Apparent Height Research Articles

Nanoscale Probing of Image-Potential States and Electron Transfer Doping in Borophene Polymorphs.

Because synthetic 2D materials are generally stabilized by interfacial coupling to growth substrates, direct probing of interfacial phenomena is critical for understanding their nanoscale structure and properties. Using field-emission resonance spectroscopy with an ultrahigh vacuum scanning tunneling microscope, we reveal Stark-shifted image-potential states of the v1/6 and v1/5 borophene polymorphs on Ag(111) with long lifetimes, suggesting high borophene lattice and interface quality. These image-potential states allow the local work function and interfacial charge transfer of borophene to be probed at the nanoscale and test the widely employed self-doping model of borophene. Supported by apparent barrier height measurements and density functional theory calculations, electron transfer doping occurs for both borophene phases from the Ag(111) substrate. In contradiction with the self-doping model, a higher electron transfer doping level occurs for denser v1/6 borophene compared to v1/5 borophene, thus revealing the importance of substrate effects on borophene electron transfer.

The effects of nanobubbles on the assembly of glucagon amyloid fibrils

Some recent studies have shown that the surface and interface play an important role in the assembly and aggregation of amyloid proteins. However, it is unclear how the gas-liquid interface affects the protein assembly at the nanometer scale although the presence of gas-liquid interfaces is very common in in vitro experiments. Nanobubbles have a large specific surface area, which provides a stage for interactions with various proteins and peptides on the nanometer scale. In this work, nanobubbles produced in solution were employed for studying the effects of the gas-liquid interface on the assembly of glucagon proteins. Atomic force microscopy (AFM) studies showed that nanobubble-treated glucagon solution formed fibrils with an apparent height of 4.02 ± 0.71 nm, in contrast to the fibrils formed with a height of 2.14 ± 0.53 nm in the control. Transmission electron microscopy (TEM) results also showed that nanobubbles promoted the assembly of glucagon to form more fibrils. Thioflavin T (ThT) fluorescence and Fourier transform infrared (FTIR) analyses indicated that the nanobubbles induced the change of the glucagon conformation to a β-sheet structure. A mechanism that explains how nanobubbles affect the assembly of glucagon amyloid fibrils was proposed based on the above-mentioned experimental results. Given the fact that there are a considerable amount of nanobubbles existing in protein solutions, our results indicate that nanobubbles should be considered for fully understanding the protein aggregation events in vitro.

Determining the potential barrier presented by the interfacial layer from the temperature induced I–V characteristics in Al/p-Si Structure with native oxide layer

The temperature induced current-voltage (I–V-T) characteristics of the Al/SiO2/p-Si diodes with the interfacial native oxide layer were experimentally investigated in present our study. The values of 24.35 and 1.02 eV for the tunneling factor (aδχ) and the potential barrier presented by the interfacial layer (χ) were determined for the Al/SiO2/p-Si metal-insulator-semiconductor (MIS) diode. The χ value obtained from the forward bias I–V-T characteristics of the SiO2/p-Si diode is a crucial result according to those from only room temperature I–V curves in literature studies. Furthermore, the temperature dependence of the apparent barrier heights of the forward bias I–V-T characteristics displayed a Gaussian distribution (GD) of inhomogeneous barrier heights (BHs). Thus, the standard deviation values of σ1s0=147.65 mV for high temperature range and σ2s0=83.66 mV for low temperature range were obtained from the GD plot of the BHs (the apparent BH versus (2kT)−1 plot). Again, for the mean barrier height Φ‾b0 from the GD plot of the BHs, the values of 1.16 eV and 0.70 eV were obtained from the high temperature region and low temperature region, respectively. Furthermore, the Richardson constant values of 54.66 and 58.42 A/K2cm2 from these temperature regions are approximately 1.70 times higher than the theoretical value of 32 A/K2cm2 of the p-type Si semiconductor.

Gaussian distribution of inhomogeneous nickel–vanadium Schottky interface on silicon (100)

This study presents the characterization of the nickel–vanadium (NiV) Schottky diode on n-type silicon (Si) in the temperature range 75 K–300 K. The experimental current–voltage (I–V) measurements are first analyzed by using the thermionic emission (TE) theory. For this purpose, the vertical optimization method is used to find the values of the TE parameters, i.e. the values of the ideality factor, barrier height, and series resistance. It is found that these parameters exhibit strong temperature dependence, i.e. an increase of the ideality factor and a decrease of the barrier height and the series resistance when the temperature decreases, which is due to inhomogeneities at the Schottky interface. Therefore, we employ Werner’s model under the assumption of a Gaussian distribution to analyze the temperature dependence of the TE parameters. The mean and standard deviation of the barrier height are obtained as and , respectively. In addition, we show that the apparent barrier height and apparent ideality factor are in accordance with Werner’s model. Furthermore, we use the modified Richardson plot to find the value of the Richardson constant. The obtained value of the latter is A cm−2 K−2 and is very close to the theoretical value of 112 A cm−2 K−2 of n-type Si. Finally, we investigate the temperature dependence of the ideality factor and show the validity of the T0-effect for the NiV/Si Schottky diode.

Bias-voltage-dependent measurement of apparent barrier height on low-work-function thin film

Using a scanning tunneling microscope, we have examined the effect of the bias voltage on the apparent barrier height. The sample used in this study was a nitrogen-doped lanthanum hexaboride film. We experimentally proved that a linear relationship exists between the apparent barrier height and the sample bias voltage. As a consequence, we estimated the work function of the film to be 2.35 eV by theoretical fitting. This value is in good agreement with that obtained by photoemission spectroscopy in a previous study. Our results demonstrate that the work function calculated through apparent barrier height measurements is guaranteed to be highly reliable in spite of the simple one-dimensional model. We anticipate that the sensitivity of the barrier height to the sample work function can be utilized for elemental identification on surfaces with characteristic work functions.

Quantum well electronic states in spatially decoupled 2D Pb nanoislands on Nb-doped SrTiO3(0 0 1)

Two-dimensional (2D) Pb nanoisland has established an ideal platform for studying the quantum size effects on growth mechanism, electronic structures as well as high-temperature superconductivity. Here, we investigate the growth and quantum well electronic states of the 2D Pb nanoislands on Nb-doped SrTiO3(001) by scanning tunneling microscopy and spectroscopy. In contrast to Pb/Si(111), Pb/Cu(111) and Pb/Ag(111), there is no wetting layer of Pb formed on the Nb-doped SrTiO3(001) surface, resulting in isolated Pb nanoislands with an apparent height of 4 atomic layers as the building blocks for the island growth. According to the thickness-dependent quantum well states resolved in both occupied and unoccupied energy regions, the constant group velocity vg = 1.804 × 106 m/s and the Fermi wavevector kF = 1.575 Å−1, have been extracted from a linear fit of the Pb(111) band dispersion along the Γ-L direction. In addition, the energy-dependent scattering phase shift φ(E) obtained by means of the phase accumulation model shows a metallic-like scattering interface analogous to Pb/Ag(111). These spatially decoupled 2D Pb nanoislands thus realize an opportunity to explore the intrinsic quantum confinement phenomena in nanoscale superconductors on the doped titanium-oxide-type substrate.

Comparison of ionospheric reflection heights for LEMPs produced by lightning return strokes of different polarity

Apparent ionospheric reflection heights estimated using electric field waveforms of negative and positive cloud-to-ground lightning return strokes (-CGs and +CGs) that occurred during the same thunderstorms have been compared. We analyzed electric field waveforms of 101 -CGs and 74 +CGs that were recorded in August 2016 in Florida. For daytime conditions, the mean ionospheric reflection height for lightning electromagnetic pulses (LEMPs) produced by + CGs is larger than that for LEMPs produced by -CGs for either first or subsequent strokes, although the difference is statistically significant only for subsequent strokes. For nighttime conditions, the trend is the same, but the sample sizes are too small to draw meaningful conclusions. For daytime conditions, the mean ionospheric reflection height for subsequent strokes in -CGs is smaller than that for first strokes, while for + CGs the mean reflection heights for first and subsequent strokes are essentially the same. This disparity is related to the fact that subsequent strokes in –CGs usually develop in the channel of the first stroke, while subsequent strokes in +CGs usually form new terminations on ground and, hence, are similar to first strokes. In our dataset, NLDN-reported peak currents for + CGs tend to be higher than for –CGs for both daytime and nighttime conditions and for either first or subsequent strokes.

Graphene as a Schottky Barrier Contact to AlGaN/GaN Heterostructures.

Electrical and noise properties of graphene contacts to AlGaN/GaN heterostructures were studied experimentally. It was found that graphene on AlGaN forms a high-quality Schottky barrier with the barrier height dependent on the bias. The apparent barrier heights for this kind of Schottky diode were found to be relatively high, varying within the range of φb = (1.0–1.26) eV. AlGaN/GaN fin-shaped field-effect transistors (finFETs) with a graphene gate were fabricated and studied. These devices demonstrated ~8 order of magnitude on/off ratio, subthreshold slope of ~1.3, and low subthreshold current in the sub-picoamperes range. The effective trap density responsible for the 1/f low-frequency noise was found within the range of (1–5) · 1019 eV−1 cm−3. These values are of the same order of magnitude as reported earlier and in AlGaN/GaN transistors with Ni/Au Schottky gate studied as a reference in the current study. A good quality of graphene/AlGaN Schottky barrier diodes and AlGaN/GaN transistors opens the way for transparent GaN-based electronics and GaN-based devices exploring vertical electron transport in graphene.

Mechanical and thermal conduction properties of carbon/carbon composites with different carbon matrix microstructures

Four carbon/carbon composites with densities of 1.75–1.81 g/cm3were produced with matrix carbons derived from (a)coal tar pitch and furfural acetone resin by impregnation-carbonization, (b) natural gas by isothermal chemical vapor infiltration and (c) xylene by film-boiling chemical vapor infiltration. Theirmechanical properties and thermal conductivities (TC) were compared and correlated to the matrix carbon microstructures. Results showed that the strength of the composites decreased as thecarbon matrix changed from natural gas pyrocarbon (PyCN), to resin-derived carbon, to xylene PyC (PyCX), and to pitch-derived carbon. The highest flexural and interlaminar shear strengths of 208.7 and 26.4MPa, respectively, were obtained for the PyCN matrix. The large amount of fiber pull-out and step-like matrix fracture contributed to a high toughness of composites with PyCN and PyCX matrices. Relatively low strength and toughness were obtained for the pitch-derived carbon. The change of TC with the matrix type was consistent with the graphitization degree and apparent crystallite height. The highest in-plane and out-of-plane TC reached 148.2 and 75.4 W/(m·K), respectively, for the PyCX matrix, which was due to its carbon layers having the highest preferred orientation. The chaotic structure and large number of defects of the resin-derived carbon produced a relatively low TC. PyCN was the most suitable matrix for composites with excellent mechanical properties. PyCXshould be used to improve the TC and toughness of the low-cost composites.

The variance of clavicular surface morphology is predictable: an analysis of dependent and independent metadata variables

BackgroundThe anatomy of the clavicle is specific and varied in reference to its topography and shape. These anatomic characteristics play an important role in the open treatment of clavicle fractures. The complex and variable topography creates challenges for implant placement, contouring, and position. Hardware prominence and irritation does influence the decision for secondary surgical intervention.MethodsComputerized tomographic scans of 350 adult clavicles with the corresponding patients' metadata were acquired and digitized. Morphologic parameters determining the shape of the clavicle were defined and computed for each digitized bone. The extracted morphologic parameters were correlated with patient metadata to analyze the relationship between morphologic variability and patient characteristics.ResultsThe morphologic parameters defining the shape, that is, the radius of the medial and lateral curves, the apparent clavicle height and width, and the clavicle bow position, correlate with the clavicle length. The clavicle length correlates with the patients' height. Gender differences in shape and form were dependent and related to individual height distribution and clavicle length. Asian populations showed a similarly predictable, but shifted, correlation between shape and clavicle length.ConclusionThis anatomic analysis shows that the clavicle shape can be predicted through the clavicle length and patients' stature. Smaller patients have shorter and more curved clavicles, whereas taller patients have longer and less curved clavicles. This correlation will aid surgeons in fracture reduction, implant curvature selection, and in optimal adaptation of clavicle implants, and represents the basis for anatomically accurate solutions for clavicle osteosynthesis.

Wetting behavior and mechanism of glass coatings on samarium–cobalt alloys in the heating process

The wetting behavior of glass coatings on samarium-cobalt alloys with different roughness at elevated temperatures in air was investigated by a sessile drop method. The wetting properties were analyzed through several parameters, including apparent contact angle, height and diameter of a glass cylinder on the samarium-cobalt alloy, determined by using a high temperature microscope. The morphology evolution of the glass coating was observed by using a scanning electron microscope. The results show that the glass cylinder contracts initially, and then swells followed by wetting and spreading on the samarium-cobalt alloy substrate. This process is explained by the role of air and the increase of capillary number. The dependence of apparent contact angle on surface roughness is related to interface reaction. It is concluded that the surface roughness firstly increases the contact angle, but then promotes wetting due to the wetting transition changing from the Cassie−Baxter state to the Wenzel state in the non-reactive wetting range. The surface roughness hinders the spreading of the glass melt due to the interface reaction between glass and samarium-cobalt alloys in the reactive wetting range.

A New Approach to Explore the Surface Profile of Clay Soil Using White Light Interferometry.

In order to have a better understanding of the real contact area of granular materials, the white light interference method is applied to explore the real surface morphology of clay soils under high stress. Analysis of the surface profile indicates that there exists a support point height z0 with the highest distribution frequency. A concept of a real contact region (from z0 to z0 + d90; d90 represents the particle size corresponding to 90% of the volume fraction) is proposed by combining a surface profile with the particle size distribution of clay soil. It was found that under the compressive stress of 106 MPa–529 MPa, the actual contact area ratio of clay soil varies between 0.375 and 0.431. This demonstrates an increasing trend with the rise of stress. On the contrary, the apparent porosity decreases with an increasing stress, varying between 0.554 and 0.525. In addition, as the compressive stress increases, the cumulative frequency of apparent profile height (from z0 − d90 to z0 + d90) has a concentrated tendency with a limited value of 0.9.

Spatially-averaged turbulent flow characteristics over ribbed surface in presence of unidirectional wave over steady current

The paper presents an experimental study on the characterization of the effect of surface-wave of different frequencies on spatially-averaged turbulent statistics over a rough bed. The model roughness comprised of periodically positioned, transverse square ribs that extended across the whole width of the channel. The three-dimensional turbulent velocity fluctuations were mapped by an acoustic Doppler velocimeter (ADV) in the flow domain at high resolution. These data were analyzed to examine time-space averaged turbulence parameters of the double averaged Navier Stokes equations and momentum transfer under the influence of the rough boundary. Further, Shannon entropy at different vertical position were also evaluated to develop insight into the energy transfer mechanism. Results show a reduction in the apparent roughness height and an increase of the intensity of turbulence under surface wave influence. Furthermore, the superposition of waves led to the increase in turbulence production and showed maximum values at the roughness layer as compared to buffer layer in current-only flow over plane bed.

Piezotronic AlGaN nanowire Schottky junctions grown on a metal substrate

The non-centrosymmetric crystal structures of polar-semiconductors comprising GaN, InN, AlN, and ZnO intrigued the scientific community in investigating their potential for a strain-induced nano-energy generation. The coupled semiconducting and piezoelectric properties produce a piezo-potential that modulates the charge transport across their heterostructure interfaces. By using conductive-atomic force microscopy, we investigate the mechanism that gives rise to the piezotronic effect in AlGaN nanowires (NWs) grown on a molybdenum (Mo) substrate. By applying external bias and force on the NWs/Mo structure using a Pt–Ir probe, the charge transport across the two adjoining Schottky junctions is modulated due to the change in the apparent Schottky barrier heights (SBHs) that result from the strain-induced piezo-potential. We measured an increase in the SBH of 98.12 meV with respect to the background force, which corresponds to an SBH variation ∂ϕ∂F of 6.24 meV/nN for the semiconductor/Ti/Mo interface. The SBH modulation, which is responsible for the piezotronic effect, is further studied by measuring the temperature-dependent I–V curves from room temperature to 398 K. The insights gained from the unique structure of AlGaN NWs/Mo shed light on the electronic properties of the metal-semiconductor interfaces, as well as on the potential application of AlGaN NW piezoelectric nanomaterials in optoelectronics, sensors, and energy generation applications.

Conductance Deep-Level Transient Spectroscopy and Current Transport Mechanisms in Au|Pt|n-GaN Schottky Barrier Diodes

The current transport mechanisms in Au|Pt|n-GaN Schottky barrier diodes are investigated in a temperature range of 40–325 K. The calculated barrier height and ideality factor are 1.12 and 2.13 eV, respectively, and it is observed that the barrier height Φb increases and the ideality factor n decreases with temperature increase. The apparent barrier height and the ideality factor derived by using thermionic emission theory are found to be strongly temperature-dependent. The increase in barrier height with increasing temperature has been explained as an effect of barrier inhomogeneity. This behavior has been interpreted based on the assumption of a Gaussian distribution of barrier heights due to barrier height inhomogeneity at the interface between the metal and semiconductor. The abnormal behavior of all these parameters can be attributed to the presence of deep levels thermally activated. Conductance deep-level transient spectroscopy (CDLTS) results shows that the two deep-level defects are observed in as-grown sample with activation energies of E1 = 0.18 eV and HL1 = 0.87 eV.

Co/aniline blue/silicon sandwich hybrid heterojunction for photodiode and low-temperature applications

The temperature dependence of the current–voltage and room temperature capacitance–voltage measurements of Co/aniline blue/ n-Si sandwich-type rectifying device was investigated.Furthermore, the effects of the illumination on the current–voltage measurements were tested with 100 mW/cm2 light intensity, and it was seen that Co/aniline blue/ n-Si sandwich-type device showed a clear response to illumination, and it may be a candidate for solar cells or photodiode applications. The rectifying device parameters, such as the barrier height (Ф), the ideality factor ( n), the rectification ratio, and the series resistance ( Rs), were obtained as a function of temperature using thermionic emission, Cheung function, and Norde function. The interface state densities versus energy were obtained. The Richardson constant ( A*) obtained from the In( Io/ T2) versus 1000/ T plot was much less than the theoretical value for n-Si. The mean Schottky barrier height[Formula: see text] and the standard deviation ( σo) were calculated using the apparent Schottky barrier height Фap versus 1/2 kT plot. So, it has been found to be 1.08 eV and 0.15 V (260–460 K) and 0.79 eV and 0.10 V (100–260 K), respectively. The results were discussed based on the presence of two Gaussian distributions of Фb potential in the contact area of Co/aniline blue/ n-Si/Al device.

The World Ends Here, the World Begins Here: Bronze Age Megalithic Monuments in Western Scotland

This paper presents a study of free-standing Bronze Age megalithic monuments across western Scotland: Argyll, Lochaber, Kintyre, and the isles of Mull, Coll and Tiree. The original project was designed to unearth the locational choices of their builders, the reasons for these choices, and what they reveal about the belief systems of these societies. Using statistical analyses and 2D and 3D GIS, it will be demonstrated that vision is the main force behind locational decisions. The GIS analyses revealed that the builders chose a particular horizon shape, defined by qualities of distance, direction and relative apparent height as viewed from the monument (altitude). Significantly, approximately half the sites have the same locational variables as all the sites considered on the isles of Coll and Tiree (labelled ‘classic sites’: Higginbottom et al. in J Archaeol Method Theory 22:584–645, 2015. https://doi.org/10.1007/s10816-013-9182-7), while the other half are the topographical reverse (‘reverse sites’), where the major ‘astronomical show’ differs due to the topographical differences between the site types. It is relevant to note that landscapes that block views of particular major astronomical phenomena in the south are significantly more common at reverse sites than at classic sites. Specific results pertaining to individual areas will also be highlighted. It will be seen that the interplay between the astronomy and the topographical choices of the builders at each site highlights possible cosmological ideologies that can be observed and that were shared across western Scotland.

Tip-induced deformation of polystyrene latex reference nanoparticles in atomic force microscopy

The measurement approach typically prescribed for sizing polystyrene latex (PSL) reference nanoparticles by atomic force microscopy (AFM) is based on a single value of the height obtained from a three-dimensional image of the particle. A major challenge is that PSLs reportedly deform during sample preparation as well as imaging. While the particle-substrate deformation is controlled by adhesive contact forces, the tip-induced deformation may vary to a large degree depending on the operational conditions and the geometrical constraints imposed by the instrument. In this paper, the authors are mainly concerned with the effect of cantilever tilt, tip shape, and setpoint voltage on tip-induced deformation of PSL reference nanoparticles. Tips are characterized by scanning electron microscopy and using a multilayer Si/SiO2 tip characterizer. The authors find that the plastic flow of materials, induced by the asymmetric imaging geometry, shifts the position of the maximum particle height away from the center. This shape-change often leads to an initial height increase for PSLs that are smaller than 40 nm. Since AFM height analysis algorithms often equate apparent particle height with the highest measured point of the particle, these results have implications from the perspective of AFM-based nanoparticle metrology.

Carbon Monoxide Stripe Motion Driven by Correlated Lateral Hopping in a 1.4 × 1.4 Monolayer Phase on Cu(111).

We report an ultra-high-vacuum low-temperature (4.6 K) scanning tunneling microscopy study of the molecular structure and dynamics of a carbon monoxide (CO) monolayer adsorbed at 20 K on Cu(111). We observe the well-known 1.4 × 1.4 phase of CO/Cu(111) for the first time in real-space imaging. At 4.6 K, the hexagonal symmetry of the monolayer is locally broken by the formation of stripes made of single and double CO rows of different apparent heights. Using density functional theory calculations, we assign the high rows to CO molecules adsorbed mostly at off-center top sites and the low rows to bridge sites. Groups of three or four very high molecules appear randomly and are assigned to nearest-neighbor, titled top site molecules. We observe simultaneous hopping of a few CO molecules between adjacent top and bridge sites, which produces the apparent motion of the stripe pattern.

Hydrogen molecules can modulate enzymatic activity and structural properties of pepsin in vitro

Hydrogen gas therapy has been recognized as the promising application merit. However, the underlying mechanism on the biological effects remains far from being understood. In this work, pepsin used as a research model, the effects of hydrogen-rich water on the protein activities and structural properties were investigated by enzymatic assay, atomic force microscopy-based peakforce quantitative nanomechanical mapping (PF-QNM) and terahertz time-domain spectroscopy (THz-TDS). We found that hydrogen-rich water can increase the protein activity and its apparent height while alter the mechanical properties (Young's modulus) and the terahertz dynamics. These results suggest a possible mode of hydrogen molecules acting with pepsin through the local changes of hydrophobic interfaces in the protein molecules, thus provide the first evidence for the direct interaction between hydrogen with proteins and a biophysical insight into the mechanism of hydrogen as well as other gases on the biological effects.