High Quality Crystalline Structure Research Articles

The Wannier-Mott Exciton, Bound Exciton, and Optical Phonon Replicas of Single-Crystal GaSe

We report the absorption and photoluminescence spectra of GaSe single crystals in the near-edge region. The temperatures explored the range from 17 to 300 K. Specifically, at a temperature of 17 K, the photoluminescence spectrum reveals an interesting phenomenon: the Wannier-Mott exciton separates into two states. These states are a triplet state with an energy of 2.103 eV and a singlet state with an energy of 2.109 eV. The energy difference between these two states is 6 meV. Furthermore, the bound exciton (BX) can be localized at an energy of 2.093 eV. It is worth noting that its phonon replicas (BX-nLO) can be clearly distinguished up to the fourth order. Interestingly, the energy gaps between these replicas exhibit a consistent spacing of 7 ± 0.5 meV. This intriguing finding suggests a high-quality crystalline structure as well as a strong coupling between the phonon and BX-nLO. Additionally, at low temperatures, both the ground state (n = 1) at 2.11 eV and the excited state (n = 2) at 2.127 eV of free excitons can be observed.

Toward sustainable nanomaterials: An innovative ecological approach for biogenic synthesis of TiO2 nanoparticles with potential photocatalytic activity

Biogenic synthesis of nanomaterials represents a promising alternative to traditional chemical synthesis due to its environmentally friendly nature, cost-effectiveness, low toxicity, and high biocompatibility. The primary objective of this study was to develop a novel biogenic synthesis method for titanium dioxide (TiO2) nanoparticles using an aqueous extract of Annona muricata L. as a stabilizing and organic reducing agent. Furthermore, our aim included a comprehensive exploration of the structural, morphological, and optical properties of these nanostructures. The methodology employed in this project was grounded in the biogenic synthesis of TiO2, utilizing the aforementioned extract as a key component. We conducted a comprehensive characterization approach to unravel the formation mechanism and validate the morphology and crystalline structure of the nanomaterial. We successfully synthesized nanoparticles with spherical morphology and an average diameter of 13.41 nm, characterized by their remarkable uniformity and high-quality crystalline structure. Additionally, we assessed the applicability of these nanoparticles in photocatalysis processes aimed at the degradation of organic dyes. Our findings indicated efficient initial activity in the kinetics of methylene blue dye degradation, with a reduction of 59.25 % within the first 30 min of exposure.

Novel Approach to High κ (∼59) and Low EOT (∼3.8 Å) near the Morphotrophic Phase Boundary with AFE/FE (ZrO2/HZO) Bilayer Heterostructures and High-Pressure Annealing.

We present herewith a novel approach of equally thick AFE/FE (ZrO2/HZO) bilayer stack heterostructure films for achieving an equivalent oxide thickness (EOT) of 4.1 Å with a dielectric constant (κ) of 56 in complementary metal-oxide semiconductor (CMOS) compatible metal-ferroelectric-metal (MFM) capacitors using a high-pressure annealing (HPA) technique. The low EOT and high κ values were achieved by careful optimization of AFE/FE film thicknesses and HPA conditions near the morphotropic phase boundary (MPB) after field cycling effects. Stable leakage current density (J < 10-7 A/cm2 at ±0.8 V) was found at 3/3 nm bilayer stack films (κ = 56 and EOT = 4.1 Å) measured at room temperature. In comparison with previous work, our remarkable achievement stems from the interfacial coupling between FE and AFE films as well as a high-quality crystalline structure formed by HPA. Kinetically stabilized hafnia films result in a small grain size in bilayer films, leading to reducing the leakage current density. Further, a higher κ value of 59 and lower EOT of 3.4 Å were found at 333 K. However, stable leakage current density was found at 273 K with a high κ value of 53 and EOT of 3.85 Å with J < 10-7 A/cm2. This is the lowest recorded EOT employing hafnia and TiN electrodes that are compatible with CMOS, and it has important implications for future dynamic random access memory (DRAM) technology.

Elastic behavior of metal-assisted etched Si/SiGe superlattice nanowires containing dislocations

We systematically investigate structural parameters, such as shape, size, elastic strain, and relaxations, of metal-assisted etched vertically modulated Si/SiGe superlattice nanowires by using electron microscopy, synchrotron-based x-ray diffraction, and numerical linear elasticity theory. A vertical Si/Ge superlattice with atomically flat interfaces is grown by using molecular beam epitaxy on Si-buffered Si(001) substrates. The lattice constants for Si and Ge are 5.43 and 5.66 Å, respectively, which indicate a lattice mismatch of 4.2%. This results in a strained layer in the boundary between Si and Ge leading to dislocations. These substrates serve as the starting material for nanostructuring the surface by using metal-assisted etching. It is shown that the high quality crystalline structure is preserved in the fabrication process, while the lattice mismatch is partially relieved by dislocation formation. Despite this highly effective relaxation path, dislocations present in the parent superlattice do not vanish upon nanostructuring for wires with diameters of down to at least 80 nm. We relate these observations to the applicability of silicon-based nanowires for high-performance thermoelectric generators.

Highly-Responsive Broadband Photodetector Based on Graphene-PTAA-SnS2 Hybrid.

The development of wearable systems stimulate the exploration of flexible broadband photodetectors with high responsivity and stability. In this paper, we propose a facile liquid-exfoliating method to prepare SnS2 nanosheets with high-quality crystalline structure and optoelectronic properties. A flexible photodetector is fabricated using the SnS2 nanosheets with graphene-poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine (PTAA) hybrid structure. The liquid-exfoliated SnS2 nanosheets enable the photodetection from ultraviolet to near infrared with high responsivity and detectivity. The flexible broadband photodetector demonstrates a maximum responsivity of 1 × 105 A/W, 3.9 × 104 A/W, 8.6 × 102 A/W and 18.4 A/W under 360 nm, 405 nm, 532 nm, and 785 nm illuminations, with specific detectivity up to ~1012 Jones, ~1011 Jones, ~109 Jones, and ~108 Jones, respectively. Furthermore, the flexible photodetector exhibits nearly invariable performance over 3000 bending cycles, rendering great potentials for wearable applications.

Transparent and conductive cellulose film by controllably growing aluminum doped zinc oxide on regenerated cellulose film

Functional applications of cellulose have attracted large amount of attentions owing to its natural, environmentally friendly, light-weight characteristics. In this study, a cellulose-based conductive film (CCF) was prepared by sputtering aluminum doped zinc oxide (AZO, a cheap and non-toxic semiconductor) on a regenerated cellulose film from bamboo fibers. Through dissolution and regenerated process of cellulose fibers, the as-prepared cellulose film featured high transmittance of 97% and low roughness of 0.943 nm as well as 117 MPa strength, which can be supportive for manufacturing cellulose-based conductive devices. Based on the cellulose film which was as the transparent substate, we systematically investigated the effects of working parameters on the performance of AZO-based cellulose conductive film, followed by a phenomenon that the crystal structure and morphology of AZO particles play decisive role on the transmittance and conductivity of CCF. With the optimized working parameters, the CCF presented low conductive resistance of 365 Ω/□, high transmittance of 86% and high-quality crystalline structure. Besides, the thermal stability and mechanical strength of CCF were also investigated. The prepared CCF is beneficial for manufacturing the transparently electronic devices with environmental-friendly merit.

A novel approach for preparation of CH3NH3PbBr3 via direct transformation of electrodeposited PbO2 for photodetector application

Organic–inorganic hybrid perovskites are crystals with efficient light absorption, high charge carrier mobility and long electron/hole diffusion path that have been developed to enhance sunlight energy application. In particular, lead-based compounds by establishing excellent performance in 3rd generation solar cells led to an increased interest in testing them in other areas such as photodetectors, diodes, and transistors. Herein, we report a simple, scalable and versatile fabrication process of CH3NH3PbBr3 layer through electrodeposition technique without using a glove box or a high vacuum system. Measurements demonstrated that a high quality crystalline structure in a pinhole free perovskite layer was obtained. The fabricated photodetector devices made of electrodeposited MAPbBr3 films displayed significant performance with the on/off current ratio of 3 × 106 under white light radiation at 0.1 V bias voltage. Increasing the thickness of photoactive absorber layer up to 1 µm led to 7% external quantum efficiency and 34.4% improvement of EQE compared to 546 nm film.

The effects of the oxygen content on the photoelectrochemical properties of LaFeO3 perovskite thin films obtained by pulsed laser deposition

The physical properties of perovskite oxides are strongly influenced by their stoichiometry and one of the key features of these materials is the tunability of their functionality by controlling the interplay between the compositional and structural properties. Here, the effects on the photoelectrochemical (PEC) water splitting properties of ferroelectric LaFeO3 thin films obtained at different oxygen partial pressures during growth are reported in conjunction with the morphological, optical and structural features. The LaFeO3 thin films have been deposited by pulsed laser deposition on Nb:SrTiO3 substrates. The strong dependence of the photocurrent values Jphoto on the growth conditions is revealed by the photoelectrochemical measurements. Strong variations of the lateral coherence lengths L‖ of LaFeO3/Nb:SrTiO3 with the oxygen partial pressure values are noticed from the X-ray diffraction (XRD) analysis. All the films are heteroepitaxial with small tensile strain levels detected in the crystalline structure, but only for a narrow interval of oxygen partial pressures the LFO/STON thin films show high quality crystalline structure with large lateral coherence length L‖ and photoelectrochemical currents.

Development of chipless, wireless current sensor system based on giant magnetoimpedance magnetic sensor and surface acoustic wave transponder.

A chipless, wireless current sensor system was developed using a giant magnetoimpedance (GMI) magnetic sensor and one-port surface acoustic wave (SAW) reflective delay line for real-time power monitoring in a current-carrying conductor. The GMI sensor has a high-quality crystalline structure in each layer, which contributes to a high sensitivity and good linearity in a magnetic field of 3–16 Oe. A 400 MHz RF energy generated from the interdigital transducer (IDT)-type reflector on the one-port SAW delay line was used as an activation source for the GMI magnetic sensor. The one-port SAW delay line replaces the presently existing transceiver system, which is composed of thousands of transistors, thus enabling chipless and wireless operation. We confirmed a large variation in the amplitude of the SAW reflection peak with a change in the impedance of the GMI sensor caused by the current flow through the conductor. Good linearity and sensitivity of ~0.691 dB/A were observed for currents in the range 1–12 A. Coupling of Mode (COM) modeling and impedance matching analysis were also performed to predict the device performance in advance and these were compared with the experimental results.

Photoluminescence of Atomic Layer Deposition Grown ZnO Nanostructures

Atomic Layer Deposition (ALD) technique was used to grow crystalline, nanostructured Zinc Oxide (ZnO) thin films, having very low surface roughness, on silicon (Si) and fused quartz (SiO2) substrates. The film thickness and structural properties were characterized by using X-ray reflectivity and X-ray diffraction techniques. The excitonic light emission of ZnO thin films wasstudied by means of photoluminescence (PL) measurements in the ultraviolet-visible spectral region. Characteristic near band edge emission (NBE) of the ZnO thin films corresponding to free excitonic recombination shows strong signal in the UV range at room temperature. Visible region of the PL spectra of ZnO nanostructures shows that there is no defect related deep level emission (DLE), suggesting the absence of defect states. The results confirm the growth of ZnO thin films of a high quality crystalline structure by ALD technique.

Properties of single crystal para-terphenyl as medium for high resolution TOF detector

In the last years organic scintillators have been largely investigated in order to achieve high light yield together with good time response. Pure organic compound with high quality crystalline structure can achieve both this goals. Among a large type of organic compound, para-terphenyl (C18H14) have proven to have practical applications as detector medium for particle physics. In this work, the characterization of different sizes high quality mono-crystal p-terphenyl samples is presented. The optical and scintillation properties (emission spectrum, light yield, attenuation length, and decay time) are investigated. Coupling a Silicon PhotoMultiplier-based readout system to the crystal, a small prototype for a high resolution TOF detector was built; the preliminary results, obtained on a 20×30×3mm3 sample, with dual-side read-out (Hamamatsu S10931-050P SiPMs) and irradiated with 90Sr source, show a time resolution of 35ps.

Structural, electric and magnetic properties of Pb(Zr0.2Ti0.8)O3–CoFe2O4 heterostructures

Electric and magnetic properties of symmetric and asymmetric Pb(Zr0.2 Ti0.8)O3–CoFe2O4 (PZT/CFO) heterostructures, grown by pulsed laser deposition on SrTiO3 (100) substrates with a 25nm SrRuO3 (SRO) buffer layer as bottom electrode, were investigated by using hysteresis and capacitance measurements. X-ray diffraction, and transmission electron microscopy investigations reveal the high quality crystalline structure and the epitaxial relationship between SRO, PZT and CFO. The electric polarization–voltage hysteresis reveals that the remnant polarization and the coercive field are significantly affected by the CFO layer. The frequency dependence of capacitance suggests a Maxwell–Wagner type relaxation at low frequencies and is also affected by the presence of the PZT/CFO interface(s). The magnetic hysteresis measurements infer the possible presence of another spinel phase (Co3O4) in the CFO film, due to the lattice mismatch at the PZT/CFO interfaces, and with direct influence on the magnetic response of the structure. According to the electric and magnetic characterization, better room temperature multiferroic properties would be expected for the symmetric heterostructure.

Flexographic printing-assisted fabrication of ZnO nanowire devices

In this study, the use of flexographic printing was investigated for low cost, high volume production of devices incorporating nanowires through the printing of zinc acetate precursors on a substrate used to form zinc oxide (ZnO) seeds for the growth of nanowires using a hydrothermal growth technique. The printing of precursors allows the selective area growth of ZnO nanowires, which has implications in high-yield production of devices incorporating ZnO nanowires. The work presented here achieved printed line widths of <60 μm with low edge distortion (<3 μm) using a printing plate with a line width of 50 μm. The hydrothermally grown ZnO nanowires show uniform density of growth over the printed area with nanowire diameters between 40 and 60 nm on both silicon and polyimide substrates. Energy-dispersive x-ray spectra showed contamination-free crystals with a 1:1 (zinc to oxygen) stoichiometry. Crystal orientation is along the c-axis with high quality crystalline structure shown using x-ray diffraction spectroscopy and high resolution transmission electron microscopy. A ZnO nanowire gas sensor, fabricated using the flexographic printing technique, is demonstrated. Such a printing-assisted fabrication offers low cost, high volume production of devices incorporating ZnO nanowires, ranging from gas sensors to field emission devices.

Graphene segregated on Ni surfaces and transferred to insulators

We report an approach to synthesize high quality graphene by surface segregation and substrate transfer. Graphene was segregated from Ni surface under the ambient pressure by dissolving carbon in Ni at high temperatures followed by cooling down with various rates. Different cooling rates led to different segregation behaviors, strongly affecting the thickness and quality of the graphene films. Electron microscopy and Raman spectroscopy indicated that the graphene films synthesized with medium cooling rates have high quality crystalline structure and well-controlled thicknesses. The graphene films were transferred to insulating substrates by wet etching and found to maintain their high quality.

Growth and Structural Properties of Indium doped SrTiO&lt;SUB&gt;3&lt;/SUB&gt; Films by Pulsed Laser Deposition

Undoped and In-doped SrTiO_3(STO) films were grown on MgO/TiN/Si(100) substrates by pulsed laser deposition(PLD).The growth mechanism,crystallinity,surface morphology,and UV- Raman spectra of the films were studied.Results indicate that undoped STO films show high quality crystalline structure with highly (200) orientation.With Indium doping,the crystallinity of the STO film deteriorate,the first order Raman peaks increase indicating the breaking of crystal symmetry,and the film growth mode change from the layer-by-layer mode to island-layer mixed one,resulting in the roughening of the film surface.Furthermore,the crystallinity and (200) orientation of In-doped STO film can be enhanced significantly by introducing an undoped STO buffer layer.

Triple-Crystal Zinc Selenide Nanobelts

One-dimensional ZnSe nanobelts with three-dimensional triple-crystal architecture have been fabricated on Au-coated Si substrates by thermal evaporation of ZnSe powders. The as-synthesized triple-crystal ZnSe nanobelts are a metastable 2H-wurtzite structure while the typical structure of ZnSe nanocrystal is a stable zinc blend. The triple-crystal nanobelts have a typical length of tens of micrometers and a thickness of 30−80 nm. The morphology and growth mechanisms of the triple-crystal nanobelts, which cannot be described by the commonly used octahedral multiple-twin growth model for similar nanostructures, are investigated and explained based on the {101̄3} twins and two fastest-growing directions of [0001] and [11̄00] of the belt. The thermodynamics of the formation of metastable wurtzite ZnSe nanostructures are also discussed in terms of the temperature and surface energy. The photoluminescence spectra show that the triple-crystal nanobelts possess high-quality crystalline structure.

Fabrication and characterization of Zn-doped CdTe nanowires

At 850 °C, Zn-doped CdTe nanowires with an average diameter of about 40 nm and lengths up to several tens of micrometers were fabricated by a CVD approach. The nanowires were detected by SEM, XRD, TEM, HRTEM, EDS, SAED, and XPS, where the as-synthesized CdZnTe nanowires have high-quality crystalline structure and grow along the 〈001〉 direction and the Cd/Zn ratios of these nanowires are close to those expected from the starting compositions. The corresponding growth mechanism of the nanowires is also explained.

Low temperature, high growth rate epitaxial silicon and silicon germanium alloy films

Epitaxial growth of silicon and silicon germanium alloy films on Si(1 0 0) substrates in an ASM Epsilon ® single wafer reactor system using trisilane and germane has been investigated. The results obtained reveal that it is possible to achieve epitaxial silicon and silicon germanium growth rates at 630 °C and below that are substantially higher than those possible using silane, while maintaining high quality crystalline structure. The films grown were characterized using Rutherford backscattering spectroscopy (RBS), high resolution X-Ray diffraction (HR-XRD), atomic force microscopy (AFM) and high resolution cross-sectional transmission electron microscopy (X-TEM).

Improvement of electrical properties of epitaxial SrTiO3 films on Si(001)-2×1 by in situ annealing

We have studied the formation of a high-quality SrTiO3 (STO) film on a Si surface which is an appropriate buffer film for fabricating high-Tc superconductor devices on Si by molecular beam epitaxy. The STO films with thicknesses of 1300–6700 Å are grown on a SrO buffer layer with a thickness of 100 Å on Si(001)-2×1 in ∼10−8 Torr. The growth temperatures for the STO films and SrO layer are 500 and 400 °C, respectively. The as-grown STO films are insufficiently oxidized regarding the Ti–O bond which is confirmed by the observation of x-ray photoemission spectroscopy, although in situ reflection high-energy electron diffraction spectroscopy and ex situ x-ray diffraction (XRD) reveal a high-quality crystalline structure. The in situ postannealing for the as-grown STO films is performed at 500–900 °C for 60 min in an oxygen atmosphere of 1×10−6 Torr. The heat treatment promotes the oxidation of STO films and results in a high resistivity of 109–1011 Ω cm and a dielectric constant of 130 at 100 kHz at room temperature. The films consist of large grains with 150–200 nm diameter on the surface in the image of atomic force microscopy. The heat treatment does not prominently affect the crystallinity of STO films in the XRD patterns.

Electrical properties of epitaxial tungsten films grown by laser ablation deposition

An investigation was made of electrical properties of tungsten films of thickness in the range of 30–140 nm, grown by laser ablation deposition in ultrahigh vacuum on [1̄012] sapphire substrate. From the data on the size effect and the temperature dependence of the resistivity r, supported with reflection high energy electron diffraction measurements, we find that the films, deposited onto clean substrates kept at temperatures higher than 500 °C, grow epitaxially with high quality crystalline structure. The effective electron mean free path changes from 300 to 1400 nm while the residual resistance ratio RRR=r (295 K)/r (4.2 K) changes from 7 to 35. At low temperatures we find the temperature dependent part ρ(T)≊ATn, with A=1.56 mΩ cm K−n, n=3–3.4 for the temperatures T&amp;lt;20 K. From the fit of the data to the equations of the classical size effect theory it was found that the main source of electron scattering at helium temperatures is interface scattering with a specular coefficient q≊0.3 and the bulk electron mean free path l∞ (4.2 K)∼200 μm, which is up to 103 times larger than the film thickness.