Sn Targets Research Articles

Influence of in-situ hydrogenation on photoelectrical properties of amorphous and nanocrystalline GeSn deposited by magnetron sputtering

This study investigates the fabrication of short-wavelength infrared (SWIR) photosensitive amorphous and nanocrystalline Ge1-xSnx:H thin films by magnetron sputtering from separate Ge and Sn targets using different Ar:H mixing ratios as working gas. Amorphous Ge1-xSnx:H films have been obtained on both c-Si and fused quartz substrates at ambient temperature, while dynamic nanocrystallization occurs in-situ when the substrate temperature during deposition is raised to 200 °C. Fourier-transform infrared spectroscopy has shown the hydrogen incorporation by detecting an absorption line at 1873 cm-1, close to the value corresponding to Ge-H bonding, only in the room temperature amorphous films. Based on that, we infer that the hydrogen concentration is very low in the films deposited at high temperature. The higher concentration of hydrogen in the amorphous samples is associated with an increase of the absorption gap to 0.5eV compared to 0.3eV in the 200oC samples. In-situ (during deposition) and ex-situ (by subsequent rapid thermal annealing) nanocrystallization have been analyzed by high-resolution transmission electron microscopy, X-ray diffraction and micro-Raman spectroscopy. SWIR spectral photosensitivity up to 2.4µm was found to be more than two orders of magnitude improved in hydrogenated amorphous films with high hydrogen content, compared to the nanocrystalline ones that are weakly hydrogenated. These findings demonstrate the potential of hydrogenation to enhance the photoelectric properties of GeSn sputtering films for optoelectronic SWIR infrared applications.

Efficient extreme ultraviolet emission by multiple laser pulses

We demonstrated an efficient extreme ultraviolet (EUV) source at a wavelength of 13.5 nm using spatially separated multiple solid-state-laser pulse irradiation. The maximum conversion efficiency (CE) achieved was 3.8% for ±30° oblique laser pulse injection, which was about twice as high as that for single laser pulse irradiation of 1.7%, with an EUV source size of about 100 μm for two spatially separated laser pulses with a total laser energy of 500 mJ at a laser intensity of 2×1011 W/cm2. In addition, we achieved an EUV CE of 4.7% for ±60° oblique laser pulse injection, which was one of the highest values ever reported, in the case of a 1-μm solid-state laser-produced planar Sn target plasma by multiple laser pulse irradiation. This result suggests that multiple laser-pulse irradiation at high repetition rate operation could credibly provide the next technology for future high-power EUV sources and exposure tools toward future EUV technology nodes.

Deposition of Fe2O3:Sn semiconducting thin films by reactive pulsed HiPIMS + ECWR co-sputtering from Fe and Sn targets

Semiconducting Fe2O3 thin films were deposited on SnO2:F (FTO) and Pt substrates by reactive high-power impulse magnetron sputtering combined with electron cyclotron wave resonance plasma (HiPIMS + ECWR). Fe2O3 films were fabricated either by sputtering from a single Fe target or by co-sputtering from an additional Sn target. Plasma parameters during co-sputtering were measured by an RF probe system enabling the comparison between HiPIMS + ECWR and only HiPIMS conditions used for the film deposition. As deposited Fe2O3 films were post-annealed in air at 450 °C and 650 °C, respectively. It was shown that as deposited Fe2O3 films were amorphous but became crystalline after post-annealing at 450 °C. Further increase of annealing temperature to 650 °C did not improve significantly the crystalline structure of the Fe2O3 film. All post-annealed Fe2O3 films exhibited photocurrents in the anodic region; generally, hematite films annealed at 650 °C exhibited higher photocurrents than those annealed at 450 °C. Films doped by Sn co-sputtering had higher photocurrents than films only doped by Sn diffusion during post-annealing from the FTO substrate. Hematite films on Pt substrate doped by Sn co-sputtering and post-annealed at 650 °C exhibited the highest photocurrents. It was verified by XPS analysis with ion sputtering depth profiling that Pt atoms also diffuse from the Pt substrate into the Fe2O3 film during the post-annealing at 650 °C and can, similar to Sn in the case of an FTO substrate, act as a dopant.

Mid-infrared emission of germanium-tin films produced by sputtering

In this work, the synthesis of germanium-tin (GeSn) films by magnetron sputtering is reported. A fractional factorial experiment was conducted; the varied factors were temperature, power applied to Ge target by a radio-frequency source, and power applied to the Sn target by a direct-current source. Vibrational modes, film composition, morphology, deposition rate, dark conductivity, Raman spectra, and Fourier-transform infrared (FTIR) spectra of the GeSn films were analyzed. Mid-infrared spectrum of emission and absorption was obtained by FTIR electroluminescence (EL) spectroscopy in the range of 400–4000cm−1, thermal emission was monitored by a FLIR camera in the range of 8–14μm, and power emitted from the GeSn films was measured in the range of 2.7–5.3μm by means of a InAsSb photodetector; results obtained by these approaches at room temperature and low-field bias were consistent. Sample Ge0.71Sn0.29 exhibited Ge Raman crystalline fraction of 85%; from FTIR EL spectrum were observed peaks of absorption located at 1084, and 606 cm−1 that was attributed to Si−Si bonds from the c-Si substrate, as well as broadband attenuation of 2% in the range of 1500−3500cm−1, this behavior was associated to the self-heating of this sample at 90 °C. Sample Ge0.3Sn0.7 showed Raman crystalline fraction of 16 and 22% for Ge and Sn, respectively; from FTIR EL spectrum were observed peaks of emission located at 2.74 μm (0.452 eV) and 6.66 μm (0.186 eV), as well as broadband emission in the range of 600–2000 cm−1 attributed to Planck’s law at a temperature of 45 °C; these results were correlated to the proper content of Ge and Sn, fluctuating current, and polymorphic morphology of this sample.

Flux and estimated spectra from a low-intensity laser-driven X-ray source

Abstract Laser-driven X-rays as probes for high-energy-density physics spans an extremely large parameter space with laser intensities varying by 8 orders of magnitude. We have built and characterized a soft X-ray source driven by a modest intensity laser of 4 × 1013 W/cm2. Emitted X-rays were measured by diamond radiation detectors and a filtered soft X-ray camera. A material-dependence study on Al, Ti, stainless steel alloy 304, Fe, Cu and Sn targets indicated 5-μm-thick Cu foils produced the highest X-ray yield. X-ray emission in the laser direction and emission in the reverse direction depend strongly on the foil material and the thickness due to the opacity and hydrodynamic disassembly time. The time-varying X-ray signals are used to measure the material thinning rate and is found to be ∼1.5 μm/ns for the materials tested implying thermal temperature around 0.6 eV. The X-ray spectra from Cu targets peaks at ∼2 keV with no emission >4 keV and was estimated using images with eight different foil filters. One-dimensional hydrodynamic and spectral calculations using HELIOS-CR provide qualitative agreement with experimental results. Modest intensity lasers can be an excellent source for nanosecond bursts of soft X-rays.

Fabrication and characterization of thin [formula omitted]Sn films for heavy-ion nuclear reaction measurements

The fabrication of thin isotopically enriched 120,124Sn targets have been presented. The thin film targets prepared have been used in nuclear physics experiments to apprehend the heavy-ion fusion and multi-nucleon transfer reaction dynamics around the Coulomb barrier. Vacuum evaporation viz. resistive heating technique has been used for the fabrication of the targets with varying areal densities in the range of 50–250 μg/cm2 backed with a carbon layer of ≈20μg/cm2 using a nominal amount of 30 mg isotopically enriched material. The fabricated targets have been characterized using multiple advanced techniques viz. Energy Dispersive X-ray Spectroscopy (EDS), Scanning Electron Microscopy (SEM), and X-ray Diffractometry (XRD). The thickness of the targets has been measured using Rutherford Back-scattering Spectrometry (RBS). The isotopic contamination levels have been ascertained with an in-beam experiment using Heavy Ion Reaction Analyzer at IUAC, New Delhi.

Enhancement of Sn plasma EUV emission by double-sided laser illumination

Advancements in state-of-the-art nanolithography technology over the past decade have been raising an ongoing demand for improvement of the power and efficiency of extreme-ultraviolet (EUV) light sources that stand at its heart. This study introduces a double-sided laser illumination scheme aimed at enhancing EUV emission from such a laser-produced Sn plasma source. Using a solid-state laser, experiments were conducted with suspended solid Sn targets of varying thicknesses, evaluating the resulting effect on EUV output intensity. A significant increase in EUV emission to the collection side was observed due to the addition of illumination of the other side, particularly for thinner targets. For targets with thicknesses of 60 and 20 nm, an increase between 50% and 150% in EUV emission was detected in comparison with single-sided illumination. Extrapolating to a long laser pulse that burns through the target, the enhancement is projected to be 17% for a 300 nm thick target. These results highlight a promising way for further improvement of output power and energy efficiency in next-generation EUV light sources.

Investigation of Electrochromic, Combinatorial TiO2-SnO2 Mixed Layers by Spectroscopic Ellipsometry Using Different Optical Models.

We determined the optimal composition of reactive magnetron-sputtered mixed layers of Titanium oxide and Tin oxide (TiO2-SnO2) for electrochromic purposes. We determined and mapped the composition and optical parameters using Spectroscopic Ellipsometry (SE). Ti and Sn targets were put separately from each other, and the Si-wafers on a glass substrate (30 cm × 30 cm) were moved under the two separated targets (Ti and Sn) in a reactive Argon-Oxygen (Ar-O2) gas mixture. Different optical models, such as the Bruggeman Effective Medium Approximation (BEMA) or the 2-Tauc-Lorentz multiple oscillator model (2T-L), were used to obtain the thickness and composition maps of the sample. Scanning Electron Microscopy (SEM) with Energy-Dispersive X-ray Spectroscopy (EDS) has been used to check the SE results. The performance of diverse optical models has been compared. We show that in the case of molecular-level mixed layers, 2T-L is better than EMA. The electrochromic effectiveness (the change of light absorption for the same electric charge) of mixed metal oxides (TiO2-SnO2) that are deposited by reactive sputtering has been mapped too.

Radiation of extreme ultraviolet source and out-of-band from laser-irradiated low-density SnO<sub>2</sub> target

The extreme ultraviolet (EUV) lithography technology required for high-end chip manufacturing is the first of 35 “bottleneck” key technologies that China is facing currently. The high conversion efficiency EUV source and low out-of-band radiation play a significant role in the application of the EUV lithography system. In this work, the EUV source and out-of-band radiation are studied by using laser irradiated solid Sn target and low-density SnO<sub>2</sub> target. The result shows that a strong EUV radiation at a wavelength of 13.5 nm is generated when the laser irradiates the two forms of Sn targets. Owing to the self-absorption effect of the solid Sn target plasma, the maximum intensity of the wavelength is not located at the position of 13.5 nm, which is working wavelength of EUV lithography system. However, the peak radiation spectrum is located at the position of 13.5 nm with low-density SnO<sub>2</sub> target due to its weaker plasma self-absorption effect. In addition, the satellite lines are weaker in low-density SnO<sub>2</sub> target than in the solid Sn target, so that the spectrum efficiency of the EUV at 13.5 nm (2% bandwidth) is increased by about 20%. On the other hand, the experimental study of the out-of-band radiation is carried out. The out-of-band radiation spectral results show that the out-of-band radiation is mainly dominated by the continuum spectrum. Compared with the solid Sn target, the low-density SnO<sub>2</sub> target contains a part of the low <i>Z</i> element O (<i>Z</i> = 8), resulting in a low-intensity continuum spectrum. In addition, the collision probability of ion-ion and electron-ion both become low when the laser irradiates the low-density SnO<sub>2</sub> target, resulting in a short out-of-band radiation duration time. Therefore, the out-of-band radiation generated by the laser irradiated on the low-density SnO<sub>2</sub> target is weak based on the above reasons. The angular distribution of out-of-band radiation measurement results shows that the intensity of out-of-band radiation decreases with the angle increasing. A cosine function <inline-formula><tex-math id="M2">\begin{document}$A \cos ^\alpha \theta$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222385_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222385_M2.png"/></alternatives></inline-formula> can fit the angular distribution of the total radiation.

Enhancing the p-type conductivity of pure phase SnO via stoichiometry control and annealing

While n-type transparent conducting oxides (TCOs) have been well developed and widely used in optoelectronic devices, the availability of high-performance p-type TCOs is still scarce which in turn hinders the further advancement of oxide based transparent optoelectronic devices. Unlike the most widely used p-type NiO, Tin monoxide (SnO) has a relatively delocalized valence band, which leads to a high hole mobility of >1 cm2/Vs. In this work, we enhance the p-type conductivity of SnO thin films by tunning the oxide stoichiometry through adjusting the growth conditions and post-growth rapid thermal annealing (RTA) treatment. Specifically, we synthesized nominally undoped Sn-rich SnO (SnO1-δ) thin films by co-sputtering an SnO target and a metallic Sn target and control the film stoichiometry by varying the sputter power of the Sn target so that SnO1-δ films with excess Sn (δ) varying from 0 to ∼5% was incorporated. We find that the addition of dilute amount of excess Sn is an effective approach to regulate the film stoichiometry so that a low p-type resistivity can be achieved after post-growth RTA. All as-grown films are amorphous and after RTA exhibit a polycrystalline tetragonal structure, with p-type resistivity decreases with increasing δ. However, metallic β-Sn clusters are formed for films with δ≳ 0.05. The presence of these β-Sn clusters results in a degraded optical transmittance by ∼10% in the visible range. With δ∼0.03 in the as-grown film, a p-type pure phase SnO film with a low resistivity of ∼0.5 Ω−cm, and a decent visible transparency of ∼60% is achieved after 300 °C RTA in N2. This p-type SnO has a wide band gap of 2.8 eV with a high valence band maximum (VBM) located in the range of 4.6–4.8 eV below the vacuum level, making it suitable for many device applications, particularly as hole transport layers in optoelectronic devices.

Direct synthesis of hollow carbon nanoonion-like particles (HCNOs) decorated uniformly with Sn nanoparticles by long-pulse-width millisecond laser ablation of Sn target in n-hexane solution

The nanocomposites that composed of hollow carbon nanoonion-like particles (HCNOs) decorated with Sn quantum dots (QDs) (Sn QDs/HCNOs nanocomposites) were directly prepared by long-pulse-width millisecond laser ablation of pure Sn metal target immersed in n-hexane solution under room conditions. Low-resolution and High-resolution transmission electronic microscope (TEM) images not only reveal that the as-obtained products are composed of two homogeneously mixed phases, Sn QDs and HCNOs, but also the tight bonding of Sn QDs with the HCNOs. Moreover, Sn QDs/HCNOs composites have uniform morphology and narrow size distribution. The HCNOs present continuous imperfect onion-like structure with hollow cores and have a diameter in the range of 80–100 nm. The Sn QDs with a diameter in the range of 3–5 nm are distributed uniformly on the HCNOs. This work indicates that the pulsed laser ablation in liquid could be applied to the direct synthesis of HCNOs from the decomposition of liquid media via ‘bottom-up’ approach and in situ decoration of them due to the formation of pure metal Sn QDs via ‘top-down’ strategy.

Cosputtered SnO2–ZnO composite nanofilms with improved dual function

AbstractSnO2–ZnO composite thin films were grown by radio‐frequency and direct‐current cosputtering of ceramic ZnO and metallic Sn targets, respectively. During the cosputtering film growth, the SnO2 matrix sputtering power was fixed at 20 W, while the additive ZnO sputtering power was varied in the range of 40–80 W. Structural and compositional analysis results showed that the ZnO sputtering power increased the relative ZnO phase content in the composite film and its surface grain size. Compared to the single‐constituent compounds, the as‐synthesized SnO2–ZnO composite films exhibited enhanced photoelectrocatalytic performances for the degradation of methyl orange dyes under irradiation. The SnO2–ZnO composite film obtained at a ZnO sputtering power of 60 W (SZ60; Zn/Sn = 11.2%) exhibited the highest photoelectrocatalytic activity among the various samples. In addition, SZ60 exhibited superior ethanol gas‐sensing performances among the various thin‐film sensors. Owing to the formation of a suitable number of SnO2/ZnO heterojunctions, SZ60 exhibited a highly efficient photo‐induced charge separation and appropriate potential barrier height to improve the gas‐sensing ability. The experimental results demonstrate a promising approach to design oxide composite films with desirable photoelectrocatalytic and gas‐sensing functions by controlling the relative content of ZnO and SnO2 in the composite film through a cosputtering process.

Preparation of isotopically enriched 112,116,120,124Sn targets at VECC

Resistive heating and mechanical rolling methods have been employed to prepare isotopically enriched thin target foils of 116Sn (∼380 μg/cm2), 124Sn (∼400 μg/cm2) and thicker foils of 112Sn (∼1.7 mg/cm2), 120Sn (∼1.6 mg/cm2), respectively. Preparation of enriched targets with a small amount of material, selection of releasing agent for thin targets and separation of deposited material in solvent were among the several challenges during fabrication of the thin targets. The uniformity of the targets has been measured using 241Am α-source. NaCl has been used as releasing agent in preparation of the thin targets. These targets have been successfully used in nuclear physics experiments at VECC.

Simultaneous Seebeck coefficient and electrical conductivity enhancement of GeSbTe films via Sn addition

Sn-added GeSbTe (GST) thin films were deposited using a co-magnetron sputtering technique. The effects of varying the Sn content through a variable Sn target sputtering power and post annealing at 673 K were investigated. The DC power density applied to the GST target was controlled at 50 W, while the power density of the Sn target was increased from 0 W to 40 W. The results demonstrate the coexistence of the fcc-GST, hcp-GST and SnTe phases in the Sn-added GST thin films. The substitution of Sn at the Ge-site increases the crystallization speed and leads to defects and lattice disordered local arrangement in the GST films, causing the Seebeck coefficient to increase. The SnTe phase was created as a result of the high Sn content in the sample due to the over-doping limit of Sn into the GST structure. The presence of SnTe in Sn-doped GST films increased the electrical conductivity. The maximum power factor of 17.0 μW/cmK2 at 450 K was obtained at an Sn content of 14.7 at%. These results indicated that the thermoelectric properties of Sn-doped GST films were improved via the formation of an appropriate amount of SnTe composite.

Mobility Enhancement in P-Type SnO Thin-Film Transistors via Ni Incorporation by Co-Sputtering

Oxide semiconductors have been considered one of the most promising candidates for flexible electronics applications owing to their low process temperatures and good reliability. However, the low mobility of p-type oxide semiconductors limits the performance of flexible oxide-TFT-based CMOS technology. In this study, p-type SnO_<i>x</i>:Ni thin films were deposited by reactive rf magnetron co-sputtering, a technique compatible with the current industrial semiconductor manufacturing technology, from Sn and Ni targets. As the Ni-gun power increased, the distribution of Ni in the SnO_<i>x</i>:Ni thin film changed from a more uniform dispersion to nanoclusters, resulting in the crystalline phase transition of SnO_<i>x</i>:Ni from <inline-formula> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula>-SnO (110)-dominant polycrystalline to amorphous and then to <inline-formula> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula>-SnO (101)-dominant polycrystalline. A high-mobility inverted-staggered p-type SnO_<i>x</i>:Ni TFT was then fabricated on a glass substrate with a maximum process temperature of 225&#x00B0;C, which is compatible with flexible polymeric substrates. The TFT fabricated at an optimal Ni-gun power of 42 W exhibited an impressive field-effect mobility of 11 cm²V^&#x2212;1s^&#x2212;1 and on current of <inline-formula> <tex-math notation="LaTeX">$35.2 ~\mu \text{A}$ </tex-math></inline-formula> per channel width-to-length ratio; these values are comparable to those of a typical n-type oxide TFT. These results should contribute toward flexible oxide-TFT-based CMOS technology.

Enhancing the conversion efficiency of extreme ultraviolet light sources using a 2 µm wavelength laser

In this study, we use the FLASH radiation hydrodynamic code and the FLYCHK atomic code to investigate the energy conversion and spectra associated with laser–Sn target interactions with 1 and 2 µm wavelength lasers. We found that the conversion efficiency (CE) reached as much as 3.38% with the 2 µm laser, which is 1.48 percentage points higher than the 1 µm laser (CE = 1.9%). In addition, we analyzed the contribution of dominant ionization states to the emission spectrum for both lasers. We observed that the growths of the out-of-band emission eventually led to a broadening of the spectrum, resulting in a reduction of spectral purity for the 1 µm laser. By contrast, the emission main peaks were all centered near 13.5 nm for the 2 µm laser, which is beneficial for efficient emission of light with a 13.5 nm wavelength (relevant for nanolithographic applications).

A Third Generation Potentially Bifunctional Trithiol Chelate, Its nat,1XXSb(III) Complex, and Selective Chelation of Radioantimony (119Sb) from Its Sn Target.

The therapeutic potential of the Meitner-Auger- and conversion-electron emitting radionuclide 119Sb remains unexplored because of the difficulty of incorporating it into biologically targeted compounds. To address this challenge, we report the development of 119Sb production from electroplated tin cyclotron targets and its complexation by a novel trithiol chelate. The chelation reaction occurs in harsh solvent conditions even in the presence of large quantities of tin, which are necessary for production on small, low energy (16 MeV) cyclotrons. The 119Sb-trithiol complex has high stability and can be purified by HPLC. The third generation trithiol chelate and the analogous stable natSb-trithiol compound were synthesized and characterized, including by single-crystal X-ray diffraction analyses.

Amorphous SiSn Alloy: Another Candidate Material for Temperature Sensing Layers in Uncooled Microbolometers

Herein, the prospect of using amorphous Si1–x Sn x alloys as alternative temperature‐sensing active materials in microbolometers is evaluated by studying their temperature‐dependent resistive properties along with their infrared optical properties. Si1–x Sn x thin films (200 nm thick), with varying Sn concentrations, are prepared at room temperature by cosputtering from Si and Sn targets using simultaneous radio frequency and DC magnetron sputter deposition. Low beam energy X‐ray microanalysis is used to estimate the atomic concentrations of the prepared films. Atomic force microscopy analysis shows an increase in the root‐mean‐square surface roughness of the prepared Si1–x Sn x thin films, with increasing Sn content. Sheet resistance versus temperature measurements are performed yielding temperature coefficients of resistance of 3.25, 2.65, and 1.72% K−1 at resistivity values of 116.18, 27.36, and 2.34 Ω cm for Sn concentrations of 35%, 44%, and 48%, respectively. Infrared ellipsometry measurements are performed to extract the optical properties of the Si1–x Sn x thin films and optical simulations confirm that a Fabry–Pérot cavity microbolometer configuration containing an Si1–x Sn x thin film can achieve high absorptance in the 8–12 μm band. This study shows that Si1–x Sn x alloys are a suitable, simple, and low‐cost replacement for thermometer layers used in uncooled infrared microbolometers.

Understanding the evolution of liquid and solid microjets from grooved Sn and Cu samples using radiography

Experiments were performed on grooved Sn and Cu samples to study the temporal evolution of microjets. Jets were generated by the impact of gun-launched flyer plates against the back of grooved targets made from either Cu or Sn (groove depth of ∼250 μm). The Hugoniot states in the various Sn targets encompassed conditions where solid phases are maintained throughout (7 and 16 GPa) and also conditions where melting occurs upon the release of compression (25 and 34 GPa); the transition occurs near a Hugoniot pressure of 23 GPa. Cu targets at 27 and 56 GPa provide comparisons in which the jets move at similar speeds but remain solid. In all cases, the spatial distribution of mass within the microjets was measured using high-speed synchrotron radiography. The result is a time history of the jet thickness profile from which quantities like total jet mass and jet velocity can be derived. In both the solid and liquid states, we generally observe that an increase in the shock strength leads to an increase in jet mass. However, this trend breaks down for Hugoniot states near the transition from continuously solid to melted-on-release. This is evidenced by the observation that there was no difference in the rate of mass flow in Sn jets at 16 and 25 GPa, while similar pressure jumps on either side of this range caused substantial changes in the jet mass. This contrasts with the behavior of smaller polishing defects that were present on the same samples (∼1 μm deep). From these, no ejecta mass was detected below the melt boundary, but obvious microjets were generated once melting occurred. This indicates that crossing the bulk melt-on-release threshold can alternately promote or inhibit the flow of mass into microjets based on the amplitude of the initial perturbation.

Metal Oxide Nanoheterostructures for Gas Sensing

1. Introduction.Metal oxides such as SnO2, MoO3. TiO2, CuO, are well-known to exhibit significant changes in their electrical resistance upon admission of certain oxidizing or reducing chemical species which constitutes the base for their application as gas sensors. These materials can be synthesized in different forms ranging from bulk ceramics to thin films. Thin-film technology has contributed significantly to the development of reliable chemical sensors as it is easily controllable and results in reproducible parameters of deposited layers [1,2]. Moreover, it is compatible with interdigitated transducer IDT electrodes which facilitates film deposition and subsequent electrical contacts with the resistance measuring units [3]. Emerging nanotechnology has led to a revolution in sensing especially as far as different forms of nanomaterials have demonstrated better response, sensitivity and selectivity to different stimuli. Moreover, the nanostructured sensors can operate much faster due to better kinetics of responses at relatively low temperatures, i.e., close to room temperature. The aim of this contribution is to review the most recent work performed in the field of thin film resistive-type gas sensors with a special emphasis on the n-n and n- p nanostructures.2. ExperimentalThin films of different stoichiometry and crystal structures have been deposited by magnetron sputtering of Ti, Sn, and Cu targets in reactive Ar+O2 atmosphere with controlled composition. Characterization of films has been performed by X-ray diffraction XRD, X-ray reflectivity, XRR, X-ray photoelectron spectroscopy XPS, atomic force microscopy, AFM, scanning electron microscopy, SEM and optical spectrophotometry over uv and visible range of the light spectrum. Gas sensing measurements both in dc and ac modes have been carried out in a custom-made set-up capable of detecting changes in the electrical resistance under stabilized temperature and humidity level. Modular XM-MTS unit from Solartron Analytical has been used to detect the impedance spectra in reference atmosphere (air) and upon gas (NO2, H2) admission.3. ResultsExperimental results concerning thin film characterization will be presented and compared with the most representative data obtained by other authors. Fundamental properties of different n-type (TiO2, SnO2) and p-type (CuO) semiconductors will be discussed.Depending on the material being sputtered and the substrate on which a thin film is deposited one can observe a growth of different nanostructures. Typically, a columnar structure is obtained in the case of TiO2 while the amorphous films of SnO2 result in a smooth top SEM image composed of small, isolated grains. CuO thin films crystallize easily with relatively large, well-developed grains.Gas sensor responses are good and reproducible in the case of n-type semiconductors such as TiO2 and SnO2. CuO being a p-type semiconductor demonstrates much lower response which can be improved by forming TiO2/CuO n-p type hetero-structure.