Nanostructured diamond micropillar tips for use as specimen mounts

Abstract

Disclosed are micro-pillar structures that include diamond micro-tips and the preparation of diamond micro-tips. The diamond micro-tips are useful, for example, in chemical analytical measurements such as atom probe tomography.

Description

NANOSTRUCTURED DIAMOND MICROPILLAR TIPS FOR USE AS SPECIMENMOUNTSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 519085, filed August 11, 2023; the contents of which is hereby incorporated by reference in its entirety for all purposes.STATEMENT OF GOVERNMENT LICENSE RIGHTS

[0002] This invention was made with Government support under DE- AC0576RL01830 awarded by U.S. Department of Energy. The Government has certain rights in the invention.BACKGROUND

[0003] Diamond has been heavily studied in recent years for many applications related to the inclusion of point defects. Diamond is a particularly good host lattice for these defects (often referred to as color centers) due to the extreme strength and stability of its crystal lattice. Additionally, due to the fact that diamond is nontoxic, diamond color centers are attractive options for in vivo applications in medicine and life science. However, these color centers begin to interfere with each other if the concentration is too high, therefore limiting the practical concentration of point defects to roughly the ppm order or magnitude. The color centers can present a problem for standard nanoscale elemental analysis techniques such as energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), which typically have detection limits no higher than roughly parts per thousand. Thus, it is challenging to achieve any degree of spatial resolution in determining the local concentrations of color centers.

[0004] For this reason, atom probe tomography (APT) has emerged as an attractive option to study color center concentrations in bulk diamond. APT relies on the field evaporation of a sample that has been milled to a fine point, which can release ions at a controlled rate toward a 2D time of flight mass spectrometer. The APT procedure results in detection limits closer to the ppm range while preserving spatial resolution, which is ideal for studying the local concentrations of point defects. Furthermore, APT is capable of detecting hydrogen, which is not possible with X-ray fluorescence-based methods. However, diamond inherently poses unique challenges for APT due to the nature of how APT works. The field evaporation process in APT is controlled by the application of a localelectric field near the tip somewhat below the level required to induce spontaneous field evaporation, and in order to control the timing of ion release, either the electric field itself or an external laser (visible or UV) is pulsed (typically the laser-assisted option is used for nonconductive samples to minimize strain) to release ions at a known time point. Diamond is a material that is renowned for its extreme hardness, and that property is preserved at the nanoscopic level as well, leading to it having the highest known evaporation field of any elemental material in excess of 150V / nm. By comparison, silicon (which is commonly used for mounting APT specimens) has an evaporation field closer to 33 V / nm. The evaporation field of diamond means that diamond requires much more energy to induce field evaporation. Besides any instrumental limitations that may exist, this is theoretically not a problem for conducting samples that can distribute charge to the surface and concentrate at the tip. Distribution of charge to the surface and concentrate at the tip is another area in which diamond does not excel, as diamond natively has extremely low conductivity, which leads to a buildup of internal charge that can cause the sample to rupture. Charge leading to sample rupture can be mitigated to an extent by using boron-doped diamond to make it more conductive.

[0005] The preparation of APT tips of diamond can itself present a challenge. Most APT samples are prepared by a focused ion beam (FIB) bulk liftout method in which a bar is lifted out of a bulk sample, sectioned onto tips, and subsequently sharpened. FIB versatile method, and one that has been used for bulk diamond samples before, but bulk liftouts that remove large amounts of material can be problematic for diamond. Due to the extreme hardness of diamond, the FIB milling requires a substantially higher ion dose than similar liftouts of other materials, which has the effect of increasing milling time, decreasing precision, and introducing more defects both by disrupting the lattice and implanting gallium ions from the FIB. As such, any interaction with the ion beam that can be eliminated will have the effect of speeding up processing time and reducing opportunities for sample damage.

[0006] Even if a sample is prepared perfectly, however, challenges remain in the APT measurement itself. As mentioned previously, diamond has both an extremely high evaporation field and an extremely low conductivity, and furthermore it is highly brittle. What the high evaporation field and low conductivity of diamond means all together is that, while the field evaporation requires a higher-than-normal voltage, too high of a voltage will cause the tip to rupture. Fortunately, laser-assisted atom probe technologies allow forlower voltages to be used by thermally exciting atoms over the barrier to evaporation. Normally, the energy contribution from the laser pulse is chosen to be relatively small compared to that of the applied voltage. The small energy contribution from the laser is both to prevent damage to the sample from overheating and to prevent thermal tailing of the mass spectrum. Thermal tailing occurs because the zero-point for the time-of-flight mass spectrometer is set as the time of the laser pulse, meaning that ions are assumed to be ejected at the exact moment of the laser pulse. However, for samples with a finite heat capacity, ions may be released at any point which the sample remains above the critical temperature for field evaporation. Samples with a finite heat capacity is an area, however, where the properties of diamond to can be an advantage.SUMMARY

[0007] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0008] In an aspect, a micro-pillar structure for analytical measurements is disclosed, with the micro-pillar structure comprising: a micro-post and a diamond microtip, where the diamond micro-tip and the micro-post are either integral or attached following the separate manufacture of the diamond micro-tip and micro-post.DESCRIPTION OF THE DRAWINGS

[0009] The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

[0010] FIGURE 1A shows a schematic of the mounting process of the diamond tips on the silicon micro-post arrays showing the initial cutting of the diamond posts at an angle of 52° from vertical, then the placement and platinum weld of the diamond on the post.

[0011] FIGURE IB shows with a scale bar at 5 pm the CVD diamond.

[0012] FIGURE 1C with a scale bar of 2 pm, shows the diamond micro-tip being placed to the micro-post.

[0013] FIGURE ID with a scale bar of 3 pm, shows the diamond micro-tip welded to the micro-post.

[0014] FIGURE IE with a scale bar of 2 pm, shows the sharpened diamond micro-tip on the micro-post.

[0015] FIGURE IF an example of one embodiment of the micro-pillar structure with the tip welded to the post, as indicated by the dividing line, and circular conic in shape.

[0016] FIGURE 1G an example of one embodiment of a monolithic micro-pillar structure that is conical in shape.

[0017] FIGURE 2A shows part 1 of the reactive ion etching process, showing the application of wafer bond adhesive to a sapphire surface followed by CVD of diamond to the wafter bond adhesive followed by the etch mask.

[0018] FIGURE 2B emphasizes the pits surrounding the posts separating them from the remaining bulk diamond.

[0019] FIGURE 2C shows SEM images show the darker sapphire substrate visible around the base of the pillars.

[0020] FIGURE 2D shows top view SEM images show the darker sapphire substrate visible around the base of the pillars.

[0021] FIGURE 3 A-FIGURE 3B shows the process of the standard liftout process compared to the disclosed liftout process to yield micro-pillars with diamond micro-tips.

[0022] FIGURE 3A shows the standard process involves masking followed by etching with FIB at a thirty-degree angle followed by the cutout being placed and adhered to the surface.

[0023] FIGURE 3B shows one embodiment of the disclosed process involves CVD of diamond followed by cutting the tip from the CVD diamond at an angle of fifty- two degrees to yield the micro-tip 105. The disclosed process involves welding the diamond micro-tip 105 to the micro-post 110.

[0024] FIGURE 4 shows mass spectrometry analysis of diamond tip with percent composition of each element as a function of z-height, with complex ions decomposed to their atomic pieces. Note that the line for nitrogen is near zero and the line for hydrogen is partially obscured by the line for oxygen.

[0025] FIGURE 5A shows an APT measurement distribution of hydrogen ions within the tip. The distribution shown is the full reconstruction, and when taken with FIGURE 5D, shows the effect of surface defects.

[0026] FIGURE 5B shows an APT measurement distribution of nitrogen ions within the tip. The distribution shown is the full reconstruction to show, and when taken with FIGURE 5E, shows the effect of surface defects.

[0027] FIGURE 5C shows an APT measurement distribution of gallium ions within the tip. The distribution shown is the full reconstruction, and when taken with FIGURE 5F, shows the effect of surface defects.

[0028] FIGURE 5D shows an APT measurement distribution of hydrogen ions within the tip. The distribution is shown is the internal section, and when taken with FIGURE 5A, shows the effect of surface defects.

[0029] FIGURE 5E shows an APT measurement distribution of nitrogen ions within the tip. The distribution is shown is the internal section and, when taken with FIGURE 5B, shows the effect of surface defects.

[0030] FIGURE 5F shows an APT measurement distribution of gallium ions within the tip. The distribution shown is the internal section, and when taken with FIGURE 5C, shows the effect of surface defects.

[0031] FIGURE 6A-FIGURE 6F show FIB damage of the diamond tip.

[0032] FIGURE 6A shows a rotated diagram showing the cross section of the tip shown in FIGURE 6B and FIGURE 6C.

[0033] FIGURE 6B shows cross sectional gallium reconstruction showing gallium planted throughout the lattice, with a higher concentration near the tip.

[0034] FIGURE 6C shows cross sectional carbon reconstruction showing a decrease in ordered structure near the tip.

[0035] FIGURE 6D shows TEM image of a diamond tip showing an amorphized layer of approximately 10 nm (scale bar = 10 nm).

[0036] FIGURE 6E shows zoomed out image of the same tip (scale bar = 500 nm) with inset showing diffraction showing crystallinity of bulk tip (scale bar = 5 nm-1).

[0037] FIGURE 6F shows a full reconstruction showing 1000 counts of each carbon species (438 counts of C6 as that is all that was measured) showing a higher concentration of larger molecular ions near the tip, indicating a more damaged region.

[0038] FIGURE 7 A shows raw time of flight spectrum centered on the12C1+peak, showing a full width at half maximum of 3.6 ns.

[0039] FIGURE 7B shows heat transfer calculations showing the cooling of a diamond tip with a base temperature of 41 K that has been irradiated at various laser pulse energies. At 1% of the FWHM of the TOF spectrum of12C1+, the tip will have cooled to 57.5 K if irradiated at 125 pj, 63.4 K if irradiated at 200 pj, and 75.8 K if irradiated at 500 pj, suggesting that the thermal broadening effect for diamond is negligible at operating laser pulse energies.

[0040] FIGURE 7C shows normalized mass spectra for diamond tips irradiated at 200 and 500 pj, showing no observable thermal broadening effect. Plots are stacked and each of the data sets have the same zero point.DETAILED DESCRIPTION

[0041] While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.

[0042] In an aspect, a micro-pillar structure for analytical measurements is disclosed, with the micro-pillar structure comprising: a micro-post and a diamond microtip, where the diamond micro-tip and the micro-post are either integral or attached following the separate manufacture of the diamond micro-tip and micro-post.

[0043] For the purposes of this disclosure, a micro-post that is integral with the micro-tip is a monolithic micro-pillar structure.

[0044] Referring to FIGURE IF, an embodiment of a micro-pillar 100 structure is illustrated that includes a diamond micro-tip 105 atop a micro-post 110. The disclosed embodiment also includes a base 115 region where the micro-pillar 100 terminates. In the disclosed embodiment the micro-pillar is mounted on a substrate 120. In the embodiment of FIGURE IF the diamond micro-tip 105 and the micro-post 110 can be the same or different materials. Similarly, the micro-post 110 and the substrate 120 can be the same or different materials. The micro-pillar 110 in some embodiments can be referred to as a “two- part,” which denotes attachment of the diamond micro-tip 105 to the micro-post 110 following their separate manufacture.

[0045] Another embodiment of a micro-pillar is illustrated in FIGURE 1G. The illustrated micro-pillar 200 is “integral” or “monolithic,” as the entire micro-pillar 200 is formed from the same diamond material. FIGURE 1G notes both a diamond micro-tip 205and a micro-post 210 region, but they are integrally joined and thus the micro-post 210 is continuously joined to the diamond micro-tip 205 and is the same material. A base 215 terminated the micro-pillar 200. The micro-pillar 200 structures comprising the integrated micro-tip 205 and micro-post 210, can have its base 215 mounted to a substrate 220. Similarly, the monolithic micro-pillar 200 (comprising of the integrated micro-tip 205 and micro-post 210 where the micro-tip 205 and micro-post 210 are the same material), the base 215, and the substrate 220 can be the same or different materials.

[0046] Diamond has an extremely high thermal conductivity which allows it to readily disperse heat throughout the lattice. Several chemical properties of diamond potentially make it a useful material for analytical chemistry techniques such as Atom Probe Tomography (APT), which is the aim for the disclosure being disclosed to show. As such, it would not be expected that thermal tailing to be much of a problem, and therefore higher laser pulse energies can be used to assist in field evaporation in the performing of analytical chemical techniques. Higher laser pulse energies are not only useful in the collection of data on diamond directly, but also potentially in the engineering of APT sample mounts that can reduce background noise and even wick away heat, which may be especially useful for “extreme” atom probe techniques that use much more powerful lasers.

[0047] In an embodiment, the micro-pillar structure (FIGURE IF) comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed, wherein the micro-pillar structure is configured for the analytical measurements atom probe tomography (APT), transmission electron microscopy (TEM), or field ionization microscopy (FIM).

[0048] In an embodiment, the monolithic micro-pillar structure (FIGURE 1G) comprising of a diamond micro-tip 205 and micro-post 210 structure is disclosed, wherein the micro-pillar structure is configured for the analytical measurements atom probe tomography (APT), transmission electron microscopy (TEM), or field ionization microscopy (FIM).

[0049] One skilled in the art will appreciate that the technology being disclosed in this disclosure can find uses outside the APT, TEM or FIM being disclosed in this disclosure. Some other techniques that the diamond tips find use is profile measurements, thickness measurements, or measurements for oxidation or degradation of materials.

[0050] In an embodiment, the micro-pillar structure (FIGURE IF) comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed, wherein themicro-pillar structure reduces background noise when performing the analytical measurements.

[0051] In an embodiment, the monolithic micro-pillar structure (FIGURE 1G) comprising of a diamond micro-tip 205 and micro-post 210 structure is disclosed, wherein the micro-pillar structure reduces background noise when performing the analytical measurements.

[0052] In an embodiment, the micro-pillar structure (FIGURE IF) comprising of a diamond micro-tip 105 mounted to a micro-post structure 110 is disclosed, wherein the micro-pillar structure is a component of a specimen support for atom probe tomography (APT), transmission electron microscopy, or field ionization microscopy, comprising a substrate and at least one micro-pillar structure having a micro-tip region configured to support a specimen, wherein the substrate and the at least one micro-tip comprise diamond.

[0053] In an embodiment, the monolithic micro-pillar structure (FIGURE 1G) comprising of a diamond micro-tip 205 and micro-post structure 210 is disclosed, wherein the micro-pillar structure is a component of a specimen support for atom probe tomography (APT), transmission electron microscopy, or field ionization microscopy, comprising a substrate and at least one micro-pillar structure having a micro-tip region configured to support a specimen, wherein the substrate and the at least one micro-tip comprise diamond.

[0054] In an embodiment, the micro-pillar structure (FIGURE IF) comprising of a diamond micro-tip mounted 105 to a micro-post structure 110 is disclosed, wherein an evaporation field of the micro-pillar tip is greater than 90 V / nm.

[0055] In an embodiment, the micro-pillar structure (FIGURE 1G) comprising of a diamond micro-tip 205 and micro-post structure 210 is disclosed, wherein an evaporation field of the micro-pillar tip is greater than 90 V / nm.

[0056] In the disclosed disclosure an array of micro-pillars on a wafer consisting of 10 pm of chemical vapor deposition (CVD) diamond on a sapphire substrate using reactive ion etching in order to minimize the interaction of the diamond sample with the FIB.

[0057] In an embodiment, the micro-pillar structure (FIGURE IF) comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed, wherein the micro-tip comprises 105 a diamond material selected from CVD-diamond, boron-doped diamond, HPHT diamond, and single-crystal diamond.

[0058] In an embodiment, the monolithic micro-pillar structure (FIGURE 1G) comprising of a diamond micro-tip 205 and micro-post 210 structure is disclosed, wherein the micro-tip comprises 205 a diamond material selected from CVD-diamond, boron-doped diamond, HPHT diamond, and single-crystal diamond.

[0059] One skilled in the art can appreciate that other materials could be substituted for the micro-tips 105 or 205. Some non-limiting substances that micro-tips 105 or 205 could be made of with success are silicon carbide, quartz, silicon germanium, alphatin, or water-ice. Furthermore, one skilled in the art will realize that many other dopants in the diamond structure could also find use in doped diamond tips of this disclosure. Some non-limiting dopants are nitrogen, sulfur, hydrogen, sulfur, nickel, iron, oxygen, germanium, tin, and antimony. Combinations of dopants are also possible.

[0060] Representative micro-pillars are roughly conical with a base 115 or 215 of 2 pm and a height of 10 pm. The disclosed dimensions are an ideal size because the mounting posts on a standard APT sample chip have a diameter of 2 pm, however the process could easily be adapted for a mounting post of any size. To mount these micro-tips 105 on a sample chip (FIGURE 1) the micro-pillars were first coated with a thin protective layer of platinum using the electron beam and then a thicker (0.5 pm) layer of platinum was deposited with the ion beam. FIGURE 2 illustrates the reactive ion etching process, emphasizing the pits surrounding the posts separating them from the remaining bulk diamond. The stage was then tilted back to vertical (52° to the ion beam) and a probe was attached, and the micro-pillar was then cut near the base. The detached micro-pillar was then brought to the mounting micro-post and platinum was deposited to fill the gap underneath the cut. The sample was then rotated 180° and a thin layer of platinum was deposited to fill any gaps on the backside. The micro-tip 105 or 205 was then sharpened using a standard sequential annular milling technique (FIGURE IE), however due to the existing shape of the micro-tips, far less milling is required for the sharpening step than what is typical for a standard liftout as shown in FIGURE 3 A. Furthermore, it would also be feasible to use lower voltages to sharpen the tips to further reduce ion implantation, whereas that would be prohibitively time-consuming for a standard liftout, and that is an area of current study.

[0061] In an embodiment, the micro-pillar structure comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed, wherein the micro-pillarstructure has a base (e.g., FIGURE IF, base 115, and FIGURE 1G, base 215) diameter or largest cross-sectional dimension of about 1 gm to about 10 gm.

[0062] In an embodiment the height of the micro-pillar, from a substrate to a tip of the micro-pillar is 150 microns or less. In an embodiment the height of the micro-pillar, from a substrate to a tip of the micro-pillar is 125 microns or less. In an embodiment the height of the micro-pillar, from a substrate to a tip of the micro-pillar is 100 microns or less. In an embodiment the height of the micro-pillar, from a substrate to a tip of the micropillar is 50 microns or less. In an embodiment the height of the micro-pillar, from a substrate to a tip of the micro-pillar is 25 microns or less. In an embodiment the height of the micro-pillar, from a substrate to a tip of the micro-pillar is 10 microns or less.

[0063] In an embodiment, the micro-pillar structure comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed, wherein the micro-pillar structure has a base 115 diameter of about 1.25 gm to about 7.5gm (FIGURE IF) or the micro-pillar structure has a base 215 diameter of about 1.25 pm to about 7.5pm (FIGURE 1G).

[0064] In an embodiment, the micro-pillar structure comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed, wherein the micro-pillar structure has a base diameter 115 of about 1.5 gm to about 5 gm (FIGURE IF) or base diameter 215 about 1.5 gm to about 5 gm (FIGURE 1G).

[0065] In an embodiment, the micro-pillar structure is arranged in a 22-specimen grid of flat top micro-tips 105 or 205 with micro-tips located with 400 microns of the edge of the micro-tip coupon. Diameter 2 microns + / - 1 micron; height 125 microns, 125 microns + / - 10 microns, 125 microns + / - 20 microns, 125 microns + / - 30 microns, on a 3mm x 7mm (+ / - 0.1mm - thicker, + / - 0.2mm - thicker, + / - 0.3mm - thicker, + / - 0.4mm - thicker, + / - 0.5mm - thicker) silicon coupon doped < 0.1 Ohm-cm (silicon coupon doped < 0.05 Ohm- cm, silicon coupon doped < 0.15 Ohm-cm, silicon coupon doped < 0.2 Ohm-cm) resistivity.

[0066] In an embodiment, the micro-pillar structure comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed, wherein a cross-sectional geometry of the micro-pillar tip has a shape defined by: any finite two-dimensional area with a continuous boundary such as circular, semicircular, or elliptical shapes (FIGUREIF); or a non-continuous boundary consisting of edges and vertices such trapezoids, squares, rectangles, parallelograms, regular polygons, or non-regular polygons (FIGUREIG). While two exemplary cross-sectional geometries are illustrated in FIGURES IF and1G, it will be appreciated that one of skill in the art could envision any of the disclosed cross-sectional geometries.

[0067] In an embodiment, the micro-pillar structure (FIGURE IF) has the micropillar tip 105 with a flat surface, a rounded surface, or pointed.

[0068] In an embodiment, the monolithic micro-pillar structure (FIGURE 1G) has the micro-pillar tip 205 with a flat surface, a rounded surface, or pointed.

[0069] In an embodiment, the micro-pillar structure (FIGURE IF) comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed, wherein the micro-pillar structure is configured for the analytical measurements atom probe tomography (APT), or field ionization microscopy.

[0070] In an embodiment, the micro-pillar structure comprising of a diamond micro-tip 205 mounted to a micro-post 210 structure is disclosed, wherein the monolithic (FIGURE 1G) micro-pillar structure is configured for the analytical measurements atom probe tomography (APT), or field ionization microscopy.

[0071] In an embodiment, the micro-pillar structure (FIGURE IF) comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed and is for analytical measurements and has the micro-post comprising of silicon, tungsten, or diamond.

[0072] In an embodiment, the micro-pillar structure comprising of a diamond micro-tip 205 mounted to a micro-post 210 structure is monolithic (FIGURE 1G) is disclosed and is for analytical measurements and has the micro-post comprising of silicon, tungsten, or diamond.

[0073] In an embodiment, the micro-pillar structure (FIGURE IF) comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed and has the specimen support substrate comprising of sapphire.

[0074] In an embodiment, the micro-pillar structure comprising of a diamond micro-tip 205 and micro-post 210 monolithic structure (FIGURE 1G) is disclosed and has the specimen support substrate comprising of sapphire.

[0075] In an embodiment, the micro-pillar structure is disclosed and has the specimen support substrate and the at least one micro-pillar structure as monolithic (Figure 1G) and where the micro-post 210 and the micro-tip 205 are formed of the same diamond.

[0076] In an embodiment, the micro-pillar comprising of a diamond micro-tip 105 mounted to a micro-post structure 110 is disclosed and has the micro-tip 105 mounted to the micro-post 110 by a weld. An embodiment of an exemplary welded micro-pillar can be found in FIGURES 1 A-1C.

[0077] In an embodiment, the micro-pillar comprising of a diamond microtip 105 mounted to a micro-post 110 structure is disclosed where the weld is platinum, gold, palladium, silver, nickel, copper, rhodium, iridium, ruthenium, osmium, rhenium, tungsten, molybdenum, or combinations thereof.

[0078] The disclosed disclosure reports successful collection of APT data on the disclosed micro-tips 105 or 205 at laser pulse energies of 200, 250, and 500 pj. All of the micro-tips 105 or 205 eventually fractured; however, significant data was collected prior to the fracture. The use of the micro-tips 105 or 205 disclosed in this disclosure is shown in FIGURE 3, at 200 pj of laser pulse energy. At 200 pj of laser pulse energy a mass spectrum was collected that showed many peaks, including carbon clusters up to seven carbon atoms as well as various organic species, hydroxides, water, and hydrogen.

[0079] In an embodiment, the micro-pillar structure (FIGURE IF) comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed, wherein the specimen support is configured to allow APT at laser pulse energy of 10 pj to 1000 pj.

[0080] In an embodiment, the monolithic (FIGURE 1G) micro-pillar comprising of a diamond micro-tip 205 and micro-post 210 structure is disclosed, wherein the specimen support is configured to allow APT at laser pulse energy of 10 pj to 1000 pj.

[0081] In an embodiment, the micro-pillar structure (FIGURE IF) comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed, wherein the specimen support is configured to allow APT at laser pulse energy of 100 pj to 750 pj.

[0082] In an embodiment, the monolithic (FIGURE 1G) micro-pillar structure comprising of a diamond micro-tip 205 and micro-post 210 structure is disclosed, wherein the specimen support is configured to allow APT at laser pulse energy of 100 pj to 750 pj.

[0083] In an embodiment, the micro-pillar structure (FIGURE IF) comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed, wherein the specimen support is configured to allow APT at laser pulse energy of 200 pj to 500 pj.

[0084] In an embodiment, the monolithic (FIGURE 1G) micro-pillar structure comprising of a diamond micro-tip 205 and micro-post 210 structure is disclosed, wherein the specimen support is configured to allow APT at laser pulse energy of 200 pj to 500 pj.

[0085] In an embodiment, the micro-pillar structure (FIGURE IF) comprising of a diamond micro-tip 105 mounted to a micro-post 110 structure is disclosed, wherein the laser pulse energy applied to the micro-pillar structure reduces background noise when performing the analytical measurements proportionally to the laser pulse energy.

[0086] In an embodiment, the micro-pillar structure (FIGURE 1G) comprising of a diamond micro-tip 205 and micro-post 210 structure is disclosed, wherein the laser pulse energy applied to the micro-pillar structure reduces background noise when performing the analytical measurements proportionally to the laser pulse energy.

[0087] There was also significant gallium implantation throughout the measured micro-tip 105 or 205. A concentration profile along the z axis (FIGURE 4), decomposing complex ions to their respective elements, showed a relative increase of Ga, O, and H near the micro-tip 105 or 205, indicating a higher degree of damage. The hydrogen and oxygen appear correlated due to the relatively high concentration of OH and OH2ions measured near the micro-tip. Nitrogen counts are low but measurable, and do not show any strong compositional trends along the z direction. However, low overall nitrogen counts may obscure some trends. Nitrogen counts obscuring some trends is nonetheless notable because the tested sample was not intentionally doped with nitrogen. Photoluminescence from nitrogen was observed indicating that intentionally-doped nitrogen should be readily measurable with these techniques. It is also notable that an increase of nitrogen near the micro-tip was not observed which correlated with the increase in oxygen and hydrogen, given that the samples were stored in air. The nitrogen results near the micro-tip indicate that nitrogen observed in diamond samples is likely to be native to the sample and contamination from atmospheric nitrogen is not a major concern.

[0088] Reconstructions showing the individual species of interest (FIGURES 5A-5F) further illustrate the previous observation from the depth profile. By looking at a cylindrical region of interest internal to the tip, surface effects can be eliminated, showing even more clearly that hydrogen and gallium decrease as the distance from the tip increases. Hydrogen is worth particularly careful examination due to the multiple sources of hydrogen that may be present. CVD diamond natively contains abundant hydrogen impurities and a relatively homogeneous hydrogen concentration throughout the bulk could be expected. It is also established by the data disclosed in this disclosure that hydrogen and oxygen are correlated due to OH and OH2, which is more abundant near the surface. Finally, APT typically has a significant hydrogen backgrounddue to the challenge of building vacuum systems that are impermeable to hydrogen. It is challenging to deconvolute these signals, however it is nonetheless promising to be able to use a technique that can measure hydrogen directly, especially for samples that have a non- homogeneous hydrogen distribution, as can be seen at the tip of the reconstruction from the data. The observed non-homogenous hydrogen distribution is likely from hydroxides. Nitrogen and gallium are more straightforward to interpret, however the low overall counts of nitrogen signify that it has a relatively noisier signal. Additionally, it needs to be considered that undercounting of nitrogen is a known issue in APT, attributable at least in part to the formation of neutral N2species. However, due to the low overall concentration of nitrogen in the tested diamond sample, it is not anticipated that dimerization is likely to occur significantly among nitrogen point defects during APT analysis.

[0089] A benefit to this method of sample preparation is the lower overall interaction the tips have with the ion beam during sample preparation. The lower overall interaction the tips should have the effect of reducing the damage that the micro-tip 105suffers prior to APT measurement. To study this with APT, a cross section was reconstructed (FIGURE 6A) to view the internal structuring of the micro-tip. Gallium implantation was observed (FIGURE 6B) throughout the measured portion of the microtip 105, signifying damage, however there was a decrease in gallium away from the surface. By mapping the carbon, a greater degree of ordering away from the micro-tip 105 was able to be observed, signifying considerable damage at the micro-tip 105 but less as the run continues. Greater degree of ordering of carbon away from the micro-tip was correlated to TEM images of a similarly prepared tip (FIGURES 6D and E), which show a layer of about 10 nm of amorphized carbon atop a relatively crystalline micro-tip 105, which correlates well to the obtained APT data. Lastly the distribution of all detected Cncounts was measured, and found that for larger values of n, the ions were concentrated near the microtip 105. The ions were concentrated near the micro-tip 105 could be attributable to greater sample damage near the tip disrupting the diamond lattice and making it easier for larger molecular ions to break off.

[0090] One of the unique properties of diamond as a material is its superior thermal conductivity. Superior thermal conductivity allows the use of much greater laser pulse energies than what would normally be tolerated in APT. The typical complication of overly high pulse energies in APT is thermal tailing of the mass spectrum, arising from the tip remaining above the critical temperature for field evaporation for a finite amount oftime, resulting in an apparently longer time of flight. Experimental results show that, of all the challenges that do exist in APT of diamond, thermal tailing is not one of them. By considering the raw time of flight (TOF) data that corresponds to the12C1+peak (i.e. the total amount of time in nanoseconds that12C1+ions take to be measured) for a tip irradiated at 200 pj with a full width at half maximum (FWHM) of 3.6 nanoseconds (FIGURE 7A). FIGURE 7B shows modeling of the heat profile of the tip over time to determine how quickly the tip cools down following the laser pulse (using a base temperature of 41 K). It was found that in just 36 picoseconds (1% of the FWHM of the TOF), even tips irradiated at 500 pj will have already cooled below liquid nitrogen temperatures, indicating that thermal effects will not significantly broaden the TOF spectrum. It is worth noting that the temperature was measured at the tip to only reach about 200K when irradiated at 500 pj, which is nearly an order of magnitude below the temperatures at which diamond undergoes a chemical reaction to graphite. The results of the modeling of heat profile of the tip over time are confirmed with experimental data showing the normalized12C1+peaks of tips irradiated at 200 and 500 pj, respectively (FIGURE 7C). The peak profiles for both are functionally identical with no evidence of thermal tailing. The peak profiles of thermal tailing serves to emphasize some potential areas where diamond may be particularly suited for APT applications. Firstly, “extreme” APT is a technique that uses laser pulses in the extreme UV region (29.6 nm), which is far more efficient at thermally exciting materials.

[0091] The monolithic micro-pillar with the integrated micro-tip 205 and micropost 210 when the material is diamond is especially suited for extreme APT conditions. The monolithic micro-pillar with the integrated micro-tip 205 and micro-post 210 when the material is diamond is suited for extreme APT conditions because the superior thermal conductivity of diamond allows the use of much greater laser pulse energies than what would normally be tolerated in APT combined with the higher field evaporation of diamond compared to other materials.

[0092] In an embodiment, a micro-pillar structure (FIGURE IF) comprising a diamond micro-tip mounted 105 to a micro-post 110 is disclosed, wherein the micro-pillar structure removes heat at such a rate thermal tails are to Boltzmann distribution.

[0093] In an embodiment, a micro-pillar structure (FIGURE 1G) comprising a diamond micro-tip 205 and micro-post 210 is disclosed, wherein the micro-pillar structure removes heat at such a rate thermal tails are to Boltzmann distribution.

[0094] In an embodiment, a micro-pillar structure (FIGURE IF) comprising a diamond micro-tip mounted to a micro-post is disclosed, wherein a time to return to cryogenic set point temperature of the specimen support from laser shut off is 0.001 ns to 1000 ns.

[0095] In an embodiment, a monolithic micro-pillar structure (FIGURE 1G) comprising a diamond micro-tip 205 and micro-post 210 is disclosed, wherein a time to return to cryogenic set point temperature of the specimen support from laser shut off is 0.001 ns to 1000 ns.

[0096] In an embodiment, a micro-pillar structure (FIGURE IF) comprising a diamond micro-tip 105 mounted to a micro-post 110 is disclosed, wherein a time to return to cryogenic set point temperature of the specimen support from laser shut off is 0.025 ns to 750 ns.

[0097] In an embodiment, a monolithic micro-pillar structure (FIGURE 1G) comprising a diamond micro-tip 205 and micro-post 210 is disclosed, wherein a time to return to cryogenic set point temperature of the specimen support from laser shut off is 0.025 ns to 750 ns.

[0098] In an embodiment, a micro-pillar structure (FIGURE IF) comprising a diamond micro-tip 105 mounted to a micro-post 110 is disclosed, wherein a time to return to cryogenic set point temperature of the specimen support from laser shut off is 0.050 ns to 500 ns.

[0099] In an embodiment, a monolithic micro-pillar structure (FIGURE 1G) comprising a diamond micro-tip 205 and micro-post 210 is disclosed, wherein a time to return to cryogenic set point temperature of the specimen support from laser shut off is 0.050 ns to 500 ns.

[0100] In an embodiment, a micro-pillar structure (FIGURE IF) comprising a diamond micro-tip 105 mounted to a micro-post 110 is disclosed, wherein a thermal broadening effect in APT is negligible at operating laser pulse energies.

[0101] In an embodiment, a monolithic micro-pillar structure (FIGURE 1G) comprising a diamond micro-tip 205 and micro-post 210 is disclosed, wherein a thermal broadening effect in APT is negligible at operating laser pulse energies.

[0102] APT technique seems particularly well-suited to the measurement of diamond, as a material that requires a high proportion of thermal excitation, for APT measurement and one that is not significantly affected by thermal tailing. Diamond notsignificantly affected by thermal tailing also suggests the potential use of diamond as a material for APT sample mounts. The best sample mount is one that doesn’t interfere with the measurement of the sample, and thus it can be concluded that a mount should ideally have a higher evaporation field than the sample so that it doesn’t create background evaporation, and it should have a higher thermal conductivity so that it doesn’t overheat and instead can act as a heat sink for the micro-tip 105 and especially for the monolithic micro-tip 205. In fact, some of the micro-tips 105 measured may have failed due to the overheating and subsequent melting of the silicon sample mounts whereas the monolithic micro-tips 205 should be more resistant due to the greater thermal conductivity of diamond. The overheating and subsequent melting of the silicon sample mounts could have been mitigated by using a more thermally conductive sample mount, such as diamond in the monolithic structure (FIGURE 1G). The electrical nonconductivity of diamond may present a problem, but this is easily resolved by using boron-doped diamond, which is conductive.

[0103] The disclosure shows a hybrid method for producing APT tips of diamond using a combination of reactive ion etching and FIB. Diamond micro-tips 105 significantly reduce the interaction of the sample with the ion beam, theoretically reducing damage. It also allows for more flexibility in terms of methods for tip sharpening that may in the future be able to reduce damage even further. APT data was collected on these micro-tips, detecting significant hydrogen and nitrogen, showing APT to be a useful method for detecting and mapping out these point defects in diamond. The damage from the FIB was characterized, which shows that the damage is reduced past the micro-tip. Areas probed by the diamond micro-tip were highlighted in which to improve future micro-tip 105 or 205 fabrication. Computational and experimental results show that the thermal conductivity of diamond allows for very high laser pulse energies to be used to thermally excite the microtips in APT, thus reducing the operating voltage, without negatively affecting the mass spectrum, which suggests that diamond would be a good candidate for “extreme” APT measurements when used as in FIGURE 1G, and further suggests that diamond would be a near-optimal material for APT sample mounting micro-posts in either the examples shown in FIGURE IF and especially in FIGURE 1G.

[0104] In an embodiment, a micro-pillar structure (FIGURE IF) comprising a diamond micro-tip 105 mounted to a micro-post 110 is disclosed, wherein the specimensupport is configured to allow APT with laser pulses frequencies between 25 kHz to 500 kHz.

[0105] In an embodiment, a monolithic micro-pillar structure (FIGURE 1G) comprising a diamond micro-tip 205 and micro-post 210 is disclosed, wherein the specimen support is configured to allow APT with laser pulses frequencies between 25 kHz to 500 kHz.

[0106] In an embodiment, a micro-pillar structure (FIGURE IF) comprising a diamond micro-tip 105 mounted to a micro-post 110 is disclosed, wherein the specimen support is configured to allow APT with laser pulses frequencies between 40 kHz to 400 kHz.

[0107] In an embodiment, a monolithic micro-pillar structure (FIGURE 1G) comprising a diamond micro-tip 205 and micro-post 210 is disclosed, wherein the specimen support is configured to allow APT with laser pulses frequencies between 40 kHz to 400 kHz.

[0108] In an embodiment, a micro-pillar structure (FIGURE IF) comprising a diamond micro-tip 105 mounted to a micro-post 110 is disclosed, wherein the specimen support is configured to allow APT with laser pulses frequencies between 55 kHz to 250 kHz.

[0109] In an embodiment, a monolithic micro-pillar structure (FIGURE 1G) comprising a diamond micro-tip 205 and micro-post 210 is disclosed, wherein the specimen support is configured to allow APT with laser pulses frequencies between 55 kHz to 250 kHz.

[0110] In another aspect, a method of performing APT utilizing the micro-pillar structure of FIGURE IF of a diamond micro-tip 105 mounted to a micro-post 110 is disclosed, with the method comprising: configuring the micro-pillar structure to have a diamond micro-tip 105, wherein the micro-tip 105 is supporting a specimen; placing an evaporation field onto the specimen; pulsing the micro-tip 105 supporting the specimen with laser frequencies between 25 kHz to 500 kHz; looking at a cylindrical region of interest internal to the micro-tip; and measuring the atomic composition of the specimen.[OHl] In another aspect, a method of performing APT utilizing the micro-pillar structure of FIGURE 1G of a diamond micro-tip 205 and micro-post 210 is disclosed, with the method comprising: configuring the micro-pillar structure to have a diamond micro-tip 205, wherein the micro-tip 205 is supporting a specimen; placing an evaporation field ontothe specimen; pulsing the micro-tip 205 supporting the specimen with laser frequencies between 25 kHz to 500 kHz; looking at a cylindrical region of interest internal to the microtip; and measuring the atomic composition of the specimen.

[0112] In an embodiment, the method of performing APT of utilizing a diamond micro-tip 105 or 205 is disclosed, wherein pulsing laser frequencies have a pulsing energy of 10 pj to 1000 pj.

[0113] In an embodiment, the method of performing APT of utilizing a diamond micro-tip 105 or 205 is disclosed, wherein performing the APT resulting in reconstruction showing carbon species resulting in further showing a higher concentration of larger molecular ions near the micro-tip.

[0114] In an embodiment, the method of performing APT of utilizing a diamond micro-tip 105 or 205 is disclosed, wherein performing the APT results in showing a distribution of ions within the micro-tip.

[0115] In an embodiment, the method of performing APT of utilizing a diamond micro-tip 105 or 205 is disclosed, wherein the ions are hydrogen, nitrogen, and gallium.

[0116] In an embodiment, the method of performing APT of utilizing a diamond micro-tip 105 or 205 is disclosed, wherein performing the APT utilizing the micro-tip results in showing surface defects of the specimen.

[0117] In an embodiment, the method of performing APT of utilizing a diamond micro-tip 105 or 205 is disclosed, wherein performing the APT involves placing an evaporation field up to 150 V / nm upon the specimen.

[0118] The disclosed techniques in the disclosure show that diamond materials are ideal for chemical analytical measurements such as APT. Diamond is shown in the disclosure to be a material that requires a high proportion of thermal excitation for APT measurement and one that is not significantly affected by thermal tailing. Not being significantly affected by thermal tailing also suggests the potential use of diamond as a material for APT sample mounts. A sample mount should ideally interfere minimally with the measurement of the sample, and thus it should have a higher evaporation field than the sample to reduce background evaporation, and it should have a higher thermal conductivity so that it doesn’t overheat and instead can act as a heat sink for the tip. Overheating rather than acting as a heat sink is highlighted by the fact that some of the tips measured here may have failed not due to a problem with the diamond itself but rather due to the overheating and subsequent melting of the silicon sample mounts, and the overheating may be mitigatedby using a more thermally conductive sample mount, as has been shown in this disclosure with diamond. While the electrical nonconductivity of pure diamond potentially presents a problem, any problem is easily addressed by using boron-doped diamond, which is conductive. The chemical characteristics also make diamond a compelling substrate for surface measurements using field ion microscopy (FIM). FIM measures the ionization of an imaging gas that is desorbed from a tip-shaped surface, and thus diamond can act as an inert substrate for the measurement of a thin film sample.

Claims

CLAIMSThe embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A micro-pillar structure for analytical measurements, the micro-pillar structure comprising: a micro-post; and a diamond micro-tip; wherein the diamond micro-tip and the micro-post are either integral or attached following the separate manufacture of the diamond micro-tip and micro-post.

2. The micro-pillar structure for analytical measurements of Claim 1, wherein the micro-post comprises silicon, tungsten, or diamond.

3. The micro-pillar structure of any of the previous claims, wherein the microtip comprises a diamond material selected from CVD-diamond, boron-doped diamond, HPHT diamond, and single-crystal diamond.

4. The micro-pillar structure of any of the previous claims, wherein the microtip is mounted to the micro-post by a weld.

5. The micro-pillar structure of Claim 4, wherein the weld is platinum.

6. The micro-pillar structure of any of the preceding claims, wherein the micro-pillar structure has a base diameter of about 1 pm to about 10 pm.

7. The micro-pillar structure of any of the preceding claims, wherein a cross- sectional geometry of the micro-pillar tip has a shape defined by: any finite two-dimensional area with a continuous boundary such as circular, semicircular, or elliptical shapes; or a non-continuous boundary consisting of edges and vertices such trapezoids, squares, rectangles, parallelograms, regular polygons, or non-regular polygons.

8. The micro-pillar structure of any of the preceding claims, wherein the micro-pillar tip has a flat surface, a rounded surface, or is pointed.

9. The micro-pillar structure of any of the preceding claims, wherein the micro-pillar structure is configured for the analytical measurements atom probe tomography (APT), transmission electron microscopy, or field ionization microscopy.

10. The micro-pillar structure of any of the preceding claims, wherein an evaporation field of the micro-pillar tip is greater than 90 V / nm.

11. The micro-pillar structure of any of the preceding claims, wherein the micro-pillar structure removes heat at such a rate that thermal tails are to Boltzmann distribution.

12. The micro-pillar structure of any of the preceding claims, wherein the micro-pillar structure is a component of a specimen support for atom probe tomography (APT) transmission electron microscopy, or field ionization microscopy, comprising a substrate and at least one micro-pillar structure having a micro-tip region configured to support a specimen, wherein the substrate and the at least one micro-tip comprise diamond.

13. The micro-pillar structure of any of the preceding claims, wherein the specimen support substrate comprises sapphire.

14. The micro-pillar structure of any of the preceding claims, wherein the specimen support substrate and the at least one micro-pillar structure is monolithic and wherein the micro-post and the micro-tip are formed of the same diamond.

15. The micro-pillar structure of any of the preceding claims, wherein the specimen support is configured to allow APT at laser pulse energy of 10 pj to 1000 pj.

16. The micro-pillar structure of any of the preceding claims, wherein the laser pulse energy applied to the micro-pillar structure reduces background noise when performing the analytical measurements proportionally to the laser pulse energy.

17. The micro-pillar structure of any of the preceding claims, wherein the specimen support is configured to allow APT with laser pulses frequencies between 25 kHz to 500 kHz.

18. The micro-pillar structure of any of the preceding claims, wherein a time to return to cryogenic set point temperature of the specimen support from laser shut off is 0.001 ns to 1000 ns.

19. The micro-pillar structure of any of the preceding claims, wherein a thermal broadening effect in APT is negligible at operating laser pulse energies.

20. A method of performing APT utilizing the micro-pillar structure of Claim 1, the method comprising: configuring the micro-pillar structure to have a diamond micro-tip, wherein the micro-tip is supporting a specimen; placing an evaporation field onto the specimen; pulsing the micro-tip supporting the specimen with laser frequencies between 25 kHz to 500 kHz;looking at a cylindrical region of interest internal to the micro-tip; and measuring the atomic composition of the specimen.

21. The method of performing APT of Claim 20, wherein pulsing laser frequencies have a pulsing energy of 10 pj to 1000 pj22. The method of performing APT of Claims 20 and 21, wherein performing the APT resulting in reconstruction showing carbon species resulting in further showing a higher concentration of larger molecular ions near the micro-tip.

23. The method of performing APT of Claims 20-22, wherein performing the APT results in showing a distribution of ions within the micro-tip.

24. The method of performing APT of Claims 20-23, wherein the ions are hydrogen, nitrogen, and gallium.

25. The method of performing APT of Claims 20-24, wherein performing the APT utilizing the micro-tip results in showing surface defects of the specimen.

26. The method of performing APT of Claims 20-25, wherein performing the APT involves placing an evaporation field up to 150 V / nm upon the specimen.

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