Controllable Doping Research Articles

Epitaxial Growth of Ga2O3: A Review.

Beta-phase gallium oxide (β-Ga2O3) is a cutting-edge ultrawide bandgap (UWBG) semiconductor, featuring a bandgap energy of around 4.8 eV and a highly critical electric field strength of about 8 MV/cm. These properties make it highly suitable for next-generation power electronics and deep ultraviolet optoelectronics. Key advantages of β-Ga2O3 include the availability of large-size single-crystal bulk native substrates produced from melt and the precise control of n-type doping during both bulk growth and thin-film epitaxy. A comprehensive understanding of the fundamental growth processes, control parameters, and underlying mechanisms is essential to enable scalable manufacturing of high-performance epitaxial structures. This review highlights recent advancements in the epitaxial growth of β-Ga2O3 through various techniques, including Molecular Beam Epitaxy (MBE), Metal-Organic Chemical Vapor Deposition (MOCVD), Hydride Vapor Phase Epitaxy (HVPE), Mist Chemical Vapor Deposition (Mist CVD), Pulsed Laser Deposition (PLD), and Low-Pressure Chemical Vapor Deposition (LPCVD). This review concentrates on the progress of Ga2O3 growth in achieving high growth rates, low defect densities, excellent crystalline quality, and high carrier mobilities through different approaches. It aims to advance the development of device-grade epitaxial Ga2O3 thin films and serves as a crucial resource for researchers and engineers focused on UWBG semiconductors and the future of power electronics.

Defect Control of Donor Doping on Dielectric Ceramics to Improve the Colossal Permittivity and Temperature Stability

As the demand for miniaturization of electronic devices increases, ceramics with an ABO3 structure require further improvement of the dielectric constant with high permittivity. In the present work, Ba1−1.5xBixTiO3 (BB100xT, x = 0.0025, 0.005, 0.0075, 0.01) ceramics were prepared via a solid-state reaction process. The effect of Bi doping on dielectric properties of lead-free relaxor ferroelectric BaTiO3-based ceramics was studied. The results showed that both colossal permittivity (37,174) and a temperature stability of TCC ≤ ±15% (−27–141 °C) were achieved in BB100xT ceramics at x = 0.5%. The A-site donor doping produces A-site vacancies, a larger space for Ti4+, and fluctuation of the component, which is partially responsible for the high permittivity and responsible for the temperature stability. Meanwhile, the contribution of defect dipoles, and IBLC and SBLC effects to polarization leads to the colossal permittivity. The formation of a liquid phase during sintering promotes mass transfer when the doping content is higher than 0.5%. This work benefits the exploration of novel multilayer ceramic capacitors with colossal permittivity and temperature stability via defect engineering.

Enhanced As(OH)3 adsorption by anatase TiO2 through facet control and Fe, N dual doping: A DFT+D3 study

Anatase and rutile, two major polymorphs of TiO2, have been used widely for environmental remediation, while anatase is apparently less effective for As(III) pollution management and needs substantial improvement. Herein, DFT calculations show that (001) rather than (101) and (100) facets of anatase are highly selective for As(III) adsorption. Facet control plays critical role during As(III) adsorption over pristine anatase surfaces and remains for mono doping, while diminishes substantially for dual doping. The second doping profoundly enhances As(III) adsorption for anatase facets with low activities and proves to be a viable strategy. Distinct from pristine surfaces where bidentate binuclear complexes prevail, monodentate complexes may become preferred due to doping, especially for dual doping where Fe site promotes adsorption via electronic effects. Doping causes As(III) oxidation when As centers interact directly with surfaces, and for mono doping, electron back-donation re-reduces As(V) to As(IV), while As(IV) occurs less for dual doping due to electron reservoir of Fe site that inhibits As(V) re-reduction. Regulatory mechanisms of facet control and effects of mono and dual doping for As(III) adsorption are further unraveled at molecular level. Results provide significant new insights for As(III) pollution management, and conduce to design As(III) scavengers and manage As-associated pollution.

N-type molecular doping of a semicrystalline conjugated polymer through cation exchange

Control of electrical doping is indispensable in any semiconductor device, and both efficient hole and electron doping are required for many devices. In organic semiconductors, however, electron doping has been essentially more problematic compared to hole doping because in general organic semiconductors have low electron affinities and require dopants with low ionization potentials that are often air-sensitive. Here, we adapt an efficient molecular doping method, so-called ion-exchange doping, to dope electrons in a polymeric semiconductor. We initially reduce the polymeric semiconductor using one electron transfer from molecular dopants, and then the ionized dopants in the resulting air-unstable films are replaced with secondary ions via cation exchange. Improved ambient stability and crystallinity of the doped polymeric semiconductors are achieved when a specific bulky molecular cation was chosen as the secondary ion, compared to conventional methods. The presented strategy can overcome the trade-off relationship between reducing capability and ambient stability in molecular dopants, and a wider selection of dopant ions will help to realize ambient-stable electron conductors.

Full-color peptide-based fluorescent nanomaterials assembled under the control of amino acid doping.

Peptide-based biofluorescents are of great interest due to their controllability and biocompatibility, as well as their potential applications in biomedical imaging and biosensing. Here, we present a simple approach to synthesizing full-color fluorescent nanomaterials with broad-spectrum fluorescence emissions, high optical stability, and long fluorescence lifetimes. By doping amino acids during the enzyme-catalyzed oxidative self-assembly of tyrosine-based peptides, we can precisely control the intermolecular interactions to obtain nanoparticles with fluorescence emission at different wavelengths. The synthesized peptide-based fluorescent nanomaterials with excellent biocompatibility and stable near-infrared fluorescence emission were shown to have potential for bioimaging applications. This research provides new ideas for the development of new bioluminescent materials that are cost-effective, environmentally friendly, and safe for biomedical use.

Tuning the magnetic properties of double transition-metal carbide CoMC (M = Ti, V, Cr, Mn, Fe, Ni) monolayers.

The intrinsic ferromagnetism of two-dimensional transition metal carbide Co2C is remarkable. However, its practical application in spintronic devices is encumbered by a low Curie temperature (TC). To surmount this constraint, double transition-metal carbide CoMC (M = Ti, V, Cr, Mn, Fe, Ni) monolayers are constructed with the aim of improving the magnetic properties and Curie temperature of Co2C. The magnetic properties of CoMC monolayers are comprehensively investigated by first-principles calculations and the effects of hole doping and biaxial strain on the magnetic properties of CoMC (M = V, Cr, Mn) monolayers are also studied. The ground states of CoTiC, CoMnC and CoNiC monolayers all favor ferromagnetic ordering, whereas the CoVC and CoCrC monolayers favor antiferromagnetic ordering and the CoFeC monolayer is non-magnetic. Excitedly, the CoMnC monolayer displays a high total magnetic moment of 4.024μB and a TC of 1366 K. Moreover, the control of hole doping can effectively improve the TC of CoVC, CoCrC, and CoMnC monolayers to 680, 1317, 3044 K, respectively. Finally, applying the in-plain biaxial strain, the CoVC monolayer can be transformed into a ferromagnetic semiconductor under a tensile strain of 6%. The TC values of CoVC, CoCrC, and CoMnC monolayers are tuned by biaxial strain to 440, 1334 and 2390 K, respectively. Their TC above room temperature demonstrates that these monolayers have potential applications in spintronic devices. These theoretical investigations provide valuable insights into guiding experimental synthesis endeavors.

Transparent Patternable Large-Area Graphene p-n Junctions by Photoinduced Electron Doping.

We present a novel approach to achieve n-type doping in graphene and create graphene p-n junctions through a photoinduced electron doping method using photobase generators (PBGs). The unique properties of PBGs allow us to spatially and temporally control the doping process via light activation. The selective irradiation of specific regions on the graphene film enables switching their doping from p- to n-type, as confirmed by changes in the electromotive force and Seebeck and Hall coefficients. We demonstrate a stable (over 2 months) high electron mobility exceeding 1000 cm2 V-1s-1 using Hall effect measurements. The precise control of doping and the creation of p-n junctions in graphene offer exciting possibilities for various electronic, optoelectronic, and thermoelectric applications. Furthermore, we fabricate transparent graphene thermocouples with a high electromotive force of approximately ca. 80 μV/K, which validates the reliability and effectiveness of our approach for temperature sensing applications. This work paves the way for high-performance graphene-based electronic devices via controlled doping and patterning techniques. These findings provide valuable insights for the practical implementation of graphene in various fields.

Modifications in structure dependent magnetic parameters of Nd-doped Ba–Ca hexaferrites synthesized by sol gel using lemon extract as a fuel

The Nd doped Ba–Ca ferrites, Ba0.5Ca0.5NdXFe12-XO19 (x = 0 to 0.2, Δx = 0.05) are synthetically prepared by sol gel auto-ignition method using lemon extract as the fuel. Differential thermal analysis of the thermogravimetric spectrum clearly exhibits the thermal decomposition till 1050 °C. The powder X-ray diffraction (XRD) patterns of the hexaferrites sintered at 1050 °C reveals the single-phase M-type hexaferrites possessing nano dimensions. The lattice parameters, unit cell volumes, densities, and porosities of the hexaferrites were computed from the XRD patterns. The morphology of the synthesized hexaferrites is analyzed from the digital images of the powder samples obtained by utilizing Field Emission Scanning Electron Microscope (FESEM). The relative abundance of the elements within the hexaferrites was studied by means of Energy Dispersive X-Ray Analysis (EDAX). The oxidation states and valence of the metal elements within the hexaferrites are confirmed by means of the X-ray photoelectron spectroscopy (XPS). Magnetic parameters such as coercivity, saturation magnetization, and remanence are measured by using Vibrating-Sample Magnetometer (VSM). The Mössbauer spectra of the hexaferrites are obtained to analyze the hyperfine interactions by measuring the parameters such as hyperfine field, isomer shift, quadrupole splitting, relative area, and outer line width. The varying Nd doping concentrations have modulated the magnetic parameters of Ba–Ca hexaferrites showing the control of Nd doping on magnetic behavior of the hexaferrite. The moderate saturation magnetization and high coercivity values suggest the possible use of the hexaferrites as the permanent magnets.

Non-local Andreev reflection through Andreev molecular states in graphene Josephson junctions

We propose that a device composed of two vertically stacked monolayer graphene Josephson junctions can be used for Cooper pair splitting. The hybridization of the Andreev bound states of the two Josephson junction can facilitate non-local transport in this normal-superconductor hybrid structure, which we study by calculating the non-local differential conductance. Assuming that one of the graphene layers is electron and the other is hole doped, we find that the non-local Andreev reflection can dominate the differential conductance of the system. Our setup does not require the precise control of junction length, doping, or super conducting phase difference, which could be an important advantage for experimental realization.

Suppression of substrate-induced charge doping in hBN-encapsulated monolayer WS2

Strong coupling between a two-dimensional material and substrate is problematic in that interlayer charge transfer at the interface often complicates optoelectronic device applications. Such substrate-induced charge doping effects are particularly large for two-dimensional materials on SiO2/Si substrate. Here, we report a Raman study of monolayer WS2 encapsulated with hexagonal boron nitride (hBN) to unveil substrate-related charge doping phenomena under the influence of laser irradiation. Raman correlation analysis between the E′ and A1′ phonon frequencies of WS2 reveals that the encapsulation of WS2 with hBN leads to a screening of electron transfer from SiO2 to WS2. Further, photo-induced charge doping in WS2 is completely suppressed by hBN encapsulation. Our results demonstrate that understanding the photo-induced charge doping effects in two-dimensional heterostructures is useful in characterizing the role of hBN encapsulation and, thus, shed light on design strategies for efficient two-dimensional optoelectronic applications where a precise control of charge doping is required.

Selective Surface Modification and Layer Thinning of MoS2 via Ultraviolet-Light Irradiation in an Ionic Solution: Implications for Multifunctional Nanoelectronic Devices

The electrical properties of transition-metal dichalcogenides (TMDs), such as MoS2, are highly dependent on carrier doping and layer thickness. The ability to selectively control these two critical characteristics is of great importance in order to develop TMD-based multifunctional nanoelectronic device applications, which remains challenging. Here, we report a strategy for controllable surface modification and layer thinning of MoS2 via ultraviolet (UV)-light irradiation in a silver ionic (Ag+) solution environment. The results show that, by adjustment of the UV irradiation time, nanostructured Ag ultrathin films (∼2.9 nm) are uniformly deposited on monolayer MoS2 and can lead to a controllable p-type doping effect, while the thickness of MoS2 from few-layer to thick-layer could be thinned to the atomic monolayer limit. Both Ag nanostructure deposition and layer thinning have been evidenced to initiate from the edges of MoS2, independent of the edge type, thus revealing a unique UV-light-assisted defect-induced surface modification and layer-thinning mechanism. Overall, this study provides a simple methodology for the selective control of doping and layer thickness in TMDs, paving the way for developing multifunctional nanoelectronics and integrated optoelectronics.

Facile Construction of Nano-Dimensional Bi Encapsulated in N-Doped Porous Carbon Frameworks for High-Performance Sodium-Ion Hybrid Capacitors

As a promising anode candidate for sodium storage, the adhibition of metallic Bi is limited by severe volume expansion and modest conductivity. To solve the issues, optimizing and designing both structures and compositions of Bi-based anodes are highly necessary. Herein, Bi nanoparticles encapsulated in N-doped porous carbon frameworks (Bi@NPC) are synthesized via a facile but efficient chemical blowing method. The size and dispersion of Bi NPs in the interconnected carbon frameworks are accurately adjusted through the control of reaction temperatures and nitrogen doping. Thanks to its attractive structural/componential merits, the optimized Bi@NPC anode shows that an excellent high-rate capability of 207.6 mA h g–1 is achieved at a high rate of 50 A g–1. In addition, it can still present a stable reversible capacity of 243.9 mA h g–1 over 2000 cycles at 10 A g–1. Furthermore, the assembled sodium-ion hybrid capacitors with Bi@NPC as the anode and commercial active carbon as the cathode realize an exceptional energy/power density of 94.2 W h kg–1/200 W kg–1 and a low capacity decay rate of 0.014% per cycle for 2400 cycles at 1 A g–1. The contribution here will guide future design of alloy-type anode materials toward advanced sodium-ion hybrid capacitors.

In Tandem Control of La-Doping and CuO-Heterojunction on SrTiO3 Perovskite by Double-Nozzle Flame Spray Pyrolysis: Selective H2 vs. CH4 Photocatalytic Production from H2O/CH3OH.

ABO3 perovskites offer versatile photoactive nano-templates that can be optimized towards specific technologies, either by means of doping or via heterojunction engineering. SrTiO3 is a well-studied perovskite photocatalyst, with a highly reducing conduction-band edge. Herein we present a Double-Nozzle Flame Spray Pyrolysis (DN-FSP) technology for the synthesis of high crystallinity SrTiO3 nanoparticles with controlled La-doping in tandem with SrTiO3/CuO-heterojunction formation. So-produced La:SrTiO3/CuO nanocatalysts were optimized for photocatalysis of H2O/CH3OH mixtures by varying the La-doping level in the range from 0.25 to 0.9%. We find that, in absence of CuO, the 0.9La:SrTiO3 material achieved maximal efficient photocatalytic H2 production, i.e., 12 mmol g-1 h-1. Introduction of CuO on La:SrTiO3 enhanced selective production of methane CH4. The optimized 0.25La:SrTiO3/0.5%CuO catalyst achieved photocatalytic CH4 production of 1.5 mmol g-1 h-1. Based on XRD, XRF, XPS, BET, and UV-Vis/DRS data, we discuss the photophysical basis of these trends and attribute them to the effect of La atoms in the SrTiO3 lattice regarding the H2-production, plus the effect of interfacial CuO on the promotion of CH4 production. Technology-wise this work is among the first to exemplify the potential of DN-FSP for scalable production of complex nanomaterials such as La:SrTiO3/CuO with a diligent control of doping and heterojunction in a single-step synthesis.

Dilute Gd hydroxycarbonate particles for localized spin qubit integration.

Molecular spins are considered as the quantum hardware to build hybrid quantum processors in which coupling to superconducting devices would provide the means to implement the necessary coherent manipulations. As an alternative to large magnetically-dilute crystals or concentrated nano-scale deposits of paramagnetic molecules that have been studied so far, the use of pre-formed sub-micronic spherical particles of a doped Gd@Y hydroxycarbonate is evaluated here. Particles with an adjustable number of spin carriers are prepared through the control of both particle size and doping. Bulk magnetic properties and continuous wave and time-domain-EPR spectroscopy show that the Gd spins in these particles are potential qubits with robust quantum coherence. Monolayers of densely-packed particles are then formed interfacially and transferred successfully to the surface of Nb superconducting resonators. Alternatively, these particles are disposed at controlled localizations as isolated groups of a few particles through Dip-Pen Nanolithography using colloidal organic dispersions as ink. Altogether, this study offers new material and methodologies relevant to the development of viable hybrid quantum processors.

Fluorine Substitution at the O-Site Imparts Enhanced Chemical Stability for Garnet-Structured Electrolytes

Garnet-based superionic conductors hold great promise in next-generation lithium-ion batteries (LIBs) because of their favorable ionic conductivity and unique stability against Li-metal anodes; however, they still face the challenge of air stability for mass production/practical application. Herein, we identify their structural features and tailor the functional elements to enhance the chemical stability via synergistic control of doping and non-stoichiometry. The optimal composition of Li6.25Ga0.2La3Zr2O11.85F0.15 (LGLZO-0.15F) garnet exhibits great air durability without noticeable impurity accumulation, even during continuous air exposure for 60 days, owing to the high affinity of the fluorine dopant for lithium occupying the octahedral site. Meanwhile, LGLZO-0.15F possesses an appreciable Li-ion conductivity of 8.4 × 10–4 S cm–1 with an activation energy of 0.29 eV. Benefiting from these properties, hybrid and all-solid-state lithium batteries constructed with LGLZO-0.15F electrolytes demonstrate low overpotential, high Coulombic efficiency, and stable cycling performance.

(Digital Presentation) MOCVD Growth of Ga2O3, Algao and Heterostructures

Ultrawide bandgap (UWBG) gallium oxide (Ga2O3) represents an emerging semiconductor material with excellent chemical and thermal stability. It has a band gap of 4.5-4.9 eV, much wider than that of the GaN (3.4 eV) and 4H-SiC (3.2 eV). The monoclinic β-phase Ga2O3 represents the thermodynamically stable crystal among the known five known phases (α, β, γ, d, ε/κ). The breakdown field of β-Ga2O3 is predicted to be 6-8 MV/cm, which is much larger than that of the 4H-SiC and GaN. These unique properties make β-Ga2O3 a promising candidate for high power electronic device and solar blind photodetector applications. Single crystal β-Ga2O3 substrates can be synthesized by scalable and low cost melting based growth techniques. Metalorganic chemical vapor deposition (MOCVD) growth technique was demonstrated to produce high quality β-Ga2O3 thin films and its ternary (AlxGa1-x)2O3 alloys. Control of background and n-type doping in β-Ga2O3 will be discussed. Record carrier mobilities of 194 cm2/V·s at room temperature and ~10,000 cm2/V·s at low temperature were measured for MOCVD β-Ga2O3 thin films. Growth and fundamental understanding of β-(AlxGa1-x)2O3 are still limited. The incorporation of Al in beta-phase Ga2O3 has not been well understood, although it was predicted up to 60% of Al composition could be incorporated into β-Ga2O3. MOCVD growth of β-AlGaO targeting for Al composition of > 40% will be discussed. N-type doping capability as a function of Al composition in (AlxGa1-x)2O3 is another important fundamental question. Charge carrier transport properties in (AlxGa1-x)2O3 will be discussed. In addition, MOCVD growth of different phases of Ga2O3 and AlGaO will be presented. Acknowledgement: The authors acknowledge the funding support from the Air Force Office of Scientific Research FA9550-18-1-0479 (AFOSR, Dr. Ali Sayir) and the National Science Foundation (1810041, 2019753, 1755479).

The Importance of Chemistry in the Control of Doping in Sports during the OlympicsMarcos Aurelio Gomes da Silva

The Importance of Chemistry in the Control of Doping in Sports during the OlympicsMarcos Aurelio Gomes da Silva

Molecular Doping Enabling Mobility Boosting of 2D Sn2+‐Based Perovskites (Adv. Funct. Mater. 38/2022)

2D Sn2+-Based Perovskites In article number 2204870, Yong-Young Noh and co-workers demonstrate the high doping efficiency of halide perovskites using a simple molecular charge transfer approach and provides a new opportunity for employing 2D perovskites in high-efficiency optoelectronic devices. A thin p-type dopant layer, F4-TCNQ and MoO3, deposited using thermal evaporation improves the control of damage-free electronic doping. The efficient charge transfer without deterioration of the perovskite microstructure improves the Hall mobility up to 100 cm2 V−1 s−1.

Raman Spectroscopy Investigation on Semi-curve Woven Fabric-graphene Synthesized by the Chemical Vapor Deposition Process

Abstract: Graphene is a single layer of two-dimensional carbon atoms bound in a hexagonal lattice structure with zero band gap semiconductor. Chemical vapor deposition (CVD) is one of the most promising, inexpensive and readily ways for synthesizing monolayer pristine graphene. We have synthesized monolayer graphene shaped in semi-curve woven frabic-graphene (SWF-G) on SiO2/Si substrate. Using Raman spectroscopy, we studied the central suspended portion (i.e., 1-6) of it exerting compression (stress) to the graphene supported on the substrate. The concentration of hole impurities on either side of the central position of semi-curve woven fabric-graphene (SWF-G) is more than on its central position. The variation of such hole doping concentration results in an upshift of 2D peak position (pos(2D)) which is opposite for high electron doping even if there is no intentional control of doping. The synthesized graphene is a single-layer high-quality new structure graphene. Keywords: Semi-curve woven fabric-graphene, Raman spectroscopy, Charge impurities, Compression, Doping.

Controllable Selenization Transformation from MoO2 to MoSe2 by Gas Pressure‐Mediated Chemical Vapor Deposition

During the chemical vapor deposition (CVD) of MoSe2, controlling its selenization reaction and understanding its reaction mechanisms are of great significance to obtain high‐quality 2D transition metal selenide semiconductors. Herein, a variable‐pressure CVD (VPCVD) method is reported to achieve the controllable transformation from MoO2 to MoSe2 monolayer based on gas pressure‐mediated selenization. At the gas pressure lower than 20 KPa, high‐temperature decomposition of MoO3 in the Ar/H2 mixture only produces MoO2 nanosheets without any selenization. When the gas pressure is between 20 and 60 KPa, quadrilateral MoO2 nanosheets are partially selenized. By further increasing the gas pressure from 60 to 100 KPa, they are completely selenized. At the downstream margins of as‐selenized films, 2D MoSe2 monolayers demonstrate a morphological evolution from triangle to hexagon and then to a continuous film. In addition, their Se vacancy concentrations and nucleation sizes depend directly on gas pressure. Therefore, the gas pressure‐mediated selenization provides a feasible way for the in situ synthetic control of chemical composition and vacancy doping of 2D transition metal selenides/oxides.