Lupan Oleg

• PhD, doctor habilitate degree (Dr. Hab.Eng.) Professor
• Professor (Full) at Technical University of Moldova

The detection of hydrogen gas is crucial for both industrial fields, as a green energy carrier, and biomedical applications, where it is a biomarker for diagnosis. TiO2 nanomaterials are stable and sensitive to hydrogen gas, but their gas response can be negatively affected by external factors such as humidity. Therefore, a strategy is required to...

In this study, a rapid and scalable technological approach was developed to grow various types of tetrapodal ZnO (T-ZnO) based on a modified flame transport synthesis. The morphological, compositional, structural, and sensing properties of the T-ZnO particles were investigated in detail using scanning electron microscopy (SEM) and transmission elec...

Acetone detection is of significant importance in various industries, from cosmetics to pharmaceuticals, bioengineering, and paints. Sensor manufacturing involves the use of different semiconductor materials as well as different metals for doping and functionalization, allowing them to achieve advanced or unique properties in different sensor appli...

Zinc oxide (ZnO) is considered to be one of the most explored and reliable sensing materials for UV detection due to its excellent properties, like a wide band gap and high exciton energy. Our current study on a photodetector based on tetrapodal ZnO (t-ZnO) reported an extremely high UV response of ~9200 for 394 nm UV illumination at 25 °C. The t-Z...

Certain biomarkers in exhaled breath are indicators of diseases in the human body. The non-invasive detection of such biomarkers in human breath increases the demand for simple and cost-effective gas sensors to replace state-of-the-art gas chromatography (GC) machines. The use of metal oxide (MOX) gas sensors based on thin-film structures solves th...

The aim of this study was to develop and characterize CuO/Cu2O functionalized with AgPt nanostructures for gas sensing applications. Environmental pollution remains a pressing global concern, requiring effective detection methods. Metal oxide nanostructures, such as those based on copper oxides, offer promising solutions due to their sensitivity an...

The aim of this study was to develop low-powered, highly selective UV sensor to continuously monitor personalized UV exposure as well as to study annealing effect on UV detection properties of the sensors. ZnO:Al structures were obtained by chemical growth method followed by thermal annealing at 625 °C for 2 h. The studied samples exhibit maximal U...

This work studies the technological preparation conditions, morphology, structural characteristics and elemental composition, and optical and photoluminescent properties of GaSe single crystals and Eu-doped β–Ga2O3 nanoformations on ε–GaSe:Eu single crystal substrate, obtained by heat treatment at 750–900 °C, with a duration from 30 min to 12 h, in...

Sensors play a crucial role in our everyday life and will become more and more demanded with the transition towards smart cities and the “Internet of Things” with the result of an ever-increasing energy demand. Thus, the research of improving the energy efficiency of sensor systems has started to move towards edge computing and neuromorphic enginee...

Certain molecules act as biomarkers in exhaled breath or outgassing vapors of biological systems. Metal oxide gas sensors are of great interest to detect these molecules. However, often they are not selective enough to identify the specific molecules. In addition, they typically lose their excellent performance at high humidity levels. In this stud...

In this paper, the morphological and sensing properties of the Sn-doped ZnO-Zn2SnO4 nanorods obtained by the hydrothermal method are presented. The developed methodology exhibits high levels of efficiency and cost-effectiveness, making it particularly suitable for implementation in the field of nanoelectronics and biomedical applications. Scanning...

The detection of radiation in the ultraviolet C (UVC) region (100–280 nm) is of great importance for numerous technical applications, such as fire detection in security devices, tracking astronomical missile trajectories, chemical-biological analyses, and medicinal applications. Wide bandgap semiconductors have emerged as ideal materials for electr...

As the world rapidly transitions towards renewable energy sources, the use of hydrogen (H2) as a green energy carrier has become increasingly important. The various applications of hydrogen in the energy sector require sensor materials that can efficiently detect small amounts of H2 in gas mixtures. One solution is the use of a Metal-organic Framew...

Reliable detection of dangerous gases by using devices based on semiconductor materials in environments, with different influencing factors, such as gamma radiation, is a challenge for a medical facility or space program. A study of the influence of gamma radiation on the electrical and sensing properties of ZnO/Al2O3 core@shell heterostructure has...

As the necessary transition to a supply of renewable energy moves forward rapidly, hydrogen (H2) becomes increasingly important as a green chemical energy carrier. The manifold applications associated with the use of hydrogen in the energy sector require sensor materials that can efficiently detect H2 in small quantities and in gas mixtures. As a p...

GaSxSe1−x solid solutions are layered semiconductors with a band gap between 2.0 and 2.6 eV. Their single crystals are formed by planar packings of S/Se-Ga-Ga-S/Se type, with weak polarization bonds between them, which allows obtaining, by splitting, plan-parallel lamellae with atomically smooth surfaces. By heat treatment in a normal or water vapo...

Ro: În respectiva monografie se face o trecere în revistă a experienței acumulate și provocărilor cu care s-a confruntat echipa Centrului Tehnologii Spațiale UTM la elaborarea nanosatelitului TUMnanoSAT în cadrul programului KiboCube, susținut de JAXA și UNOOSA. Lucrarea are scopul de a familiariza cititorii cu abordările și soluțiile propuse la pr...

Batteries play a critical role in achieving zero-emission goals and in the transition toward a more circular economy. Ensuring battery safety is a top priority for manufacturers and consumers alike, and hence is an active topic of research. Metal-oxide nanostructures have unique properties that make them highly promising for gas sensing in battery...

Certain molecules act as biomarkers in exhaled breath or outgassing vapors of biological systems. Specifically, ammonia (NH3) can serve as a tracer for food spoilage as well as a breath marker for several diseases. H2 gas in the exhaled breath can be associated with gastric disorders. This initiates an increasing demand for small and reliable devic...

Metal oxide gas sensors are of great interest for applications ranging from lambda sensors to early hazard detection in explosive media and leakage detection due to their superior properties with regard to sensitivity and lifetime, as well as their low cost and portability. However, the influence of ambient gases on the gas response, energy consump...

In this work it was investigated the reliability to ionizing radiation of Eu-doped ZnO nanostructured films functionalized with Pd. Morphological, sensorial and electrical properties of sensors were studied initially, after irradiation and after 6 months to observe the influence of irradiation.

In this paper, we report on the gas sensing properties of mixed oxide Zn-Cu nanostructures obtained by self-organized chemical deposition are presented. The nanosensors are made from individual ZnO whiskers and are coated with CuO/Cu2O. They exhibit selectivity towards H2 and NH3 over other tested gases. Measurements were made in the temperature ra...

Dielectric materials are of great interest in a vast amount of applications ranging from cable insulation to advanced electronic devices. The emerging trend of device miniaturization is creating an increased demand for dielectric thin films that can be produced precisely on the nanometer scale. In addition, special mechanical properties are often r...

Monitoring volatile organic compounds (VOCs) in harsh environments, especially for safety applications, is a growing field that requires specialized sensor structures. In this work, we demonstrate the sensing properties toward the most common VOCs of columnar Al2O3/ZnO heterolayer-based sensors. We have also developed an approach to tune the sensor...

In this work, the gas sensing properties of the non-planar heterostructures based on CuO thin films, grown by the direct ink writing and covered with an ultrathin Al2O3 layer, are presented as a function of the operating temperature. The obtained results demonstrates the excellent selectivity to volatile organic compounds (VOCs) vapors, namely n-bu...

In this work, gas phase synthesis of NPs is applied as it offers the benefit of a high purity, surfactant free deposition that is compatible with a broad range of substrates. At the example of three fundamentally different NP assemblies it is showcased, how the unique properties of NPs make them promising building units for electronic devices with...

Initiated chemical vapor deposition (iCVD) is a solvent-free polymer thin film deposition process which can be used to produce high quality dielectric thin films with nanoscale control and circumvents thus these problems. This work demonstrates the versatility of the iCVD process in the field of electrical applications by some new application examp...

Gas sensors are demanded in many different application fields. Especially the ever-growing field of batteries creates a great need for early hazard detection by gas sensors. Metal oxides are well known for gas sensing; however, moisture continues to be a major problem for the sensors, especially for the application in battery systems. This study re...

In this work, the individual hexagonal boron nitride (h-BN) microtubular structures with different diameter (ranging from ≈0.2 to ≈2.5 μm) and a wall thickness below 25 nm were investigated for the first time by integration on SiO2/Si substrate using a method based on focused ion beam deposition (FIB/SEM). The current-voltage (I-V) measurements wer...

Semiconducting metal oxide - based gas sensors exhibit outstanding sensitivity, although humidity in the analyte typically hampers precise measurements. In this work it was shown that a 5−6 nm thin Al2O3 nano-layer is particularly beneficial in reducing the interference due to humidity of p-type conductivity copper oxide-based gas sensors. An effec...

Lithium-ion batteries (LIBs) still need continuous safety monitoring based on their intrinsic properties, as well as due to the increase in their sizes and device requirements. The main causes of fires and explosions in LIBs are heat leakage and the presence of highly inflammable components. Therefore, it is necessary to improve the safety of the b...

Heterojunctions are used in solar cells and optoelectronics applications owing to their excellent electrical and structural properties. Recently, these energy-efficient systems have also been employed as sensors to distinguish between individual gases within mixtures. Through a simple and versatile functionalization approach using noble metal nanop...

Semiconducting metal oxide - based gas sensors exhibit outstanding sensitivity, although humidity in the analyte typically hampers precise measurements. In this work it was shown that a 5-6 nm thin Al2O3 nano-layer is particularly beneficial in reducing the interference due to humidity of p-type conductivity copper oxide-based gas sensors. An effec...

The undoped and metal‐doped zinc oxide columnar films (ZnO:Sn, ZnO:Fe, ZnO:Ag, and ZnO:Cu) are covered with an ultra‐thin layer of SiO2 (10–20 nm). The electrical, UV, and volatile organic compounds (VOCs) sensing properties are evaluated under different ambient conditions for ≈7 months to investigate the impact of the top SiO2‐layer on the long‐te...

A comparative investigation of the post-electroplating treatment influence on the gas detecting performances of single ZnO nanorod/nanowire (NR/NW), as grown by electrochemical deposition (ECD) and integrated into nanosensor devices, is presented. In this work, hydrothermal treatment (HT) in H2O steam and conventional thermal annealing (CTA) in a f...

In this study, a strategy to prepare CuO/Cu2O/Cu microwires which is fully covered by a nanowire network using a simple thermal oxidation process is developed. The CuO/Cu2O/Cu-microwires are fixed on Au/Cr pads with Cu microparticles. After thermal annealing at 425 °C, these CuO/Cu2O/Cu microwires are used as room-temperature 2-propanol sensors. Th...

In this work, the β-Ga2O3 nanostructures were obtained by thermal annealing in air of β-Ga2S3 single crystals at relatively high temperatures of 970 K, 1070 K and 1170 K for 6 h. The structural, morphological, chemical and optical properties of β-Ga2O3–β-Ga2S3 layered composites grown at different temperatures were investigated by means of X-ray di...

The excellent gas sensing performance of metal oxide based nano- and microstructures, including a fast response time and good sensitivity, is typically limited by their low selectivity. Therefore, novel approaches and strategies are required to gain a precise control of the selectivity. Here, we introduce a nanoporous few-layer graphene oxide (GO)...

For a fast and reliable monitoring of hazardous environments, the discrimination and detection of volatile organic compounds (VOCs) in the low ppm range is highly demanded and requires the development...

Supporting Information 3-D printed sensors

In this work, a facile two-step fabrication and characterization of printed acetone sensors based on mixed semiconducting metal oxides is introduced. The devices are fabricated by Direct Ink Writing metal microparticle (MP) stripes of commercially available pure iron and copper particles onto the surface of a glass substrate, forming a bridging mul...

Copper oxide nanostructured films were synthesized via a chemical synthesis (SCS) method and annealed in low vacuum. The morphological properties were investigated using scanning electron microscopy (SEM). The elaborated sensor structures based on CuO/Cu2O films were tested to 100 ppm of acetone vapor. It was observed that by applying different tem...

Sensors start to play an ever increasing role in human life and new technologies for their cost-effective mass production are required. In this work, the one-step 3D-printing of nanoflakes—nanowire covered Fe2O3/Fe–CuO/Cu2O/Cu microparticles (MPs) with diameters of ~10 µm on the surface of glass substrate successfully forming an ordered net is repo...

The impact of (bulk) material and rear surface (contact) quality to the efficiency is found to be quite hard to measure on a processed solar cell. We will show with this paper that CELLO (solar cell local characterization) photo-impedance-spectroscopy measurements are capable of separating bulk from rear side effects on locally resolved maps. This...

Nano- and microscale tetrapodal shaped ZnO particles (T-ZnO) are considered to be truly multi-functional and have a tremendous potential for a large variety of applications ranging from gas/vapor sensors to biomedical implants. In this approach highly porous interconnected networks were formed from T-ZnO particles produced by the versatile flame tr...

In this work, we investigated performances of individual and multiple networked Au nanoparticles (NPs)-functionalized ZnO nanowires (NWs) integrated into nanosensor devices using dual beam focused ion beam/scanning electron microscopy (FIB/SEM) and tested them as gas sensors at room temperature. Such important parameters as diameter and relative hu...

The synthesis of new nanomaterials with a large surface-to-volume ratio is of high interest for sensing applications, and especially for gas sensors with high performances. In this work, a thin layer of CdS is deposited onto tubular graphitic/aerographite microstructures using RF magnetron sputtering for further integration into sensing devices usi...

In this research, the low temperature single-step electrochemical deposition of arrayed ZnO nanowires (NWs) decorated by Au nanoparticles (NPs) with diameters ranging between 10-100 nm is successfully demonstrated for the first time. The AuNPs and ZnO NWs were grown simultaneously in the same growth solution in consideration of the HAuCl4 concentra...

Gallium oxide (β-Ga2O3) nanowires were synthesized by heat treatment of single crystal β-GaS plates in air. Crystal structure and composition of synthesized materials were studied by X-ray diffraction, energy dispersive X-ray spectroscopy and Raman spectroscopy. Thermal treatment of β-GaS plates at 1023 K leads to the formation of a Ga2O3 (native o...

Nanomaterials for highly selective and sensitive sensors towards specific gas molecules of volatile organic compounds (VOCs) are most importantly for developing the new generation detector devices e.g. used as biomarkers for diseases, as well as for continuous air quality monitoring. Here, we present an innovative preparation approach for engineeri...

Supporting information for paper "3D-Printed Chemiresistive Sensor Array on Nanowires CuO/Cu2O/Cu Heterojunction Net". In this work, the one-step 3D-printing of 20 nm nanowire covered CuO/Cu2O/Cu microparticles (MPs) with diameters of 15-25 µm on the surface of glass substrate forming an ordered net is successfully reported for the first time. 3D-p...

can detect acetone vapor

In this work, the one-step 3D-printing of 20 nm nanowire covered CuO/Cu2O/Cu microparticles (MPs) with diameters of 15-25 µm on the surface of glass substrate forming an ordered net is successfully reported for the first time. 3D-printed Cu MPs-based stripes formed non-planar CuO/Cu2O/Cu heterojunctions after thermal annealing at 425 C for 2 h in a...

In this paper, the effect of the thickness of nano-structured TiO 2 thin films (12–40 nm) and successive deposition of different noble metal nanoparticles on the performances of propanol vapor and H 2 gas sensors was investigated. The obtained titania thin films were integrated into a device for UV, gas, and gas/vapor sensing studies at different o...

Morphology is a critical parameter for various thin film applications, influencing properties like wetting, catalytic performance and sensing efficiency. In this work, we report on the impact of oxygen partial flow on the morphology of ceramic thin films deposited by pulsed DC reactive magnetron sputtering. The influence of O2/Ar ratio was studied...

We report on memsensors, a class of two terminal devices that combines features of memristive and sensor devices. Apart from a pinched hysteresis (memristive property) and stimulus dependent electrical resistance (sensing property) further properties like dynamic adaptation to an external stimulus emerge. We propose a three component equivalent cir...

Novel gas sensors have been realized by decorating clusters of tubular Aerographite with CdTe using magnetron sputtering techniques. Subsequently, individual microtubes were separated and electrically contacted on a SiO2/Si substrate with pre-patterned electrodes. Cathodoluminescence, electron microscopy and electrical characterization prove the su...

Rapid detection and fast response of nanoelectronic devices based on semiconducting oxides is nowadays a modern and stringent subject of research. Device performances depend mainly on the morphologies of the metal oxide nanostructures. In the scope of this work, the influence of the structural morphology of three-dimensional (3-D) ZnO nano-and micr...

Rapid detection and fast response of nanoelectronic devices based on semiconducting oxides is nowadays a modern and stringent subject of research. Device performances depend mainly on the morphologies of the metal oxide nanostructures. In the scope of this work, the influence of the structural morphology of three-dimensional (3-D) ZnO nano- and mic...

A new strategy based on the functionalization and doping of semiconducting oxides was proposed for tuning their properties. A considerable increase in the gas sensing ability of Fe-doped ZnO (ZnO:Fe) films is achieved via functionalization using oxidized silver nanoparticles (AgO/Ag NPs) with a diameter of ~7 nm. AgO/Ag-decorated ZnO:Fe (Ag/ZnO:Fe)...

The massive application requests for high-performance sensors indicate on the importance of precise controlling of the semiconducting oxide characteristics. The sensor longevity needed for remote areas in harsh environments is mandatory and can benefit greatly from self-cleaning abilities. To serve this demand, we present in our work ultra-thin TiO...

Figure S1 for paper "Ultra-thin TiO2 films by atomic layer deposition and surface functionalization with Au nanodots for sensing applications"

Noble metals and their oxide nano-clusters are considered to be the most promising candidates for fabricating advanced H2 gas sensors. Through this work, we propose a novel strategy to growth and modulate the density of PdO/PdO2 nanoparticles uniformly on nanostructured Pd-doped ZnO (ZnO:Pd) films by one step solution approach followed by thermal a...

In this work, an individual zinc oxide (ZnO) nanosheet was integrated into a sensor device for detection of UV light with ultra-high photosensitivity. Three-dimensional (3-D) and two-dimensional (2-D) highly porous ZnO micro- and nanostructures networks were synthesized via a simple oxidation of Zn metal powder in a furnace. The ultra-high photosen...

Buckminster fullerene (C60) based hybrid metal oxide materials are receiving considerable attention because of their excellent fundamental and applied aspects, like semiconducting, electron transfer, luminescent behaviors, etc. and this work briefly discusses about the successful fabrication of C60 decorated ZnO tetrapod materials and their detaile...

Tin oxide nanowires (SnO2 NWs) exhibit large potential for applications in sensor and detector technology. Using a flame transport synthesis method, high-quality single crystalline SnO2 nanowires (NWs) with Zn2SnO4 dots functionalized surface were synthesized on a large scale. The individual SnO2:Zn2SnO4 nanowire based ultraviolet photodetector and...

Detection and differentiation of volatile organic compounds (VOC) is highly important since these gaseous pollutants degrade air quality and represent, even in small amounts, a threat to human health. In this work, a simple and cost-efficient method to synthesize a multilayered (CuO-Cu2O)/ZnO:Al nanostructured film forming non-planar heterojunction...

In this work, a simple method of ZnAl2O4-functionalization of ZnO microstructures is presented. The different characterization methods (structural, chemical and micro-Raman) demonstrated the presence of only ZnO and ZnAl2O4 crystalline phases. ZnAl2O4 nano-crystallites grow on the surfaces of ZnO 3D microstructures having diameters of 50-100 nm and...

The structural morphology of metal oxide nano- and microstructures plays a crucial role in the performances of sensors and especially of nanosensors. Here, a simple approach on the synthesis of three-dimensional (3D) highly porous ZnO nano- and microstructure networks with four different arm morphologies in the same process is reported. Systematic...

A method for surface doping and functionalization of ZnO nanowires (NWs) with Pd (Pd/ZnO) in a one – step process is presented. The main advantage of this method is to combine the simultaneous growth, surface doping and functionalization of NWs by using electrochemical deposition (ECD) at relatively low temperatures (90 °C). Our approach essentiall...

Individual micro- and nanostructures of metal oxides are known to be highly sensitive to surface phenomena due to their enhanced surface-to-volume ratio. In this work, an individual Bi2O3-functionalized ZnO microwire (Bi2O3/ZnO MW) with a diameter of ~2.2Â μm was integrated into a sensing device using its direct transfer and placement in a focused...