Haibin Huo

The thresholds of surface nano-/micro-morphology modifications with femtosecond laser pulse irradiations

We studied the pulse energy threshold of surface nano-/micro-morphology modifications by irradiating Si, GaAs, GaP, InP, Cu and Ti surfaces with 100 fs laser pulses at a wavelength of 800 nm in air and in water. We found that the laser pulse energy thresholds required for the permanent modification in water are up to 30% lower than those in air. Different non-equilibrium dynamics processes of the surface melting layer cause the different thresholds in water and in air.

Surface-enhanced Raman scattering sensor on an optical fiber probe fabricated with a femtosecond laser.

A novel fabrication method for surface-enhanced Raman scattering (SERS) sensors that used a fast femtosecond (fs) laser scanning process to etch uniform patterns and structures on the endface of a fused silica optical fiber, which is then coated with a thin layer of silver through thermal evaporation is presented. A high quality SERS signal was detected on the patterned surface using a Rhodamine 6G (Rh6G) solution. The uniform SERS sensor built on the tip of the optical fiber tip was small, light weight, and could be especially useful in remote sensing applications.

Surface Enhanced Raman Scattering Sensing with Nanostructures Fabricated by Soft Nanolithography

The nanospike structures formed with femtosecond laser irradiations have been successfully replicated on the surface of a polyurethane (PU) polymer using a low cost soft nanolithography method. The surface enhanced Raman scattering (SERS) of rhodamine 6G (Rh6G) and dinitrotoluene (DNT) molecules have been measured with silver coated PU nanospike surfaces by a simple portable Raman spectrometer. Compared to a flat silver coated surface, where no Raman Scattering of the molecules can be detected by the simple portable Raman spectrometer, the Raman spectra are enhanced by more than 4 orders of magnitudes. This indicates that the high area/volume ratio and small size of the PU nanospikes can be used for SERS sensing.

Enhanced protein binding on femtosecond laser ablated poly(methyl methacrylate) surfaces

Poly(methyl methacrylate) (PMMA) substrates were ablated through a fast femtosecond (fs) laser scanning process to create patterns for enhanced protein binding. Typically, two patterns with lines and grids were produced and the protein binding was evaluated by studying the adsorption of fluorescein isothiocyanate (FITC)-labeled bovine serum albumin (BSA). It was found that the adsorption of FITC-BSA was increased up to tenfold on both patterns compared with the untreated PMMA surface, indicating the potential application of the fs laser ablated PMMA surfaces as protein assay substrates.

The electric field effect on the sensitivity of tin oxide gas sensors on nanostructured substrates at low temperature

A novel low-temperature SnO2 gas sensor was prepared and studied on silicon nanostructures formed by femtosecond laser irradiation. By applying a bias voltage on the silicon substrate to alter the charge distribution on the surface of the SnO2, carbon monoxide (CO), and ammonia (NH3) gas can be distinguished by the same sensor at room temperature. The experimental results are explained with a mechanism that the sensor works at low temperature because of adsorption of gas molecules that trap electrons to the surface of the SnO2.

Surface-assisted laser desorption and ionization mass spectrometry using low-cost matrix-free substrates.

Surface-assisted laser desorption/ionization (SALDI) substrates have been fabricated using nanospiked polyurethane (PU) substrates that are replicated by a low-cost soft nanolithography method from silicon nanospike structures formed with femtosecond laser irradiations. The strongest mass spectrometry (MS) signal of Angiotensin II was obtained on 45-nm Au-coated nanospiked PU substrates. The effective ionization appears to be due to surface plasmon excitation. Such low-cost and identical SALDI substrates can be used for MS analysis of various molecules with high reproducibility.

Highly sensitive gas sensors on low-cost nanostructured polymer substrates

SnO2 thin-film gas sensors have been successfully fabricated on nanospiked polyurethane polymer surfaces, which are replicated by a low-cost soft nanolithography method from silicon nanospike structures formed with femtosecond laser irradiations. Measurements revealed significant response to carbon monoxide (CO) gas at room temperature, which is considerably different from the sensors of SnO2 thin films coated on smooth surfaces that show no response to CO gas at room temperature. The high area/volume ratio and sharp structures of the nanospikes enhance the sensitivity of SnO2 at room temperature. This will greatly decrease the electrical power consumption of the gas sensor and the cost for calibrations, and has great potential for application in other sensing systems.

Surface area enhancement of microcantilevers by femto-second laser irradiation

A dry single-step process for enhancing the surface area of a silicon microcantilever is described. In this process, a flat microcantilever is irradiated with ∼100-femto-second-long laser pulses. The silicon surface melts and rapidly cools, resulting in the formation of nanoscale pillars. The shape and size of these nanostructures can be tuned by changing the energy of the pulses. Resonance measurements on surface-enhanced microcantilevers show that the irradiation process reduces the stiffness and the resonance frequency of the cantilevers. Fluidic dissipation measurements provide an estimate for the surface area increase. Both the enhanced surfaces and the fluidic characteristics of these microcantilevers may be useful in bio-chemical sensing applications.

Platinum nanostructures formed by femtosecond laser irradiation in water

Platinum nanostructures with various morphologies, such as spike-like, ripple-like and array-like structures, have been fabricated by 400 nm and 800 nm femtosecond laser irradiation in water. Different structures can be formed on the surfaces as a function of the laser wavelength, the fluence and scan methods. The reflectance measurements of these structures show much larger absorption on the irradiated surfaces than untreated platinum surfaces.

Using metal nanostructures to form hydrocarbons from carbon dioxide, water and sunlight

Based on experimental results, we propose a mechanism that allows the use of metal nanostructures to synthesize hydrocarbons and carbohydrates from carbon dioxide, water and sunlight. When sunlight impinges on cobalt nanostructures in a glass chamber, its intensity is greatly enhanced around the tips of the nanostructures through surface plasmon excitations focusing effect, and it then photodissociates the water and carbon dioxide molecules through enhanced photon absorptions of ions around the tips of the nanostructures. The photodissociated molecules in excited states remain on the cobalt nanostructure surfaces and various hydrocarbons and carbohydrates then will be formed around the surfaces at temperatures much lower than 100 oC.