Optical fabrication and Optical manipulation of semiconductor nanoparticles Ashida lab. Nawaki Yohei 1 Contents • Introduction – – – – Optical fabrication and manipulation Advantage of particles Photo Induced force Resonant force • Purpose – Previous study – My study • Experimental setup – Ablation and Manipulation – Scanning electric microscopy • Optical fabrication – Tablet of GaN – Crystal of GaN • Optical manipulation – Zinc oxide • Summary Introduction 2 Ablation and manipulation Ablation laser Ablation Fabrication method of particles using laser sputtering Manipulation laser Si substrate Manipulation Transporting method by the resonant radiation force Introduction 3 Low-dimensional structures Thin film Quantum wire E Nano particle E DOS DOS DOS DOS Bulk E enhancement of oscillator strength E Introduction 4 Photo induced force Scattering and Absorption pressure Optical axis Gradient Force Photo induced force Gradient force Scattering and Absorption pressure Photo induced force: 光誘起力 Gradient force: 勾配力 Scat. And abs. pressure: 散逸力 Introduction 5 Gradient force The force pushing objects to the focal point Electrical gradient Stabilization point Gaussian beam Introduction 6 Scattering and Absorption force The force arising from the momentum transfer from the light ℏ𝜈 absorption scattering power Introduction 7 Manipulation in various scale Atom Nanoparticle Microparticle It’s difficult for optical manipulation. ~1nm No Structural dependence resonance Laser cooling 1nm~1mm 1mm~ Structural dependence Structural dependence resonance or No resonance No resonance Optical tweezers Introduction 8 Resonant or Non-resonant light Non resonant Resonant Resonant E 𝐸 = 𝐸𝑔 − 𝐸𝑏 + ∆𝐸 ∆𝐸 Energy of applied light ≠ 2 2 𝜋 ℏ of exciton level Energy = 2𝑀𝑎2 a Energy of applied light = Energy of exciton level Resonant Introduction 9 Enhancement by resonant light Numerical calculation example (CuCl) Using resonant light Ref: T.Iida and H. Ishihara Phys. Rev. Lett. 90, 057403 (2003) Photo induced force is drastically enhanced. 100 times of gravitational acceleration Purpose 10 Previous study Our group has succeeded manipulation of nanoparticles Wide-gap semiconductor CuCl K. Inaba phys.stat.sol. (b)243, No.14, (2006) ZnO S. Okamoto master thesis (2011) Purpose 11 My study GaN bulk ablation GaN particles manipulation Manipulated GaN particles Experimental setup 12 Fabrication method ablation laser Nd:YAG cryostat wavelength :525nm pulse duration :10ns manipulation laser Ti:sapphire SHG Si substrate sample pulse duration :100fs Vacuum state (300K) wavelength :726nm back substrate Superfluid He state (2K) wavelength :718nm front substrate Experimental setup 13 Observation method Scanning electron microscope Electron beam Secondary electron SEM measurement To take 2D image Cathode Luminescence CL measurement Character X-ray Energy Dispersive X-ray Spectrometry sample To analyze element Scanning electron microscope: 走査型電子顕微鏡 Secondary electron: 二次電子 Cathode luminescence :電子線励起による発光 Character X-ray: 特性X線 14 Optical fabrication Ablation 15 Gallium Nitride Wide-gap semiconductor GaN: 3.4eV cf. ZnSe, SiC, ZnO, CuCl GaN has wide controllable range of bandgap with ternary crystal semiconductor InN, AlN. Crystal growth is difficult 0.7eV~6.1eV Blue- and UV-Light emitting diode and laser Ablation 16 Tablet of GaN Powder Tablet Press! Ablation 17 SEM images Ablation conditions Vacuum state Nd:YAG power 0.5mJ I could fabricate particles... Ablation 18 Element analysis EDS data SEM image Ga mapping image Nitrogen peak was expected. 19 Particles were oxidized. Ablation 20 Crystal of GaN The reason why is that oxidized particle were fabricated. Tablets included many impurity. The surface of powders were oxidized. Crystal I used crystal of GaN Ablation 21 SEM image Ablation conditions Vacuum state Nd:YAG power :1.5mJ Ablation 22 Element analysis A broken piece by ablation EDS data SEM image Ga mapping image Nitrogen was observed. Ablation 23 Element analysis Fabricated particle by ablation EDS data SEM image Ga mapping image Nitrogen peak was expected. 24 Particles have nitrogen defect. Ablation 25 Superfluid Helium condition Superfluid Helium Low temperature Resonant energy very sharp For ablation Viscosity becomes zero. Small destabilizing effect Suitable for optical manipulation The particles can be cool rapidly. Ablation 26 Crystal of GaN Ablation conditions Superfluid He state Nd:YAG power 0.5mJ Ablation 27 Crystal of GaN EDS data SEM image Ga mapping image Nitrogen peak was expected. 28 Particles have nitrogen defect. Ablation 29 Results The particles had nitrogen defect and contained oxygen. In such condition Tablet from powder Vacuum condition superfluid He condition Crystal Vacuum condition superfluid He condition 30 Optical manipulation manipulation 31 Zinc Oxides Wide-gap semiconductor Band-gap energy of ZnO is 3.4eV. ZnO is very stable material, because It’s oxidation products. 1 cm 1mm Polygonal shape manipulation 32 Problem of size distribution Advantage of particle Density state become sharply. Size distribution Density of state becomes cloudy. Density of state manipulation 33 Pulse laser spectra ps pulse laser 3.35 Intensity (a.u.) Intensity(a.u.) fs pulse laser 3.36 3.37 3.38 3.39 3.40 Photon energy(eV) 3.35 3.36 3.37 3.38 3.39 Photon energy (eV) 3.40 Y. Saito Master thesis (2009) 100fs Pulse duration 3.38eV Peak energy 20meV Spectrum width 1ps 3.38eV 2meV Resonance radius under 100nm radius specific radius manipulation 34 Decrease of size distribution fs pulse laser ps pulse laser 12 10 粒子数 粒子数 8 6 4 8 6 4 2 2 0 0 0 10 20 30 40 50 60 70 80 90 100 粒子直径 (nm) 0 10 20 30 40 50 60 70 80 90 100 粒子直径 (nm) Y. Saito Master thesis (2009) The Size distribution reduced in response to spectrum width. I try to measure size distribution from spectrum width of photoluminescence. 35 Summary Optical fabrication I can’t fabricate GaN particles The particles fabricated by ablation have nitrogen defect and contained oxygen. Optical manipulation I try to measure size distribution from spectrum width of photoluminescence. 36 Appendix Appendix 37 Photo induced force Gradient force Fgrad 3 3 2 nb n r m 1 2 2 b 2 E E 2 2 m 2 Radiation pressure I 0 128 r c 34 5 6 Fscat 2 m 1 2 nb m 2 2 Optical letters vol.11, No. 5, 288 (1986) Appendix 38 First experiment samples material transparent latex spheres size 0.59, 1.31, 2.68mm laser CW argon laser TEM00 = 0.5145mm w0= 6.2mm Power 19mW The author measured sphere moved at 26±5mm/sec 39 Laser cooling Appendix 40 Quantum confinement 弱閉じ込めモデル a > ab 2ab 2a CuCl 強閉じ込めモデル ab > a 2ab 2a a ab 励起子ボーア半径 0.68nm ドット半径 数nm :ドット半径 :励起子ボーア半径 弱閉じ込めモデル ドット内に励起子が閉じ込められる 励起子の重心運動が量子化 ΔE 2a 量子サイズ効果によりエネルギーレベルが変化 ℏ2 𝜋 2 ∆𝐸 = 2𝑀𝑒𝑥 𝑎2
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