Photoinduced phase transition in VO2 nanocrystals: ultrafast control of surface-plasmon resonance

We study the ultrafast insulator-to-metal transition in nanoparticles of VO2, obtained by ion implantation and self-assembly in silica. The nonmagnetic, strongly correlated compound VO2 undergoes a reversible phase transition, which can be photoinduced on an ultrafast time scale. In the nanoparticles, prompt formation of the metallic state results in the appearance of surface-plasmon resonance. We achieve large, ultrafast enhancement of optical absorption in the near-infrared spectral region that encompasses the wavelength range for optical-fiber communications. One can further tailor the response of the nanoparticles by controlling their shape.     

Size-dependent optical properties of VO2 nanoparticle arrays

The size effects on the optical properties of vanadium dioxide nanoparticles in ordered arrays have been studied. Contrary to previous VO2 studies, we observe that the optical contrast between the semiconducting and metallic phases is dramatically enhanced in the visible region, presenting size-dependent optical resonances and size-dependent transition temperatures. The collective optical response as a function of temperature presents an enhanced scattering state during the evolving phase transition. The effects appear to arise because of the underlying VO2 mesoscale optical properties, the heterogeneous nucleation behind the phase transition, and the incoherent coupling between the nanoparticles undergoing an order-disorder-order transition. Calculations that support these interpretations are presented.     

纳米VO2/ZnO复合薄膜的热致变色特性研究

为提高VO₂薄膜的热致变色性能,采用纳米结构和复合结构二者相结合的方法,通过磁控溅射技术先在玻璃衬底上制备高(002)取向ZnO薄膜,再在ZnO层上室温沉积钒金属薄膜,最后经热氧化处理获得纳米结构VO₂/ZnO复合薄膜.利用变温拉曼光谱观察分析了VO₂/ZnO薄膜相变前后的晶格畸变和键态的演变过程,讨论了薄膜的结构与热致红外开关特性和相变温度的内在关系.结果显示,与相同条件获得的同厚度的单层VO₂薄膜相比,纳米VO关键词： ZnO 2')" href="#">VO₂ 纳米复合薄膜 热致变色 拉曼光谱     

Broad band light emission from Ag-ion implanted silicon nanocrystals

Silicon nanoparticles formed using low energy (<50 keV) silver ion implantation in crystalline Si exhibit broad band light emission from ultraviolet (UV) to green. The formation of nanoparticles is confirmed using high resolution electron microscopy (HRTEM) and the resulting microscopy is used to obtain the size distribution of Si nanoparticles. Photoluminescence (PL) spectra were observed in the range of the UV to the green. The origin of emission is most likely from highly localized defects at the Si/SiO2 which is further confirmed from Photoluminescence Excitation (PLE) and effective mass theory estimation.     

Influence of ion implantation on depth dependent phase transition in TiO2 films,anatase nanostructures and photo-absorption behavior

The present study explores the role of Ti ion implantation in structural phase transition in TiO₂ thin films. Raman and TEM results reveal that after implantation Rutile phase in films increases at the expense of Anatase nanostructures. Though the as-deposited films display the presence of bigger anatase nanoparticles, after implantation, predominantly phonon confined smaller (∼ 8 nm in size) anatase nanostructures are observed. GIXRD and Raman results further reflect presence of a critical fluence, 1 × 10¹³ ions/cm², where the initial transformation from anatase to Rutile phase is observed. The role of Oxygen vacancies, in this transformation, has been explored here by XPS. Modifications in UV–Vis and Bandgap results show rich behavior which also reflects phase transformation at the critical fluence. Results further indicate that the phase transition gets first initiated deeper in the film and later on the surface. Interestingly, aggregation of larger Anatase nano-particles appears to be responsible for the structural transformation as observed here.     

用离子束增强沉积从V2O5粉末制备高热电阻温度系数VO_2薄膜

采用了一种用离子束增强沉积从V2O5粉末直接制备VO2薄膜的新方法,将纯度为997%的V2O5粉末压成溅射靶,在用Ar离子束溅射的同时,用氩氢混合束对沉积膜作高剂量离子注入,使沉积膜中V2O5的V—O键断裂,进而被注入的氢还原,退火后获得热电阻温度系数(TCR)高达4%的VO2薄膜.高剂量的氩氢混合束注入对薄膜引入应力,使薄膜的转换温度降低、电阻温度曲线斜率变大,是薄膜TCR增大的原因 关键词： 离子束增强沉积 VO2薄膜 热电阻温度系数     

Nonlinear properties of composites based on dielectric layers containing copper and silver nanoparticles

Nonlinear optical characteristics of copper and silver nanoparticles in glass host matrices are studied by the Z-scan method at the wavelength of a Nd:YAG laser (λ=1064 nm) in a field of picosecond pulses. It is found that the third-order nonlinear susceptibility is more pronounced in glasses with copper nanoparticles than in glasses with silver nanoparticles. On the basis of experimental data obtained for samples with copper nanoparticles synthesized by ion implantation, it is shown for the first time that the nonlinear absorption of laser radiation with a wavelength lying out of the plasmon resonance region can be caused by a two-photon effect in metal particles. The character of the optical limiting process in the samples with copper nanoparticles when two-photon absorption is involved is discussed.     

Ion synthesis of copper nanoparticles in sapphire and their modification by high-power excimer laser pulses: A review

Composite layers made in sapphire by implantation of 40-keV Cu⁺ ions at a dose of 1 × 10¹⁷ cm⁻² and an ion beam current density varying from 2.5 to 10 μA/cm² are studied. It is shown that ion implantation makes it possible to synthesize a composite layer containing copper nanoparticles at the surface of the insulator. However, the nanoparticle size distribution in this layer is nonuniform. The composite layer is exposed to high-power excimer laser radiation with the aim of modifying the size and size distribution of the metal nanoparticles in it. The resulting structures are examined by Rutherford backscattering, optical reflection spectroscopy, and atomic force microscopy. It is found that the laser irradiation diminishes copper nanoparticles in the composite layer. Experimental data on laser modification may be explained by photofragmentation and/or melting of the nanoparticles in the sapphire matrix under the action of nanosecond laser pulses.     

PcNi-VO2复合膜相变光谱特性研究

采用射频磁控溅射的方法在蓝宝石衬底上沉积了高品质的VO2薄膜,并在其上旋涂了酞菁镍[C8H17O]8PcNi薄膜.通过XRD研究了VO2薄膜的微结构.利用红外光谱仪观察了PcNi/VO2复合膜相变前后光学性质的改变,发现PcNi膜在1.5～5.5 μm对VO2膜有增透作用,PcNi/VO2复合膜相对于VO2膜的热色性和相变温度都没有改变.预期PcNi/VO2膜比单一PcNi膜和VO2膜的光限幅能力会更强.     

Ion synthesis and laser annealing of Cu nanoparticles in Al2O3

Al₂O₃ samples with Cu nanoparticles, synthesised by ion implantation at 40 keV with a dose of 1×10¹⁷ ion/cm² and a current density from 2.5 to 12.5 μA/cm², were annealed using ten pulses from a KrF excimer laser with a single pulse fluence of 0.3 J/cm². The copper depth distribution, formation and modification of metal nanoparticles under the ion implantation and laser treatment were studied by Rutherford backscattering (RBS), energy dispersive X-ray (EDX) analysis, atomic force microscopy (AFM) and optical spectroscopy. It was found that laser annealing leads to a reduction in the nanoparticle size without diffusion of metal atoms into the bulk. The change in particle size and the possibility for oxidation of the copper particles are examined in the framework of Mie theory. Calculations presented show that under excimer laser treatment, Cu nanoparticles are more likely to be reduced in size than to undergo oxidation. Received: 19 April 2001 / Accepted: 7 November 2001 / Published online: 23 January 2002     

Optical properties of metal nanoparticles synthesized in a polymer by ion implantation: A review

Polymer composite layers irradiated by 30-keV Ag⁺ ions with doses from 3.1×10¹⁵ to 7.5×10¹⁶ cm^?2 and an ion current of 4 µA/cm² are investigated. The composites were examined using Rutherford backscattering (RBS), transmission electron microscopy (TEM), and optical spectroscopy. As follows from electron microscopy and electron microdiffraction data, ion implantation is a promising tool for synthesizing silver nanoparticles in the surface region. The optical density spectra taken of these composites demonstrate that the silver nanoparticles exhibit unusually weak plasma resonance. The formation of silver nanoparticles in layers carbonized by ion implantation is considered. Based on the Mie theory, optical extinction spectra for silver particles in the polymer and carbon matrices are simulated and optical spectra for complex silver core-carbon sheath nanoparticles are calculated. The physics behind the experimental optical spectra of the composite is discussed.     

Excimer laser-assisted annealing of silicate glass with ion-synthesized silver nanoparticles

The effect of KrF excimer laser radiation on a composite layer consisting of sodium-potassium silicate glass with silver nanoparticles is studied as a function of the number of laser nanosecond pulses. The silver nanoparticles are synthesized by ion implantation. The measured optical absorption of the composite layer demonstrates that the silver nanoparticle size decreases monotonically as the number of laser pulses increases. Rutherford backscattering shows that laser annealing is accompanied by silver diffusion into the bulk of the glass and partial metal evaporation from the sample surface. The detected decrease in the silver nanoparticle size is discussed in terms of simultaneous melting of silver nanoparticles and the glass matrix due to the absorption of laser radiation.     

相变前后VO2薄膜光学性质的研究

测量了玻璃、熔融石英及蓝宝石衬底上VO2 薄膜变温过程的红外透过率谱 ,对样品相变前后的光学性质进行了研究。特定温度下VO2 薄膜发生相变 ,其光学性质随之发生突变。不同衬底、不同制作工艺影响相变发生的温度以及相变前后光学性质的变化量。蓝宝石衬底上磁控溅射所得的VO2 膜 5 μm处透过率的减小量ΔT为 70 % ,相对变化ΔT TRT为 94 % ,玻璃衬底上磁控溅射所得的VO2 膜 2 5 μm处ΔT =6 4 2 % ,而ΔT TRT高达 98% ,接近于 1。     

Formation of gold nanoparticles in single-layer and multi-layer ensembles of light-emitting silicon nanocrystals using ion implantation

The possibility of ion beam formation of gold nanoparticles in SiO2 and Al2O3 matrices with presynthesized single-layer and multi-layer ensembles of silicon nanocrystals is revealed by analyzing the spectra of optical transmission. The parameters of gold nanoparticles are estimated. It is shown that luminescent properties of Si nanocrystals are preserved under irradiation with gold ions.     

Laser annealing of dielectrics with metal nanoparticles

The effect of nanosecond excimer laser pulses on a composite layer of sodium-calcium silicate glass with silver nanoparticles has been investigated. Nanoparticles were synthesized by ion implantation. Based on measuring the optical absorption and reflection spectra of the composite layers, it is found that an increase in the number of laser pulses leads to a monotonic decrease in the size of silver nanoparticles. However, laser irradiation with a longer duration leads to the growth of nanoparticles with their subsequent destruction. The effects observed are discussed in terms of heating a glass composite layer as a result of the effective absorption of laser radiation.     

Structural ordering in a silica glass matrix under Mn ion implantation

Mn(+)-implanted, amorphous SiO(2) samples were synthesized using pulsed-ion implantation without thermal annealing. The crystal and electronic structures have been studied using x-ray diffraction and synchrotron-based soft x-ray absorption and emission spectroscopy at the Si and Mn L(2,3) edges. We find a combination of small MnO clusters and Si crystallites at shallow depths while tetrahedral Mn coordination is found deeper in the host target. Through a combination of techniques, we find that the implantation process simultaneously decreases the long-range order in the near-surface region and increases order deeper in the SiO(2) host. Our results suggest Mn substitution into Si sites at deep levels catalyzes the formation of α-quartz, providing insight into the complex interactions that determine the local structure around the impurities as well as the overall changes to the crystallinity of implanted SiO(2).     

Photoluminescence enhancement induced from silver nanoparticles in Tb3+ -doped glass ceramics

We experimentally verify that surface plasmon (SP) enhances the photoluminescence (PL) of visible light from Tb3+ -doped 60SiO2 -20Al2O3 -20CaF2 :0.3Tb 3+ , 20Yb 3+ glass ceramics by using electron beam lithography to fabricate silver nanoparticles on the surface of the glass ceramics. Numerical calculation for the SP enhancement spectroscopy is achieved by using the finite-difference time-domain algorithm. A PL enhancement of Tb3+ by as much as 1.6 times is observed. The PL enhancement is mainly due to the coupling of excitation from 7 F 6 to 5 D 4 transition dipole of Tb 3+ ion with SP mode induced from the silver nanoparticles.     

Engineering embedded metal nanoparticles with ion beam technology

In this paper, we summarize our recent results of study on how to engineer the embedded metal nanoparticles in silica by ion implantation and ion irradiation technologies, including controlling the size, distribution and morphology of nanoparticles. The optical properties of the tailored nanoparticle composites are studied. Thermal annealing, electron beam irradiation, and chemical erosion are used to study the stability of these embedded nanoparticles by ex situ or in situ transmission electron microscopy observation.     

离子束增强沉积VO_2多晶薄膜的温度系数

用改进的离子束增强沉积方法和恰当的退火从V2 O5粉末直接制备了VO2 多晶薄膜 .实验测试表明 ,薄膜的取向单一、相变特性显著、结构致密、界面结合牢固、工艺性能良好 ,薄膜的电阻温度系数 (TCR)最高可达 4 2 3% K .从成膜机理出发 ,较详细地讨论了离子束增强沉积VO2 多晶薄膜的TCR高于VOx 薄膜的TCR的原因 .分析认为 ,单一取向的VO2 结构使薄膜晶粒具有较高的电导激活能 ,致密的薄膜结构减少了氧空位和晶界宽度 ,使离子束增强沉积VO2 多晶薄膜结构比其他方法制备的VOx 薄膜更接近于单晶VO2 是其具有高TCR的原因     

离子束增强沉积VO2多晶薄膜的温度系数

用改进的离子束增强沉积方法和恰当的退火从V2O5粉末直接制备了VO2多晶薄膜.实验测试表明，薄膜的取向单一、相变特性显著、结构致密、界面结合牢固、工艺性能良好，薄膜的电阻温度系数（TCR）最高可达4.23%/K.从成膜机理出发，较详细地讨论了离子束增强沉积 VO2多晶薄膜的TCR高于VOx薄膜的TCR的原因.分析认为，单一取向的VO2结构使薄膜晶粒具有较高的电导激活能，致密的薄膜结构减少了氧空位和晶界宽度，使离子束增强沉积 VO2多晶薄膜结构比其他方法制备的VOx薄膜更接近于单晶VO2是其具有高TCR的原 关键词： VO2多晶薄膜 离子束增强沉积 热电阻温度系数