Research On The Fabrication Of Single Quantum Dot Decorated Nanoprobe For Nano-optics

Scanning near-field optical microscopy(SNOM)can break the diffraction limit of the light,the fundamental limit for the spatial resolution of traditional optical microscopes.It enables researchers to characterize the optical properties of samples with nanometer spatial resolution.In this dissertation,we study the fabrication of nano-optical probe,the key component scanning near-field optical microscopes.Two types of probes are discussed,namely the single quantum dot decorated nanoprobes and inverted pyramid pyramidal probes.The optical properties of luminescent nanocrystals,including quantum dots and upconverting fluorescent nanoparticles,are sensitive to their local environment,including photon density,temperature,electric field,magnetic field and permittivity.They can therefore be used as ultra-sensitive nanosensors to detect the local environment.Especially with the help of scanning probe microscopy,the use of a single luminescent nanoparticle can even map the physics field with nano-spatial resolution,providing a powerful tool for studying nanoscale chemical and physical processes.The quantum dot(QD)probe also provides a tool for study the coupling phenomena between single QD and optical devices,including optical antennas,micro-waveguides,and optical microcavities.This is extremely useful for building high performance single photons sources,optical switches,and nanolasers.Driven by the applications,the thesis is focused on the fabrication of high performance QD probes.We first proposed a simple and reliable method for preparing single quantum dot probes.With a cantilevered fiber tip,a single quantum dot is successfully picked up and glued to the tip of the fiber tip,and there is no need for an expensive feedback system to control the distance between the tip and the sample.During the experiment,we tried three kinds of quantum dots:CsPbBr3 QD,NaYF4 NC,and CdSe QD.All of them successfully prepared single quantum dot probes.By modifying the glass substrate,the quantum dots synthesized by the oil phase can be uniformly dispersed on the substrate.In addition,by measuring the luminescence spectrum of the quantum dot before and after the tip of the needle,it is concluded that the optical fiber tip does not affect the luminescent characteristics of the quantum dot.The success rate of this preparation method is around 70%(21 out of 30 tips).Quantum dots can be successfully extracted after the ATPMS process.Because the interaction of the tip with the quantum dot is inherently weak,30%of the tip fails to pick up the quantum dot after it is pressed onto the quantum dot.In addition to the technique for picking up single QDs,we developed the pyramid fiber probe in order to have a high signal collection efficiency.Inversed pyramid structures in a Si substrate were used here as the template,and pyramid probes were fabricated using UV-imprint technique.This preparation method is simple and reliable.High quality pyramid probes can be successfully duplicated with a tip size of about 100 nm at a high yield(close to 100%).Experiments show that submicrometer gratings can be clearly resolved using the probes.