2.7 Surface acoustic wave

2.4 Vapor-phase route (pulsed laser deposition)

2.5 RF sputtering

Gas Sensors

well [60].

method [62].

boat [63].

10 min [64].

66

for 15 min at 350°C [61].

2.6 Carbothermal reduction

wafer sputtered with a 30<sup>o</sup>

target (Zn target with 99.9% purity) to produce fluence (1.3 J/cm<sup>2</sup>

layer nearly 40 mm thick, when exposed with 2000 laser pulses [59].

ZnO nanorods were grown onto the long-period gratings (LPGs), followed by a two-step process. They contain pulsed laser deposition (Zn layer onto optical fiber), followed by the growth of ZnO nanostructures in aqueous solution. Zinc precursor layer was deposited by a laser beam (248 nm KrF excimer) that was focused on

material was deposited on the optical fibers located at 6 cm apart from the target. According to identical conditions, the deposition on substrate has resulted in Zn

A seeding of ZnO was sputtered (5 nm) on the recommended area of CMOS devices and illustrated with metal shadow mask. The as-prepared substrate was dipped in 25 mM equimolar solution of zinc nitrate hexahydrate (Zn(NO3)26H2O) and hexamethylenetetramine and was maintained for 2 h at 90°C. The device was removed from the nutrient solution after ZnO NWs' growth washed with deionized water and dried. This process is suitable for simultaneously growing ZnO NWs on microhotplate and provides an economic process for thin film level growth as

By RF sputtering process, deposit a layer of 50 nm on the glass substrate. Wash the substrate with standard process and keep the substrate in its holder. The NRs of ZnO:Ti were grown onto the ZnO sputtered by reactive evaporation with hot-wire resistance in a furnace. After the growth of ZnO:Ti NRs, the Pt electrodes were deposited by photolithography and liftoff technique on the substrate. For better ohmic contact, anneal the samples in an Ar ambient atmosphere

Prepare nanostructured thin film with pure ZnO (25 at. wt%) and MoO3 for gas

In a particular growth mechanism, 0.3 g zinc powder and 0.6 g effective carbon were adequately mixed in an agate mortar. The mixture was transferred into an alumina boat and kept in a horizontal muffle furnace at 900°C with 25°C/min for 2 h under normal pressure. Finally, the yellowish product formed and massed in the

Carbothermal reduction technique can be used to synthesize ZnO NWs from graphite and ZnO powder in horizontal muffle furnace. At the downstream, the Si

quartz tube at approximately 10<sup>2</sup> Torr, and Ar gas was introduced at 100 sccm. The temperature was increased to 900°C, and O2 gas was introduced with 2 sccm for 30 min. After the growth of single crystalline ZnO NWs, an SnO2 shell layer was

deposited, and the temperature of the furnace cooled from 900 to 700°C. Tetramethyltin ((CH3)4Sn, 99.999%, UP Chemical Co., Ltd.) was kept in the quartz tube at 0.5 sccm of Ar as carrier gas and introduced with 2 sccm oxygen for

A Au coating. A rotary pump was used to evacuate the

sputtering and annealing process. The sensor chips containing Au-IDE and thin film Pt-heater structures were comprehended by means of DC magnetron sputtering, plasma etching, and UV-lithography. Gold wires (diameter of 50 μm) were made to contact for sensor testing body that mounted on TO-8 header by microwelding

response. Deposit it on the surface of as-prepared alumina sensor chips by

). The evaporated

The ZnO nanorod sensor was designed on Y-cut LiNbO3 substrate for ethanol sensing. The performance of SAW is excellent due to electromechanical coupling coefficient (k2 = 4.5%) offered by LiNbO3 and small attenuation at high temperature. The interdigital transducers (IDTs) have a gap of 12 mm delay line, and each contains 50 pairs of electrodes. The width and the spacing inside the adjacent IDT electrodes are adjusted 15 μm. The IDT electrodes have length of 3 mm. The propagation of SAW elongated in x-direction of the crystal as IDTs is oriented on the surface of wafer.

Deposit a photoresistive layer by spin coated process and decorate it with window covering delay line for the construction of sensor. ZnO layer (100 nm) was sputtered with ZnO ceramic target by DC sputtering (conditions for sputtering, pressure = 2.7 Pa, in the presence of 80% argon and 20% oxygen) and the current required was 0.25 A DC. Acetone removed the photoresist layer leaving behind seed layer of ZnO. The devices were suspended with ZnO seed layer inverted in the solution of zinc nitrate, hexamethylenetriamine, and polyethylenimine. The bottle was incubated for 4 h at 95°C. The substrates were taken off from the solution, washed, and dried at room temperature [65].
