Focused Ion Beam Etching Research Articles

Quantum-Cascade Ring Resonator Laser with 7–8 μm Wavelength and Surface Radiation Output

We have created a quantum-cascade laser with 7–8 μm wavelength and surface radiation output through a lattice formed by focused ion beam etching of the upper cladding of the waveguide. The active area of the quantum-cascade laser heterostructure was formed on the basis of the solid alloy heteropair In0.53Ga0.47As/Al0.48In0.52As with two-phonon depletion of the cascade lower level. We demonstrate laser generation in the spectral band 7–8 μm for the created lasers with the selective ring resonator. The studies of the generation spectra for the temperatures in 8–77 K range have shown, that the mode spacing in the generation spectra of these lasers correspond to the whispering-gallery modes.

Large-Scale Thin CsPbBr3 Single-Crystal Film Grown on Sapphire via Chemical Vapor Deposition: Toward Laser Array Application.

Single-crystal perovskites with excellent photophysical properties are considered to be ideal materials for optoelectronic devices, such as lasers, light-emitting diodes and photodetectors. However, the growth of large-scale perovskite single-crystal films (SCFs) with high optical gain by vapor-phase epitaxy remains challenging. Herein, we demonstrated a facile method to fabricate large-scale thin CsPbBr3 SCFs (∼300 nm) on the c-plane sapphire substrate. High temperature is found to be the key parameter to control low reactant concentration and sufficient surface diffusion length for the growth of continuous CsPbBr3 SCFs. Through the comprehensive study of the carrier dynamics, we clarify that the trapped-related exciton recombination has the main effect under low carrier density, while the recombination of excitons and free carriers coexist until free carriers plays the dominate role with increasing carrier density. Furthermore, an extremely low-threshold (∼8 μJ cm-2) amplified spontaneous emission was achieved at room temperature due to the high optical gain up to 1255 cm-1 at a pump power of 20 times threshold (∼20 Pth). A microdisk array was prepared using a focused ion beam etching method, and a single-mode laser was achieved on a 3 μm diameter disk with the threshold of 1.6 μJ cm-2. Our experimental results not only present a versatile method to fabricate large-scale SCFs of CsPbBr3 but also supply an arena to boost the optoelectronic applications of CsPbBr3 with high performance.

Anomalous enhancement of focused ion beam etching by single raster propagating toward ion beam at glancing incidence

Focused ion beam (FIB) sample preparation for electron microscopy often requires large volumes of materials to be removed. Prior efforts to increase the rate of bulk material removal were mainly focused on increasing the primary ion beam current. Enhanced yield of etching at glancing ion beam incidence is known but has not found widespread use in practical applications. In this study, etching at glancing ion beam incidence was explored for its advantages in increasing the rate of bulk material removal. Anomalous enhancement of material removal at glancing angles of ion beam incidence was observed with single-raster etching in along-the-slope direction with toward-FIB direction of raster propagation. Material removal was inhibited in an away-from-FIB direction of raster propagation. The effects of glancing angles and ion doses on depth of cut and volume of removed materials were also recorded. We demonstrated that the combination of single-raster FIB etching at glancing incidence in along-the-slope direction with toward-FIB raster propagation and a “staircase” type of etching strategy holds promise for reducing the processing time for bulk material removal in FIB sample preparation applications.

Damage mechanism of graphene nanoribbons field effect transistors during focused ion beam etching

The fabrication of graphene nanoribbons (GNRs) is a familiar method to open the band gap of graphene. As one of the most novel means, focused ion beam (FIB) etching is expected to become the mainstream of GNRs production. Monte Carlo analysis is devoted to simulate the process of ion scattering in FIB etching GNRs. In the process of scattering, charged ions collide with solid materials continuously, which changes the direction and energy of ions in solid. Therefore, the information such as the motion track of the scattered ions, the damage of recoil atoms and the sputtering of surface atoms can be obtained, through the calculation of the scattering angle as well as nuclear energy loss of the charged ions. Combined with Raman spectroscopy and atomic force microscope (AFM) characterization, it is revealed that FIB etching indirectly induces the structure defects on GNRs and affects electrical performance.

Neon and helium focused ion beam etching of resist patterns

Helium ion microscopy has attracted many applications in imaging, nanofabrication and analysis. One important field of study in nanofabrication using ion beam is the milling or etching of materials using a helium or neon focused ion beam (FIB), with and without chemical gas assistance. In particular, the neon FIB has a relatively high sputtering rate with a lower probability of swelling and less re-deposition issues compared to a helium FIB. Here, both neon and helium FIB etchings are investigated for milling and repairing electron-beam lithography (EBL) defined hydrogen silsesquioxane (HSQ) and polymethyl methacrylate (PMMA) resist patterns. Different dosages of neon FIB etching result in distinct etching profiles. Using the appropriate doses, arrays of uniform gap with aspect ratio more than 20 can be achieved on HSQ nanostructures. The neon FIB etching has a resolution of 20 nm on HSQ patterns. With XeF2 assistance, neon FIB etching can be enhanced for etching depth by a factor of ∼1.2. Whereas, helium FIB can also etch thick HSQ patterns, with much lower etch rates. But with XeF2 assistance, helium FIB etching depth can be enhanced significantly by a factor of around 5. Furthermore, both helium and neon FIB etching methods have been employed to selectively remove residual particles in deep and narrow trenches without affecting the resist patterns. The chemical analysis of these residual particle composition and resist patterns can be also performed using helium ion microscopy coupled with secondary ion mass spectrometry (SIMS) using neon FIB. Besides, a neon FIB can also effectively etch PMMA patterns which are commonly used in nanofabrication and the unwanted connections can be etched away.

Focused Ion Beam Milling of Single-Crystal Sapphire with A-, C-, and M-Orientations.

Sapphire substrates with different crystal orientations are widely used in optoelectronic applications. In this work, focused ion beam (FIB) milling of single-crystal sapphire with A-, C-, and M-orientations was performed. The material removal rate (MRR) and surface roughness (Sa) of sapphire with the three crystal orientations after FIB etching were derived. The experimental results show that: The MRR of A-plane sapphire is slightly higher than that of C-plane and M-plane sapphires; the Sa of A-plane sapphire after FIB treatment is the smallest among the three different crystal orientations. These results imply that A-plane sapphire allows easier material removal during FIB milling compared with C-plane and M-plane sapphires. Moreover, the surface quality of A-plane sapphire after FIB milling is better than that of C-plane and M-plane sapphires. The theoretical calculation results show that the removal energy of aluminum ions and oxygen ions per square nanometer on the outermost surface of A-plane sapphire is the smallest. This also implies that material is more easily removed from the surface of A-plane sapphire than the surface of C-plane and M-plane sapphires by FIB milling. In addition, it is also found that higher MRR leads to lower Sa and better surface quality of sapphire for FIB etching.

Nanoscale profiling of multilayer graphene films on silicon carbide by a focused ion beam

The controlled and reproducible formation of a nanoscale interelectrode gap is crucial for the development of next-generation nanoelectronics devices, such as nano-electromechanical systems or field emission structures. This paper reports an etching of multilayer graphene (MLG) film on silicon carbide using focused ion beam (Ga+). The main task is to obtain nanoscale width trenches for the formation of isolated planar nanostructures based on MLG. MLG were obtained by thermal decomposition of silicon carbide in vacuum. We used 6H-SiC as a substrate. The analysis of the Raman spectrum showed the presence of about 10 layers of graphene in the film. The influence of the focused ion beam (FIB) parameters on the distribution of the Ga+ ions concentration in the SiC substrate was estimated by the Monte Carlo method. We revealed the maximum concentration of Ga+ ions in the SiC substrate is at a depth of 19 nm at the ion energy of 30 keV and the incidence angle of the ion beam on the substrate relative to the normal 0°. The results of local nanoscale etching of MLG on SiC by using FIB are presented. The AFM-studies confirm the dependence of the geometric dimensions of the etching area on the FIB etching parameters. The resolving power of the method is determined on the basis of a number of detectable nanoscale trenches at various currents of the FIB.

Microstructure of fibres pressure-spun from polyacrylonitrile–graphene oxide composite mixtures

Suspensions containing 8 and 10 wt% polyacrylonitrile (PAN) and 1, 2, 3, 5, 7 and 10 wt% graphene oxide (GO) were prepared using a special mixing routine and fibres were generated from these mixtures by pressurised gyration. The combination of pressure and gyration speed was effective in controlling the fibre morphology and fibre diameter which ranged from 1 to 20 μm. Fibres were pyrolysed to remove the polymer and only the 10 wt% PAN fibres survived. The microstructure of the pre- and post-pyrolysis products were characterised by scanning electron microscopy, both with and without focussed ion beam etching, Fourier-transformed infrared and Raman spectroscopies. Pyrolysed fibre electrical conductivities were measured and only those containing 1 and 2 wt% GO were conductive.

Investigating electrical properties of controllable graphene nanoribbon field effect transistors

It is always an important issue to open the energy gap for graphene while retaining its high carrier mobility. Narrowing down large-area graphene into graphene nanoribbons (GNRs) is one of the ways to open the energy gap to achieve field-effect transistors (FET) suitable for logic circuits. But it has been a problem to obtain GNRs with controllable width and specific boundary structure. In this work, we proposed a simple high-precision preparation method for GNRs. In the process, GNRs with a width of 200 nm and smooth edges were prepared by a focused ion beam (FIB) etching process. Graphene nanoribbon field-effect transistors (GNR-FET) were fabricated by electron beam lithography (EBL). In this device, due to the proximity of the edge of the He+ during the FIB etching process, the carbon atom structure of the GNRs edge was changed, resulting in variations in electron transport properties. The electrical performance test demonstrated that the on/off current ratio of the GNR-FET device was up to 103 at room temperature. The structural defects of the GNRs caused the device carrier mobility down to 371.6 cm2V−1s−1. The structural defects in the GNRs edge introduced by FIB can improve the on/off current ratio of the device and hence enhanced its electrical regulation performance. Our work provides a simple method of making controllable GNRs to fabricate field effect transistors.

Fabrication and tensile characterization of FIB doped Si nanostructures

This paper describes the fabrication method of Silicon (Si) nanowires to evaluate the mechanical properties of Si, which is widely used as a based material in Micro Electro Mechanical System (MEMS). Nanoscale Si nanowires are fabricated by gallium (Ga) ion doping on monocrystalline silicon using Focus Ion Beam (FIB) and alkaline etching using Tetra methyl ammonium hydroxide (TMAH). In addition, fabricate Si nanowires with changed the various conditions of FIB ion dope and determine optimal conditions for fabricate Si nanowires.

Etching of Disc and Ring Patterns in Si3N4/GaN Structure by Ga+ FIB

The work presents experimental data of Ga+ focused ion beam etching of disc and ring patterns in Si3N4/GaN structure. The reasons for the difference in etching depth between the discs and the rings are described.

Enhanced luminescence property of InGaN/GaN nanorod array light emitting diode

Three-dimensional (3-D) InGaN/GaN nanorod array light emitting diode (LED) (nanorod-LED) with fine periodicity has been successfully fabricated by the focused ion beam (FIB) etching technique. After FIB etching, the uniformity of nanorod array is 94.3%, manifesting that FIB can control the etch size and etch depth exactly. After KOH etching, nanorod array exhibits comparatively smooth sidewalls. Compared to planar LED, the microphotoluminescence integrated intensity of nanorod-LED is enhanced by 15.7%. Additionally, the finite difference time domain simulations demonstrate that more photons can be extracted by nanorod array and spread to the further region, which is mainly due to the reduction of transform from radiation pattern to modified guided modes.

Optical Cavity Based on GaN Planar Nanowires Grown by Selective Area Metal‐Organic Vapor Phase Epitaxy

GaN planar nanowires (NWs) are fabricated by selective area metal‐organic vapor phase epitaxy using focused ion beam etching of trench pattern in the Si3N4 mask. Two crystallographic orientations of NWs along and directions are investigated. The coherent growth is confirmed for both directions; however, the best morphology, crystalline and optical properties are found in the GaN planar NWs fabricated along the axis. Cathodoluminescence (CL) at 5 K reveals a presence of Fabry–Perot modes in the region of 1.8–2.5 eV for the NWs fabricated in the direction. The position and intensity of the Fabry–Perot peaks vary depending on measured point within the NW, which is explained by the model based on the Purcell coefficient calculations. It is shown that small fluctuations in the NW thickness cause a noticeable shift of the Fabry–Perot modes energies, while the enhancement or reduction of the emission intensity for the Fabry–Perot peaks depend on the position of the emitter inside the planar NW.

Structural color printing with a dielectric layer coated on a nanotextured metal substrate: simulation and experiment.

The printing of plasmonic structural colors relies on noble metal nanostructures fabricated on Si, glass, or plastic substrates. This paper presents a simple surface structure for producing vivid structural colors directly from common metal substrates. The structure is formed by texturing the surface of stainless steel (STS) via imprinting and coating it with a dielectric layer. Diverse colors are generated simply by varying the thickness of the dielectric layer. The colors arise from surface plasmon resonance and guided-mode resonance of the incident light, which are excited on the textured STS surface and inside the dielectric layer, respectively. A finite-difference time-domain simulation shows that 500 nm is the optimum texture periodicity with regard to the tunability and vividness of the colors. This is experimentally verified by printing many differently colored images on the surface of STS substrates with a texture period of 500 nm. The proposed structure/method does not require a nanofabrication technique such as electron-beam lithography or focused ion beam etching. The results of the study provide a facile route for producing vivid structural colors on metals, which may find various applications, including surface decoration, product identification, anti-counterfeiting, and perfect absorbers.

The study of photoluminescence properties of AlGaAs/GaAs heterostructure after Ga+ focused ion beam etching

One of the promising tools for monolithic photonic integrated circuits (PICs) fabrication is focused ion beam (FIB) lithography. It’s well-known that FIB etching process induces radiation defects formation and consequently leads to losses in internal quantum efficiency of luminescence. We demonstrate the possibility of restoring luminescence properties of etched AlGaAs/GaAs heterostructure by means of annealing. Achieved results give an opportunity for fabrication of active PICs elements by FIB.

Enhancing the focused ion beam etch rate of Ag films by Joule heating

In this paper, the authors report on using Joule heating to increase the etch rate of focused ion beam (FIB) for etching Ag films. FIB is widely used as a tool for processing micro/nanomaterials. In this process, material atoms are expelled when the ion beam is irradiated on the material surface. On the other hand, Joule heating has been used for the structural modification of small-scale materials. Because in the FIB etching, the atoms are expected to be easily expelled by decreasing the density of grain boundaries of a metal, the FIB etch rate of the metal might be enhanced by structural modification with Joule heating. In this research, an Ag film was subjected to current-stressing, and FIB etching was carried out. It was confirmed that grains in the film grew due to Joule heating and that the FIB etch rate for Ag increased. The authors showed that the FIB etch rate for Ag could be enhanced by Joule heating. The results of this study will help in developing metal etch processes for micro/nanomaterials.

Molecular dynamic simulation of orientation-dependent effect on silicon crystalline during sputtering process of focused ion beam

In this paper, experiments and molecular dynamic simulation are performed to investigate the crystal orientation-dependent effects in a focused ion beam (FIB) sputtering etching process on silicon crystal planes. The experimental results indicate that different silicon orientation planes have different etched profiles, aspect ratios on microstructures, and sputtering yields under the same process conditions, which brings difficulty in deciding the process parameters for the fabrication of high-resolution nanostructures. Molecular dynamic simulation based on empirical potential is carried out to explain this effect on an atomic scale. The sputtered profiles of different silicon crystal planes after hundreds of impacts by Ga+ ions are analyzed. Both the simulation and experimental results show that with the same FIB etching conditions, structures on an Si (111) plane have the maximum opening width and minimum depth. Compared with the etched profile on an Si (100) plane, trenches on Si (110) have a smaller width, but greater depth. The Si (111) plane has the minimum sputtering yield. Furthermore, simulation results on the distribution of Ga+ ions remaining inside the substrate, number of ions sputtered out of the surface, and common neighbor analysis (CNA) can explain the orientation-dependent effect during FIB sputtering etching.

Effect of CdCl2 passivation treatment on microstructure and performance of CdSeTe/CdTe thin-film photovoltaic devices

The effects of the CdCl2 passivation treatment on thin-film CdTe photovoltaic films and devices have been extensively studied. Recently, with an addition of CdSeTe layer at the front of the absorber layer, device conversion efficiencies in excess of 19% have been demonstrated. The effects of the CdCl2 passivation treatment for devices using CdSeTe has not been studied previously. This is the first reported study of the effect of the treatment on the microstructure of the CdSeTe /CdTe absorber. The device efficiency is < 1% for the as-deposited device but this is dramatically increased by the CdCl2 treatment. Using Scanning Transmission Electron Microscopy (STEM), we show that the CdCl2 passivation of CdSeTe/CdTe films results in the removal of high densities of stacking faults, increase in grain size and reorientation of grains. The CdCl2 treatment leads to grading of the absorber CdSeTe/CdTe films by diffusion of Se between the CdSeTe and CdTe regions. Chlorine decorates the CdSeTe and CdTe grain boundaries leading to their passivation. Direct evidence for these effects is presented using STEM and Energy Dispersive X-ray Analysis (EDX) on device cross-sections prepared using focused ion beam etching. The grading of the Se in the device is quantified using EDX line scans. The comparison of CdSeTe/CdTe device microstructure and composition before and after the CdCl2 treatment provides insights into the important effects of the process and points the way to further improvements that can be made.

Effect of Ga+ focused ion beam etching on photoluminescence of AlGaAs/GaAs heterostructure.

The effect of focused ion beam (FIB) etching by 30 keV Ga+ on photoluminescence of AlGaAs/GaAs heterostructure is studied. During etching process, high-energy ions induce radiation defects that lead to a decrease of heterostructure internal quantum efficiency of luminescence. We used the SRIM software to simulate the radiation defects penetration depths in AlGaAs/GaAs heterostructure, then carried out FIB etching guided by received information. Annealing of the structure at 300 °C showed partial recovery of the internal quantum efficiency. Subsequent annealing at 620 °C showed almost full recovery of quantum efficiency depending on the etching depth. Experimental findings allowed us to affirm that FIB etching with subsequent annealing is a potential tool for making photonic nanodevices.

Resistance Anomalies at Superconducting Transition in Multilayer N/S/F/S/N Heterostructures

We have prepared lateral N/S/F/S/N heterostructures from perovskite bilayer YBa2Cu3O7−x (YBCO (70 nm), as superconductor S) and La1−xSrxMnO3 (LSMO (30 nm), as ferromagnet F) covered ex situ by Au layer (normal metal N, 50 nm) and Ti layer (50 nm). Whereas the Ti layer serves as a mask at Ar+ ion beam etching, the gold layer protects the properties of bilayer LSMO/YBCO during the fabrication process mainly during Ga+ focused ion beam etching. In many cases, the resistance vs. temperature (R(T)) dependences of the heterostructures exhibited some peculiarities (resistance peaks and dips) at superconducting transition. To explain these anomalies, we used transport effects emerging between resistances of individual layers and resistances of their interfaces. Our simulations fit very well the experimental ${R(T)}$ dependences of N/S/F/S/N heterostructures and show that transport effects can play an important role in multilayer structures which can be used in spintronics.