Direct probing of semiconductor barium titanate via electrostatic force microscopy

Abstract

Electrostatic force microscopy (EFM) was used to directly probe surface potential in doped barium titanate semiconducting ceramics. EFM measurements were performed using noncontact scans at a constant tip-sample separation of 75 nm with varied bias voltages applied to the sample. The applied voltage was mapped up to 10 V and the distribution of potential across the sample showed changes in regions that matched the grain boundaries, displaying a constant barrier width of 145.2 nm. Keywords: electrostatic force microscopy, electric potential, barriers, barium titanate Ceramics based on doped barium titanate are ferroelectric polycrystals exhibiting a wide variety of electrical phenomena, which are commonly employed in applications such as sensors and actuators due to their wide variations in electrical resistance as a function of temperature [4][5][6][7]. The electronic characteristics of many electronic ceramics are determined by grain boundaries and grain boundary states. For example: the temperature dependence of donor-doped BaTiO 3 based PTC thermistor ceramics is determined by acceptor states at the grain boundaries [8]. These behaviors are accounted for by the incorporation of donors. It has been accepted that the PTC in donor-doped BaTiO 3 originates from the potential barrier that is formed at the grain boundaries increasing the electrical resistance [4-8, 10, 11]. These materials display an electrical behavior characterized by an abrupt increase in resistivity as a function of temperature close to the Curie temperature (T C ) [7,8,11]. This effect occurs in barium titanate during the shift from cubic to tetragonal phase when cooling to temperatures below 130 °C and it is a grain boundary effect that depends strongly on the microstructure [11][12][13][14][15]. The most widely accepted models attribute the PTC phenomena to the formation of potential barriers at grain boundaries, increasing the resistivity when temperatures * Apresentado no V Encontro da Sociedade Brasileira de Pesquisa em Materiais, Florianópolis, SC (2006) Resumo

Mapping grain boundary heterogeneity at the nanoscale in a positive temperature coefficient of resistivity ceramic

“…Overall the presence of resistive grain boundaries is consistent with models proposed for the electrical structure of the grains using impedance analysis 23 and other techniques. 14,21 While this result is almost expected based on various models, local measurements showing resistive boundaries at room temperature with an applied electric field in this lateral geometry have hitherto not been carried out directly. The concentration of potential contours at the grain boundaries provides direct evidence towards the existence of resistive boundaries and highlights them as the clear regions of interest.…”

“…12,13 However, direct analysis of grain boundaries linked to PTCR behavior on the nanoscale that could unequivocally establish the clear role of grain boundaries has been limited in previous studies. 14 …”

Influence of Grain Boundaries on Nanoscale Charge Transport Properties of Transparent Conductive ZnO-Based Electrodes

“…During the second scan, the cantilever was elevated to a height of 40 nm to minimize the influence of van der Waals forces. This elevation allowed for the detection of variations in the electrical force gradient, effectively isolating the electrical effects from topography . The scan was performed while a voltage of −4 V was applied to the tip.…”

“…This elevation allowed for the detection of variations in the electrical force gradient, effectively isolating the electrical effects from topography. 52 The scan was performed while a voltage of −4 V was applied to the tip. The image in Figure 3b shows the distribution of electrostatic forces on the film's surface.…”

MEDIDAS ELÉTRICAS E DIELÉTRICAS EM CERÂMICAS DE BaTIO3 DOPADAS COM SIO2 E Nb2O5

“…Possui constante dielétrica relativamente alta (Yan et al, 2015), em temperatura ambiente no seu estado de pureza, em torno de 1.500 a 2.000 e resistividade na ordem de grandeza de até 10 10 .cm, aproximadamente (Mahbub et al, 2013) . Quando dopado com óxidos metálicos a sua constante dielétrica tende a se elevar em ordens de 10³ a 10 5 (Luoa et al, 2018) e a sua resistividade elétrica tende a diminuir para ordens entre 10 e 10 4 .cm, podendo, desta forma, exercer características de material semicondutor (Cheng, 1989;Pu et al, 2005;Gheno et al, 2007) Óxidos da família perovskita são amplamente utilizados na indústria de eletrocerâmicos, eletroeletrônicos, eletromecânicos e eletro-ópticos (Al-Shakarchi, 2010;López-Joárez et al, 2011;Asimalopoulos et al, 2014). O titanato de bário, por ser um material ferroelétrico com alta constante dielétrica em temperatura ambiente, é bastante utilizado na fabricação de capacitores multicamadas, termistores com coeficientes de temperatura positiva (PTCs), transdutores piezoelétricos e uma variedade de dispositivos ópticos (Wang et al, 2015;Mancini e Filho, 2007).…”