Annular Milling Research Articles

Design and Characterization of a Continuous Melt Milling Process Tailoring Submicron Drug Particles

Solid crystalline suspensions (SCSs) containing submicron particles were introduced as a competitive solution to increase dissolution rates and the bioavailability of poorly water-soluble drugs. In an SCS, poorly water-soluble drug crystals are finely dispersed in a hydrophilic matrix. Lately, melt milling as an adapted wet milling process at elevated temperatures has been introduced as a suitable batch manufacturing process for such a formulation. In this work, the transfer from batch operation to a two-step continuous process is demonstrated to highlight the potential of this technology as an alternative to other dissolution-enhancing methods. In the first step, a powder mixture of a model drug (griseofulvin) and a carrier (xylitol) is fed to an extruder, where a uniform suspension is obtained. In the second step, the suspension is transferred to a custom-built annular gap mill, where comminution down to the submicron region takes place. The prototype’s design was based on batch grinding results and a narrow residence time distribution, intended to deliver large quantities of submicron particles in the SCS. The throughput of the mill was found to be limited by grinding media compression. By inclining the mill at an angle, the grinding media position was manipulated, such that compression was avoided. Different states of the grinding media in the grinding chamber were identified under surrogate conditions. This strategy allows the maintenance of an energy-optimized comminution without adaption of the associated process parameters, even at high throughputs. Using this new process, the production of an SCS with 80–90 % submicron particles in a single passthrough was demonstrated.

Fs-laser preparation of half grid specimens for atom probe tomography and transmission electron microscopy

For atom probe tomography (APT) and transmission electron microscopy (TEM) half grids are commonly applied as specimen carriers, serving as mount for focused ion beam (FIB) processed lift-outs. This technical note presents an alternative way to fabricate half grids directly from the material to be investigated using femtosecond (fs)-laser ablation. After cutting ∼200 µm thin in-plane and cross-plane slices from a TiN coated cemented carbide substrate using a precision cutting saw, two different half grid geometries, one suitable for APT and the other for TEM, were cut via fs-laser processing. Freestanding posts for APT were further sharpened and the areas intended for TEM were thinned top-down using the fs-laser system followed by final annular FIB milling of the APT and thinning of the TEM specimens. For proof of concept, the TiN APT half grid specimens in in- and cross-plane direction were successfully measured in voltage and laser-assisted mode, utilizing a local electrode atom probe, while electron transparency of the in- and cross-plane TEM half grid specimens was proven using a scanning electron microscope equipped with a scanning transmission electron microscopy (STEM) detector. The herein presented method is simple, fast and omits the necessity of a lift-out, reducing the complexity of FIB operations. Additionally, a frequently considered weak point of APT lift-out specimens, the Pt weld between specimen and half grid or microtip coupon is avoided, whilst a wide range of materials can be processed and consumables consumption is reduced. Thus, this work clearly demonstrates the great potential of fs-laser processing for APT and TEM specimen preparation.

In Situ Sputtering From the Micromanipulator to Enable Cryogenic Preparation of Specimens for Atom Probe Tomography by Focused-Ion Beam.

Workflows have been developed in the past decade to enable atom probe tomography analysis at cryogenic temperatures. The inability to control the local deposition of the metallic precursor from the gas-injection system (GIS) at cryogenic temperatures makes the preparation of site-specific specimens by using lift-out extremely challenging in the focused-ion beam. Schreiber et al. exploited redeposition to weld the lifted-out sample to a support. Here, we build on their approach to attach the region-of-interest and additionally strengthen the interface with locally sputtered metal from the micromanipulator. Following standard focused-ion beam annular milling, we demonstrate atom probe analysis of Si in both laser pulsing and voltage mode, with comparable analytical performance as a presharpened microtip coupon. Our welding approach is versatile, as various metals could be used for sputtering, and allows similar flexibility as the GIS in principle.

Efficient preparation of microtip arrays for atom probe tomography using fs-laser processing

Microtip arrays, also called microtip coupons, are routinely used in atom probe tomography (APT) as specimen carriers. They are commercially available consumables, usually made of Si with high electrical conductivity, produced via dedicated shaping techniques. Their purpose is to act as a specimen mount after focused ion beam (FIB) based lift-out procedures. Within this work, an alternative approach to prefabricated microtip coupons is presented, by directly creating a microtip array on the sample to be investigated utilizing fs-laser processing. An exemplary array of microtip posts was fs-laser processed from a TiN coating on Si substrate and subjected to final preparation via annular FIB milling. Subsequently, APT specimen of the TiN coating as well as of the Si substrate were successfully measured in laser assisted mode, using a commercial local electrode APT system. To further emphasize the versatility of the proposed approach, additional voltage measurements of highly conductive B doped Si arrays as well as exemplarily fs-laser processed microtip arrays of various other materials are provided as supplementary material to this article. The presented methodology bypasses the lift-out and avoids the necessity of a Pt weld between specimens and coupon posts which is frequently considered to represent a weak spot. It reduces consumables consumption and provides a high number of specimens in short time, while it is applicable for a wide range of materials and has thus the potential to revolutionize APT specimen preparation.

Developing Atom Probe Tomography to Characterize Sr-Loaded Bioactive Glass for Bone Scaffolding

AbstractIn this study, atom probe tomography (APT) was used to investigate strontium-containing bioactive glass particles (BG-Sr10) and strontium-releasing bioactive glass-based scaffolds (pSrBG), both of which are attractive biomaterials with applications in critical bone damage repair. We outline the challenges and corresponding countermeasures of this nonconductive biomaterial for APT sample preparation and experiments, such as avoiding direct contact between focussed ion beam micromanipulators and the extracted cantilever to reduce damage during liftout. Using a low imaging voltage (≤3 kV) and current (≤500 pA) in the scanning electron microscope and a low acceleration voltage (≤2 kV) and current (≤200 pA) in the focussed ion beam prevents tip bending in the final stages of annular milling. To optimize the atom probe experiment, we considered five factors: total detected hits, multiple hits, the background level, the charge-state ratio, and the accuracy of the measured compositions, to explore the optimal laser pulse for BG-Sr10 bioactive glass. We show that a stage temperature of 30 K, 200–250 pJ laser pulse energy, 0.3% detection rate, and 200 kHz pulse rate are optimized experimental parameters for bioactive glass. The use of improved experimental preparation methods and optimized parameters resulted in a 90% successful yield of pSrBG samples by APT.

On the fabrication of atom probe tomography specimens of Al alloys at room temperature using focused ion beam milling with liquid Ga ion source.

In this work, a simple rectangular milling technique was demonstrated to prepare needle shape atom probe tomography (APT) specimens from Al alloys by focused-ion-beam (FIB) milling using Ga+ ions at room temperature. Ga has high miscibility in Al owing to which electropolishing technique is preferred over Ga+ ion FIB instruments for the fabrication of APT specimens. Although, site specific sample preparation is not possible by the electropolishing technique. This led to the motivation to demonstrate a new rectangular milling technique using Ga+ FIB instrument that resulted a significant reduction of Ga+ ion impregnation into the specimens. This is attributed to the reduction of milling time (<30 s at 30 kV acceleration voltage) and the use of lower currents (<0.3nA) compared to the conventional annular milling method. The yield of specimens during field evaporation in APT was also significantly increased from around 8 million ions to more than 86 million ions due to the avoidance of Ga+ ion embrittlement. Therefore, the currently demonstrated rectangular milling technique can be used to prepare APT specimens from Al-alloys and obtained accurate compositions of matrix, phases, and hetero-phase interfaces with Ga < 0.1at%. RESEARCH HIGHLIGHTS: Feasibility of using Ga+ ions for the preparation of needle shaped specimens at room temperature from aluminum alloys. Demonstration of using a rectangular milling technique instead of annular milling technique that led to a significant reduction in impregnation of Ga+ ions into the specimen needles. Due to very low Ga+ ion damage, the yield of the APT data increased by 10-12 times.

Rapid manufacturing of large diameter Cu micropillars by micro-electrical discharge machining and focused ion beam

A hybrid manufacturing method consisting of micro-electrical discharge machining and focused ion beam milling to fabricate single-crystal Cu micropillars with a diameter of several tens of microns or more was proposed. The method first utilized micro-electrical discharge machining, which adopted a micro-tool made of WC-Co material, to fabricate the coarse micropillars, one by one. It took approximately 70 s to fabricate each coarse micropillar. Seventy-six coarse micropillars were fabricated in the process of exploring optimum input parameters of supply voltage and capacitance value. Energy dispersive spectroscopy and electron backscatter diffraction analyses revealed that pristine Cu material could be obtained by removing only 1.2 μm of surface layer. The micropillar was finished using a focused ion beam to form a 15 μm diameter smooth micropillar with an aspect ratio of 3. The desired micropillar was produced by removing a surface layer of 6 μm or more from the side surface to avoid the micro-electrical discharge machining effect. It took approximately 2.5 h to complete the fabrication of a micropillar by stepwise annular milling. In the case of the hybrid method, it was possible to fabricate a high-quality micropillar 17 times faster than the focused ion beam only method.

Numerical Study of an Annular Bead Mill by the Advanced DEM-CFD Method

Numerical Study of an Annular Bead Mill by the Advanced DEM-CFD Method

Cryo-focused ion beam preparation of perovskite based solar cells for atom probe tomography

Focused-ion beam lift-out and annular milling is the most common method used for obtaining site specific specimens for atom probe tomography (APT) experiments and transmission electron microscopy. However, one of the main limitations of this technique comes from the structural damage as well as chemical degradation caused by the beam of high-energy ions. These aspects are especially critical in highly-sensitive specimens. In this regard, ion beam milling under cryogenic conditions has been an established technique for damage mitigation. Here, we implement a cryo-focused ion beam approach to prepare specimens for APT measurements from a quadruple cation perovskite-based solar cell device with 19.7% efficiency. As opposed to room temperature FIB milling we found that cryo-milling considerably improved APT results in terms of yield and composition measurement, i.e. halide loss, both related to less defects within the APT specimen. Based on our approach we discuss the prospects of reliable atom probe measurements of perovskite based solar cell materials. An insight into the field evaporation behavior of the organic-inorganic molecules that compose the perovskite material is also given with the aim of expanding the applicability of APT experiments towards nano-characterization of complex organo-metal materials.

DESIGN OF CONTROL FOR THE DEVICE USING FOR THE DETERMINATION OF RESIDUAL STRESSES BY RING-CORE METHOD

Urgency of the research. Residual stresses in machine parts and constructions greatly affect their service life and reliability. They are introduced into the manufactured object at each production process and their level can change significantly due to the operation of the product. Their main risk lies in the fact that they add up to the external load and can be the cause of the failure of the construction. Residual stresses can not be determined by simulation methods. They can only be determined using experimental methods. One of these method is the Ring-Core method, the principle of which is to form an annular groove around the strain gauge. Creating of annular groove releases the internal stresses, which can be recorded by a strain gauge. The quality of the formed groove has a significant impact on the overall results of residual stress determination, so it is important to make it as accurate as possible. For this reason, it is necessary to have the most reliable device to form an annular groove. Target setting. Our goal was to design the drive and control for the measuring device for milling the annular groove. This will make it possible to mill the annular groove more precisely, and the resulting residual stresses will be minimally affected by the inaccuracy of the groove. Actual scientific researches and issues analysis. When designing the control of the device and preparing this paper, we took into account not only current sources – publications and papers dealing with the current state of existing measuring devices used for determining residual stresses by Ring-Core method, but – we also took into account our practical experience gained in numerous residual stress determinations by experimental methods. Uninvestigated parts of general matters defining. A modified device requires thorough testing, which has not been implemented during the research for this paper. The research objective. The goal of the research was to create a control for the existing mechanical measuring device used for creating annular groove for determining residual stresses by Ring-Core method. The statement of basic materials. The original mechanical device was supplemented by actuators, which were designed to automate the movement in horizontal axes as well as in the vertical axis. Thanks to this, we have achieved greater precision when positioning the work tool above the center of the strain gauge. At the same time, the original equipment was completed with a servo motor that serves to drive the cutter. For all these elements, control by Programmable Logic Controller was proposed. Conclusions. Our task was to design control for the original device used for residual stress measurement by the RingCore method. We needed to design drives to automate the device. For our needs, we decided to apply linear actuators selected according to the requested criteria. After designing of the electric drives and modifying of the original device, we proceeded to implement control by Programmable Logic Controller. After that, we created a control program in the Automation studio software. This modified measuring device is able to achieve a much higher precision of the annular groove milling, which makes it possible to deter-mine the residual stresses in the structures more precisely

Modern Focused-Ion-Beam-Based Site-Specific Specimen Preparation for Atom Probe Tomography.

Approximately 30 years after the first use of focused ion beam (FIB) instruments to prepare atom probe tomography specimens, this technique has grown to be used by hundreds of researchers around the world. This past decade has seen tremendous advances in atom probe applications, enabled by the continued development of FIB-based specimen preparation methodologies. In this work, we provide a short review of the origin of the FIB method and the standard methods used today for lift-out and sharpening, using the annular milling method as applied to atom probe tomography specimens. Key steps for enabling correlative analysis with transmission electron-beam backscatter diffraction, transmission electron microscopy, and atom probe tomography are presented, and strategies for preparing specimens for modern microelectronic device structures are reviewed and discussed in detail. Examples are used for discussion of the steps for each of these methods. We conclude with examples of the challenges presented by complex topologies such as nanowires, nanoparticles, and organic materials.

Fabrication and in situ compression testing of Mg micropillars with a nontrivial cross section: Influence of micropillar geometry on mechanical properties

Micropillars with a nontrivial cross-sectional shape but constant cross-sectional area were fabricated from a pure magnesium single crystal with (0001) orientation by a focused gallium ion beam using a modified annular milling method. The basic mechanical properties (compressive modulus, strength at different plastic strain levels and hardening exponent) of those structures were determined under compression by means of in situ nanoindentation in scanning electron microscope and correlated by the micropillar cross-sectional circumference. It was observed that the modulus and strength increased with increasing circumference. The values of the modulus for the complex cross sectional shapes are on average higher by 5%, and the yield strength, ranging between 274MPa and 342MPa, is on average higher by 20% relative to micropillars with a simple circular or polygonal cross section. Surprisingly, the hardening exponent remains nearly constant regardless of the micropillar cross section.

Multi-microscopy study of the influence of stacking faults and three-dimensional In distribution on the optical properties of m-plane InGaN quantum wells grown on microwire sidewalls

The optical properties of m-plane InGaN/GaN quantum wells grown on microwire sidewalls were investigated carrying out a correlative scanning transmission electron microscopy (STEM), atom probe tomography (APT), and micro-photoluminescence study applied on single nanoscale field-emission tips obtained by a focused ion beam annular milling. Instead of assuming simple rectangular composition profiles, yielding misleading predictions for the optical transition energies, we can thus take into account actual compositional distributions and the presence of stacking faults (SFs). SFs were shown to be responsible for a lowering of the recombination energies of the order of 0.1 eV with respect to those expected for defect-free quantum wells (QWs). Such energy reduction allows establishing a good correspondence between the transition energies observed by optical spectroscopy and those calculated on the basis of the QWs In measured composition and distribution assessed by STEM structural analysis and APT chemical mapping.

The Grinding and Test of Annular Milling Cutter with Double-Circular-Arc

For the problem of the non standard cutter shape cutting edge not smooth transition connection and flank face of cutting tool grinding precision difference, the influence of wheel deformation is analyzed to different grinding linear speed, and the grinding wheel deformation error compensation grinding method is studied in this work. The grinding of annular milling cutter with double-circular-arc is processed in five axis CNC tool grinder. Finally the machining precision of annular milling cutter with double-circular-arc is tested by the tool test center, the result show that the wheel grinding method based on compensation of grinding can realize smooth transition in different parts of cutting edge belt of annular milling cutter with double-circular-arc and flank grinding precision is ensured.

A novel approach for site-specific atom probe specimen preparation by focused ion beam and transmission electron backscatter diffraction.

Atom probe tomography (APT) is a suitable technique for chemical analyses with almost atomic resolution. However, the time-consuming site-specific specimen preparation can be improved. Recently, transmission electron backscatter diffraction (t-EBSD) has been established for high resolution crystallographic analyses of thin foils. In this paper we present the first successful application of a combined focused ion beam (FIB)/t-EBSD preparation of site-specific APT specimens using the example of grain boundary segregation in technically pure molybdenum. It will be shown that the preparation of a grain boundary can be substantially accelerated by t-EBSD analyses in-between the annular milling FIB procedure in the same microscope. With this combined method, a grain boundary can easily be recognized and positioned in the first 220nm of an APT sample much faster than e.g. with complementary investigations in a transmission electron microscope. Even more, the high resolution technique of t-EBSD gives the opportunity to get crystallographic information of the mapped area and, therefore, an analysis of the grain boundary character to support the interpretation of the APT data files. To optimize this newly developed technique for the application on needle-shaped APT specimens, a parameter study on enhanced background correction, acceleration voltage, and tilt angle was carried out. An acceleration voltage of 30kV at specimen surface tilt angles between -45° and -35° from horizontal plane leads to the best results. Even for molybdenum the observation of crystal orientation data up to about 200nm specimen thickness is possible.

The influence of focused-ion beam preparation technique on microcompression investigations: Lathe vs. annular milling

Two commonly used focused ion beam (FIB) milling techniques were employed for Mg micropillar fabrication to investigate the influence of the individual FIB technique on the microcompression testing method. Results from lathe milled pillars show that the relatively high ion exposure of this technique relative to annular milling greatly affects both stress–strain response and deformation morphology; stresses reached are up to four times higher than for the annular milled pillars and cracking of a surface layer is observed.

Nanoscale characterization of compound semiconductors using laser-pulsed atom probe tomography

Laser-pulsed atom probe tomography is introduced as a novel tomographic technique and its basic principles are explained. Atom probe provides 3-dimensional chemical maps with nanoscale resolution. For semiconductor research, needle-shaped atom probe samples are produced by focused ion beam lift-out and annular milling. An InAs buried quantum dot material was studied using laser-pulsed atom probe. The dot size, morphology and composition were evaluated as well as the wetting layers and interface composition. A laterally shifted In-rich core was visualised within the dots. Furthermore, a GeMn-based thin film was investigated to better-understand the mechanisms leading to the magnetic characteristics of this material system, which has potential applications as a magnetic semiconductor. We conclude that laser-pulsed atom probe has great potential for compound semiconductor research.

Application of Focused Ion Beam to Atom Probe Tomography Specimen Preparation from Mechanically Alloyed Powders

Focused ion-beam milling has been applied to prepare needle-shaped atom probe tomography specimens from mechanically alloyed powders without the use of embedding media. The lift-out technique known from transmission electron microscopy specimen preparation was modified to cut micron-sized square cross-sectional blanks out of single powder particles. A sequence of rectangular cuts and annular milling showed the highest efficiency for sharpening the blanks to tips. First atom probe results on a Fe95Cu5 powder mechanically alloyed in a high-energy planetary ball mill for 20 h have been obtained. Concentration profiles taken from this powder sample showed that the Cu distribution is inhomogeneous on a nanoscale and that the mechanical alloying process has not been completed yet. In addition, small clusters of oxygen, stemming from the ball milling process, have been detected. Annular milling with 30 keV Ga ions and beam currents >or=50 pA was found to cause the formation of an amorphous surface layer, whereas no structural changes could be observed for beam currents <or=10 pA.

Transmission electron microscopy and atom probe specimen preparation from mechanically alloyed powder using the focused ion-beam lift-out technique

The preparation of transmission electron microscopy (TEM) and atom probe-field ion microscopy (AP-FIM) specimens from mechanically alloyed Ti-Cu-Ni-Sn powder has been explored. Applying the focused ion beam (FIB) based in situ lift-out technique, it has been demonstrated that specimen preparation can be carried on single micrometre-sized powder particles without the use of any embedding media. Since the particles did not incorporate any micropores, as revealed by cross-sectioning, the standard procedure known for bulk samples could be simply implemented to the powder material. A sequence of rectangular cuts and annular milling was found to be a highly efficient way of forming a tip-shaped AP-FIM specimen from a square cross-section blank. A Ga level < or =1 at.% was detected if a low beam current of 10 pA was chosen for the final ion-milling stages. Implanted Ga ions were mostly confined to a zone of about 2 nm in thickness and indicated that ion-induced structural transformations were negligible.

Atom probe specimen preparation with a dual beam SEM/FIB miller

Dual beam scanning electron microscope/focused ion beam (SEM/FIB) methods complement electropolishing methods and enable specimens to be made from a wider range of materials. Several methods have been developed to fabricate specimens from different forms of materials, including thin ribbons, mechanically ground sheet and fine powders. In addition, FIB-based methods can be used in conjunction with electropolishing methods to improve the shape, surface finish and taper angle of specimens. Several lift-out (LO) methods have been developed for selecting specific microstructural features or other regions of interest such as phases, interfaces, grain boundaries, subsurface or implanted regions and interdendritic regions. These LO methods make use of an in situ nanomanipulator and platinum deposition to transfer and attach the lifted out volume to a post for final annular milling into a needle-shaped specimen. In order to improve the efficiency and to facilitate the LO procedure, some special specimen mounts that hold both the specimen and the support post at the appropriate working distance have been developed.