Well-defined Surface Structures Research Articles

Atomically dispersed ruthenium in transition metal double layered hydroxide as a bifunctional catalyst for overall water splitting

Efficient and sustainable energy conversion depends on the rational design of single-atom catalysts. The control of the active sites at the atomic level is vital for electrocatalytic materials in alkaline and acidic electrolytes. Moreover, fabrication of effective catalysts with a well-defined surface structure results in an in-depth understanding of the catalytic mechanism. Herein, a single atom ruthenium dispersed in nickel-cobalt layered hydroxide (Ru-NiCo LDH) is reported. Through the precise controlling of the atomic dispersion and local coordination environment, Ru-NiCo LDH//Ru-NiCo LDH provides an ultra-low overpotential of 1.45 mV at 10 mA cm−2 for the overall water splitting, which surpasses that of the state-of-the-art Pt/C/RuO2 redox couple. Density functional theory calculations show that Ru-NiCo LDH optimizes hydrogen evolution intermediate adsorption energies and promotes O-O coupling at a Ru-O active site for oxygen evolution, while Ni serves as the water dissociation site for effective water splitting. As a potential model, Ru-NiCo LDH shows enhanced water splitting performance with potential for the development of promising water-alkaline catalysts.

Efficient reduction of photopolymerization shrinkage stress through microporous particles templated from Pickering emulsion droplets

Photopolymerization of acrylate based resin is a rapid, efficient and low-energy curing process that is achieving wide applications in many industrial fields. However, the volumetric shrinkage and the shrinkage stress of the cured resin have long been the major factor reduces adhesion strength of UV curable coatings onto the substrate. In this paper, the Pickering emulsion template method is employed to prepare elastic microporous particles with well-defined surface and internal structures and these microporous particles are thus added into the UV curable resin formulation to verify their capability to reduce polymerization stress through the microporous structure. The gel point time of UV-curable materials is delayed by 11 s with 1.5 wt% addition of the microporous particles and the double bond conversion at the gel point is subsequently increased. By real time MIR-photo-rheology and 3D line scanning laser confocal measurement, it is found that addition of microporous particles into the resin formulation can reduce the volume shrinkage of the resin by 61.2 % with only 1.5 wt% microporous particles, while the excellent mechanical and thermal properties of the cured resin is basically maintained.

Acrylonitrile Butadiene Styrene/Thermoplastic Polyurethane Blends for Material Extrusion Three-Dimensional Printing: Effects of Blend Composition on Printability and Properties.

Blend filaments of acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU) were prepared at different weight ratios, i.e., 100:0, 70:30, 50:50, 30:70, and 0:100, for FDM printing; the prepared filaments, with an average diameter of 2.77 ± 0.19 mm, were encoded as A100, A70T30, A50T50, A30T70, and T100, respectively. The properties and printability of the filaments were thoroughly investigated. The blend composition, as well as the printing parameters, were optimized to obtain the FDM-printed objects with a well-defined surface structure and minimized warpages. The glass transition temperatures of ABS and TPU in the blends were not much altered from those of the parent filaments, whereas the thermal degradation characteristics of the blend filaments still fell between those of the neat filaments. The fractured surfaces of the filaments, observed by SEM, appeared smoother when higher amounts of TPU integrated; the smoothest surface of the ABS-based filament was found in A30T70, indicating the well-compatible blend characteristic. This was also confirmed by its rheological behavior examined by a parallel plate rheometer at 225 °C. Not only was the printability of the filaments improved, but also the warpages of the 3D-printed specimens were decreased when increasing amount of TPU was incorporated into the filaments. Among the printed objects, the A30T70 specimen exhibited the evenest surface morphology with the lowest surface roughness value of 32.9 ± 13.2 nm and the most uniform and consistent linear printing structure when being fabricated at the nozzle temperature of 225 °C and the printing bed temperature of 60 °C. However, the incorporation of TPU into the filaments markedly cut down both strength and modulus values of the fabricated materials up to about half but assisted the printed articles to absorb more energy, demonstrating that this polymer served as a good and effective toughener for ABS.

Highly Effective Electrochemical Water Splitting with Enhanced Electron Transfer between Ni2Co Layered Double Hydroxide Nanosheets Dispersed on Carbon Substrate

A reasonable design of nickel-based catalysts is key to efficient and sustainable energy conversion. For electrocatalytic materials in alkaline electrolytes, however, atomic-level control of the active sites is essential. Moreover, the well-defined surface structure contributes to a deeper understanding of the catalytic mechanism. Here, we report the loading of defective nickel–cobalt layered double hydroxide nanosheets (Ni2Co-LDH@C) after carbonization of silk. Under the precise regulation of the local coordination environment of the catalytic active site and the presence of defects, Ni2Co-LDH@C can provide an ultra-low overpotential of 164.8 mV for hydrogen evolution reactions (HERs) at 10 mA cm−2, exceeding that of commercial Pt/C catalysts. Density functional theory calculations show that Ni2Co-LDH@C optimizes the adsorption energy of the intermediate and promotes the O-O coupling of the active site in the oxygen evolution reaction. When using Ni2Co-LDH@Cs as cathodes and anodes to achieve overall water splitting, a low voltage of 1.63 V is required to achieve a current density of 10 mA cm−2. As an ideal model, Ni2Co-LDH@C has excellent water splitting properties and has the potential to develop water–alkali electrocatalysts.

Uniform Catalytic Nanocrystals: From Model Catalysts to Efficient Catalysts

ConspectusSolid catalysts play a key role in the chemical industry, energy, and the environment. Fundamental understanding of heterogeneous catalysis exerted by solid surfaces is useful for structural designs of efficient catalysts but is challenging due to the complexity. Emerging uniform catalytic nanocrystals (NCs) with controlled and well-defined surface structures have brought new opportunities for fundamental understanding and directed explorations of efficient catalysts. In a previous Account ( Acc. Chem. Res. 2016, 49, 520−527), I postulated and exemplified a concept of oxide nanocrystal model catalysts for the fundamental investigations of oxide catalysis without the “materials gap” and “pressure gap” which are often encountered using the traditional single crystal model catalysts. In this Account, I summarize our effort in fabricating efficient uniform nanocrystal catalysts based on the fundamental understanding of structure–activity relations and reaction mechanisms acquired by oxide nanocrystal model catalyst studies. Directed by the fundamental understanding that the Cu2O{110} facet is active in catalyzing propylene epoxidation with O2 and the fine Cu2O nanocube exposes high densities of Cu2O{110} edge sites, we successfully explore fine Cu2O nanocubes as a highly selective catalyst for propylene epoxidation with O2. Directed by the fundamental understanding that the Cu{100} facet is the active Cu facet in catalyzing the water–gas shift (WGS) reaction, we successfully fabricate a highly active ZnO/fine Cu nanocube WGS catalyst with enhanced ZnO-CuCu{100} active site density. Directed by the fundamental understanding of TiO2 facet effects on the surface band bending and adsorbate–surface interfacial energy level alignment, and consequent photocatalytic performance, we successfully fabricate highly active TiO2{001} NC-based photocatalysts for photocatalytic CH4 conversions. These results adequately exemplify the concept of fundamental understanding-directed explorations of efficient catalysts following a strategy of “identification of active site structure + maximization of active site density”, which, together with the advancement of controlled-synthesis methods, is expected to greatly accelerate the explorations of novel and efficient catalysts in future.

Optimised diamond to graphite conversion via a metastable sp1-bonded carbon chain formation under an ultra-short femtosecond (30 fs) laser irradiation

An application of an ultra-short femto-second (fs) pulsed laser (30 fs, 800 nm, 1 kHz) radiation under a simultaneously varied laser fluence (0.6, 1.2 and 1.8 J/cm2) and number of pulses (2000–32,000 pulses per irradiation site) to process diamond has been investigated to determine an optimal conversion of the diamond's tetrahedral sp3 phase into an aromatic sp2 phase with a high degree of crystallinity and without a formation of an sp2 olefinic fraction, thermal damage or an irradiation-induced surface cracking. The highest sp2 aromatic crystallinity and the most significant sp3-to-sp2 conversion efficiency in diamond was attained at 1.2 J/cm2 with 32,000 pulses. The sp3-to-sp2 phase transition was marked by a formation of a metastable carbon in the sp1 hybridisation (carbyne), evidenced by the characteristic Raman mode at ca. 2065 cm−1. Inclusions of covalently bound carbonyl (-CO) at ca. 1705 cm−1 were also observed on diamond under lower irradiation doses. Both the sp1 and carbonyl contributions resolved gradually as irradiation dose increased. Well-defined laser-induced periodic surface structures (LIPSS) (aka. nano-ripples) with a high spatial frequency distribution and periodicity of around 100 nm were observed forming in the irradiated regions on diamond owing to the interaction of the laser pulse with the surface plasmons; an ordered and homogeneous formation of LIPSS structures has been observed at 1.2 J/cm2 with 8000 pulses. The impact and implications of these findings on the design and development of future ‘all-carbon’ devices by means of a direct non-ablative fs laser processing of diamond are discussed.

Electrical double layer design for proton-coupled electron transfer electrode processes: Recent advances in well-defined Electrode–Electrolyte interface

Understanding the roles of the electrical double layer (EDL) structure in proton-coupled electron transfer (PCET) electrode processes is important for designing high-performance electrode and electrolyte materials. Here, we highlight the recent advances in the electrocatalytic PCET processes at well-defined electrode−electrolyte interfaces. Non-covalent interaction, which is regulated by the cation/anion features, is known to play a pivotal role in the interfacial water and adsorbate environments correlated to electrocatalytic properties since the seminal and continuous studies made by Frumkin and his colleagues initiated in 1930s. However, the microscopic view on this interaction is still a representative enigma in modern science. Recent studies using single-crystal model electrodes uncovered unconventional aspects of the cation effect based on the well-defined surface and solid-liquid interfacial structure. Furthermore, recent developments in EDL structure design based on functional ions and molecules offer several strategies to achieve highly efficient electrode−electrolyte systems.

Zn2+–Modulated bimetallic carbides synergized with macro-mesoporous N-rich carbon enabling accelerated polysulfides conversion for high-performance Li-S batteries

• Zn 2+ modulated Co 3 ZnC-based catalysts are constructed via a one-pot approach. • Zn 2+ could regulate the valence states of the cobalt active sites. • Co 3 ZnC@NC interlayer can promote the adsorption and redox kinetic of polysulfides. • Co 3 ZnC@NC contributes to superb cycling capacities and high-rate performance. Metal cations could serve as the active sites to adsorb lithium polysulfides (LiPSs) and catalyze the associated multi-electrons redox reactions. Valence modulating/engineering of the metal active centers is an underlying tactic to expedite the sluggish kinetics of LiPSs for high performance lithium-sulfur (Li-S) batteries. Herein, we craft Zn 2+ -modulated bimetallic carbides electrocatalyst of Co 3 ZnC-embedded carbon submicrospheres anchoring on 3D macro-mesoporous N-doped carbon (denoted as Co 3 ZnC@NC) via a facile one-pot synthesis that employs dicyandiamide as the carbon/nitrogen precursor. Results demonstrate that the balance of the predominantly active Co 2+ /Co 0 pair can be effectively modulated by the incorporated zinc cations, which leads to inhibited shuttle effect and accelerates the catalytic conversion kinetics of LiPS intermediates. When acted as the interlayer to modify commercial separator, Co 3 ZnC@NC confers the superb cycling stability on corresponding Li-S batteries with high discharge capacities and exceptionally high-rate performance, owing to the well-defined surface structure and the increased Co 2+ active sites of Co 3 ZnC@NC. Even the sulfur loading is kept at 4 mg cm −2 , the battery achieves an areal capacity of 3.22 mAh cm −2 after 50 cycles. This work unveils the potential of cation modulated bimetal-based electrocatalysts and also inspires an alternative avenue to exploit surface-mediated redox electrocatalysts for high-performance Li-S batteries.

Atomically unraveling the dependence of surface microstructure on plasmon-induced hydrogen evolution on Au/SrTiO3

Strong light-matter interaction and coupled catalytic surface in plasmonic photocatalysts offer a unique opportunity for solar-to-chemical energy conversion. The interface/surface engineering is significant strategy to modulate the performance of plasmon-induced water splitting. This situation motivates the demand of a plasmonic heterostructure with well-defined atomic surface structures but identical bulk structure for plasmon-induced water splitting. In this work, using Au/SrTiO3 as a prototype, we found that altering the Ti-terminated and Sr-terminated surface of SrTiO3 gives rise to a remarkable difference in plasmon-induced hydrogen evolution activity. The efficiency of charge separation at the Sr-terminated surface is inferior compared with which at the Ti-terminated structure, while the reaction kinetics of Sr-terminated surfaces is faster than the counterpart, thus leading to a high plasmon-induced hydrogen evolution performance at Au/ SrTiO3 with surfaces of Sr-termination. Modulation of the interface/surface structure of Au/SrTiO3 changes not only charge separation but surface catalysis in plasmonic photocatalysts, where the catalysis process dominates the final photocatalytic performance. This work paves a way to design efficient plasmonic photocatalysts for solar-to-chemical energy conversion.

Engineering single-atomic ruthenium catalytic sites on defective nickel-iron layered double hydroxide for overall water splitting

Rational design of single atom catalyst is critical for efficient sustainable energy conversion. However, the atomic-level control of active sites is essential for electrocatalytic materials in alkaline electrolyte. Moreover, well-defined surface structures lead to in-depth understanding of catalytic mechanisms. Herein, we report a single-atomic-site ruthenium stabilized on defective nickel-iron layered double hydroxide nanosheets (Ru1/D-NiFe LDH). Under precise regulation of local coordination environments of catalytically active sites and the existence of the defects, Ru1/D-NiFe LDH delivers an ultralow overpotential of 18 mV at 10 mA cm−2 for hydrogen evolution reaction, surpassing the commercial Pt/C catalyst. Density functional theory calculations reveal that Ru1/D-NiFe LDH optimizes the adsorption energies of intermediates for hydrogen evolution reaction and promotes the O–O coupling at a Ru–O active site for oxygen evolution reaction. The Ru1/D-NiFe LDH as an ideal model reveals superior water splitting performance with potential for the development of promising water-alkali electrocatalysts.

Identifying and Engineering Active Sites at the Surface of Porous Single-Crystalline Oxide Monoliths to Enhance Catalytic Activity and Stability

Identifying and engineering active sites play a key role in many catalytic reactions. Herein, we create well-defined surface structures through the growth of porous single-crystalline Mn3O4 and Mn2...

How the anisotropy of surface oxide formation influences the transient activity of a surface reaction

Scanning photoelectron microscopy (SPEM) and photoemission electron microscopy (PEEM) allow local surface analysis and visualising ongoing reactions on a µm-scale. These two spatio-temporal imaging methods are applied to polycrystalline Rh, representing a library of well-defined high-Miller-index surface structures. The combination of these techniques enables revealing the anisotropy of surface oxidation, as well as its effect on catalytic hydrogen oxidation. In the present work we observe, using locally-resolved SPEM, structure-sensitive surface oxide formation, which is summarised in an oxidation map and quantitatively explained by the novel step density (SDP) and step edge (SEP) parameters. In situ PEEM imaging of ongoing H2 oxidation allows a direct comparison of the local reactivity of metallic and oxidised Rh surfaces for the very same different stepped surface structures, demonstrating the effect of Rh surface oxides. Employing the velocity of propagating reaction fronts as indicator of surface reactivity, we observe a high transient activity of Rh surface oxide in H2 oxidation. The corresponding velocity map reveals the structure-dependence of such activity, representing a direct imaging of a structure-activity relation for plenty of well-defined surface structures within one sample.

The influence of modifying nanoflower and nanostar type Pd coatings on low temperature hydrogen permeability through Pd-containing membranes

Methodsof modifying the surface of Pd–23%Ag alloy films have been developed in order to increase the rate of hydrogen permeability and to produce palladium-containing nanostar and nanoflower type coatings. Modifying coatings have been synthesized by electrolytic deposition at a reduced current density compared to classical methods. Low current densities affect the formation of pentagonally structured surface modifiers. The low deposition rate of Pd and Ag particles on a thin palladium-silver film allows them to line up in clearly defined structures, probably due to the properties of the surfactant used. The methods developed for modifying palladium-containing membranes makes it possible to create palladium nanostructures not only with a well-defined surface structure, but also with morphologies that have never been achieved by other approaches. Modification of the membrane surface makes it possible to measure the permeability in the temperature range up to 100°С. Membranes modified with nanoflower and nanostar type pentagonally branched crystallites show a hydrogen flux of up to 0.008 mol s−1 m−2 and up to 0.01 mol s−1 m−2 at a pressure of 0.3 MPa in the low temperature range (<100 °C). The hydrogen flux for membranes modified by such coatings is twice as much as the flux of hydrogen through membranes modified by the classical palladium black method, despite the fact that the latter is slightly more developed. The results obtained during the experiment may indicate that the contribution to the increase in activity and consequently the increase in the hydrogen permeability rate through the membrane that is in a stage of surface limitation by surface effects is made not only by the increased surface area but also by the structural organization characteristics of the membrane modifying layer.

Intelligent composite foam with reversible tunable superwettability for efficient and sustainable oil/water separation and high-concentration organic wastewater purification

Design and development of robust and advanced separation materials with superwettability for efficient oil/water separation are of great interest and significance because of the increasing serious oil pollution problems. Herein, we have fabricated a copper foam-based superwettable membrane material with intelligent switchable wettability, favorable durability and corrosion resistance via a facile and scalable method. Benefitting from the synergetic effect of the well-defined hierarchical 3D porous surface structure and appropriate chemistry containing pH responsive groups, the resulting superwettable material can exhibit two distinct durable surface wettabilities via pH-triggered change of dominant functional groups on its surface. By virtue of the reversible tunable superwettability, the as-prepared material is successfully exploited for intelligent and sustainable separation of multiple oil/water mixtures, especially the complex crude oil/water mixture and high concentration organic wastewater, showing superior separation performance, favorable oil/organic solvents recoverability and durability. It is well known that the application of superwettable membranes in treating complex chemical systems has been seldom reported in current works. Therefore, it is believed that the intelligent superwettable material can be widely scaled up to various oily wastewater treatment and oil spills cleanup, which will be of great significance for practical potential applications and sustainable development of ecological environment.

Mesoporous carbon materials with enantioselective surface obtained by nanocasting for selective adsorption of chiral molecules from solution and the gas phase

Separation of enantiomers is an everlasting challenge in chemistry, catalysis, and synthesis of pharmaceuticals. The design and fabrication of chiral adsorbent materials is a promising way to increase the surface area of chiral information, as well as to maximize the available surface for the adsorption of one enantiomer. Porous materials such as silica or metal-organic-frameworks are established compounds in this field, due to their well-defined surface structure and ease of functionalization with chiral groups. As another class of porous materials, carbons provide the advantages of high thermal and chemical stability, resistance against moisture, electrical conductivity, and widely tunable pore size. Although they are well established in many adsorption-related applications, carbons received far less attention in enantioselective adsorption processes because the controlled functionalization of their surface is rather difficult due to the chemically heterogeneous atoms in the network. A suitable approach to overcome this limitation is the synthesis of chiral carbons directly from chiral precursors. So far, chiral carbons synthesized from chiral precursors used salt-templating as a way of introducing porosity, which resulted in mainly microporous materials or materials with broad pore size distribution. In the present study, the possibility of combining nanocasting as an alternative templating approach with chiral ionic liquids as a carbon precursor is demonstrated. Chiral recognition is measured in the gas phase, by adsorption of chiral gas, as well as in the solution, by using isothermal titration calorimetry.

Fabrication of homogenous subwavelength grating structures on metallic glass using double-pulsed femtosecond lasers

We report a formation of highly homogenous subwavelength grating structures on the bulk Fe-based metallic glass, using two nondegenerate linear polarization of femtosecond laser pulse sequences at certain temporal delays. In contrast to the previous observations, the well-defined surface structures can take place across the entire laser ablation regions, with the spatial period and the modulation depth of 722 nm and 115 nm, respectively. Through the Fourier transformation analysis, we introduce two parameters to quantitatively evaluate the structure uniformity. The underlying mechanisms are attributed to the surface scattered wave of the second femtosecond laser pulse onto the transient material surface tailored by the first laser pulse. Moreover, different diffusion coefficients of the chemical elements are found responsible for their various removal percentages after laser irradiation.

Interfacial Superconductivity in FeSe Ultrathin Films on SrTiO_{3} Probed by InSitu Independently Driven Four-Point-Probe Measurements.

We investigated the superconducting transport properties of the one-unit-cell FeSe ultrathin films epitaxially grown on undoped SrTiO_{3}(001) (STO) with a well-defined surface structure by insitu independently-driven four-point-probe measurements. Our results unambiguously revealed the detection of the two-dimensional electrical conduction of the films without parallel conduction through the underlying substrate, both in the normal and superconducting states. The monolayer film exhibited a superconducting transition at an onset temperature of 40K. Surprisingly, the onset of superconductivity was constantly observed at 40K even for three- and five-unit-cell-thick FeSe films, even though the normal resistivity decreased with increasing thickness. These results agree with the picture of the interfacial superconductivity, where only the FeSe/STO interface and/or the adjacent first layer of FeSe becomes superconducting while the upper layers stay in the normal metallic state. The observed T_{c} is much lower than that reported by a previous in situ transport measurement for FeSe/Nb:STO but consistent with the results obtained by exsitu measurements for FeSe-undoped STO with a capping layer. This suggests that the capping layer is not an essential factor to limit T_{c}. We rather propose that the charge transfer from the doped substrate has a key role to achieve the higher temperature superconductivity in the one-unit-cell FeSe.

Laser ablation and structuring of CdZnTe with femtosecond laser pulses

We report an experimental investigation on laser ablation and associated surface structuring of CdZnTe by femtosecond Ti:Sa laser pulses (laser wavelength λ≈800 nm, ≈35 fs, 10 Hz), in air. By exploiting different static irradiation conditions, the fluence threshold and the incubation effect in CdZnTe are estimated. Interestingly, surface treatment with a low laser fluence (laser pulse energy E≈5-10 μJ) and number of shots (5≤ N ≤50) show the formation of well-defined cracks in the central part of the shallow crater, which is likely associated to a different thermal expansion coefficients of Te inclusions and matrix during the sample heating and cooling processes ensuing femtosecond laser irradiation. Irradiation with a larger number of pulses (N≈500, 1000) with higher pulse energies (E≈30-50 μJ) results in the formation of well-defined laser-induced periodic surface structures (LIPSS) in the outskirts of the main crater, where the local fluence is well below the material ablation threshold. Both low spatial frequency and high spatial frequency LIPSS perpendicular to the laser polarization are found together and separately depending on the irradiation condition. These are ascribed to a process of progressive aggregation of randomly distributed nanoparticles produced during laser ablation of the deep crater in the region of the target irradiated by a fluence below the ablation threshold with many laser pulses.

Tuning the period of femtosecond laser induced surface structures in steel: From angled incidence to quill writing

Exposure of metal surfaces to multiple ultrashort laser pulses under certain conditions leads to the formation of well-defined periodic surface structures. We show how the period of such structures in steel can be tuned over a wide range by controlling the complex interaction mechanisms triggered in the material. Amongst the different irradiation parameters that influence the properties of the induced structures, the angle of incidence of the laser beam occupies a prominent role. We present an experimental and theoretical investigation of this angle dependence in steel upon irradiation with laser pulses of 120 fs duration and 800 nm wavelength, while moving the sample at constant speed. Our findings can be grouped into two blocks. First, we observe the spatial coexistence of two different ripple periods at the steel surface, both featuring inverse scaling upon angle increase, which are related to forward and backward propagation of surface plasmon polaritons. To understand the underlying physical phenomena, we extend a recently developed model that takes into account quantitative properties of the surface roughness to the case of absorbing metals (large imaginary part of the dielectric function), and obtain an excellent match with the experimentally observed angle dependence. As second important finding, we observe a quill writing effect, also termed non-reciprocal writing, in form of a significant change of the ripple period upon reversing the sample movement direction. This remarkable phenomenon has been observed so far only inside dielectric materials and our work underlines its importance also in laser surface processing. We attribute the origin of symmetry breaking to the non-symmetric micro- and nanoscale roughness induced upon static multiple pulse irradiation, leading to non-symmetric modification of the wavevector of the coupled surface plasmon polariton.

Electronic properties of GaAsBi(001) alloys at low Bi content

Despite its potential in the fields of optoelectronics and topological insulators, experimental electronic band structure studies of Bi-doped GaAs are scarce. The reason is the complexity of growth which tends to leave bulk and in particular surface properties in an undefined state. Here we present an in depth investigation of structural and electronic properties of GaAsBi epilayers grown by molecular beam epitaxy with high (001) crystalline order and well-defined surface structures evident from low-energy electron diffraction. X-ray and ultraviolet photoemission spectrocopy as well as angle-resolved photoemission data at variable photon energies allows to disentangle a Bi-rich surface layer with $(1\times3)$ symmetry from the effects of Bi atoms incorporated in the GaAs bulk matrix. The influence of Bi concentrations up to $\approx 1$\% integrated in the GaAs bulk are visible in angle-resolved photoemission spectra after mild ion bombardment and subsequent annealing steps. Interpretation of our results is obtained via density functional theory simulations of bulk and $\beta 2(2\times 4)$ reconstructed slab geometries with and without Bi. Bi-induced energy shifts in the dispersion of GaAs heavy and light hole bulk bands are evident both in experiment and theory, which are relevant for modulations in the optical band gap and thus optoelectronic applications.