He-ion Beam Research Articles

Vortex matching at 6 T in YBa2Cu3O7−δ thin films by imprinting a 20-nm periodic pinning array with a focused helium-ion beam

Controlled engineering of vortex pinning sites in copper-oxide superconductors is a critical issue in manufacturing devices based on magnetic flux quanta. To address this, we employed a focused He-ion beam (He-FIB) to irradiate thin YBa2Cu3O7−δ films and create ultradense hexagonal arrays of defects with lattice spacings as small as 20 nm. Critical current and magnetoresistance measurements demonstrate efficient pinning by a matching field of 6 T visible in a huge temperature range from the critical temperature Tc down to 2 K. These results show that He-FIB irradiation provides excellent opportunities for the development and application of superconducting fluxonic devices based on Abrikosov vortices. In particular, our findings suggest that such devices can operate at temperatures far below Tc, where superconductivity is robust. Published by the American Physical Society 2024

Tuning of the electronic and vibrational properties of epitaxial MoS2 through He-ion beam modification

Atomically thin transition metal dichalcogenides (TMDs), like MoS2 with high carrier mobilities and tunable electron dispersions, are unique active material candidates for next generation opto-electronic devices. Previous studies on ion irradiation show great potential applications when applied to two-dimensional (2D) materials, yet have been limited to micron size exfoliated flakes or smaller. To demonstrate the scalability of this method for industrial applications, we report the application of relatively low power (50 keV) 4He+ ion irradiation towards tuning the optoelectronic properties of an epitaxially grown continuous film of MoS2 at the wafer scale, and demonstrate that precise manipulation of atomistic defects can be achieved in TMD films using ion implanters. The effect of 4He+ ion fluence on the PL and Raman signatures of the irradiated film provides new insights into the type and concentration of defects formed in the MoS2 lattice, which are quantified through ion beam analysis. PL and Raman spectroscopy indicate that point defects are generated without causing disruption to the underlying lattice structure of the 2D films and hence, this technique can prove to be an effective way to achieve defect-mediated control over the opto-electronic properties of MoS2 and other 2D materials.

On-demand generation of optically active defects in monolayer WS2 by a focused helium ion beam

We demonstrate that optically active emitters can be locally generated by focusing a He-ion beam onto monolayer WS2 encapsulated in hBN. The emitters show a low-temperature photoluminescence spectrum, which is well described by an independent Boson model for localized emitters. Consistently, the photoluminescence intensity of the emitters saturates at low excitation intensities, which is distinct to the photoluminescence of excitonic transitions in the investigated WS2 monolayers. The demonstrated method allows us to position defect emitters in WS2 monolayers on demand. A statistical analysis suggests the generation yield of individual emitters to be as high as 11% at the highest investigated He-ion doses.

Ion bombardment technique induced alterations in the surface chemical composition and shielding parameters of polymeric material

At present, ion beam technology is one powerful technique to improve the physico-chemical properties of polymeric material. In this work, ultra high molecular weight polyethylene samples were bombarded with 1 MeV He-ion beam at fluences ranging from 1×1013 to 5×1014 ions/cm2. The changes in the chemical composition of the treated layer caused by the ion beam were investigated. The hydrogen escapes due to the ion beam irradiations were measured by the nuclear reaction analysis (NRA) technique using the 1H(15N, αγ)12C reaction. The oxygen uptake has been studied by the Rutherford backscattering spectrometry (RBS) and Fourier transform infrared spectrometer (FTIR) techniques. The partial and total mass attenuation coefficients of photons at energies 81, 356, 511 and 1332 keV were estimated using the XCOM program (version 3.1). The obtained results showed that the hydrogen release was increasing with an increase in ion fluence. Moreover, important oxygen uptake of bombarded samples was also observed. These effects led to significant improvements in the surface characteristics of the treated materials such as changes in the shielding parameters. The changes in the mass attenuation coefficients (μ/ρ) were calculated relying on the incoming photon energies and the atomic concentrations of the elements that are present in the target material. The total atomic cross-sections and effective atomic numbers were calculated by using the data of the total mass attenuation coefficients. A decrease in both the total atomic cross-section and effective atomic numbers was noticed with an increase in the ion beam fluence.

Nanoscale Electrical Excitation of Distinct Modes in Plasmonic Waveguides.

The electrical excitation of guided plasmonic modes at the nanoscale enables integration of optical nanocircuitry into nanoelectronics. In this context, exciting plasmons with a distinct modal field profile constitutes a key advantage over conventional single-mode integrated photonics. Here, we demonstrate the selective electrical excitation of the lowest-order symmetric and antisymmetric plasmonic modes in a two-wire transmission line. We achieve mode selectivity by precisely positioning nanoscale excitation sources, i.e., junctions for inelastic electron tunneling, within the respective modal field distribution. By using advanced fabrication that combines focused He-ion beam milling and dielectrophoresis, we control the location of tunnel junctions with sub-10 nm accuracy. At the far end of the two-wire transmission line, the guided plasmonic modes are converted into far-field radiation at separate spatial positions showing two distinct orthogonal polarizations. Hence, the resulting device represents the smallest electrically driven light source with directly switchable polarization states with possible applications in display technology.

Improve the structure and optical surface properties of LDPE by ion bombardment technique

Nowadays, ion bombardment became one of the powerful methods usually carried out to modify the surface characteristics of the polymeric materials. In this work, low-density polyethylene (LDPE) polymer samples were bombarded with different fluences by 130 keV He-ion beam. The X-ray diffraction patterns of the untreated sample as well as those exposed to He-ion beam revealed the crystalline nature of the samples. The effects of He-ion beam bombardment on the structural parameters e.g. crystal size, dislocation density, inter-chain separation, micro-strain, and distortion were studied. The optical absorption coefficient and refractive index were calculated as a function of He-ion beam fluences. The optical energy gap and Urbach energy were also evaluated. Wemple-DiDomenico effective single oscillator and Sellmeier models were both used to describe adequately the refractive index dispersion in the low absorption region. Graphical representation of the complex dielectric constant and dissipation factor was also presented. A significant modification in the structural and optical parameters was obtained by ion bombardment technique.

He-ion Beam Imaging for Accurate Hardware Trojan Detection

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Atomistic Positioning of Defects in Helium Ion Treated Single-Layer MoS2.

Structuring materials with atomic precision is the ultimate goal of nanotechnology and is becoming increasingly relevant as an enabling technology for quantum electronics/spintronics and quantum photonics. Here, we create atomic defects in monolayer MoS2 by helium ion (He-ion) beam lithography with a spatial fidelity approaching the single-atom limit in all three dimensions. Using low-temperature scanning tunneling microscopy (STM), we confirm the formation of individual point defects in MoS2 upon He-ion bombardment and show that defects are generated within 9 nm of the incident helium ions. Atom-specific sputtering yields are determined by analyzing the type and occurrence of defects observed in high-resolution STM images and compared with Monte Carlo simulations. Both theory and experiment indicate that the He-ion bombardment predominantly generates sulfur vacancies.

Ionic Conductance through Graphene: Assessing Its Applicability as a Proton Selective Membrane.

Inspired by recent reports on possible proton conductance through graphene, we have investigated the behavior of pristine graphene and defect engineered graphene membranes for ionic conductance and selectivity with the goal of evaluating a possibility of its application as a proton selective membrane. The averaged conductance for pristine chemical vapor deposited (CVD) graphene at pH1 is ∼4 mS/cm2 but varies strongly due to contributions from the unavoidable defects in our CVD graphene. From the variations in the conductance with electrolyte strength and pH, we can conclude that pristine graphene is fairly selective and the conductance is mainly due to protons. Engineering of the defects with ion beam (He+, Ga+) irradiation and plasma (N2 and H2) treatment showed improved areal conductance with high proton selectivity mostly for He-ion beam and H2 plasma treatments, which agrees with primarily vacancy-free type of defects produced in these cases confirmed by Raman analysis.

A single nano-void precisely positioned in SiO2/Si substrate by focused helium ion beam technique

We report on the formation of a single nano-void, precisely positioned in SiO2/Si, using He-ion beam technique. The in-plane position of the void can be achieved by the direct writing capability of the He-ion beam system. While the depth and size of void are able to be determined by the acceleration voltage and dosage of the He+-ions, respectively. The as-written sample shows an ellipsoidal shape amorphous region in Si. Thermal treatments aggregate He-vacancy complexes and He bubble defects to form a void in the central of the region. At the same time, recrystallization starts from the boundary between the amorphous and crystal Si. Through HAADF imaging, EDX scanning profile and SEM imaging, we show the existence of a nano-void at a predicted depth. For the sample annealed at 825 °C, we observed a single void formed by {111} facets.

Heavy metal incorporated helium ion active hybrid non-chemically amplified resists: Nano-patterning with low line edge roughness

Helium (He) ion lithography is being considered as one of the most promising and emerging technology for the manufacturing of next generation integrated circuits (ICs) at nanolevel. However, He-ion active resists are rarely reported. In this context, we are introducing a new non-chemically amplified hybrid resist (n-CAR), MAPDSA-MAPDST, for high resolution He-ion beam lithography (HBL) applications. In the resist architecture, 2.15 % antimony is incorporated as heavy metal in the form of antimonate. This newly developed resists has successfully used for patterning 20 nm negative tone features at a dose of 60 μC/cm2. The resist offered very low line edge roughness (1.27±0.31 nm) for 20 nm line features. To our knowledge, this is the first He-ion active hybrid resist for nanopatterning. The contrast (γ) and sensitivity (E0) of this resist were calculated from the contrast curve as 0.73 and 7.2 μC/cm2, respectively.

Nanofabrication Limits in Layered Ferroelectric Semiconductors via He-ion Beam

Nanofabrication Limits in Layered Ferroelectric Semiconductors via He-ion Beam

He-Ion Induced Defect Generation and Doping of 2D MoS2 Monolayers

In recent years, two-dimensional Transition Metal Dichalcogenide (TMDC) materials such as MoS2 have drawn considerable interest due to their intriguing electrical, optical, sensing, and catalytic properties [Castellanos-Gomez et al. 2012]. While Graphene-based devices have shown high carrier mobility up to ~ 105 cm2/Vs [Bolotin et al. 2008] and cut-off frequency higher than ~ 100 GHz [Liao et al., 2010], the inherent zero – band gap electronic structure of graphene results in high OFF state current. On the other hand, monolayer MoS2 is a semiconductor with a direct band gap of ~1.9eV [Mak et al. 2010]. MoS2 transistors are a promising alternative for the semiconductor industry due to their large ON/OFF current ratio (> 10e10) [Yoon et al., 2011], immunity to short channel effects, and abrupt switching. However, realization of practical mono/few layer MoS2 devices is limited by the free charge density in intrinsic MoS2 (10e10/cm2) [Rastogi et al. 2014]. The objective of this work is to utilize He-ion beam patterning to write pattern of vacancies (< 10 nm) onto CVD synthesized 2D MoS2. The vacancies thus generated are then doped via molecular doping technique to improve upon the intrinsic free carrier concentration in 2D MoS2. Briefly, the method is as follows. (a) First, highly crystalline 2D MoS2 are synthesized on SiO2/Si substrate using MoO3 and S powder as the precursors in a CVD furnace. (b) Next, He-ion beam patterning is used to generate vacancies in only the very top S layer. The shorter de Broglie wavelength of He-ions allows for milling at higher resolution than other charged particle microscopes. (c) Next, solution-based molecular doping method is used to realize non-degenerate n-type doping in 2D MoS2. This is accomplished by soaking the patterned 2D layers in 1, 2-dichloroethane (DCE) solution at room temperature for about 12 hours. As a result, the patterned vacancies are occupied by Cl atoms which donate the extra electrons to the MoS2 system. The electronic properties are tuned by varying the MoS2 layer thickness and solution concentration. Post-doping, the electrostatic properties are measured by using PL measurements and different modes of AFM, including Kelvin force microscopy (KFM) and Scanning microwave microscopy (SMM). An important contribution of this work is the presentation of optimized He-ion beam conditions, including the accelerating voltage and the effects of defect generation on the sub-surface layers. He-ion beam based defect generation creates a shallow penetration depth, which makes them more suitable for single S vacancies. Finally, the changes in the surface potential and a quantitative analysis of the dopant density were measured suing KFM and SMM respectively, indicating that doping is in the non-degenerate regime.

Electron-beam domain patterning on the nonpolar surfaces of lithium niobate crystals

ABSTRACTWe compare electron-beam writing of domains and domain patterns in He-implanted planar optical waveguides fabricated on X-cut LiNbO3 crystals to the results of domain writing on the nonpolar surfaces in unimplanted LiNbO3. The characteristics of written patterns, in particular the exposure dependences of the domain length L and spatial regularity of written domain gratings depend on the relation between the domain depth Td controlled by the acceleration voltages U, and thickness D of the optical barrier, determined by He-ion beam energy. An increased average L in domain gratings as compared to isolated domains is discussed with account for dependence of the electron emission coefficient σ on U.

Polarization Control via He-ion Beam Induced Nanofabrication in Layered Ferroelectric Semiconductors

Rapid advances in nanoscience rely on continuous improvements of material manipulation at near-atomic scales. Currently, the workhorse of nanofabrication is resist-based lithography and its various derivatives. However, the use of local electron, ion, and physical probe methods is expanding, driven largely by the need for fabrication without the multistep preparation processes that can result in contamination from resists and solvents. Furthermore, probe-based methods extend beyond nanofabrication to nanomanipulation and to imaging which are all vital for a rapid transition to the prototyping and testing of devices. In this work we study helium ion interactions with the surface of bulk copper indium thiophosphate CuM(III)P2X6 (M = Cr, In; X= S, Se), a novel layered 2D material, with a Helium Ion Microscope (HIM). Using this technique, we are able to control ferrielectric domains and grow conical nanostructures with enhanced conductivity whose material volumes scale with the beam dosage. Compared to the copper indium thiophosphate (CITP) from which they grow, the nanostructures are oxygen rich, sulfur poor, and with virtually unchanged copper concentration as confirmed by energy-dispersive X-ray spectroscopy (EDX). Scanning electron microscopy (SEM) imaging contrast as well as scanning microwave microscopy (SMM) measurements suggest enhanced conductivity in the formed particles, whereas atomic force microscopy (AFM) measurements indicate that the produced structures have lower dissipation and are softer as compared to the CITP.

Polarization Control via He-Ion Beam Induced Nanofabrication in Layered Ferroelectric Semiconductors.

Rapid advances in nanoscience rely on continuous improvements of material manipulation at near-atomic scales. Currently, the workhorse of nanofabrication is resist-based lithography and its various derivatives. However, the use of local electron, ion, and physical probe methods is expanding, driven largely by the need for fabrication without the multistep preparation processes that can result in contamination from resists and solvents. Furthermore, probe-based methods extend beyond nanofabrication to nanomanipulation and to imaging which are all vital for a rapid transition to the prototyping and testing of devices. In this work we study helium ion interactions with the surface of bulk copper indium thiophosphate CuM(III)P2X6 (M = Cr, In; X= S, Se), a novel layered 2D material, with a Helium Ion Microscope (HIM). Using this technique, we are able to control ferrielectric domains and grow conical nanostructures with enhanced conductivity whose material volumes scale with the beam dosage. Compared to the copper indium thiophosphate (CITP) from which they grow, the nanostructures are oxygen rich, sulfur poor, and with virtually unchanged copper concentration as confirmed by energy-dispersive X-ray spectroscopy (EDX). Scanning electron microscopy (SEM) imaging contrast as well as scanning microwave microscopy (SMM) measurements suggest enhanced conductivity in the formed particles, whereas atomic force microscopy (AFM) measurements indicate that the produced structures have lower dissipation and are softer as compared to the CITP.

Flux threshold measurements of He-ion beam induced nanofuzz formation on hot tungsten surfaces

We report measurements of the energy dependence of flux thresholds and incubation fluences for He-ion induced nano-fuzz formation on hot tungsten surfaces at UHV conditions over a wide energy range using real-time sample imaging of tungsten target emissivity change to monitor the spatial extent of nano-fuzz growth, corroborated by ex situ SEM and FIB/SEM analysis, in conjunction with accurate ion-flux profile measurements. The measurements were carried out at the multicharged ion research facility (MIRF) at energies from 218 eV to 8.5 keV, using a high-flux deceleration module and beam flux monitor for optimizing the decel optics on the low energy MIRF beamline. The measurements suggest that nano-fuzz formation proceeds only if a critical rate of change of trapped He density in the W target is exceeded. To understand the energy dependence of the observed flux thresholds, the energy dependence of three contributing factors: ion reflection, ion range and target damage creation, were determined using the SRIM simulation code. The observed energy dependence can be well reproduced by the combined energy dependences of these three factors. The incubation fluences deduced from first visual appearance of surface emissivity change were (2–4) × 1023 m−2 at 218 eV, and roughly a factor of 10 less at the higher energies, which were all at or above the displacement energy threshold. The role of trapping at C impurity sites is discussed.

Low-energy He-ion beam modifications the surface properties of biomaterial

In the present work, ultra-high-molecular-weight polyethylene (UHMWPE) films were irradiated with 130 keV He ions. The fluence of the ion beam was ranged from 1 × 1012 to 1 × 1016 cm−2. The chemical, morphological, and crystallite structure changes resulted from the ion bombardment were obtained using different spectroscopic techniques. These techniques were Fourier transform infrared spectrometer, scanning electron microscope, X-ray diffraction, and UV–vis spectrophotometry. The surface free energy for untreated and ion-beam-treated samples was determined by means of contact angle measurements of three different liquids. Our results showed a decrease in the crystallinity of UHMWPE and formation of C=O groups on the polymer surface for modified samples as well. A remarkable shifting in the UV–vis spectra toward lower energy and increase in the optical absorption were observed as the ion fluence increases. Measurements of the contact angle indicate remarkable increase in the surface free energy as a function of ion fluence.

The Radiation Chemistry of CMPO: Part 2. Alpha Radiolysis

Octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) dissolved in dodecane was subjected to α-irradiation using a He-ion beam, 244 Cm isotopic α-rays, and He and Li ions created by the n,α reaction of 10B in a nuclear reactor. Post-irradiation samples were analyzed for the radiolytically-induced decrease in CMPO concentration, the appearance of degradation products, and their Am solvent extraction distribution ratios. The –G CMPO-value for the radiolytic degradation of CMPO was found to be very low compared to values previously reported for γ-irradiation. Additionally, isotopic irradiation to absorbed α-doses as high as 600 kGy in aerated solution had no effect on Am solvent extraction or stripping. The main CMPO radiolysis products identified in He-ion beam irradiated samples by ESI-MS include amides, an acidic amide, and amines produced by bond rupture on either side of the CMPO carbonyl group. Deaerated samples irradiated using the reactor in the absence of an aqueous phase, or with a dilute nitric acid aqueous phase showed small but measurable decreases in CMPO concentration with increasing absorbed doses. Higher concentrations of nitric acid resulted in lower decomposition rates for the CMPO. The radio-protection by dissolved oxygen and nitric acid previously found for γ-irradiated CMPO also occurs for α-irradiation. This suggests that similar free-radical mechanisms operate in the high-LET system, but with lower degradation yields due to the lower overall radical concentrations produced.

Sub-10 nm patterning by focused He-ion beam milling for fabrication of downscaled graphene nano devices

In this work, a novel hybrid fabrication method for graphene quantum dot devices with minimum feature sizes of ∼3nm and high yield is described. It is a combination of e-beam lithography and direct milling with the sub-nm focused helium ion beam generated by a helium ion microscope. The method is used to fabricate graphene quantum dot devices contacted with metal to allow electrical characterization. An annealing step is described that reduces hydrocarbon contamination on the sample surface and allows complete removal of graphene by the helium ion beam and therefore successful isolation of side gates. The electrical characterization of the final device demonstrates the successful fabrication of the first electrically characterized He-ion beam patterned graphene device. The highly controllable, fine scale fabrication capabilities offered by this approach could lead to a more detailed understanding of the electrical characteristics of graphene quantum devices and pave the way towards room-temperature operable graphene quantum dot devices.