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Abstract We investigate, through XPS and AFM, the pseudo layer-by-layer growth of Ge native oxide across Ge(001), (110) and (111) surfaces in ambient environment. More significantly, our study reveals a universal set of valence and conduction band offset (VBO and CBO) values observed for Ge(001), Ge(110), and Ge(111) surfaces as a function of Ge-oxide concentration. We find that the band offsets appear to be the same across these low-index Ge surfaces i.e., for Ge-oxide/Ge heterostructures with the same Ge-oxide overlayer concentration or thickness. In contrast, different oxidation rates for Ge(001), Ge(110), and Ge(111) surfaces were observed, where the oxidation rate is fastest for Ge(001), compared to Ge(110) and Ge(111). This can be attributed to the different number of unsatisfied Ge dangling bonds (2 vs 1) associated to the respective ideal Ge surface in forming Ge-oxide. Thus, at any given oxidation time, the oxide concentration or thickness for each type of low index Ge surface will be different. This in turn will lead to different band offset value observed for each type of Ge surface. More significantly, we show that while oxidation rates can differ from different Ge surface-types, the band offset values can be estimated simply based on the Ge-oxide concentration regardless of Ge surface type.

Abstract During the milling process of palm oil, the degree of palm fruit ripeness is a critical factor that affects the quality and quantity of the oil. As the palm fruit matures, its chlorophyll level decreases, and since chlorophyll in oil has undesirable effects on hydrogenation, bleachability, and oxidative degradation, it’s important to monitor the chlorophyll content in palm oil during the milling process. This study investigated the use of light-induced chlorophyll fluorescence (LICF) for non-invasive and real-time monitoring of chlorophyll content in diluted crude palm oil (DCO) located at the dilution and oil classification point in palm oil mill. An LICF probe was installed at the secondary pipe connected to main DCO pipeline, and the system communicates with a computer located in a separate control room via a Wi-Fi connection. Continuous measurements were recorded with an integration time of 500 ms, averaging of 10, and a time interval of 1 min between each recording during the oil mill’s operation. All data were stored on the computer and in the cloud. We collected 60 DCO samples and sent them to the laboratory for American Oil Chemists’ Society (AOCS) measurement to compare with the LICF signal. The LICF method achieved a correlation coefficient of 0.88 with the AOCS measurements, and it also provided a direct, quantitative, and unbiased assessment of the fruit ripeness in the mill. By incorporating Internet of Things (IoT) sensors and cloud storage, this LICF system enables remote and real-time access to data for chemometrics analysis.

Abstract Microscopy by Achromatic X-rays With Emission of Laminar Light (MAXWELL) is a new X-ray/visible technique with attractive characteristics including isotropic resolution in all directions, large-volume imaging and high throughput. An ultrathin, laminar X-ray beam produced by a Wolter type I mirror irradiates the sample stimulating the emission of visible light by scintillating nanoparticles, captured by an optical system. Three-dimensional (3D) images are obtained by scanning the specimen with respect to the laminar beam. We implemented and tested the technique with a high-brightness undulator at SPring-8, demonstrating its validity for a variety of specimens. This work was performed under the Synchrotrons for Neuroscience—an Asia–Pacific Strategic Enterprise (SYNAPSE) collaboration.

Abstract We developed a new digital etch process that allows precise etching of Germanium or Germanium-tin (Ge1−x Sn x ) materials. The digital etch approach consists of Ge1−x Sn x oxide formation by plasma oxidation and oxide removal in diluted hydrochloric acid at room temperature. The first step is a self-limiting process, as the thickness of oxide layer grows logarithmically with the oxidation time and saturates fast. Consistent etch rates in each cycle were found on the Ge1−x Sn x samples, with the surfaces remaining smooth after etch. The digital etch process parameters were tuned to achieve various etch rates. By reducing the radio frequency power to 70 W, etch rate of sub-1.2 nm was obtained on a Ge0.875Sn0.125 sample. The digital etch process was employed to fabricate the Ge1−x Sn x fin structures. Extremely scaled Ge0.95Sn0.05 fins with 5 nm fin width were realized. The side walls of the Ge0.95Sn0.05 fins are smooth, and no crystal damage can be observed. This technique provides an option to realize aggressively scaled nanostructure devices based on Ge1−x Sn x materials with high-precision control.

Ge0.94Sn0.06 films with high tensile strain were grown on strain-relaxed InyGa1-yP virtual substrates using solid-source molecular beam epitaxy. The in-plane tensile strain in the Ge0.94Sn0.06 film was varied by changing the In mole fraction in InxGa1-xP buffer layer. The tensile strained Ge0.94Sn0.06 films were investigated by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. An in-plane tensile strain of up to 1% in the Ge0.94Sn0.06 was measured, which is much higher than that achieved using other buffer systems. Controlled thermal anneal experiment demonstrated that the strain was not relaxed for temperatures up to 500?°C. The band alignment of the tensile strained Ge0.94Sn0.06 on In0.77Ga0.23P was obtained by high resolution x-ray photoelectron spectroscopy. The Ge0.94Sn0.06/In0.77Ga0.23P interface was found to be of the type I band alignment, with a valence band offset of 0.31?±?0.12?eV and a conduction band offset of 0.74?±?0.12?eV. [ABSTRACT FROM AUTHOR]

The effect of room temperature sulfur passivation of the surface of Ge0.83Sn0.17 prior to high-k dielectric (HfO2) deposition is investigated. X-ray photoelectron spectroscopy (XPS) was used to examine the chemical bonding at the interface of HfO2 and Ge0.83Sn0.17. Sulfur passivation is found to be effective in suppressing the formation of both Ge oxides and Sn oxides. A comparison of XPS results for sulfur-passivated and non-passivated Ge0.83Sn0.17 samples shows that sulfur passivation of the GeSn surface could also suppress the surface segregation of Sn atoms. In addition, sulfur passivation reduces the interface trap density Dit at the high-k dielectric/Ge0.83Sn0.17 interface from the valence band edge to the midgap of Ge0.83Sn0.17, as compared with a non-passivated control. The impact of the improved Dit is demonstrated in Ge0.83Sn0.17 p-channel metal-oxide-semiconductor field-effect transistors (p-MOSFETs). Ge0.83Sn0.17 p-MOSFETs with sulfur passivation show improved subthreshold swing S, intrinsic transconductance Gm,int, and effective hole mobility μeff as compared with the non-passivated control. At a high inversion carrier density Ninv of 1 × 1013 cm-2, sulfur passivation increases μeff by 25% in Ge0.83Sn0.17 p-MOSFETs. [ABSTRACT FROM AUTHOR]

The wet etching of germanium-tin (Ge1-xSnx) alloys (4.2%1-xSnx is proportional to the square root of the etch time t and decreases exponentially with increasing x for a given t. In addition, X-ray photoelectron spectroscopy results show that increasing t increases the intensity of the Sn oxide peak, whereas no obvious change is observed for the Ge oxide peak. This indicates that an accumulation of Sn oxide on the Ge1-xSnx surface decreases the amount of Ge atoms exposed to the etchant, which accounts for the decrease in etch rate with increasing etch time. Atomic force microscopy was used to examine the surface morphologies of the Ge0.918Sn0.082 samples. Both root-mean-square roughness and undulation periods of the Ge1-xSnx surface were observed to increase with increasing t. This work provides further understanding of the wet etching of Ge1-xSnx using APM and may be used for the fabrication of Ge1-xSnx-based electronic and photonic devices. [ABSTRACT FROM AUTHOR]

We investigate the impact of pulsed excimer laser anneal on fully strained germanium-tin alloys (Ge1-xSnx) epitaxially grown on Ge substrate by molecular beam epitaxy. Using atomic force microscopy, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy, the morphological and compositional evolution of Ge1-xSnx with Sn content up to 17% after annealing using various conditions is studied. Ge0.83Sn0.17 samples annealed at 80 mJ/cm2 or 150 mJ/cm2 have no observable changes with respect to the as-grown sample. However, Ge0.83Sn0.17 samples annealed at 250 mJ/cm2 or 300 mJ/cm2 have Sn-rich islands on the surface, which is due to Sn segregation in the compressively strained epitaxial film. For Ge0.89Sn0.11, significant Sn redistribution occurs only when annealed at 300 mJ/cm2, indicating that it has better thermal stability than Ge0.83Sn0.17. A mechanism is proposed to explain the formation of Sn-rich islands and Sn-depleted regions. [ABSTRACT FROM AUTHOR]

This work demonstrates and describes for the first time an unusual strain-relaxation mechanism by the formation and self-assembly of well-ordered tin wires during the thermal annealing of epitaxial Ge0.83Sn0.17-on-Ge(001) substrate. Fully strained germanium-tin alloys (Ge0.83Sn0.17) were epitaxially grown on Ge(001) substrate by molecular beam epitaxy. The morphological and compositional evolution of Ge0.83Sn0.17 during thermal annealing is studied by atomic force microscopy, X-ray diffraction, transmission electron microscopy. Under certain annealing conditions, the Ge0.83Sn0.17 layer decomposes into two stable phases, and well-defined Sn wires that are preferentially oriented along two orthogonal <100> azimuths are formed. The formation of the Sn wires is related to the annealing temperature and the Ge0.83Sn0.17 thickness, and can be explained by the nucleation of a grain with Sn islands on the outer front, followed by grain boundary migration. The Sn wire formation process is found to be thermally activated, and an activation enthalpy (Ec) of 0.41 eV is extracted. This thermally activated phase transformation, i.e., 2D epitaxial layer to 3D wires, occurs via a mechanism akin to "cellular precipitation." This synthesis route of Sn wires opens new possibilities for creation of nanoscale patterns at high-throughput without the need for lithography. [ABSTRACT FROM AUTHOR]

Plane-wave density functional theory is used to investigate the impact of hydrogen passivation of the p(2x2) reconstructed Ge1-xSnx surface on Sn segregation, aggregation, and distribution. On a clean surface, Sn preferentially segregates to the surface layer, with surface coverages of 25%, 50%, and 100% for total Sn concentrations of 2.5%, 5.0%, and 10.0%, respectively. In contrast, a hydrogen passivated surface increases interlayer migration of Sn to subsurface layers, in particular, to the third layer from the surface, and results in surface coverages of 0%, 0%, and 50% corresponding to Sn concentrations of 2.5%, 5.0%, and 10.0%, respectively. Hydrogen transfer from a Ge-capped surface to the one enriched with increasing Sn surface coverage is also an unfavorable process. The presence of hydrogen therefore reduces the surface energy by passivating the reactive dangling bonds and enhancing Sn interlayer migration to the subsurface layers. For both clean and hydrogenated surfaces, aggregation of Sn at the surface layer is also not favored. We explain these results by considering bond enthalpies and the enthalpies of hydrogenation for various surface reactions. Our results thus point to reduced Sn segregation to the surface in a Ge1-xSnx epitaxial thin film if CVD growth, using hydride precursors in the hydrogen limited growth regime, is used. This would lead to a more abrupt interface and is consistent with recent experimental observation. Hydrogenation is therefore a promising method for controlling and manipulating elemental population of Sn in a Ge1-xSnx epitaxial thin film. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry was used to investigate the optical response of pseudomorphic Ge1–xSnx (0≤x≤0.17) alloys grown directly on Ge (100) by molecular beam epitaxy. A detailed compositional study of amplitudes, broadenings, energies, and phase angles associated with critical points E1, E1+Δ1, E0', and E2 of GeSn alloys was carried out using a derivative analysis. The results can be understood in terms of the electronic bandstructure of Ge or relaxed GeSn alloys with the following differences. First, broadening parameters in pseudomorphic alloys are found to have lower values compared to relaxed alloys indicating lower dislocation density in our pseudomorphic alloys relative to relaxed alloys. Second, the amplitudes of E1 and E1+Δ1 are enhanced and reduced, respectively, with respect to relaxed GeSn alloys, and the trends are captured using the k.p method as a biaxial stress induced effect. Third, phase angles are lower than Ge for all the critical points suggesting reduction of excitonic effects in GeSn with respect to Ge. [ABSTRACT FROM AUTHOR]

In situ ultrahigh vacuum transmission electron microscopy is used for observing the dynamics of both the coalescence and decay of two-dimensional [Fe.sub.13][Ge.sub.8] islands on an atomically smooth Ge(001) surface. The quasi-1D island decay process is driven by adatom concentration differences between coalescing and decaying islands, where island decay has occurred along the large d channel between islands and is affected by the local environment.

The growth behaviors of C60 molecules on SiC nanomesh at room temperature is systematically investigated using in situ scanning tunneling microscopy. After deposition of 1 ML C60, a complete layer of hexagonally close-packed C60 molecules forms on top of the SiC nanomesh.

We investigate the thermal stability of germanium-tin (Ge1-xSnx) fins under rapid thermal annealing in N2 ambient. The Ge1-xSnx fins were formed on a GeSn-on-insulator substrate and were found to be less thermally stable than blanket Ge1-xSnx films. The morphology change and material quality of the annealed Ge1-xSnx fin are investigated using scanning electron microscopy, Raman spectroscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy. Obvious degradation of crystalline quality of the Ge0.96Sn0.04 fin was observed, and a thin Ge layer was formed on the SiO2 surface near the Ge0.96Sn0.04 fin region after 500 °C anneal. A model was proposed to explain the morphology change of the Ge0.96Sn0.04 fin. [ABSTRACT FROM AUTHOR]

We investigated the critical thickness (h c) for plastic relaxation of Ge1-xSnx grown by molecular beam epitaxy. Ge1-xSnx films with various Sn mole fraction x (x ≤ 0.17) and different thicknesses were grown on Ge(001). The strain relaxation of Ge1-xSnx films and the hc were investigated by high-resolution x-ray diffraction and reciprocal space mapping. It demonstrates that the measured hc values of Ge1-xSnx layers are as much as an order of magnitude larger than that predicted by the Matthews and Blakeslee (M-B) model. The People and Bean (P-B) model was also used to predict the hc values in Ge1-xSnx /Ge system. The measured hc values for various Sn content follow the trend, but slightly larger than that predicted by the P-B model. [ABSTRACT FROM AUTHOR]

Arrays of ZnO/CdSSe core/shell nanowires with shells of tunable band gaps represent a class of interesting hybrid nanomaterials with unique optical and photoelectrical properties due to their type II heterojunctions and chemical compositions. In this work, we demonstrate that direct focused laser beam irradiation is able to achieve localized modification of the hybrid structure and chemical composition of the nanowire arrays. As a result, the photoresponsivity of the laser modified hybrid is improved by a factor of ∼ 3. A 3D photodetector with improved performance is demonstrated using laser modified nanowire arrays overlaid with monolayer graphene as the top electrode. Finally, by controlling the power of the scanning focused laser beam, micropatterns with different fluorescence emissions are created on a substrate covered with nanowire arrays. Such a pattern is not apparent when imaged under normal optical microscopy but the pattern becomes readily revealed under fluorescence microscopy i.e. a form of Micro-Steganography is achieved. [ABSTRACT FROM AUTHOR]

Lattice-matched In0.49Ga0.51P was grown on a p-type Ge(100) substrate with a 10° off-cut towards the (111) by low temperature molecular beam epitaxy, and the band-alignment of In0.49Ga0.51P on Ge substrate was obtained by high resolution x-ray photoelectron spectroscopy. The valence band offset for the InGaP/Ge(100) interface was found to be 0.64 ± 0.12 eV, with a corresponding con-duction band offset of 0.60 ± 0.12 eV. The InGaP/Ge interface is found to be of the type I band alignment [ABSTRACT FROM AUTHOR]

The band-alignment of atomic layer deposited (ALD)-HfO2/In0.18Al0.82N was studied by high resolution angle-resolved X-ray photoelectron spectroscopy measurements. The band bending near the HfO2/In0.18Al0.82N interface was investigated, and the potential variation across the interface was taken into account in the band alignment calculation. It is observed that the binding energies for N 1s and Al 2p in In0.18Al0.82N decreases and the corresponding extracted valence band offsets increases with increasing h (i.e., closer to the HfO2/In0.18Al0.82N interface), as a result of an upward energy band bending towards the HfO2/In0.18Al0.82N interface. The resultant valence band offset and the conduction band offset for the ALD-HfO2/In0.18Al0.82N interface calculated was found to be 0.69 eV and 1.01 eV, respectively. [ABSTRACT FROM AUTHOR]

Sulfur mono-layer doped In0.53Ga0.47As films were investigated by infrared spectroscopic ellipsometry. The complex dielectric function of doped layers shows free carrier response which can be described by a single Drude oscillator. Electrical resistivities, carrier relaxation times, and active carrier depths are obtained for the shallow n-In0.53Ga0.47As films. Our results indicate that sub-10 nm sulfur-doped layers with active carrier concentration as high as 1.7×1019 cm-3 were achieved. Sheet resistances estimated from infrared spectroscopic ellipsometry are in good agreement with those obtained by electrical methods. [ABSTRACT FROM AUTHOR]

Solid silicon nanowires and their luminescent properties have been widely studied, but lesser is known about the optical properties of mesoporous silicon nanowires (mp-SiNWs). In this work, we present a facile method to generate greenish-blue photoluminescence (GB-PL) by fast scanning a focused green laser beam (wavelength of 532 nm) on a close-packed array of mp-SiNWs to carry out photo-induced chemical modification. The threshold of laser power is 5 mWto excite the GB-PL, whose intensity increases with laser power in the range of 5-105 mW.The quenching of GB-PL comes to occur beyond 105 mW.The in-vacuum annealing effectively excites the GB-PL in the pristine mp-SiNWs and enhances the GB-PL of the laser-modified mp-SiNWs. A complex model of the laser-induced surface modification is proposed to account for the laser-power and post-annealing effect. Moreover, the fast scanning of focused laser beam enables us to locally tailor mp-SiNWs en route to a wide variety of micropatterns with different optical functionality, and we demonstrate the feasibility in the application of creating hidden images. [ABSTRACT FROM AUTHOR]

The complex dielectric function of biaxially strained Ge1-xSnx (0≤x≤0.17) alloys grown on Ge (100) has been determined by spectroscopic ellipsometry from 1.2 to 4.7 eV. The effect of substitutional Sn incorporation and the epitaxial strain on the energy transitions E1, E1 + Δ1, E0′, and E2 of GeSn alloys is investigated. Our results indicate that the strained GeSn alloys show Ge-like electronic bandstructure with all the transitions shifted downward due to the alloying of Sn. The strain dependence of E1 and E1+Δ1 transitions is explained using the deformation potential theory, and values of -5.4±0.4 eV and 3.8±0.5 eV are obtained for the hydrostatic and shear deformation potentials, respectively. [ABSTRACT FROM AUTHOR]

Car-Parrinello molecular dynamics (CPMD) are widely used to investigate the dynamical properties of molecular systems. An important issue in such applications is the dependence of dynamical quantities such as molecular vibrational frequencies upon the fictitious orbital mass μ. Although it is known that the correct Born-Oppenheimer dynamics are recovered at zero μ, it is not clear how these dynamical quantities are to be rigorously extracted from CPMD calculations. Our work addresses this issue for vibrational frequencies. We show that when the system is sufficiently close to the ground state the calculated ionic vibrational frequencies are ωM = ω0M[1 - C(μ/M)] for small μ/M, where ω0M is the Born-Oppenheimer ionic frequency, M the ionic mass, and C a constant that depends upon the ion-orbital coupling force constants. Our analysis also provides a quantitative understanding of the orbital oscillation amplitudes, leading to a relationship between the adiabaticity of a system and the ion-orbital coupling constants. In particular, we show that there is a significant systematic dependence of calculated vibrational frequencies upon how close the CPMD trajectory is to the Born-Oppenheimer surface. We verify our analytical results with numerical simulations for N2, Sn2, and H/Si(100)-(2×1). [ABSTRACT FROM AUTHOR]

Using Co-decoration technique coupled with in situ scanning tunneling microscope (STM), the evolution of epitaxial graphene was found to preferentially begin at step edges of the silicon carbide surface and occurs with loss of Si and breakdown of C-rich [formula] template, which provides the C source for graphene growth. Interestingly, a new C-rich phase is also formed at the interface and it acts as a buffer layer for graphene from underlying bulk. STM reveals that graphene lies 2.3±0.3 Å above the buffer layer, larger than sp3 C–C bond length (1.54 Å) but shorter than graphite interlayer separation (3.37 Å), suggesting a pseudo-van der Waals interfacial interaction. [ABSTRACT FROM AUTHOR]

The thermal stability and germanium–tin (Ge–Sn) interdiffusion properties were studied in epitaxial Ge/GeSn multiple-quantum-well (MQW) structure. No obvious interdiffusion was observed for annealing temperatures of 300 °C or below, while observable interdiffusion occurred for annealing temperatures of 380 °C and above. High-resolution x-ray diffraction was used to obtain the interdiffusion coefficient by analyzing the decrease rate of Ge/GeSn periodic satellite peaks. The interdiffusion coefficient is much higher, and the activation enthalpy of 1.21 eV is substantially lower in Ge/GeSn MQW structure than that previously reported in silicon–germanium (Si–Ge) systems. When the annealing temperature is increased to above 500 °C, Ge–Sn interdiffusion becomes severe. Some small pits appear on the surface, which should be related to Sn out-diffusion to the Ge cap layer, followed by Sn desorption from the top surface. This work provides insights into the Ge–Sn interdiffusion and Sn segregation behaviors in Ge/GeSn MQW structure, and the thermal budget that may be used for fabrication of devices comprising Ge/GeSn heterostructures. [ABSTRACT FROM AUTHOR]

Discusses research conducted by researchers at the National University of Singapore on nanomaterials at the atomic scale. Importance of understanding nanomaterials; Advantages of using scanning tunnelling microscopy and X-ray photoelectron spectroscopy in the research; Expectations on semiconductor devices made from self-assembled silicon nanoclusters.

Recent work has shown that the most stable graphene-adsorbed dimers of Fe, Co, and Ni have top-atom magnetic moments larger than those of the free dimers. Here we investigate the dependence of the binding energy and the top-atom magnetic moment upon composition, cluster size, and cluster dimensionality by considering the trimer and the tetramer, that is, the smallest two-dimensional and three-dimensional clusters, respectively. We find that for trimers the highest binding energy occurs for configurations that are perpendicularly bound and have the largest charge transfer to graphene. For tetramers, the binding energy is highest for the compact configurations with the largest charge transfer to graphene. Binding is generally strongest at the hole site of the graphene lattice. The charge transfer to graphene is mainly from the base atoms, while the s-d orbital configuration of the top atom is close to that in the free cluster, indicating electronic shielding of the top atom from the graphene substrate. Thus, the binding energy of mixed trimers and tetramers to graphene is determined largely by the elemental identity of the base atoms, while the magnetic moment of the top atom depends on the elemental identity of the top atom. We show that graphene-adsorbed mixed clusters FeCo2 and FeCo3 with top Fe atom are strongly bound and have large top-atom magnetic moments, indicating the potential for magnetic storage applications. [ABSTRACT FROM AUTHOR]