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Surface confined quantum well state (scQWS) is a QWS confined around the surface of a thin film whose electronic energy is smaller than the work function of the film. The scQWS is rather rare in most thin films. Here, we show the existence of scQWS in thin films of transition metal dichalcogenides, MoS2. Signatures of scQWS are identified as the overall downward band dispersion in the bulk gap of 2 H-MoS2 thin film at larger binding energy range. These scQWSs are also characterized with a Shockley-type surface state having an inverse parabolic decay into the film and a symmetric (asymmetric) distribution of projected charge density at the two surfaces of odd-layer (even-layer) films. Our findings of scQWS in MoS2 shed some light on understanding the electronic properties of 2D materials with implications in future 2D electronic devices. [ABSTRACT FROM AUTHOR]

We investigated the switching performance of Cu-oxide films with Al, Pt, and Ti electrodes. Compared with Pt electrode, the Al electrode shows better stability, preferable endurance, and larger resistance ratio. An interface AlOx layer is detected by transmission electron microscopy and Auger electron spectroscopy. This layer can strongly affect the movement of oxygen vacancies. However, the sample with pure Ti electrode almost has no switching characteristics. Ti/TiN electrode with thin Ti exhibits good switching behavior. The thickness control of Ti layer is quite critical. So we suggest that the oxygen diffusion in electrode is another important factor for switching performance. [ABSTRACT FROM AUTHOR]

The electronic structures of amorphous, metastable, and stable phases of Ge1Sb2Te4 film were investigated by high-resolution x-ray photoelectron spectroscopy. The Te 4d core level showed a negligible change in binding energy (BE). In the stable phase, the Ge 3d and Sb 4d core levels were, respectively, dominated by a spin-orbit-split feature at 0.1 eV-lower BE and a well-defined component at 0.4 eV-higher BE than those in the amorphous phase. The analysis suggests that the amorphous phase and the stable phase is respectively represented by a broad and a well-defined electronic structure and that the metastable phase is represented by two different kinds of local electronic structures. The valence-band structures showed a trend similar to that reported by Klein et al. [Phys. Rev. Lett. 100, 016402 (2008)] between the amorphous and metastable phases. [ABSTRACT FROM AUTHOR]

The chemical state of N in N-doped amorphous Ge2Sb2Te5 (a-GST) samples with 0–14.3 N at. % doping concentrations was investigated by high-resolution x-ray photoelectron spectroscopy (HRXPS) and Ge K-edge x-ray absorption spectroscopy (XAS). HRXPS showed negligible change in the Te 4d and Sb 4d core-level spectra. In the Ge 3d core-level spectra, a Ge nitride (GeNx) peak developed at the binding energy of 30.2 eV and increased in intensity as the N-doping concentration increased. Generation of GeNx was confirmed by the Ge K-edge absorption spectra. These results indicate that the N atoms bonded with the Ge atoms to form GeNx, rather than bonding with the Te or Sb atoms. It has been suggested that the formation of Ge nitride results in increased resistance and phase-change temperature. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry is used to characterize charge trapping defect states in thin HfO2 gate dielectric films deposited by atomic layer deposition on chemically oxidized p-type Si (100) substrates. The intensity of specific absorption features detected below the band gap of HfO2 at 2.9 and 4.75 eV is clearly distinguished from the Si critical points; however, repeating this spectroscopic evaluation for identical HfO2 films deposited and annealed on fused silica substrates results in no defect features detected. The HfO2/Si(100) results, therefore, suggest these oxygen deficient defects are not intrinsic to HfO2 but reside primarily at the interface with the silicon substrate. The feasibility of utilizing spectroscopic ellipsometry to identify stoichiometric variations at the SiO2/Si(100) interface and the corresponding changes associated with the electrical performance is presented. [ABSTRACT FROM AUTHOR]

Atomically flat, fully strained Si1-xGex layers with thicknesses ranging from 40 to 240 nm were grown on Si(001) at 450 °C by ultrahigh-vacuum chemical vapor deposition and subjected to annealing at 1000 °C for 20 min to induce relaxation. In order to minimize surface diffusion during annealing and thereby inhibit strain-induced roughening in favor of misfit dislocation formation, SiO2 capping layers are deposited prior to annealing. The overall process results in smooth, relaxed alloy layers without the necessity of using several-μm-thick compositionally graded buffer layers. [ABSTRACT FROM AUTHOR]

Threshold voltage (VTH) instability in metal oxide semiconductor field transistors (MOSFETs) with high dielectric constant (k) gate dielectrics has been investigated with an inversion pulse measurement technique, which can detect fast dielectric charging/discharging within microseconds (μs). The results indicate that VTH instability can be significantly underestimated by conventional VTH measurement techniques. Based on temperature-dependent stress data, it is suggested that charging and discharging are determined by direct tunneling and thermally assisted processes, respectively. [ABSTRACT FROM AUTHOR]

We report the selective growth of InAs self-assembled quantum dots (SAQDs) on silicon-dioxide/silicon (SiO[sub 2]/Si) substrates patterned in nanometer scale. The SiO[sub 2] thin film is found to be an efficient mask material for prohibiting the growth of InAs SAQDs, while the formation of stable SAQDs is observed on the exposed surface of Si. We have utilized this selectivity to demonstrate almost one-dimensional alignment of InAs SAQDs on Si stripes. The crystallinity of SAQDs is also identified by high-resolution transmission electron microscope observation. Our study opens up a possibility of reliably integrating III-V quantum dot devices with conventional Si circuits. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The magnetization and critical magnetization current densities of sinter-forged YBa2Cu3O7-δ samples of nearly theoretical density have been studied. The magnetization curves can be well fitted by Kim’s critical state equation Jc(B)=α/(B0+B) with a flat plate geometry. The results revealed an anisotropy in the lower critical field and the critical current density with respect to the forging axis. The deduced critical current density in the favorable direction is larger than the value of isotropic polycrystalline samples. [ABSTRACT FROM AUTHOR]

Examines the energy relaxation of two-dimensional carriers in strained germanium/Si[sub 0.4]Ge[sub 0.6] and silicon/Si[sub 0.7]Ge[sub 0.3] quantum wells. Observation of power law dependence of carrier temperature; Difference of measured values for the current exponent for both samples; Role of phonon dimensionality in the exponent difference.

The transverse magnetoresistance and Hall effect have been studied for n-type gray tin epilayers grown on (001)CdTe substrates by the molecular beam epitaxy technique. Shubnikov–de Haas oscillations were observed in samples having Hall mobilities ≥104 cm2 /V s at low temperatures. Measurements were carried out using both the dc method and field modulation techniques in the temperature range from 1.2 to 10 K and in magnetic fields up to 10 T. Beat patterns were observed in the Shubnikov–de Haas spectra which we ascribe either to inhomogeneous doping, arising from the diffusion of Cd and Te from the substrate, or to quantization of the motion in the direction parallel to the film normal. The Shubnikov–de Haas carrier concentration of a 1210 Å film was determined to be nSdH =2.3×1017 cm-3, in good agreement with the Hall density. [ABSTRACT FROM AUTHOR]

Thin films of YBaCu(F)O were deposited on SrTiO3(100) substrates by multilayer deposition from three electron guns containing Y, BaF2, and Cu under a pressure of 5×10-5 Torr of O2. The films were later annealed in a separate chamber under a flowing O2-H2O atmosphere. X-ray diffraction studies reveal that the resulting structure is highly oriented with the a axis perpendicular to the substrate. Scanning electron micrographs show a morphology consisting of an array of orthogonal, interconnecting bars with well-developed junctions. High-resolution electron microscopy and electron diffraction patterns show that these junctions are atomically abrupt and that the associated c axes are mutually perpendicular. These epitaxial films show a sharp resistive transition with Tc(R=0) as high as 90 K. The zero field critical current density, determined from magnetization measurements, is 2.9×106 A/cm2 at 4.2 K and 5.0×104 A/cm2 at 77 K. [ABSTRACT FROM AUTHOR]

Y-Ba-Cu-O thin films have been deposited on MgO substrates by dc magnetron sputtering from a stoichiometric YBa2Cu3O7-δ target, after which they are subjected to a short heat treatment. Zero resistance is routinely achieved near 60 K, and one film shows zero resistance at 68.0 K. [ABSTRACT FROM AUTHOR]

The chemical state of N in N-doped amorphous Ge2Sb2Te5 (a-GST) samples with 0–14.3 N at. % doping concentrations was investigated by high-resolution x-ray photoelectron spectroscopy (HRXPS) and Ge K-edge x-ray absorption spectroscopy (XAS). HRXPS showed negligible change in the Te 4d and Sb 4d core-level spectra. In the Ge 3d core-level spectra, a Ge nitride (GeNx) peak developed at the binding energy of 30.2 eV and increased in intensity as the N-doping concentration increased. Generation of GeNx was confirmed by the Ge K-edge absorption spectra. These results indicate that the N atoms bonded with the Ge atoms to form GeNx, rather than bonding with the Te or Sb atoms. It has been suggested that the formation of Ge nitride results in increased resistance and phase-change temperature. [ABSTRACT FROM AUTHOR]

Endoscopy, enabling high-resolution imaging of deep tissues and internal organs, plays an important role in basic research and clinical practice. Recent advances in photoacoustic microscopy (PAM), demonstrating excellent capabilities in high-resolution functional imaging, have sparked significant interest in its integration into the field of endoscopy. However, there are challenges in achieving functional PAM in the endoscopic setting. This Perspective article discusses current progress in the development of endoscopic PAM and the challenges related to functional measurements. Then, it points out potential directions to advance endoscopic PAM for functional imaging by leveraging fiber optics, microfabrication, optical engineering, and computational approaches. Finally, it highlights emerging opportunities for functional endoscopic PAM in basic and translational biomedicine., Competing Interests: The authors have no conflicts to disclose., (© 2024 Author(s).)

A non-contact method for efficient, non-invasive excitation of mechanical waves in soft media is proposed, in which we focus an ultrasound (US) signal through air onto the surface of a medium under study. The US wave reflected from the air/medium interface provides radiation force to the medium surface that launches a transient mechanical wave in the transverse (lateral) direction. The type of mechanical wave is determined by boundary conditions. To prove this concept, a home-made 1 MHz piezo-ceramic transducer with a matching layer to air sends a chirped US signal centered at 1 MHz to a 1.6 mm thick gelatin phantom mimicking soft biological tissue. A phase-sensitive (PhS)-optical coherence tomography system is used to track/image the mechanical wave. The reconstructed transient displacement of the mechanical wave in space and time demonstrates highly efficient generation, thus offering great promise for non-contact, non-invasive characterization of soft media, in general, and for elasticity measurements in delicate soft tissues and organs in bio-medicine, in particular.

We present single-shot phase-sensitive imaging of propagating mechanical waves within tissue, enabled by an ultrafast optical coherence tomography (OCT) system powered by a 1.628 MHz Fourier domain mode-locked (FDML) swept laser source. We propose a practical strategy for phase-sensitive measurement by comparing the phases between adjacent OCT B-scans, where the B-scan contains a number of A-scans equaling an integer number of FDML buffers. With this approach, we show that micro-strain fields can be mapped with ∼3.0 nm sensitivity at ∼16 000 fps. The system's capabilities are demonstrated on porcine cornea by imaging mechanical wave propagation launched by a pulsed UV laser beam, promising non-contact, real-time, and high-resolution optical coherence elastography.

We determine the surface enhanced Raman (SER) capability of indium tin oxide nanorods (ITO NRs) whose physical, chemical, and optical properties are precisely and uniformly controlled during synthesis. We demonstrate that the Raman intensities observed from varying concentrations of the pure and mixed molecules of rhodamine 6G and 4',6-diamidino-2-phenylindole are much larger on ITO NRs relative to those measured on commercially available ITO-coated glass or Si. Our efforts signify the first attempt to assess the SER capability of precisely controlled metal oxide NRs and will be highly beneficial to many basic and applied Raman applications requiring exceptional detection sensitivity.

A soft x-ray absorption and x-ray magnetic circular dichroism (XMCD) study of the ferromagnetism in solution-grown EuS nanocrystals (NCs) is reported. The absorption edges of Eu M(5) and M(4), S K, O K, and P K were probed to determine elementally specific contributions to the magnetism of EuS NCs. Differential spin absorption was observed by XMCD at the Eu M(5,4) edges confirming the presence of a magnetic moment on the Eu(2+) 4f shell. No dichroic signal was observed for S, O, or P. Vibrating sample magnetometry of ensembles of NCs shows ferromagnetic properties consistent with the XMCD studies.