Crystalline Coatings Research Articles

Mechanical properties of single and polycrystalline α-Al2O3 coatings grown by chemical vapor deposition

Abstract Due to the highly anisotropic mechanical properties of corundum, the lifetime of α-Al2O3 coated cutting tools is strongly influenced by its texture. However, limited literature is available on orientation dependent mechanical properties of α-Al2O3 coatings. Thus, in the present study, (0001), (11-20), (1-102) oriented single crystalline α-Al2O3 coatings and a state of the art (0001) textured polycrystalline α-Al2O3 coating were synthesized using chemical vapor deposition (CVD) on sapphire and cemented carbide substrates and the mechanical properties were investigated. The morphology of the coatings was studied by scanning electron microscopy and the respective orientation verified by electron backscatter diffraction. The (0001) oriented α-Al2O3 single crystalline coating yielded a slightly higher hardness of 34.4 ± 2.0 GPa compared to the other oriented coatings. Also, the maximum Young's modulus was observed for the (0001) oriented α-Al2O3 single crystalline coating, with a value of 451 ± 25 GPa. Furthermore, micromechanical tests were carried out to determine the fracture stress and fracture toughness, where the (11-20) oriented single crystalline coating exhibited the highest values of 11.2 ± 0.4 GPa and 4.1 ± 0.2 MPa m1/2, respectively. Compared to the (0001) oriented single crystalline coating, the state of the art (0001) textured polycrystalline coating exhibits lower hardness, Young's modulus, fracture stress and fracture toughness values.

Size-Specific, Dynamic, Probabilistic Material Flow Analysis of Titanium Dioxide Releases into the Environment.

Most of the existing exposure models for engineered nanomaterials (ENMs) do not consider particle size, crystalline forms, and coating materials that all may influence the material's fate, transport, and toxicity. Our work aimed to incorporate particle size distributions into a material flow analysis (MFA) to develop a size-specific, dynamic, probabilistic MFA model (ss-DPMFA). Using titanium dioxide (TiO2) as a first case study, we aimed to determine the contribution of conventional TiO2 pigments to the total amount of nanoscale TiO2 released into the environment. Besides providing information on mass flows, the new model used particle size distributions and crystalline forms to describe the stocks and flows of TiO2. The most striking modeling result to emerge was that before TiO2 ENMs came onto the market as such in 2000, 22,400 tons of nanosized (<100 nm) TiO2 particles had already been released into the environment, originating from conventional TiO2 pigments. Even in 2016, 50% of the nanosized TiO2 particles released into wastewater came from the nanosized fraction of TiO2 particles in pigments. Quantitative data on the particle size distribution of TiO2 particles released into the environment can be used as input for environmental fate models. Our new ss-DPMFA model's additional insights about crystalline forms and coatings could pave the way for advanced size- and form-specific hazard and risk assessments for other nanomaterials in ecological systems.

Crystalline and amorphous PEO based ceramic coatings on AA6061: Nanoindentation and corrosion studies

Present study reports the detailed nanomechanical and corrosion behaviours of crystalline and amorphous plasma electrolytic oxidation (PEO) coatings developed on Aluminium alloy-6061. The concentration of sodium silicate in the electrolyte is tailored to achieve crystalline and amorphous natures of the PEO coatings. X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoprofilometry techniques are utilized to investigate microstructural and morphological properties of the PEO coatings. XRD studies confirmed that crystalline ceramic phases are obtained at lower silicate concentration while amorphous nature occurred for comparatively higher concentration of silicate in the electrolyte. Nanoindentation technique is utilized to study the mechanical properties such as hardness (H) and Young's modulus (E) of the PEO coatings. The scatter of the data is treated with well-established Weibull statistical method. Finally, in depth corrosion behaviour of the coatings are investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. Amorphous coatings exhibited superior mechanical properties compared to the crystalline coatings. This is possibly linked with the presence of aluminosilicate phases and difference in silicon content in the coatings. However, as expected crystalline PEO coatings offer better corrosion resistance than the amorphous coatings and this behaviour is explained in terms of porosity contents of the coatings.

Synthesis and characterization of plasma sprayed functional gradient bioceramic coating for medical implant applications

The dissolution of plasma-sprayed hydroxyapatite (HA) coating in physiological media is complex and involves numerous factors. It is generally believed that the highly crystalline HA coatings are beneficial for long-term stability, whereas amorphous layers dissolve more quickly and promote early biointegration. In the present study, the functionally gradient coating (FGC) was formulated in three successive layers over Ti6Al4V alloy using an atmospheric plasma spray (APS) process. At the inner layer, the titania (TiO2) bond coat is applied to enhance adhesion strength. In the middle layer, crystalline hydroxyapatite (HA) coating was deposited to provide long-term stability. In contrast, the outer amorphous layer of as-sprayed HA coating was assumed to promote the early implant bonding with host bone. The crystallinity level of the middle HA layer was increased by post coating heat treatment at 700̊ C for 1 h. There is an improvement in microhardness value after heat treatment from 276.6 ± 91.2 HV to 316.3 ± 41.4 HV. The corresponding porosity and surface roughness values decreased from 15 to 11% and 5.81 ± 1.00 to 5.22 ± 0.84 μm, respectively. In addition, the post coating heat treatment of the middle layer minimized the plasma spray process defects, such as micro-cracks and voids. Furthermore, a corrosion study in the ringer solution shows that heat treatment effectively enhanced the corrosion resistance of the middle crystalline HA layer. Nevertheless, the TiO2 bond coat enhanced the adhesion strength of functional gradient coating from 21.70 MPa to 30.50 MPa. The findings of this study indicate that surface modification with functional gradient coating is a promising approach to improve the performance of the Ti6Al4V alloy for biomedical applications.

Halogenated Terephthalic Acid "Antenna Effects" in Lanthanide-SURMOF Thin Films.

Lanthanide-based crystalline coatings have a great potential for energy-conversion devices, but until now luminescent surface-anchored materials were difficult to fabricate. Thin films, called lanthanides surface-mounted metal-organic frameworks (SURMOFs) with tetrasubstituted halide (fluorine, chlorine, and bromine) terephthalic acid derivative linkers as a basic platform for optical devices, exhibit a high quantum yield of fluorescence visible to the naked eyes under ambient light. We show that we can tune the luminescent properties in thin films by halide substitution, which affords control over the molecular structure of the material. We rationalize the mechanism for the modulation of the photophysical properties by "antenna effect", which controls the energy transfer and quantum yields using experimental and theoretical techniques for chelated lanthanides as a function of the type of atom substitutions at the phenyl rings and the resulting dihedral angle between phenyl rings in the linkers and carboxylate groups.

Наноиндентирование и механические свойства материалов в субмикро- и наношкале. Недавние результаты и достижения (О б з о р)

The review discusses the details of various materials mechanical behavior in submicro- and nanoscale. Significant advances in this scope result from the development of wide family of load based precise nanotesting techniques called nanoindentation. But nowadays, nanomechanical properties are studied not only by nanoindentation techniques in narrow sense, i.e. local loading of macro, micro and nanoscale objects. Nanomechanical load testing is discussed here within a wider scope employing precise deformation measurement with nanometer scale resolution caused by various types of low load application to the object under study including uniaxial compression or extension, shearing, bending or twisting, optionally accompanied by in situ monitoring sample microstructure using scanning and transmission electron microscopy and Laue microdiffraction technique. The main courses of experimental techniques development in recent ten years along with the results obtained using them in single, poly and nano crystalline materials, composites, films and coatings, amorphous solids and such biomaterials as tissues, living cells and macromolecules are described. Special attention is paid to deformation size effects and atomic mechanisms in nanoscale. This review is a natural continuation and development of the review published at Fiz.Tverd.Tela vol.50, issue 12, 2008 of the same author that discusses details of nanomechanical properties of solids. Current review includes wider range of nanomechanical testing concepts and recent achievements in the scope. The work was supported by RFBR grant for project #19-12-50235.

Superhard Boron-Rich Boron Carbide with Controlled Degree of Crystallinity

Superhard boron-rich boron carbide coatings were deposited on silicon substrates by microwave plasma chemical vapor deposition (MPCVD) under controlled conditions, which led to either a disordered or crystalline structure, as measured by X-ray diffraction. The control of either disordered or crystalline structures was achieved solely by the choice of the sample being placed either directly on top of the sample holder or within an inset of the sample holder, respectively. The carbon content in the B-C bonded disordered and crystalline coatings was 6.1 at.% and 4.5 at.%, respectively, as measured by X-ray photoelectron spectroscopy. X-ray diffraction analysis of the crystalline coating provided a good match with a B50C2-type structure in which two carbon atoms replaced boron in the α-tetragonal B52 structure, or in which the carbon atoms occupied different interstitial sites. Density functional theory predictions were used to evaluate the dynamical stability of the potential B50C2 structural forms and were consistent with the measurements. The measured nanoindentation hardness of the coatings was as high as 64 GPa, well above the 40 GPa threshold for superhardness.

Phase-Selective and Localized TiO2 Coating on Additive and Wrought Titanium by a Direct Laser Surface Modification Approach.

Titanium has been the material of interest in biological implant applications due to its unique mechanical properties and biocompatibility. Their design is now growing rapidly due to the advent of additive manufacturing technology that enables the fabrication of complex and patient-customized parts. Titanium dioxides (TiO2) coatings with different phases (e.g., anatase, rutile) and morphologies have shown to be effective in enhancing osteointegration and antibacterial behavior. This enhanced antibacterial behavior stems from the photocatalytic activity generated from crystalline TiO2 coatings. Anatase has commonly been shown to be a more photocatalytic oxide phase compared to rutile despite its larger band gap. However, more recent studies have suggested that a synergistic effect leading to increased photocatalytic activity may be produced with a combination of oxides containing both anatase and rutile phases. Here, we demonstrate the selective and localized formation of TiO2 nanostructures on additive and wrought titanium parts with anatase, rutile, and mixed phases by a laser-induced transformation approach. Compared to conventional coating processes, this technique produces desired TiO2 phases simply by controlled laser irradiation of titanium parts in an oxygen environment, where needed. The effects of processing conditions such as laser power, scanning speed, laser pulse duration, frequency, and gas flow on the selective transformation were studied. The morphological and structural evolutions were investigated using various characterization techniques. This method is specifically of significant interest in creating phase-selective TiO2 surfaces on titanium-based bioimplants, including those fabricated by additive manufacturing technologies.

The Influence of Magnetron Sputtering Conditions on the Structure of Zr–Pd Coatings

Using the method of DC magnetron sputtering, nonstructured amorphous metal coatings of Zr75Pd25 composition were obtained with an average deposition rate of 1.3 nm/s at a substrate temperature of 40°C, while crystalline coatings were formed at a higher substrate temperature. A crystalline coating with equilibrium phase composition was obtained at 350°C. Coatings deposited at intermediate temperatures contained predominantly a PdZr phase, in contrast to the equilibrium PdZr2 phase. The surface roughness of amorphous coatings was on a level of 0.2–0.5 nm, which was about ten times lower than the mean roughness of crystalline coatings with the same composition.

Electroplating of zinc and tin alloys with nickel and cobalt from ammonium oxalate electrolytes

A possibility of preparing good quality electrolytic alloys zinc-nickel, zinc-cobalt, tin-nickel, and tin-cobalt from ammonium oxalate electrolytes of various compositions was shown. The alloy coatings of high quality can be obtained at the current density range from 1 to 3 A dm−2. The introduction into the electrolyte of ammonium oxalate capable of forming stable complexes with Zn2+, Sn2+, Ni2+, and Co2+ ions makes it possible to increase the working pH range. Electroplating occurs with high cathodic polarization favoring the formation of qualitative finely crystalline coatings of the plated alloys.

Atomic layer deposition of thermoelectric layered cobalt oxides

Layered cobalt oxides based on the hexagonal CoO2 layer, e.g., NaxCoO2 and [CoCa3O3]0.62CoO2 (or “Ca3Co4O9”), are promising thermoelectric materials. Here, the authors investigate the atomic layer deposition (ALD) of these materials in a thin-film form; this is not trivial, in particular, for the former compound, as both Na and Co are little challenged as components of ALD thin films. The authors employ diketonate precursors for all the metal constituents and ozone as the source of oxygen. In both cases, a postdeposition heat-treatment in O2 is applied to get crystalline coatings; the processes are found amazingly robust in terms of metal precursor pulsing ratios. A striking difference between the two processes is the resultant morphology: while the Ca3Co4O9 films grow highly homogeneous and smooth, the NaxCoO2 coatings exhibit a rather unique reproducible 10–20 μm scale channel-like island structure for all x values investigated. Finally, the authors characterized their ALD Ca3Co4O9 films for their chemical, structural, and physical property details not previously reported.

Duplex surface treatment of metallic alloys combining cold-spray and plasma electrolytic oxidation technologies

Plasma electrolytic oxidation (PEO) is widely used to improve the corrosion and wear resistance of lightweight metals such as aluminium alloys by the formation of a ceramic oxide coating. However, the PEO process remains ineffective for ferrous metals and, when applied to magnesium alloys, oxide coatings are usually thin and porous. To overcome these limitations, the feasibility of applying a duplex treatment combining cold-spray deposition (CS) and PEO is investigated. Cold-sprayed aluminium coatings are deposited on magnesium (EV31) and steel (S235) substrates prior to PEO processing. Investigation of this duplex process evidences the efficiency of such a two-steps process to form thick, dense and crystalline alumina coatings on both magnesium and steel substrates. The growth kinetic of the duplex CS-PEO oxide layer is enhanced by a factor of 3 compared to single-step PEO processing of bulk aluminium substrates. Results are discussed by considering the effect of the porosity through the cold-sprayed aluminium coating on the mechanism of oxidation during the subsequent PEO treatment.

An Effect of Parameters of the Reverse Electrolysis Mode on Composition and Properties of Zinc–Nickel–Cobalt Alloy

The use of reverse polarization during the electrodeposition of the Zn–Ni–Co alloy made it possible to increase the amount of alloying components, Ni and Co, in the composition of the deposit. It is established that the inclusion of cobalt in the composition of the Zn–Ni coating and the use of the reverse electrolysis mode contribute to the production of finer crystalline coatings with corrosion resistance exceeding this characteristic of the chromated zinc coating.

Progress in the measurement and reduction of thermal noise in optical coatings for gravitational-wave detectors.

Coating thermal noise is a fundamental limit for precision experiments based on optical and quantum transducers. In this review, after a brief overview of the techniques for coating thermal noise measurements, we present the latest worldwide research activity on low-noise coatings, with a focus on the results obtained at the Laboratoire des Matériaux Avancés. We report new updated values for the Ta2O5, Ta2O5-TiO2, and SiO2 coatings of the Advanced LIGO, Advanced Virgo, and KAGRA detectors, and new results from sputtered Nb2O5, TiO2-Nb2O5, Ta2O5-ZrO2, MgF2, AlF3, and silicon nitride coatings. Amorphous silicon, crystalline coatings, high-temperature deposition, multi-material coatings, and composite layers are also briefly discussed, together with the latest developments in structural analyses and models.

Production of Ba(Zr,Ti)O3 coatings on ternary (Ti,Zr)N thin film electrodes by plasma electrolyte oxidation

Cubic perovskite barium zirconate titanate [Ba(Zr,Ti)O3; BZT] coatings were produced over ternary (Ti,Zr)N seeding layers by plasma electrolytic oxidation (PEO). (Ti,Zr)N thin films serving as the working electrode were deposited on Si substrates by unbalanced magnetron sputtering. PEO was conducted in the alkaline electrolytes consisting of 0.5 M Ba(OH)2 with a potentiostatic power mode at applied voltages ranging from 30 to 80 V for 30 s. Spark plasma discharges occurred over the thin film electrodes at reaction voltages above 50 V, characterized as a PEO regime. Sintered-like BZT coatings with porous morphology were obtained. The PEO-produced coatings exhibited substantially higher integrated diffraction peak intensities and growth rates, compared to the electrochemically oxidized coatings synthesized at lower applied voltages. X-ray photoelectron spectroscopy revealed chemical compositions of the BZT coatings. This clearly demonstrates that crystalline BZT coatings could be facilely produced over complex (Ti,Zr)N seeding layers by PEO. Possible reaction routes and formation mechanisms of the coatings were also proposed. The PEO-made BZT coatings have great potential for many dielectric and ferroelectric applications.

Влияние условий магнетронного распыления на структуру Zr-Pd покрытий

Structureless Zr75Pd25 amorphous metal coatings were obtained using DC magnetron sputtering with an average deposition rate of 1.3 nm/s and a substrate temperature of 40 oC, as well as the crystalline coatings at a higher temperature. The equilibrium phase composition is observed at a temperature 350 oC. At intermediate temperature mainly the PdZr phase is formed against the equilibrium PdZr2 phase. The roughness of the obtained amorphous coatings is of 0.2–0.5 nm, which is an order of magnitude lower than that of crystalline coatings of the same composition.

Net versus gross erosion of silicon carbide in DIII-D divertor

Gross and net erosion rates of silicon from silicon carbide (SiC) coatings were measured in the divertor of DIII-D under well diagnosed reactor-relevant plasma conditions. Amorphous and crystalline SiC coatings on graphite with thickness of ∼80 nm and ∼250 μm, respectively, were exposed near an attached outer strike point of lower single null L-mode plasmas using the Divertor Material Evaluation System (DiMES). Plasma density and electron temperature near the center of the coatings were ne ∼ 4 × 1019 m−3 and Te ∼ 23 eV. Gross erosion of Si from all samples was measured spectroscopically using the Si II 636 nm line. It was found to be a factor of ∼4 higher for the amorphous coatings compared to the crystalline one. The thin amorphous coatings allowed measurements of net Si erosion with Rutherford backscattering. Net average Si erosion rate of ∼3 × 1016 cm−2 s−1 was measured on the amorphous coatings with toroidal extent of 1 mm, where, according to ERO code modeling, the local redeposition of Si was about 30%. Using this rate, spectroscopic measurements, measured D+ ion fluxes, and corrections from ERO-OEDGE modeling, effective SXB coefficient for the Si II 636 nm line of ∼52 and Si sputtering yield of ∼0.017 Si/D were calculated. Deuterium retention on SiC coatings was measured by 2.5 MeV 3He nuclear reaction analysis at 0.5–2.5 × 1017 atoms cm−2, consistent with retention due to implantation into a surface undergoing net erosion.

Arsenáty mědi z dobývky na žíle Geschieber - sever (patro Daniel), Svornost, jáchymovský rudní revír (Česká republika)

An interesting mineral association of Cu arsenates was found at abandoned ore stope at the Geschieber vein - north at the Daniel level of the Svornost mine, the Jáchymov ore district, Krušné hory, Czech Republic. Tangdanite forms thin tabular crystals up to 3 mm in size and coatings and fine crystalline aggregates on the area up to some cm2. It has light green, bluish-green to emerald green color and perfect cleavage. It is monoclinic, space group C2/c, the unit-cell parameters refined from X-ray powder diffraction data are: a 54.335(12), b 5.579(2), c 10.459(2) Å, β 95.42(3)° and V 3156(2) Å3; its chemical analyses correspond to the empirical formula Ca1.99(Cu8.72Zn0.09Ni0.04Al0.04)Σ8.89[(AsO4)3.83 (PO4)0.14(SiO4)0.03]Σ4.00(SO4)0.41(OH)8.97·9H2O on the basis As+P+Si+V = 4 apfu. The results of Raman and infrared spectroscopy confirmed an absence of carbonate group in studied tangdanite. K-rich lavendulan was found as a relatively abundant sky blue crusts and coatings on the area up to some cm2 and hemispherical aggregates with a radial structure or rarely as a group of thin tabular crystals up to 0.2 mm in size. It is monoclinic, space group P21/n, the unit-cell parameters refined from X-ray powder diffraction data are: a 10.081(12), b 19.469(12), c 10.033(9) Å, β 90.32° and V 1969(2) Å3; its chemical analyses correspond to the empirical formula (Na0.63K0.16)Σ0.79Ca1.12(Cu4.82Al0.01)Σ4.83[(AsO4)3.86(PO4)0.07 (SO4)0.06(SiO4)0.01]Σ4.00Cl0.96·5H2O on the basis As+P+V+Si+S = 4 apfu. Olivenite occurs as olive green spherical aggregates with radial structure up to 8 mm in size and rarely as groups of acicular crystals in association with strashimirite and köttigite. It is orthorhombic, space group Pnnm, the unit-cell parameters refined from X-ray powder diffraction data are: a 8.6204(10), b 8.2332(9), c 5.9337(11) Å and V 421.13(7) Å3; its chemical analyses correspond to the empirical formula (Cu1.94Ni0.01Al0.01)Σ1.96[(AsO4)0.97(VO4)0.02(PO4)0.01]Σ1.00(OH)0.93 on the basis As+V+P = 1 apfu. Strashimirite forms there light green crystalline coatings on the area up to several cm2 and spherical aggregates with a radial structure in association with olivenite and lavendulan. Strashimirite is probably monoclinic, space group P2, the unit-cell parameters refined from X-ray powder diffraction data are: a 9.991(9), b 18.466(9), c 8.986(8) Å, β 96.5(2)° and V 1574(3) Å3; its chemical analyses correspond to the empirical formula (Cu7.83Ni0.18Ca0.09Zn0.06Co0.02Al0.02)Σ8.20 [(AsO4)3.81(PO4)0.07 (SO4)0.07(VO4)0.03(SiO4)0.02]Σ4.00 (OH)4.45·5H2O on the basis As+P+Si+V+S = 4 apfu. Chalcophyllite was found as rare emerald green thin tabular crystals up to 0.5 mm in size and crystalline aggregates. Its chemical composition is possible to express on the basis As+S+P+Si = 7 apfu by the empirical formula Cu17.83Al1.97[(AsO4)4.00(PO4)0.09]Σ4.09[(SO4)2.80(SiO4)0.11]Σ2.91 (OH)23.27·36H2O. Brochantite, devilline, köttigite, erythrite and gypsum were also found in the association with Cu arsenates. The origin of the described mineral association is connected with (sub)recent weathering of primary ore minerals (tennantite, sphalerite, nickelskutterudite) in relatively dry conditions of abandoned mine adits.

On the controls of mineral assemblages and textures in alkaline springs, Samail Ophiolite, Oman

Interactions between meteoric water and ultramafic rocks in the Oman Ophiolite generate waters of variable physicochemical characteristics. The discharge of these waters forms complex alkaline pool networks, in which mineral precipitation is triggered by mixing, evaporation, and uptake of atmospheric CO2. A systematic and co-localized sampling of waters and solids in two individual spring sites allowed us to determine the saturation state of a range of minerals and correlate them to the different water and precipitate types. We subdivided the waters of the spring sites into three distinctive types: i) Mg-type; moderately alkaline (7.9<pH<9.5), Mg2+–HCO3−-rich waters, ii) Ca-type; hyperalkaline (pH>11.6), Ca2+–OH−-rich waters, and iii) Mix-type; alkaline to hyperalkaline (9.6 < pH < 11.5) waters with intermediate chemical composition. We first report the occurrence of hydrated magnesium (hydroxy-) carbonate phases in Mg-type waters. Nesquehonite forms in these waters via evaporation and transforms into dypingite and hydromagnesite under CO2-rich conditions. In Ca-type waters, the coupling of atmospheric CO2 uptake with evaporation leads to the formation of a calcitic crystalline crust on the air-water interface. The crusts are aragonite- and brucite-bearing, where Mg-type and Ca-type waters discharge and vigorously mix at the same pool. Unlike the Mg-type and Ca-type waters, the pools of Mix-type waters host massive aragonite-dominated deposits due to high Mg/Ca ratio that favors the growth of aragonite over calcite. The hydrodynamics during mixing spatially control brucite precipitation and restrict its formation and accumulation around specific mixing zones, where a continuous supply of Mg of inflowing Mg-type waters takes place. Crystal morphologies record the effect on the values of supersaturation and supersaturation rates in the pools due to mixing processes, evaporation and CO2 uptake. In Ca-type waters, CO2 uptake and evaporation dictate the textural characteristics of calcite both in crystalline crusts and rock coatings. Textural evolution of aragonite from crystalline sheaves to spheroidal shapes underlines the different supersaturation rates of calcium carbonate crystallization in flocculent material of Mix-type waters. Geochemical models of mixing between Mg-type and Ca-type waters revealed the evolution of mineral saturation indices under various mixing proportions, and their relation to the observed mineralogy and geochemistry of the pool waters. The thorough documentation of mineral assemblages and crystal morphologies enabled us to provide a more detailed account of how water composition, mixing, and mineral precipitation co-evolve in the alkaline spring systems, where CO2 is sequestered.

Thickness uniformity measurements and damage threshold tests of large-area GaAs/AlGaAs crystalline coatings for precision interferometry.

Precision interferometry is the leading method for extremely sensitive measurements in gravitational wave astronomy. Thermal noise of dielectric coatings poses a limitation to the sensitivity of these interferometers. To decrease coating thermal noise, new crystalline GaAs/AlGaAs multilayer mirrors have been developed. To date, the surface figure and thickness uniformity of these alternative low-loss coatings has not been investigated. Surface figure errors, for example, cause small angle scattering and thereby limit the sensitivity of an interferometer. Here we measure the surface figure of highly reflective, substrate-transferred, crystalline GaAs/AlGaAs coatings with a custom scanning reflectance system. We exploit the fact that the reflectivity varies with the thickness of the coating. To increase penetration into the coating, we used a 1550 nm laser on a highly reflective coating designed for a center wavelength of 1064 nm. The RMS thickness variation of a two inch optic was measured to be 0.41 ± 0.05 nm. This result is within 10% of the thickness uniformity, of 0.37 nm RMS, achieved with ion-beam sputtered coatings for the aLIGO detector. We additionally measured a lower limit of the laser induced damage threshold of 64 MW/cm 2 for GaAs/AlGaAs coatings at a wavelength of 1064 nm.