Ga Implantation Research Articles

Implantation of Gallium into Layered WS2 Nanostructures is Facilitated by Hydrogenation.

Bombarding WS2 multilayered nanoparticles and nanotubes with focused ion beams of Ga+ ions at high doses, larger than 1016 cm-2, leads to drastic structural changes and melting of the material. At lower doses, when the damage is negligible or significantly smaller, the amount of implanted Ga is very small. A substantial increase in the amount of implanted Ga, and not appreciable structural damage, are observed in nanoparticles previously hydrogenated by a radio-frequency activated hydrogen plasma. Density functional calculations reveal that the implantation of Ga in the spaces between adjacent layers of pristine WS2 nanoparticles is difficult due to the presence of activation barriers. In contrast, in hydrogenated WS2, the hydrogen molecules are able to intercalate in between adjacent layers of the WS2 nanoparticles, giving rise to the expansion of the interlayer distances, that in practice leads to the vanishing of the activation barrier for Ga implantation. This facilitates the implantation of Ga atoms in the irradiationexperiments.

Nanoscale Compositional Mapping of Commercial LiNi0.8Co0.15Al0.05O2 Cathodes Using Atom Probe Tomography

Nickel-rich cathodes provide improved specific capacity, which leads to higher gravimetric energy density, which, in turn, is critical for electric vehicles. However, poor long-term capacity retention at elevated temperatures/high C rates (the rate of charge and discharge on a battery) stems from material issues: surface phase changes, corrosive side reactions with the electrolyte, ion dissolution, and propagation of cracks. Introducing dopants, developing nanoscale surface coatings, and graded core–shell structures all improved the electrochemical performance of nickel-rich cathodes. However, material-level understanding of the effect of Li composition and distribution in Ni-rich cathodes is limited due to a lack of characterization methods available that can directly image Li at the nanoscale. Hence, it is critical to establish methods such as atom probe tomography (APT) that have both nanometer-scale spatial resolution and high compositional sensitivity to quantitatively analyze battery cathodes. To fully realize its potential as a method for quantitative compositional analysis of commercial Li-ion batteries, we provide a comprehensive description of the challenges in sample preparation and analyze the dependency of the analysis parameters, specifically laser pulse energy on the measured stoichiometry of elements in a high-Ni-content cathode material LiNi0.8Co0.15Al0.05O2 (NCA). Our findings show that the stoichiometry variations cannot be explained by charge–state ratios or Ga implantation damage alone during FIB preparation, indicating that additional factors such as crystallographic orientation may need to be considered to achieve quantitative nanoscale compositional analysis of such battery cathodes using APT.

Antimicrobial and Anti-inflammatory Gallium-Defensin Surface Coatings for Implantable Devices.

Emerging and re-emerging infections are a global threat driven by the development of antimicrobial resistance due to overuse of antimicrobial agents and poor infection control practices. Implantable devices are particularly susceptible to such infections due to the formation of microbial biofilms. Furthermore, the introduction of implants into the body often results in inflammation and foreign body reactions. The antimicrobial and anti-inflammatory properties of gallium (Ga) have been recognized but not yet utilized effectively to improve implantable device integration. Furthermore, defensin (De, hBD-1) has potent antimicrobial activity in vivo as part of the innate immune system; however, this has not been demonstrated as successfully when used in vitro. Here, we combined Ga and De to impart antimicrobial activity and anti-inflammatory properties to polymer-based implantable devices. We fabricated polylactic acid films, which were modified using Ga implantation and subsequently functionalized with De. Ga-ion implantation increased surface roughness and increased stiffness. Ga implantation and defensin immobilization both independently and synergistically introduced antimicrobial activity to the surfaces, significantly reducing total live bacterial biomass. We demonstrated, for the first time, that the antimicrobial effects of De were unlocked by its surface immobilization. Ga implantation of the surface also resulted in reduced foreign body giant cell formation and expression of proinflammatory cytokine IL-1β. Cumulatively, the treated surfaces were able to kill bacteria and reduce inflammation in comparison to the untreated control. These innovative surfaces have the potential to prevent biofilm formation without inducing cellular toxicity or inflammation, which is highly desired for implantable device integration.

Local Ga Ion Implantation as a Source of Diverse Ferroelectric Properties of Hafnium Oxide

Ferroelectricity patterning in a thin HfO2 film paves a new way for designing innovative switchable photonics devices and microelectronic nonvolatile memory based on hybrid heterostructures of 2D material/ferroelectric (FE) films. For inducing local ferroelectricity, implantation of Ga ions into an amorphous HfO2 film by a pattern is conducted using a focused ion beam followed by rapid thermal annealing. It is demonstrated that the way of Ga implantation as well as the way of annealing play crucial roles in the FE properties of Ga‐doped HfO2, including the remnant polarization and the distribution of internal bias fields across the film. Furthermore, the ion implantation in itself is the source of unusual FE properties. The correlation of FE properties with a Fourier analysis of the high‐resolution transmission electron microscopy images and results of atomic force microscopy and piezoresponse force microscopy reveals the origin of the observed macroscopical FE performances. It is demonstrated that the ultimate spatial resolution of ferroelectricity patterning is determined by the size of the focused ion beam in the surface plane and thus it reaches 40 nm, which enables new prospects for applications in shortwave active photonics.

GaAs epitaxial growth on modified on-axis Si(001) substrates

In this work, the effect of the dose of implantation of Ga atoms into the silicon surface on the epitaxial growth of GaAs was investigated. We demonstrate that the deposition of GaAs occurs mainly on modified areas. Separate crystallites of GaAs with an irregular shape are formed on modified areas at the lowest dose of Ga implantation equal to 1 pC/μm2, whereas an increase in the dose of Ga implantation leads to the coalescence of GaAs areas. At a maximum dose of 21 pC/μm2, degradation of the morphology and a decrease in the degree of filling of the area are observed, which is also confirmed by an increase in the roughness of the structure.

Highly Enhanced Curie Temperature in Ga‐Implanted Fe3GeTe2 van der Waals Material

AbstractAmong many efforts in the research of van der Waals (vdW) magnetic materials, increasing the Curie temperature above room temperature has been at the center of research in developing spintronics technology using vdW materials. Here an effective and reliable method of increasing the Curie temperature of ferromagnetic Fe3GeTe2 vdW materials by Ga implantation is reported. It is found that implanting Ga into Fe3GeTe2 by the amount of 10−3 Ga Å−3 could greatly enhance the Fe3GeTe2 Curie temperature by almost 100%. Spatially resolved microdiffraction and element‐resolved X‐ray absorption spectroscopy show little changes in the Fe3GeTe2 crystal structure and Fe valence state. In addition, the Ga implantation changes the Fe3GeTe2 magnetization from out‐of‐plane direction at low temperature to in‐plane direction at high temperature. The result opens a new opportunity for tailoring the magnetic properties of vdW materials beyond room temperature.

Phase masks for electron microscopy fabricated by thermal scanning probe lithography

Nano-structured phase masks offer intriguing possibilities in electron-beam shaping. The fabrication of such phase masks is typically achieved by focused (Ga+-)ion beam milling of thin membranes. To overcome the problem of Ga implantation in the phase mask, we explore the fabrication of silicon-nitride phase masks using thermal scanning probe lithography combined with wet and dry etching. The functionality of the phase masks is demonstrated by generation of electron Vortex and Bessel beams. Major benefit of thermal scanning probe lithography in addition to the absence of ion implantation is the high accuracy and control over the patterned structure and depth.

Hybrid refractive-diffractive microlenses in glass by focused Xe ion beam

The combination of refractive and diffractive components in a single optical element provides miniaturization of optical systems and enhancement of their performance. Thus, hybrid singlet lenses with diffractive structures added on top of the refractive curved surface were shown to have reduced chromatic and spherical aberration. Optical systems based on such hybrid lenses have reduced dimensions as they require fewer lenses for aberrations-correction. Diffractive elements provide additional possibilities of light manipulation and enable the realization of miniaturized multifocal systems, spectrometers, and other devices. Glass hybrid lenses are typically realized by diamond turning or glass moulding. These techniques, however, are not applicable for the fabrication of lenses in brittle materials or microlenses (hundreds of micrometers in diameter or less). On the other hand, direct writing techniques, such as focused ion beam (FIB) milling (typically Ga), offer a high resolution and flexibility of patterning on curved lens surfaces made of a great variety of materials. The disadvantages of FIB milling are its slow speed and Ga implantation that may alter or degrade the optical performance of fabricated components. FIB systems based on high brightness plasma ion sources provide more than an order of magnitude increase in milling rates with noble gas ions (e.g., Xe) compared with Ga FIBs. Here, the authors demonstrate the feasibility of rapid, direct milling of hybrid refractive-diffractive microlenses in glass using >60 nA of Xe ion current. Microlenses with up to 300-μm diameter were milled and diffraction gratings were realized on top of their curved surfaces. The performance of the lenses was characterized by mapping the transmitted intensity at different positions. Due to the introduction of diffraction gratings on the surface of the lenses, their optical performance is modified with the emergence of additional focal spots spatially separated by distances consistent with the theoretical and simulated values. The results indicate the applicability of the plasma focused ion beam systems for rapid fabrication of high-quality hybrid optical elements directly in hard substrates.

INVESTIGATION OF FOCUSED ION BEAM IMPLANTATION PROFILE OF Ga+ IONS FOR APPLICATIONS IN SILICON PHOTONICS

Use of focused ion beam (FIB) as a nanostructuring platform for fast prototype device development in the area of photonics has been attracting a considerable interest. In this study, we report a systematic investigation of focused ion beam (FIB) induced Ga+ ion implantation in silicon on insulator (SOI) structures. The local implantation of Ga+ ions during milling was studied for a wide range of ion doses, ranging from about 1014 to 1017 ions/cm2, using X-ray photoelectron spectroscopy (XPS). Ion implantation has been realized on identically sized areas for each dose by varying the FIB parameters such as dwell time and loop number. It was found that the most of the Ga+ is within the first 50 nm of Si. This suggests that it can be possible to potentially reduce optical losses caused by the ion implantation in any optical application. Methods such as thermal annealing and wet or dry chemical etching can result in removal of the 50 nm implanted layer of SOI, as a result removing the layer causing potentially high optical losses.

Removal of Ga Implantation on FIB-prepared Atom Probe Specimens Using Small Beam and Low Energy Ar+ Milling

Removal of Ga Implantation on FIB-prepared Atom Probe Specimens Using Small Beam and Low Energy Ar+ Milling

Effect of Ga Implantation and Hole Geometry on Light Transmission through Nanohole Arrays in Al and Mg

The study of plasmonic nanostructures in the ultraviolet (UV) is a relatively uncharted field because of the challenges in both engineering and materials science. In this work, two-dimensional periodic nanohole arrays in aluminium (Al) and magnesium (Mg) films were fabricated using gallium (Ga) focused ion beam. Optical transmission through the arrays was obtained in the UV–visible range for varying array periodicity. Transmission results show strong resonance transmission enhancement and suppression with corresponding red shift as the period increases and the presence of stationary waveguide modes. Comparing Al and Mg, Al hole arrays enable greater transmission than those of Mg. Numerical analysis was carried out through the finite-difference time-domain method, which showed far-field transmission consistent with experiments. The simulation model was constructed based on transmission electron microscopy of cross-sectioned samples to take into account tapered sidewall geometry and undercut into the substrate. Energy-dispersive X-ray spectroscopy was used to assess elemental composition, including oxidation and alloying. The effect of Ga implantation was qualitatively studied, which indicates that Ga implants inside the hole, with greater implantation concentration within Mg than within Al, and affects the transmission through both Al and Mg arrays.

On the mechanism of ion-induced bending of nanostructures

This contribution concentrates on ion-induced bending phenomena which may serve as a versatile tool to manufacture nanostructured devices. In particular bending was studied in free standing Au cantilevers. The preparation and irradiation of the cantilevers were performed using a TESCAN LYRA dual beam system. Cantilevers with thicknesses ranging between 90 and 200 nm were irradiated with 30 keV Ga ions normal to the sample surface up to a maximum fluence of ∼3 × 1020 Ga/m2. The bending of the cantilevers towards the incident beam is discussed in terms of local volume change due to accumulation of radiation-induced vacancies and substitutional Ga atoms in the Ga implantation layer, as well as due to accumulation of interstitial type clusters in the region beyond the Ga penetration range. A model is proposed to explain the observations, based on a set of rate equations for concentrations of point defects, i.e. vacancies, self-interstitials and implanted Ga atoms. The influence of preexisting defects is also discussed. The work shows that an in-depth understanding the ion-beam bending can play a predictive role in a quantitative control in for the micro- and nanofabrication of small-sized products.

Electrical properties of in-plane-implanted graphite nanoribbons

We studied the effect of low energy (30 keV) ionic implantation of Ga+ in the direction parallel to the graphene planes (perpendicular to the c-axis) in oriented graphite ribbons with widths around 500 nm. Our experiments have reproducibly shown a reduction of electrical resistance upon implantation consistent with the occurrence of ionic channeling in our devices. Our results allow for new approaches in the modulation of the charge carrier concentration in mesoscopic graphite.

Comparative study of image contrast in scanning electron microscope and helium ion microscope.

Images of Ga+ -implanted amorphous silicon layers in a 110 n-type silicon substrate have been collected by a range of detectors in a scanning electron microscope and a helium ion microscope. The effects of the implantation dose and imaging parameters (beam energy, dwell time, etc.) on the image contrast were investigated. We demonstrate a similar relationship for both the helium ion microscope Everhart-Thornley and scanning electron microscope Inlens detectors between the contrast of the images and the Ga+ density and imaging parameters. These results also show that dynamic charging effects have a significant impact on the quantification of the helium ion microscope and scanning electron microscope contrast.

Gallium-Doped Poly-Si:Ga/SiO2 Passivated Emitters to n-Cz Wafers With iV oc >730 mV

We form gallium-doped poly-Si:Ga/SiO2 passivated contacts on n-type Czochralski (n-Cz) wafers using ion implantation of Ga and Ga-containing spin-on dopants. After annealing and passivation with Al2O3 , the contacts exhibit $iV_{{\rm{oc}}}$ values of >730 mV with corresponding $J_{{\rm{oe}}}$ values of $ . These are among the best-reported values for p-type poly-Si/SiO2 contacts. Secondary ion mass spectroscopic depth profile data show that, in contrast to B, Ga does not pileup at the SiO2 interface in agreement with its known high diffusivity in SiO2. This lack of Ga pileup may imply fewer dopant-related defects in the SiO2, compared with B dopants, and account for the excellent passivation.

Tuning the electrical transport of type II Weyl semimetal WTe2 nanodevices by Ga+ ion implantation

Here we introduce lattice defects in WTe2 by Ga+ implantation (GI), and study the effects of defects on the transport properties and electronic structures of the samples. Theoretical calculation shows that Te Frenkel defects is the dominant defect type, and Raman characterization results agree with this. Electrical transport measurements show that, after GI, significant changes are observed in magnetoresistance and Hall resistance. The classical two-band model analysis shows that both electron and hole concentration are significantly reduced. According to the calculated results, ion implantation leads to significant changes in the band structure and the Fermi surface of the WTe2. Our results indicate that defect engineering is an effective route of controlling the electronic properties of WTe2 devices.

Deflection behavior of focused-ion-beam deposited carbon nanocantilever and overhung structures

Elastic properties of nanostructures are crucial for the adequate design and long term use of nano/micro-electro-mechanical system (NEMS/MEMS) as well as their utility in nanoindentation. Carbon nanostructures were fabricated by focused ion beam (FIB) assisted deposition and milling using Naphthalene (C10H8) as a precursor gas. Cantilevers of size 3-10 µm were fabricated and their elastic properties were monitored. An end point load was applied by successive deposition of Pt or carbon in a form of vertical column. Euler–Bernoulli beam theory was applied to examine the mechanical properties of the cantilever. It has been observed that expected deflection of the carbon nano-cantilever is significantly different compared to most of the reported micro or nano-sized carbon or diamond structures. Initial investigation of such a discrepancy suggests that Ga implantation and presence of core-shell type structure are the main causes of altered mechanical properties.

Lithography-free positioned GaAs nanowire growth with focused ion beam implantation of Ga

The authors report on a technique to grow GaAs nanowires at defined positions by molecular beam epitaxy without the need for a lithographic process. Here, a focused ion beam is used to implant Ga ions into Si (1 0 0) and Si (1 1 1) substrates, forming nanoscale droplets on the surface after an annealing step, which are in turn used as nucleation centers for self-catalyzed nanowire growth. This procedure completely avoids organic chemicals, as needed in other lithographic processes, and therefore allows nanowire growth in defined and flexible geometries, while being fully compatible with ultraclean environments. A minimum required pitch width is determined from implanted Ga point arrays, which were annealed to form droplets. The epitaxial yield for GaAs nanowires on Si (1 0 0) and Si (1 1 1) substrates is evaluated with respect to the acceleration voltage and implanted dose. The nanowire diameter is determined by thermodynamic properties at the growth surface while being insensitive to implantation parameters.

Ga contamination in silicon by Focused Ion Beam milling: Dynamic model simulation and Atom Probe Tomography experiment

Focused Ion Beam (FIB) milling is a widely used and important technique to prepare Transmission Electron Microscopy (TEM) lamella samples. However, it unavoidably introduces contamination in the samples like implanted ions. While the conventional ion-solid simulation model, Binary Collision Approximation (BCA), is unable to describe the FIB process, a dynamic BCA model is used in this study to predict the level of Ga implantation along the substrate depth. The FIB process involves significant material transport and local composition alteration, which requires a dynamic model for simulation. To validate the dynamic BCA model's application on simulating the FIB process, atomic level composition analysis Atom Probe Tomography (APT) is performed on Ga FIB processed silicon samples. The experimental data confirm that the dynamic BCA model is capable to predict FIB induced Ga ion implantation in silicon samples.

Effect of annealing on carrier transport properties of GaN-incorporated silicon

GaN nanocrystals were formed in a silicon matrix by sequential implantation of Ga+ and N2+ ions followed by either Furnace Annealing (FA) or Rapid Thermal Annealing (RTA).