Conductive Surface Layer Research Articles

Diamond FET Biosensor Fabrication and Application

Diamond is renowned as the ultimate semiconductor thanks to its exceptional physical properties, including unmatched hardness, exceptional wear resistance, superior mechanical and tribological characteristics, and high fracture strength. Diamond solution-gate field-effect transistors (D-SGFETs) leverage these advantages, along with their outstanding high-power and high-frequency performance, excellent thermal conductivity, wide bandgap, high carrier mobility, and rapid saturation speed. These features make D-SGFETs highly promising for fast and precise biomedical detection applications. This paper provides a comprehensive review of the fabrication techniques for diamond SGFETs, encompassing diamond film synthesis, surface conduction layer formation, source/drain fabrication, and FET packaging. Furthermore, the study delves into the surface functionalization of diamond SGFETs and their diverse applications in biomedical detection. Finally, the paper discusses the future outlook of diamond SGFETs in advancing biomedical detection technologies.

AlN/Si interface engineering to mitigate RF losses in MOCVD-grown GaN-on-Si substrates

Fabrication of low-RF loss GaN-on-Si high electron mobility transistor stacks is critical to enable competitive front-end-modules for 5G and 6G applications. The main contribution to RF losses is the interface between the III-N layer and the HR Si wafer, more specifically the AlN/Si interface. At this interface, a parasitic surface conduction layer exists in Si, which decreases the substrate effective resistivity sensed by overlying circuitry below the nominal Si resistivity. However, a clear understanding of this interface with control of the parasitic channel is lacking. In this Letter, a detailed physical and electrical description of metalorganic chemical vapor deposition-grown AlN/Si structures is presented. The presence of a SiCxNy interfacial layer is revealed, and its importance for RF losses is shown. Through C–V and I–V characterization, an increase in the C concentration of this interfacial layer is linked to the formation of negative charge at the AlN/Si interface, which counteracts the positive charge present in the 0-predose limit. The variation of the TMAl predose is shown to allow precise tuning of the C composition and, consequently, the resulting interface charge. Notably, a linear relationship between the predose and the net interface charge is observed and confirmed by the fabrication of an AlN/Si sample with close to zero net charge. In addition, a higher Dit (∼2×1012cm−2) for such compensated samples is observed and can contribute to low-RF loss. An exceptionally high effective resistivity of above 8 kΩ cm is achieved, corresponding to an RF loss below 0.3 dB/mm at 10 GHz.

Determining Liquid Limit and Plastic Limit of Clay Soils by Electrical Surface Conduction and Diffuse Double Layer Thickness

The aim of this study was to propose a new approach to determine the liquid limit and plastic limit of clay soils by considering electrical conductivity (EC) measurements. The proposed method included incorporating a new parameter, F, which is the ratio of the volumetric water contents of diffuse double layer (DDL) water and free water. In addition, the EC parameter, σ, was considered as the ratio of electrical surface conductivity and electrical conductivity of water. The changes in the thickness of DDL (χ) were also assessed to obtain corresponding equations to establish a connection with clay mineralogy, water content, and specific gravity in the final prediction. Three-dimensional surface analyses were conducted to find a correlation among F, σ, and χ to identify an appropriate method to predict liquid limit and plastic limit. The study was conducted with 39 different types of samples, and the outcomes from the EC approach were validated against the conventional methods. Overall, the coefficient of determination, R2 = 0.90, and Lin’s concordance correlation coefficient, (LCCC) = 0.91, were obtained for liquid limit prediction, whereas R2 = 0.64 and LCCC = 0.80 were obtained for plastic limit determination.

Highly sensitive strain sensors based on PVA hydrogels with a conductive surface layer of graphene

Highly sensitive strain sensors based on PVA hydrogels with a conductive surface layer of graphene

Comparative X-ray photoelectron spectroscopy analysis of nitrogen atoms implanted in graphite and diamond

Introduction: Insertion of N atoms at a nanoscale subsurface depth in single-crystal diamond (SCD) may enable new generations of quantum electronics devices. In this sense, it is critical to understand the interaction between implanted N atoms and C atoms in the diamond lattice.Methods: The investigation of the interaction of N atoms with SCD at the atomic scale using X-ray photoelectron spectroscopy (XPS) analysis involves in situ bombardment of the SCD surface with relatively low-energy (5,000 eV) N2 ions. In situ XPS analyses of SCD and highly oriented pyrolytic graphite (HOPG) before and after N-atom implantation are compared with published XPS analyses of C-N materials (e.g., g-CN, N in poly/single-crystal diamond).Results: The analyses revealed three N 1s peaks at 398–399 eV (N1), 399–400.5 eV (N2), and 401–403 eV (N3), with the N1 and N2 peaks assigned to C-N bonds and an N3 peak inaccurately assigned, in prior publications, to N-bonded contaminants (e.g., O, NH). In situ cleaning of the SCD and HOPG surfaces prior to N-atom implantation was performed to eliminate all atmospheric contaminants. This cleaning process revealed that the N3 peak is associated with N-C-bonded atoms and not the C-O/NH linkage, as previously suggested. Ex situ high resolution transmission electron microscopy (HRTEM) studies of N-implanted SCD show a defect-structured subsurface region.Discussion: An important side effect of the relatively low-energy N implantation in SCD is the formation of a 5–8 nm electrically conductive surface layer, an effect that may open the pathways for future research in diamond-based micro- and nano-electronics.

Defensive and Ion Conductive Surface Layer Enables High Rate and Durable O3-type NaNi1/3 Fe1/3 Mn1/3 O2 Sodium-Ion Battery Cathode.

Na-based layered transition metal oxides with an O3-type structure are considered promising cathodes for sodium-ion batteries. However, rapid capacity fading, and poor rate performance caused by serious structural changes and interfacial degradation hamper their use. In this study, a NaPO3 surface modified O3-type layered NaNi1/3 Fe1/3 Mn1/3 O2 cathode is synthesized, with improved high-voltage stability through protecting layer against acid attack, which is achieved by a solid-gas reaction between the cathode particles and gaseous P2 O5 . The NaPO3 nanolayer on the surface effectively stabilizes the crystal structure by inhibiting surface parasitic reactions and increasing the observed average voltage. Superior cyclic stability is exhibited by the surface-modified cathode (80.1%vs 63.6%) after 150 cycles at 1C in the wide voltage range of 2.0V-4.2V (vs Na+ /Na). Moreover, benefiting from the inherent ionic conduction of NaPO3 , the surface-modified cathode presents excellent rate capability (103mAhg-1 vs 60mAhg-1 ) at 10C. The outcome of this study demonstrates a practically relevant approach to develop high rate and durable sodium-ion battery technology.

Surface conductivity in SmB6

We present a study of low temperature electron transport (resistivity, magnetoresistance and Hall coefficient) in SmB6 single crystals having different polar (100) and nonpolar (110) and (111) surfaces after mechanical polishing and chemical etching. The estimation of effective parameters for surface and bulk charge carriers allows us to conclude that surface conductivity is very sensitive to the method of surface treatment. The most pronounced change is observed for the polar (100) surface, for which the related Hall concentration of charge carriers at 2 K decreases more than by 2 orders of magnitude and the Hall mobility increases by a factor of 15 after etching these faces in diluted nitric acid. We suggest that the strong dependence of surface properties on the type of treatment may result from both topological protection, which is influenced by intrinsic defects or surface reconstruction, and band bending effects, which modulate the properties of the surface conduction layer in case of polar faces.

Electric fields and local heating in additively manufactured nanocomposite parts

Conventional methods of thermoplastic manufacture suffer from high capital costs, while fused deposition modeling (FDM) faces the challenge of poor adhesion between printed layers. We have previously shown that carbon nanotubes can be used as electric field susceptors to locally heat the interfaces between printed layers. We also showed that dielectric barrier discharge (DBD) plasma applicators mounted on FDM nozzles can pass current to printed parts for welding. Little is known, however, about the interaction between the electric field and the printed part. In this work, we simulate the internal heating behavior of printed parts with local variations in conductivity. These studies show that thermal penetration scales with conductive surface layer thickness; the results also indicate that conductive inclusions within parts can create hotspots. These findings explain the heating behavior of FDM printed parts when coupled to a DBD applicator and show that inclusions within the parts could create mechanical defects.

Porous structure induced crack redistribution in surface conductive layer for high‐performance fiber‐based flexible strain and pressure sensors

AbstractConstructing crack structure has been proven as an effective method to prepare highly sensitive strain/pressure sensors. However, the crack‐structured strain/pressure sensors usually show limited sensing range because of the rapid destruction of conductive networks. Herein, a porous poly(styrene‐b‐ethylene‐b‐butylene‐b‐styrene) (SEBS)‐based fiber with surface carbon nanotube (CNT) conductive layer is prepared by melt extrusion foaming and ultrasonic treatment. Cracks generate in the conductive layer under stretching due to the modulus mismatch. It is found that the introduction of porous structure leads to the redistribution of surface cracks. The conductive layer around pores cracks first under small strain due to the stress concentration effect, and the conductive layer away from pores then cracks under large strain, which prevents the rapid destruction of the conductive networks. Consequently, the porous conductive fiber‐based strain sensors exhibit both high sensitivity (gauge factor of 27.2 at the strain of 350%) and wide sensing range (0%–350%). Furthermore, a high‐performance flexible pressure sensor is fabricated by perpendicularly stacking two porous SEBS@CNTs fibers, which can be applied in wearable human motion monitoring and information transmission. Our study inspires a new idea and proposes a simple strategy for fabricating high‐performance crack‐structured flexible strain/pressure sensors with high sensitivity over a wide sensing range.

Conducting surface layers formed by hydrogenation of O-implanted β-Ga2O3

Lightly n-type β-Ga2O3 grown by Halide Vapor Phase Epitaxy (HVPE) on heavily n-type doped β-Ga2O3 substrate was implanted with 1 MeV O ions to a fluence of 1016 cm−2. The film remained β-polymorph and showed no broadening of the x-ray rocking curve width after irradiation even though the calculated number of primary defects was very high. The implanted region was characterized by a strong compensation, likely due to the presence of a high density of split Ga vacancy acceptors. Treatment of the irradiated film in dense hydrogen plasma at 330 °C for 0.5 h led to the formation of a conducting surface layer about 0.5 µm-thick with carrier density 1017 cm−3, a suppression of the signal due to Fe acceptors in Deep Level transient Spectroscopy (DLTS) and a strong enhancement of DLTS peak caused by centers at Ec-0.74 eV (so called E2 * traps). The mechanism appears to be that hydrogen plasma treatment leads to creation of a high number of donor states due complexing of hydrogen with Ga vacancies and to passivation of Fe acceptors with hydrogen donors.

Surface anisotropic magnetoresistance in the antiferromagnetic semiconductor CrSb2

We report on large anisotropic magnetoresistance (AMR) in surface states of an antiferromagnetic semiconductor $\mathrm{Cr}{\mathrm{Sb}}_{2}$. The low-temperature measurement of angle-dependent magnetoresistance (ADMR) is performed in high magnetic fields up to 24 T. At 1.4 K, where the surface conduction is dominant, ADMR exhibits clear twofold symmetry consistent with AMR due to magnetic-field-induced change of antiparallel magnetic structure. The AMR magnitude reaches 9.3% despite the small angle dependence of the net magnetic moments, suggesting strong spin-orbit interaction in the surface conduction layer.

The Role of Oxygen Transfer in Oxide Heterostructures on Functional Properties (Adv. Mater. Interfaces 11/2022)

Oxygen Transfer in Oxide Heterostructures In article number 2101867, Zachary Corey, Quanxi Jia, Aiping Chen, and co-workers demonstrate that the growth of an oxide layer in a suitable condition can lead to oxygen transfer from the substrate to the film during growth. Such oxygen transfer forms a conductive substrate surface layer that contributes to the observed high carrier mobility.

A facile in situ Mg surface chemistry strategy for conditioning-free Mg[AlCl4]2 electrolytes

Developing a simple and reliable strategy for modulating overpotential of Mg plating/stripping is crucial for realizing overall high performance of rechargeable Mg batteries, which have been demonstrated to be rather challenging. Herein, we report a facile LiI-assisted Mg surface chemistry to reduce Mg plating/stripping overpotential via in situ solubilization mechanism and ion conductive surface layer formation mechanism. As a result, we successfully formulate a new conditioning-free Mg[AlCl4]2-based Mg electrolyte system that improves Mg plating/stripping from the very first cycle. The overpotential of Mg plating/stripping of the as-prepared electrolyte with a LiI electrolyte additive is remarkably reduced to 240/240 mV at a current density of 1000 µA cm−2. Using this electrolyte, a rechargeable Mg battery coupled with PANi intercalated V2O5 (V2O5-PANi) cathode and Mg anode delivers a stable discharge specific capacity of nearly 50 mA h g−1 after an impressively prolonged cycle life of 500 cycles. Our finding provides a new inspiration of in situ Mg surface chemistry to activate Mg anode surface with high Mg ion conductivity.

Atom probe analysis of electrode materials for Li-ion batteries: challenges and ways forward.

The worldwide development of electric vehicles as well as large-scale or grid-scale energy storage to compensate for the intermittent nature of renewable energy generation has led to a surge of interest in battery technology. Understanding the factors controlling battery capacity and, critically, their degradation mechanisms to ensure long-term, sustainable and safe operation requires detailed knowledge of their microstructure and chemistry, and their evolution under operating conditions, on the nanoscale. Atom probe tomography (APT) provides compositional mapping of materials in three dimensions with sub-nanometre resolution, and is poised to play a key role in battery research. However, APT is underpinned by an intense electric field that can drive lithium migration, and many battery materials are reactive oxides, requiring careful handling and sample transfer. Here, we report on the analysis of both anode and cathode materials and show that electric-field driven migration can be suppressed by using shielding by embedding powder particles in a metallic matrix or by using a thin conducting surface layer. We demonstrate that for a typical cathode material, cryogenic specimen preparation and transport under ultra-high vacuum leads to major delithiation of the specimen during the analysis. In contrast, the transport of specimens through air enables the analysis of the material. Finally, we discuss the possible physical underpinnings and discuss ways forward to enable shielding from the electric field, which helps address the challenges inherent to the APT analysis of battery materials.

Numerical simulation of novel designed perovskite/silicon heterojunction solar cell

In this work, novel designed solar cell is proposed for first time for doped perovskite based silicon heterojunction solar cells where (n/p)-type doped perovskite used as ultra-thin emitter layer and (p/n)-type silicon as absorber layer. Performance of two different types of solar cells, n-type doped perovskite with p-type based crystalline silicon (p-cSi) solar cells and p-type doped perovskite with n-type based crystalline silicon (n-cSi) solar cells are studied and highest efficiency of 28.82% and 29.48% respectively are achieved by optimizing their properties. Thicknesses of silicon wafer and perovskite layer, band gap of MAPbI3 layer, doping density of ultra-thin perovskite (emitter) layer, doping density of c-Si layer, texturing of silicon wafer, metal work function of different materials at front contact and back contact & its band bending on using different metals, and role of ZnO and ITO as conducting surface layer has been studied and optimized in the present work. AFORS-HET automat simulation software is used to study the performance of these simulated solar cells.

Laser-induced novel ohmic contact formation for effective charge collection in diamond detectors

In this study, we employed an authentic process for the device fabrication of diamond detectors, wherein thin, highly conductive surface layers were processed in bulk diamond substrate using a nanosecond-pulsed excimer laser with liquid-immersion irradiation. The incorporation of high-concentration phosphorus dopants at 40 nm under the irradiated surface characterized the irradiated areas with much lower electrical resistivity, which was adequate for demonstrating ohmic contacts even with the tungsten probe heads at room temperature. In particular, a low activation energy (<54 meV) of irradiated surfaces enabled space-charge-free build-up effects between the diamond film and external connection. Moreover, the electrical characterization revealed an improved carrier-collection efficiency that was more than three orders of magnitude greater than that of typical Ti/Au diamond ohmic contacts, including a high-response speed of the current pulse to irradiation burst. The laser treatment of diamond films displayed promising results for the fabrication of diamond detectors with minimum power consumption, fastest process rate, and highest visible-light detection that could maintain smooth and stable charge transport. The process allowed selective, patterned doping of the diamond surface, which could be electrically contacted more readily. Furthermore, they could be operated at high temperatures and in radiation-harsh environments with sustainable efficiency.

Influence of Electrolyte on the Electrode/Electrolyte Interface Formation on InSb Electrode in Mg-Ion Batteries.

Achieving the full potential of magnesium-ion batteries (MIBs) is still a challenge due to the lack of adequate electrodes or electrolytes. Grignard-based electrolytes show excellent Mg plating/stripping, but their incompatibility with oxide cathodes restricts their use. Conventional electrolytes like bis(trifluoromethanesulfonyl)imide ((Mg(TFSI)2) solutions are incompatible with Mg metal, which hinders their application in high-energy Mg batteries. In this regard, alloys can be game changers. The insertion/extraction of Mg2+ in alloys is possible in conventional electrolytes, suggesting the absence of a passivation layer or the formation of a conductive surface layer. Yet, the role and influence of this layer on the alloys performance have been studied only scarcely. To evaluate the reactivity of alloys, we studied InSb as a model material. Ex situ X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy were used to investigate the surface behavior of InSb in both Grignard and conventional Mg(TFSI)2/DME electrolytes. For the Grignard electrolyte, we discovered an intrinsic instability of both solvent and salt against InSb. XPS showed the formation of a thick surface layer consisting of hydrocarbon species and degradation products from the solvent (THF) and salt (C2H5MgCl−(C2H5)2AlCl). On the contrary, this study highlighted the stability of InSb in Mg(TFSI)2 electrolyte.

Nitrogen‐Doped Hollow Carbon Polyhedrons with Carbon Nanotubes Surface Layers as Effective Sulfur Hosts for High‐Rate, Long‐Lifespan Lithium–Sulfur Batteries

AbstractEffectively confining lithium polysulfides inside porous material matrix with a high electrical conductivity represents a judicious way to extend lifespan and enhance rate performance of lithium‐sulfur (Li‐S) batteries. Herein, nitrogen‐doped hollow carbon polyhedrons with a thin CNTs conductive surface layer (CNTs/HNC) were prepared by directly pyrolyzing the CNTs coated ZIF‐8 polyhedrons crystallite precursors, and subsequently served as sulfur hosts in Li‐S batteries. The resulted product CNTs/HNC‐800 comprises a nitrogen content of 4.94 at.% as well as a high electrical conductivity of 8.43×10−1 S cm−1, which help to effectively adsorb/confine lithium polysulfides and substantially improve the rate capacity of Li‐S batteries. With a sulfur loading of 1.60 mg cm−2, the S@CNTs/HNC based cathode shows a discharge capacity of 870.7 mAh g−1 at 1.0 C, and can maintain 76.4 % of its initial capacity after 500 charge‐discharge cycles, corresponding to a capacity fade rate of only 0.047 % per cycle. While with a higher sulfur loading of 2.46 mg cm−2, a discharge capacity of 649.7 mAh g−1 can be achieved at 0.5 C, along with a capacity fade rate of merely 0.044 % per cycle during 200 cycles. When sulfur loading is further increased to 5.39 mg cm−2, it can also maintain a considerable initial discharge capacity of 812 mAh g−1 at 0.1 C. This work enriches the ways to prepare complicate nano structured sulfur hosts for long‐life and high‐rate Li‐S batteries.

Two models for determination of the effective conductivity of concentrated suspensions of ellipsoidal particles with surface phenomena

Many multicomponent materials such as rocks or nanofluids are characterized by the presence of conductive surface layers at the interface. These conductive layers can change effective physical properties (for example, effective thermal or electrical conductivities) of such materials. A suspension of ellipsoidal particles with surface conductivity is considered. Two theoretical models are presented for the solution of the so-called one-particle problem that can be used then in any homogenization scheme for determination of the effective conductivity of such suspension. The first model is based on the modification of the boundary conditions for the electric current density (the jump boundary conditions). The second model is based on the confocal ellipsoids. The effect of surface conductivity is obtained for this model by limiting transition to the infinitely thin external ellipsoidal shell.For the calculation of the effective conductivity of the medium containing the ellipsoidal particles with the surface phenomena one of the popular homogenization scheme named by Differential Effective Medium (DEM) method is used. Comparison of numerical results obtained by this method for two different solution of the one-particle problem show that these results are rather close even for very large values of the surface conductivity.

Numerical calculation of the potential distribution on the Si(111)-7 × 7 surface for scanning tunneling potentiometry

Scanning tunneling potentiometry enables us to obtain electrochemical potential distribution of the sample surface in sub-nanometer-scale spatial resolution, and provides information on electrical resistances at the surface and local defects on it. In order to evaluate the influence of the conductance through the substrate in the measurements, we performed numerical simulation using a resistance network model that consists of a conductive surface layer with one resistive site at the center, representing the metallic surface states of the Si(111)7 × 7 surface and its single height step, respectively. The calculated results demonstrate that the substrate conductance modifies the surface potential distribution, in particular around the electrodes attached at the sides of the surface layer, and reduces the amount of the potential drop at the step and the potential gradient on the terrace nearby. In spite of the modification, however, the ratio of the conductivity of the step to that of the terrace estimated from the potential profile, is not affected by the substrate conductance as far as a low-doped substrate (103 Ω · cm or larger) is used in the case of the Si(111)7 × 7 surface.