Direct Electron Beam Research Articles

Direct electron beam writing of kinoform micro-axicon for generation of propagation-invariant beams with long non-diffracting distance

To enhance the non-diffracting distance of propagation-invariant beams, fabrication of an axicon with large aperture diameter and height is essential. It is noted, however, that fabrication of continuous surface profile micro-optical elements with a large physical height (thick resist) is prone to various fabrication constraints and errors. We employ the kinoform technique to alleviate such problems in the fabrication of axicons. In this paper kinoform micro-axicons and kinoform micro-double-axicons are designed and fabricated employing electron beam lithography techniques to generate a Bessel beam and a self-imaged bottle beam with long non-diffracting distance. Furthermore, a detailed study of power conversion efficiency of kinoform structures is discussed.

Imprinted silicon-based nanophotonics

We demonstrate and optically characterize silicon-on-insulator based nanophotonic devices fabricated by nanoimprint lithography. In our demonstration, we have realized ordinary and topology-optimized photonic crystal waveguide structures. The topology-optimized structures require lateral pattern definition on a sub 30-nm scale in combination with a deep vertical silicon etch of the order of ~300 nm. The nanoimprint method offers a cost-efficient parallel fabrication process with state-of-the-art replication fidelity, comparable to direct electron beam writing.

Direct electron beam writing of channel waveguides in nonlinear optical organic crystals

We report on optical channel waveguiding in an organic crystalline waveguide produced by direct electron beam patterning. The refractive index profile as a function of the applied electron fluence has been determined by a reflection scan method in the nonlinear optical organic crystal 4-N, N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST). A maximal refractive index reduction of Deltan1 = -0.3 at a probing wave-length of 633 nm has been measured for an electron fluence of 2.6mC/cm(2). Furthermore, a new concept of direct channel waveguide patterning in bulk crystals is presented and waveguiding has been demonstrated in the produced structures by end-fire coupling. Mach-Zehnder modulators have been successfully realized and a first electro-optic modulation at a wavelength of lambda= 1.55mum has been demonstrated therein.

High Resolution Electron Beam Lithographic Deposition of Metal and Metal Oxide Films from Metal Complexes

ABSTRACTIn this paper, a method of direct electron beam lithographic deposition of metal and metal oxide films is demonstrated using metal organic complexes. In this method, a solution of a metal complex is used to spin coat a substrate to obtain a precursor film. The precursor film is then directly patterned by electron beam writing. A solvent is then used to develop the latent image. Using examples of titanium, tantalum, zirconium, and gold, we illustrate patterning of metal and metal oxide films and both positive and negative deposition. The feature size demonstrated is as low as 14 nm while the demonstrated aspect ratio is as high as 11.

Image reversal for direct electron beam patterning of protein coated surfaces

Electron beam lithography (EBL) is used to create surfaces with protein patterns, which are characterized by immunofluorescence and atomic force microscopies. Both negative and positive image processes are realized by electron beam irradiation of proteins absorbed on a silicon surface, where image reversal is achieved by selectively binding a second species of protein to the electron beam exposed areas on the first protein layer. Biofunctionality at the cellular level was established by culturing cortical cells on patterned lines of fibronectin adsorbed on a bovine serum albumin background for 7 days in culture.

Improvement of the wear resistance of titanium alloyed with boron nitride by electron beam irradiation

Surface alloying of commercially pure titanium was carried out with an electron beam (EB) apparatus using a boron nitride powder which was previously deposited on its surface by Atmospheric Plasma Spraying (APS) in order to produce a composite layer with high wear resistance. Electron beam surface alloying is an important surface engineering routine that involves melting of a pre-deposited layer or concomitantly added alloying elements/compounds with a part of the underlying substrate by direct energy electron beam irradiation to form an alloyed zone characterized by a novel microstructure and composition. The present study is concerned with the influences of EB-remelting process on the wear resistance of the alloyed titanium material. The microstructure, corrosion resistance and phase analysis were also examined. Scanning electron microscopy (SEM), light microscopy (LM) and X-ray Diffraction (XRD) were performed to characterize the phase modification and morphology after the EB treatment. The sliding wear as well as the hardness of the remelted material was significantly improved (in comparison with pure Ti) through this alloying technique. The corrosion behaviour of the modified surfaces was compared with that of Ti in order to demonstrate that its initial good corrosion resistance is not strongly influenced due to surface alloying.

A six-circle diffractometer system for synchrotron X-ray studies of surfaces and thin film growth by molecular beam epitaxy

A new ultrahigh vacuum (UHV) surface diffractometer system equipped with molecular beam epitaxy (MBE) capabilities has been developed. It has a versatile 6-circle configuration for defining the diffraction geometry, and a three-axis translation stage for controlling the sample position. Rugged mechanical components are employed in the design to allow accurate diffraction measurements. Sample cooling is facilitated by passing liquid nitrogen into a reservoir in the base of a sample mount. The sample can be heated to very high temperatures by either direct current heating or electron beam bombardment. During film growth and processing, the sample temperature, monitored by thermocouples, can be continuously and rapidly varied between ∼110K to above room temperature. A charge coupled device (CCD) camera, attached to the μ circle, allows rapid reciprocal space mapping for real time studies of sample growth and evolution during deposition and annealing. A beam stop and a baffle are implemented to minimize stray scattered radiation.

Fairly pure ultraviolet electroluminescence from ZnO-based light-emitting devices

Fairly pure ultraviolet (UV) electroluminescence (EL) was realized on a ZnO-based metal-insulator (SiOx,x⩽2)-semiconductor structure on a silicon substrate, which was easily fabricated by the reactive direct current sputtering and electron beam evaporation. The UV EL originated from the near-band-edge (NBE) emission of ZnO was achieved at room temperature when the device was under sufficient forward bias with the negative voltage applied on the silicon substrate. Moreover, the intermediate SiOx layer should be thick enough to confine the electrons in the conduction band of ZnO beneath the ZnO∕SiOx interface, which is critical for generation of NBE emission from ZnO.

Integration of a multimode interference coupler with a corrugated sidewall Bragg grating in planar polymer waveguides

We demonstrate the integration of a 3-dB multimode interference coupler with a corrugated sidewall Bragg grating in planar polymer waveguides by direct electron beam writing. Both transmission and reflection spectra of the Bragg grating are measured through this integrated device directly. We use the thermooptic effect to tune the integrated waveguide grating, achieving a tuning range of 6.2 nm and a bandwidth variation of 0.3 nm within a temperature change of 62/spl deg/C.

280 nm Emission Deep UV LEDs with Integrated Fresnel Microlenses

AbstractWe report on the integration of flowable oxide based Fresnel microlenses with AlGaN based 280 nm light emitting diodes (LED). The lenses were fabricated on the back side of the LED sapphire substrates using direct electron beam writing. Ten concentric rings with different width and variable thickness were designed for 360 degree phase correction. Within each ring the thickness was varied in five steps to approximate a linear profile. The width of each thickness step varied from 100 nm to several microns. Outer diameter of the lens was 65μm. A focal distance of 68 μm was measured for the fabricated microlenses. At the focal plane a FWHM of intensity profile as small as 14 μm was measured for lenses integrated with 30 μm diameter UV LEDs . The maximum intensity at focal plane exceeded the background radiation by a factor of 50. Comparison of the LED performance before and after the lens fabrication did not reveal any degradation of integral efficiency of devices. These results demonstrate the feasibility of using flowable oxide Fresnel microlenses in optical systems based on micro-pixel deep UV AlGaN LEDs.

Photosensitive quantum dot composites and their applications in optical structures

Commercially available CdSe∕ZnS and PbSe colloidal semiconductor quantum dots were employed to produce both an electron beam sensitive poly(methyl methacrylate) (PMMA)-quantum-dot (QD) positive composite via a prepolymerization processing and an electron beam and ultraviolet (UV) light sensitive SU-8-QD negative composite via a direct dispersion procedure. Compared to the QDs in the original colloidal solutions, the photoluminescence of the composites shifts to shorter wavelength due to the oxidation of the surfaces of the QDs. Using the QD composites, optical integrated circuits such as grating and waveguide structures were fabricated by direct electron beam writing and UV optical lithography. The characterization results show promising applications in optoelectronics for the QD composites.

Direct electron beam writing of optical devices on Ge-doped flame hydrolysis deposited silica

Electron beam irradiation of silica is a very flexible technique for the fabrication and trimming of optical circuits for the telecommunications and biosensing areas. In this paper, we review the effects induced by electron beam irradiation of germanium-doped, flame-hydrolysis deposited (FHD) silica. The structural modifications were studied with Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The compaction of the material was characterized by profilometry and the refractive index variation and index distribution of channel waveguides were characterized using the m-line technique and microreflectivity, respectively. Finally, some optical devices were fabricated using this technique with application in optical fluorescence sensing. The technique appears as a very interesting way of fabrication low-loss optical waveguides in silica.

Nanoparticle Arrays Patterned by Electron-Beam Writing: Structure, Composition, and Electrical Properties

Direct electron beam writing in nanoparticle films is employed to create nanoscale wires between prepatterned gold electrodes on SiO(2)/Si wafers. Characterization of these nanowires using AFM, SEM, and EDX reveals a core/sheath morphology, where a gold-rich core is surrounded by a sheath which is mainly of carbon. Z-contrast STEM images indicate that the central core consists of a distribution of metal cores in a carbon network. The results suggest that the nanoparticle network is created through cross-linking of the ligands of adjacent particles. The high resistivities obtained in conductivity measurements are consistent with this picture. The work illustrates the ability to generate patterned nanoparticle arrays which can be addressed electrically.

HAADF and EFTEM Studies of Patterned Nanorings by Direct Electron Beam Lithography in an Iron Phosphate Glass

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Preferential nucleation of silicon nano-crystals on electron beam exposed SiO2 surfaces

We propose a new method, based on a direct electron beam exposure of the SiO 2 substrate surface, to create nucleation sites for silicon nano-crystals (Si-Ncs) grown via SiH 4 chemical vapor deposition. Thus, control of the Si-Ncs in the growth plane can be obtained. Electron beam exposure has been used to induce local modifications of the chemical properties of the SiO 2 layer, due to oxygen desorption. After this writing step, 5 nm diameter Si-Ncs have been deposited. Si-Ncs nucleate preferentially on the exposed area. Starting from experimental results and theoretical simulations, we demonstrate the possibility of achieving Si-Ncs spatial location in this way; these results are promising and open new paths for the realisation of single-electron components.

Preferential nucleation of silicon nano-crystals on electron beam exposed SiO 2 surfaces

We propose a new method, based on a direct electron beam exposure of the SiO 2 substrate surface, to create nucleation sites for silicon nano-crystals (Si-Ncs) grown via SiH 4 chemical vapor deposition. Thus, control of the Si-Ncs in the growth plane can be obtained. Electron beam exposure has been used to induce local modifications of the chemical properties of the SiO 2 layer, due to oxygen desorption. After this writing step, 5 nm diameter Si-Ncs have been deposited. Si-Ncs nucleate preferentially on the exposed area. Starting from experimental results and theoretical simulations, we demonstrate the possibility of achieving Si-Ncs spatial location in this way; these results are promising and open new paths for the realisation of single-electron components.

Polymeric multi-channel bandpass filters in phase-shifted Bragg waveguide gratings by direct electron beam writing

We apply direct electron beam writing to fabricate corrugated sidewall Bragg gratings in polymer waveguides and demonstrate multi-channel passband filters based on a phase-shifted design. Experimental results are compared with numerical fittings to analyze the impact of signal polarization and waveguide cladding material upon device performance.

Soft lithography replication of polymeric microring optical resonators

We have developed a soft lithography method to replicate polymeric integrated optical devices. In this method, the master device and the molded replica are made of the same materials, allowing direct comparison. To evaluate the quality of the replication, microring optical resonators are chosen as test devices because of their sensitivity to small fabrication errors. The master devices are precisely fabricated using direct electron beam lithography. The replicas are produced by the molding technique and subsequent ultraviolet curing. Compared with the master devices, the molded devices show minimal change in both physical shape and optical performance. This correspondence indicates the merits of soft lithographic methods for fabrication of precision integrated optical devices.

Two-dimensional structures of ferroelectric domain inversion in LiNbO3 by direct electron beam lithography

We report on the fabrication of domain-reversed structures in LiNbO3 by means of direct electron beam lithography at room temperature without any static bias. The LiNbO3 crystals were chemically etched after exposure of the electron beam, and then the patterns of domain inversion were characterized by atomic force microscopy (AFM). In our experiment, an interesting phenomenon occurred when the electron beam wrote a one-dimensional grating on the negative c face: a two-dimensional (2D) dotted array was observed on the positive c face, which is significant for its potential to produce 2D and three-dimensional photonic crystals. Furthermore, we also obtained 2D ferroelectric domain inversion in the whole LiNbO3 crystal by writing the 2D square pattern on the negative c face. Such a structure may be utilized to fabricate 2D nonlinear photonic crystal. AFM demonstrates that a 2D domain-reversed structure has been achieved not only on the negative c face of the crystal, but also across the whole thickness of the crystal.

Structural Characterization Using X-ray Diffraction of Ti Indiffused Periodically Poled LiNbO3 Fabricated by Direct Electron Beam Bombardment

Periodic poling in titanium indiffused lithium niobate by direct electron beam irradiation is reported in this paper and the benefits the technique of X-ray diffraction (XRD) as a method to examine the structure of ferroelectric domains is presented. It is shown that in the case of periodically poled crystals with a grating period lower or equal than a few microns, XRD enables to straightforwardly access the domain inverted grating period. The use of analytical functions to model the XRD profiles allows this method to be easily implemented for on line non-destructive characterization of the devices.