Muhammad Taha Sultan

PPy/PANI-functionalized silicon nanowires exhibit enhanced response kinetics and long-term stability, enabling reliable real-time respiratory waveform monitoring for wearable sensing applications. The graphical abstract was created with Blender and Genspark.

Ammonia (NH₃) is a corrosive and toxic gas to which exposure can cause serious health problems and even death. Elevated levels of it in exhaled breath can serve as a biomarker for various diseases. Consequently, monitoring NH₃ in the ambient air and for medical diagnostics is important for public health and safety. However, developing NH₃ gas sensors that function effectively in high humidity conditions, such as those found in human breath, has proven challenging. In this study, we present a simple and cost-effective NH₃ gas-sensor based on a structure of interconnected silicon nanwires (SiNWs), fabricated with metal-assisted chemical etching. Two different versions were made and compared; SiNWs, with and without germanium nanoparticles. The sensing mechanism is attributed to the formation of a hole accumulation layer in the air, whose width decreases upon exposure to NH₃. It was also observed that bundling of individual nanowires enhances the sensor’s response time, down to approximately 70 s, which is an order of magnitude faster response than that of similar SiNW structures reported in the literature.

We investigate the structural and metal–insulator transition (MIT) behavior of epitaxial V2O3 films fabricated by reactive direct current magnetron sputtering on r, a, c, and m-plane Al2O3 substrates, in both as-received and annealed states. Characterization of MIT of the V2O3 films grown on annealed substrates demonstrated significant changes in observed MIT properties, i.e., r-plane films showed ≈2 order increase in transition magnitude, m-plane ≈6 orders, and c-plane films exhibited a reduction of ≈3 orders, compared to un-annealed substrates, whereas for V2O3 on annealed a-plane, it revealed a shift in the transition to higher values, with reduction in hysteresis width. Structural characterization conducted via x-ray diffraction and atomic force microscopy revealed a reduction in out-of-plane compressive strain for annealed substrates, along with decreased lateral grain size. Additionally, the correlation between the V2O3 MIT and its underlying structural phase transition was verified by temperature-dependent x-ray diffraction analysis. These findings highlight the role of substrate orientation and pre-annealing in tuning the MIT behavior of V2O3 films grown on the Al2O3 substrate.

Ammonia (NH 3) is a corrosive gas that can pose significant risks to human health, even at low concentrations. Its presence in exhaled breath can also serve as an indicator of various health conditions. This study demonstrates that silicon nanowires (SiNWs) exhibit high sensitivity to NH 3 , with notably improved performance in humid environments. Incorporation of tungsten trioxide (WO 3) nanoparticles further enhances the sensor's sensitivity and accelerates its response time under a range of humidity conditions. These findings advance the development of robust, simple, and efficient NH 3 sensors, with potential applications in both environmental monitoring and medical diagnostics.

We study the dependence of photo-spectral intensity on tri- and multilayers of SiO₂/[SiGe [ d SiGe ]/SiO₂] _N with repetitions N = 1 to 10 and thicknesses d SiGe = 5 –100 nm. Photocurrent analysis reveals a bimodal spectral feature. A comparison of the photocurrent analysis between tri- and multilayers shows that in the multilayer structures, the photo-spectral intensity increases with increasing repetition N. The change in intensity could then be further tuned by changing the thickness of the SiGe layers d SiGe . We attribute the change in intensity to an increase in tensile strain, along with increased Ge atomic concentration and reduced SiGe-nano cluster size.

SiGe‐SiO₂‐based structures present high interest for their high photosensitivity from visible to short‐wavelength infrared. Herein, two postdeposition annealing procedures, that is, rapid thermal annealing (RTA) and rapid‐like furnace annealing (FA), are compared. Both RTA and FA are performed at 600 °C for 1 min for SiGe nanocrystals (NCs) formation in SiO₂ matrix in Si/SiO₂/SiGe/SiO₂ structures deposited by magnetron sputtering. The FA imitates RTA resulting in enhanced spectral response. X‐ray diffraction, transmission electron microscopy, and Raman spectroscopy are carried out showing Ge‐rich SiGe NCs with 11.3 ± 1.2 nm size for RTA and 9.4 ± 0.8 nm for FA. Photocurrent spectra for both structures show several peaks that are annealing dependent. The photocurrent intensity for FA samples is ≈7 times higher than RTA samples while cutoff wavelengths are slightly different, that is, 1365 nm for FA and 1375 nm for RTA. The FA structures show (at −1.5 V) over 4 A W⁻¹ responsivity at 730 nm, 6.4 × 10⁷ Jones detectivity at 735 nm, and 2.2 × 10⁷ Jones at about 1210 nm. FA structures contain small SiGe NCs with incorporated residual strain, while RTA ones are formed of columnar SiGe NCs separated by SiGeO_x amorphous regions and show increased tensile strain in the SiGe.

Accurate and fast breath monitoring is of great importance for various healthcare applications, for example, medical diagnoses, studying sleep apnea, and early detection of physiological disorders. Devices meant for such applications tend to be uncomfortable for the subject (patient) and pricey. Therefore, there is a need for a cost-effective, lightweight, small-dimensional, and non-invasive device whose presence does not interfere with the observed signals. This paper reports on the fabrication of a highly sensitive human respiratory sensor based on silicon nanowires (SiNWs) fabricated by a top-down method of metal-assisted chemical-etching (MACE). Besides other important factors, reducing the final cost of the sensor is of paramount importance. One of the factors that increases the final price of the sensors is using gold (Au) electrodes. Herein, we investigate the sensor’s response using aluminum (Al) electrodes as a cost-effective alternative, considering the fact that the electrode’s work function is crucial in electronic device design, impacting device electronic properties and electron transport efficiency at the electrode–semiconductor interface. Therefore a comparison is made between SiNWs breath sensors made from both p-type and n-type silicon to investigate the effect of the dopant and electrode type on the SiNWs respiratory sensing functionality. A distinct directional variation was observed in the sample’s response with Au and Al electrodes. Finally, performing a qualitative study revealed that the electrical resistance across the SiNWs renders greater sensitivity to breath than to dry air pressure. No definitive research demonstrating the mechanism behind these effects exists, thus prompting our study to investigate the underlying process.

This study incorporates the structural and magnetic characterization of epitaxial Ni 80 Fe20 films grown by direct cur-rent magnetron sputtering on MgO(001) and MgO(001)||VN(001) substrates. A series of samples grown with different N 2 flow settings for the deposition of VN and similar permalloy deposition parameters was utilized to investigate the effect of morphological evolution and buffer layer induced strain on the magnetic properties of Ni 80 Fe20. X-ray diffraction analysis reveals an epitaxial nature of the VN(001) and Py(001) films grown on MgO substrates. Angular dependent magneto-optical Kerr effect characterization reveals a cubic anisotropy for Ni 80 Fe20 on MgO with a coercivity of ~0.8 Gauss along the easy directions. Incorpo-rating an epitaxial VN buffer, the structures showed a transition from a cubic to isotropic magneto-crystalline anisotropy with coercivity varying from 2.5 to 25 Gauss for Ni 80 Fe20 deposition on VN (with N2 varying from 5 to 12 sccm). The variation is attributed to the microstructural evolution of the Ni 80 Fe 20 to 3D structures along with an induced structural strain.