国际上广大科研工作者的高度重视，从此PLD 成为一种重要的制膜技术]1[1。 由于脉冲激光沉积技术具有许多优点，它被广泛用于铁电、半导体、金刚石(类金刚石)等多种功能薄膜以及生物陶瓷薄膜的制备上，可谓前途光明。 1. PLD 技术装置图及工作原理 1.1 PLD系统 脉冲沉积系统样式比较多，但是结构差不多，一般由准分子脉冲激光器、光路系统(光阑扫描器、会聚透镜、激光窗等)；沉积系统(真空室、抽真空泵、充气系统、靶材、基片加 热器)；辅助设备(测控装置、监控装置、电机冷却系统)等组成]2[2，如图1-1所示。 1[1]邓国联，江建军．脉冲沉积技术在磁性薄膜制备中的应用[J]．材料导报2003，17(2)：66—68．原文：“1987年，美国Bell实验室首次成功地利用短波长脉冲准分子激光制备了高质量的钇钡铜氧(YBCO)超导薄膜，脉冲激光沉积(Pulsed Laser Deposition，简称PLD)技术才成为一种重要的制膜技术受到国际上广大科研工作者的高度重视。” 2[2] 高国棉陈长乐陈钊李谭王永仓金克新赵省贵(1西北工业大学理学院，西安
脉冲激光沉积 目录 编辑本段定义 脉冲激光沉积（Pulsed Laser Deposition，PLD），也被称为脉冲激光烧蚀（pulsed laser ablation，PLA），是一种利用激光对物体进行轰击，然后将轰击出来的物质沉淀在不同的衬底上，得到沉淀或者薄膜的一种手段。 编辑本段历史背景 早于1916年，爱因斯坦（Albert Einstein）已提出受激发射作用的假设。可是，首部以红宝石棒为产生激光媒介的激光器，却要到1960年，才由梅曼（Theodore H. Maiman）在休斯实验研究所建造出来。总共相隔了44年。使用激光来熔化物料的历史，要追溯到1962年，布里奇（Breech）与克罗斯（Cross）利用红宝石激光器，汽化与激发固体表面的原子。三年后，史密斯（Smith）与特纳（Turner）利用红宝石激光器沉积薄膜，视为脉冲激光沉积技术发展的源头。 编辑本段发展历程 不过，脉冲激光沉积的发展与探究，处处受制。事实上，当时的激光科技还未成熟，可以得到的激光种类有限；输出的激光既不稳定，重复频率亦太低，使任何实际的膜生成过程均不能付诸实行。因此，PLD在薄膜制作的发展比其它技术落后。以分子束外延（MBE）为例，制造出来的薄膜质素就优良得多。 往后十年，由于激光科技的急速发展，提升了PLD的竞争能力。与早前的红宝石激光器相比，当时的激光有较高的重复频率，使薄膜制作得以实现。随后，可靠的电子Q开关激光（electronic Q-switches lasers）面世，能够产生极短的激光脉冲。因此，PLD能够用来做到将靶一致蒸发，并沉积出化学计量薄膜。由于紫外线辐射，薄膜受吸收的深度较浅。之后
脉冲激光烧蚀技术的研究现状及进展1 徐兵2，宋仁国 （浙江工业大学机械制造及自动化教育部重点实验室，杭州 310014） 摘要：本文综述了脉冲激光烧蚀技术的原理、特性及研究现状，并对其发展前景进行了展望。 关键词：脉冲激光烧蚀，现状，前景 Research Status and Development of Pulsed Laser Ablation Technology Xu Bing SONG Ren-Guo (The MOE Key Laboratory of Mechanical Manufacturing and Automation，ZheJiang University of Technology, HongZhou 310014) Abstract: This paper presents a summary on the theory, the properties and the research status of pulsed laser ablation, as well as the prospect of the development of this technology. Keyword: pulsed laser ablation；state；prospect 一、引言 自1960年第一台激光器问世以来，人们对激光的特性进行了研究，由于激光具有高能量密度、高单色性、高相干性和高方向性等性能，从而使其在各个领域得到了广泛的应用[1-3]。 近20年来，激光制造技术已渗入到诸多高新技术领域和产业中，并开始取代或改造某些传统的加工业。尤其是纳米技术的兴起，人们对其加工技术的要求也愈来愈高。而脉冲激光烧蚀技术(Pulsed laser ablation，PLA)就是一种最近发展起来制备纳米粒子，纳米粉和纳米薄膜的高端技术。正是由于脉冲激光烧蚀技术的重要性和诱人的前景，使其成为当今世界上的研究热点之一[4-8]。 二、脉冲激光烧蚀技术的原理和特性 2.1、脉冲激光烧蚀技术的原理 60年代初，人们就发现了激光与物质的相互作用。而脉冲激光烧蚀技术就是基于此物理基础，它是用一束高能脉冲激光辐射靶材表面,使其表面迅速加热融化蒸发,随后冷却结晶的一种制备材料的技术。其工作原理是将具有很高亮度的激光束经透镜聚焦后，能在焦点附近产生数千度乃至上万度的高温，此高温几乎 1浙江省自然科学基金青年科技人才培养项目R405031资助及浙江省留学回国基金Z01102001 2E-mail : xubing198287@https://www.doczj.com/doc/d214729080.html, 地址：浙江工业大学研241号信箱
超短脉冲激光烧蚀技术应用探究 近年来随着超短脉冲激光烧蚀技术的发展，该技术被广泛应用于工业领域。短脉冲激光与物质相互作用时间介于纳秒与飞秒之间，其峰值功率可达兆瓦级，因此在加工中可应用于高精度、高硬材料的精细加工上，同时也可以实现材料的三维加工，该方式称为“冷”加工。文章旨在介绍超短脉冲技术的应用研究，使人们对该技术有一定的宏观认识。 标签：超短脉冲；激光烧蚀；应用探究；宏观认识 1 短脉冲激光器与金属相互作用理论 短脉冲诱导烧蚀材料的过程的建立需要一定的时间，并且与激光强度有直接关系。当脉宽给定时，只有当激光场的强度超过一定值时，形成的等离子体才能发生不可逆的损伤阈值，该阈值范围通常以激光的能流阈值表示。根据文献指出，脉冲宽度从连续到几十个皮秒范围内，烧蚀过程为离子雪崩过程，开始于内部电子。通过对超短脉宽烧蚀阈值的研究发现，当偏离了脉冲宽度平方根法则的时候，能量在很大范围内变动均可引起材料的烧蚀，如图1所示为超短脉冲激与金属作用的过程。 当前人们于超短脉冲激光烧蚀物质的机理和研究还没有获得完全的认知，研究的模型是将物质看做一个总体的系统去考虑，只有达到了该物质的沸点或熔点时，使得物质蒸发或者熔化而使材料被去除。应用傅里叶传热模型对上述过程可进行具体的描述，但是他不适用于描述和分析超短脉冲激光与金属薄膜或者介质膜的作用过程。原因是由于载流子的特征尺寸与膜层的厚度相当，同时其特征时间与传输能量的时间接近。 当超短脉冲激光与金属材料作用发生激光烧蚀时，材料的表面的电子吸收激光的能量后变为非平衡状态，发生了相互制约的现象。造成电子爆炸运动速度接近于费米速率。同时热电子通过碰撞作用使得内部电子获得加热，之后参与碰撞的电子达到短暂的呈费米分布的热平衡态。电子与晶格通过碰撞耦合效应，使得电子温度降低和晶格温度升高，最终电子温度与材料的晶格温度达到平衡。 2 短脉冲激光烧蚀研究方法 激光烧蚀的研究方法包括：实验方法测定，理论计算分析和数值模拟。实验方法能够准确的对后两种方法进行检验。但实验方法需要的成本巨大。理论计算分析和数值模拟方法是一种对于研究激光烧蚀问题的非常有的方法，其理论分析过程非常严谨，但是也存在一定的边界条件限制，需要进行相应的假设，处理问题的范围有限。但其可低成本、高精度模拟短脉冲烧蚀机理内的复杂问题，一直是各大科研院校应用的最广泛的方法。若条件允许会采用实验方法进行验证，不断修正算法达到近乎理想的模拟及精密数值计算水平。
英文原文： CHAPTER 1 Pulsed Laser Deposition of Complex Materials: Progress Towards Applications DAVID P. NORTON University of Florida, Department of Materials Science and Engineering, Gainesville, Florida 1.1 INTRODUCTION In experimental science, it is a rare thing for a newly discovered (or rediscovered) synthesis technique to immediately deliver both enhanced performance and simplicity in use in a field of accelerating interest. Nevertheless, such was the case with the rediscovery of pulsed laser deposition(PLD) in the late 1980s. The use of a pulsed laser as a directed energy source for evaporative film growth has been explored since the discovery of lasers [Hass and Ramsey, 1969; Smith and Turner, 1965]. Initial activities were limited in scope and involved both continuous-wave (cw) and pulsed lasers. The first experiments in pulsed laser deposition were carried out in the 1960s; limited efforts continued into the 1970s and 1980s. Then, in the late 1980s, pulsed laser deposition was popularized as a fast and reproducible oxide film growth technique through its success in growing in situ epitaxial high-temperature superconducting films [Inam et al., 1988]. The challenges for in situ growth of high-temperature superconducting oxide thin films were obvious. The compounds required multiple cations with diverse evaporative properties that had to be delivered in the correct stoichiometry in order to realize a superconducting film. Simultaneously, the material was an oxide, requiring an oxidizing ambient during growth. Pulsed laser deposition had several characteristics that made it remarkably competitive in the complex oxide thin-film research arena as compared to other film growth techniques. These principle attractive features were stoichiometric transfer, excited oxidizing species, and simplicity in initial setup and in the investigation of arbitratry oxide compounds. One could rapidly investigate thin-film deposition of nearly any oxide compound regardless of the complexity of the crystal chemistry. Significant development of pulsed laser deposition has continued and over the past 15 years, PLD has evolved from an academic curiousity into a broadly applicable technique for thin-film deposition research [Saenger, 1993; Kaczmarek, 1997; Willmott and Huber, 2000; Dubowski, 1988; Dieleman et al., 1992]. Today, PLD is used in the deposition of insulators, semiconductors, metals, polymers, and even biological materials. Few material synthesis techniques have enjoyed such rapid and widespread penetration into research and application venues. Pulsed Laser Deposition of Thin Films: Applications-Led Growth of Functional Materials Edited by Robert Eason Copyright # 2007 John Wiley & Sons, Inc. 3