Tin-doped Indium Oxide (ITO) Nanocrystal Superlattices (Surface Chemistry, Charge Transport, and Sensing Applications)

This cumulative dissertation is based on three publications. It investigates the surface chemistry of nanocrystals (NC), charge transport in NC superlattices, and energy level alignment at organic/inorganic interfaces. The materials of choice are tin-doped indium oxide (ITO) NCs as well as the organic semiconductors metal-4,4',4″,4‴-tetraaminophthalocyanine (M4APc) and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). A wet chemical approach is used to synthesize the NCs and to control the doping concentration. Macroscopic superlattices of ITO NCs are prepared by a Langmuir-type self-assembly at the air/liquid interface followed by simultaneous ligand exchange with Cu4APc. X-ray photoelectron spectroscopy (XPS), grazing-incidence small-angle X-ray scattering (GISAXS), and ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy are used to track the chemical changes on the nanocrystals’ surface before and after ligand exchange and develop a detailed picture of the various components which dominate the surface chemistry of this material. It is demonstrated that the semiconductor molecules largely replace the native surfactant from the ITO NC surface and act as cross-linkers between neighboring particles. Transport measurements reveal a significant increase in electrical conductance, suggesting that Cu4APc provides efficient electronic coupling for neighboring ITO NCs. This material provides the opportunity to study charge and spin transport through phthalocyanine monolayers. Next, the choice of the metal center of M4APc is expanded to Cu, Co, Fe, Ni, and Zn. These ligands are incorporated into the array of ITO NCs, and the charge carrier transport and resistance-mediated vapor sensing are investigated. Varying the metal center provides the opportunity to systematically study the sole effect of the tunneling barrier height on charge transport through the nanocrystal array, while all other parameters are kept constant. Transport measurements, focusing on the effect of the metal center of the ligand, reveal a ligand-dependent increase in electrical conductance. The resulting I–V characteristics as well as the temperature dependence of the zero-voltage conductance indicates that at low temperatures, transport across the arrays occurs via a sequence of inelastic cotunneling events. At higher temperatures, a crossover to 3D Mott variable range hopping (VRH) mechanism is observed. The vapor sensitivity of chemiresistors made from ITO NCs arrays is investigated by dosing the sensors with four different analytes and concentrations as low as 100 ppm. By testing different classes of analytes, different selectivities of the materials is also registered, depending on whether the analytes behave more vapor- or more gas-like. Finally, a wide range of substrates (unreactive, reactive or passivated metals and polymers) with different work functions and coupling interactions are used to investigate the electronic structure at the substrate/PTCDA interface by XPS, ultraviolet photoelectron spectroscopy (UPS), and electrostatic calculations. For thick layers of PTCDA, nearly unchanged electron and hole injection barriers on all substrates are observed without any dependence on the type of substrate. For few monolayers of PTCDA, this seemingly universal Fermi level pinning is perturbed depending on the nature of the substrate and the thickness. This behavior is explained with a large induced density of interface states. Using standard electrostatic calculation models as well as introducing extensions to previously reported approaches, the origin of universal Fermi level pinning and its underlying mechanism is investigated. The simulation results demonstrate how the shape of the DOS near the interface has long-range influence on key parameters (e.g. the barrier to charge injection) of the entire organic film.Die vorliegende kumulative Dissertation basiert auf drei Publikationen. Sie behandelt die Oberflächenchemie von Nanokristallen (NC), Ladungstransport in NC Übergittern und die Energieniveauausrichtung an organisch/anorganischen Grenzflächen. Bei den untersuchten Materialien handelt es sich um Indiumzinnoxid (ITO) NCs und organische Halbleiter der Metall-4,4',4″,4‴-tetraaminophthalocyanine (M4APc) und Perylen-3,4,9,10-tetracarbonsäuredianhydrid (PTCDA). Eine nasschemische Herangehensweise wird für die Synthese der NCs und die Kontrolle ihrer Dotierungskonzentration gewählt. Durch eine Langmuir-artige selbst-Assemblierung an der Flüssig-Gas-Grenzfläche mit parallel ablaufendem Ligandenaustausch mit Cu4APc werden makroskopische Übergitter aus ITO-NCs hergestellt. Röntgenphotoelektronenspektroskopie (XPS), Röntgenkleinwinkelstreuung unter streifendem Einfall (GISAXS) und UV/Vis/NIR-Spektroskopie werden verwendet, um die chemischen Veränderungen der Oberfläche der Nanokristalle vor und nach Ligandenaustausch zu verfolgen und um ein detailliertes Bild der unterschiedlichen Komponenten zu erhalten, die die Oberflächenchemie dieses Materials dominieren. Es wird gezeigt, dass die halbleitenden Moleküle die ursprünglichen Liganden von der ITO Oberfläche größtenteils ersetzen und als Vernetzer zwischen benachbarten Partikeln fungieren. Transportmessungen weisen eine signifikante Erhöhung der elektrischen Leitfähigkeit auf und legen damit nahe, dass Cu4APc zu einer effizienten elektronischen Kopplung benachbarter ITO NCs führt. Dieses Material bietet die Möglichkeit, Ladungs- und Spintransport durch Phthalocyaninmonolagen zu untersuchen. Im nächsten Schritt wird die Wahl des Metallzentrums von M4APc auf Cu, Co, Fe, Ni und Zn ausgedehnt. Diese Liganden sind in die Anordnung der ITO NCs integriert, und es werden Ladungsträgertransport sowie die Widerstands-abhängige Detektion von Dampf dieser hybriden Materialien untersucht. Die Variation des Metallzentrums ermöglicht es, systematisch den alleinigen Effekt der Höhe der Tunnelbarriere auf den Ladungstransport durch die Nanokristallanordnung zu untersuchen, während alle anderen Parameter konstant gehalten werden. Transportmessungen, die sich auf den Effekt des Metallzentrums des Liganden fokussieren, zeigen eine Liganden-abhängige Erhöhung der elektrischen Leitfähigkeit. Die resultierende I-V-Kennlinie und die Temperaturabhängigkeit Leitfähigkeit im Niedrigfeld deuten darauf hin, dass bei niedrigen Temperaturen Ladungstransport durch das Gitter durch eine Sequenz von inelastischen Ko-Tunnelereignissen erfolgt. Bei höheren Temperaturen wird ein Übergang zum 3D Mott-VRH Mechanismus beobachtet. Die Empfindlichkeit der Chemosensoren, die aus ITO NCs Anordnungen bestehen, wird gegenüber Dämpfen untersucht, indem die Sensoren mit vier unterschiedlichen Analyten und Konzentrationen – bis hinab zu 100 ppm – beladen werden. Es zeigt sich durch Untersuchung verschiedener Analytenarten, dass das Material unterschiedliche Selektivitäten aufweist, die davon abhängen, ob sich die Analyten eher dampf- oder gasartig verhalten. Zuletzt wird eine Vielzahl an Substraten (inerte, reaktive oder passivierte Metalle und Polymere) mit unterschiedlichen Austrittsarbeiten und Kopplungswechselwirkungen eingesetzt, um die elektronische Struktur der Substrat/PTCDA Grenzfläche mittels XPS, Ultraviolettphotoelektronenspektroskopie (UPS) und elektrostatischen Berechnungen zu untersuchen. Bei dicken PTCDA-Schichten werden, ohne eine Abhängigkeit von der Art des Substrates ausmachen zu können, nahezu unveränderte Elektronen- und Lochinjektionsbarrieren auf allen Substraten beobachtet. Für wenige Monolagen an PTCDA wird diese scheinbare universelle Fixierung des Ferminiveaus abhängig von der Natur des Substrats und der Filmdicke gestört. Dieses Verhalten wird mit einer großen induzierten Grenzflächenzustandsdichte erklärt. Durch Verwendung von standardmäßigen elektrostatischen Kalkulationsmodellen und durch Einführung von Erweiterungen zu bereits berichteten Herangehensweisen wird der Ursprung der universellen Fixierung des Ferminiveaus und dessen zugrundeliegender Mechanismus untersucht. Die Simulationsergebnisse demonstrieren, wie die Form der Zustandsdichte in der Nähe der Oberfläche einen Einfluss langer Reichweite auf Schlüsselparameter (z. Bsp. die Barriere der Ladungsträgerinjektion) des gesamten organischen Films hat

Učinci konkurentnih trenažnih protokola na snagu, aerobni kapacitet, fleksibilnost i sastav tijela

In this study we evaluated the effect of concurrent resistance and endurance training on body composition, aerobic power and muscular endurance in college students and compared the two concurrent exercise protocols. Forty-two male students (22.02±1.91 years of age) were divided into three groups: Concurrent Distinct Endurance-Resistance (CDER), Concurrent Parallel Endurance-Resistance (CPER) and No Training controls (C). The subjects performed two training protocols per week for 12 weeks. In CDER group, resistance training and endurance training were performed on different days each week (two and two days per week). CPER group performed endurance and resistance training on the same days each week (two days per week). After a 12-week training period, fat-free mass, muscular strength [weight lifted in squat and bench press (kg)], muscular endurance [pull-ups and sit-ups (numbers)], aerobic power, flexibility and Sargent jump height increased similarly in both experimental groups (CDER and CPER). Also, decreases in body fat percentage, mean time in 60 m running and agility occurred in CDER and CPER. A significant difference in body fat percentage was seen in CPER when compared to CDER and C. Body mass increased significantly in CPER when compared to CDER and C. Although body mass increased only after the CPER protocol application, it can be concluded that both CDER and CPER protocols were similarly effective in positive transformation of body composition, aerobic power and muscular endurance.U ovom su istraživanju vrednovani učinci konkurentnoga treninga s opterećenjem i treninga izdržljivosti na sastav tijela, aerobnu izdržljivost i mišićnu izdržljivost studenata i ta su dva konkurentna protokola vježbanja uspoređena. Uzorak ispitanika činila su 42 studenta (22,02±1,91 godina) koji su podijeljeni u tri grupe: CDER – konkurentni programi su se primjenjivali odvojeno, CPER – konkurentni program su se primjenjivali usporedo i kontrolna grupa (C). Eksperimentalni programi vježbanja su se provodili tijekom 12 tjedana. U CDER grupi je trening izdržljivosti i trening s opterećenjem organiziran u različitim danima u tjednu (4 dana u tjednu). CPER grupa je provodila trening izdržljivosti i trening s opterećenjem istoga dana u tjednu (2x tjedno). Nakon 12 tjedana treninga u obje eksperimentalne grupe (CDER i CPER) zabilježeno je jednako povećanje u bezmasnoj masi tijela, u maksimalnoj snazi (mjereno čučnjem i potiskom s ravne klupe), repetitivnoj snazi (mjereno zgibovima i pretklonima trupa iz ležanja), aerobnom kapacitetu, fleksibilnosti i visini skoka u Sargentovom testu. Također, u obje eksperimentalne grupe zabilježeno je i smanjenje postotka tjelesne masti, te poboljšanje rezultata u sprintu na 60 metara te u testu agilnosti. Značajna razlika u postotku tjelesne masti zabilježena je između CPER grupe te CDER i C grupe. Značajno povećanje mase tijela zabilježeno je u CPER grupi u odnosu na grupe CDER i C. Iako je zabilježeno povećanje tjelesne mase samo nakon primjene CPER protokola, može se zaključiti kako su oba protokola primjene konkurentnoga treninga podjednako učinkovita u smislu pozitivne transformacije sastava tijela, aerobnoga kapaciteta i mišićne izdržljivosti

Investigation and Sensitivity analysis of experimental methods for estimating evaporation from free surface of Choghakhor lake

Evaporation losses from free surface water in reservoir dams are one of the important processes in meteorology and hydrology. Each experimental methods estimates the evaporation based on the climatic conditions of each region. For this reason, calibration of the relationship between evaporation estimates in different regions are required (Vanzyl et al., 1989). experimental methods are common in engineering sciences. Most scholars, by modifying experimental methods and discovering new relationships, try to find a simple and high-level relationship to replace with the field methods. More than 50 experimental relationships have been proposed for estimating evapotranspiration by various researchers (Naorem and Devi, 2014). Despite the importance of evaporation in hydrology, less attention has been paid to it. However, with the correct estimation, it can be applied in water resource planning with fewer errors (Saadatkhah et al., 2002).In this research, the experimental methods of Mayer, Marciano, Shahthin, Henfer, Ivanov and USBR have been used to study the evaporation from the free surface of the Choghakhor lake, located in Chaharmahal and Bakhtiari province of Iran. The results have been compared with actual evaporation values from the free surface

Enhancement of Antibiotic Activity and Reversal of Resistance in Clinically Isolated Methicillin-Resistant Staphylococcus aureus by Trachyspermum ammi Essential Oil

Background and objectives: Methicillin-resistant Staphylococcus aureus (MRSA) has resulted in a worldwide threat due to the virulence and broad distribution in the hospital and community. Novel antibiotics are required to combat the emergence of multidrug-resistant bacteria such as MRSA. In the present study, the antibacterial activity of Trachyspermum ammi essential oil alone and in combination with fifteen antibiotics of different classes against a standard and five clinical strains of MRSAs was investigated. Methods: Chemical composition of the essential oil was investigated by using gas chromatography-mass spectrometry (GC-MS). The possible synergistic interaction of several antibiotics in combination with essential oil was screened by disc diffusion method. Interaction of the essential oil and the candidate antibiotic was investigated by checkerboard assay. Results: The essential oil was rich in thymol (74.2%), p-cymene (16%), and γ-terpinene (7.1%). Combination of sub-inhibitory concentrations of essential oil with vancomycin or gentamicin increased their inhibition zones against MRSA ATCC 33591 and clinically isolated MRSAs. All of the clinically isolated MRSAs were resistant to gentamicin, while combination of gentamicin with the essential oil caused augmentation of the antibacterial activity and 4 to 520-fold decrease in gentamicin minimum inhibitory concentrations was observed against different MRSA strains with fractional inhibitory concentration indices ranging from 0.50 to 0.75. Combination of essential oil with ciprofloxacin or imipenem increased the inhibition zones against some clinically isolated MRSAs. Conclusion: Combination of sub-inhibitory concentrations of T. ammi essential oil and gentamicin could be considered as a new choice for treatment of infectious diseases caused by MRSA strains.  </strong

Colloidal PbS nanoplatelets synthesized via cation exchange for electronic applications

In this work, we present a new synthetic approach to colloidal PbS nanoplatelets (NPLs) utilizing a cation exchange (CE) strategy starting from CuS NPLs synthesized via the hot-injection method. Whereas the thickness of the resulting CuS NPLs was fixed at approx. 5 nm, the lateral size could be tuned by varying the reaction conditions, such as time from 6 to 16 h, the reaction temperature (120 °C, 140 °C), and the amount of copper precursor. In a second step, Cu+ cations were replaced with Pb2+ ions within the crystal lattice via CE. While the shape and the size of parental CuS platelets were preserved, the crystal structure was rearranged from hexagonal covellite to PbS galena, accompanied by the fragmentation of the monocrystalline phase into polycrystalline one. Afterwards a halide mediated ligand exchange (LE) was carried out in order to remove insulating oleic acid residues from the PbS NPL surface and to form stable dispersions in polar organic solvents enabling thin-film fabrication. Both CE and LE processes were monitored by several characterization techniques. Furthermore, we measured the electrical conductivity of the resulting PbS NPL-based films before and after LE and compared the processing in ambient to inert atmosphere. Finally, we fabricated field-effect transistors with an on/off ratio of up to 60 and linear charge carrier mobility for holes of 0.02 cm2 V−1 s−1

MicroRNAs as Biomarkers for Early Diagnosis, Prognosis, and Therapeutic Targeting of Ovarian Cancer

Ovarian cancer is the major cause of gynecologic cancer-related mortality. Regardless of outstanding advances, which have been made for improving the prognosis, diagnosis, and treatment of ovarian cancer, the majority of the patients will die of the disease. Late-stage diagnosis and the occurrence of recurrent cancer after treatment are the most important causes of the high mortality rate observed in ovarian cancer patients. Unraveling the molecular mechanisms involved in the pathogenesis of ovarian cancer may help find new biomarkers and therapeutic targets for ovarian cancer. MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression, mostly at the posttranscriptional stage, through binding to mRNA targets and inducing translational repression or degradation of target via the RNA-induced silencing complex. Over the last two decades, the role of miRNAs in the pathogenesis of various human cancers, including ovarian cancer, has been documented in multiple studies. Consequently, these small RNAs could be considered as reliable markers for prognosis and early diagnosis. Furthermore, given the function of miRNAs in various cellular pathways, including cell survival and differentiation, targeting miRNAs could be an interesting approach for the treatment of human cancers. Here, we review our current understanding of the most updated role of the important dysregulation of miRNAs and their roles in the progression and metastasis of ovarian cancer. Furthermore, we meticulously discuss the significance of miRNAs as prognostic and diagnostic markers. Lastly, we mention the opportunities and the efforts made for targeting ovarian cancer through inhibition and/or stimulation of the miRNAs