Simple Physical Vapor Deposition Research Articles

Silicon based solar cells using a multilayer oxide as emitter

In this work, n-type silicon based solar cells with WO3/Ag/WO3 multilayer films as emitter (WAW/n-Si solar cells) were presented via simple physical vapor deposition (PVD). Microstructure and composition of WAW/n-Si solar cells were studied by TEM and XPS, respectively. Furthermore, the dependence of the solar cells performances on each WO3 layer thickness was investigated. The results indicated that the bottom WO3 layer mainly induced band bending and facilitated charge-carriers separation, while the top WO3 layer degraded open-circuit voltage but actually improved optical absorption of the solar cells. The WAW/n-Si solar cells, with optimized bottom and top WO3 layer thicknesses, exhibited 5.21% efficiency on polished wafer with area of 4 cm2 under AM 1.5 condition (25 °C and 100 mW/cm2). Compared with WO3 single-layer film, WAW multilayer films demonstrated better surface passivation quality but more optical loss, while the optical loss could be effectively reduced by implementing light-trapping structures. These results pave a new way for dopant-free solar cells in terms of low-cost and facile process flow.

Mid-infrared photodetectors based on InSb micro/nanostructures grown on low-cost mica substrates

Thin films consisted of InSb micro/nanostructures are grown on mica substrates by a simple physical vapor deposition method. The deposition temperature plays a major role in the surface morphology and material quality of the InSb films synthesized on mica substrates as evidenced by scanning electron microscopy and X-ray diffraction measurements. Mid-infrared photodetectors were also fabricated from the InSb films and superior device performance was obtained from the InSb films grown at elevated temperature.

Physical vapor deposition synthesis of two-dimensional orthorhombic SnS flakes with strong angle/temperature-dependent Raman responses.

Anisotropic layered semiconductors have attracted significant interest due to the huge possibility of bringing new functionalities to thermoelectric, electronic and optoelectronic devices. Currently, most reports on anisotropy have concentrated on black phosphorus and ReS2, less effort has been contributed to other layered materials. In this work, two-dimensional (2D) orthorhombic SnS flakes on a large scale have been successfully synthesized via a simple physical vapor deposition method. Angle-dependent Raman spectroscopy indicated that the orthorhombic SnS flakes possess a strong anisotropic Raman response. Under a parallel-polarization configuration, the peak intensity of Ag (190.7 cm(-1)) Raman mode reaches the maximum when incident light polarization is parallel to the armchair direction of the 2D SnS flakes, which strongly suggests that the Ag (190.7 cm(-1)) mode can be used to determine the crystallographic orientation of the 2D SnS. In addition, temperature-dependent Raman characterization confirmed that the 2D SnS flakes have a higher sensitivity to temperature than graphene, MoS2 and black phosphorus. These results are useful for the future studies of the optical and thermal properties of 2D orthorhombic SnS.

Superhydrophobic SERS Substrates Based on Silver-Coated Reduced Graphene Oxide Gratings Prepared by Two-Beam Laser Interference

Reported here is the fabrication of reduced graphene oxide (RGO) grating structures by two-beam laser interference (TBLI) for the development of highly efficient SERS substrates via simple physical vapor deposition (PVD) coating of silver. TBLI has been utilized to make hierarchical RGO grating structures with microscale gratings and nanoscale folders through a laser treatment induced ablation and photoreduction process. The hierarchical structures contribute to the formation of plasmonic structures after silver coating, giving rise to the formation of plenty of SERS "hot spots", while the RGO substrate would provide chemical enhancement of Raman signal through interaction with analytes molecules. The significantly increased roughness with respect to the hierarchical structures in combination with the removal of hydrophilic oxygen-containing groups endow the resultant substrates with unique superhydrophobicity, which leads to the enrichment of analytes and further lowers the detection limit. The synergistic effects make the silver coated RGO gratings a highly efficient SERS substrate; in the detection of Rhodamine B, our SERS substrates showed high SERS enhancement and good reproducibility, a detection limit of 10(-10) M has been achieved.

A high performance HfSiON/TaN NMOSFET fabricated using a gate-last process

A gate-last process for fabricating HfSiON/TaN n-channel metal-oxide-semiconductor-field-effect transistors (NMOSFETs) is presented. In the process, a HfSiON gate dielectric with an equivalent oxide thickness of 10 Å was prepared by a simple physical vapor deposition method. Poly-Si was deposited on the HfSiON gate dielectric as a dummy gate. After the source/drain formation, the poly-Si dummy gate was removed by tetramethylammonium hydroxide (TMAH) wet-etching and replaced by a TaN metal gate. Because the metal gate was formed after the ion-implant doping activation process, the effects of the high temperature process on the metal gate were avoided. The fabricated device exhibits good electrical characteristics, including good driving ability and excellent sub-threshold characteristics. The device's gate length is 73 nm, the driving current is 117 μA/μm under power supply voltages of VGS = VDS = 1.5 V and the off-state current is only 4.4 nA/μm. The lower effective work function of TaN on HfSiON gives the device a suitable threshold voltage (∼ 0.24 V) for high performance NMOSFETs. The device's excellent performance indicates that this novel gate-last process is practical for fabricating high performance MOSFETs.

Gas phase-based growth of highly sensitive single-crystal rectangular micro- and nanotubes

In this study, we report the preparation of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) micro/nanotubes (M/NTs) by a simple physical vapor deposition (PVD) process, and it was found that tubular structures with a diameter from 300 nm to 5 μm and lengths up to tens of micrometres were obtained on a glass substrate at a deposition temperature of 350–400 °C. Detailed studies revealed that PTCDA M/NTs were formed via curling and seaming of a 2D lamellar structure constructed by virtue of the cooperation of some noncovalent interactions such as π–π interactions and H-bonds, and it was a temperature-activated process. Devices based on single PTCDA microtubes with different diameters exhibited resistance decreased by 2 orders of magnitude in reducing hydrazine vapor (even for such a low concentration as 5 ppm). Such a successful application of the PVD process to simple organic molecules and highly efficient performance in devices are expected to provide great opportunities for the formation of diverse functional organic hollow nanostructures.

Amplified spontaneous emission from single CdS nanoribbon with low symmetric cross sections

CdS nanoribbons with various cross sections offer the opportunity to deeply understand the interaction between optical cavity and spontaneous emission. Herein, long tapered nanoribbons with the cross sections gradually changing were synthesized by a simple physical vapour deposition method. Morphology dependent micro-region photoluminescence (PL) spectroscopy is employed to show Purcell effect along different low symmetry cross sections. Spikes on the PL spectra reveal that local density of optical modes increases when the mode match happens between optical cavity and spontaneous emission. Bound exciton complex related amplified spontaneous emission is observed in a single CdS nanoribbon with well-defined elliptical cross sections and optimized width/thickness ratio ∼1.45. Polarized Raman and TEM confirmed that the nanoribbon with the elliptical cross section adopts the [0002] growth direction with good quality. The results suggest that the cross section resonant cavity would be of importance for both fundamental and practical application of cavity quantum electrodynamics in CdS nanoribbon.

Nearly Monodispersed Perylene Nanotablets: Easy Fabrication and Unique Optical Properties

Here we describe a simple physical vapor deposition (PVD) method to prepare large quantity of highly monodispersed perylene nanotablets with a deposition-temperature controlled approach. The nanotablets produced are 1 microm octagon with 100-200 nm thickness. Confocal microscopic images of the nanotablets excited with a UV light show not only yellow color emission which is quite different from perylene monomers but also the obvious light-wave guiding properties. The formation of beta form nanocrystals shows that our method is highly selective for only one kind of perylene nanocrystals, which makes sure the uniform optical and electronic properties of the whole thin film. The morphology of the unique perylene nanotablets is significantly decided by the strictly required temperature of the depositing substrates. This approach is simple and template free and the as-prepared nanotablets possess smooth surface. The coating of the nanotablets can change the superhydrophilic surface to a superhydrophobic one which is an important application property for fabricating stable nanodevices.

Growth and photoluminescence of vertically aligned ZnO nanowires/nanowalls

By controlling the incoming gas flow, vertically aligned ZnO nanowires and nanowalls have been successfully synthesized on a Si (1 0 0) substrate by the simple physical vapour deposition method. The growth process of the ZnO nanowalls was observed by adjusting the growth time. The probable growth mechanisms of the ZnO nanowires and nanowalls were discussed in detail. In contrast to the photoluminescence results of nanowires, an enhancement of the LO phonon signal was observed in ZnO nanowalls, which was attributed to an additional channel of electron–phonon coupling induced by the residual strains in the ZnO nanowalls during the coalescence growth process.

Characteristics of high-quality HfSiON gate dielectric prepared by physical vapour deposition

This paper presents a method using simple physical vapour deposition to form high-quality hafnium silicon oxynitride (HfSiON) on ultrathin SiO2 buffer layer. The gate dielectric with 10 Å (1Å = 0.1 nm) equivalent oxide thickness is obtained. The experimental results indicate that the prepared HfSiON gate dielectric exhibits good physical and electrical characteristics, including very good thermal stability up to 1000°C, excellent interface properties, high dielectric constant (κ = 14) and low gate-leakage current (Ig = 1.9 × 10−3 A/cm2@Vg = Vfb − 1V for EOT of 10 Å). TaN metal gate electrode is integrated with the HfSiON gate dielectric. The effective work function of TaN on HfSiON is 4.3 eV, meeting the requirements of NMOS for the metal gate. And, the impacts of sputtering ambient and annealing temperature on the electrical properties of HfSiON gate dielectric are investigated.

Sputtered magnesium diboride thin films: Growth conditions and surface morphology

Magnesium diboride (MgB 2) thin films were deposited on C-plane sapphire substrates by sputtering pure B and Mg targets at different substrate temperatures, and were followed by in situ annealing. A systematic study about the effects of the various growth and annealing parameters on the physical properties of MgB 2 thin films showed that the substrate temperature is the most critical factor that determines the superconducting transition temperature ( T c ), while annealing plays a minor role. There was no superconducting transition in the thin films grown at room temperature without post-annealing. The highest T c of the samples grown at room temperature after the optimized annealing was 22 K. As the temperature of the substrate ( T s ) increased, T c rose. However, the maximum T s was limited due to the low magnesium sticking coefficient and thus the T c value was limited as well. The highest T c , 29 K, was obtained for the sample deposited at 180 °C, annealed at 620 °C, and was subsequently annealed a second time at 800 °C. Three-dimensional (3D) AFM images clearly demonstrated that the thin films with no transition, or very low T c , did not have the well-developed MgB 2 grains while the films with higher T c displayed the well-developed grains and smooth surface. Although the T c of sputtered MgB 2 films in the current work is lower than that for the bulk and ex situ annealed thin films, this work presents an important step towards the fabrication of MgB 2 heterostructures using rather simple physical vapor deposition method such as sputtering.

Fabrication and green emission of ZnO nanowire arrays

Well-aligned single-crystalline wurzite zinc oxide (ZnO) nanowire arrays were successfully fabricated on a Si substrate by a simple physical vapor-deposition (PVD) method at a relatively low temperature of about 500°C. The as-fabricated nanowires were preferentially arranged along the [001] direction of ZnO. The photoluminescence spectrum of ZnO nanowire arrays showed two emission bands: a strong green emission at around 500 nm and a weak ultraviolet emission at 380 nm. The strong green light emission was related to the existence of the oxygen vacancies in ZnO crystals. Corresponding growth mechanism of the ZnO nanowires was briefly discussed.

Construction and fluorescence of organic nanotube arrays by template-based physical vapor deposition method

Well-aligned organic nanotubes including acenaphthylene, carbazole, anthracene, phenanthrene and naphthalene have been fabricated within the nanochannels of the porous anodic alumina (PAA) membranes by a simple physical vapor deposition (PVD) method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal that these organic nanotubes are highly ordered with a uniform diameter in range of 100–200nm and a length of up to tens of microns. The fluorescence spectra of these nanotubes exhibit obvious blue shift compared to those of the bulk crystals, which can be attributed to the surface effect of the nanostructures.

Synthesis and electrical properties of TiSi2 nanocables

Uniform TiSi2 nanocables were synthesized on large substrates using a simple physical vapor deposition method. X-ray diffraction, scanning electron microscopy, and transmission electronic microscopy were employed to characterize the samples. It reveals that the as-grown TiSi2 nanocables are of high quality single crystal inside with thin amorphous SiO2 sheathing layer. Electrical properties of these core-shell structure nanowires are also presented. Insulativity of the outer layer and stable metallic characters of the inside single crystal TiSi2 were observed. Moreover, carrying capacity of current density is up to 1011A∕m2. The nanoscale structure and excellent electrical performance make the TiSi2 nanocables good candidate for electrical interconnection in potential nanodevices.

Catalyst-free synthesis of macro-scale ZnO nanonail arrays on Si substrate by simple physical vapor deposition

Macro-scale ZnO nanonail arrays have been synthesized on silicon wafer by a simple physical vapor deposition approach without any catalyst. These synthesized ZnO nanonails grow vertically on the substrate with their caps upside. This probably results from the crowding effect. Each ZnO nanonail has a large hexagonal cap and a thinner shaft of several microns in length. Most of the nanonails are perfect single crystals with wurtzite structure and their preferred growth orientation is along [001] direction. The growth mechanism is VS mechanism and the detailed growth process is also proposed. The macro-scale nanonail arrays on Si substrate could offer novel opportunities for both fundamental research and technological applications.

Structure and Photoluminescence Properties of Aligned ZnO Nanobolt Arrays

Well-aligned ZnO nanorod and nanobolt arrays were synthesized on p-type Si(100) substrates by a simple physical vapor deposition method. During the growth process when the carrier gas was switched from Ar to air, the nanorods changed into nanobolts completely. The mechanism for this transformation process is discussed. The room-temperature photoluminescence spectrum of nanobolts showed a strong ultraviolet emission at 3.26 eV coupled with a weak deep level energy emission at 2.48 eV. The origin of the ultraviolet emission of nanobolts was investigated by temperature-dependent photoluminescence spectra.

The influence of growth temperature on ZnO nanowires

ZnO nanowires have been successfully synthesized on Si(100) substrate by a simple physical vapor deposition method. Thin film ZnO layer used as the nucleation site can avoid the contamination from the metal catalysts, and it can also control the growth direction of ZnO nanowires. Well-aligned ZnO nanowire arrays along the normal direction of the substrate can be obtained by controlling different growth temperature, which was demonstrated by XRD and FESEM analysis. A strong ultraviolet emission at room temperature was observed in all ZnO nanostructures. In addition, the growth mechanisms of the ZnO nanowires with different growth temperature is discussed in details.

Correlation between photoluminescence and varied growth pressure of well-aligned ZnO nanorods on fused silica substrate

Well-aligned ZnO nanorods with variable diameters were fabricated on fused silica substrates by the simple physical vapor deposition method with and without pre-deposited NiO particles. The diameter control of ZnO nanorods on the fused silica substrates was achieved by varying the growth pressure. The room-temperature photoluminescence spectra of the ZnO nanorods exhibit strong exciton emission at 3.25eV that reveals good crystal quality. The exciton emission peak shifts toward 3.22eV for the samples made at the larger growth pressure that is attributed to the influence of the electron-acceptor-level transition. The ZnO nanorods were examined by high resolution transmission electron microscopy and X-ray diffraction to show single crystal quality and preferentially c-axis alignment. Furthermore, we used scanning electron microscope to verify not only the size but also the growth mechanisms of ZnO nanorods. The results show a ZnO buffer layer formed between the flat top-facet nanorods and the substrate. In comparison with the samples without pre-deposited NiO particles on the substrate, the pre-deposited NiO particles act as nucleation centers for Zn vapor during the deposition process that improves the quality of the buffer layer.

Photoluminescence of ZnO nanowires grown on sapphire (1 1 2¯ 0) substrates

ZnO nanowires were fabricated on c-plane (0 0 0 1), a-plane (1 1 2¯ 0) sapphire, and boron doped p-type (1 0 0) Si substrates in vacuum furnace by simple physical vapor deposition. Room temperature photoluminescence spectra of the nanowires show the near band-edge emission and the deep-level green light emission. The ZnO nanowires formed on sapphire (1 1 2¯ 0) substrates exhibited enhancement on optical properties and better crystalline structures than those of nanowires grown on other substrates. The formation mechanism and the effect of substrate direction on structural and optical properties of the nanowires are discussed.

The substrate effect on the in-plane orientation of vertically well-aligned ZnO nanorodsgrown on ZnO buffer layers

Vertically well-aligned ZnO nanorods were synthesized without employing any metal catalysts onvarious substrates including glass, Si(111), 6H-SiC(0001) and sapphire (0001), which were pre-coatedwith c-oriented ZnO buffer layers, by simple physical vapour deposition. The alignments ofthe ZnO nanorods on the different substrates depend on the crystallographicalignments of the pre-coated ZnO buffer layers. The ZnO nanorods grown on glass andSi(111) are vertically aligned but randomly oriented in the in-plane direction. Incontrast, the vertically aligned ZnO nanorods on 6H-SiC(0001) and sapphire(0001) show an in-plane alignment with azimuthally sixfold symmetry, whichindicates the epitaxial relationship between ZnO and the substrate. Similarly,photoluminescence measurements show the distinct appearance of ZnO nanorods ondifferent substrates. Besides the UV band, which was attributed to the recombination offree excitons near the band edge, defect-related visible emissions were also observedfor the samples grown on both glass and Si(111) substrates. However, the ZnOnanorods exhibit only strong band edge emission peaks with no noticeable deep levelemissions when grown on the 6H-SiC(0001) and sapphire (0001) substrates, whichconfirms the good crystalline and optical quality of the epitaxial ZnO nanorods.