Z-contrast Scanning Transmission Electron Microscopy Research Articles

Selective Antisite Defect Formation in WS2 Monolayers via Reactive Growth on Dilute W-Au Alloy Substrates.

Defects are ubiquitous in 2D materials and can affect the structure and properties of the materials and also introduce new functionalities. Methods to adjust the structure and density of defects during bottom-up synthesis are required to control the growth of 2D materials with tailored optical and electronic properties. Here, the authors present an Au-assisted chemical vapor deposition approach to selectively form SW and S2W antisite defects, whereby one or two sulfur atoms substitute for a tungsten atom in WS2 monolayers. Guided by first-principles calculations, they describe a new method that can maintain tungsten-poor growth conditions relative to sulfur via the low solubility of W atoms in a gold/W alloy, thereby significantly reducing the formation energy of the antisite defects during the growth of WS2 . The atomic structure and composition of the antisite defects are unambiguously identified by Z-contrast scanning transmission electron microscopy and electron energy-loss spectroscopy, and their total concentration is statistically determined, with levels up to ≈5.0%. Scanning tunneling microscopy/spectroscopy measurements and first-principles calculations further verified these antisite defects and revealed the localized defect states in the bandgap of WS2 monolayers. This bottom-up synthesis method to form antisite defects should apply in the synthesis of other 2D materials.

Vacancy and solute co-segregated η1 interface in over-aged Al-Zn-Mg alloys

We present a combined first-principles and scanning transmission electron microscopy (STEM) study of the η1/Al interfaces in an over-aged Al-Zn-Mg alloy. As one of the major η-MgZn2 precipitate types, η1 tends to form highly coherent interfaces with Al matrix, along with various solute segregation patterns on its interfacial layers. The interface phase diagram suggests either an Mg-rich or a Zn-rich interface, depending on the chemical potential range of Zn. Further segregation calculations, however, strongly suggest the STEM Z-contrast imaged interface to be a vacancy and solute co-stabilized Mg-rich structure that is favored at relatively low Zn chemical potentials. Based on our experimental and calculation results, the profound thermodynamics origin of the η1/Al interface and its intricate segregation behavior is clarified and described using a generalized structure model. The η1/Al interface structure and segregation at higher Zn chemical potentials are also predicted for future experimental validation.

On Vacancy and Solute Co-Segregated η1 Interface in Over-Aged Al-Zn-Mg Alloys

We represent a combined first-principles and scanning transmission electron microscopy (STEM) study of the η1A1 interfaces in an over-aged Al-Zn-Mg alloy. As one of the major η-MgZn2 precipitate phase variants, η1A1 tends to form highly coherent interfaces with Al matrix, along with various unique solute segregation patterns on its interfacial layers. The interface phase diagram suggests either an Mg-rich or a Zn-rich interface, depending on the chemical potential range of Zn. Further segregation calculations, however, strongly suggest the STEM Z-contrast imaged interface to be a vacancy and solute co-stabilized Mg-rich structure that is favored at relatively low Zn chemical potentials. Based on our experimental and calculation results, the profound thermodynamics origin of the η1A1 interface and its intricate segregation behavior were clarified and described using a generalized structure model. The η1A1l interface structure and segregation at higher Zn chemical potentials were also predicted for future experimental validation.

Strategy for simultaneously increasing both hardness and toughness in ZrB2-rich Zr1−xTaxBy thin films

Refractory transition-metal diborides exhibit inherent hardness. However, this is not always sufficient to prevent failure in applications involving high mechanical and thermal stress, since hardness is typically accompanied by brittleness leading to crack formation and propagation. Toughness, the combination of hardness and ductility, is required to avoid brittle fracture. Here, the authors demonstrate a strategy for simultaneously enhancing both hardness and ductility of ZrB2-rich thin films grown in pure Ar on Al2O3(0001) and Si(001) substrates at 475 °C. ZrB2.4 layers are deposited by dc magnetron sputtering (DCMS) from a ZrB2 target, while Zr1−xTaxBy alloy films are grown, thus varying the B/metal ratio as a function of x, by adding pulsed high-power impulse magnetron sputtering (HiPIMS) from a Ta target to deposit Zr1−xTaxBy alloy films using hybrid Ta-HiPIMS/ZrB2-DCMS sputtering with a substrate bias synchronized to the metal-rich portion of each HiPIMS pulse. The average power PTa (and pulse frequency) applied to the HiPIMS Ta target is varied from 0 to 1800 W (0 to 300 Hz) in increments of 600 W (100 Hz). The resulting boron-to-metal ratio, y = B/(Zr+Ta), in as-deposited Zr1−xTaxBy films decreases from 2.4 to 1.5 as PTa is increased from 0 to 1800 W, while x increases from 0 to 0.3. A combination of x-ray diffraction (XRD), glancing-angle XRD, transmission electron microscopy (TEM), analytical Z-contrast scanning TEM, electron energy-loss spectroscopy, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and atom-probe tomography reveals that all films have the hexagonal AlB2 crystal structure with a columnar nanostructure, in which the column boundaries of layers with 0 ≤ x < 0.2 are B-rich, whereas those with x ≥ 0.2 are Ta-rich. The nanostructural transition, combined with changes in average column widths, results in an ∼20% increase in hardness, from 35 to 42 GPa, with a simultaneous increase of ∼30% in nanoindentation toughness, from 4.0 to 5.2 MPa√m.

A Tungsten-Based Nanolaminated Ternary Carbide: (W,Ti)4C4- x.

Nanolamellar transition metal carbides are gaining increasing interests because of the recent developments of their two-dimensional (2D) derivatives and promising performance for a variety of applications from energy storage, catalysis to transparent conductive coatings, and medicine. To develop more novel 2D materials, new nanolaminated structures are needed. Here we report on a tungsten-based nanolaminated ternary phase, (W,Ti)4C4- x, synthesized by an Al-catalyzed reaction of W, Ti, and C powders at 1600 °C for 4 h, under flowing argon. X-ray and neutron diffraction, along with Z-contrast scanning transmission electron microscopy, were used to determine the atomic structure, ordering, and occupancies. This phase has a layered hexagonal structure ( P63 /mmc) with lattice parameters, a = 3.00880(7) Å, and c = 19.5633(6) Å and a nominal chemistry of (W,Ti)4C4- x (actual chemistry, W2.1(1)Ti1.6(1)C2.6(1)). The structure is comprised of layers of pure W that are also twin planes with two adjacent atomic layers of mixed W and Ti, on either side. The use of Al as a catalyst for synthesizing otherwise difficult to make phases, could in turn lead to the discovery of a large family of nonstoichiometric ternary transition metal carbides, synthesized at relatively low temperatures and shorter times.

Correlation between spin transport signal and Heusler/semiconductor interface quality in lateral spin-valve devices

We show direct evidence for the impact of Heusler/semiconductor interfaces atomic structure on the spin transport signals in semiconductor-based lateral spin-valve (LSV) devices. Based on atomic scale Z-contrast scanning transmission electron microscopy and energy dispersive x-ray spectroscopy we show that atomic order/disorder of ${\mathrm{Co}}_{2}{\mathrm{FeAl}}_{0.5}{\mathrm{Si}}_{0.5}$ (CFAS)/$n$-Ge LSV devices is critical for the spin injection in Ge. By conducting a postannealing of the LSV devices, we find 90% decrease in the spin signal while there is no difference in the electrical properties of the $\mathrm{CFAS}\text{/}n$-Ge contacts and in the spin diffusion length of the $n$-Ge layer. We show that the reduction in the spin signals after annealing is attributed to the presence of intermixing phases at the Heusler/semiconductor interface. First-principles calculations show how that intermixed interface region has drastically reduced spin polarization at the Fermi level, which is the main cause for the significant decrease of the spin signal in the annealed devices above $300{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$.

Anisotropic Ordering in 1T' Molybdenum and Tungsten Ditelluride Layers Alloyed with Sulfur and Selenium.

Alloying is an effective way to engineer the band-gap structure of two-dimensional transition-metal dichalcogenide materials. Molybdenum and tungsten ditelluride alloyed with sulfur or selenium layers (MX2xTe2(1-x), M = Mo, W and X = S, Se) have a large band-gap tunability from metallic to semiconducting due to the 2H-to-1T' phase transition as controlled by the alloy concentrations, whereas the alloy atom distribution in these two phases remains elusive. Here, combining atomic resolution Z-contrast scanning transmission electron microscopy imaging and density functional theory (DFT), we discovered that anisotropic ordering occurs in the 1T' phase, in sharp contrast to the isotropic alloy behavior in the 2H phase under similar alloy concentration. The anisotropic ordering is presumably due to the anisotropic bonding in the 1T' phase, as further elaborated by DFT calculations. Our results reveal the atomic anisotropic alloyed behavior in 1T' phase layered alloys regardless of their alloy concentration, shining light on fine-tuning their physical properties via engineering the alloyed atomic structure.

3D analysis of semiconductor devices: A combination of 3D imaging and 3D elemental analysis

3D analysis of semiconductor devices using a combination of scanning transmission electron microscopy (STEM) Z-contrast tomography and energy dispersive spectroscopy (EDS) elemental tomography is presented. 3D STEM Z-contrast tomography is useful in revealing the depth information of the sample. However, it suffers from contrast problems between materials with similar atomic numbers. Examples of EDS elemental tomography are presented using an automated EDS tomography system with batch data processing, which greatly reduces the data collection and processing time. 3D EDS elemental tomography reveals more in-depth information about the defect origin in semiconductor failure analysis. The influence of detector shadowing and X-rays absorption on the EDS tomography's result is also discussed.

Highly Symmetric AB2 Framework Related to Tridymite in the Disordered Nitridosilicate La24Sr14-7x[Si36N72](O1-xFx)14 (x = 0.489).

La24Sr14-7x[Si36N72](O1-xFx)14 with x = 0.489 was obtained as a microcrystalline product by metathesis at 1500 °C in a radio-frequency furnace starting from Si(NH)2, La(NH2)3, SrH2, LaF3, and CeF3. The structure of the new nitridosilicate oxide fluoride was determined by combining transmission electron microscopy (TEM) and single-crystal X-ray diffraction using a microfocused synchrotron beam. The structure model with pronounced disorder [P63/mmc, Z = 1, a = 16.2065(3), c = 9.4165(1) Å, R1(obs) = 0.0436] was confirmed by electron diffraction and aberration-corrected Z-contrast scanning TEM. The highly symmetric AB2 framework, which was theoretically predicted but not yet realized, consists of all-side vertex-sharing SiN4 tetrahedra that form channels along [001] filled with La, Sr, O, and F atoms. The connectivity pattern is related to that of tridymite. X-ray spectroscopy and bond-valence-sum calculations were further taken into account for assignment of the N, O, and F atoms.

Strategy for reliable strain measurement in InAs/GaAs materials from high-resolution Z-contrast STEM images

Geometric phase analysis (GPA), a fast and simple Fourier space method for strain analysis, can give useful information on accumulated strain and defect propagation in multiple layers of semiconductors, including quantum dot materials. In this work, GPA has been applied to high resolution Z-contrast scanning transmission electron microscopy (STEM) images. Strain maps determined from different g vectors of these images are compared to each other, in order to analyze and assess the GPA technique in terms of accuracy. The SmartAlign tool has been used to improve the STEM image quality getting more reliable results. Strain maps from template matching as a real space approach are compared with strain maps from GPA, and it is discussed that a real space analysis is a better approach than GPA for aberration corrected STEM images.

Impact of Evolving Electrode Morphology on Fuel Cell Performance: From the Nano to Mesoscale

The performance of polymer electrolyte membrane fuel cells (PEMFCs) is primarily controlled by the materials within membrane electrode assemblies (MEAs), which consist of an anode and cathode separated by a proton-conducting membrane. Developing highly stable MEAs is one key to wide-spread commercialization of this clean energy technology. The electrodes consist of a complex hierarchal structure, which must be capable of simultaneously transporting hydrogen, protons, electrons, oxygen, and water to and way from the critical electrocatalytic active sites. In conventional PEMFCs, Pt serves as the active catalyst, and is sometimes alloyed with a transition metal such as Co or Ni to enhance activity or lower cost.[1] In non-platinum group metal (non-PGM) electrodes, the catalytically active site takes the form of Fe or Co metal-nitrogen-carbon (M-N-C) complexes.[2] In either case, understanding the evolution of these catalysts, and the complex support structures in which they reside, in relation to observed performance losses is essential for furthering fuel cell development. Scanning transmission electron microscopy (STEM) is an ideal analytical characterization tool for performing both pre- and post-mortem nano to mesoscale compositional and structural characterization of the individual material components in MEAs. STEM has been used to quantify key changes responsible for performance gains and losses during fuel cell conditioning and cycling.[3,4] These structural changes can vary widely in both extent and scale, from carbon-corrosion-related electrode thinning at the micron scale to dealloying-induced reordering on the surfaces of advanced Pt-alloy catalysts at the atomic scale. This presentation will focus on three topics spanning multiple length scales in the MEA. Beginning at the atomic scale, strain effects and skeleton structures arising from in situ Ni dealloying in Pt-alloy nanostructured thin films (NSTF) will be presented. The surface structure and composition is critical to electrocatalytic activity, and, as shown by the aberration-corrected Z-contrast STEM image in Fig. 1a, these structures can be resolved with atomic resolution. Changes in surface structure/strain will be studied as a function of fuel cell cycling and electrochemical activity. At the nanoscale, carbon support effects on Pt anchoring and agglomeration will be presented, highlighting the critical role that catalyst-support interactions and corrosion-resistant supports play in MEA durability (Fig. 1b). Finally, at the mesoscale, changes in electrode structure with aging in non-PGM MEAs will be presented, highlighting the key role that hierarchal pore structures (spanning the micro to macro) play in fuel cell performance. Complementary imaging and compositional mapping by energy dispersive X-ray spectroscopy, as shown in Fig. 1c, provide unique insight into how both changes in mechanical and chemical structure impact durability. References V. R. Stamenkovic et al., Nat. Mater. 6 (2007) 241.G. Wu, K. L. More, C. M. Johnston, P. Zeleany, Science 332 (2011) 443.D. A. Cullen et al., J. Mater. Chem. A, 3 (2015) 1660. B. Han et al., Energy Environ. Sci., 8, 258 (2015). Acknowledgements Research sponsored by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE) and ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility. Figure 1

Magnetic Annealing of Pt-Alloy Nanostructured Thin Film Catalysts

High field magnetic processing, in which materials are exposed to magnetic fields in excess of 9 Tesla (T), is a powerful technique for modifying microstructure and facilitating phase transformations [1,2]. In this work, the potential of high magnetic field annealing to produce highly active surface structures on Pt-alloy oxygen reduction reaction (ORR) catalysts is explored. The most active ORR catalysts consist of Pt alloyed with Fe, Co, and Ni, which are also the main ferromagnetic metals [3]. This innovative approach aims to exploit the magnetic properties of these alloys through high magnetic field annealing to modify catalyst surface structures, compositions, and properties under conditions which are both scalable and commercially viable. 3M’s Pt3Ni7 nanostructured thin films (NSTF) have been selected as the primary test structure for these experiments. Oak Ridge National Lab magnetic processing facility houses a horizontal superconducting magnet with an 5” diameter warm bore and uniform 9 T field strength over a 12” work zone that is coupled with a 9 kW commercial-scale induction heating system capable of heating to 2200oC. Figure 1 demonstrates the setup for these high magnetic field annealing experiments. Sections of Pt3Ni7 NSTF were heated to 400oC in either an inert (Ar) or reducing (H2) environment in the presence of a 9T field. The modified structures produced by magnetic annealing are under investigation by rotating disk electrode (RDE), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning transmission electron microscopy (STEM). Complementary secondary electron and Z-contrast STEM images are presented in Fig. 2 for various annealing conditions. These same structures will be studied following RDE characterization, as it has been shown that electrode conditioning/break-in in either RDE or in membrane electrode assemblies (MEA) can have significant impact on alloy catalyst morphology and composition [4]. The experimental thrust is accompanied by modeling efforts using screened Korringa-Kohn-Rostoker (SKKR) method, a density functional theory method ideal for modeling disordered alloy system. This fully relativistic, all-electron model will be used to calculate a wide range of physical properties, including d-band shifts, stability of new structures with respect to surface/bulk composition, and magnetic phase diagrams. Figure 1. (a) Schematic of magnetic annealing setup. Photographs of (b) 9T horizontal superconducting magnet, (c) gas delivery system for annealing in H2 and Ar gases Figure 2. (top) Secondary electron and (bottom) Z-contrast STEM images of Pt3Ni7 NSTF submitted to different annealing conditions, including high-field magnetic annealing. References Z. H. I. Sun, M. Guo, J. Vleugels, O. Van der Biest, B. Blanpain, Curr. Opin. Solid St. M., 16, 254 (2012).Y. Ma, L. Xiao, L. Yan, Chinese Sci. Bull., 51, 2944 (2006).V. R. Stamenkovic et al., Nat. Mater., 6, 241 (2007).B. Han et al., Energy Environ. Sci., 8, 258 (2015). Acknowledgements This work was supported by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy under the 2015 Lab Call and through a user project supported by ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility. Special thanks to A.J. Steinbach and D. van der Vliet of 3M for providing NSTF material and for helpful discussions. Figure 1

La3BaSi5N9O2:Ce3+ – A Yellow Phosphor with an Unprecedented Tetrahedra Network Structure Investigated by Combination of Electron Microscopy and Synchrotron X-ray Diffraction

Due to the relationship between structure and luminescence properties, detailed crystal structure determination for microcrystalline phosphors is necessary for a profound understanding of materials properties. The yellow phosphor La3BaSi5N9O2:Ce3+ (λmax = 578 nm; fwhm ∼4700 cm–1) was characterized by a combination of transmission electron microscopy (TEM) and synchrotron microfocus diffraction as only agglomerates of crystals with a maximum size of a few μm could be obtained yet. La3BaSi5N9O2:Ce3+ was synthesized from LaF3, La(NH2)3, BaH2, Si(NH)2, and CeF3 in a radio frequency furnace. It crystallizes in space group Pmn21 (no. 31) with a = 9.5505(8), b = 19.0778(16), c = 12.1134(9) A, and Z = 8. Its interrupted three-dimensional tetrahedra network contains zehner and dreier rings of vertex-sharing SiN4 and SiN2O2 tetrahedra. The crystal structure was confirmed by high-resolution TEM and Z-contrast scanning TEM. The element distribution was derived by bond-valence sum calculations. The infrared spectrum p...

Deep ultraviolet distributed Bragg reflectors based on graded composition AlGaN alloys

Distributed Bragg reflectors (DBRs) with peak reflectivity at approximately 280 nm, based on compositionally graded AlxGa1−xN alloys, were grown on 6H-SiC substrates by plasma-assisted molecular beam epitaxy. DBRs with square, sinusoidal, triangular, and sawtooth composition profiles were designed with the transfer matrix method. The crystal structure of these DBRs was studied with high-resolution x-ray diffraction of the (1¯015) reciprocal lattice point. The periodicity of the DBR profiles was confirmed with cross-sectional Z-contrast scanning transmission electron microscopy. The peak reflectance of these DBRs with 15.5 periods varies from 77% to 56% with corresponding full width at half maximum of 17–14 nm. Coupled mode analysis was used to explain the dependence of the reflectivity characteristics on the profile of the graded composition.

Low-Frequency Raman Fingerprints of Two-Dimensional Metal Dichalcogenide Layer Stacking Configurations.

The tunable optoelectronic properties of stacked two-dimensional (2D) crystal monolayers are determined by their stacking orientation, order, and atomic registry. Atomic-resolution Z-contrast scanning transmission electron microscopy (AR-Z-STEM) and electron energy loss spectroscopy (EELS) can be used to determine the exact atomic registration between different layers, in few-layer 2D stacks; however, fast optical characterization techniques are essential for rapid development of the field. Here, using two- and three-layer MoSe2 and WSe2 crystals synthesized by chemical vapor deposition, we show that the generally unexplored low frequency (LF) Raman modes (<50 cm(-1)) that originate from interlayer vibrations can serve as fingerprints to characterize not only the number of layers, but also their stacking configurations. Ab initio calculations and group theory analysis corroborate the experimental assignments determined by AR-Z-STEM and show that the calculated LF mode fingerprints are related to the 2D crystal symmetries.

Unexpected bismuth concentration profiles in metal-organic vapor phase epitaxy-grown Ga(As1−xBix)/GaAs superlattices revealed by Z-contrast scanning transmission electron microscopy imaging

A set of GaAs1−xBix/GaAs multilayer quantum-well structures was deposited by metal-organic vapor phase epitaxy at 390 °C and 420 °C. The precursor fluxes were introduced with the intent of growing discrete and compositionally uniform GaAs1−xBix well and GaAs barrier layers in the epitaxial films. High-resolution high-angle annular-dark-field (or “Z-contrast”) scanning transmission electron microscopy imaging revealed concentration profiles that were periodic in the growth direction, but far more complicated in shape than the intended square wave. The observed composition profiles could explain various reports of physical properties measurements that suggest compositional inhomogeneity in GaAs1−xBix alloys as they currently are grown.

S–Te Interdiffusion within Grains and Grain Boundaries in CdTe Solar Cells

At the CdTe/CdS interface, a significant Te–S interdiffusion has been found a few nanometers into the CdTe grain interiors with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy. This interdiffusion happens on both as-grown and CdCl2-treated CdTe. S substitution at Te sites has been directly resolved in CdTe with STEM Z-contrast images, which further confirms the S diffusion into CdTe grain interiors. Moreover, when a sufficient amount of S substitutes for Te, a structural transformation from zinc-blende to wurtzite has been observed. In the CdCl2-treated CdTe, Cl segregation has also been found at the interface. STEM electron-beam-induced current shows that the p-n junction occurs a few namometers into the CdTe grains, which is consistent with the S diffusion range we observe. The shift of the p-n junction suggests a buried homojunction which would help reduce nonradiative recombination at the junction. Meanwhile, long-range S diffusion in CdTe grain boundaries (GBs) has been detected, as has Te and Cl diffusion in CdS GBs.

Observation of atomic ordering of triple-period-A and -B type in GaAsBi

We report the observation of atomic ordering of triple-period (TP)-A and -B type in low temperature (LT) grown GaAsBi alloy using transmission electron microscopy (TEM). In addition to previous reports, where only TP-A ordering was identified in III-V alloys, here, we confirm by electron diffraction, high-resolution (HR) TEM, and HR Z-contrast scanning TEM that two ordering variants coexists for LT-GaAsBi. We find that the TP-A ordering variant dominates over the TP-B variant. TP-A domains extend over 50–100 nm (projected lateral width) and are of higher perfection compared to TP-B domains. HR Z-contrast scanning TEM on different domains reveals a variation in the Bi occupancy in the {111} planes with triple period sequence. Since the formation of ordered phases has been directly linked to the occurrence of specific surface reconstructions, our results suggest a correlation between the TP-A and B type domains and the multiple stability of n × 3 and 3 × n reconstructions on the (001) surface of GaAsBi under low temperature growth.

Correlations between atomic structure and giant magnetoresistance ratio in Co2(Fe,Mn)Si spin valves

We show that the magnetoresistance of Co2FexMn1−xSi-based spin valves, over 70% at low temperature, is directly related to the structural ordering in the electrodes and at the electrodes/spacer (Co2FexMn1−xSi/Ag) interfaces. Aberration-corrected atomic resolution Z-contrast scanning transmission electron microscopy of device structures reveals that annealing at 350 °C and 500 °C creates partial B2/L21 and fully L21 ordering of electrodes, respectively. Interface structural studies show that the Ag/Co2FexMn1−xSi interface is more ordered compared to the Co2FexMn1−xSi/Ag interface. The release of interface strain is mediated by misfit dislocations that localize the strain around the dislocation cores, and the effect of this strain is assessed by first principles electronic structure calculations. This study suggests that by improving the atomic ordering and strain at the interfaces, further enhancement of the magnetoresistance of CFMS-based current-perpendicular-to-plane spin valves is possible.

New Insights into the adsorption of aurocyanide ion on activated carbon surface: electron microscopy analysis and computational studies using fullerene-like models.

Despite decades of concerted experimental studies dedicated to providing fundamental insights into the adsorption of aurocyanide ion, Au(CN)2(-), on activated carbon (AC) surface, such a mechanism is still poorly understood and remains a contentious issue. This adsorption process is an essential unit operation for extracting gold from ores using carbon-in-pulp (CIP) technology. We hereby attempt to shed more light on the subject by employing a range of transmission electron microscopy (TEM) associated techniques. Gold-based clusters on the AC surface are observed by Z-contrast scanning TEM imaging and energy-filtered TEM element mapping and are supported by X-ray microanalysis. Density functional theory (DFT) calculations are applied to investigate this adsorption process for the first time. Fullerene-like models incorporating convex, concave, or planar structure which mimic the eclectic porous structures on the AC surface are adopted. Pentagonal, hexagonal, and heptagonal arrangements of carbon rings are duly considered in the DFT study. By determining the favored adsorption sites in water environment, a general adsorption trend of Au(CN)2(-) adsorbed on AC surface is revealed whereby concave > convex ≈ planar. The results suggest a tendency for Au(CN)2(-) ion to adsorb on the carbon sheet defects or edges rather than on the basal plane. In addition, we show that the adsorption energy of Au(CN)2(-) is approximately 5 times higher than that of OH(-) in the alkaline environment (in negative ion form), compared to only about 2 times in acidic environment (in protonated form), indicating the Au extraction process is much favored in basic condition. The overall simulation results resolve certain ambiguities about the adsorption process for earlier studies. Our findings afford crucial information which could assist in enhancing our fundamental understanding of the CIP adsorption process.