Cr-doped Films Research Articles

Fabrication and Tribological Properties of Diamond-like Carbon Film with Cr Doping by High-Power Impulse Magnetron Sputtering

The present study aims to investigate the advantages of diamond-like carbon (DLC) films in reducing friction and lubrication to address issues such as the low surface hardness, high friction coefficients, and poor wear resistance of titanium alloys. Cr-doped DLC films were deposited by high-power impulse magnetron sputtering (HiPIMS) in an atmosphere of a gas mixture of Ar and C2H2. The energy of the deposited particles was controlled by adjusting the target powers, and four sets of film samples with different powers (4 kW, 8 kW, 12 kW, and 16 kW) were fabricated. The results showed that with an increase in target power, the Cr content increased from 3.73 at. % to 22.65 at. %; meanwhile, the microstructure of the film evolved from an amorphous feature to a nanocomposite structure, with carbide embedded in an amorphous carbon matrix. The sp2-C bond content was also increased in films, suggesting an intensification of the film’s graphitization. The hardness of films exhibited a trend of initially increasing and then decreasing, reaching the maximum value at 12 kW. The friction coefficient and wear rate of films showed a reverse trend compared to hardness variation, namely initially decreasing and then increasing. The friction coefficient reached a minimum value of 0.14, and the wear rate was 2.50 × 10−7 (mm3)/(N·m), at 8 kW. The abrasive wear was the primary wear mechanism for films deposited at a higher target power. Therefore, by adjusting the target power parameter, it is possible to control the content of the metal and sp2/sp3 bonds in metal-doped DLC films, thereby regulating the mechanical and tribological properties of the films and providing an effective approach for addressing surface issues in titanium alloys.

Cr doping-induced ferromagnetism in SnTe thin films

Transition-metal doped topological insulators have been widely explored since the observation of quantum anomalous Hall effect (QAHE). Subsequently, the magnetic (Pb,Sn)(Te,Se) was predicted to possibly possess a high-temperature QAHE state. However, the fundamental understanding of Cr-doping-induced ferromagnetism in this system remains unclear. Here, we report the stable ferromagnetism in the high-crystalline Cr-doped SnTe films. Upon Cr doping, the magnetoconductance unveils a crossover from weak antilocalization to weak localization. Further increasing the Cr concentration to Cr0.17Sn0.83Te introduces a strong ferromagnetism with a Curie temperature of ~140 K. We detected a sizable spin moment ms = 2.28 ± 0.23 μB/Cr and a suppressed orbital moment ml = 0.02 μB/Cr. Cr dopants prefer to substitute the Sn sites and behave as divalent cations, as indicated by the experimental results and density function theory calculations. The controllable growth of magnetic SnTe thin films provides enlightenment towards the high-temperature QAHE in magnetic TCIs for the desired dissipationless transport in electronics.

Competitive nature of weak anti-localization and weak localization effect in Cr-doped sputtered topological insulator Bi2Se3 thin film

In the present study, we have investigated the effect of magnetic Cr doping on the transport properties of a sputtered Bi2Se3 thin film on the SrTiO3 (110) substrate. The high-resolution x-ray diffraction and Raman spectroscopy measurements revealed the growth of rhombohedral Bi2Se3 thin films. Further electronic and compositional analysis was done by x-ray photoemission spectroscopy and Rutherford backscattering spectroscopy, and the x-value was estimated to be 0.18 in the Bi2−xCrxSe3 thin film. The variation in the resistivity with temperature (2–300 K) revealed the metallic nature in undoped Bi2Se3 up to 30 K and upturn resistivity below 30 K. The Cr-doped Bi2Se3 resistivity data show a traditional semiconducting nature up to 25 K and take an abrupt upturn resistivity below 25 K. The resistivity behavior of both samples was explained by adopting a model that consists of the total resistance, a combination of bulk and surface resistance in parallel. The bulk bandgap value determined by this method is obtained to be 256 meV in an undoped Bi2Se3 thin film. Magnetoconductance data of the undoped thin film revealed a weak anti-localization (WAL) effect, while the Cr-doped thin film showed a weak localization (WL) effect at low temperatures (<50 K). At low magnetic field and low temperature, a competing nature of WAL and WL effects was prominent in the Cr-doped film. A drastic increase in the electrical resistance suggests that Cr doping can significantly modify the electrical properties of Bi2Se3 thin films, which could have potential applications in futuristic devices.

Structural and magneto-transport properties of sputtered Cr-doped Bi2Te3 films

Structural and magneto-transport properties of sputtered Cr-doped Bi2Te3 films

Tailoring defects in electron transporting Zn2SnO4 layers by multilayer engineering and Cr doping towards efficient and stable carbon-based perovskite solar cells

The quality of the electron transporting layer (ETL) is crucial for perovskite solar cell (PSC) performance and stability. Defects in the ETL can cause charge recombination losses and device instability. Herein, crystalline chromium-doped zinc stannate (Cr-doped Zn2SnO4) nanoparticles bilayered with a compact zinc tin oxide (c-ZTO) are proposed as an efficient ETL in PSCs. It was found that Cr incorporation improved the quality of the ZTO crystal by inducing more crystal lattice oxygen, reducing the surface defects, and narrowing the particle size distribution. A perovskite film with larger grains was achieved on the Cr-doped ZTO film. The best PSC showed power conversion efficiency (PCE) of 15.32% and a reduction in the device hysteresis effect. The PSC based on Cr-doped ZTO exhibited superior thermal and UV light stability compared to the conventional single c-ZTO PSC. The main improvement in device performance and device stability was attributed to the suppression of defect trap density. Additionally, the colloidal Cr-doped ZTO solution could be reused for at least 10 months, making it suitable for industrial PSC manufacturing due to the negligible solution aging effect. Our bilayered c-ZTO/Cr-ZTO nanoparticles provide a high quality ETL, offering great potential for efficient and stable PSCs.

Optoelectronic, photocurrent sensitivity and photocatalytic dye degradation behaviour of spray deposited Cr doped SnO2 thin films

Undoped and SnO2:Cr doped thin films (Cr: 0.25, 0.50, 0.75 and 1 wt%) were deposited by economically home-made spray pyrolysis method. The characteristic behaviour of the deposited films was studied by X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Photoluminescence (PL), Ultraviolet–visible (UV–vis.) spectroscopy, Current-Voltage (I–V) and photocatalytic studies. The XRD analysis confirms the tetragonal rutile structure of SnO2 with predominant orientation along the (2 1 1) plane and the decrease in crystallite size from 48 to 30 nm by Cr-doping. The EDAX and XPS studies reveal the elements and its chemical state of Sn, O and Cr. The SnO2:Cr thin films exhibit an 85% average optical transmittance in the visible region of the electromagnetic spectrum. The SEM micrographs clearly show the well-defined grains with boundaries, and it is evident that grain size drastically reduces from 155 nm to 48 nm as a function of Cr-doping. Photoluminescence analysis confirms the defect-related emission (360 nm, 440 and 490 nm). The photocatalytic activity of all thin films is assessed using malachite green (MG) dye under UV light irradiation. 0.75 wt% Cr-doped SnO2 film shows improved photocatalytic performance (60.37%) than undoped thin film (32.03%). The I–V characteristics of undoped and SnO2:Cr thin films are performed in visible light, showing photo-linear response behaviour. The highest figure of merit (FOM) obtained for SnO2:Cr (0.75 wt%) thin film is 7.07 × 10−6 Ω−1. The obtained values of the FOM and photocatalytic performance are discussed in the context of the suitability of these materials for transparent and conducting window materials in solar cells and photocatalytic degradation applications.

Quantum anomalous Hall interferometer

Electronic interferometries in integer and fractional quantum Hall regimes have unfolded the coherence, correlation, and statistical properties of interfering constituents. This is addressed by investigating the roles played by the Aharonov–Bohm effect and Coulomb interactions on the oscillations of transmission/reflection. Here, we construct magnetic interferometers using Cr-doped (Bi,Sb)2Te3 films and demonstrate the electronic interferometry using chiral edge states in the quantum anomalous Hall regime. By controlling the extent of edge coupling and the amount of threading magnetic flux, distinct interfering patterns were observed, which highlight the interplay between the Coulomb interactions and Aharonov–Bohm interference by edge states. The observed interference is likely to exhibit a long-range coherence and robustness against thermal smearing probably owing to the long-range magnetic order. Our interferometer establishes a platform for (quasi)particle interference and topological qubits.

Facile Synthesis of Pure and Cr-Doped WO3 Thin Films for the Detection of Xylene at Room Temperature.

This paper focused on the preparation of pure and Cr-doped tungsten trioxide (WO3) thin films using the spray pyrolysis method. Different techniques were adopted to analyze these films' structural and morphological properties. The X-ray detection analysis showed that the average crystallite size of the WO3-nanostructured thin films increased as the Cr doping concentration increased. The atomic force microscopy results showed that the root-mean-square roughness of the films increased with Cr doping concentration up to 3 wt % and then decreased. The increased roughness is favorable for gas-sensing applications. Surface morphology and elemental analysis of the films were studied by field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy measurements. The 3 wt % Cr-WO3 has a large nanoflake-like structure with high surface roughness and porous morphology. Gas-sensing characteristics of undoped and Cr-doped WO3 thin films were investigated with various gases at room temperature. The results showed that 3 wt % Cr-doped WO3 film performed the maximum response toward 50 ppm of xylene with excellent selectivity at room temperature. We believe that increased lattice defects, surface morphology, and roughness due to Cr doping in the WO3 crystal matrix might be responsible for increased xylene sensitivity.

Optical characteristics with high accuracy of diluted Cr doped In2O3 thin films using spectroscopic ellipsometry for optoelectronic devices

Chemical reactions were used to create (In1-xCrx)2O3 powder with (x = 0, 2, 4, 6, 8 and 10 at.%), and an electron beam gun was used to evaporate thin films in a high vacuum. The impacts of Cr doping concentration on the structure and optics characteristics of the In2O3 layers were investigated. All Cr-doped In2O3 films had the cubic structure of In2O3 without secondary phases according to the X-ray diffraction findings. A study of the chemical makeup of each Cr-doped In2O3 compound revealed that they were all almost stoichiometric. To extract the optical characteristics and energy gap, a three-layer model simulated the experimental data of the spectroscopic ellipsometer. With increasing the Cr doping concentration, the optical band gap shifted the blue was seen. With increasing Cr content, the band gap in the (In1-xCrx)2O3 thin film was raised from 3.21 to 3.46 eV. Using the Murmann's exact equation, the refractive index and extinction coefficient that were obtained through spectroscopic ellipsometry could be utilized to fit the measured transmission data. As a function of Cr content, the change in structural parameters was be used to explain the change in the optical parameters. The (In1-xCrx)2O3 thin film are recommended for optoelectronic devices due to its tunability in the structural and optical properties.

Sputter-Deposited Binder-Free Nanopyramidal Cr/γ-Mo2N TFEs for High-Performance Supercapacitors

Due to their outstanding power density, long cycle life and low cost, supercapacitors have gained much interest. As for supercapacitor electrodes, molybdenum nitrides show promising potential. Molybdenum nitrides, however, are mainly prepared as nanopowders via a chemical route and require binders for the manufacture of electrodes. Such electrodes can impair the performance of supercapacitors. Herein, binder-free chromium (Cr)-doped molybdenum nitride (Mo2N) TFEs having different Cr concentrations are prepared via a reactive co-sputtering technique. The Cr-doped Mo2N films prepared have a cubic phase structure of γ-Mo2N with a minor shift in the (111) plane. While un-doped Mo2N films exhibit a spherical morphology, Cr-doped Mo2N films demonstrate a clear pyramid-like surface morphology. The developed Cr-doped Mo2N films contain 0–7.9 at.% of Cr in Mo2N lattice. A supercapacitor using a Cr-doped Mo2N electrode having the highest concentration of Cr reveals maximum areal capacity of 2780 mC/cm2, which is much higher than that of an un-doped Mo2N electrode (110 mC/cm2). Furthermore, the Cr-doped Mo2N electrode demonstrates excellent cycling stability, achieving ~ 94.6% capacity retention for about 2000 cycles. The reactive co-sputtering proves to be a suitable technique for fabrication of binder-free TFEs for high-performance energy storage device applications.Graphical

Cr-doped Sb2Te materials promising for high performance phase-change random access memory

Transition metal doping is an effective strategy to improve the properties of phase-change random access memory (PCRAM), while the underlying mechanism remains to be sufficiently investigated. Herein, a Cr-doped Sb2Te film is fabricated by co-sputtering and the enhancement mechanism of Cr-doping is deeply investigated by experiments and first-principles calculations. The CrxSb2Te film exhibits excellent performances involving high crystallization temperature (238.9 °C) and good data retention (10 years @161.7 °C) for Cr0.56Sb2Te, low density change rate (3.8%) and high reversible switching speed (5 ns) for Cr0.29Sb2Te, providing a variety of options for different applications. The calculated results show that Cr atoms preferentially substitute the Sb1 site and the CrTe bonds display a stronger ionic bond character in contrast to the covalent bonded SbTe, thus improving the crystalline phase stability and crystallization temperature. Moreover, ab initio molecular dynamics simulations demonstrate that in the amorphous phase Cr atoms locate in defective octahedral coordination. Meanwhile, the homopolar SbSb wrong bond increased with Cr doping and the Cr atoms tend to form tight cluster in the amorphous phase which could benefit for the fast phase-change speed. Our present findings of Cr0.29Sb2Te PCRAM device clearly reveal the enhancement mechanism by Cr doping which provides guidance for developing high-performance PCRAM devices.

Nanophotonic-structured front contact for high-performance perovskite solar cells

We report the design of a nanophotonic metal-oxide front contact aimed at perovskite solar cells (PSCs) to enhance optoelectronic properties and device stability in the presence of ultraviolet (UV) light. High-quality Cr-doped ZnO film was prepared by industrially feasible magnetron sputter deposition for the electron transport layer of PSCs. As a means, the influence of the Cr content on the film and device was systematically determined. In-depth device optics and electrical effects were studied using advanced three-dimensional opto-electrical multiphysics rigorous simulations, optimizing the front contact for realizing high performance. The numerical simulation was validated by fabricating PSCs optimized to reach high performance, energy conversion efficiency (ECE) = 17.3%, open-circuit voltage (VOC) = 1.08 V, short-circuit current density (JSC) = 21.1 mA cm−2, and fill-factor (FF) = 76%. Finally, a realistic front contact of nanophotonic architecture was proposed while improving broadband light absorption of the solar spectrum and light harvesting, resulting in enhanced quantum efficiency (QE). The nanophotonic PSC enables JSC improvement by ∼17% while reducing the reflection by 12%, resulting in an estimated conversion efficiency over 23%. It is further demonstrated how the PSCs’ UV-stability can be improved without considerably sacrificing optoelectronic performances. Particulars of nanophotonic designed ZnO:Cr front contact, PSCs device, and fabrication process are described.

Effect of Selective Lateral Chromium Doping by RF Magnetron Sputtering on the Structural, and Opto-Electrical Properties of Nickel Oxide

In this study, chromium (Cr)-doped nickel oxide (NiO) thin films were deposited by employing selective lateral doping of Cr in NiO by radio-frequency magnetron sputtering at different doping times ranging from 0 s (undoped) to 80 s. The structural, optical, and electrical properties of the resulting Cr-doped NiO thin films were investigated. Structural investigation from XRD patterns indicated that the grown Cr-doped NiO layer crystallized in a cubic phase. Broadening of the diffraction peak with increasing doping time from 0 s to 80 s led to a reduction in the crystallite size that varied from 23.52 nm to 14.65 nm. Compared with the undoped NiO, the diffraction peak along the (200) plane shifted from left to right as a function of doping time. This result indicated that Cr+3 could easily enter the NiO lattice. Results from the Hall-effect study disclosed that electrical properties of Cr-doped NiO was highly dependent on doping time. The conductivity of NiO was increased with doping time, and the highest conductivity (8.73 × 10−2 Scm−1) was achieved at a doping time of 80 s. Finally, optical investigations revealed that as doping time increased, the optical bandgap of Cr-doped NiO films dropped from 3.43 eV to 3.28 eV. The highest Urbach energy at higher doping time indicated that crystallinity became poorer, and the degree of defects increased with increasing doping time.

Microstructural and electrochemical supercapacitive properties of Cr‐doped CuO thin films: Effect of substrate temperature

Transition metal oxides have attracted a special interest in the applications of energy storage and conversion devices because of their distinctive structural, electronic, and catalytic properties. In the current study, the effect of substrate temperature on binder-free undoped CuO and Cr-doped CuO (~4.5 at. %) thin-film electrodes prepared by radio frequency sputtering technique is reported for supercapacitor applications. X-ray diffraction studies revealed the formation of undoped CuO and Cr-doped CuO films with monoclinic structure, while field emission scanning electron microscopy showed a significant change in the shape and size of the grains as a function of the substrate temperature. X-ray mapping indicated a uniform distribution of the elements present in these films. Substitution of Cr of ~4.5 at. % has not altered the primary monoclinic structure of CuO, but the doped CuO thin-film electrodes showed an improved conductivity. The electrochemical supercapacitive performance of the thin-film electrodes was studied using cyclic voltammetry, galvanostatic cycling with potential limitation, and electrochemical impedance spectroscopy techniques in 1 M KOH. The electrochemical measurements revealed that the thin-film electrode of Cr-doped CuO electrode developed at the substrate temperature of 573 K exhibited the highest areal capacitance of 209 mF cm−2 at a scan speed of 10 mV s−1, which is five times higher than that of the pure CuO (38 mF cm−2) thin-film. Furthermore, the Cr-doped CuO thin-film electrode exhibited excellent cycling stability with the capacity retention of 88% for 3000 continuous CV cycles in 1 M KOH. These results suggested that the binder-free Cr-doped CuO film electrodes prepared at the substrate temperature of 573 K is an excellent candidate material for the supercapacitor applications.

Enhancement of multifunctional optoelectronic and spintronic applications of nanostructured Cr-doped SnO2 thin films by conducting microstructural, optical, and magnetic measurements

A chemical synthesis method was used to produce Cr-doped SnO2 nanoparticles. By using the TEM technique, the nanocrystalline nature of the Sn1-xCrxO2 (0.0 ≤ x ≤ 0.1) nanopowder was confirmed. With different Cr concentrations, the electron beam deposition technique was used to deposit a series of Sn1-xCrxO2 nanocrystalline thin films on a silica substrate. X-ray diffraction (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and vibrating sample magnetometry (VSM) techniques were used to examine the physical properties of the deposited films. The nanocrystalline nature of the Sn1-xCrxO2 (0.0 ≤ x ≤ 0.1) thin film was confirmed by XRD and AFM morphology measurements. The XRD spectrum of the Sn1-xCrxO2 nanocrystalline film demonstrated a tetragonal crystal structure with no detectable extra phases. The optical measurements showed that as the Cr content increases, the direct optical energy gap Eg decreases without any sign of solubility limit up to x ≤ 0.1. The decrease in Eg is attributed to the sp-d exchange interaction. Also, the spectral behavior of the refractive index dispersion of the Cr-doped SnO2 indicates that as the Cr dopant increases, the refractive index of the deposited film also increases, which is attributed to the increase in the polarizability. Moreover, as the Cr content raises the atomic number, the density of the deposited film increases from 1.43 × 1022 cm−3 for SnO2 to 1.57 × 1022 cm−3 for Sn0·9Cr0·1O2. Further, the behavior of the refractive index dispersion of the deposited film was revealed using a single oscillator model proposed by Wemple-DiDomenico (WDD). Our calculations revealed that as the Cr concentration increases, the value of oscillator energy Eo decreases owing to the decrease in Eg, whereas the value of dispersion energy Ed increases because of the chemical structural changes such as the lattice parameters. Finally, the magnetic studies revealed that incorporating a small fraction of Cr into SnO2 produces room temperature ferromagnetism in the film, which is gradually suppressed by a further increase in Cr doping. These findings indicate that the Cr-doped SnO2 film can be recommended for optoelectronic and spintronic device applications.

Effect of chromium percentage doping on the optical, structural, morphological and electrical properties of ZnS:Cr thin films

Zinc sulfide (ZnS) and chromium-doped zinc sulfide (ZnS:Cr) thin films were grown on glass and Si substrates by cathodic radio-frequency (RF) sputtering. The deposition time and RF power were fixed respectively at 90 min and 200 W while chromium content was varied between 3 and 7%. The effect of Cr percentage on the structural, morphological and optical properties of the deposited thin films have been studied. X-ray diffraction analysis indicated that all the sputtered ZnS films were monophasic with a preferred growth orientation along the (111) plane of the zinc-blend (ZB) phase. The Cr-doped films, on the other hand, showed the (111), (2 2 2), and (311) peaks of the same phase that was confirmed by TEM . The crystallite size was about 17.75 nm for undoped ZnS films for RF power of 200 W and increased from 16.3 nm to 25.5 nm for ZnS:Cr. The strain was shown to decrease from 2.2 × 10 −3 to1.45 × 10 −3 . The optical properties (mainly the thicknesses, refractive index , absorption coefficient and optical band gap) were determined from optical transmission measurements in the ultraviolet–visible-near-Infrared wavelength range. Scanning electron microscopy observations revealed smooth film surfaces. Energy Dispersive Spectroscopy (EDS) revealed that the chromium sputtering rate is smaller than the Zn and S ones. UV–Visible transmission measurements revealed an average transmittance on the order 70% for the ZnS films while that of the ZnS:Cr was less than 60% in the visible wavelength region. Moreover, it was observed that the optical band-gap of the ZnS films is 3.72 eV, and slightly decreases from 3.68 to 3.44 eV as the chromium percentage increases, while the films thickness increased. The electrical resistivity of thin films has decreased from 5.2 × 10 5 Ω cm to 1.1 × 10 5 Ω cm as the chromium percentage increases from 3 to 7%. • XRD patterns showed that the particles crystallized in cubic lattice. • The crystallite size was observed to increase with increasing the chromium percentage. • It is observed that the energy band gap decreases from 3.7eV to 3.44 eV. • The resistivity decrease as Cr contents increasing.

Increase of electromechanical coupling coefficient k t 2 in (0001)-oriented AlN films by chromium doping

Piezoelectric AlN films possess high bulk acoustic wave velocity, low acoustic attenuation, and good temperature characteristics. However, AlN film bulk acoustic wave resonators (FBARs) have a relatively small electromechanical coupling coefficient k eff 2. It was recently reported that Cr doping in AlN films increased the piezoelectric constant d 33. The k t 2 of AlN FBARs may thus be enhanced by Cr doping. In this study, we investigated the effect of Cr doping in (0001)-oriented AlN films on k t 2 from the frequency characteristics of high overtone bulk acoustic wave resonators. k t 2 of the Cr-doped AlN films was increased for Cr contents of less than 3%. The maximum k t 2 observed for the Cr0.012Al0.088N film was 5.9%, which was approximately 1.4 times higher than that of pure AlN film (k t 2 = 4.4%).

Fabrication of pulsed laser-deposited Cr-doped zinc oxide thin films: structural, morphological, and optical studies

High-quality c-axis-oriented Cr-doped ZnO thin films were grown on 100-μm-thick Si (100) wafer substrate by Pulsed Laser Deposition (PLD) technique. The PLD is a versatile technique for growing thin films and a wide range of materials. The structural analyses confirm the wurtzite structure of synthesized samples and are preferentially oriented along c-axis perpendicular to substrate the surface. The intensity of defect-induced mode frequency for Cr-doped ZnO film increased due to the formation of highly crystalline films. In Raman spectra, E2 (high) mode shows redshift owing to optical phonon confinement induced by uncertainty in photon wave vectors i.e., downshift of Raman peaks. Cr-doped ZnO thin film consists of nanorod-shaped grains of different sizes. Each rod possesses width in a range of 85–93 nm and length upto several hundred nanometres. The decrease in peak intensity of Cr-doped ZnO film photoluminescence (PL) spectrum is attributed to a fall in the electron–hole recombination process. In visible region of PL spectra, green light emission peak at about 567 nm was associated with defects in ZnO. It is observed after doping root mean square (RMS) roughness increases with which means the surfaces becomes rough and grain size increases.

Ultra-sensitive anomalous Hall effect sensors based on Cr-doped Bi2Te3 topological insulator thin films

The observation of anomalous Hall effect (AHE) in magnetically doped topological insulators brings a new candidate of Hall sensor with low power consumption. In this work, the transport properties and the sensitivity of AHE sensors based on Cr-doped Bi2Te3 thin films were studied. Obvious AHEs induced by ferromagnetic ordering were presented in all Cr x Bi2-x Te3 sensors. At the optimized doping concentration of x= 0.09, a high sensitivity of 6625 Ω T−1 was achieved, which has increased by 2.5 times compared to the highest reported one in Cr-doped Bi2Te3. More importantly, a considerable sensitivity of 4082 Ω T−1 can be obtained up to 20 K, which implies a higher working temperature than other reports. Our findings suggest Cr-doped Bi2Te3 sensor could be a good candidate for highly sensitive AHE sensors and reveal the extraordinary potential of magnetic TIs in the applications of field detection.

Nanoscale charge transport and local surface potential distribution to probe the defect passivation in Cr-substituted earth abundant CZTS absorber layer

The non-stochiometric deviations in CZTS often results in certain detrimental point defects that act as trap centers causing non-radiative recombination and potential fluctuations, eventually results in large open circuit voltage (VOC) deficit in CZTS solar cells. Cationic substitution in CZTS layer is one of the leading approaches to capture the great potential of kesterite solar cells for future cost-effective photovoltaic technology. Here, chromium incorporation in CZTS is studied for cationic substitution in CZTS layer, as it renders multiple chemical states including +1, +2 and + 4 of Cu, Zn and Sn cations in CZTS. The CZTS films determine to have good crystallinity and morphology with no significant disparity among pristine and Cr-doped CZTS films, apart from slight shift of XRD (112) peak indicating partial cation substitution by smaller Cr atoms. However, the Zn content is found to be decreased with increasing Cr content in CZTS layer. Substantial enhancement in the absorption of Cr-doped CZTS films indicate intermediate band (IB) within the band gap. Photoluminescence (PL) emission spectra strongly suggests reduced non-radiative recombination and potential fluctuations in Cr-CZTS films. X-ray photoelectron spectroscopy investigations reveal Zn substitution by Cr in CZTS crystal geometry. Using nanoscale Kelvin Probe Force Microscopy (KPFM) and Conducting Atomic Force Microscopy (CAFM), we verify the surface potential variation and nanoscale electrical conductivity in pristine and Cr-CZTS films. Additionally, Zn substitution by Cr eventually lead to suppression of ZnSn deep level defects segregated at grain boundaries (GBs). CAFM strongly confirms the GB passivation in Cr-CZTS films. This work widens the opportunity of exploring potential cationic substitution in CZTS for developing high efficiency CZTS solar cells.