H.W.M. Salemink

InP-based two-dimensional photonic crystals filled with polymers

Polymer filling of the air holes of indium-phosphide-based two-dimensional photonic crystals is reported. After infiltration of the holes with a liquid monomer and solidification of the infill in situ by thermal polymerization, complete filling is proven using scanning electron microscopy. Optical transmission measurements of a filled photonic crystal structure exhibit a redshift of the air band, confirming the complete filling.

Nanopillar growth by focused helium ion-beam-induced deposition

A 25 keV focused helium ion beam has been used to grow PtC nanopillars on a silicon substrate by beam-induced decomposition of a (CH(3))(3)Pt(C(P)CH(3)) precursor gas. The ion beam diameter was about 1 nm. The observed relatively high growth rates suggest that electronic excitation is the dominant mechanism in helium ion-beam-induced deposition. Pillars grown at low beam currents are narrow and have sharp tips. For a constant dose, the pillar height decreases with increasing current, pointing to depletion of precursor molecules at the beam impact site. Furthermore, the diameter increases rapidly and the total pillar volume decreases slowly with increasing current. Monte Carlo simulations have been performed with realistic values for the fundamental deposition processes. The simulation results are in good agreement with experimental observations. In particular, they reproduce the current dependences of the vertical and lateral growth rates and of the volumetric deposition efficiency. Furthermore, the simulations reveal that the vertical pillar growth is due to type-1 secondary electrons and primary ions, while the lateral outgrowth is due to type-2 secondary electrons and scattered ions.

Fast single-step fabrication of nanopores

We report a new method for the fabrication of sub-10 nm nanopores in a fast single process step. The pore formation is accomplished by exploiting the competition between sputtering and deposition in ion-beam-induced deposition (IBID) on a thin membrane. The pore diameter can be controlled by adjusting the ion beam and gas exposure conditions. The pore diameter is well below the limit that can be achieved by focused ion beam (FIB) milling alone. There is no need of preparation and successive treatments. Apart from simplicity and speed, this method offers an additional advantage of a broad choice of material and thickness of the deposit and the membrane.

Birefringence-induced mode-dependent tuning of liquid crystal infiltrated InGaAsP photonic crystal nanocavities

Mode-dependent shifts of resonant frequencies of cavities in liquid crystal (LC) infiltrated planar photonic crystals (PhC) are experimentally observed when the temperature is varied across the LC ordering transition. The shifts can be in opposite directions, even for two very similar nearly degenerate modes. The behavior is attributed to the different interactions of the modes with the two components of the refractive index of the LC infill and directly demonstrates that at least a substantial amount of the LC is oriented perpendicular to the PhC-hole axis.

Compact Mach-Zehnder interferometer based on self-collimation of light in a silicon photonic crystal

We demonstrate a compact silicon photonic crystal Mach-Zehnder interferometer operating in the self-collimation regime.The 2-D and 3-D simulation results, silicon membrane nanofabrication, near-field propagation and MZ output are discussed.

Strain Sensitive Effect in a Triangular Lattice Photonic Crystal Hole-Modified Nanocavity

This paper reports the theoretical and experimental investigations of the strain-induced resonant wavelength shift effect of a modified single-defect 2-dimensional (2D) photonic crystal (PhC) nanocavity resonator. The nanocavity was created by modifying the geometry, i.e., the diameters and shapes, of some specific holes in the triangular-lattice 2D PhC. Structural and optical simulations were performed based on the finite element method (FEM) and finite difference time domain (FDTD), respectively, to theoretically determine the optical characteristics and the strain sensitive effect of the nanocavity. Simulation results showed a linear relationship between strain and the shift of resonant wavelength of the nanocavity. The wavelength shifts due to longitudinal and transverse strains were theoretically determined to be 1.9 and 0.25  pm/ μstrain , respectively. The PhC nanocavity was also fabricated and the strain sensitive effect was measured. Experimental results confirmed the strain-induced resonant wavelength shift effect in the nanocavity. The resonant peak of the nanocavity was shifted about 100 pm to the longer wavelength when the nanocavity was stretched with a tensile strain of 300 μstrain along the light-transmission direction. These results show a potential of using a PhC cavity to detect the strain by monitoring its resonant wavelength shift.

TEM study of locally coated nanopore fabricated by ion-beam-induced deposition in a thin membrane.

We studied the formation of locally coated sub-10-nm nanopores fabricated by ion-beam milling and ion-beam-induced deposition (IBID) in a thin silicon nitride membrane. Two typical precursor gases representing conductive ((CH(3))(3)Pt(CpCH(3)), CPC for short) and insulating (tetra ethyl oxysilane, TEOS for short) material deposition are used. Three-dimensional electron tomography, EDX and EELS analysis are used to measure the changes in chemical composition and shape of the pores after their formation and at various stages of pore shrinkage. The formation and shrinkage are shown to be due to a shifting competition between IBID and material sputtering during ion-beam exposure. The chemical distribution at the rim of the nanopore is dependent on the precursor gases used: CPC forms a thin carbon layer with small embedded Pt particles at the top and inner surfaces of the nanopore, whereas TEOS forms SiO(x)C(y) with Ga particles dispersed at the rim of the nanopore.

Photoluminescence enhancement in thin films of PbSe nanocrystals

Remarkable photoluminescence enhancement (PLE) in submonolayer films of PbSe nanocrystals (NCs) upon continuous illumination was observed. The intensity increase from films on InP substrates was highest in vacuum, while for films on Si/SiO2 substrates the PLE was stronger in air. The magnitude of the PLE was found to depend on the excitation intensity, being higher for a weaker irradiation power. The possible mechanisms behind the phenomenon of the PLE are discussed and it is suggested to originate mainly from charge trapping outside the NCs core.

2D InP photonic crystal fabrication process development

We have developed a reliable process to fabricate high quality 2D air-hole and dielectric column InP photonic crystals with a high aspect ratio on a STS production tool using ICP N2+Cl2 plasma. The photonic crystals have a triangular lattice with lattice constant of 400 nm and air-hole and dielectric column radius of 120 nm. Large efforts have been devoted on developing a proper mask. We obtained a perfect, clean and vertical profiled SiNX mask. The next main effort is InP pattern transfer in Cl2+N2 plasma. Etching selectivity, smooth sidewall and etch profile are directly related to plasma process condition, besides the quality of SiNX mask. We have optimized the N2+Cl2 plasma condition to obtain high aspect ratio, vertical profile and smooth sidewall InP structures. Cylindrical holes (2 micron depth) and rodlike pillars (2.4 micron height) are uniformly fabricated. An aspect ratio of 18 for 100nm trench lines has been obtained. AFM measurement evidences that etched surfaces are smooth. The root mean square roughness of pillar and hole is 0.7 nm and 0.8 nm, respectively. The optical transmission characterization of ridge waveguides has been carried out. Transmission spectrum of 1 micron wide waveguide has been obtained.

Strain sensitivity of a modified single-defect photonic crystal nanocavity for mechanical sensing

This paper reports the theoretical and experimental investigations of the strain sensitive effect of a 2D photonic crystal (PhC) nanocavity resonator for mechanical sensing applications. By using finite element method (FEM) using ANSYS software and finite different time domain (FDTD) simulation using CrystalWave software, the strain sensitivity of a high quality factor PhC nanocavity has been studied. Linear relationships between strain and shift of resonant wavelength of the cavity have been obtained. The sensitivities to longitudinal and transverse strains have been determined to be 1.9 nm/me and 0.25 nm/me, respectively. The sample structure were fabricated and characterized. The initial results show that the cavity peak with Q factor estimated to be 3800 had been obtained.