Non-catalytic Thermal Evaporation Research Articles

Time dependent growth of ZnO nanoflowers with enhanced field emission properties

Herein, we report the facile growth of ZnO nanoflowers composed of nanorods on silicon substrate by non-catalytic thermal evaporation process. The grown nanoflowers were examined in terms of their morphological, structural, optical and field emission properties. The detailed characterizations revealed that the nanoflowers are grown in high density, possessing well-crystallinity and exhibiting wurtzite hexagonal phase. The Raman-scattering spectrum shows a sharp optical-phonon E2 mode at 437cm−1 which confirmed the wurtzite hexagonal phase for the grown nanoflowers. The room-temperature PL spectrum depict a strong ultraviolet emission at 381nm, revealed good optical properties for the ZnO nanoflowers. The field emission studies revealed that a turn-on field for the ZnO nanoflowers based field emission device was 4.3V/μm and the emission current density reached to 0.075mA/cm2 at an applied electric field of 7.2V/μm and exhibit no saturation. The field enhancement factor ‘β’ for the fabricated device was estimated from the F-N plot and found to be ~2.75×103. Finally, systematic time-dependent experiments were performed to determine the growth process for the formation of ZnO nanoflowers composed of nanorods.

Growth and Properties of Sn-Doped ZnO Nanowires for Heterojunction Diode Application

ABSTRACTWell-crystalline Sn-doped ZnO nanowires were grown on p -type silicon substrates by simple non-catalytic ther-mal evaporation process. The prepared nanowires were examined in terms of their morphological, composi-tional and structural properties which revealed that the as-grown nanowires are well-crystalline Sn-doped ZnO,possessing wurtzite hexagonal phase structure and grown in very high density over whole silicon substrate.Further, the as-grown n -Sn-doped ZnO nanowires were used to fabricate n -Sn-ZnO/ p -Si heterojunction diode.Temperature dependant electrical properties (294Ð353 K and 373Ð433 K) of the fabricated heterojunction diodewere studied in the forward and reverse bias conditions and presented in this paper. The currentÐvoltage char-acteristics at varying temperature of the heterojunction diode reveal that both the quality factor and Schottkybarrier height depend on temperature. However, the mean barrier height is estimated 1.2 eV in one attempt ofanalysis when a Gaussian distribution of low barrier heights is considered and found almost 1 eV in anotherattempt when the Richardson plot is linearized. Furthermore, effective barrier heights of 0.55Ð0.75 eV areextracted in the temperature range 294Ð433 K when Tung model is used. These correspond to barrier heightsof 0.93Ð0.35 eV extracted from C Ð V analysis in the same range of temperatures. Although the latter resultsfrom C Ð V analysis exhibit closer correlation with the Schottky barrier heights extracted from IÐ V analysis butthe discrepancy between them still exist.KEYWORDS: Sn-Doped ZnO Nanowires, Heterojunction Diodes, IÐ V Characteristics, Electrical Properties.

Growth of In-Doped ZnO Hollow Spheres Composed of Nanosheets Networks and Nanocones: Structural and Optical Properties

This work reports the facile growth and characterizations of In-doped ZnO hollow spheres composed of nanosheets networks and nanocones. The In-doped ZnO hollow spheres composed of nanosheets networks and nanocones were grown on Si (100) substrate by simple and non-catalytic thermal evaporation process using metallic zinc and indium powders in the presence of oxygen. The prepared materials were examined in terms of their morphological, compositional, structural and optical properties. The detailed morphological studies revealed that the synthesized products are hollow spheres composed of nanosheet networks and nanocones and grown in high-density. The observed structural properties exhibited well-crystallinity and wurtzite hexagonal phase for the grown materials. The room-temperature photoluminescence (PL) spectrum showed a broad band in the visible region with a suppressed UV emission and hence due the enhancement in the green emission, the prepared materials exhibits a great interest in the area of ZnO phosphors, such as field emissive display technology, etc.

Structural, Optical and Field Emission Properties of Urchin-Shaped ZnO Nanostructures

In this work, well-crystallized urchin-shaped ZnO structures were synthesized on silicon substrate by simple non-catalytic thermal evaporation process by using metallic zinc powder in the presence of oxygen as source materials for zinc and oxygen, respectively. The synthesized ZnO structures were characterized in detail in terms of their morphological, structural, optical and field emission properties. The detailed morphological investigations revealed that the synthesized structures possess urchin-shape and grown in high-density over the substrate surface. The detailed structural and optical characterizations revealed that the synthesized urchin-shaped ZnO structures are well-crystallized and exhibiting good optical properties. The field emission analysis for urchin-shaped ZnO structures exhibits a turn-on field of 4.6 V/microm. The emission current density reached to 0.056 mA/cm2 at an applied electrical field of 6.4 V/microm and shows no saturation. The calculated field enhancement factor 'beta', from the F-N plot, was found to be approximately 2.2 x 10(3).

Intense ultraviolet emission from needle-like WO3 nanostructures synthesized by noncatalytic thermal evaporation

Photoluminescence measurements showed that needle-like tungsten oxide nanostructures synthesized at 590°C to 750°C by the thermal evaporation of WO3 nanopowders without the use of a catalyst had an intense near-ultraviolet (NUV) emission band that was different from that of the tungsten oxide nanostructures obtained in other temperature ranges. The intense NUV emission might be due to the localized states associated with oxygen vacancies and surface states.

Well-Crystalline ZnO Nanowire Based Field Effect Transistors (FETs)

Well-crystalline ZnO nanowires were grown on Si(100) via non-catalytic thermal evaporation process using metallic zinc powder in presence of oxygen. The detailed morphological characterizations by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) confirmed that the synthesized products are nanowires with the typical diameter and lengths of approximately 55 +/- 5 nm and several micrometers, respectively and are grown in high density over the silicon substrate. The detailed structural characterizations by high-resolution TEM and X-ray diffraction confirmed that the synthesized nanowires are well-crystalline and possessing wurtzite hexagonal phase. The presence of Raman-active optical-phonon E2(high) mode at 437 cm(-1) in the Raman-scattering spectrum confirms good crystal quality for the as-grown ZnO nanowires. The electrical transport properties of the as-grown nanowires were explored by fabricating single nanowire based field effect transistors (FETs). The fabricated single ZnO nanowire based FET exhibits carrier concentration and electron mobility of approximately 7.49 x 10(17) cm(-3) and approximately 8.42 cm2V(-1)s(-1), respectively.

Growth of Aligned Hexagonal ZnO Nanorods on FTO Substrate for Dye-Sensitized Solar Cells (DSSCs) Application

This article reports a facile growth of well-crystalline aligned hexagonal ZnO nanorods on fluorine-doped tin-oxide (FTO) substrate via non-catalytic thermal evaporation process. The morphological investigations done by field-emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM) reveal that the grown products are aligned hexagonal ZnO nanorods which are grown in a very high density over the whole substrate surface. The detailed structural properties observed by high-resolution TEM equipped with selected area electron diffraction (SAED) and X-ray diffraction (XRD) pattern confirmed that the synthesized nanorods are well-crystalline possessing wurtzite hexagonal phase and preferentially grown along the c-axis direction. A sharp and strong UV emission at 381 nm in room-temperature photoluminescence (PL) spectrum showed that the as-grown ZnO nanorods possess excellent optical properties. The as-grown nanorods were used as photo-anode for the fabrication of dye-sensitized solar cells (DSSCs) which exhibits an overall light-to-electricity conversion efficiency (ECE) of 0.7% with V(oc) of 0.571 V, J(sc) of 2.02 mA/cm2 and FF of 0.58.

Growth and Properties of Ultra-Violet Emitting Aligned Zinc Oxide Nanocones with Hexagonal Caps

Ultraviolet-emitting, single-crystalline aligned zinc oxide (ZnO) nanocones with hexagonal caps were grown on silicon substrate via simple non-catalytic thermal evaporation process. High-purity metallic zinc powder and oxygen were used as source materials for zinc and oxygen, respectively. The detailed structural characterizations confirmed that the formed products are single-crystalline, possess a wurtzite hexagonal phase and grown along the c-axis direction. Raman-active optical-phonon E2(high) mode at 437 cm(-1) with sharp and strong UV emission at 385 nm in room-temperature photoluminescence (PL) spectrum demonstrated that the as-grown ZnO nanocones with hexagonal caps possess good-crystal quality with the excellent optical properties. Finally, a plausible growth mechanism for the formation of as-grown ZnO nanocones with hexagonal caps was also proposed.

Detailed Study on Photoluminescence Property and Growth Mechanism of ZnO Nanowire Arrays Grown by Thermal Evaporation

The photoluminescence (PL) property and growth mechanism of ZnO nanowires, which are essential to both fundamental and applied studies, are not yet well understood. Here extensive investigations have been carried out to deeply understand the two issues. At first, ZnO nanowire arrays are fabricated on bare glass substrate via a noncatalytic thermal evaporation method. Afterward, the PL measurements reveal that the emission peaks located at 405 and 616 nm are related to the Zn vacancy defect, and the red peak located in the region between 750 and 800 nm has relations with the interaction between the Zn vacancy and Zn interstitial defects. Detailed experiments show that the oxygen flux plays a very important role in the morphology evolution of the as-grown products, which change from nanoflakes to nanowires and finally to nanonails with the increase of oxygen flow rate. The competition between the axial growth and the radial growth results in the morphology evolution. Finally, a two-stage vapor−solid (VS) gr...

Detailed Study on Photoluminescence Property and Growth Mechanism of ZnO Nanowire Arrays Grown by Thermal Evaporation

The photoluminescence (PL) property and growth mechanism of ZnO nanowires, which are essential to both fundamental and applied studies, are not yet well understood. Here extensive investigations have been carried out to deeply understand the two issues. At first, ZnO nanowire arrays are fabricated on bare glass substrate via a noncatalytic thermal evaporation method. Afterward, the PL measurements reveal that the emission peaks located at 405 and 616 nm are related to the Zn vacancy defect, and the red peak located in the region between 750 and 800 nm has relations with the interaction between the Zn vacancy and Zn interstitial defects. Detailed experiments show that the oxygen flux plays a very important role in the morphology evolution of the as-grown products, which change from nanoflakes to nanowires and finally to nanonails with the increase of oxygen flow rate. The competition between the axial growth and the radial growth results in the morphology evolution. Finally, a two-stage vapor−solid (VS) growth model is proposed to interpret the growth behavior of the ZnO nanowires. Our results have made a positive progress toward the PL property and growth mechanism of ZnO nanowires.

High-Yield Synthesis and Properties of Symmetrical Comb-Like ZnO Nanostructures on Aluminum Foil Substrate

Highly-symmetrical well-crystallized comb-like ZnO nanostructures were grown in a very large-quantity on the aluminum foil via non-catalytic thermal evaporation method by using metallic zinc powder in the presence of oxygen at low temperature of 440 degrees C. Detailed morphological investigations revealed that the as-grown combs are made with a ribbon-like stem and aligned nanorod/nanowire arrays attached uniformly and nicely along one side of the ribbon-like stem. The X-ray diffraction (XRD) pattern and high-resolution transmission electron microscopy (HRTEM) revealed that the as-grown nanocombs are crystalline and possessing a wurtzite hexagonal phase. The optical properties were observed by room-temperature photoluminescence (PL) and Raman-scattering which exhibited good optical properties for the as-grown products. A plausible growth mechanism has also been proposed for the formation of highly symmetrical comb-like ZnO nanostructures.

Structural and optical properties of ZnO whiskers grown on ZnO-coated silicon substrates by non-catalytic thermal evaporation process

Well-crystallized with excellent optical properties, tetrapod-like and multipod-like ZnO whiskers were successfully synthesized by two steps: pulsed laser deposition (PLD) and catalyst-free thermal evaporation method. Firstly, the ZnO films were pre-deposited on Si(1 1 1) substrates by PLD. The ZnO whiskers grew on ZnO-coated Si(1 1 1) substrates by the simple thermal evaporation of the metallic zinc powder at 800 °C in the air without any catalysts or additives. The pre-deposited ZnO films by PLD on the substrates can provide growing sites for the ZnO whiskers. Also it can further advance the growth of the ZnO whiskers accordingly. The as-synthesized ZnO whiskers were characterized by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and Fourier transform infrared spectrum. The results showed that the legs of the ZnO whiskers were highly crystalline with the wurtzite hexagonal structure phase, grown along the [0 0 0 1] in the c-axis direction. Room-temperature photoluminescence spectrum of the as-synthesized whiskers showed UV (390 nm) and green (517 nm) emission, respectively. In addition, the possible growth mechanism of ZnO whiskers is also discussed based on the experimental results.

Synthesis, characterization and optical properties of flower-like ZnO nanorods by non-catalytic thermal evaporation

Abstract Well-crystallized with excellent optical properties, flower-like zinc oxide (ZnO) nanorods have been successfully synthesized on Si(1 1 1) substrates using a pulsed laser deposition (PLD) prepared Zn film as “self-catalyst” by the simple thermal evaporation oxidation of the metallic zinc powder at 800 °C without any other catalysts or additives. The pre-deposited Zn films by PLD on the substrates can promote the formation of the ZnO nuclei effectively. Also it can further advance the growth of flower-like ZnO nanorods accordingly. A number of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectrum (FTIR) and photoluminescence (PL) were used to characterize the structural and optical properties of the obtained ZnO nanorods. The results indicate that the nanorods are highly crystalline with the wurtzite hexagonal phase, grown along the [0 0 0 1] in the c -axis direction. The PL spectrum showed that the as-synthesized ZnO nanorods showed UV (383 nm) and green (512 nm) emission, respectively. In addition, the growth mechanism of the ZnO nanorods are discussed based on the reaction conditions.

Single ZnO Nanowire Based High-Performance Field Effect Transistors (FETs)

The electrical properties of single ZnO nanowire were examined by fabricating single nanowire based field effect transistors (FETs) via two approaches, i.e., back- and top-gate approaches by using electron beam lithography (EBL) and photolithography processes. The ZnO nanowires were synthesized by non-catalytic simple thermal evaporation process by using metallic zinc powder in the presence of oxygen. The as-grown ZnO nanowires were characterized in terms of their structural and optical properties which confirmed that the grown nanowires are well-crystallized with the wurtzite hexagonal phase and exhibiting good optical properties. The peak transconductances of the back- and top-gate FETs were approximately 3.2 and approximately 7.4 nS, respectively. The field effect mobilities (micro(eff)) for the back- and top-gate FETs were measured to be 3.4 and 7.87 cm2/V x s, respectively. Our studies conclude that the fabricated top-gate FETs exhibited higher and good electrical properties as compared to ZnO nanowire FETs fabricated using back-gate approaches.

Single ZnO Nanobelt Based Field Effect Transistors (FETs)

Electrical properties of single ZnO nanobelt have been examined by fabricating single nanobelt based field effect transistors (FETs). The ZnO nanobelts were grown via non-catalytic simple thermal evaporation process by using metallic zinc powder in the presence of oxygen. The detailed structural and optical characterizations confirmed that the grown nanobelts are well-crystalline with the wurtzite hexagonal phase and exhibiting good optical properties. The passivation effect on the electrical characteristics of the as-grown nanobelts was also evaluated by passivating the fabricated FETs with polymethyl methacrylate (PMMA). The passivated single ZnO nanobelt based FETs exhibited higher electrical performance as compared to non-passivated FETs due to reduction in the physically absorbed chemisorbed species such as O-, O2-, O2, or OH- etc. The field effect mobility (micro(eff)) of the fabricated nanobelt based non-passivated and passivated FETs was estimated to be approximately 21.3 and 59 cm2/V x s, respectively. Moreover the carrier concentration and peak transconductance of the fabricated non-passivated and passivated FET were calculated to be approximately 8.73 x 10(17) and approximately 1.86 x 10(18) cm(-3) and approximately 0.76 and 1.4 microS, respectively. This work offers substantial opportunities for further practical electronics and photonics nanodevice applications of ZnO based nanostructures.

Growth of Comb-like ZnO Nanostructures for Dye-sensitized Solar Cells Applications

Dye-sensitized solar cells (DSSCs) were fabricated by using well-crystallized ZnO nanocombs directly grown onto the fluorine-doped tin oxide (FTO) via noncatalytic thermal evaporation process. The thin films of as-grown ZnO nanocombs were used as photoanode materials to fabricate the DSSCs, which exhibited an overall light to electricity conversion efficiency of 0.68% with a fill factor of 34%, short-circuit current of 3.14 mA/cm2, and open-circuit voltage of 0.671 V. To the best of our knowledge, this is first report in which thin film of ZnO nanocombs was used as photoanode materials to fabricate the DSSCs.

High Aspect-Ratio ZnO Nanowires Based Nanoscale Field Effect Transistors

High aspect-ratio ZnO nanowires were grown onto the copper foil, in a large-quantity, by non-catalytic thermal evaporation method. The detailed morphological observations revealed that the diameters and lengths of as-grown nanowires are in the range of 60-100 nm and 10-30 microm, respectively exhibiting a very high-aspect ratio. Detailed structural characterizations confirmed that the as-grown nanowires are well crystalline and possess a wurtzite hexagonal phase, grown along the c-axis direction in preference. The presence of a sharp and strong UV emission at 381 nm in the room temperature photoluminescence (PL) spectrum affirmed that the obtained nanowires have good optical properties. The electrical transport properties of the as-grown nanowires was explored by fabricating the field effect transistors (FETs) using a single ZnO nanowire. From the fabricated single ZnO nanowire based FET, the electron carrier density and field effect mobility were estimated to be approximately 6.7 x 10(13) cm(-3) and approximately 3.8 cm2/Vs, respectively.

Structural, optical and field emission properties of ZnO nanowires grown by non-catalytic thermal evaporation process

Well-crystallised vertically aligned ZnO nanowires have been synthesised on silicon substrate via simple thermal evaporation process without the use of metal catalysis or additives at 750°C by using metallic zinc powder and oxygen gas as source materials for zinc and oxygen, respectively. The X-ray diffraction (XRD) pattern of the grown nanowires reveals that the grown structures are well-crystalline and possessing a wurtzite hexagonal phase. The room-temperature PL spectrum exhibited a sharp and strong UV emission with a broad green emission confirming good optical properties for the as-grown ZnO nanowires. The field emission characterisation exhibited that a turn-on field for the vertically aligned ZnO nanowires was 3.7 V/μm and the emission current density reached to 0.014 mA/cm² at an applied electrical field of ∼5.5 V/μm and shows no saturation. Moreover, the ZnO nanowire based field emission device exhibited a uniform light emission.

Comparison Between the Electrical Properties of ZnO Nanowires Based Field Effect Transistors Fabricated by Back- and Top-Gate Approaches

Large-quality, well-crystallized growth of ZnO nanowires was done via non-catalytic thermal evaporation process on silicon substrate only by using metallic zinc powder and oxygen as source materials for zinc and oxygen, respectively. The electrical properties of the as-grown ZnO nanowires were examined by fabricating a single nanowire based FETs which were fabricated via two approaches, i.e., back- and top-gate approaches by using electron beam lithography (EBL) and photolithography processes. ZnO FETs electrical properties were characterized by I(DS)-V(DS) and I(DS)-V(GS) measurement. The fabricated single ZnO nanowire based FETs by back- and top-gate approaches exhibited field effect mobilities of approximately 4.25 and approximately 12.76 cm2/Vs, respectively. Moreover, the carrier concentrations for the fabricated back- and top-gate FETs were approximately 1.6 x 10(17) and approximately 1.37 x 10(18) cm(-3), respectively. From our studies it was observed that the fabricated top-gate FETs exhibited higher and good electrical properties as compared to ZnO nanowire FETs fabricated using back-gate approaches.

Growth Mechanism and Optical Properties of Aligned Hexagonal ZnO Nanoprisms Synthesized by Noncatalytic Thermal Evaporation

Vertically aligned perfectly hexagonal-shaped ZnO nanoprisms have been grown on a Si(100) substrate via a noncatalytic thermal evaporation process by using metallic zinc powder in the presence of oxygen gas. The as-grown nanoprisms consist of ultra smooth Zn-terminated (0001) facets bounded with the {0110} surfaces. The as-synthesized products are single-crystalline with the wurtzite hexagonal phase and grown along the [0001] direction, as confirmed from the detailed structural investigations. The presence of a sharp and strong nonpolar optical phonon high-E2 mode at 437 cm(-1) in the Raman scattering spectrum further confirms good crystallinity and wurtzite hexagonal phase for the as-grown products. The as-grown nanoprisms exhibit a strong near-band-edge emission with a very weak deep-level emission in the room-temperature and low-temperature photoluminescence measurements, confirming good optical properties for the deposited products. Moreover, systematic time-dependent experiments were also performed to determine the growth process of the grown vertically aligned nanoprisms.